109 e3b against spitfire II [Archive] - Official Fulqrum Publishing forum

ICDP

06-14-2011, 01:26 PM

U cant. SpitII simply better. It was in RL too (The messer can climb higher, but its dont work in game now). E3 -in this configuration- is spanish civil war era (early '39 - LW get the first planes there), Spit II the BOB most advanced RAF type (Aug. '40). Untill LW cant get E-4, E-7, .../N planes, the SpitII banned in most (historical) servers.

Fly with E-3. Difference with E-3/B only the bomb rack, it makes the plane slower.

edit. Ahh, and one more thing :) The E-3, E-3/B manual Prop pitch is much slower, than should be, big disadvantage anyway with this. We hope, it will be fixed in next patch.

The 109E3 was not a Spanish civil war variant, the 109B was. Also the just like the Mk I Hurricane and Mk I Spitifres, the 109E went through various changes from the early 1939 variant at the start of the war to the versions that saw action in August 1940 over Britain.

More powerfull engines were introduced during the production run which kept the 109E competitive with even the Mk II Spitfire. What the problem is with Cliffs of Dover is that the Spitfire Mk IIa matches the performance of the real +12lbs boost Mk II while the 109E comes nowhere near its historical 1939 figures let alone its 1940 figures.

The Hurricane Mk I Rotol is also getting speeds that match a real +6lbs boost version instead of +12lbs boost, so it is also too slow for a BoB era Hurricane. The Spitfire Mk I, Mk Ia and Hurricane DH are massively underperforming and don't get close to real figures for +6lbs versions let alone +12lbs boost versions. Then we have the Bf110 which matches the performance of a DB601-A variant, the problem is that around 50% of the Bf110s in the battle had DB601-N engines which ran on 100 octane fuel giving them a large performance boost.

What we have are some woefully underperforming fighters that don't match any published figures and seem to use generally made up performance based on nothing in particular.

Spitfire Mk Ia (Rotol)
Spitfire Mk I (DH)
Bf109E3
Fiat G.50
Hurricane Mk I (DH)

We have a total lack of any +12lbs boost Spitfire Mk Is or Hurricane Mk Is that would have been the most common variants at front line squadrons. We also have a total lack of the DB601-N equipped Bf110.

Online servers have a serious issue. Allow the Spitfire Mk IIa, which is the ONLY RAF aircraft with close to real life performance. The problem being that it totally dominates the woefully underperforming 109E and Fiat G.50s. Or ban the Spitfire Mk IIa and watch the domination swing way in fovour for the 109E because the Spitfire and Hurricane Mk Is have performance that is even further from reality than that of the CoD 109E.

A lot of work is required on the majority of FMs and aircraft performance.

VO101_Tom

06-14-2011, 01:55 PM

The 109E3 was not a Spanish civil war variant, the 109B was.

Im totally agree, FM necessary to fix, on both sides.

E-3 was not the main fighter, but in spanish civil war, "early in the year (1939) J/88 had recieved 40 new cannon-armed Bf 109 E fighters, and the outdated early marks were passed to Gruppo 5-G-5. On 5 March Mölders's replacement as leader of 3 Staffel." (Osprey Airwar3 - Christopher Shores: Spanish Civil War Air Forces, page 42)"

In this configuration: MG-FF cannon, non automatic cooling system, non automatic Prop pitch system, basic DB601 engine, this is spanish civ war variation. Couple of these aircrafts using in BOB (much less than E-1, E-4, i dont know, why chosen this airplane), but this does not make changes in it, that this machine of what date, and that the LW was much more advanced type under the BOB period.

Im totally understand the virtual RAF pilots situation, 100 octane fuel, +12lbs boost is missing, but LW missing whole series, not just components :rolleyes: Untill LW cant get "BOB era" planes, the (historical) mission makers have no other opportunity, have to create Battle of France maps.

Danelov

06-14-2011, 01:58 PM

ICDP: A short number of E-1 and maybe some experimental E-3 were used by the Legion Condor in the last stages of the war. The I-16 sometimes was more of a match for the early 109 versions.

ICDP

06-14-2011, 05:46 PM

ICDP: A short number of E-1 and maybe some experimental E-3 were used by the Legion Condor in the last stages of the war. The I-16 sometimes was more of a match for the early 109 versions.

I am aware of this, I was responding to VO101_Tom's post on the 109E3 in the Spanish Civil war. Upon re-reading his post I now realise that he meant the current CoD 109E3 is actually performing closer to the very early 109E3 as it was configured in early 1939 (i.e. pre-war). If this was his point then I agree, though the 109E and early Mk I Spitfires and Hurricanes are actually performing slower than they should even for this period.

Grand_Armee

06-14-2011, 06:53 PM

That´s quite accurate if we want speak always about realism. And that must be also, with very little difference, the same for the Mk.I. Always in theme realism, the E-1 MG only armed must also be present. A good number of this version were still operative by Aug 1940.

Honestly, dude. Who do you think is gonna fly it online? Who's gonna make a mission guaranteed to make half the flyers say: "See ya later!" Might as well make a mission where red has only the Tiger Moth to fly.

ZaltysZ

06-14-2011, 07:36 PM

Honestly, dude. Who do you think is gonna fly it online?

Why not? Especially when MGs with incendiary ammo are so effective in CoD.

Grand_Armee

06-14-2011, 08:12 PM

Surely there has to be some limit to the amount of incendiary/tracer you can load? Eh, what am I thinking about. Sense?

CaptainDoggles

06-14-2011, 08:13 PM

There's also the argument to be made for the eventual completeness of the plane set.

Being able to do proper Spanish Civil war scenarios, for example.

Grand_Armee

06-14-2011, 08:47 PM

That would take a lot of planes. Would be cool, though. Cr-42, I-15, He-51...what other kind of stuff could we learn to argue FM's about? LOL

Yep...lotta work there...even if you were only covering the early monoplanes.

335th_GRAthos

06-14-2011, 08:48 PM

Very nice post ICDP,

Just on that sentence
Or ban the Spitfire Mk IIa and watch the domination swing way in favour for the 109E because the Spitfire and Hurricane Mk Is have performance that is even further from reality than that of the CoD 109E.

I think we are very far from the Bf109 having an advantage to their favour.

Most fly "crappy" (I beg for forgiveness for this comment). Bf pilots can not Boom & Zoom which is the only thing the Bf109 was good at, because of three deadly parameters:
#1: No usable propeller pitch: congrats to the guys which made it "historically correct" and screwed up probably 99% percent of Bf pilots to that day. May God (ehem Oleg...) punish them by letting them stick to this Bf flight model for the next five years! :(
I admit I am subjective here, please read under 99 percent just myself, I stopped flying Bf and flying Spits, so it is a strictly private opinion/ it is mine and I will have to live with it (and I can, by not flying Bf109 any more).

2. Head movement restriction in gunsight mode makes a Bf109 pilot not been able to track the opponent while manouvering verticaly and aim for deflection shots at the same time ("lose sight, lose fight").
I spend seven years of my life flying Bf109 exclusively in IL2FB only to find myself unable to dogfight and shoot in a Bf109 in CoD :(
May God punish Luthier by having him dogfight non-stop in Bf109 gunsight mode for the next five years... ;)

3. To add insult to injury(point #2): Poor graphics performance and smaller airplane size (maybe it is my subjective opinion) make difficult to recognise and track and airplane with the ground as background. Since the only way for the Bf109 to win a fight is on the vertical, it is much more difficult to track the enemy in CoD than in IL2FB.
My heart is full of condolence when I see these poor SODs in their Bf online, losing sight of me and by the time they have regained situational awareness my Spit is already behind them, and then game over. I can not even feel proud of shooting down Bf109s nowadays :(

Just my 2cts, I am sorry if I sound bitter, I am honestly not, I am more sarcastic than serious, now that I jumped the fence (and switched to Spit) my problem is solved and I enjoy the game. And hope for the best...with the patch, in three days ;)

~S~

TomcatViP

06-14-2011, 09:19 PM

ZaltysZ

06-14-2011, 09:20 PM

2. Head movement restriction in gunsight mode makes a Bf109 pilot not been able to track the opponent while manouvering verticaly and aim for deflection shots at the same time ("lose sight, lose fight").

Then don't use gunsight mode.

VO101_Tom

06-14-2011, 10:29 PM

I am aware of this, I was responding to VO101_Tom's post on the 109E3 in the Spanish Civil war. Upon re-reading his post I now realise that he meant the current CoD 109E3 is actually performing closer to the very early 109E3 as it was configured in early 1939 (i.e. pre-war). If this was his point then I agree, though the 109E and early Mk I Spitfires and Hurricanes are actually performing slower than they should even for this period.

Yes, it was. Partially. :)

E-3 enters in service early '39 in Spain. If this would not be enough, ingame performance less than should be (especially in high altitude), bacause of weak modelled engine. Early Spit and Hurri have same problem, but its irrelevant to E-3b vs Spit II question, bacause Spit IIa has no problem like this. :rolleyes:

The other thing, we miss what the German engineers developed until one and a half years (at least till aug '40, when Spit II enters service, but its far from end of BOB). Nothing important, only new engines, 100 octane fuel, MG-FF/M gun with mine effect ammo, automatic cooling and PP system. Luthier promised it already, that if not all of them, but we receive some things of these... (We hope, not in Battle of Moscow dvd http://www.pumaszallas.hu/forum/images/smilies/tok-tok.gif :grin:)

Ivan Fooker

06-14-2011, 10:40 PM

I am actually a Spit flyer....
By all those comments i jumped into the Bf109 to ckeck it myself....
FFS...i can understand each pilot "whining" due a Bf109 in CloD.
It feels like the hurricane Mk1 in Il2FB.
Totally unstable in slow flight, turning like a Bf109G10 in Il2FB.
The revi is almost useless in hectic dogfights.

All your comments above are much more detailed for sure.
Nevertheless i can understand, if just a few pilots are fancy flying a Bf109 on servers, coz it feels like XXXX
Hopefully sth gets changed in the next patch in the Bf109FM, as i am not interested to fly a 5:1 (red:blue) on servers.

335th_GRAthos

06-14-2011, 10:51 PM

Then don't use gunsight mode.

I presume you fly Bf109 all the time without gunsight mode so, I respect your experience (and hope there is more Bf109 pilots which share the same point of view).

Unfortunately, my LCD screen is too precious and I will not stick a chewing gum in the centre to compensate for the REVI... comedian! :(

VO101_Tom

06-14-2011, 11:03 PM

With TrackIR, i can fly without gunsight mode (i have to...). Anyway i fly with 90 FOV in dogfight, all time. But took time while I got used to it :rolleyes:
I dont know how can dogfighting anyone withouth trackir, or freetrack...

VO101_Tom

06-14-2011, 11:10 PM

I am actually a Spit flyer....
By all those comments i jumped into the Bf109 to ckeck it myself....
FFS...i can understand each pilot "whining" due a Bf109 in CloD.
It feels like the hurricane Mk1 in Il2FB.
Totally unstable in slow flight, turning like a Bf109G10 in Il2FB.
The revi is almost useless in hectic dogfights.

All your comments above are much more detailed for sure.
Nevertheless i can understand, if just a few pilots are fancy flying a Bf109 on servers, coz it feels likeXXXX
Hopefully sth gets changed in the next patch in the Bf109FM, as i am not interested to fly a 5:1 (red:blue) on servers.

do not be flying low!
if you are flying low, do not turn!
if you turn low, do not turn slowly!
if you turn low, slowly, do not be surprised!
;)

jg27_mc

06-14-2011, 11:14 PM

ZaltysZ

06-15-2011, 04:59 AM

I presume you fly Bf109 all the time without gunsight mode so, I respect your experience (and hope there is more Bf109 pilots which share the same point of view).

Yes, all the time. Zero experience required - just center the Revi. :)

335th_GRAthos

06-15-2011, 12:02 PM

Yes, all the time. Zero experience required - just center the Revi. :)

He, he, so you do centre the Revi after all.... ;)

and fly outside gunsight mode with the Revi centered.

And all the other poor sods without 6DOF will get stuck in their fate :(

PS. or can I do that without 6DOF as well?

Viper2000

06-15-2011, 12:37 PM

resume of above edit :

Q: Why the 109 is useless against Spit II
A(s):
a/It's historical fact
b/we got crappy FM and the Spit hve to get the 12lbthat & that thing (that I miiss from IL2 )
c/ (added certainly to makes good figure) Oh ..; by the way the Hurri shld also get the 12lb eng

and so on and so on ...

C'mon guys : there was no 12lb Spits - there was AN EMERGENCY SWITCH in SOME of the plane based in england !
The Merlin XX did get 9lb boost and it was an after BoB engine
The FM of the Spits is simply surrealistic even for the MkI
This is not the number (perf achieved ) it's in the way it can turn and climb (E grabber) - TAKE TIME to fly in ALL the planes we hve for now: IT'S SO OBVIOUS !

So pls be constructive not selfish and don't touch the superb FM we hve for now for both the Hurri and the 109 to fit your own expectation.

Those men were brave. There were not in anyway counting on any X-men to fight for their freedom.

Pretty much all Spitfires & Hurricanes were running on 100 octane fuel with +12 psi war emergency power available during the battle. This is extensively documented.

All Spitfires and Hurricanes had boost control cutouts until later in the war when gated thottles began to appear.

You can get into an argument about how much boost was developed by operating the cutout; but at sea level it was never less than +12 (early Merlins prior to the +12 mods would actually deliver about +17 with the cutout operated, much to the detriment of the engine given that prior to +12 mods they were running on 87 octane).

Very few Merlin XXs took part in the Battle of Britain.

It's possible that they might only have been cleared to +9 in FS gear in the very early days. I haven't investigated this because I've never been especially interested in the early production Hurricane II; it's perhaps analogous to getting deeply involved in the performance of the Bf-109F0 in the same time period.

However, it seems extremely unlikely that the Merlin XX would not have been cleared to at least a +12 combat rating in MS gear at entry into service because in MS gear it's turning the 10.25" supercharger at 8.1516 times crankshaft rpm. This is lower than the Merlin III (8.588 ) or XII (9.089) and would therefore produce a lower charge temperature.

The Merlin in Perspective credits the XX with a +14 combat rating in MS gear and a +16 rating in FS gear, with the takeoff boost being +12.

So really you don't have much of a leg to stand on unless you want to take the view that 100 octane fuel was some kind of collective hallucination by everybody involved...

The most likely explanation for the +9 rating is either a typographical error, or simply the use of a non-combat rating for whatever test you've got that figure from.

This, of course, is a debate about reality. Matters are complicated by the fact that, at least at present, the sim has quite a strange FM which seems to have some important problems, not least of which is erroneous engine indications for all the Spitfires & Hurricanes.

The Spitfire II, when last I tested it, has optimistic +12 performance but questionable full throttle heights and incorrect boost indications, and therefore almost certainly other problems.

The Spitfire I seems to have some kind of hybrid 87 octane performance, but again I'm not really sure what's going on because the boost indications are actually wrong for that as well.

At the moment, I don't think you can really say that the Spitfire is too good or too bad, because the testing that I've done suggests that it's just plane wrong in a sufficiently large number of particulars that it's almost pointless to get into that kind of debate.

In any case, it takes two to tango, and although I'm no expert on the 109, I have absolutely no reason to believe that it's been modelled perfectly either.

I think that the solution is to wait until the sim stabilises a bit, perhaps after the US release, and then set about a rigorous test programme to actually get to the bottom of what's going on.

Of course, even if we get kinematic performance of all the aeroplanes to closely match test data, that's just the start; we've also got to deal with the reliability and cooling difficulties associated with running at high power, because otherwise everybody will be screaming along in war emergency power the whole time, which might well have "balance" implications, in as much as some aeroplanes would probably gain more from this unrealistic performance capability than others...

ZaltysZ

06-15-2011, 12:39 PM

PS. or can I do that without 6DOF as well?

If I recall correctly: middle mouse button + right mouse button gives you additional 2 DOF. Move head to right and leave it there. Should work with panning, but I am not sure about snap views.

TomcatViP

06-15-2011, 04:12 PM

Kurfürst

06-15-2011, 04:20 PM

Pretty much all Spitfires & Hurricanes were running on 100 octane fuel with +12 psi war emergency power available during the battle. This is extensively documented.

Actually, this was discussed many times already. Sure there's extensive documentation of 100 octane use, which perfectly warrants that we have 100 octane variants of Spitfires & Hurricanes in the sim.

However, the claim that all of them were running on the fuel is quite simply baseless and there's no evidence of this, and it can be considered a bit wishful. On the contrary, there's convincing evidence found in archives detailed fuel use and decisions that the proccess of conversion begun in the spring of 1940 only (preceeded by various trials), and much of the force was still flying on 87 octane and lower engine power during the battle, until toward the end of 1940.

TomcatViP

06-15-2011, 05:41 PM

If I recall correctly: middle mouse button + right mouse button gives you additional 2 DOF. Move head to right and leave it there. Should work with panning, but I am not sure about snap views.

Post of the year IMHO. Thx ! :-P

*Buzzsaw*

06-15-2011, 05:42 PM

Actually, this was discussed many times already. Sure there's extensive documentation of 100 octane use, which perfectly warrants that we have 100 octane variants of Spitfires & Hurricanes in the sim.

However, the claim that all of them were running on the fuel is quite simply baseless and there's no evidence of this, and it can be considered a bit wishful. On the contrary, there's convincing evidence found in archives detailed fuel use and decisions that the proccess of conversion begun in the spring of 1940 only (preceeded by various trials), and much of the force was still flying on 87 octane and lower engine power during the battle, until toward the end of 1940.

Once again Kurfurst continues his proud tradition of providing one sided disinformation, with no facts to back up his case.

This issue has been gone over many times and on many boards, it has been written about, published etc.

And the conclusions are clear. RAF Fighter Command had 100 octane fuel in plentiful supply at all of its major 10, 11, and 12 Group fields. (and these fields provided the supply for their satellite fields)

The best debate on this issue occurred on the WWII Aircraft forum which has very high standards of proof required. The discussion was led by 'Glider', real name Gavin Bailey, who is published on the subject of high octane fuel use by the Allies in WWII. His article "The Narrow Margin of Criticality: The Question of the Supply of 100-Octane Fuel in the Battle of Britain" was published by THE ENGLISH HISTORICAL REVIEW, a well respected historical journal whose material is subject to critical scrutiny by the best of English historians.

Article here:

http://ehr.oxfordjournals.org/content/CXXIII/501/394.abstract

The debate on the WWII Aircraft forum can be found in two threads. If you are seriously interested in understanding the facts, then take the time to read both threads in their entirety.

http://www.ww2aircraft.net/forum/aviation/use-100-octane-fuel-raf-pt-2-a-20108.html

http://www.ww2aircraft.net/forum/technical/use-100-octane-fuel-raf-during-bob-16305.html

Kurfurst was present there, and added his usual disinformation, refused to provide references and was banned from the forum.

For Kurfurst to continue to put forward his disinformation here, despite all the other occasions where that disinformation has been discredited is just another example of his lack of objectivity.

For CLIFFS OF DOVER to have an accurate set of aircraft models, it should have the following:

Hurricane I (two speed prop, +6 boost 87 octane)
Hurricane I (two speed prop, +12 boost 100 octane)

Hurricane I (constant speed prop, +12 boost)

Spitfire I (two speed prop, +6 boost 87 octane)
Spitfire IA (constant speed prop, +12 boost 100 octane)

Spitfire IIA (constant speed prop, +12 boost 100 octane)

It is not good enough to have only a Spitfire II with +12 boost performance. Historically Spitfire IIA's only equipped 3 Squadrons during the battle, most Spitfires were the I model, running +12 boost.

Hurricanes must have a +12 boost version, including the two speed prop version, since Hurricanes were converted later than the Spitfires to constant speed, and there were quite a number of two speed prop versions in use in July and August running +12 boost.

The +6 boost versions of the Spitfire and Hurricane are required for 1939 and January to April 1940 scenarios.

VO101_Tom

06-15-2011, 06:01 PM

Once again Kurfurst continues his proud tradition of providing one sided disinformation, with no facts to back up his case

....

Article here:

http://ehr.oxfordjournals.org/content/CXXIII/501/394.abstract

The debate on the WWII Aircraft forum can be found in two threads. If you are seriously interested in understanding the facts, then take the time to read both threads in their entirety.

http://www.ww2aircraft.net/forum/aviation/use-100-octane-fuel-raf-pt-2-a-20108.html

http://www.ww2aircraft.net/forum/technical/use-100-octane-fuel-raf-during-bob-16305.html

Thanks, very good links, i noticed one thing, what was topic here, the "constant using 12lbs"topic...

"1st August 1940 Memo from Downing re the Handling of the Merlin Engine
This note is advising the pilots that there is an increase in engine failures in the overuse of the emergency 12lb boost.
The interesting thing is that this memo was sent to ALL fighter groups. Had we been talking about the 16 squadrons or less this would not have been the case. It would have been sent to the squadrons involved."

This clears up that question rather unambiguously. :rolleyes:

Seadog

06-15-2011, 06:03 PM

2. we hve started from a 6.5lb with an emergency boost of 12lb on a 87 oct and we were discussing abt a 100oct at 12lb vs what I think is a Merlin 100oct topped a 9 (my Merlin argumentation based on the RR sources you know pretty well and based on Qualorific assumption (the amount of heat generated).
Now if I read you well we shld hve a 17lb 100oct ? Humm will I hev to fear reading in the upcoming weeks about the Jet eng being available during BoB (see spitperf.com and blablabla) ? ;)
)

The Merlin XX was given official approval to use 12lb boost for combat in MS gear in Nov 1940, but the engine was cleared for 12lb boost/3000rpm for TO right from the beginning, and so was available to any pilot who cared to use it during combat.
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-limits-10june40.jpg
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-15nov40.jpg

Approval for 14 and then 16lb boost was added later, along with the appropriate boost override modifications.

Kurfürst

06-15-2011, 06:17 PM

And the conclusions are clear. RAF Fighter Command had 100 octane fuel in plentiful supply at all of its major 10, 11, and 12 Group fields.

Source please.

(and these fields provided the supply for their satellite fields)

Source please. This was already discussed. http://forum.1cpublishing.eu/showpost.php?p=290490&postcount=38

Based on the current evidence (feel free to add new sources showing 100 octane at the said airfield during the Battle and I'll update the list) shows that 100 octane aviation spirit was supplied to

8 out of 19 Sector Airfields
9 out of 32 Fighter Airfields (however 7 of the 32 functioning as satellite airfield for rotation etc., with no Sqn permanently based there).

The best debate on this issue occurred on the WWII Aircraft forum which has very high standards of proof required. The discussion was led by 'Glider', real name Gavin Bailey, who is published on the subject of high octane fuel use by the Allies in WWII. His article "The Narrow Margin of Criticality: The Question of the Supply of 100-Octane Fuel in the Battle of Britain" was published by THE ENGLISH HISTORICAL REVIEW, a well respected historical journal whose material is subject to critical scrutiny by the best of English historians.

Glider has nothing to do with Gavin Bailey, nor anyone participating in the thread for the matter.

As for Bailey's article, it doesn't state anywhere that 100 octane was universal for fighter use; actually, it gives little attention to subject of the extent of use, and instead it concentrates on belittlening the - allegedly widely and wrongly perceived - importance of American 100 octane imports, and the put emphasis of CSP propellerers.

On the matter of 100 octane use, it writes:

By the time war broke out, the available stocks of aviation fuel had risen to 153,000 tons of 100-octane and 323,000 tons of other grades (mostly 87-octane).35 The actual authorisation to change over to 100-octane came at the end of February 1940 and was made on the basis of the existing reserve and the estimated continuing rate of importation in the rest of the year.36 The available stock of 100-octane fuel at this point was about 220,000 tons. Actual use of the fuel began after 18 May 1940, when the fighter stations selected for the changeover had completed their deliveries of 100-octane and had consumed their existing stocks of 87-octane. While this was immediately before the intensive air combat associated with the Dunkirk evacuation, where Fighter Command units first directly engaged the Luftwaffe, this can only be regarded as a fortunate coincidence which was contingent upon much earlier decisions to establish, store and distribute sufficient supplies of 100-octane fuel.

Then it goes back again how little American supplies meant in RAf plans, how limited the importance of 100 octane was compared to CSPs etc. There's no doubt some nationalistic odor to it.

Comparison table of FC's sorties vs. the amount of 100 octane and 'other' (ie. 87 octane) aviation fuel issued during the month clearly show that Figther Command was relying on 87 octane for a number of its operational fighter Squadrons.

http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/100-87issues-FC_sorties_duringBoB.png

A few of my own observations:

a, It seems clear that 100 octane has begun replacing 87 octane towards the end of September / start of October. Until then, 87 octane is by far the major fuel consumed.
b, This corresponds with what the Lord Beaverbook memo noted about re-starting the conversion
c, Its also very appearant that issues have a bit of 'delay' built into them. Obviously supply's nature is that they re-supply after the fuel at the airfields has been used and there's reported need for new issues. This takes time.
d, 100 octane issue curves are clearly responding to FC sorties number increase/decrease. Though that's not news, FC used that fuel. But it should be kept in mind that number of Blenheim Sqns also used and were issued 100 octane fuel, and a Blenheim sortie would consume 4-6 times the fuel a fighter sortie would.
e, On the other hand, 87 octane issues ALSO clearly reacts to FC sorties number increase/decrease. It shouldn't, if all frontline Sqns would be using only 100 octane. ;)
f, Obviously the 87 octane curve reaction is less pronounced, as
fa, A good percentage of FC used 100 octane, so they don't their needs 'do not exists' from the 87 octane issues POV
fb, A large number of other aircraft also uses 87 octane, and many of them - bombers, patrol craft etc. - consume much more fuel than small fighters.

In my opinion, the most conclusive evidence that even towards the end of October a number of fighter squadrons were flying on 87 octane is evident by the sudden and perfectly parallel rise of both 87 octane issues and FC sorties curves at the time.

Tendencies to have British aircraft using only the best possible configurations are nothing more than the naked truth of gamers wanting more advantage to their aircraft, regardless of historical accuracy.

TomcatViP

06-15-2011, 06:21 PM

The Merlin XX was given official approval to use 12lb boost for combat in MS gear in Nov 1940, but the engine was cleared for 12lb boost/3000rpm for TO right from the beginning, and so was available to any pilot who cared to use it during combat.
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-limits-10june40.jpg
http://www.wwiiaircraftperformance.org/hurricane/merlin-xx-15nov40.jpg

Approval for 14 and then 16lb boost was added later, along with the appropriate boost override modifications.

T.O low speed no ram effect + Optimum Air flow in term of Mass of air to cool the supercharger (see above what two speed use is abt)

@VO101_Tom : Nice found but I am sry this argument is not valid. Any Army makes the circulation of Info a strategical issue : you are flying in a fighter -> you get all the info cleared for your security level regarding that type of fighter.

It does not mean that they all hve used the famous 100oct

But As I hve alry said : let's give them their Barracuda engines that years of stupid mods can get a justification (and spare my own free time)

@Kurf : this is a neat explanation with proof reasoning. I hve read it the first time you put it on the forum and still wait for any argumentation since

*Buzzsaw*

06-15-2011, 06:48 PM

Source please.

Source please. This was already discussed. http://forum.1cpublishing.eu/showpost.php?p=290490&postcount=38

Based on the current evidence (feel free to add new sources showing 100 octane at the said airfield during the Battle and I'll update the list) shows that 100 octane aviation spirit was supplied to

8 out of 19 Sector Airfields
9 out of 32 Fighter Airfields (however 7 of the 32 functioning as satellite airfield for rotation etc., with no Sqn permanently based there).

Glider has nothing to do with Gavin Bailey, nor anyone participating in the thread for the matter.

As for Bailey's article, it doesn't state anywhere that 100 octane was universal for fighter use; actually, it gives little attention to subject of the extent of use, and instead it concentrates on belittlening the - allegedly widely and wrongly perceived - importance of American 100 octane imports, and the put emphasis of CSP propellerers.

On the matter of 100 octane use, it writes:

Then it goes back again how little American supplies meant in RAf plans, how limited the importance of 100 octane was compared to CSPs etc. There's no doubt some nationalistic odor to it.

Comparison table of FC's sorties vs. the amount of 100 octane and 'other' (ie. 87 octane) aviation fuel issued during the month clearly show that Figther Command was relying on 87 octane for a number of its operational fighter Squadrons.

http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/100-87issues-FC_sorties_duringBoB.png

A few of my own observations:

a, It seems clear that 100 octane has begun replacing 87 octane towards the end of September / start of October. Until then, 87 octane is by far the major fuel consumed.
b, This corresponds with what the Lord Beaverbook memo noted about re-starting the conversion
c, Its also very appearant that issues have a bit of 'delay' built into them. Obviously supply's nature is that they re-supply after the fuel at the airfields has been used and there's reported need for new issues. This takes time.
d, 100 octane issue curves are clearly responding to FC sorties number increase/decrease. Though that's not news, FC used that fuel. But it should be kept in mind that number of Blenheim Sqns also used and were issued 100 octane fuel, and a Blenheim sortie would consume 4-6 times the fuel a fighter sortie would.
e, On the other hand, 87 octane issues ALSO clearly reacts to FC sorties number increase/decrease. It shouldn't, if all frontline Sqns would be using only 100 octane. ;)
f, Obviously the 87 octane curve reaction is less pronounced, as
fa, A good percentage of FC used 100 octane, so they don't their needs 'do not exists' from the 87 octane issues POV
fb, A large number of other aircraft also uses 87 octane, and many of them - bombers, patrol craft etc. - consume much more fuel than small fighters.

In my opinion, the most conclusive evidence that even towards the end of October a number of fighter squadrons were flying on 87 octane is evident by the sudden and perfectly parallel rise of both 87 octane issues and FC sorties curves at the time.

Tendencies to have British aircraft using only the best possible configurations are nothing more than the naked truth of gamers wanting more advantage to their aircraft, regardless of historical accuracy.

All of this disinformation is more of the same, all put forward by you in the threads I linked from the WWII Aircraft forum, and all have been proven to be false.

You are a broken record Kurfurst, posting twenty times does not make a false statement anymore correct than if you post once.

Anyone who takes the time to read through the threads from WWII Aircraft will see how credible you are with your homemade tables and lack of original documents.

To deal with your point there was more 87 octane fuel issued, the reason was simple:

RAF Bomber command was conducting a night offensive throughout the battle, bomber fuel loads are roughly twenty to thirty times that of a fighter aircraft.

If you look at 100 octane usage, the figures are clearly in line with what consumption should be for the roughly 400 fighter aircraft based at 10, 11 and 12 Group fields. In 1944 and 1945, the whole of the 2nd TAF usage of 150 octane fuel was roughly 10,000 tons per month, and that was for over 900 aircraft, Spitfires, Typhoons, Tempests and Mustangs, all of which had larger fuel tanks, plus all of which were loaded with drop tanks for every mission, the drop tanks alone for '44/'45 aircraft held more fuel than a '40 aircraft held in its internal tanks. Drop tanks were not in use by the RAF during the BoB.

But I am not going to lay out all the arguments here, they have already been presented in the WWII Aircraft forum thread in more than enough detail.

Yes, I mis-linked 'Glider' with Gavin Bailey, the name Bailey actually uses in the thread is 'Gavin B', another 'G', in any case, Gavin Bailey clearly disagrees with Kurfurst in the threads, Kurfurst ends up insulting him and that is one of the reason Kurfurst is banned.

The links again:

http://www.ww2aircraft.net/forum/avi...2-a-20108.html

http://www.ww2aircraft.net/forum/tec...bob-16305.html

VO101_Tom

06-15-2011, 06:54 PM

@VO101_Tom : Nice found but I am sry this argument is not valid. Any Army makes the circulation of Info a strategical issue : you are flying in a fighter -> you get all the info cleared for your security level regarding that type of fighter.

It does not mean that they all hve used the famous 100oct

But As I hve alry said : let's give them their Barracuda engines that years of stupid mods can get a justification (and spare my own free time)

If was used continuously the 12lbs boost, and the engine was ruined continuously, it does not interest, if COD makes the same one. :)
If I misunderstood it, then excuse me, but the object of the debate in the other topic, that the 12 lbs were useful without the damaging of engine - from what it follows, that let COD not take it into consideration...

Kurfürst

06-15-2011, 07:24 PM

Buzzsaw, apart from your usual tirades and various lies about my person,

A, can you produce even a single primary document saying all of Fighter Command using 100 octane fuel and 100 octane fuel only?
B, can you explain, that if FC would use only 100 octane fuel, why do 87 octane issues suddenly rise at the moment Fighter Command is flying more operational sorties?

Should you be able to do so, I may be able to take you seriously.

Kurfürst

06-15-2011, 07:26 PM

Seadog

06-15-2011, 07:42 PM

B, can you explain, that if FC would use only 100 octane fuel, why do 87 octane issues suddenly rise at the moment Fighter Command is flying more operational sorties?

Because 87 octane is being used by Coastal Command, Bomber Command, RN, OTU and flight training units, all of whom will increase their activities during periods of good weather, which was when the Luftwaffe also increased it's activity over Britain.

335th_GRAthos

06-15-2011, 08:10 PM

Originally Posted by ZaltysZ
If I recall correctly: middle mouse button + right mouse button gives you additional 2 DOF. Move head to right and leave it there. Should work with panning, but I am not sure about snap views.

Post of the year IMHO. Thx ! :-P

+1

I will check that out, if it works it would be a great improvement, thanks!

Viper2000

06-15-2011, 08:35 PM

ViP

1. I am referring to the XX as it top off the III perf. . The XX is a well known referenced eng with plenty of raw data available and introduced latter in the war as an improved eng. Draw your own conclusion but I doubt pilot will have been happy to see their eng changed for the "less powerful" XX when they were asked to fly across the channel to bring the fight to the enmy.

So as you say that "very few XX took part in BoB" you are right on what I am pointing out

2. we hve started from a 6.5lb with an emergency boost of 12lb on a 87 oct

No - 87 octane limited the engine to +6.5. In this period, the boost control cutout was a safety feature to permit the pilot to manually control the throttle valves if the ABC failed. Fully opening the throttle at sea level static would give about +17 psi boost. This would be very bad for the engine.

Of course, in theory you could operate the cutout and then manually set the throttle to provide any arbitrary amount of boost that the supercharger was able to deliver at your altitude.

So a Spitfire or Hurricane pilot in 1938 could have overboosted their engine anywhere up to about +17 on 87 octane. But this would have rapidly damaged the engine and would have been completely against the instructions in the Pilot's Notes etc.

I have seen no evidence that anybody did this deliberately (though doubtless somebody did it by accident, because if it's possible to do something silly then somebody probably will). However, it was obviously known that +17 would result from operation of the cutout in its initial state because this is clearly set out in documents which I have cited in my thread on the subject of the effects of operating the boost control cutout in Spitfires & Hurricanes using 87 octane fuel.

and we were discussing abt a 100oct at 12lb

With 100 octane fuel, the engine could safely operate at +12. The boost control cutout system was then modified by drilling a bleed hole so that operating the cutout would now provide no more than +12 psi boost. This meant that the cutout could be used to provide a regulated level of emergency combat power instead of operating simply as a safety device.

The cutout could be wired "off" with thin wire, so that operation of the cutout would provide a tell-tale for the groundcrew. This was therefore a very elegant solution.

vs what I think is a Merlin 100oct topped a 9 (my Merlin argumentation based on the RR sources you know pretty well and based on Qualorific assumption (the amount of heat generated). Climb power for the Merlin XX is +9 psi at 2850 rpm. This is the most likely source of your +9 figure.

Now if I read you well we shld hve a 17lb 100oct ? Not at all. See above.

Humm will I hev to fear reading in the upcoming weeks about the Jet eng being available during BoB (see spitperf.com and blablabla) ? ;)

3. You are mixing your argumentation with a lot of data that many young reader can't understand and that hve no meaning here. Just let make it clears MS gear refer to the charger's impeler de-multiplication (the speed at witch it turn related to the main crankshaft) that had to be kept bellow a certain speed for the efficiency of the overall boosting process.
MS = Medium Supercharge
FS = Full Supercharge

Supercharger efficiency depends upon where you are on the compressor map. You'd generally plot non dimensional flow vs pressure ratio and include constant speed lines.

What you find is that centrifugal impellers are pretty forgiving machines, and will operate over quite a wide range of flows and pressure ratios at any given speed without surging.

Really you only care about tip speed for 3 reasons:
Structural strength
Supercharger power consumption
Charge temperature

So ideally you want to run the engine with a wide open throttle and turn the supercharger at the lowest speed at which it is able to deliver the pressure ratio required to give the boost you want at your current ambient conditions.

But this would be too complicated for 1940.

So you compromise.

The Merlin XX had a 2 speed supercharger drive gearbox, so 2 compromise speeds were available instead of 1 for the earlier engines. This allowed better overall performance, though it didn't have any direct impact upon peak power.

There is no link with the SHAP but only with the fighter speed and the alt of this perf. giving that the supercharger was designed for fighters on the base of procurement policy (by the way I read that the twin speed supercharger was patented by Farman and hev a hard time figuring in witch Farman's plane he wanted this installed :rolleyes:). Pls don't smoke the debate. Logic is at the reach of everyone (pls make the V hand sign reading this). Farman patented the gearchange mechanism; RR just licensed the IP. IIRC there were a couple of other gear change mechanisms on the shelf, and some of the Packard engines may have used a different one for production reasons.

In any case, it was an IP licensing thing rather than a case of Farman having specifically produced technology with the Merlin in mind.

4.you alrdy stated about installed eng power that match only what I have here as an eng not fitted with a supercharger (the 1.3k+HP data) - maybe shld you look at your references. Merlin without supercharger = Meteor. It would give something in the region of 650-850 bhp. It's quite hard to be concrete because Meteors were generally reconditioned (ie crashed, non-airworthy) Merlins and so they were never going to perform "as new".

By the way ~S! and thx to forgive me for my bad English grammar & spelling :oops:

~S

Seadog

06-15-2011, 08:50 PM

No - 87 octane limited the engine to +6.5. In this period, the boost control cutout was a safety feature to permit the pilot to manually control the throttle valves if the ABC failed. Fully opening the throttle at sea level static would give about +17 psi boost. This would be very bad for the engine.

The Merlin III was allowed the use of 16lb boost on the Sea Hurricane IB, so I doubt that 17lb boost would be instantly fatal with 100 octane fuel, but with 87 octane bad things would happen.

ICDP

06-15-2011, 10:25 PM

The Merlin III was allowed the use of 16lb boost on the Sea Hurricane IB, so I doubt that 17lb boost would be instantly fatal with 100 octane fuel, but with 87 octane bad things would happen.

You mean just like he said? He never mentioned 100 octane fuel, he is specifically referring to 87 octane fuel in that scenario. Why is it that whenever anyone mentions a Merlin engine could blow up you have to jump in to save the day and explain to all us mere mortals why the Merlin was perfect.

335th_GRAthos

06-15-2011, 11:00 PM

Originally Posted by ZaltysZ
If I recall correctly: middle mouse button + right mouse button gives you additional 2 DOF. Move head to right and leave it there. Should work with panning, but I am not sure about snap views.

I will check that out, if it works it would be a great improvement, thanks!

-1

It does not work, yes you can move to center the gunsight but as soon as you turn the TRACKIR on, it centers again automaticaly to normal view.

What a bunch of rubish! :(

TomcatViP

06-15-2011, 11:06 PM

Climb power for the Merlin XX is +9 psi at 2850 rpm. This is the most likely source of your +9 figure.

Pls take a close look at your doc - Merlin XX. I hve here maximum perf calibration with max speed being plotted. It does not look like anything like a climb setting

Oh and it does come from RR..

Supercharger efficiency depends upon where you are on the compressor map.

I don't see the sense of what your wrote here. You might hve pasted half the sentence from your original doc here ;)

physically given that the SC is accordingly dimensioned (flows and struct) , the heat generated is what will drive the overall efficiency. And what drive away that heat : the flow of air (or air mixture) that is pushed by the impeller blades.

Hence there is a max amount of calorific E that a s/c can work with. Raise the oct -> you'll reach sooner the the max sustainable value

This is why I said that Max boost level hve very little chance to be reachable at an alt where the impeller hve alrdy to compensate for lower air density if the eng was not designed for

etc... etc...

What you find is that centrifugal impellers are pretty forgiving machines, and will operate over quite a wide range of flows and pressure ratios at any given speed without surging.

Modern supercharger : yes. At the time of BoB hummm that's a pretty acrobatic assumption

The Merlin XX had a 2 speed supercharger drive gearbox, so 2 compromise speeds were available instead of 1 for the earlier engines. This allowed better overall performance, though it didn't have any direct impact upon peak power.

pls see the above

In any case, it was an IP licensing thing rather than a case of Farman having specifically produced technology with the Merlin in mind.

I wld hve been pls to see a Farman 220 with 4xMerlins. Damn just to see that huge parasol wing being blown away by the engines airstream :rolleyes:

By the way, most patent are cross border documents. There is no shame using a Patent from an other country. Aviation is full of this. let us remind that if Aviation pioneer did not get inspiration from each other all over the world, we wld still cross the pound on steaming boat.

Merlin without supercharger = Meteor. It would give something in the region of 650-850 bhp. It's quite hard to be concrete because Meteors were generally reconditioned (ie crashed, non-airworthy) Merlins and so they were never going to perform "as new".

Supercharging the eng was meant to keep power at alt (the rated alt) and increased the fighter perfs (smaller engine) where the bomber stream were expected . This is not NHRA supercharging although a direct benefit were a low perf improvement and climb rate to alt.

I hve arldy quoted the Merlin XX data with and without s/c (your 12lb thread)

You'd see that the s/c being driven by the eng shaft use a 7 to 20 % of eng power. Hence teh 1.3k SHP and 1.175k BHP or something like that

Anyhow, the team that did code those FM game have proved superior man skills in the field. I am looking frwd for the next released giving they can work without too much pressure away from 1C SC
(read Spit Complex )
~S

Viper2000

06-15-2011, 11:20 PM

Pls take a close look at your doc - Merlin XX. I hve here maximum perf calibration with max speed being plotted. It does not look like anything like a climb setting

Oh and it does come from RR..

I don't see the sense of what your wrote here. You might hve pasted half the sentence from your original doc here ;)

physically given that the SC is accordingly dimensioned (flows and struct) , the heat generated is what will drive the overall efficiency. And what drive away that heat : the flow of air (or air mixture) that is pushed by the impeller blades. No. The efficiency is the ratio of useful work to input work. In general, we'd use the isentropic adiabatic compression work for the pressure ratio achieved by the system as the definition of the "useful work".

Hence there is a max amount of calorific E that a s/c can work with. Raise the oct -> you'll reach sooner the the max sustainable value This makes no sense.

Better fuel = higher max charge temperature, all other things being equal (which they are for merlin development as the basic piston engine (bore, stroke, CR, valve timing, max rpm etc were the same throughout its production life).

This is why I said that Max boost level hve very little chance to be reachable at an alt where the impeller hve alrdy to compensate for lower air density if the eng was not designed for The engine is flat-rated to a maximum safe boost pressure. The supercharger is designed to deliver this boost WOT at the FTH. Below FTH the supercharger is throttled.

Modern supercharger : yes. At the time of BoB hummm that's a pretty acrobatic assumption Not really. Compare the ease with which RR developed their centrifugal flow jets with the massive difficulty they experienced trying to get the AJ.65 to work. It's all relative.

Modern compressors of all types will have better polytropic efficiency and deliver more work per stage, but the basic trends haven't changed.

I wld hve been pls to see a Farman 220 with 4xMerlins. Damn just to see that huge parasol wing being blown away by the engines airstream :rolleyes:

By the way, most patent are cross border documents. There is no shame using a Patent from an other country. Aviation is full of this. let us remind that if Aviation pioneer did not get inspiration from each other all over the world, we wld still cross the pound by steaming boat. I work with patents quite frequently, and hold a couple of my own. They're only cross border if you've got the money to chase the legal paperwork, and they only mean anything much at all if you've got the money to sue whoever might infringe... I don't see why you'd ascribe any particular moral value to the nationality of the inventor to whom a patent you've decided to license is attributed. Most engineers have better things to do...

Supercharging the eng was meant to keep power at alt (the rated alt) and increased the fighter perfs (smaller engine) where the bomber stream were expected . Direct benefit were a low perf improvement and climb rate at alt. Supercharging is really about making the engine smaller.

The non dimensional flow that a piston engine can handle at fixed rpm is basically constant.

Supercharging allows you to cram more absolute mass flow rate into a given non dimensional flow rate.

How you choose to rate the engine is another debate. But in most cases, people only flatrated because fuel quality prevented them from operating WOT at lower altitudes.

I hve arldy quoted the Merlin XX data with and without s/c (your 12lb thread)

You'd see that the s/c being driven by the eng shaft use a 7 to 20 % of eng power. Hence teh 1.3k SHP and 1.175k BHP or something like that

No, your data quotes the power consumed by the supercharger, and the power produced by the engine.

This is not the same thing as operating without the supercharger. Without the supercharger you can't get above 0 boost by definition. Hence you get something like 650-850 bhp.

Obviously the Supercharger consumes fewer horsepower than it adds via the boost increase it creates - otherwise nobody would bother!

Anyhow, the team that did code those FM game have proved superior man skills in the field. I am looking frwd for the next released giving they can work without too much pressure.

~S

Superior to what? It's not as though there's a whole lot of competition in the Flight sim market these days...

TomcatViP

06-16-2011, 12:18 AM

At first I wld like to say that I'm sry to all reader for this dual exchange.

Secondly I did not quote you to shorten those otherwise long answers that tend to be felt as walls in a forum pulling away the reader interested by the title of this topic

Let's go :

Adiabatic = when E is exchanged without loss of Calorific energy

Simply said the s/c depend of it's operating inside Temp that drive the efficiency of the compression

There is no adiabatic transformation. Isentropic is also an approximation to figure out the inside Temp that RR could not measure in 1940. But yes that what you plot. But who cares ?

Better fuel : higher piston head temp -> eng wearing. This is well known from car's tuner. You'd see a lot of interesting threads on that subject without over complicated words.

By the way the DB605 is no more than a revamped DB601 but with the same minor details that change and took so little time to arrange before being sent in full production

Wasn't WOT 5000 ft ? -> it's far from any rated alt - look like more for a naturally aspirated eng. I guess that the redesign of the intake was the partition they played here ;)

Yes yes you 'r right impeller are quite easy technology once you 've got the backup of strong industry supplying nice raw materials proof of any small glitch. Oh yes you'r right ... Of course the Russians, The Italians and the Japanese just might hve miss read the same early studies.

Si vis pacem para bellum : UK proved here her superior "governing awareness" (despite the Munich debacle)

RAF not NHRA :rolleyes:

Using copy/Paste as well :

Merlin XX !!

ALT(ft) SHP BHP (diff correspond to the power used to drive the supercharger)
15K 1267 1048
20K 1298 1073
20K+ 1362 1126
25K 1162 960
30K 945 778
35K 700 568

At 20K the eng is fed with sufficient amount of air to regain is low alt power. But it still hve to drive the s/c. This everything abt turbo-charging an eng.

FM : 1c far superior to any Modder (I am sry to hve to write that)

Patents ? I never doubt you was a talented individual. Well let's pat our back and share our patents together one day ;)

Blackdog_kt

06-16-2011, 01:59 AM

..........
d, 100 octane issue curves are clearly responding to FC sorties number increase/decrease. Though that's not news, FC used that fuel. But it should be kept in mind that number of Blenheim Sqns also used and were issued 100 octane fuel, and a Blenheim sortie would consume 4-6 times the fuel a fighter sortie would.
..........
f, Obviously the 87 octane curve reaction is less pronounced, as
fa, A good percentage of FC used 100 octane, so they don't their needs 'do not exists' from the 87 octane issues POV
fb, A large number of other aircraft also uses 87 octane, and many of them - bombers, patrol craft etc. - consume much more fuel than small fighters.

In terms of Bomber Command usage, the pilot's operating handbook for the Blenheim Mk.IV confirms the above points.

Actually, the Mk.IV used both types of fuel.

What happened?
1) They needed more range so they added two more fuel tanks, one in each wing (the outboard tanks).
2) This made the aircraft heavier so it needed more power to get off the ground safely when fully bombed-up and fueled.
3) Engines were modified and a boost cut-out installed, so that maximum boost could raised from +5 lbs to +9 lbs.
4) This needed fuel with more resistance to detonation (aka 100 octane), but it was also important for Fighter Command use.

So, what they did was load 100 octane only in the outboard tanks and use 87 octane in the inboard tanks.

When loaded for long range, takeoff was done on 100 octane fuel from the outboard tanks with the boost over-ride enabled and +9 lbs boost, then immediately after take-off they throttled back and switched to 87 octane from the inboard tanks.

When flying shorter range sorties only the inboard tanks were loaded with 87 octane and the normal maximum of +5 lbs boost was used, in order to let the fighter boys have more of the 100 octane supply.

Another consideration was that only the outboard tanks had jettison valves. So, they used the 87 octane fuel from the inboard tanks first, during the climb out and cruise, because in the event of an emergency they couldn't dump it. Then they switched to outboard tanks and 100 octane fuel for the remainder of the trip.

The ability to use +9lbs when running on 100 octane as an emergency rating would probably factor in tactical considerations as well, so maybe they switched to outboard tanks when in dangerous airspace or over the target/during the bomb run, just to be able to pull the boost cut-out and throttle up to +9 if they needed.

In case of a long-range run (like the raid on the Cologne power station on August 12th 1941), this would probably mean using 87 octane on the outbound leg, switching to 100 octane near the target, switching back to 87 octane once outside the "danger zone" (if any was still left in the tanks) and finally, switching back to 100 octane fuel for the remainder of the trip back home.

In any case, this could make up for a sizable part of fuel expense for both types of fuel, especially if we consider that during the BoB they were operating throughout the battle:
a) in the long range reconnaissance role (as far as Germany itself) and
b) attacking targets as far as Denmark.

After the description of their manufacturing restrictions and resulting operating procedures above, it's more or less clear that the more far-away a Blenheim target was the more 100 octane fuel would be used, since close-range targets would only need the inboard tank fuel load and could be flown solely on 87 octane fuel (less weight, less boost needed for take-off-->no need for 100 octane)

The difficult part here is getting a similar graph for Blenheim sorties and factoring in target range, so that we can actually know how much of the 100 octane fuel expenditure could be attributed to them.

I don't have the wealth of references some of you guys have, but i thought this might interest you and you may be able to dig deeper into it ;)

*Buzzsaw*

06-16-2011, 04:13 AM

Salute

Thanks for the info Blackdog.

And of course, the Blenheim was only the smallest of the bombers which the RAF had available and was the only bomber to use 100 octane, but as you say, only in the outside wing tanks, and only for takeoff.

Bomber Command had 207 Armstrong Whitworth Whitley's the 33,000 lb heavy.

They had even more Hampdens, over 250, as well as close to 200 Wellingtons. All these bombers used huge amounts of 87 octane fuel, they flew missions all over Northern Germany, as far as Berlin, many times the range of the short hops the fighters made in their intercepts.

In addition, coastal command aircraft also flew constant patrols, over very long distances, the anti-U-Boat campaign was already a major priority.

All of this explains the heavier usage of 87 octane fuel.

335th_GRAthos

06-16-2011, 09:42 AM

im mean i know the importance of altitude adavantage, but on the small dogfight maps, i couldnt gain it before i was already chased.

Hallo David,
You asked a rather simple question and I am afraid your thread got kidnaped :D

I think the best book to have and read is:
Fighter combat: tactics and maneuvering by Robert L. Shaw
as it explains the differences between maneuveurability and speed and tactics against different types of oponents.
Despite that, there are some serious "deficiencies" in the CoD aiplane models (judging by the tenacity people argue about their 87oct vs 100oct fuel (I do not belong to this club)) and "deifiencies" in the game graphics engine (low quality ground, small size representation of enemy planes, head movement restriction) which will considerably hinder your capability of applying what you will learn in this book in practice in this game.
Usualy the best solution to solve the problem is flying in pairs (with a wingman) and everybody covers each others back. This is the only technick that always work, even against massively superior opponents (e.g. the "Thatch-wave" technik American pilots used in the Pacific as the only way to defend their Wildcats against the vastly superior Zeros) but it requires in most cases that you enter a squadron and train a lot in navigation, formation flying, deflection shooting and voice communications in order to perfection the art of wingman.

Sorry I could not give a quick and simple solution.

~S~

David198502

06-16-2011, 02:28 PM

true,but it turned in an interesting debate.
thx for the book recommendation.i will buy it if i find it.i thought a lot of times about joining a squadron...may be its time to become a member of one.

Kurfürst

06-16-2011, 02:34 PM

In terms of Bomber Command usage, the pilot's operating handbook for the Blenheim Mk.IV confirms the above points.

Actually, the Mk.IV used both types of fuel.

What happened?
1) They needed more range so they added two more fuel tanks, one in each wing (the outboard tanks).
2) This made the aircraft heavier so it needed more power to get off the ground safely when fully bombed-up and fueled.
3) Engines were modified and a boost cut-out installed, so that maximum boost could raised from +5 lbs to +9 lbs.
4) This needed fuel with more resistance to detonation (aka 100 octane), but it was also important for Fighter Command use.

So, what they did was load 100 octane only in the outboard tanks and use 87 octane in the inboard tanks.

etc. etc.

Hi,

I generally agree. I've heard of Blenheims using 100 octane in the outer tanks only for boosting purposes (presumably take off with heavy loads as you say). I don't have the Blenheim manual, unfortunately - do you have link perhaps?

OTOH, the documents supplied by Glider suggest that the actual modus operandi was to have select Blenheim stations at No. 2 Group (Wytton, Watton, Wattisham, West Rayam) receiving only 100 octane fuel, with 87 octane removed at the same time from the storage tanks. I suppose this was probably done to avoid nasty incidents of mistakenly filling tanks w. 87 octane - its rather unhealty to loose all power due to engine failuire in heavily bomb laden bomber on takeoff..

http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/Item36thMeetingactionsfrom5thmeetingA-1.jpg
http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/Item46thMeetingactionsfrom5thMeetingB-1.jpg

Given the above, I believe in practice these Blenheims concerned were fueled with 100 octane only.

[QUOTE]The difficult part here is getting a similar graph for Blenheim sorties and factoring in target range, so that we can actually know how much of the 100 octane fuel expenditure could be attributed to them.

Indeed it is complicated I fully agree. As a rough guess, I presume that assuming 5 times the consumption for a Blenheim Squadron compared to a S/H fighter squadron is a reasonable assumption, given they had twice the engine and at least twice the range to target.

Kurfürst

06-16-2011, 02:35 PM

Crumpp

06-16-2011, 02:58 PM

the 12 lbs were useful without the damaging of engine

Geez....

You people are still debating this? Where is the common sense?

:o

Seadog

06-16-2011, 05:15 PM

A, can you produce even a single primary document saying all of Fighter Command using 100 octane fuel and 100 octane fuel only?
B, can you explain, that if FC would use only 100 octane fuel, why do 87 octane issues suddenly rise at the moment Fighter Command is flying more operational sorties?

We know that the RAF was using vast amounts of 100 octane fuel. If RAFFC wasn't using it, who was? You have never produced a single document stating that some of RAFFC was still using 87 octane and the burden of proof is upon you.

Flight activity of all kinds will increase with good weather. This is such a simple concept, that it will be instantly apparent to almost everyone.

http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/100-87issues-FC_sorties_duringBoB.png

The RAFFC flew 5700 sorties and the RAF issued about 4500 tons of 100 octane fuel during the 1st week of September. 5700 sorties at 75 gallons per sortie = 427500 gallons or 1374 tons (assuming every fighter does a dead stick landing with empty tanks, it only rises to 1650 tons). This leaves more than 3000 tons for use in RAFBC and all other assorted and sundry users, more than enough for every twin engined Merlin bomber and fighter to be using 100 octane fuel and still leave lots left over for use by RAFFC.

TomcatViP

06-16-2011, 11:36 PM

Geez....

You people are still debating this? Where is the common sense?

:o

There is too much things that does not match

Blackdog_kt

06-17-2011, 12:39 AM

Salute

but as you say, only in the outside wing tanks, and only for takeoff.

Not really, what i said was indeed "only in outboard tanks" but it is far from saying "only for takeoff": unless they were planning a one-way trip they would have to burn that 100 octane on the return leg of the sortie as it was the only supply available to them after the inboard tanks had gone dry :-P

What i previously described amounts to "on takeoff and half of the cruise portion of the flight", which is half the fuel burn for the sortie.

In other words, quite a lot of 100 octane fuel in case of long range sorties and as low as none at all in short range sorties (unless they were bending the rules and carrying a few minutes worth of it to get better WEP boost values in case of trouble, but that would be a negligible amount).

In conclusion, if the Blenheims generated enough sorties at long ranges or were routinely tasked with loitering around a certain area on patrol duty (eg, U-boats, reconnaissance, etc), they could account for quite a lot of 100 octane use. If on the other hand they were mostly flying cross-Channel hops in nuisance raids, they would mostly burn 87 octane.

Until someone can produce a relevant document that deals with the amount, type and range/duration of their sorties during the BoB the argument can swing either way ;)

Kurfürst

06-17-2011, 04:18 AM

This might prove relevant:

"the Bomber Stations concerned was practically complete (these Stations are Wyton Watton, Wattisham, West Rayham)"

http://www.ww2aircraft.net/forum/attachments/aviation/101699d1249771277-use-100-octane-fuel-raf-pt-2-item-5-6th-meeting-minute-.jpg

Quite clearly only four Bomber/Blenheim bases were 'concerned' with 100 octane fuel. If those four stations held all Blenheim Squadrons, your claim may be true, but somehow I doubt it.

Wyton had two Blenheim Squadrons at the time: Nos. 15 and 40
"In December 1939, both Wyton squadrons were sent to France and Nos. 15 and 40 Squadrons returned from the Continent to Wyton, the first step in converting Battle squadrons to Blenheims. Both squadrons flew their first bombing raids from Wyton on May 10, 1940 against targets in the Low Countries. The Blenheims of No. 57 Squadron were based briefly at Wyton in June before going south, returning for two weeks the following month before flying north only to appear again at Wyton in late October. "

Wattisham had also two, Nos. 107 and 110 Squadrons http://www.raf.mod.uk/bombercommand/s30.html
http://www.raf.mod.uk/bombercommand/s106.html

Watton also had two Blenheim Squadrons: Nos.21 and 82 Squadrons
http://www.raf.mod.uk/bombercommand/s31.html

West Rayham had only one Blenheim Squadron, No. 139, and possibly from June 1940 also no. 18 also operating.

That's 7 or more like 8 Blenheim Squadrons on 100 octane. At that time there were 15 Bomber Command Sqns. operating Blenheim IVs. But this pretty much explains where 100 octane fuel went in such quantities - even those 8 Blenheim Squadrons were consuming a lot. Total tankage was 468 imp. gallons compared to 85 gallons on the Spit - a worth of about 45 Fighter Squadrons.. ;)

Seadog

06-17-2011, 06:16 AM

But this pretty much explains where 100 octane fuel went in such quantities - even those 8 Blenheim Squadrons were consuming a lot. Total tankage was 468 imp. gallons compared to 85 gallons on the Spit - a worth of about 45 Fighter Squadrons.. ;)

No.
468 gallons is with no bomb load
Total internal fuel capacity was 280 imperial gallons, or less, when used as a bomber. Normal TO weight = 13500 lb and 14300lb max.

Empty weight = 9790 lbs
Bombs = 1000lb
crew = 600 lbs
oil = 200lb (28 gallons)
fuel = 280 gals = 2016lb (468 gallons = 3370lb and 15300lb TO weight with 1000lb bomb load)
------------------------
= 13886lbs, when normal max was 13,500lbs and overload = 14,400lb

13500lb = ~230 gallons with a 1000lb bomb load.

Most BofB Blenheim missions were tactical strikes into France or as fighters where even 230 gallons was far more than was required.

Kurfürst

06-17-2011, 03:43 PM

We know that the RAF was using vast amounts of 100 octane fuel.

5-10 000 tons a month - out of 50 000 tons total per months or compared to about 90 000 tons per month consumed by the Luftwaffe is hardly 'vast amounts'.
Its a tiny amount, even compared to 1940 overall or later RAF consumption.

[QUOTE=Seadog;298133]If RAFFC wasn't using it, who was?

Bomber Command (at least 8 Squadrons of Blenheims for example), engine manufacturers for running ins and testing, Squadrons for non-operational flying and practice. One Squadron in August 1940 for example did

You have never produced a single document stating that some of RAFFC was still using 87 octane and the burden of proof is upon you.

Of course I did. Ironically, just two posts above. Besides yo simply display the logical fellacy of the Invisible Pink Unicorn: you seem to believe that if you claim something, without being capable proving it, and if others don't prove you wrong, you are automatically right. Right? Well, its just utter nonsense. See: http://en.wikipedia.org/wiki/Invisible_Pink_Unicorn

All Figther Command Aircraft were operating on 87 octane previously; in March 1939 a decision was made to convert sixteen fighter Squadrons to 100 octane by September 1940, and in around May 1940 it was noted that 'certain' fighter squadrons were to be supplied with 100 octane fuel.

Certain, not all. Well its not too hard figure out what the other-than-certain Fighter Squadrons were still running on, my dear Watson?

http://i38.photobucket.com/albums/e133/Kurfurst/BoB%20Stuff/Item36thMeetingactionsfrom5thmeetingA-1.jpg

The RAFFC flew 5700 sorties and the RAF issued about 4500 tons of 100 octane fuel during the 1st week of September. 5700 sorties at 75 gallons per sortie = 427500 gallons or 1374 tons (assuming every fighter does a dead stick landing with empty tanks, it only rises to 1650 tons). This leaves more than 3000 tons for use in RAFBC and all other assorted and sundry users, more than enough for every twin engined Merlin bomber and fighter to be using 100 octane fuel and still leave lots left over for use by RAFFC.

That's an interesting claim. Can you tell me how much 100 octane was spent on operational training, engine testing, run-in, was used up by Bomber Command's Blenheims etc..? Without that, your calculation is an extremely crude and wishful example..

Seadog

06-17-2011, 07:59 PM

All Figther Command Aircraft were operating on 87 octane previously; in March 1939 a decision was made to convert sixteen fighter Squadrons to 100 octane by September 1940, and in around May 1940 it was noted that 'certain' fighter squadrons were to be supplied with 100 octane fuel.

That's an interesting claim. Can you tell me how much 100 octane was spent on operational training, engine testing, run-in, was used up by Bomber Command's Blenheims etc..? Without that, your calculation is an extremely crude and wishful example..

RAFFC had about 45 Merlin engined fighter squadrons and 5 Blenheim Squadrons operational under RAFFC command on July 08. About 10 - 12 Hurricane, non operational squadrons were forming up.

so lets say that RAFFC had 57 operational squadrons during the 1st week of Sept. 57 squadrons into 5700 sorties = 100 sorties week/squadron. Lets assume 15 Blenheim squadrons (5 x RAFFC and 10 X RAFBC) = 1500 sorties at 230 gallons/sortie = 1108 tons of 100 octane. So our 5 Blenheim squadrons flew 500 of RAFFC's sorties leaving 5200 to be flown by Merlin engined fighters @ 75 gallons/sortie = 1254 tons, so total RAFFC and RAFBC 100 octane use = 2362 tons. This is only about 1/2 the total consumption of 100 octane and it accounts for 5200 SE fighter and 1500 hundred twin engined Blenheim sorties. There simply isn't enough 100 octane fuel users left over to consume the ~4400 tons if RAFFC isn't using 100% 100 octane.

5-10 000 tons a month - out of 50 000 tons total per months or compared to about 90 000 tons per month consumed by the Luftwaffe is hardly 'vast amounts'.
Its a tiny amount, even compared to 1940 overall or later RAF consumption.

According to the graph you supplied, the RAF used about 15000 tons of 100octane and ~ 24000 tons of other grade during Sept 1940. How much 100 octane did the Luftwaffe use?

Can you present evidence stating that even one RAFFC Merlin engined squadron was using 87 Octane from July to Oct 1940? If I was an RAFFC pilot and my Hurricane/Spitfire was using 87 octane, when the squadron down the road was using 100 octane, you can be sure that I would have mentioned it my memoirs or complained about it while writing up a combat report: "The Ju-88 got away because I couldn't use overboost..." Yet there isn't a single statement anywhere about RAFFC pilots complaining about the lack of 100 octane engines or fuel, during the Battle.

TomcatViP

06-20-2011, 02:41 PM

Did they complain abt the lack of reheat on their Jet engines ?

Kurfürst

06-20-2011, 06:08 PM

I wonder, is there a single statement anywhere about Luftwaffe pilots complaining about the lack of 100 octane engines or fuel, during the Battle..? Or the Italians..?

Seadog

06-20-2011, 06:29 PM

I wonder, is there a single statement anywhere about Luftwaffe pilots complaining about the lack of 100 octane engines or fuel, during the Battle..? Or the Italians..?

Yes...

"...Goering turned to me. I did not hesitate long. 'I should like an outfit of Spitfires for my group..."'
Galland, The First and the Last.

VO101_Tom

06-20-2011, 07:13 PM

Yes...

"...Goering turned to me. I did not hesitate long. 'I should like an outfit of Spitfires for my group..."'
Galland, The First and the Last.

Does the history work so? Did you read this book? You would quote it what wrote in the next sentences?

ICDP

06-20-2011, 07:17 PM

Yes...

What a tool, and you wonder why nobody takes you seriously.

Here is a quote directly from the book as made by Galland (you obviously haven't read it).

"The theme of fighter protection was chewed over again and again. Goering clearly represented the point of view of the bombers and demanded close and rigid protection. The bomber, he said, was more important than record bag figures. I tried to point out that the Me109 was superior in the attack and not so suitable for purely defensive purposes as the Spitfire, which, although a little slower, was much more manoeuvrable. He rejected my objection. We received many more harsh words. Finally, as his time ran short, he grew more amiable and asked what were the requirements for our squadrons. Moelders asked for a series of Me109's with more powerful engines. The request was granted. 'And you ?' Goering turned to me. I did not hesitate long. 'I should like an outfit of Spitfires for my group.' After blurting this out, I had rather a shock, for it was not really meant that way. Of course, fundamentally I preferred our Me109 to the Spitfire, but I was unbelievably vexed at the lack of understanding and the stubbornness with which the command gave us orders we could not execute - or only incompletely - as a result of many shortcomings for which we were not to blame. Such brazen-faced impudence made even Goering speechless. He stamped off, growling as he went."

So Galland even in his own book states he preferred the 109 over the Spitfire and that his quote was made purely to get at Goering. How can you expect to be taken seriously when you twist words and meanings to suit your own agenda?

VO101_Tom

06-20-2011, 07:25 PM

What a tool, and you wonder why nobody takes you seriously.

...

So Galland even in his own book states he preferred the 109 over the Spitfire and that his quote was made purely to get at Goering. How can you expect to be taken seriously when you twist words and meanings to suit your own agenda?

+1 :rolleyes:

CaptainDoggles

06-20-2011, 07:45 PM

Yes...

Never seen someone's credibility evaporate quite so quickly.

Seadog

06-20-2011, 07:49 PM

Moelders asked for a series of Me109's with more powerful engines.

So Galland asked for Spitfires and Moelders wanted 100 octane Me109s...

CaptainDoggles

06-20-2011, 08:35 PM

So Galland asked for Spitfires and Moelders wanted 100 octane Me109s...

Work on your reading comprehension skills a bit?

Galland asked for spitfires facetiously, because he was receiving orders from above that the escort fighters were to stay close to the bombers, a role to which the spitfire was better suited than the 109. He was trying to make a point that his fighters were not being used to their strengths, not that he felt the spitfire was superior.

Similarly Moelders did not ask for "100 octane 109s" since the Germans didn't classify their fuel that way (and in some cases measured the octane number differently). He asked for 109s with more powerful engines.

Seadog

06-20-2011, 11:03 PM

He asked for 109s with more powerful engines.

Luftwaffe fighter pilots, like all fighter pilots, wanted aircraft with better performance. This is abundantly clear from the above quotes and they pressed their claims with Goering himself! One way to get better performance was through the introduction of the 100 octane rated DB601N engine and it is clear that Luftwaffe fighter pilots were pressing for its introduction...( I can't wait for the torrent of claims that Luftwaffe pilots "didn't want any stinking 100 octane rated engines...":rolleyes:) RAFFC pilots also wanted better performance, and they got a complete transition to 100 octane fuel, a transition which was completed prior to the start of the battle.

Danelov

06-20-2011, 11:07 PM

Salomonic hipotetic solution: Luftwaffe must buy some A6M2 Zero(Or buy the licence)and everybody is happy.

CaptainDoggles

06-20-2011, 11:07 PM

Luftwaffe fighter pilots, like all fighter pilots, wanted aircraft with better performance. This is abundantly clear from the above quotes and they pressed their claims with Goering himself! One way to get better performance was through the introduction of the 100 octane rated DB601N engine and it is clear that Luftwaffe fighter pilots were pressing for its introduction...( I can't wait for the torrent of claims that Luftwaffe pilots "didn't want any stinking 100 octane rated engines...":rolleyes:) RAFFC pilots also wanted better performance, and they got a complete transition to 100 octane fuel, a transition which was completed prior to the start of the battle.His exact words were "Moelders asked for a series of Me109's with more powerful engines."

You can't just make stuff up and attribute it to a historical figure. You don't really know what octane the pilots wished they had, did you?

The Germans generally didn't concern themselves with RO Numbers; their fuel was graded alphanumerically. C-3 fuel was what the Allies would have called 130 Octane fuel (150 after 1942 IIRC).

Seadog

06-20-2011, 11:34 PM

His exact words were "Moelders asked for a series of Me109's with more powerful engines."

You can't just make stuff up and attribute it to a historical figure. You don't really know what octane the pilots wished they had, did you?

The Germans generally didn't concern themselves with RO Numbers; their fuel was graded alphanumerically. C-3 fuel was what the Allies would have called 130 Octane fuel (150 after 1942 IIRC).

Fighter pilot don't give a damn about octane ratings except to get more power. One way to get more power (at least on the Merlin) is to run the engine on a higher octane fuel and increase the boost pressure. RAFFC did this to every Merlin powered fighter in its operational inventory, and thus no pilots are recorded as wanting 100 octane fuel, "like my pal has in the squadron done the road".

Luftwaffe pilots also pressed for "more powerful engines" and again high octane fuel made this a much easier proposition. Asking for more power is exactly the same as asking for higher octane fuel. ( I didn't have to wait long for the "we don't need no stinking 100 octane fuel" claims from the Lufters...:-P )

CaptainDoggles

06-20-2011, 11:38 PM

Fighter pilot don't give a damn about octane ratingsCouldn't agree more.

( I didn't have to wait long for the "we don't need no stinking 100 octane fuel" claims from the Lufters...:-P )Please quote where I said that.

Kurfürst

06-20-2011, 11:44 PM

RAFFC pilots also wanted better performance, and they got a complete transition to 100 octane fuel, a transition which was completed prior to the start of the battle.

Source please. Oh wait, we have your word for it, and everything it worth for. :D

Yet there isn't a single statement anywhere about RAFFC pilots complaining about the lack of 100 octane engines or fuel, during the Battle.

Fighter pilot don't give a damn about octane ratings except to get more power.

No comment :D

Seadog

06-21-2011, 12:04 AM

Source please. Oh wait, we have your word for it, and everything it worth for. :D

No comment :D

We have a source:

https://lh4.googleusercontent.com/-0QgyynI6HjY/Tfrgg69OY4I/AAAAAAAAACQ/gbyH2vsdlT0/s640/All_merlin_100oct.jpg

and you have not presented a single shred of evidence to contradict it.

Quote:
Originally Posted by Seadog
Yet there isn't a single statement anywhere about RAFFC pilots complaining about the lack of 100 octane engines or fuel, during the Battle.
Quote:
Originally Posted by Seadog
Fighter pilot don't give a damn about octane ratings except to get more power.

No comment

Of course you have no comment. The whole point of 100 octane fuel was give engines more power through higher boost pressure, and no RAFFC pilot flying a Merlin engined fighter during the BofB is on record of complaining that he can't use overboost, and so was deprived of 30% more power than his buddy in another squadron.

CaptainDoggles

06-21-2011, 12:25 AM

no RAFFC pilot flying a Merlin engined fighter during the BofB is on record of complaining that he can't use overboost, and so was deprived of 30% more power than his buddy in another squadron.

As I said earlier, absence of evidence does not imply evidence of absence.

Your source, if I remember from way back in the thread, is a 3rd-party book. I asked if they had references since this is not a primary source and you ducked the question.

Seadog

06-21-2011, 12:43 AM

As I said earlier, absence of evidence does not imply evidence of absence.

Your source, if I remember from way back in the thread, is a 3rd-party book. I asked if they had references since this is not a primary source and you ducked the question.

I didn't duck it. We have a source that states that RAFFC went completely to 100 octane, and there is no source that states that this is incorrect, and there is a large body of evidence that supports the view that RAFFC used 100% 100 octane fuel operationally during the BofB. If you don't accept the above source, than present some evidence that from July 10 to October 30 1940, that even a single RAFFC Merlin powered squadron was using 87 octane during combat operations.

There was about 46 RAFFC Merlins engined fighter squadrons available on July 08 1940. Surely you can find evidence that one of them was using 87 octane operationally during the battle. Just one...;)

Crumpp

06-21-2011, 01:58 AM

there is no source that states that this is incorrect,

Yes there is a primary source that refutes the secondary source you posted, Seadog.

The seventh conference on 18 May 1940 clearly states that certain units in Fighter Command will make the switch.

That document has been posted ad nauseum.

As this on going fuel debate....

The best source on German Aviation Fuels is the Fischer Tropsch Archives.

http://www.fischer-tropsch.org/

They have a good collection of documents online anyone can learn about German fuels. Allied Fuel and German fuels were not directly comparable.

B4 is slightly better than 87 grade Allied fuels and is roughly equal to 91/~115 octane.

C3 began as the equivalent to 100/130 grade allied fuels and was later improved to 100/140 grade which allowed such improvements as a straight manifold pressure increase without additional knock limiting performance enhancement to 1.62ata in the BMW801D2 series and 1.98ata in the DB605 series engines.

C3 was adopted in 1940 and was used during the BoB.

http://img40.imageshack.us/img40/3662/c3inthebob.jpg (http://imageshack.us/photo/my-images/40/c3inthebob.jpg/)

The whole debate is silly and pointless. The arguments are put forth by gamers to make their personal game play more enjoyable such that a game shape performance can overcome their own inadequacies. It is an agenda advanced by clowns who focus on whatever specific portion paints the desired picture without regard to the whole.

The facts are the German fuel was roughly equal but on the whole slightly inferior to the natural petroleum. The Allied fuels were better but allied engine technology could not take full advantage of their superior fuels. The German materials technology, chemical engineering, and fuel metering technology was much better and made up for the lower quality fuels.

Just the fact the Germans had direct fuel injection technology and the allies never did balances any fuel differences. One can make considerable power gains without changing fuel type just by changing the fuel metering system from a carburetor or Throttle Body Injection to Direct Injection. In a 1000 hp engine, you can expect to gain 80-150 hp just by changing the fuel metering method.

The whole debate ends up being a wash.

VO101_Tom

06-21-2011, 02:08 AM

Fighter pilot don't give a damn about octane ratings except to get more power. One way to get more power (at least on the Merlin) is to run the engine on a higher octane fuel and increase the boost pressure....

Its not true. Moelders asked for a series of Me109's with more powerful engines. DB 601 A-1, DB 601 Aa, DB 601 N, later DB 601 E (for F), DB 605 engine family (for G-K). All were stronger than the previous type, without it that they would use the 100 octane C3 fuel instead of the 87 octane B4 ones. Of course, if they use C3 fuel, MW30, MW50, or GM1 system, the strength of the engine is growing rather yet. But purely visible, that it is possible to make stronger engine, using the same fuel (B4):

http://www.enginehistory.org/German/DB/Fig00.jpg
http://www.enginehistory.org/German/DB/Chart01.jpg

Seadog

06-21-2011, 03:29 AM

Yes there is a primary source that refutes the secondary source you posted, Seadog.

The seventh conference on 18 May 1940 clearly states that certain units in Fighter Command will make the switch.

and the accepted dates for the BofB are July 10 to Oct 30, 1940.

Crumpp

06-21-2011, 11:10 AM

Seadog,

18 May 1940 is only 6 weeks from the start of the Battle of Britain.

The language in that primary source document refers to "certain units" and not "ALL" units.

Very importance difference.

Seadog

06-21-2011, 05:20 PM

Seadog,

18 May 1940 is only 6 weeks from the start of the Battle of Britain.

The language in that primary source document refers to "certain units" and not "ALL" units.

Very importance difference.

The German Army defeated France in 6 weeks...6 weeks is a long time.

RAFFC had many units which did not require 100 octane, such as OTU and a few squadrons of Gladiators. In any event, again all the evidence points to RAFFC operational Merlin engined squadrons using 100% 100 octane. There isn't a single source that states that an operational Merlin engined fighter squadron was using anything else.

Blackdog_kt

06-21-2011, 05:42 PM

Asking for more power is exactly the same as asking for higher octane fuel. ( I didn't have to wait long for the "we don't need no stinking 100 octane fuel" claims from the Lufters...:-P )

No it's not. An engine of a sufficiently bigger displacement running "normal" fuel with the appropriate boost values will still outperform an engine with a lower displacement. If they have similar displacement a smaller engine running 100 octane could reach or even surpass the HP of a bigger one running 87 octane, but a sufficiently bigger displacement would ensure superior performance even when running fuel of a lesser octane rating.

And that's without even taking into account other things like supercharger design and gearing and propeller design, things which affect not only the powerband of the engine but also the appropriate altitudes where the extra power can be better used.

What i'm trying to say is that asking for engines with more HP can mean a combination of many different things. When you are discounting them all and pretend its only the octane rating that matters you are just simplifying for the sake of pushing a personal viewpoint without having to come up with the supporting proof: "they asked for more power, so they should surely mean a better octane rating".

I'm all for Spits and Hurricanes getting their 100 octane and constant speed prop variants. Keep the current ones for battle of France scenarios (i mean we already have much of the map so why lose the ability to create such missions) and let's also add the proper battle of Britain variants.

I'm also in favor of having a 50% chance (or whatever the appropriate percentage was) of spawning with DB601N engines on your 110, which you make absolutely no mention off in any of your arguments. I've given you the benefit of doubt until now but you're gradually exhausting that reserve.

No offence meant and i'm not saying you're just pushing for a gameplay advantage for your favorite ride because i'm not the kind of fool that will pretend to know what's in another person's mind. What i'm saying is that you sure sound like that more and more as time goes by, i just don't have a way to confirm it, which makes me averse to getting convinced out of a matter of principle. I guess this goes for many others as well.

Seadog

06-21-2011, 06:34 PM

1)What i'm trying to say is that asking for engines with more HP can mean a combination of many different things. When you are discounting them all and pretend its only the octane rating that matters you are just simplifying for the sake of pushing a personal viewpoint without having to come up with the supporting proof: "they asked for more power, so they should surely mean a better octane rating".

I'm all for Spits and Hurricanes getting their 100 octane and constant speed prop variants. Keep the current ones for battle of France scenarios (i mean we already have much of the map so why lose the ability to create such missions) and let's also add the proper battle of Britain variants.

2)I'm also in favor of having a 50% chance (or whatever the appropriate percentage was) of spawning with DB601N engines on your 110, which you make absolutely no mention off in any of your arguments. I've given you the benefit of doubt until now but you're gradually exhausting that reserve.

3)No offence meant and i'm not saying you're just pushing for a gameplay advantage for your favorite ride because i'm not the kind of fool that will pretend to know what's in another person's mind. What i'm saying is that you sure sound like that more and more as time goes by, i just don't have a way to confirm it, which makes me averse to getting convinced out of a matter of principle. I guess this goes for many others as well.

1) Again, pilots wanted more power. In the Merlin III, 30% more power was available through a simple mod, that could be done in an afternoon using fuel that was readily available. RAF pilots had been aware of this for several years, and they got a full transition to 100 octane prior to the BofB, indeed many France based Hurricane squadrons used it during the BofF. I don't and haven't discounted other options, but raising displacement, for example, invariably means greater weight and greater frontal area, something that pilots don't want.

2) see my post #71:
http://forum.1cpublishing.eu/showpost.php?p=299921&postcount=71
By all means, include all historical engine and aircraft variants.

3) No, I am pushing for a game that sims RL. In RL Merlin III aircraft have access to much higher power at low altitude. At high altitude these advantages dwindle and the Me109 has many advantages, and this will force the Me109 pilots to fly as per RL, IE, stay high, and fight in the vertical. Dogfighting Hurricanes at low altitude is not a great idea. The RAFFC made a rapid transition to 100 octane engines and CS props and it was a much tougher proposition than the Luftwaffe had been led to believe, but thats how it was.

Kurfürst

06-21-2011, 10:05 PM

I don't and haven't discounted other options, but raising displacement, for example, invariably means greater weight and greater frontal area, something that pilots don't want.

Compared to that theory, German DB 601 was same size as weight as single stage Merlin, 605 actually lighter then two staged Merlin, while the French 35-liter class Hispano Suize V12s were considerably lighter than both.

The only practical way a smaller displacement engine can keep up with larger ones is by heavy supercharging, but that does not comes free, superchargers and their systems add weight, and so does decreasing fuel effiency: more fuel need to be carried for same range.

Seadog

06-21-2011, 11:25 PM

Crumpp

06-22-2011, 12:05 AM

Check the math on that document....

1430lbs / 1175hp = 1.21 lb/hp not 1.13lb/hp....

The Merlin has the same power to weight at the DB601.

Seadog

06-22-2011, 12:21 AM

Check the math on that document....

1430lbs / 1175hp = 1.21 lb/hp not 1.13lb/hp....

The Merlin has the same power to weight at the DB601.
It actually states 1450 lbs but also 1240hp at 2850rpm @ 10,000ft (two values given for the Merlin XX)

However, the DB601N power is WEP. The equivalent figure for a Merlin XX would be 1485hp at 14lb/3000rpm @ 6000ft and 1490hp at 16lb/3000rpm @ 12500 ft and 1280hp at 3000rpm/12lb @ TO, at least in 1942 but the TO figure is applicable to 1940 as well.

robtek

06-22-2011, 06:32 AM

you actually implement that in a comparision wep is set against full mil.????
You are talking about the N, not the A.

Crumpp

06-22-2011, 01:06 PM

Merlin XX would be 1485hp at 14lb/3000rpm @ 6000ft and 1490hp at 16lb/3000rpm @ 12500 ft and 1280hp at 3000rpm/12lb @ TO

The document compares the operational engines at the time it was prepared. At 17500 feet, the document is correct in the power output of a Merlin XX at it's approved Emergency Power rating of +9lbs at the time the engine were compared. It is also correct in its assessment of the DB601N series.

It is not correct in its math of the power to weight ratio of the engines. The Merlin XX is the same as the DB601N.

You need to look at the DB605 series to compare those other ratings. Also ensure you are looking at the correct power, ie...indicated, static or RAM, Brake or Thrust, and if it takes into account exhaust thrust...

Seadog

06-22-2011, 05:14 PM

The document compares the operational engines at the time it was prepared. At 17500 feet, the document is correct in the power output of a Merlin XX at it's approved Emergency Power rating of +9lbs at the time the engine were compared. It is also correct in its assessment of the DB601N series.

It is not correct in its math of the power to weight ratio of the engines. The Merlin XX is the same as the DB601N.

In Nov 1940 the operational limits of the Merlin XX were 12lb/3000rpm TO = 1280hp, and 12lb/3000rpm @8500ft = ~1360hp in MS gear. Operation of the boost cutout would give ~14lb in FS gear, but I don't know exactly when official approval was given, however this capability was present in all Merlin XX engines.

At 1280hp and 1450lb weight gives lbs/hp = 1.13 but I agree that the values given in the chart were confusing.

TomcatViP

06-22-2011, 09:13 PM

So I understand now what's all abt lol; You hve been so scared abt the dynamic capacities of the Spit ? The guys that did mod the FM in IL2 did used badly wrong assumptions.

Stay at high speed . Don't over G. Don't put yourself where you'll need AoA and I swear you'll knock down any 109 even at full mil power. Big wings are made for that !

Damn Seadog Is that really a "Cat" tht hve to ensure you on this point ?!! :rolleyes:

Viper2000

06-23-2011, 12:07 PM

Compared to that theory, German DB 601 was same size as weight as single stage Merlin, 605 actually lighter then two staged Merlin, while the French 35-liter class Hispano Suize V12s were considerably lighter than both.

The only practical way a smaller displacement engine can keep up with larger ones is by heavy supercharging, but that does not comes free, superchargers and their systems add weight, and so does decreasing fuel effiency: more fuel need to be carried for same range.

Actually, if you do the thermodynamic analysis, you'll tend to find that supercharging doesn't particularly damage fuel efficiency, provided that you have reasonable component efficiencies and make a fair comparison (which is the difficult bit).

Power:weight at sea level will tend to be fairly insensitive to supercharge because the supercharged engine sees higher pressures and therefore has to be heavier, whilst OTOH the unsupercharged engine is bigger. So you end up with a small area of thick metal vs a large area of thick metal.

The supercharged engine has a higher power density, and this will tend to make life harder for the cooling system.

If you compare at fixed cruising speed, there will be an optimum degree of supercharge, beyond which you'll lose more from the increased cooling problems than you've gained from the smaller engine. OTOH, because the supercharged engine is smaller, it has less non-cooling drag, and so you'd expect to cruise faster, which helps to make the radiator smaller.

In the end, the trade space is complex, and it isn't especially easy to make a general case that one approach to engine design is better than another. Hence the diversity of engine designs; if there was a trivial optimum then engine designers would have swiftly converged upon it, and the world would be a much less interesting place.

Viper2000

06-23-2011, 12:49 PM

Just the fact the Germans had direct fuel injection technology and the allies never did balances any fuel differences. One can make considerable power gains without changing fuel type just by changing the fuel metering system from a carburetor or Throttle Body Injection to Direct Injection. In a 1000 hp engine, you can expect to gain 80-150 hp just by changing the fuel metering method.

The whole debate ends up being a wash.

Direct injection isn't necessarily the best approach.

If you're supercharging then putting fuel into the flow upstream of the supercharger will cool the flow by about 25 K due to the latent heat of evaporation of the fuel.

This considerably reduces the compression work required from the supercharger, which is equivalent to an increase in its polytropic efficiency.

I would suggest that the mixture distribution is likely to be pretty good downstream of the supercharger under design conditions, because the fuel is completely evaporated.

Direct injection will obviously achieve better mixture distribution at low rpm where the supercharger delta H isn't sufficient to guarantee that all of the fuel is evaporated. So DI will give you better performance close to idle. This is very important for car engines, but not so much for aeroplanes.

Furthermore, as you develop your engine and increase the amount of supercharge, you'll tend to cruise higher. Even at constant boost, you'll see a higher supercharger delta H and higher charge temperature, which makes the advantage of adding fuel upstream of the supercharger more important.

It's also much easier and cheaper to make and maintain a single point fuel injection system (be it via a pump or a carb) than it is to make individual injectors for each cylinder.

http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200562.html
http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200563.html
http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200569.html

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

See also:
http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf
(The chronology of engine ratings and outputs may also be of general interest; presumably Mr. Lovesey counts as a primary source...)

CaptainDoggles

06-23-2011, 03:09 PM

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

But engine design was heading towards turboprops in those years (and obviously turbojets), what with the "trent-meteor" hybrid that was instrumental in the development of Rolls-Royce's Dart engines.

Crumpp

06-23-2011, 03:18 PM

2009 Technology of the Year: Direct Fuel Injection

Direct injection-squirting pressurized fuel straight into each cylinder-is the key to keeping internal-combustion engines relevant in the future. For enabling a major step forward in gas and diesel engine power, efficiency, and cleanliness, direct fuel injection is AUTOMOBILE MAGAZINE's 2009 Technology of the Year.

While injecting fuel into the combustion chamber requires approximately fifty times the pressure used with port injection and additional electronic control sophistication, significant benefits are delivered. Since no fuel is deposited on intake-port walls, the air/fuel mixture can be more precisely maintained, benefitting both mileage and emissions. In addition, the cooling effect of gasoline droplets changing to vapor inside the combustion chamber facilitates a higher compression ratio without incurring detonation. Squeezing the mixture harder during compression and allowing it to expand longer on the power stroke wrings additional power out of every ounce of gasoline.

http://www.automobilemag.com/features/awards/0811_2009_technology_of_the_year_direct_injection/index.html

Single point injection has no advantages over direct fuel injection at all. The Supercharger is on a completely separate circuit and the engine still receives all the benefits of supercharging with the additional benefits of direct injection.

Crumpp

06-23-2011, 03:21 PM

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking.

The Allies did not have any direct injection engine technology to use.....

They could not make direct injection workable or practical using their fuel metering technology. Bosch's design, up until recently was the pinnacle of direct injection technology. It requires very high fuel pressures and the German system used a high pressure pump for each cylinder.

As already pointed out, post war, the turbine was supreme so why would any nation waste resources for a post war piston engine aircraft?????

Crumpp

06-23-2011, 03:42 PM

Great Wartime article Viper. Thanks for posting that.

http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200569.html

http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200563.html

http://www.flightglobal.com/pdfarchive/view/1941/1941%20-%200562.html

An article definitely written to contain the public relations damage from intelligence on German fuel metering technology.

Rolls Royce's basic message is the German engines are not as efficient as they could be and only somewhat more efficient than the our engines.....

AND we can make a carburetor heat system that will overcome icing....

:grin:

TomcatViP

06-23-2011, 04:07 PM

OTOH, because the supercharged engine is smaller, it has less non-cooling drag, and so you'd expect to cruise faster, which helps to make the radiator smaller.

Funny that Merlin Vs DB tell the opposite.

Seems you forgot one parameter : rpm and charging raise the strain and the temp with negative consequence on efficiency: try to win the 24h Le Mans race with a 2L engine and then jump in 7.0L 'vette ;)

To put it in perspective : there was no successful post war Merlin engined airliner. But lot of with P&W primitives big radials ;)

TomcatViP

06-23-2011, 04:19 PM

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

Sry but you are bypassing economics realities : the Industrial war machine was in such a strain at the end of WWII that minimal change in production were made where there was not strategical importance in order to downsize the level of investments. Many non-allied advanced tech were simply rejected in face of this.

Civil Aviation (the only one still interested in piston engine at the time) loose for long Injected eng, Fadec (without D and E ;)), canards foreplane etc.. Some of the very much "advanced" tech that was rushed back on the GA shelves as "new" products in the late 80's and 90's.

The conclusions you give does not convince me - Sry I am duplicating earlier comments of very good quality

Viper2000

06-23-2011, 05:01 PM

Funny that Merlin Vs DB tell the opposite.

Seems you forgot one parameter : rpm and charging raise the strain and the temp with negative consequence on efficiency: try to win the 24h Le Mans race with a 2L engine and then jump in 7.0L 'vette ;)

To put it in perspective : there was no successful post war Merlin engined airliner. But lot of with P&W primitives radials ;)

rpm isn't especially interesting. Piston speed is generally a better metric.

Liquid cooled engines run colder than air cooled engines, and actually one of the main problems for the Merlin was over-cooling of the charge during cruising flight, which necessitated modification of the aftercooler to act as a heater to prevent the charge temperature falling below 40ºC.

The Merlin powered version of the DC-4, the Canadair Northstar (http://en.wikipedia.org/wiki/Canadair_North_Star) was considerably faster than its radial engined equivalent. Noise was a problem initially due to the stub exhausts; the big radials tended to have collector rings; a crossover exhaust for the Merlin mitigated this to some extent. It wasn't an unsuccessful machine, but it wasn't ever going to capture the US market because it wasn't American.

As for perspective, how many DB powered airliners were there post WWII?

The Merlin wasn't successful as an airliner engine for many reasons - it hadn't be designed for that sort of duty for a start. It did rather better than the V-1710 though.

But perhaps the main reason for its "failure" as an airliner was that there just weren't suitable British airliners to bolt it onto. Lancastrian, York & Tudor could hardly compete with contemporary products from Lockheed & Douglas, because Britain had basically stopped airliner development in 1939 whilst the Americans had continued throughout the War (because they needed long-range transports anyway). They weren't about to put British engines onto their aeroplanes if they could possibly help it, so the considerable technical lead of the American airframers translated directly into market share for their engine manufacturers.

It's probably better to compare the Merlin's civil record with that of Hercules & Centaurus, which faced a similar airframe problem (though of course at this time Bristol had an aeroplane division as well, which provided them with a captive market for their engines).

In this context, the Merlin doesn't look so bad.

Viper2000

06-23-2011, 05:13 PM

The Allies did not have any direct injection engine technology to use.....

They could not make direct injection workable or practical using their fuel metering technology. Bosch's design, up until recently was the pinnacle of direct injection technology. It requires very high fuel pressures and the German system used a high pressure pump for each cylinder.

As already pointed out, post war, the turbine was supreme so why would any nation waste resources for a post war piston engine aircraft?????

Post WWII, it was perfectly within the Allies' rights to confiscate any and all German IP that they were interested in. So they could have made Bosch fuel injectors and put them into their engines at no great cost. They chose not to.

As for post-war engine development, the US government funded considerable development work on the R-3350 turbocompound, and indeed also upon the R-4360, both of which found their way into airline service.

Britain funded development of the Napier Nomad, which was a more ambitious take on the turbocompound idea (I strongly suspect that this engine was cancelled due to failure to meet its quoted performance; I modelled it in considerable detail a couple of years ago, and I could never make the quoted component efficiencies add up to the quoted SFC...).

Direct injection makes a lot of sense for naturally aspirated engines, compression ignition engines, or engines which operate over a wide power range. It's less attractive for a big aero-engine because if you're operating at fixed power with a reasonable amount of supercharge you should be able to attain excellent mixture distribution, and so the pragmatic solution is to have single point injection into the eye of the supercharger - which is basically what everybody ended up doing.

Of course, these days people aren't designing big piston aero-engines anymore, and they aren't supercharging*, so DI makes sense.

*and turbochargers tend to be bought from turbocharger companies, which means that injection into the eye of the turbo-supercharger impeller isn't really an option because it would be too much of a nightmare to organise the development effort - who pays for what etc?

Viper2000

06-23-2011, 05:52 PM

http://www.automobilemag.com/features/awards/0811_2009_technology_of_the_year_direct_injection/index.html

Single point injection has no advantages over direct fuel injection at all. The Supercharger is on a completely separate circuit and the engine still receives all the benefits of supercharging with the additional benefits of direct injection.

The supercharger is driven by the engine.

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

Supercharger power consumption is just W*Cp*deltaT, ie W*deltaH.

Supercharger isentropic efficiency is

deltaH[actual]/deltaH[isentropic]

In the case of the Merlin, this figure was about 70%.

For isentropic, adiabatic compression,

T2 = T1(P2/P1)^(gamma/(gamma-1))

Hence it's trivial to calculate the isentropic deltaT, and deltaH.

DeltaT and deltaH both get smaller if we reduce T1.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

This reduces the temperature rise across the supercharger, which is equivalent to increasing its adiabatic efficiency.

Clearly this confers an advantage to engines which inject fuel upstream of the supercharger. Given the considerable difficulty associated with increasing the aerodynamic efficiency of compressors, this advantage is not insignificant.

Mixture distribution is going to be very good provided that the charge temperature is sufficiently high for complete evaporation to be ensured. This will basically always be the case at high powers because deltaT is 100 K or more; indeed intercooling & aftercooling start to become necessary once you've got a lot of supercharge.

These advantages vanish at low non-dimensional power settings. Cars spend most of their time at very low non-dimensional power settings, and therefore DI wins hands down most of the time, especially if you go for CI, in which case it's almost no-contest.

In the end, the nature of all engineering trade studies is that the devil is in the detail. The optimum is a strong function of engine size and duty cycle, and we just don't build the sort of highly supercharged, high power spark ignition engines for which single point injection is attractive these days.

To use an analogy, old amplifiers used valves and therefore tended to have large transformers & rectifiers to produce the high DC voltages which allowed them to function. Most modern amplifiers are solid state, and they don't need those high voltages.

This doesn't mean that high DC voltages aren't still a good idea for valve amplifiers; I've got a pair of hundred watt half stacks sat next to me which run in excess of 400 V DC and sound great. But probably 99% of modern amplifiers for domestic use are solid state and so if you just ask "are high voltages a good idea for amplifiers" then the short answer is "probably not".

CaptainDoggles

06-23-2011, 06:18 PM

As for perspective, how many DB powered airliners were there post WWII?

I suspect there is politics involved with that.

Viper2000

06-23-2011, 06:25 PM

Quite.

To a lesser degree the same argument applies to British engines, given that the most successful airliner airframes were American in 1945. Therefore comparison between the Merlin and the R-2800, R-3350 or R-4360 in the civil market isn't really fair; it makes more sense to compare it with the Bristol Hercules or Centaurus, and if you perform that comparison then the Merlin doesn't look quite so much of a "failure" in the civil market anymore...

TomcatViP

06-23-2011, 06:59 PM

... so the pragmatic solution is to have single point injection into the eye of the supercharger ...

I like that ... Good point.

However this shld lead to a certain amount of "latency" with DI eng being more reactive upon power changes by the pilot

Regarding the Merlin as an airliner eng, it has proved unreliable as high power value were run only at high boost and then prove to be non-efficient (the cruise power has always been low); Add to the disastrous engineering of Britain's airliner projects tht seems to hve been hand-ended by gvrnmt officials (don't take me wrong France had to face the very same situation until legitimate firms could emerge out of the bundle in earlies 60's) and you'll end with a more pragmatic vision of the failure of the British industry in perspective of the US success stories like Boeing/Doug/Lockheed right after war end.

Humm hve we run OT (out of topic) again?

Crumpp

06-23-2011, 07:44 PM

I suspect there is politics involved with that.

It was....

Both Daimler-Benz and BMW were forbidden from even being in the aviation market.

Post-war, both companies withdrew from anything to do with aviation and produced automobile engines instead. Both are industry leaders from the moment they entered the market and that leadership continues today.

They produced some of the best engines in the world.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

And injecting fuel directly into the combustion chamber is even better, Viper. How hard is that to understand?

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

And that it is much more efficient to realize the power gains by directly injecting fuel into the combustion chamber than it is by dumping it into an intake manifold......

It's less attractive for a big aero-engine because if you're operating at fixed power with a reasonable amount of supercharge you should be able to attain excellent mixture distribution, and so the pragmatic solution is to have single point injection into the eye of the supercharger - which is basically what everybody ended up doing.

No, it is attractive and if we had the technology to do it on a cost effective basis, we would have done it. It is the ultimate fuel metering method for a piston engine in terms of power and efficiency. A single point injection simply cannot maintain a stoichiometric mixture in all the cylinders. That is why the EGT and CHT will always be different in each cylinder unless you have direct fuel injection.

Crumpp

06-23-2011, 08:01 PM

In fact in the 1950's, we started doing it.....

In the R-4360C Wasp Major power-plant with CH 9 turbo-blower.....

The most important differences between the BH 4 installation (Fig. 3)
and the new power-plant (Fig. 4) are the elimination of the
intergral mechanically-driven supercharger and the carburettor
in the former in favour of the direct fuel injection and
no secondary (internal) supercharger in the latter.

http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200248.html

Viper2000

06-23-2011, 08:48 PM

It was....

Both Daimler-Benz and BMW were forbidden from even being in the aviation market. AFAIK they had to quit for 3 years. Thereafter they didn't get back into aerospace because they didn't have a market rather than anything else.

However, Daimler has quite a big stake in EADS, whilst BMW started a joint venture with RR to make turbofans in Germany from 1990, though now this is 100% owned by RR.

And injecting fuel directly into the combustion chamber is even better, Viper. How hard is that to understand?
Why do you think it's better?

A supercharger is a pretty effective way to homogenise a mixture. The intake manifold is going to end up at roughly charge temperature, which for a Merlin at high power is going to be about 90ºC. You are very unlikely to see condensation of the fuel onto the manifold at that temperature. FAR will therefore be pretty constant from one end of the manifold to the other.

Charge distribution may well vary, which would modify CHT somewhat, but the same argument applies to air distribution.

FAR will become variable when supercharger delivery temperature is low, and this will affect acceleration behaviour, especially from low boost & revs. But aero-engines spend most of their time at fixed, relatively high, power settings, and so this sort of transient behaviour is far less of a problem for an aero-engine than for a car engine.

And that it is much more efficient to realize the power gains by directly injecting fuel into the combustion chamber than it is by dumping it into an intake manifold......
If you are supercharging then you'll win by injecting into the supercharger and thereby reducing supercharger work.

The supercharger is basically adiabatic if you're not injecting fuel or water into it. However, isentropic efficiency of superchargers tends to be much lower than the isentropic efficiency of the compression stroke of a piston engine.

In any case, you're always going to gain more by reducing temperature as early in the compression process as possible, because compressors (whether steady-flow or non-flow) produce temperature ratios in exchange for pressure ratios, whilst the absolute work required for the compression process is proportional to deltaH, i.e. Cp*deltaT.

If you reduce the starting temperature then you reduce the deltaT all the way down the chain, and the benefit multiplies. Therefore, if your fuel is liquid, you really want to inject it at or before the start of the compression process in order to maximise the thermodynamic benefit associated with its latent heat of evaporation.

Clearly for a naturally aspirated engine you might as well go for direct injection, especially if the number of cylinders is small.

The cylinders & pistons are very far from being adiabatic, but are very efficient at performing compression work. The limiting factor is the rate at which they can pass non-dimensional flow through their intake & exhaust valves at any given rpm. Hence supercharging; pre-compressing the air allows you to get more absolute mass flow rate into the fixed non-dimensional mass flow capacity of the piston engine. That's the objective of the exercise.

You use a steady flow machine upstream of the unsteady flow machine because unsteady flow machines are inherently bigger than steady flow machines, and therefore you can shrink the physical size of the engine in relation to its effective flow capacity.

No, it is attractive and if we had the technology to do it on a cost effective basis, we would have done it. It is the ultimate fuel metering method for a piston engine in terms of power and efficiency. A single point injection simply cannot maintain a stoichiometric mixture in all the cylinders. That is why the EGT and CHT will always be different in each cylinder unless you have direct fuel injection. That's only true for naturally aspirated engines.

EGT and CHT will be different anyway because that's life; holding FAR constant is great but it's not magic; airflow into the cylinder depends upon induction manifold design and engine speed. Induction manifold design is quite a complex business, and compromises are inevitable.

DI is very useful if you want to vary non-dimensional power setting over a wide range, but this isn't so important for an aero-engine, and so the higher design-point efficiency offered by injecting into the eye of the supercharger is a pretty compelling argument, before you even consider the cost, mass and complexity advantages.

Modern GA engines are going DI because they're going CI (in order to burn Jet-A and save money), and also because they don't have a lot of cylinders, which means that the cost of injectors is inherently less important.

Viper2000

06-23-2011, 09:27 PM

In fact in the 1950's, we started doing it.....

In the R-4360C Wasp Major power-plant with CH 9 turbo-blower.....

http://www.flightglobal.com/pdfarchive/view/1951/1951%20-%200248.html

The benefit comes from getting more work out of the turbocharger; if you cruise higher then the turbocharger has a bigger expansion ratio to work with and can therefore get more work out of the exhaust.

Charge temperature is limiting, and you'd obviously rather get your supercharger work from the turbine than the crankshaft. So you throw away the supercharger, but that means you need to either go to DI or else inject into the eye of the turbosupercharger impeller to homogenise the mixture.

The turbocharger came from GE, whilst the piston engine came from P&W.

Fuel injection into the turbocharger wasn't viable because of the fire risk, both in case of leaks between the hot and cold sides of the turbocharger, and because of the relatively long ducting from turbocharger to piston engine, which would otherwise have been full of stoichiometric mixture. But most importantly, it wasn't viable because it would have been almost impossible to start the engine unless the turbocharger was clutched to the crankshaft for that purpose, which in turn wasn't possible due to the physical separation between turbocharger and piston engine which was itself a consequence of the historical decision that GE would make turbochargers in isolation from the piston engine manufacturers.

The thermodynamic benefit comes from utilisation of exhaust enthalpy which would otherwise have gone to waste. However, there is an enthalpy loss equal to the sum of enthalpy drop across the aftercooler, and the cooling drag on the cold side thereof; if fuel had been injected upstream of the turbosupercharger, the compression process would have had a higher apparent isentropic efficiency, and the aftercooler would have had less work to do because the compressor delivery temperature would have been lower.

In essence, the benefit comes from improved matching/work balance rather than from going to DI itself. In other words, they wanted to throw away the supercharger to get more of their compressor work from the turbocharger, and this drove them to DI because they then didn't have a method to homogenise the mixture. So DI is a consequence rather than a cause.

CaptainDoggles

06-23-2011, 10:50 PM

That's an interesting take on direct injection, Viper.

I'd always assumed DI was first introduced to more reliably control mixture, eliminate pre-ignition and get a stratified charge in CI systems.

Viper2000

06-24-2011, 12:31 AM

That's an interesting take on direct injection, Viper.

I'd always assumed DI was first introduced to more reliably control mixture, eliminate pre-ignition and get a stratified charge in CI systems.

DI was indeed initially introduced to improve mixture control and avoid the various problems associated with carburettors.

In general, a single carburettor isn't likely to give good mixture distribution to a multi-cylinder naturally aspirated piston engine, because evaporation isn't completed before the charge reaches the intake manifold, and so you get a fairly complex multi-phase flow.

However, if you've got a supercharger between the carburettor and the intake manifold, things get a lot better because the supercharger homogenises the mixture and also increases its static temperature. This means that much more, if not all of, the fuel evaporates; diffusion is then very helpful in further homogenising the mixture. Furthermore, the flow is likely to warm the induction manifold sufficiently that fuel doesn't condense upon contact with it.

This means that supercharged engines which put the fuel into the airflow (whether via a carburettor or some kind of injection system) upstream of the supercharger will tend to deliver a pretty consistent FAR to all of their cylinders. This removes one of the main motivations for direct injection.

However, it must be stressed that this is something of a special case; take the supercharger away and FAR will vary considerably from cylinder to cylinder, whereas with DI you can set FAR quite accurately.

As an aside, WWII vintage technology would just meter the fuel into the cylinders, which is an open-loop approach. You'd still get FAR variations from cylinder to cylinder because although the fuel mass injected would be the same for all cylinders, the airflow would not.

A modern car engine would use an oxygen sensor to tune the fuel mass injected into the cylinder so as to maintain stoichiometry throughout the operating range of the engine; this is vital to the operation of 3-way catalysts. However, this sort of closed-loop approach requires computers, and it is primarily driven by emissions legislation rather than engine performance (power, SFC) considerations.

Without such constraints you'd run the engine leaner to improve SFC, or richer to improve power.

Fuel injection is very useful for CI engines because injection timing can be controlled in order to control the timing of the combustion event; it also allows the pressure profile of the combustion event to be controlled.

Limiting the peak cylinder pressure allows you to make the engine lighter.

With modern engines you can also just stop fuelling cylinders in order to reduce power. This is useful because the turn-down ratio of the injectors is limited if you want good atomisation; poor atomisation leads to reduced combustion efficiency and increased emissions (especially CO and UHC). The alternative is to use multiple injectors per cylinder, but that's a pain.

(If you really really want to then you can build a CI engine with a carburettor, but it's hard work, and it tends to be difficult to control combustion in a satisfactory manner, which hurts thermal efficiency and will tend to cause vibration due to considerable cycle-to-cycle variations in engine behaviour. You'll also find that the smoke limit is set by the richest cylinder, and smoke is a factor then this inevitably limits output.)

Anyway, DI is great for mixture control, but as with all aspects of engine design, it's an option within a tradespace, rather than an unmitigated upside.

If you're mostly interested in operating at a fixed design point then the advantages of DI may easily be outweighed by other options, especially if you're supercharging heavily. OTOH, if you're making a small engine for an economical passenger car today, it's very hard to beat a turbocharged CI engine with DI.

So I'm not suggesting that carburettors are magic; what I'm saying is that DI isn't magic either. Which is better depends upon your priorities, and the job you're trying to make your engine do.

In the very specific example of R-4360C, the primary goal was to get rid of the supercharger so that more useful work could be extracted from the exhaust via the turbocharger. The removal of the supercharger then drove the design towards DI. But it's not reasonable to say that DI is thermodynamically superior; the advantage comes from the improved utilisation of exhaust enthalpy, and DI is just a tool which allows this to be done. Indeed, had it been possible to inject fuel upstream of the turbosupercharger's impeller, superior performance would have been attained.

So DI is analogous to a bridge in this case; the economic benefit comes from the traffic which the bridge carries, rather than the bridge itself, and life would have been easier & cheaper if there had been no need to build a bridge in the first place.

But I must stress again that I'm talking about big aero-engines with high degrees of supercharge here; very different conclusions would be reached if the engine in question was designed to power a car, or even a significantly smaller aeroplane.

Crumpp

06-24-2011, 01:45 AM

Why do you think it's better?

It is better Viper. An intake manifold cannot precisely meter fuel to the cylinders irregardless of having supercharger on it or not.

Have you ever flow an piston engine aircraft with individual EGT/CHT? The CHT and EGT will be vastly different if the fuel metering system is not direct injection.

Each cylinder is being meter a different amount of fuel. That means power loss just in the thermal differences!

Not to mention that none of them are a stoichiometric mixture. Add to that, it is impossible to optimize the timing advance. All of your cylinders are developing different power levels and none of them are optimal.

There is no why to precisely control how much fuel goes to each cylinder in an intake manifold.

With direct injection, you can not only optimize timing advance to the power curve, you can maintain a stoichiometric mixture. The thermal losses are eliminated because your CHT/EGT's are the same.

In any case, you're always going to gain more by reducing temperature as early in the compression process as possible, because compressors (whether steady-flow or non-flow) produce temperature ratios in exchange for pressure ratios, whilst the absolute work required for the compression process is proportional to deltaH, i.e. Cp*deltaT.

Add to that, the fuel cools the combustion chamber much more efficiently than cold air.

A simple illustration of that basic principle.

1006 J/kgC

460 J/kgC

2100 J/kgC

To change the temperature of a mass of 1 Kg of each by 2 degrees….

Air = 1006 J/kgC * 1kg* 2 C = 2012J
Fuel = 2100J/kgC*1kg*2 C = 4200J
Steel = 460J/kgC * 1kg * 2 C = 920J

Our 4200J of fuel energy goes to cool the 15C air…

4200J * 1kg /1006J/kgC = Change in T = 4.17 C

15C - 4.17C = 10.83C

Now let us dump our fuel on the hot steel of our combustion chamber.

4200J * 1kg / 420J/kgC = Change in T = 10 C

15C - 10C = 5C

5 degrees Celsius is much colder than 10 degrees Celsius.

Crumpp

06-24-2011, 01:58 AM

I'd always assumed DI was first introduced to more reliably control mixture, eliminate pre-ignition and get a stratified charge in CI systems.

That is correct.

Viper says:
If you are supercharging then you'll win by injecting into the supercharger and thereby reducing supercharger work.

A supercharger is a intake system has nothing to do with the fuel metering.

Every supercharged engine has to have a fuel metering system. The Merlin for example uses a carburetor. It has a supercharger but fuel is metered by the carburetor.

Read the article you posted. Rolls Royce does not make the argument a carburetor with a supercharger is better, they argue their engines are not as inefficient as people think when compared to the direct injection used by the Germans.

The only drawback to Direct Injection is complexity and expense.

Crumpp

06-24-2011, 02:05 AM

Nice article on direct injection:

http://books.google.com/books?id=byEDAAAAMBAJ&pg=PA88&lpg=PA88&dq=Direct+Fuel+Injection+power+gains+over+carburet ed&source=bl&ots=C8G0ABDuDS&sig=rUOkR4Ptxzx27in-hhzJVcHeS0g&hl=en&ei=D-0DToyEJJTogQe20Jm7DQ&sa=X&oi=book_result&ct=result&resnum=5&sqi=2&ved=0CC4Q6AEwBA#v=onepage&q&f=false

Viper2000

06-24-2011, 08:54 AM

Go back to the paper (http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf) given by Lovesey which I posted earlier.

Engine shaft power is proportional to mass flow rate.

Mass flow rate, W, is given by

W=0.422*Ncylinders*(Pcharge-(1/6)*Pexhaust)/Tcharge

Charge temperature & pressure are measured in the intake manifold. In this equation, W is in lb/minute; piston engines are tiny.

You will note that Lovesey cites a 7% improvement in supercharger pressure ratio from injecting fuel into the eye of the supercharger.

This is very significant given the pretty awful isentropic efficiency of the supercharger.

You can go through the data, and calculate the supercharger work from the efficiency curves in Figure 11.

You can calculate the actual engine air consumption iteratively by assuming that the FAR is about 1/12 at high power. Hence, given the SFC curve and the full throttle power vs altitude curve, you can use the fuel flow to calculated the total rate of charge consumption.

You can use the total rate of charge consumption to calculate the supercharge power consumption as a function of inlet temperature. You must of course add this supercharger power consumption to the brake power in order to calculate the shaft power, because it is the shaft power, not the brake power, which is directly proportional to fuel flow.

This means that you'll need to iterate in order to achieve convergence.

Try this with and without fuel injection into the eye of the supercharger, which may be modelled as a 25 K temperature reduction exchanged for a 1/12 mass flow rate increase.

Because the supercharger work is W*Cp*deltaT, you will find that injecting fuel into the eye of the supercharger results in a considerable reduction in the supercharger power required for any given boost pressure, which naturally improves brake power and brake SFC.

Your argument regarding cylinder temperature is spurious because the engine has a cooling system to maintain CHT, and because the reduction in induction manifold temperature results in a considerable reduction in the charge temperature during the compression stroke because compression through a fixed volume ratio results in a fixed temperature ratio rather than a fixed absolute temperature increment.

This means that there is less compression work.

Peak cycle temperature is essentially fixed by dissociation, and therefore the reduction in charge temperature translates directly into an increase in BMEP.

Alternatively, you could hold constant charge temperature and reduce the size of the aftercooler. Either way, you're still getting a benefit from the latent heat of evaporation of the fuel; but this benefit is greater overall when the fuel is injected into the eye of the supercharger.

Arguments about stoichiometry as less important for an aero-engine at high power than for a car engine because you're not bothered about emissions (at least in this period). Therefore you run the whole thing rich of peak.

Cylinder to cylinder variation in FAR will be small so long as the induction manifold temperature is kept reasonably high; this may be seen from the discussion about lead fouling towards the end of Lovesey's paper; charge distribution is good down to intake manifold temperatures of about 35ºC.

Cylinder to cylinder charge consumption will vary due to intake manifold aerodynamics.

But this actually means that if you go for 1940s DI you'll get a variation in FAR from cylinder to cylinder because the injection system would give each cylinder equal fuel irrespective of its actual air consumption. Modern engines would use an oxygen sensor in the exhaust to maintain stoichiometry. However, this would preclude operations rich of stoichiometric, so the benefit is to BSFC and emissions rather than to absolute power.

I have flown a Citabria with modern after-market engine instrumentation. Obviously the CHTs vary because it's air cooled; you're never going to get the back cylinders as cool as the front ones. Likewise, mixture distribution will always be questionable for a naturally aspirated engine, even on a hot day in South Carolina.

That sort of engine would obviously benefit from DI; and in the modern world, the philosophy is to turbo-normalise if altitude performance is wanted. The convenience of maintaining a fixed engine operating point independent of altitude is considerable. Modern compressors are very much more efficient than those from the 1940s, and therefore there is less compressor work to save in the first place. Additionally, with substantial exhaust energy being dumped out of the waste-gate, there is obviously less motivation to reduce compressor work. So there are a variety of factors driving modern engines towards DI.

This does not mean that single point injection upstream of a supercharger does not have advantages, especially if you have a high degree of supercharge.

Modern piston engines simply have different design goals than the high-powered piston aero-engines of the 1940s.

Kurfürst

06-24-2011, 09:30 AM

Because the supercharger work is W*Cp*deltaT, you will find that injecting fuel into the eye of the supercharger results in a considerable reduction in the supercharger power required for any given boost pressure, which naturally improves brake power and brake SFC.

Pretty redundant if you ask me, if you are already using a variable speed supercharger adjusted already for supercharging needs, as DB did with its barometrically controlled hydraulic clutch.. the supercharger wasn't making less waste, it made almost no waste at all.

Correct me if I am wrong, but injecting fuel into the supercharger eye reduces charge temperature, delaying detonation point. Direct fuel injection does the same (in the combustion chamber), but later, and with better fuel effiency, no risk of backfires, and no negative G problems. High octane fuel is a pretty expensive agent for charge cooling..

Viper2000

06-24-2011, 09:55 AM

You're confusing throttling losses, which are avoided by varying supercharger speed, with the aerodynamic losses associated with the supercharger's design, which are not.

The aerodynamic losses increase the temperature rise associated with a given pressure rise, which increases the work required.

Because compression through a given pressure ratio tends to produce a given temperature ratio, you reduce the absolute deltaT by reducing the initial temperature, all other factors remaining constant. This reduces compressor work, which is equivalent to an increase in compressor efficiency.

You obviously get a greater benefit from cooling the working fluid at the start of the compression process.

Eg

Start at 288 K. Cool by 25 K. T = 263 K. Compress through a temperature ratio of 1.5, and then further through a temperature ratio of 2. Temperature = 263*1.5*2 = 789 K. Delta T from start = 501 K.

Compare with:

Start at 288 K. Compress through temperature ratio 1.5, cool by 25 K and then compress through temperature ratio of 2. Final temperature is then 814 K, so delta T is 526 K.

Thus, compressor work differs by 5% or so in this example.

This is the reason for the reduction in the isentropic efficiency associated with a given polytropic efficiency as compressor pressure ratio increases.

Crumpp

06-24-2011, 11:01 AM

Direct fuel injection does the same

Injecting into the eye of the supercharger is no more efficient than a carburetor at fuel metering.

Eg

Start at 288 K. Cool by 25 K. T = 263 K. Compress through a temperature ratio of 1.5, and then further through a temperature ratio of 2. Temperature = 263*1.5*2 = 789 K. Delta T from start = 501 K.

Compare with:

Start at 288 K. Compress through temperature ratio 1.5, cool by 25 K and then compress through temperature ratio of 2. Final temperature is then 814 K, so delta T is 526 K.

Thus, compressor work differs by 5% or so in this example.

You are still getting the compression from a supercharger and directly cooling the combustion chamber with direct fuel injection.

I am sorry Viper but it does not change the fact you cannot precisely meter the fuel thru an intake, either.

Modern engine designs are now starting to employ direct-injection.
Here fuel is introduced straight into the cylinder rather than
being premixed outside. This technique has major advantages
as it allows more accurate control of the quantity of fuel used and
the injection timing, leading to an increase in the vehicle’s
horsepower combined with a lower fuel intake.

Direct-injection is far more efficient than traditional
injection techniques, raising performance levels while requiring less fuel.

http://www.onsemi.com/site/pdf/PSDE_0411.pdf

Viper2000

06-24-2011, 11:40 AM

Injecting into the eye of the supercharger is no more efficient than a carburetor at fuel metering. Of course it's better than a carburettor; you're not reliant upon venturi suction to get the fuel into the airflow; you're positively chucking it in with a pump.This will provide considerably better matching across the flow range.

Because you're injecting fuel under pressure, you can positively atomise it, achieving a considerably lower Sauter mean diameter (http://en.wikipedia.org/wiki/Sauter_mean_diameter) of fuel droplets than is possible with a simple carburettor, which means that it will evaporate much faster. This means that more of the temperature drop happens earlier in the compression process, which increases the overall efficiency bonus.

Once the fuel has evaporated, the mixture distribution problem goes away.

You are still getting the compression from a supercharger and directly cooling the combustion chamber with direct fuel injection. This is inherently less efficient. It's relatively simple thermodynamics.

I am sorry Viper but it does not change the fact you cannot precisely meter the fuel thru an intake, either. Fuel metering is not a particular problem. You measure the flow through the intake, and inject fuel in proportion thereto. It's much easier to get this measurement & injection process right at a single point than it is to get it right at 12 points.

Fuel distribution may be a problem at low manifold temperatures where the fuel fails to evaporate fully, but that is a separate problem.

You seem to be mostly hung up on fuel metering issues, which certainly exist for naturally aspirated engines with carburettors, especially away from their design point.

However, fuel metering is not especially important at high power if you don't care about emissions. You run rich of stoichiometric, and fuel flows say +/- 5% won't make a great deal of difference to power output. Obviously the SFC is pretty bad at that point; you can clearly see this on the SFC curve in Lovesey's paper.

Mixture distribution is not a problem at high induction manifold temperature.

The reductions in supercharger work and intercooler size are far more important than the slight increase in fuel mass fraction which you might suffer from the need to keep the leanest cylinder sufficiently rich to avoid detonation. The cost of a single point system is far lower than a multi-point system, and the fuel pressure required is lower than for true direct injection. (Port injection is a pretty horrid compromise which only makes sense if the alternative is a carburettor which would produce bad mixture distribution.)

For a supercharged spark-ignition aero-engine, operating at a fixed non-dimensional power setting, provided that you've got enough induction manifold temperature to avoid condensation, the mixture distribution will be good and the single point system wins.

Multi-point FI is an expensive solution to mixture distribution problems. It is great for naturally aspirated engines, and probably pragmatic for turbo-normalised engines, especially if the engine manufacturer isn't responsible for the turbocharger.

But if you're using a mechanical supercharger and will mostly operate the with reasonably high induction manifold temperatures, then there's no great mixture distribution problem unless your induction manifold is horrible, so multi-point injection offers limited benefit, whilst single point injection into the eye of the supercharger reduces supercharger drive power requirements. So single point injection is a pretty obvious choice.

Now, if you're designing a sports car engine, you might supercharge it to get high power, but most of the time it would operate at very low non dimensional power settings, so mixture distribution would be a major problem with single point injection, and therefore you'd probably go for multi-point FI.

But that's because the sports car engine isn't really designed for high performance. It's designed to make an expensive noise and very occasionally provide bursts of acceleration to impress the girl in the passenger seat. Most of the time it's practically ticking over, and so you're much more bothered about part-load characteristics than would be the case for an aero-engine. You're also trying to meet modern emissions regulations, which means that you're paranoid about stoichiometry so that you don't poison your catalyst. It's a totally different world, with different trades and different drivers.

TomcatViP

06-24-2011, 01:51 PM

But that's because the sports car engine isn't really designed for high performance. It's designed to make an expensive noise and very occasionally provide bursts of acceleration to impress the girl in the passenger seat.

I hve to disagree loudly with the above comment. It's the worst thing to do ;) Having a fat diesel with a body kit is what impress the girl nowadays :(

Crumpp

06-24-2011, 02:23 PM

http://www.slideshare.net/rjperformance/how-direct-fuel-injection-works-by-rj-performance

It works in any engine to increase power and performance over any other fuel metering system no matter if the intake is supercharged or not.

http://www.steerbythrottle.com/hccyong/files/DFI.pdf

Advantages of direct fuel injection

Combined with ultra-precise computer management, direct injection allows more accurate control over fuel metering (the amount of fuel injected) and injection timing (exactly when the fuel is introduced into the cylinder). The location of the injector also allows for a more optimal spray pattern that breaks the gasoline up into smaller droplets. The result is more complete combustion -- in other words, more of the gasoline is burned, which translates to more power and less pollution from each drop of gasoline.
Disadvantages of direct fuel injection

The primary disadvantages of direct injection engines are complexity and cost. Direct injection systems are more expensive to build because their components must be more rugged -- they handle fuel at significantly higher pressures than indirect injection systems and the injectors themselves must be able to withstand the heat and pressure of combustion inside the cylinder.
How much more powerful and efficient is direct injection?

Cadillac sells the CTS with both indirect and direct injection versions of its 3.6 liter V6 engine. The indirect engine produces 263 horsepower and 253 lb-ft of torque, while the direct version develops 304 hp and 274 lb-ft. Despite the additional power, EPA fuel economy estimates for the direct injection engine are 1 MPG higher in the city (18 MPG vs 17 MPG) and equal on the highway. Another advantage: Cadillac's direct injection engine runs on regular (87 octane) gasoline. Competing cars from Infiniti and Lexus, which use 300 hp V6 engines with indirect injection, require premium fuel.

http://cars.about.com/od/thingsyouneedtoknow/a/directinjection.htm

A good primer article on Direct Injection. It explains very well the difference between the various types of fuel injection and why Direct Injection is the ultimate fuel metering system for power and performance.

http://www.driverside.com/auto-library/the_wonder_of_direct_injection-350

Here is a good article that explains the German Direct injection systems in easily understandable terms:

http://www.motorcycleproject.com/motorcycle/text/inject.html

The German systems were far from perfect but they certainly did their job and allowed them to level the playing field in terms of aircraft engine performance.

IIRC, the British and United States did a combined effort to develop a Direct Injection engine that was used in a tank at the end of the war.

Crumpp

06-24-2011, 02:35 PM

You seem to be mostly hung up on fuel metering issues

Viper, direct injection is a fuel metering system. Supercharging is an intake system and does not have a thing to do with fuel metering.

It is two completely separate things you want to combine.

You point to the thermal benefits of introducing the fuel ahead of the supercharger instead of downstream of it. I agree it is there when compared to introducing fuel downstream of the supercharger in your INTAKE SYSTEM.

Got it but that does not make it more thermally more efficient that directly injecting the fuel in the combustion chamber. You are not looking at the heat capacity but are stuck on upstream vs downstream fuel introduction for your intake.

As Rolls Royce points out, direct injection is much more efficient than metering your fuel downstream or anywhere in the intake system. Just because that small part of the intake system becomes more efficient vs introducing fuel downstream does not make the whole system more efficient.

A simple illustration of that basic principle.

1006 J/kgC – Specific Heat Capacity of Normal Air

460 J/kgC – Specific Heat Capacity of Steel

2100 J/kgC – Specific Heat Capacity of Gasoline

To change the temperature of a mass of 1 Kg of each by 2 degrees….

Air = 1006 J/kgC * 1kg* 2 C = 2012J
Fuel = 2100J/kgC*1kg*2 C = 4200J
Steel = 460J/kgC * 1kg * 2 C = 920J

Our 4200J of fuel energy goes to cool the 15C air…

4200J * 1kg /1006J/kgC = Change in T = 4.17 C

15C - 4.17C = 10.83C

Why do you think direct injection is the ultimate fuel metering technology and so desirable to have in an engine? If was not for the complexity and expense, all engines would be direct injected because it is the most efficient system mankind knows of at the present for metering fuel.

Rolls Royce also shows in the article you posted their system is not as efficient as directly injecting fuel into the combustion chamber combined with your supercharged intake.

Why? YOU STILL MUST HAVE A FUEL METERING SYSTEM ON YOUR ENGINE. Introducing the fuel ahead of the supercharger does not eliminate the basic problem of NON DIRECT INJECTED FUEL METERING SYSTEM, uneven fuel mixtures found by introducing fuel ANYWHERE in the intake system.

;)

The only way to eliminate that is too directly inject fuel into the combustion chamber.

Direct injection engines with a supercharger STILL benefit from that supercharger intake system.

Crumpp

06-24-2011, 03:14 PM

Doesn't a supercharger (or turbocharger for that matter) run as a single intake, and then splits a tube towards each cylinder?

Yes and you are correct in that metering fuel anywhere in the intake system is not going to give you the power gains compared to injecting precisely metered fuel directly into the combustion chamber.

The drawbacks to direct injection are the expense and complexity. The BMW801 series used 14 high pressure fuel pumps and consisted of more parts than the entire rest of the engine.

The supercharger technology of the allies combined with better fuels restored the balance.

You cannot point to Direct Injection technology and say it was decisive and gave the German engines better performance over the allied ones anymore than you can point to better fuel quality and supercharger technology of the allies as being better than the German engines.

In the air war over Europe, all sides developed their engines and fielded 2000 hp plus designs by the wars end. The implications made a few folks that fuel technology was decisive are not correct when one takes in the whole picture. Fuel quality and supercharger technology simply maintained the balance with fuel metering technology as well as superior chemical engineering.

That any of these engines were routinely operated outside of their published guidelines is another ludicrous idea hatched in the gaming world but that is another subject.

:)

Viper2000

06-24-2011, 04:40 PM

Doesn't a supercharger (or turbocharger for that matter) run as a single intake, and then splits a tube towards each cylinder?

If that's the case, isn't fuel/air being routed towards each cylinder even while that cylinder isn't in its intake cycle? How could adding the fuel pre-supercharger give as precise a charge to each cylinder, when its being routed towards many cylinders that aren't prepared to accept the charge, as a direct injection which pumps it directly into the cylinder head only when the cylinder is needing it?

Air is a mixture of gasses which have different molecular weights. But you wouldn't expect that the issues you allude to above would modify the composition of air going into the cylinders.

If the fuel has evaporated, and is in a gaseous phase, which is perfectly reasonable if the induction manifold temperature is high, the exact same argument applies; inertial separation of species within the gaseous mixture is unlikely because the forces are insufficient to overcome the diffusive tendency of the gas.

All the math and numbers aside, yes, your air/fuel mix via a supercharger/turbocharger, is mixed well, but you're still backing it up against a closed valve for 3/4 of the cycle, then pushing this in when the valve opens. Also, backpressures and eddies in the airflow probably effect the droplets of fuel, allowing them to consolidate (albeit very little) before the valve opens. This might add to the compression, which might help power output, but surely can't be great for precise fuel metering.

If the fuel is still liquid in the intake manifold then mixture distribution will be bad. This is often the case with naturally aspirated engines because the induction manifold temperature is essentially ambient.

The benefit of single point injection into the eye of the supercharger is that it improves the effective isentropic efficiency of the supercharger, and thus reduces supercharger work, increasing the brake horsepower output of the engine when compared with multi-point injection into the cylinders or ports.

I'm getting pretty tired of trying to explain this relatively simple concept.

Here's a nice big paper (http://gltrs.grc.nasa.gov/reports/2006/CR-2006-214059.pdf). It's got a lot of interesting stuff in it, but the bit that is germane to this discussion is the analysis of the effects of water injection upon compressor performance. It doesn't matter whether you're injecting fuel or water, the latent heat reduces the temperature rise through the compressor, which is analogous to an increase in compressor efficiency.

Happy reading.

CaptainDoggles

06-24-2011, 05:22 PM

In one of Viper's earlier points he argues that if you don't care about emissions and purposely run a bit rich, then minor variations in fuel/air ratio will not cause problems. Temperatures on the downstream side of the supercharger ought to be plenty high enough to cause evaporation of the fuel droplets, particularly if you aren't intercooling.

On a turbocharged, intercooled engine I'd wager that direct injection would be superior since the turbo is already much more thermodynamically efficient than a supercharger. But on a supercharged engine where the supercharger can pull as much as 30% of the crankshaft's power it's a sound engineering decision to try to increase that efficiency foremost.

Al Schlageter

06-24-2011, 05:41 PM

Besides yo simply display the logical fellacy of the Invisible Pink Unicorn: you seem to believe that if you claim something, without being capable proving it, and if others don't prove you wrong, you are automatically right. Right? Well, its just utter nonsense.

Now this is hilarious coming from Barbi when all he can produce is,

"The proposed changes to units equipped with Bf 109 were as follows:

OKL, Lw.-Führüngstab, Nr. 937/45 gKdos.(op) 20.03.45"

(it is not an original document either)

unit - on hand - serviceable - type
"I./JG 27 - 29 - 13 - Bf 109 K
III./JG 27 - 19 - 15 - Bf 109 K and some 109 Gs
III./JG 53 - 40 - 24 - Bf 109 K and some 109 Gs
IV./JG 53 - 54 - 27 - Bf 109 K and some 109 Gs"

for the use of 1.98ata boost on 109K-4s.

Just have to love that double standard. :lol:

Seadog

06-24-2011, 07:16 PM

The proof is in the pudding. The Merlin III/12lb boost was producing much more power than equivalent DB601 engines:

http://www.spitfireperformance.com/spit1-109e-eng.jpg

From what I can gather on the web, the DB601 also had a 100 hr TBO versus 240 for the Merlin. Does anyone have other figures?

TomcatViP

06-25-2011, 12:06 AM

The proof is in the pudding. The Merlin III/12lb boost was producing much more power than equivalent DB601 engines:

This is true but only because of the higher boost level ..... hence a slightly more shaft power consuming s/c (the RAF had to build a high alt engine with lower cubic inches)... hence ...

http://www.spitfireperformance.com/spit1-109e-eng.jpg

this diag depict Merlin without s/c (test on grd) and a DB with SC!

But it is true that Merlin had a superior TBO although I am not sure what the value were for the BoB period

By the way with this curve I am not sure that the FC would hve selected "your Merlin" as the max power requirement was for high alt (at the time 20kfeet (my own guess) )

TomcatViP

06-25-2011, 12:12 AM

Now this is hilarious coming from Barbi when all he can produce is,

"The proposed changes to units equipped with Bf 109 were as follows:

OKL, Lw.-Führüngstab, Nr. 937/45 gKdos.(op) 20.03.45"

(it is not an original document either)

unit - on hand - serviceable - type
"I./JG 27 - 29 - 13 - Bf 109 K
III./JG 27 - 19 - 15 - Bf 109 K and some 109 Gs
III./JG 53 - 40 - 24 - Bf 109 K and some 109 Gs
IV./JG 53 - 54 - 27 - Bf 109 K and some 109 Gs"

for the use of 1.98ata boost on 109K-4s.

Just have to love that double standard. :lol:

Pls stay focused on facts and BoB period - Thx

Seadog

06-25-2011, 12:20 AM

This is true but only because of the higher boost level ..... hence a slightly more shaft power consuming s/c (the RAF had to build a high alt engine with lower cubic inches)... hence ...

this diag depict Merlin without s/c (test on grd) and a DB with SC!

But it is true that Merlin had a superior TBO although I am not sure what the value were for the BoB period

So what figures do you propose for HP?

240 hrs was the BofB TBO figure for the Merlin. It was raised progressively to about 350 hrs by 1945, for combat aircraft.

TomcatViP

06-25-2011, 12:22 AM

It doesn't matter whether you're injecting fuel or water, the latent heat reduces the temperature rise through the compressor, which is analogous to an increase in compressor efficiency.

Great ! but don't forget the Mass flow : Lowered Heat + increased Mass Flow = higher efficiency

TomcatViP

06-25-2011, 12:29 AM

TomcatViP

06-25-2011, 12:48 AM

A simple illustration of that basic principle.

1006 J/kgC – Specific Heat Capacity of Normal Air

460 J/kgC – Specific Heat Capacity of Steel

2100 J/kgC – Specific Heat Capacity of Gasoline

To change the temperature of a mass of 1 Kg of each by 2 degrees….

Air = 1006 J/kgC * 1kg* 2 C = 2012J
Fuel = 2100J/kgC*1kg*2 C = 4200J
Steel = 460J/kgC * 1kg * 2 C = 920J

Our 4200J of fuel energy goes to cool the 15C air…

4200J * 1kg /1006J/kgC = Change in T = 4.17 C

15C - 4.17C = 10.83C

I understand your (strong) point). Don't forget the stochio ratio (1 to 8 (?)) that even the above result.

Sry for the red thumb down... I hve really no idea how it came here

Al Schlageter

06-25-2011, 12:50 AM

Pls stay focused on facts and BoB period - Thx

Just pointing out the double standard that Barbi uses.

TomcatViP

06-25-2011, 12:55 AM

So what figures do you propose for HP?

240 hrs was the BofB TBO figure for the Merlin. It was raised progressively to about 350 hrs by 1945, for combat aircraft.

Everywhere I look it's a 1150/75 value ON the Spitfire. What ever we think logic would ask for a lower value than the latter XX that is well documented (see my post for the Merlin XX on the Hurri)

Kurfürst

06-25-2011, 10:25 AM

From what I can gather on the web, the DB601 also had a 100 hr TBO versus 240 for the Merlin. Does anyone have other figures?

TBO for DB 601A-1 was 200 hours. RR TBOs were understood as a figure that 1/3 of the engines could satisfy, and if a single cause of failiure did not amount to more than 2/3 of the cases IIRC.

Kurfürst

06-25-2011, 10:26 AM

Viper2000

06-25-2011, 11:42 AM

This is true but only because of the higher boost level ..... hence a slightly more shaft power consuming s/c (the RAF had to build a high alt engine with lower cubic inches)... hence ...

this diag depict Merlin without s/c (test on grd) and a DB with SC!

Nope; it's plotting BHP.

I'm pretty certain that I've posted the RM1 rating from Harvey-Bailey several times now, which gives the rating at 1310 bhp at 9000', +12 psi.

I really don't understand why you keep trying to "de-rate" the Merlin. There's no shortage of source material on the subject (you can cross check the power output of the Merlin III against figure 6 in Lovesey's paper (http://www.wwiiaircraftperformance.org/merlin-lovesey.pdf) for example), and in any case, given that we also have no shortage of data about the performance of the Spitfire & Hurricane, even if you managed to persuade 1c that the Merlin made less power than was actually the case, that would just mean that they had to artificially reduce airframe drag to match the known speed and climb performance.

The result of that would be that the RAF would have an unrealistic advantage in shallow dives against the Luftwaffe. Frankly, if I was one of the "make my plane better irrespective of realism" crowd, I'd rather have less drag than more horsepower, because B&Z is a rather more effective strategy than T&B.

It may well be that http://www.wwiiaircraftperformance.org/ doesn't post the best performance data for Axis aeroplanes, but I haven't seen any evidence to suggest that the source material it contains is fabricated. I might not necessarily agree with some of the interpretation, but that's irrelevant given that most people here just repost the source material and debate it, rather than reposting the gloss from the site.

BTW, if anything, the +12 FTH of 9000' is an underestimate because it doesn't include intake ram AFAIK.

If you cross-check the Merlin 66 horsepower chart (http://www.spitfireperformance.com/merlin66hpchart.jpg) which includes 400 mph intake ram against the RM10SM rating in Harvey-Bailey, you'll find that the MS gear +18 FTH from the rating is 5750', whereas the chart gives an FTH of over 9000'. Likewise, the rating specifies the FTH in FS gear as 16000', whereas the chart shows an FTH of about 20000'.

You can cross-check the ram pressure rise against the FTH by using a standard atmosphere calculator like this one (http://www.aerospaceweb.org/design/scripts/atmosphere/) if you feel that way inclined.

So actually the power comparison is unrealistic in as much as it's based upon the Merlin's static FTH. In reality, at about 300 mph you'd see an increase in FTH of a couple of thousand feet.

You can easily cross-check this if you look at airframe speed vs altitude diagrams; max TAS is achieved at the rammed FTH for whatever boost they're using, and this is invariably higher than the FTH for the engine rating quoted in Harvey-Bailey.

I don't know what the basis of the DB601 power curve is, so I can't comment on whether or not it includes intake ram.

Reference:
Harvey-Bailey, A. (1995) The Merlin in Perspective - the combat years. 4th edition. Derby: Rolls-Royce Heritage Trust.

Al Schlageter

06-25-2011, 12:23 PM

There's no sign of "proposed" in the original document. See for details: http://www.kurfurst.org/Engine/Boostclearances/605D_clearance198.html

Those are your words I posted Barbi. I don't see any original document in the link.

TomcatViP

06-25-2011, 12:53 PM

You are picking what suit better to your thesis and once again put a layer of complicated arguments to dissimulate this fact.

You are right there is the intake ram effect. Just like exhaust gazes propulsive effect ... and a lot of drag with the cooling system that did not take into account the boundary layer drag even at a late stage in the war.

It does not mean that you can add all the Power gains RR refer in its doc and then say that the merlin had the a total of BHP equal to the cumulative effect measured on the test bed.

Note that the intake ram effect went as a benefit only after a major redesign witch hve to be dated :rolleyes:

The diag you show is difficult to interpret as it it shown put out of any contest. And we are talking abt early war tech not late achieved Merlin boost. In 1944/45 the war for the Spit has switch from high alt air interception to low level mud fighting and interdiction witch favor over-boosting. (we also know that those level of boost proved unreliable and were lowered on the field - the griff engine being put forward has the 2K HP piston eng - Oh... and yes there is the Merlin Hornet but... wait is that not an evidence that DH has superior engineering capacities in term of aero when Supermarine despite strong gov support only produced contestable design ?)

In term of FM and drag for the spit, just catch the six of a 109 in the game and follow him in her maneuver for a min. If you are not laughing after 30 sec and still need to be convinced, pls take a similar ride in the Excellent Hurri we hve for now.

So no drag reduction! My humble opinion wld bend me in the direction of some change toward the set of modeling eq that might not apply to a 300mph fighters (in fact modelizing the Spit wing as a trapezoidal wing of similar wing surface/wing root chord and thickness wld lead to better accurate results without changing the overall FM engine). But this is pure guess as I don't know anything abt CoD FM engine :-P

So, to resume my self : you can't take a pce of this or that and build a convenient result

For example if you build your opinion on the spit only reading my posts here you'll conclude that the spit was an antique machine unsuitable for fighting even if this is not what I am thinking.

I repeat myself : The spit/Merlin were great design but with some major flaw that a simple look at history puts in perspective (search the web for a Elliptical winged B2 or floating carburetor PT6 turboprop or a Malcom Hooded BlackBird ;) )

Osprey

06-25-2011, 05:34 PM

Can't believe Kurfurst is still peddling out these BS arguments still? Ordinarily I wouldn't care a jot but he's doing his best to get what he wants and ruin any chance of a more realistic FM.

What could his agenda be?

Kongo-Otto

06-25-2011, 07:22 PM

Crumpp

06-25-2011, 11:08 PM

Air is a mixture of gasses which have different molecular weights. But you wouldn't expect that the issues you allude to above would modify the composition of air going into the cylinders.

If the fuel has evaporated, and is in a gaseous phase, which is perfectly reasonable if the induction manifold temperature is high, the exact same argument applies; inertial separation of species within the gaseous mixture is unlikely because the forces are insufficient to overcome the diffusive tendency of the gas.

Viper,

It does not work that way.....

If you have flown an aircraft with individual Exhaust Gas Temperature Gauges and Cylinder Head Temperature gauges you would know their is a wide variance in the temperatures with any fuel metering system that introduces fuel to the intake.

100 degrees or more is considered normal variance........

Why? The fuel mixture is different for each of the cylinders.

Crumpp

06-25-2011, 11:16 PM

There is no such thing as a direct injection aircraft engine in General Aviation. All fuel injection is single point injection much like the Allied designs of WWII.

If an engine has bayonet probes in all cylinders, it is not unusual to see variations in CHT readings on fuel injected engines of 100o F between cylinders, and as much as 150ø F on engines with float-type carburetors.

With the latter, an important cause of the variation is
the kind of distribution of fuel and air to the individual cylinders.

Don’t be surprised to see variations in temperature between individual cylinders where there is a probe for every cylinder. It is fairly typical to see an average 100o F variation with fuel injection, and as much as 200o F variation with a float-type carburetor. The latter (carburetor) variation tends to be greater because fuel/air distribution is not as good
as with fuel injection.

In a direct injection engine, there is almost no variation in CHT or EGT between the cylinders.

It is that temperature variation that robs a single point fuel metering system of power.

http://www.costaricaaviation.com/flightschool/LycomingEnginesOperations_rev1.pdf

TomcatViP

06-26-2011, 11:49 AM

There is no such thing as a direct injection aircraft engine in General Aviation. All fuel injection is single point injection much like the Allied designs of WWII.

In a direct injection engine, there is almost no variation in CHT or EGT between the cylinders.

It is that temperature variation that robs a single point fuel metering system of power.

http://www.costaricaaviation.com/flightschool/LycomingEnginesOperations_rev1.pdf

Crumpp,

At first, thx for all the excellent references you are giving on many of your post.

I understand you point on DI vs SPI (single point injection). DI has clearly many advantage and was the panacea at the time.

Viper care much abt theory and given that you run at cte regime and that the ducting are of equal length after the s/c (what is not feasible) the SPI has clearly an edge in terms of practical answer.

DI however as you has pointed out offer much more advantage on reality grounds and this clearly can be seen in ehaust temp even in today cars (Ask GrandPa about engine backslash and loud bang with carburetor engined cars before the 80's GTI went out) ;)

Coming back on the BoB, I believed that RR had however an advantage with the s/c being inline with the engine witch simplified the routing of the air with a relative symmetry (the DB has some prob and a slight differences btw raws of left and right cylinder due to the s/c being on the port side ). This tend to makes the RR simpler ... and what is simpler is much easier to improve : a strong point for any strategical war item ;)

Crumpp

06-28-2011, 12:26 PM

I'd rather have less drag than more horsepower,

As a pilot, slick aircraft are problematic when it comes to maneuvering. They are good for cross country performance but poor in maneuverability. That is why you don't see many slick aerobatic platforms.

Drag with appropriate power gives a pilot precise speed control allowing him to reach and maintain his aircraft's design performance speeds quickly.

As a pilot, there is nothing worse than having too much speed and not being able to get rid of it when you need the airplane to maneuver or require maximum performance from it.

Crumpp

06-28-2011, 12:49 PM

At first, thx for all the excellent references you are giving on many of your post.

You are most welcome. Thanks for your contributions to the discussion too.

I understand you point on DI vs SPI (single point injection). DI has clearly many advantage and was the panacea at the time.

The technological advantage of DI allowed the German designs to be equal to despite strategic material shortages.

Maintaining equality with inferior materials came at a high cost though.

simpler is.....

Exactly. The main drawback of Direct Injection is the expense and complexity. Germany is just a little smaller than the state of Montana in terms of square miles and had a strategic material shortage even before the war began.

For a resource poor country of that size to take on most of the civilized world in an all out war of attrition, complex and expensive is something to be avoided.

Viper2000

06-28-2011, 04:54 PM

There is no such thing as a direct injection aircraft engine in General Aviation. All fuel injection is single point injection much like the Allied designs of WWII. Actually pairs of these things fly over my head every day... (http://www.austroengine.at/cms/upload/Technical_Data/AE_300_Technical_Data.pdf)

In a direct injection engine, there is almost no variation in CHT or EGT between the cylinders. CHT is dominated by cooling; EGT is dominated by stoichiometry. CHT variations are an inevitably fact of life for air-cooled engines.

It is that temperature variation that robs a single point fuel metering system of power. A perfectly reasonable statement if and only if you are comparing identical intake conditions.

CaptainDoggles

06-28-2011, 07:22 PM

CHT is dominated by cooling; EGT is dominated by stoichiometry. CHT variations are an inevitably fact of life for air-cooled engines

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

Viper2000

06-28-2011, 08:46 PM

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

I was responding to this:

If you have flown an aircraft with individual Exhaust Gas Temperature Gauges and Cylinder Head Temperature gauges you would know their is a wide variance in the temperatures with any fuel metering system that introduces fuel to the intake.

...

Crumpp

06-28-2011, 08:59 PM

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

Correct. Thank you.

What I am saying is obvious for anyone who has flown a piston engine aircraft with individual CHT/EGT. You can see the power robbing temperature differences of introducing fuel anywhere in the intake system.

Only by metering fuel with a direct injection system will the cylinders have equal EGT's and CHT's across the engine.

Actually pairs of these things fly over my head every day...

I did not know the DA-42 diesels were direct injection. It figures, diesel is the easiest type of engine to direct inject.

Crumpp

06-28-2011, 09:15 PM

I was responding to this:

You misunderstood it.

Of course EGT is not going to equal CHT in an individual cylinder, that is a silly concept. Only in direct injection will the EGT and CHT be equal across the cylinders of your engine.

Fuel introduced in the intake will cause the cylinders to draw different mixture ratios as the firing order is cycled. The different fuel mixture ratio will cause each cylinder to have a different CHT and EGT from the other cylinders in the engine. This is a very common known fact for pilots as you see it every time you fly so you don't get worried when one cylinder has a temperature 100 degrees lower than another cylinder. That is just a by product of introducing fuel into the intake system instead of directly injecting it in the cylinders so the mixture can precisely metered.

Viper2000

06-28-2011, 09:51 PM

I did not know the DA-42 diesels were direct injection. It figures, diesel is the easiest type of engine to direct inject. In many ways it's tougher because the pressures are higher. However, the alternatives are worse, so injection becomes the route of least resistance sooner.

Crumpp

06-29-2011, 11:37 AM

In many ways it's tougher because the pressures are higher.

Diesels are some the first engines to be successfully directly injected. DI eliminated the need for a complicated pre-mix chamber and the mechanical gearing required to control the mixture.

You don't have to worry about getting fuel and spark to the chamber at the right time, just the fuel.

Crumpp

06-29-2011, 01:20 PM

if you are comparing identical intake conditions.

Any fuel metering system that introduces fuel into the intake system cuts down on the efficiency of that intake just by being there.

Sure the fuel cools the charge but the airflow volume is restricted by the fuel metering device. Carburetors, whether float, SU, or TBI restrict the airflow volume.

With Direct Injection, the intake can be designed free from the volume and flow obstruction of a fuel metering system component.

catito14

08-01-2011, 06:44 PM

It was not solved in the "Spitfire II" the problem of negative G?

catito14

08-01-2011, 07:33 PM

Oh, i see. Thanks for the clarification cheesehawk!

Regards

Das Attorney

08-01-2011, 08:41 PM

It was a lady's orifice....err idea

http://en.wikipedia.org/wiki/Miss_Shilling's_orifice

whoarmongar

08-02-2011, 03:55 PM

A stop gap "fix" to the neg G cut out came in March 1941 with the fitting of the famous "Miss Shillings orifice" developed by Miss Tilly Shilling this was superseded by true negative G carbs fitted from 1943 onwards.

TomcatViP

08-02-2011, 04:34 PM

catito14

08-08-2011, 06:09 PM

It is possible that the devs have made a mistake by putting the "Spitfire IIa" when it should be the "Spitfire Ia" ROTOL? ´Cause I see no performance difference between one and another, except for the best use of prop.
So i believe that the "Spitfire IIa" IS really an Spitfire Ia with rotol with an grammatical mistake.

Das Attorney

08-08-2011, 07:24 PM

Here's part of the engine config from the I, Ia and IIa

Spitfire I

Propulsion Engine Rolls-Royce MerlinIII Propellor deHavilland 5-20

Spitfire Ia

Propulsion Engine Rolls-Royce MerlinIII Propellor Rotol RMS-7

Spitfire IIa

Propulsion Engine Rolls-Royce MerlinXII Propellor Rotol RMS-7

Looks like it's got the Rotol to me. Whether it's working properly in game is another matter.

TomcatViP

08-09-2011, 05:56 AM

I flew in the new vers of the Spit that came with the last patch and what ever the version (flew on Syndicate server) it has ridiculous FM. This thing can loop on it self (and certainly inside the roomy space of my Hurri cockpit) and create E or inverse the gravity field like no other in any Hollywood movies. And I am not referring to the cockpit view that hide nothing to the rear just like some popular Brazilian underwear :rolleyes:

So what ever it is a I, I Rotol or a IIa ... IT'S NOT A SPIT !

CaptainDoggles

08-09-2011, 07:46 AM

TomcatViP

08-09-2011, 11:55 AM

yes if you are looking at the nbr (speed, climb and bla bla bla). But when you start to shake that tail, bank and turn it's industrial ironing vs Moscow Ballets :(

CaptainDoggles

08-09-2011, 05:12 PM

yes if you are looking at the nbr (speed, climb and bla bla bla). But when you start to shake that tail, bank and turn it's industrial ironing vs Moscow Ballets :(

I actually have no idea what any of that means. But I don't have trouble shooting down spitfires online unless it's the MkII variant which outclasses the 109 quite easily in almost every aspect.

As for the MkI and MkIa, the 109 can outclimb them at almost any altitude, and is faster in level flight at high altitudes.

VO101_Tom

08-09-2011, 06:01 PM

I don't have trouble shooting down spitfires online unless it's the MkII variant which outclasses the 109 quite easily in almost every aspect.
As for the MkI and MkIa, the 109 can outclimb them at almost any altitude, and is faster in level flight at high altitudes.

+1

CaptainDoggles

08-09-2011, 06:28 PM

I think that we're faster at sea-level too, I have yet to be caught when running for home at wave-top height. Or maybe I am just lucky enough to not have run into someone with a better grasp of CEM on the Spits yet.You're probably right, I've never really tried it so I didn't want to say one way or the other.

Talisman

08-09-2011, 07:28 PM

http://en.wikipedia.org/wiki/Aircraft_of_the_Battle_of_Britain#cite_note-27

The above is a link to a source that has something to say under the heading of 100 octane fuel. Below is an extract. Is this seen as a reliable source?

A meeting was held on 16 March 1939 to consider the question of when the 100 octane fuel should be introduced to general use for all RAF aircraft, and what squadrons, number and type, were to be supplied. The decision taken was that there would be an initial delivery to 16 fighter and two twin-engined bomber squadrons by September 1940.[27] However, this was based on a pre-war assumption that US supplies would be denied to Britain in wartime, which would limit the numbers of front-line units able to use the fuel. On the outbreak of war this problem disappeared; production of the new fuel in the US, and in other parts of the world, increased more quickly than expected with the adoption of new refining techniques. As a result 100 octane fuel was able to be issued to all front-line Fighter Command aircraft from early 1940.[28] [nb 1]

Happy landings,

Talisman

CaptainDoggles

08-09-2011, 07:56 PM

Is this seen as a reliable source?

You're not seriously asking if wikipedia is a reliable source are you?

TomcatViP

08-09-2011, 08:30 PM

I actually have no idea what any of that means. But I don't have trouble shooting down spitfires online unless it's the MkII variant which outclasses the 109 quite easily in almost every aspect.

As for the MkI and MkIa, the 109 can outclimb them at almost any altitude, and is faster in level flight at high altitudes.

Witch one inspire you most in term of agility ?

Note that IMHO the 109's FM are great as are those of the Hurri.

CaptainDoggles

08-09-2011, 08:43 PM

Witch one inspire you most in term of agility ?Are you asking which RAF fighter I feel is more agile? Hard to say, probably the spitfire.

Note that IMHO the 109's FM are great as are those of the Hurri.The 109 FM is not particularly accurate IMO. It's undermodeled (probably the RAF fighters are as well, and yes that includes the spit)

TomcatViP

08-09-2011, 08:50 PM

Humm did you not see the pictures of the ballerina (aka the spit) and the iron (aka the 109) ? :shock:

Regarding the 109 FM it's not under modeled. I feel them like perfect (ok ok it lack a lot of buffeting, dyn stalls etc ..) but those are way ahead of the previous IL2 series.

If you take any IL2 moded FM as a reference of course CoD planes have lower perfs but ... it's not related anyway to the CoD devs.

They hve done a tremendous work . ;-)

CaptainDoggles

08-09-2011, 09:53 PM

Humm did you not see the pictures of the ballerina (aka the spit) and the iron (aka the 109) ? :shock: I have absolutely no idea what you are talking about.

Regarding the 109 FM it's not under modeled. I feel them like perfect (ok ok it lack a lot of buffeting, dyn stalls etc ..) but those are way ahead of the previous IL2 series.

If you take any IL2 moded FM as a reference of course CoD planes have lower perfs but ... it's not related anyway to the CoD devs.

They hve done a tremendous work . ;-) The 109 and early spits don't get their historical performances. That is undermodeled. I'm not comparing it to IL2 or mods or anything.

TomcatViP

08-09-2011, 10:40 PM

Rgr that. No jokes btw cats and dogs

But I hve no prob with the 109 perfs. Perhaps at alt but there is no one flying there most of the time.

Hurri is just perfect.

Spits can still out turn a hurri (in fact it seems as it can turn inside the cockpit of the hawker, raise her nose faster than a 109 at any sped and stall only for a microsecond before being given back a positive vario. Oh and the max available power is always linked to max revs low pitch making that pit awfully noisy (I wld prefer rather be on the mower for an entire day than behind that propeller for an hour :rolleyes:).

Frankly everyone will gain having a more realistic Spit model with contested dogfights instead of this.

CaptainDoggles

08-09-2011, 11:19 PM

We'll have to agree to disagree, then. I don't find the spitfire Mk1 and 1a to be uber.

VO101_Tom

08-10-2011, 01:25 AM

One thing missing from at least the Spits, is the Negative G cutout. Historically, I've read that the engine would completely shut off if held in neg-G, but I just did 2 negative G loops with the Spit, and while it sputters, it absolutely does not shut off. Full forward on the stick.

I remember, this an old story, it was changed in the first patch Il-2 Sturmovik: Cliffs of Dover: Patch 1.00.14072 -ARIL 15 (http://forum.1cpublishing.eu/showthread.php?t=21452). "Completely removed overload assessment from carburetters. Rolls-Royce engines will now cut if overload is negative, and will not cut if it is positive. (old values were sneezing at .5G, and cut-out at .25 which we felt were dead on, but this apparently confused most of the players)".

They may not have written, that simply made the RAF planes easier :rolleyes: I don't know, how much this value now. Some topics started, but without a result.
Please keep the realism! (http://forum.1cpublishing.eu/showthread.php?t=21459)
Realism or accessibility, what decision should be made? (http://forum.1cpublishing.eu/showthread.php?t=21667)

IvanK

08-10-2011, 06:56 AM

Ze-Jamz

08-10-2011, 07:22 AM

Spit under modeled as far as boost goes.

109 under modeled as far as top speed goes

There...that was easy

Plenty and plenty of posts on this matter and I'm sure the Devs know

TomcatViP

08-10-2011, 09:07 AM

VO101_Tom

08-10-2011, 09:46 AM

This has been argued at length. The documented values taken from Instrumented aircraft are shown in the images below. These from documents from the national archives. The Devs have these values:
http://img59.imageshack.us/img59/5658/vegcutfile.jpg
http://img593.imageshack.us/img593/7585/vegcutfile2.jpg
So the first onset will occur at +0.1g

Hi. Based on a undated (? 1940-1941 who knows) sheet of paper, the Englishs was obtained this development in their all existed airplane? I guess to these modifications there is a more tangible source, when, into which airplane, where and who mounted it in? Could we see them?

Compared with this, as you wrote it in the topic (109s autoprop - did it ever existed? (http://forum.1cpublishing.eu/showthread.php?t=22204)):
IvanK: "By general operational employment I am referring to general Squadron use, i.e. How many aircraft were equipped with it and at what date."

There were not enough to the German auto prop pitch, that were published a manual in 1939 (maybe from a joke it would be printed), and the german aug.-oct. 1940 somehow not part of the BOB era anymore...
I will be curious, there will be an automatics in the E-4, E-7 after these (Will be E-7 at all?). I hope so yes, otherwise this -beside all respect- is double standard.

VO101_Tom

08-10-2011, 09:51 AM

->There is no prob with the speed. I'll try to post some vids.

->The boost story is highly controversial.

-> the carburetor behavior was difficult to handle. True. But we would hve ultimately learn how to do with that. Tht's what a simulator is all about - eg have a look at all the airliner simulator aficionados ! I hope we will see it back one day or another.

~S!

You tried to climb above 8000 metres? Or you watched how fast the airplanes on 6000-7000 metres? The (edit: the 109 E-3...) top speed is ok on sea level... but the high altitude flying is totally wrong...

TomcatViP

08-10-2011, 01:20 PM

Effectively I was talking abt low to med alt speed. I will check the high alt perf with a quick test on my next flight.

Regarding your reply to IvanK : they do what they want, no ? It's upon to them to choose on which grd they make this sim credible (and I pay credit to them to be on that ground !)

Personally I found that the neg G carb cut out was a superb feature giving CoD a truly unique taste of credibility regarding effort made down to the details. This has been lacking before in several BoB era Sim since long !

I have for many years read about the cut out in spits by a lot diff and credible historians. I hve no doubt that the utmost majority of RAF planes were affected and that until really late (1942 ?).

Just want to say here (not to you Tom) that it's not because devs in some sort choose to share their enthusiasm with the community that it has to be a place for all sort of exigence. Man hve to be grateful for the possibility to put forward their case (opinion) but shld accept that their idea cld not be followed without any sort of justifications (and I know what I mean :rolleyes: !!).

catito14

08-10-2011, 03:26 PM

The only moment that i had a cut out, was in a Spitfire Ia at 15000 feets when i started an vertical dive. Then the engine stopped completely, and when i pulled up it started again.

VO101_Tom

08-10-2011, 03:50 PM

Regarding your reply to IvanK : they do what they want, no ?

Theoretically yes, practically no. If the historical accuracy is important (they said this many times), and not only while it is appropriate for their side, it would not be allowed to do things like this then (to reduce serious but existing deficiencies on a subjective manner).

VO101_Tom

08-10-2011, 03:52 PM

You guys went off on a tangent, I was talking about negative G, not speed or boost. Two full negative g loops and no cut out.

I write about it (among other things) :-P

Ze-Jamz

08-10-2011, 04:26 PM

You guys went off on a tangent, I was talking about negative G, not speed or boost. Two full negative g loops and no cut out.

yea we know :)

I was adding my input to the thread geezer... Thats the issues i have with both AC and have had from the first day playing this sim

41Sqn_Stormcrow

08-10-2011, 10:47 PM

Spit under modeled as far as boost goes.

109 under modeled as far as top speed goes

There...that was easy

Plenty and plenty of posts on this matter and I'm sure the Devs know

Unfortunately nothing is done on this issue. However, a lot of good things (more realistic cut out behaviour of early Merlins removed) are tuned down ...

Crumpp

08-11-2011, 03:38 AM

I think the original cut out was a bit drastic

I don't know what the original cut out in your game was....

I do know that if you push the float up in a float carburetor, the flow of fuel stops.

While my airframe is aerobatic, my engine has a float carburetor. The mere suggestion of negative G's will cause the engine to spool down.

There is no way a float carburetor can perform a negative G loop. :rolleyes:

IvanK

08-11-2011, 06:12 AM

Hi. Based on a undated (? 1940-1941 who knows) sheet of paper, the Englishs was obtained this development in their all existed airplane? I guess to these modifications there is a more tangible source, when, into which airplane, where and who mounted it in? Could we see them?

Compared with this, as you wrote it in the topic (109s autoprop - did it ever existed? (http://forum.1cpublishing.eu/showthread.php?t=22204)):
IvanK: "By general operational employment I am referring to general Squadron use, i.e. How many aircraft were equipped with it and at what date."

There were not enough to the German auto prop pitch, that were published a manual in 1939 (maybe from a joke it would be printed), and the german aug.-oct. 1940 somehow not part of the BOB era anymore...
I will be curious, there will be an automatics in the E-4, E-7 after these (Will be E-7 at all?). I hope so yes, otherwise this -beside all respect- is double standard.

Err what exactly are you on about Tom? The first paragraph of the document is valid. This refers to the documented value of +0.1G that cut out effects commence. Thats the relevant bit ... the remaining bit of the document refers to a "proposed system" to reduce the effects. No one is suggesting anywhere that this "proposed system" be incorporated in CLOD. The document was provided for the sole purpose of providing a documented value of cut out (in terms of G) in original early Merlins .... i.e. those without any mods at all.

This is a single page of a two page document that is dated in the usual pattern in the signature block on the last page, the document date is 21/12/1940. The remaining documents in the file are dated 20/12/1940 and 21st February 1941.

What is the relevance of the 109 Auto Prop pitch statement ??

VO101_Tom

08-11-2011, 09:48 AM

Err what exactly are you on about Tom? The first paragraph of the document is valid. This refers to the documented value of +0.1G that cut out effects commence.
...
No one is suggesting anywhere that this "proposed system" be incorporated in CLOD.

Well, the truth that I have to apologise, you're right, I responded to cheesehawk post, that myself did not check the things.
I was able to make a negative loop with the RAF types in the case that the CEM is turned off only...

What is the relevance of the 109 Auto Prop pitch statement ??

Nothing.

Al Schlageter

08-11-2011, 01:30 PM

The cut out was a 2 stage event. The 1st stage caused a momentary loss of power > a lean cut out. The 2cd stage of the cut out was the more serious cut out as the float floated the wrong way and openedthe inlet fully allowing full fuel pressure to the carb and thus flooding the engine > rich cut out.

skouras

08-11-2011, 02:25 PM

i usually fly with the E1
Much better for me than the E3 [to much shaking when you fired the cannons
:)]
plus that i have more records with the E1..:-P

catito14

08-11-2011, 03:24 PM

Really i can´t see any difference (in performance) between the Ia and the IIa, except for the Rotol constant pitch control, except of that, both of them has +6 lb, same speed, same climb rate, same maneuverability, same guns ... why most servers don´t allow to play with them?

catito14

08-11-2011, 07:12 PM

Look at the gauges then, the speed difference between the two is over 100mph.

Really?!? :confused:

Ze-Jamz

08-11-2011, 07:13 PM

Crumpp

08-12-2011, 01:21 AM

The cut out was a 2 stage event.

The fuel metering system does not change and the air/fuel ratio does not change very much.

That is the whole purpose of leaning the mixture to maintain that ratio as the density altitude gets higher.

whoarmongar

08-12-2011, 01:38 AM

Engine flooding was a very common and well known event.
Indeed an aircraft with a flooded engine was very often reported as being hit and going down trailing black smoke when in fact all that had happened was the pilot had flooded the engine usually by slaming the throttle open and or taking evasive diving manouvers.

catito14

08-12-2011, 01:57 AM

you serious?

Obviously i didn´t made the comparison in the right way :oops::mrgreen:

Al Schlageter

08-12-2011, 03:02 AM

The fuel metering system does not change and the air/fuel ratio does not change very much.

That is the whole purpose of leaning the mixture to maintain that ratio as the density altitude gets higher.

What ever you say Eugene.:rolleyes: You can contact Graham White and tell him he is a clueless gamer.

The fuel metering certainly does change when the fuel pump is pushing more fuel through the jets.

Crumpp

08-18-2011, 02:08 AM

The fuel metering certainly does change when the fuel pump is pushing more fuel through the jets.

I did not catch your explaination of the your "stages" Milo, it is clearer what you are saying. I thought you were saying it was more serious in the second stage of the supercharger.

If you are in the second stage of your supercharger then your altitude is increased and the air density is decreased. To maintain the same ratio of fuel and air you must reduce the amount of fuel.

It is not a two "stage" event, it is two different types of cut outs you can experience with a float type carburetor. You can experience both of them in one flight pulling negative G's in your float type carbureted engine.

You either have a lean cut out or a rich cut out. A lean cut out occurs when you subject the airplane to rapid onset negative G such as a bunt. The float rises up and shuts off the flow of fuel.

A rich cut out occurs when you subject the airplane to low amounts of prolonged gradual onset Negative G. The float does not rise up and shut off the flow of fuel. Instead fuel continues to flow, the engine sputters and skips but does not cut out. The fuel collects in the top of the bowl forcing the float down, opening the fuel flow to maximum and flooding the engine. This is more serious because the engine will not automatically restart like a lean cut out will. The engine is flooded and the fuel amount must be reduced in the cylinders.

If you take a float carburetor and subject it to negative G's, the engine cuts out immediately in a lean cut out.

Even in a small 180hp Lycoming engine.....sipping 10 gallons per hour empties the bowl immediately.

Accident - The pilot of a southern California Long-EZ was seriously injured and his passenger suffered a broken hip when the airplane crashed into a dry riverbed. The eyewitnesses to the accident reported that the airplane was doing aerobatics. It appeared to enter the beginning of a loop, did not have enough speed, fell out of the maneuver. The engine stopped. (negative "g" will cause a carbureted engine to suffer fuel starvation) the aircraft nosed over and spiraled down to about 100 feet, where its wings were leveled and it descended until it struck the ground. The aircraft hit a 20 degree embankment almost wings level and slid forward only about two feet. There was no fire, although the right fuel tank was ruptured.

http://v2.ez.org/cp34-p5%28.htm

You take a large 12 cylinder Merlin gulping 120 gallons per hour and the small amount of fuel in the carburetor bowl will not last a blink of eye.....

The engine will quit....
The prop will windmill....

AND as soon as the float opens back up and fuel flow is restored the engine will restart.

Anything else is gamer fantasy.

Even with a TBI or pressure carburetor, if you pull asymmetrical loads, the engine will skip as the fuel metering changes....

The TBI must be mounted in an orientation that places the metering tube in a horizontal plane. If the metering tube is not in a horizontal plane, positive or negative "G" forces acting on the diaphragm will alter fuel metering.

http://www.ellison-fluid-systems.com/manual/section2.htm

CaptainDoggles

08-18-2011, 02:50 AM

Anything else is gamer fantasy.

Please understand most of us know that the ingame behaviour is incorrect and that the flight models are not 1:1 with reality in many aspects. It's not "gamer fantasy" so much as it's "the simulation model is incomplete".

Al Schlageter

08-18-2011, 12:38 PM

Your reading comprehension certainly leaves a lot to be desired Eugene. So nice of you to repeat what I already said.

Crumpp

08-18-2011, 02:39 PM

Your reading comprehension certainly leaves a lot to be desired Eugene. So nice of you to repeat what I already said

No it was not a repeat. It was to clearly put out what happens in a float bowl type carburetor when subjected to negative G.

You wrongly stated it was a "two stage" event with the implication being it takes time.

No, it happens almost immediately and is two separate events brought about by subjecting the fuel metering system to negative G.

In a lean cut out, it immediately quits but will restart as soon as fuel is delivered.

A rich cut out immediately begins skipping and then quits.... It does not restart immediately and delivery of more fuel only prolongs the restart.

Even a pressure carb or TBI will have issues under Negative G. It is a distinct disadvantage for piston power fighters using such a metering system.

Only a direct injection metering system is immune to accelerations.

Crumpp

08-18-2011, 02:52 PM

Please understand most of us know that the ingame behaviour is incorrect and that the flight models are not 1:1 with reality in many aspects. It's not "gamer fantasy" so much as it's "the simulation model is incomplete".

I understand and don't take offense please at the "gamer fantasy." I refer to people who distort the way the physical works to get some desired advantage in a game.

There was a distinct disadvantage in fuel metering technology. One that was frustrating for Allied pilots in a dogfight. Solving it got the attention of aeronautical research agencies on both sides of the Atlantic.

Pressure Carbs and TBI helped considerably but were not in use during the Battle of Britain.

Al Schlageter

08-18-2011, 03:13 PM

No it was not a repeat. It was to clearly put out what happens in a float bowl type carburetor when subjected to negative G.

You wrongly stated it was a "two stage" event with the implication being it takes time.

No, it happens almost immediately and is two separate events brought about by subjecting the fuel metering system to negative G.

In a lean cut out, it immediately quits but will restart as soon as fuel is delivered.

A rich cut out immediately begins skipping and then quits.... It does not restart immediately and delivery of more fuel only prolongs the restart.

LOL!!! :rolleyes:

It is a 2 stage event. First there is the lean cut out which is followed by the rich cut out. They don't, and can't, occur simultaneously. Yes it takes time!!! Your 'almost immediately' says so.

CaptainDoggles

08-18-2011, 04:42 PM

TomcatViP

08-18-2011, 06:38 PM

Crump took some time to argument his reply so please take some too before answering.

Unless you are here to impose the ridicule point of views of spitperf.com and alike I don't know how you can't agree with simple logic and commune observation.

There is some vid on youtube with ppl playing with liquids and G wile doing some acrobatic flying. Have a look !

Crumpp

08-18-2011, 09:16 PM

It is not a two-stage process. What you are describing are two separate phenomena, occurring sequentially.

A lean mixture cutout is not necessarily followed by a rich mixture cutout.

Similarly a rich mixture cutout can happen without being preceded by a lean mixture cutout.

Exactly

Here this genius tries some Negative G's in a carburetor C172. This is why I don't rent airplanes.

He experiences a lean cut out. Listen to the engine. As soon as Negative G are applied, the engine quits and restarts at the end.

http://www.youtube.com/watch?v=RCIPx68ril0&feature=related

There is some vid on youtube with ppl playing with liquids and G wile doing some acrobatic flying. Have a look !

Yes, you can see as soon as the float comes up, it cuts the flow of fuel to the engine.

Ze-Jamz

08-18-2011, 09:31 PM

lol

Crumpp

08-26-2011, 08:24 PM

The supercharger is driven by the engine.

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

Supercharger power consumption is just W*Cp*deltaT, ie W*deltaH.

Supercharger isentropic efficiency is

deltaH[actual]/deltaH[isentropic]

In the case of the Merlin, this figure was about 70%.

For isentropic, adiabatic compression,

T2 = T1(P2/P1)^(gamma/(gamma-1))

Hence it's trivial to calculate the isentropic deltaT, and deltaH.

DeltaT and deltaH both get smaller if we reduce T1.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

This reduces the temperature rise across the supercharger, which is equivalent to increasing its adiabatic efficiency.

Clearly this confers an advantage to engines which inject fuel upstream of the supercharger. Given the considerable difficulty associated with increasing the aerodynamic efficiency of compressors, this advantage is not insignificant.

Mixture distribution is going to be very good provided that the charge temperature is sufficiently high for complete evaporation to be ensured. This will basically always be the case at high powers because deltaT is 100 K or more; indeed intercooling & aftercooling start to become necessary once you've got a lot of supercharge.

These advantages vanish at low non-dimensional power settings. Cars spend most of their time at very low non-dimensional power settings, and therefore DI wins hands down most of the time, especially if you go for CI, in which case it's almost no-contest.

In the end, the nature of all engineering trade studies is that the devil is in the detail. The optimum is a strong function of engine size and duty cycle, and we just don't build the sort of highly supercharged, high power spark ignition engines for which single point injection is attractive these days.

To use an analogy, old amplifiers used valves and therefore tended to have large transformers & rectifiers to produce the high DC voltages which allowed them to function. Most modern amplifiers are solid state, and they don't need those high voltages.

This doesn't mean that high DC voltages aren't still a good idea for valve amplifiers; I've got a pair of hundred watt half stacks sat next to me which run in excess of 400 V DC and sound great. But probably 99% of modern amplifiers for domestic use are solid state and so if you just ask "are high voltages a good idea for amplifiers" then the short answer is "probably not".

Viper,

The basic premise you posted is entirely wrong for all practical purposes. Your math does not take into account the heat of the engine and heat transfer to the manifold.

The conclusion reached is incorrect when it comes to engines...

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

Injecting fuel into the intake raises the charge temperature. Liquid fuel transfers and has more heat capacity than air. That means the fuel allows the charge to absorb more of the intake manifold's heat and the over all effect is the charge temperature is higher which is therefore less dense.

You can confirm this with a copy of:

V.L. Maleev, Internal-Combustion Engines: Theory and Design, 2nd ed. (New York: McGraw-Hill Book Company, Inc., 1945).

http://books.google.com/books/about/Internal_combustion_engines.html?id=fgvHHgAACAAJ

So why does an IO-360 (fuel injected) have a higher peak power than a O-360 (carbureted)? The answer is that fuel injection reduces losses in the intake system. The first reason is that the venturi in the carburetor is another constriction in the flow, which manifests itself as a pressure drop in the intake manifold. This pressure drop is eliminated with a fuel injection system, thus allowing a higher pressure to reach the cylinders, and thus a larger amount of fuel/air charge to enter the cylinder.

The second reason is that the fuel/air charge is colder, and thus denser when it reaches the cylinder, again allowing a larger amount of fuel/air charge to enter the cylinder. Just like when you add carb heat, the density of the fuel/air charge is reduced when it is heated. So you're asking "Why would it be heated?" In some carbureted engines, the intake manifold is heated to assist distribution. Even without intake manifold heating, the intake manifold will be hotter than the ambient air simply because it is attached to the engine. Heat transfer studies have shown that the liquid fuel on the walls on the intake manifold increases the rate of heat transfer. (Ref 1) Thus, in a carbureted engine, the small drops of fuel in the fuel/air charge cause the charge to heat up more passing through the intake manifold than dry air would passing through the same intake manifold. Therefore, the density of the fuel/air charge is decreased, reducing the amount of charge entering the cylinder. Experiments have shown that volumetric efficiency may be increased by 10% by direct injection of the fuel into the cylinders. This also prevents loss of fuel because of valve overlap. Fuel injection into the intake port (just outside the intake valve) shows a smaller, but appreciable improvement. (Ref 1)

http://www.eaa1000.av.org/technicl/engemp/engemp3.htm#References