Spit Mk1 Boost?

[SEE]

I can't seem to see or get any noticeable performance change with 'boost cut off' enabled or disabled.

I have been testing it at various altitudes climbing/level flight/throttle variables, etc. I would be grateful if someone could offer their results.

[Ze-Jamz]

~S~ m8

Are you getting yer 110% out the throttle too?

[Plt Off JRB Meaker]

Are you flying with 'Complex engine management'?,this would be important to establish.

[superman]

I had problem with this too, till i ffigured out what the "cutout" does.

Boost cut out is a little lever that prevents the throttle from going all the way forward (in the "red")

If you disable cutoff,you will be able to move throttle a little bit extra.

But if you already have your throttle at 100% you won´t be able to push it further so you have to move it back a bit to "reset". and then you can get that extra 10% (or whatever). You will hear sound effects warning you that its not a good idea to leave it for long :-)

But the cutoff itself does nothing to your power. Look closely at the throttle and you will figure it out.

[ATAG_Snapper]

I had problem with this too, till i ffigured out what the "cutout" does.

Boost cut out is a little lever that prevents the throttle from going all the way forward (in the "red")

If you disable cutoff,you will be able to move throttle a little bit extra.

But if you already have your throttle at 100% you won´t be able to push it further so you have to move it back a bit to "reset". and then you can get that extra 10% (or whatever). You will hear sound effects warning you that its not a good idea to leave it for long :-)

But the cutoff itself does nothing to your power. Look closely at the throttle and you will figure it out.

Good post. "Boost cutout" is a bit of an obtuse label. It should've been "Throttle Gate" which could be toggled open or closed. At least with this beta we can now close the gate after going full boost if we want to. I believe in the real Spits there was a bit of wire that would be cut if full boost was used to clue in the ground crew that further engine checks were in order.

[Plt Off JRB Meaker]

Yes spot on Snapper it's the smallest little 'gate' in red with 'PUSH' on it positioned at the front of the throttle,and just allows you to move the throttle about another 10% as Ze-Jamz and Superman have already informed us.

The new patch now allows us to switch this off,which as Superman points out is important,as you don't want this on for long periods.

[SEE]

Thanks guys, I know how to use it but has anyone tested to see what performance increase they are actually seeing in flight with it enabled?

[Das Attorney]

Hi See,

I posted the following up in the ATAG thread: This is taken from the game data using kegetys.dll. These are pre_beta so not sure if it's changed since. Basically, the MkI and Ia have 0.002 lbs/sq in extra boost (ie nothing)

You need to look at the NominalPressure entry for normal max manifold pressure, and the WEPPressure entry for boost cut out.


The Mark I and Ia are modelled up to 6.25 lbs/sq in. Boost is 6.252 lbs/sq in. Yes, that's an increase of 0.002 lbs/sq in when boost is engaged.

Check the MerlinIII entry in the engine.fmd file:

Supercharger SingleStageSupercharger Efficiency 0.5 LimiterInput Manifold NominalPressure +6.25 lbsqin ContinuousPressure +4.5 lbsqin WEPPressure +6.252 lbsqin NominalAltitude 16250 feet
Valvetrain Generic SlowRunningEfficiency 0.9
FuelPump Pushrod NominalPressure 9 lbsqin at 500 RPM
Carburettor RollsRoyceFloat DiffuserBore 6.1 cm OrificeSlowFast 1.0 sec Heater AutoEngineOil Altimetric DensityRatio Dresser BoostDriven Input +4.5 lbsqin to +6.25 lbsqin Output 1.0 to 1.01

The Spit IIa has +9 lbs/sq in boost.

From the MerlinXII entry:

Supercharger SingleStageSupercharger Efficiency 0.5 LimiterInput Manifold NominalPressure +6.25 lbsqin ContinuousPressure +4.5 lbsqin WEPPressure +9.0 lbsqin NominalAltitude 13500 feet
Valvetrain Generic SlowRunningEfficiency 0.9
FuelPump Pushrod NominalPressure 9 lbsqin at 500 RPM
Carburettor RollsRoyceFloat DiffuserBore 6.1 cm OrificeSlowFast 1.0 sec Heater AutoEngineOil Altimetric DensityRatio Dresser BoostDriven Input +4.5 lbsqin to +6.25 lbsqin Output 1.0 to 1.01

Cheers

EDIT: Don't forget that you need to jiggle the throttle a little after engaging the boost otherwise it won't 'take'.

[=XIII=Wedge]

Isn't that because all you are doing is overriding the automatic boost control system.

With an engine modification to the Merlin III and the use of 100 octane fuel it was possible to to override the automatic boost control system and get up to + 12 lbs boost although this is considered an overload condition.

With the automatic boost control engaged the boost is limitied to + 6.25 lbs.

Unfortunately we do not have this in the game currently - e.g unmodified Merlin III engine using 87 octane fuel.

[SEE]

Hi See,

I posted the following up in the ATAG thread: This is taken from the game data using kegetys.dll. These are pre_beta so not sure if it's changed since. Basically, the MkI and Ia have 0.002 lbs/sq in extra boost (ie nothing)

That explains why I am not seeing any worthwhile gain but risk manfold pressure failure if enabled for too long. Best ignore it on those figures.

Cheers Das.

[TomcatViP]

Isn't that because all you are doing is overriding the automatic boost control system.

With an engine modification to the Merlin III and the use of 100 octane fuel it was possible to to override the automatic boost control system and get up to + 12 lbs boost although this is considered an overload condition.

With the automatic boost control engaged the boost is limitied to + 6.25 lbs.

Unfortunately we do not have this in the game currently - e.g unmodified Merlin III engine using 87 octane fuel.

Oh no here it goes again with the 12lb

Ohooo and what a surprise it's a new name :rolleyes:

I tell you one thing oh great devs for the sake of this forum, never put a new Spit in game. ;)

[SEE]

I tell you one thing oh great devs for the sake of this forum, never put a new Spit in game. ;)

.....fixing the ones already in it would be nice ......Spit Mk1a top speed 230/240mph at 18K, wrong prop and 0.002lbs boost? They neeed to check the MOD performace reports carried out in 1938 on the Spit Mk1 ...even with a two speed prop it is signicantly better than in CloD!

[Al Schlageter]

Agreed, same with the 109. All the FM's are off, most worse than others (IIa is the exception for fighters). But should they fix the FM's and not worry about the actual game engine first? That's counter-productive, as then fixing the engine would break the FM's again (the FM's are coded according to the engine). Give it time... 1946 is what, 13 years old? And its still being patched...

1946 certainly didn't come out in 1998, it was Dec 2006 and in NA in March 2007. Il-2 Sturmovik was released Nov 2001.

[Ze-Jamz]

I tell you one thing oh great devs for the sake of this forum, never put a new Spit in game. ;)

They can put what they like in TC on whatever side they too just make sure the both sides have the correct FM's to play with

[=XIII=Wedge]

Oh no here it goes again with the 12lb

Ohooo and what a surprise it's a new name :rolleyes:

I tell you one thing oh great devs for the sake of this forum, never put a new Spit in game. ;)

I do not see how having a low post count makes me a new name, having joined this forum 8 months before you kind self. :confused:

I answered the question of why I understand there is no affect when disabling the ABC in the Spitfire Mk1.

I have no problem with what we have in the game, however would support any changes to the FM for any plane of any nation that would be more in line with the factual reality or close approximation based on historical sources.

However, you clearly do not share this goal. :(

[TomcatViP]

Seems I alrdy read this :rolleyes: ... and I know how it goes when they say "based on historical sources" and bla bla bla

No offense Wedge but I tell you this way of putting the case frwd is alrdy over done.

What is surprising me most of the time is that this kind of debate turns always ard the myth of 12lb eng when the FM of the Spitfire we have in game is alrdy grossly over enthusiastic and so much wld hve to be done. Only Flipper the Dolphin won't see that. But that is seldom heard

[SEE]

In fairness, Wedge is supporting accurate FM for all ac. Thats the holy grail and tough to get right. Some of these ac are still flying, we have many Pilot accounts as well as technical literature avaialble to get it 'approximate' .

It may well be that we would be mightily disappointed if the FM were modelled 100% ....:evil:

I spoke to a BoB vet Spit pilot at the Duxford Air Show (Group Captain Peter Gilpin - CBE, DFC 253 Squadron). I asked him many questions about the various Spits he flew. He answered every question then, out of curiosity, asked why I wanted to know such intricate and precise details. I explained to him I had a 'Simulator' and described CloD as a piece of software, the MP aspect, etc........he replied......" How interesting, sounds like a good game'......if only he knew how serious we take it. :grin:

[TomcatViP]

I don't think we are taking it seriously (I don't) but has long grown kids we pay attention to details and are unforgivable about what a modern Sim shd be.

As I hve alrdy said I am not expecting CoD devs to accuratly simulate the full range of mechanical and fluids mechanical behavior of a WWII plane. What we are expecting (and let me talk not only on my own name) is an average comprehension of the environment where things behave in an orderly manner with drag, lift, gravity, eng pw and dyn forces and so on the only words spoken by the FM engine. And not popularity, pubic expectations, dark lobbying etc...

IMHO CFS & IL2 did prove that the contrary is not anymore enjoyable by the masses of potential players (take a look at the nbr of copies sold and the average nbr of online players). Only some dozen heavily represented on public forums were satisfied with that.

The future lies on Online gaming. This is where the revenue's margins would be taken.

It is just like any sport. The first thing to do is to draw a squared box on the ground and write a few rules that the enjoyment begin.ANd billions are made on that very basic principles !

But wait .... it seems fairly opposite to any savage modding ;)

[SEE]

I agree Cheesehawk, BTW, I never asked Peter Gilpin any questions regards the Axis ac, just techy questions about the various Spits he flew.

As for Spit Pilot recollections, a good read for Spit Jockeys is 'Malta Spitfire' which was written during and shortly after the Malta campaign by Canadian Spit Pilot George Beurling. You pick up all sorts of useful info - MG Ammo Loadouts, etc, (Inc - Tracer - Ap - Ball).

Also, not only a useful discussion for ourselves but feedback to the Devs.....look at the number of hits on these FM threads alone.

[=XIII=Wedge]

Realism in IL2-Cliffs of Dover
"The flight sim we've built in Cliffs of Dover is much bigger than anything we've built before. We made it more realistic in every respect: graphics, plane models, physics, aerodynamics, weapons, customisability, and more."
Ilya Shevchenko - Pilot's Notes - Special Edition

The goal of greater realism is one the development team share.

For example, if the game currently modelled the Spitfire Mk 1A with 2 x 20 mm Hispano cannon, I would conclude that this was an genuine mistake on the part of the developer and raise it as a bug. If the developer then responded that this was by design then I would not be interested in using such a sim, they might might as well have modelled X-Wing fighters instead.

Also what would be the value in modlling different models of the same aircraft, not just the different marks, but even down to different propellors.

The fact is they wouldn't if they did not intend to strive for greater realism.

Whilst we can all discuss the merits of various sources regarding aircraft performance, ultimately it is down to the developers to decide on what parameters they want to use.

However if they did not want to strive for realism then it seems strange to spend time developing and engine to model so many features. If realism was not a goal then a simpler engine design would suffice saving time and money.

Whilst FM discussions are difficult, some elements can be modelled with a reasonable level of realism, hence...

Back to the Boost Cutout
So getting back on topic we end up with a couple of questions ;)

Given a Spitfire Mk1A with with an unmodified Merlin III engine using 87 octane fuel.
When the boost cutout is engaged
Then what behaviour is expected? (as intended by the developers)
And how does this correspond with actual behaviour observed in the current version of the game.

Another question is what would the actual effect be on a real 1940's Spitfire?

The first question is easy for the developer to answer, the second is something that I am interested in from an understanding point of view.

[41Sqn_Banks]

AP 1590B Merlin II and III Aero-Engines:
"257A. In its unmodified condition, the boost control cut-out valve permitted the boost pressure to rise very considerably."

[TomcatViP]

Woaaaww... "Considerably" ? :cool:

@Wedge : can you consider that given the Spit FM are alrdy optimistic adding the extra boost cld hve proved so outraging that the devs might hve decided to lower this value on the Spit ?

[41Sqn_Banks]

Yes considerably ...

http://www.spitfireperformance.com/spit1-12lbs.jpg


full throttle would give about 17 lbs. sq.in.

[41Sqn_Stormcrow]

If however I well understood, the boost cut out was put because this high pressure was damaging to the engine in the long run and therefore its use was limited to real emergency cases.

Could the fact that it is limited right now be linked to that perhaps?

[Osprey]

TomcatVIP, would you please stop posting if you aren't going to add anything other than hearsay to this. From reading the thread =XIII=Wedge has made some very interesting points - I for one am trying to understand the detail of this but clearly I'm a bit more stupid than other pilots. Understandably I don't really appreciate you throwing in undermining comments based on your own personal knowledge and trying to deride other posters arguments on the spurious suggestion that the length of registration on a forum somehow dictates your knowledge on the topic. Should Jeffrey Quill have registered today would you be telling him the same thing?

Frankly, if you are one of those people that doesn't believe that the RAF had the 100 octane in use on fighters thus achieving 12lbs boost then I'm afraid I don't think I'll be able to take anything you say seriously, ever. I'm confident that the development team aren't so unreasonable when it comes to looking at evidence.

=XIII=Wedge, please carry on.

[=XIII=Wedge]

Function of the Automatic Boost Control
My understanding was that the original reason for the throttle being design with an automatic boost control was to reduce the workload on the pilot and prevent over-boosting the engine.

It allowed them to set the desired boost pressure with the throttle lever and the ABC would ensure that that desired pressure setting was maintained up to the rated altitude.

Without it the pilot would constantly have to keep adjusting the throttle to maintain the same boost as the plane changed altitude.

Using the boost cutout disables this function.

@TomcatViP - It is possible, but it is more likely that pressure to release the product meant that development was scaled back.

There is clear evidence of this, due to having two variants of spitfire MK 1A that differ only by propellor. (DH-2S and Rotol-CS)

No problem with this it happens all the time, features are dropped to get a release to the market place.

However if you take these pressures out of the equation, a more realistic flight model is still a desirable attribute and is infact a major selling point.

Red vs Blue arguments don't really come into it.

Multiplayer is an important aspect of the game, but with out greater realism we might as well be playing Tom Clancy's H.A.W.X.

[41Sqn_Banks]

Function of the Automatic Boost Control
My understanding was that the original reason for the throttle being design with an automatic boost control was to reduce the workload on the pilot.

It allowed them to set the desired boost pressure with the throttle lever and the ABC would ensure that that desired pressure setting was maintained up to the rated altitude.

Without it the pilot would constantly have to keep adjusting the throttle to maintain the same boost as the plane changed altitude.

Using the boost cutout disables this function.

This is correct. This are exactly the points mentioned in the Merlin II/III engine manual.

Some notes:
You discribe a "variable datum type" automatic boost control. Early production Merlin II engines had a "fixed datum type" automatic boost control (however even the manual mentions that these are replaced by the "variable datum type"). As you already wrote with a "variable datum type" boost control each throttle setting gives you always the same boost (up to rated altitude). The "fixed datum type" had the follwing drawback:

AP 1590B Merlin II and III Aero-Engines

240. (...) With the fixed datum type of automatic unit for which the control has been set, maximum permissible boost is obtained soon after the throttle is opened past the slow-running position. In consequence of this, below rated height and particularly near the ground level, it is only possible to open the throttle a small amount with the result that a considerable degree of lost motion in the cockpit throttle operating lever occurs.



What the "modification" to the boost control does is simply limiting the boost pressure to rise above +12lbs even if the boost control was disabled. However my understanding is that you don't have the benefits of the "variable datum type" boost control anymore (as long as boost control cut out is enabled). In later Merlin marks this was changed and the "boost control cut out" didn't really disable the boost control but it did set a higher boost for each throttle setting.

[=XIII=Wedge]

So given that we currently have an earlier Spitfire using only 87 octane fuel:-


With the ABC enabled (normal situation)

The maximum boost obtainable will be +6.25 lbs.
Once set the selected boost (datum) will be maintained regardless of changes in altitude up to the rated altitude.
Above rated altitude the pressure will drop off, but the datum point will remain the same.
Pilot workload is reduced and there is no risk of overboosting the engine.
With the ABC disabled (done by operating the cutout)

The maximum boost obtainable would be +17 lbs @ sea level.
Any rise above + 6.25 would have disasterous impact on the engine due to pre-ignition of the fuel.
Provided that the pilot retarded the throttle they would have manual control of the boost, but would have to be careful not to overboost the engine.
The indicated boost pressure would change as the altitude changed.
Assuming that this is a correct description then from a game design point of view their are a few options.
The operation of the cutout would only be of value if the game simulated failures to the ABC unit either through the damage model or the physical weathering setting.
If this was not the case then the cutout option could be removed (Only the sadistic would take pleasure from using the cut-out to intentionally overboost a Merlin)
If any of my assumptions are incorrect then please let me know.

Does this seem like a reasonable analysis of the issue?

[Osprey]

I feel more clever already ;)

[TomcatViP]

Really ?

If you get 6.25 op. WHy wld you hve 17 then ?

Just a reminder 6.25x2=12.5
6.25x3 = 18.75

So nearly two third of Merlin "power" (let's say for a second that boost ctr linearly the available power) was spared from the normal eng op that was used to qualified the type in the RAF FC !

What do you think they tried to spare Sidney pride ?

What is to be sure is that I m getting old with that endless debate as much as if the time on the CoD forum was highly boosted !!

[Osprey]

With every post of yours the more I realise that you know nothing about the subject. He plainly says that you would fatally damage the engine by going up to that rating. Furthermore the ABC job is to stop that from happening but you can disable it in order to achieve some increased power for a short period (WEP) or manage your own boost pressures.

Did I understand that correctly Wedge?

[TomcatViP]

I think you are the one that do my dear.

If you think that the FC was modifying the Merlin's engines like a car tuner will do, tht is a real problem.

As I have alrdy said it's not my personal thinking that prevail in my word. You are wrong on the all line. If I had a personal idea on the subject I won't bother other with my own thinking.

I think you 100octer and 17lber shld read this with much attention and stop lobbying every forum that deal with the Spitfire and smokes any discussions with insult and name calling etc.. etc..;

As I alrdy said, this theory does not makes any sense either on historical or mechanical grounds.

If there was a switch for emergency boost right on summer 1940 it certainly wasn't for a 17lb boost that even in 1944 still posed some problem.

Oh yeah let me guess, if you unfold your SpitPufPuff.com doc you certainly are already with injected nitroglycerin and so on at this same date.

The fact is that guys like you are bitching so much on every forum with YOUR idea of the spit (not the real one) that no sim devs can makes a FM with serenity.

What is senseless is that if such is done, it would be a really good plane to fly and fight.

By the way stop bad mouthing on me Osprey that's getting pretty boring. You don't know me. Thx

[pupo162]

I think you are the one that do my dear.

If you think that the FC was modifying the Merlin's engines like a car tuner will do, tht is a real problem.

As I have alrdy said it's not my personal thinking that prevail in my word. You are wrong on the all line. If I had a personal idea on the subject I won't bother other with my own thinking.

I think you 100octer and 17lber shld read this with much attention and stop lobbying every forum that deal with the Spitfire and smokes any discussions with insult and name calling etc.. etc..;

As I alrdy said, this theory does not makes any sense either on historical or mechanical grounds.

If there was a switch for emergency boost right on summer 1940 it certainly wasn't for a 17lb boost that even in 1944 still posed some problem.

Oh yeah let me guess, if you unfold your SpitPufPuff.com doc you certainly are already with injected nitroglycerin and so on at this same date.

The fact is that guys like you are bitching so much on every forum with YOUR idea of the spit (not the real one) that no sim devs can makes a FM with serenity.

What is senseless is that if such is done, it would be a really good plane to fly and fight.

By the way stop bad mouthing on me Osprey that's getting pretty boring. You don't know me. Thx


you clearly missed the point.

the plane could go to 17+ boost, but would go BOOOM if they tried to go that way. Im sure eventually they got aroudn that problem and managed better engines who could go more than +6.5.

Even myself who thinks of a pittie as a uselless kite, can get the fair point wedge is making.

[TomcatViP]

Believe me or not but military services do test planes to remove any Go&Boom features.

If there was such a lever, it wld be instantly sealed, locked and patched with every possible red tapes ;)

Bench test is not Flight test that is no Op Tests that are not them self Op limits. And I did it short.:cool:

[41Sqn_Banks]

Sorry Tomcat you really didn't understand the concept of a supercharged engine. Below full throttle height every supercharged engine produces more boost than it can handle. Guess where the name full throttle height comes from ... exactly it's the height where the throttle can be moved fully forward without overboosting the engine.

There is no magic device needed to get +17 boost from the engine, it's simply the supercharger that is capable of producing this pressure at sea level. Of course this is a overboost condition for the engine and will kill your engine in no time. That's the problem with supercharged engines, the pilot has to keep the boost below the limits and has to adjust the throttle with every altitude change (as boost changes with altitude).

Thats why there is the automatic boost control that limits the engine boost below full throttle heigth automatically. However there might be a failure in the automatic boost control or a emergency situation ... so there was a boost control cut-out that disabled it and allowed the pilot to control the boost himself. Then however he could seriously overboost the engine. So they modified the engine that even with disabled boost control the boost pressure couldn't be raised above +12 boost.

So the "modification" didn't allow the engine to produce higher boost, in fact it limited the boost from around +17 to +12.

PS: Please use whole words to write your sentences it's hard to make sense of these abbreviations.

[Valec]

http://www.airpages.ru/eng/uk/spitf1.shtml http://www.airpages.ru/eng/lw/bf109e1.shtml

[TomcatViP]

One Question Banks : when do you actually get max boost with a supercharged engine ?

And by the way if you were not charging us every three month on the same subject and with the same arguments I would hve been pleased to check out any abbreviations out of my phrases.

As I hve alrdy said, in the RR test manual the latter merlin is rated at 9lb of boost at 15kft not 12 or ...17

By the way I think I am qualified to deal with that subject - just went to check my diplomas just in case ;)

[41Sqn_Banks]

One Question Banks : when do you actually get max boost with a supercharged engine ?

I suspect this is a hypothetical question: Highest boost possible boost is at lowest possible altitude at highest possible engine rpm with throttle valve fully open.

Highest allowed boost is available at with highest allowed engine rpm at all altitudes below full throttle height.

But really it's not about getting a high boost at low altitudes but make the engine survive the high boost. No one is telling that +17 boost didn't kill the engine.


As I hve alrdy said, in the RR test manual the latter merlin is rated at 9lb of boost at 15kft not 12 or ...17

So what is your point? There is a difference between "maximum-possible-boost-produced-by-the-supercharger-at-sea-level-that-the-engine-can't-handle-at-all" (around +17), "maximum-allowed-boost-in-case-of-emergency-for-no-longer-than-5-minutes" (+12 for 100octane fuel, +6 1/4 for 87octane fuel), "maximum-allowed-boost-for-no-longer-than-30 minutes" and "maximum-boost-for-infinite-time-...-well-not-infinite-as-your-engine-will-die-even-with-that-boost-after-200hrs-running-without-inspection"

There is no difficulty in getting a high boost at low altitudes from a supercharged engine. The difficulty are:
- Find the highest boost that does only acceptable "damage" to the engine and find ways to reduce the "damage" even further to permit (=allow) the use of higher boosts
- Find ways to maintain the high boost at high altitudes

[Osprey]

And by the way if you were not charging us every three month on the same subject and with the same arguments I would hve been pleased to check out any abbreviations out of my phrases.


But he's not giving you an argument. He's giving you a documented fact from Rolls Royce and the RAF. If you don't believe this to be true then I would suggest you provide the evidence, though I suspect you've been asked in the past and haven't managed to. My questioning was around understanding this evidence because I have seen this data in the past and never understood what it actually meant. I want to operate the engine properly and I am grateful to Wedge and Banks for the explanation, now I understand what the cutout actually does.

PS. A personal diploma isn't evidence btw, it just says you went to a college and passed some tests. Congratulations.

[Robo.]

There is no magic device needed to get +17 boost from the engine, it's simply the supercharger that is capable of producing this pressure at sea level. Of course this is a overboost condition for the engine and will kill your engine in no time. That's the problem with supercharged engines, the pilot has to keep the boost below the limits and has to adjust the throttle with every altitude change (as boost changes with altitude).

Thats why there is the automatic boost control that limits the engine boost below full throttle heigth automatically. However there might be a failure in the automatic boost control or a emergency situation ... so there was a boost control cut-out that disabled it and allowed the pilot to control the boost himself. Then however he could seriously overboost the engine. So they modified the engine that even with disabled boost control the boost pressure couldn't be raised above +12 boost.

So the "modification" didn't allow the engine to produce higher boost, in fact it limited the boost from around +17 to +12.

PS: Please use whole words to write your sentences it's hard to make sense of these abbreviations.

This is a very good answer Tomcat, well known facts btw. Just read any articles or books about the history if the Merlin II & III engines and you'll see it really is as simple as that. The actual boost was around +16PSI, that was considered as unsafe for normal service and engine life, therefore, a 3mm hole has been drilled to get the excessive pressure out of the system limiting it to +12PSI. That was what it says - Boost Control Cut-Out so it simply overrided the rated limit by moving certain bits to block certain openings via bowden cable. The actual gauge only showed +8PSI and slightly above (was +4PSI max. only on first production Spitfires and +8PSI max on later Spits) and pressure went from +6.25 to +12PSI straigt away, eg no boost of say +10PSI was possible. You can find exact technical info about how exactly this was achieved, you can find another pieces of information about the RAF pilots flying over France well before BoB period ''pulling the plug'' all the time. You can also find info about a +25PSI rated Speed Spitfire (same Merlin III) if you really care.

No matter what your opinion is, these are simple and well researched facts, not much space to argue I am afraid.

I am a blue pilot and not a Spitfire jockey, mind you. ;)

[Jugdriver]

. You can also find info about a +25PSI rated Speed Spitfire (same Merlin III) if you really care.

Oh god now you have done it...


JD
AKA_MattE

[SEE]

So given that we currently have an earlier Spitfire using only 87 octane fuel:-


With the ABC enabled (normal situation)

The maximum boost obtainable will be +6.25 lbs.
Once set the selected boost (datum) will be maintained regardless of changes in altitude up to the rated altitude.
Above rated altitude the pressure will drop off, but the datum point will remain the same.
Pilot workload is reduced and there is no risk of overboosting the engine.
With the ABC disabled (done by operating the cutout)

The maximum boost obtainable would be +17 lbs @ sea level.
Any rise above + 6.25 would have disasterous impact on the engine due to pre-ignition of the fuel.
Provided that the pilot retarded the throttle they would have manual control of the boost, but would have to be careful not to overboost the engine.
The indicated boost pressure would change as the altitude changed.



Thanks guys, just one qestion. At alt 17K and above, the manifold pressure in Clods Spit Mk1 drops significantly (less than 2 Ibs per Sq.in.) - full throttle - straight and level - The boost cut out has no effect as pointed out earlier in the thread. So, based on the above - this appears to be incorrect for that altitude?

[Crumpp]

The maximum boost obtainable would be +17 lbs @ sea level.

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

[Skoshi Tiger]

Although not Merlin engines, I assume these engines were running above their maximum allowed boost!

http://www.youtube.com/watch?v=aUkXriHjQeI

http://www.youtube.com/watch?v=vq5cjNhN_po&feature=fvwp&NR=1

Well at least it put a smile on my dial!

Cheers!

[Blackdog_kt]

Thanks guys, just one qestion. At alt 17K and above, the manifold pressure in Clods Spit Mk1 drops significantly (less than 2 Ibs per Sq.in.) - full throttle - straight and level - The boost cut out has no effect as pointed out earlier in the thread. So, based on the above - this appears to be incorrect for that altitude?



You got me curious so i set forth to investigate this by converting some units and making a couple of simple comparisons :-P

My personal conclusion is that while i can't be sure if it's accurate because i don't have original performance specs, +2 boost is nothing to scoff at in the wider sense of things.

First of all boost is measured in relative units, it's PSI above the normal sea level ambient pressure or in other words, zero boost means full throttle at sea level in a non-supercharged engine.

To put this in perspective, +0 boost would be equivalent to about 1 Ata (for Luftwaffe aircraft) or 29.92 inches of mercury (for USAF aircraft)

According to conversion tables, 1 psi = 2.036 inHG = 0.068046 atmospheres.

I don't know if Ata units correspond exactly to standard atmospheres, but here's how it looks thus far with relative boost measuring:
1 atmosphere = 29.92 inches Hg = +0 psi boost

If we measured absolute psi we'd get:
1 atmosphere = 29.92 inches Hg = 14.696 psi (absolute)

If this gets confusing, just keep in mind that boost is like setting the scale arbitrarily: +0 psi boost = 14.696 psi absolute


Following this train of thought we have:
+2 psi boost = 16.696 psi absolute (14.696 absolute + 2 from the boost) = 1.13609 atmospheres = 33.993 inHg

If we keep in mind that variants of late war fighters with turbo-charged engines like the P-47 were limited to about 42 inches Hg, getting the equivalent of 33.99inHg from a supercharged Merlin (no turbos involved) is not shabby at all.

Like i said i don't know how accurate it is, it's just that it doesn't seem implausible when making comparisons to later designs. I know this doesn't answer your question in a satisfactory manner, i was just in the mood for some investigating until someone with more accurate data can pop in ;)

[TomcatViP]

PS. A personal diploma isn't evidence btw, it just says you went to a college and passed some tests. Congratulations.

So you throw the insults. I respond politely to calm you down and then you add another layer of xxxxxxxx ?

Where is your mum that I made an urgent request for some (boosted) slap on your pinky butt ? That also I hev done and was rather good :twisted:

Just to remind you after reading BlkDg post : btw 1940 and 1944 there was Four (4) years of harsh technological development. If they had such boosted Merlin, the MkII would hve been called a MkIX etc.. etc..

WHen dealing with history You need to put things in perspective or you end with acrobatic assumptions such as where we are now.

When dealing with a fleet of airplane at war you need to understand taht factory made does not mean fleet wide or you'll end to say that the F35 is actually in full service just because a couple have just been delivered to an instructor unit (both wings are still on guys ;)) .

And by the way I did alrdy put RR data on the forum. It does not say 17lb at all : 9 lb max op boost at rated alt. And it was in late 1940 early 41 (cant remember).

I would come back latter for the max boost and alt question but I think I (we) hve alrdy discuss this one alrdy. Just remind that that the boost (the supercharger) was not there for max low speed but for increasing the climb rate and maximizing the overall speed at alt. As I hve alrdy said this is not a car tuning. You don't plug the biggest supercharger to get the max peak power.

~S

PS: the FM of the spit is more of a concern for me
PSS : I am (wwe are) not historian(s). Instead of recreating evidences we shld stick to what are the data in the literature. There is enough to discuss on how any data cld impact the FM. Valec as alrdy post a realy good link to source out any perfs

http://www.airpages.ru/eng/uk/spitf1.shtml http://www.airpages.ru/eng/lw/bf109e1.shtml

[SEE]

Thanks for taking the time to do the maths Blackdog. I don't use the 'boost' because I have never really noticed any gains that are worth the risk of engine damage if you forget to disable it.

But I do look at the manifold pressure guage to check I haven't blown a gasket......:grin:

I have read Spit pilot accounts where they describe (in passing) enabling 'boost' or 'throttle through the gate' to get out of trouble and head for base.

If I fly straight and level - full throttle, with the boost cut out positioned for that extra bit of throttle movement - I don't see any increase in RPM, IAS, etc. That left me wondering what should I expect to read on my gauge at 18000ft for example and what performance gains I should expect to see or get.

[Al Schlageter]

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

The maximum boost obtainable would be +17 lbs @ sea level.

There is a difference in 'would' and 'were'. ;)

Merlin III
1,310 hp at 9,000 ft, +12 lb/sq.in, with 100 octane fuel (5-minute limit).
1,440 hp at 3,000 rpm, +16 lb/sq.in boost, 5,500 ft in Sea Hurricane

Harvey-Bailey, A. The Merlin in Perspective - the combat years. Derby, England: Rolls-Royce Heritage Trust, 1983. ISBN 1-872922-06-6

[Crumpp]

The discussion is the Battle of Britain. Sea Hurricanes are a much later development and the boost increase came after some significant upgrades to the engine.

A 1940 Merlin II and III were only capable of +12 lbs and that boost was achieved by engaging the boost cut out.

[Al Schlageter]

The first of the Sea Hurricanes to see service with the Fleet Air Arm arrived in February 1941.

Yes be sure that is much later than the BoB.

[Robo.]

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

Yes, Sir, you're kind of correct - +12PSI is the rated boost for a Merlin III with the plug pulled. +17PSI was never a rated boost for this engine, but the engine was actually capable of it.

In fact, the BCC-O was still limiting the 'natural' boost DOWN TO +12PSI by drilling a 3mil hole in there. It is also known fact that some pilots during Battle of France liked to put a matchstick into that hole getting +16PSI effectively on Waybridge prop Hurricanes, beating the hell out of the poor thing. No, I don't want that modelled, I just mentioned it because I find it interesting.

Noone ever said the Spitfires were flying at +17PSI, even the +12PSI was restricted. The reason he mentioned it was TomcatVIP's post regarding overboosting I believe.

[Robo.]

And by the way I did alrdy put RR data on the forum. It does not say 17lb at all : 9 lb max op boost at rated alt. And it was in late 1940 early 41 (cant remember).

TomcatViP, you seem to be wrong - Merlin III in question was rated +6.25PSI and +12PSI with BCC-O and 100 octane fuel before the BoB actually started (10.7.1940), there many are official documents and with this topic being well documented, there is not much space for arguing or guessing I am afraid.

I really recommend reading any good book about this topic, ''Merlin in prespective'' is pretty much comprehensive and sheds a lot of light on how RR approached aircraft engines in that era compared to say DB - awesome reading.

The +17PSI is not mentioned in any Spitfire book, this is simply a figure the Merlin III achieved (not safely mind you!) without limiting the boost to certain PSI considered as safe and giving the engine reasonable life. That PSI is called 'rated boost' and it was +6.25PSI for Merlin III until they rated it for +12PSI with better fuel. The +12PSI was not standard rating, but highest permissable for short periods of time. Simple as that.

If you have any information about Merlin III being rated at +9PSI max, please provide, I quite like reading about engines.

[Robo.]

Oh god now you have done it...


JD
AKA_MattE

Hehe I know what you mean, but please read what I wrote in context - I only mentioned the Speed Spitfire because it was relevant to the Merlin III overboosting (and the story is actually very interesting, RR lads were nuts!), but I hate the 25lbs Spits with passion in Il-2. :grin:

[Ze-Jamz]

Thanks for taking the time to do the maths Blackdog. I don't use the 'boost' because I have never really noticed any gains that are worth the risk of engine damage if you forget to disable it.

But I do look at the manifold pressure guage to check I haven't blown a gasket......:grin:

I have read Spit pilot accounts where they describe (in passing) enabling 'boost' or 'throttle through the gate' to get out of trouble and head for base.

If I fly straight and level - full throttle, with the boost cut out positioned for that extra bit of throttle movement - I don't see any increase in RPM, IAS, etc. That left me wondering what should I expect to read on my gauge at 18000ft for example and what performance gains I should expect to see or get.

Id like to know this..

TC, help please

[Ze-Jamz]

Where is your mum that I made an urgent request for some (boosted) slap on your pinky butt ?


Brilliant..

[Seadog]

The maximum boost is only +12lbs at sea level in emergency override in the Spitfire Mk I.

That is all the Merlin II and III were capable of handling and that was a definite over boosting of the engine.

The Merlin III was capable of handling 16lb boost:

http://www.wwiiaircraftperformance.org/merlin3-rating.jpg

and the Sea Hurricane IC used 16lb boost in combat, but not in 1940.

[Robo.]

If I fly straight and level - full throttle, with the boost cut out positioned for that extra bit of throttle movement - I don't see any increase in RPM, IAS, etc. That left me wondering what should I expect to read on my gauge at 18000ft for example and what performance gains I should expect to see or get.

At 18000ft, the gain with BCC-O enabled was rather marginal afik.

Enabling the boost on the ground (sea level) for example, would increase the Boost (manifold pressure) from +6.25PSI to +12PSI resulting in extra 270hp (cca) coming from your engine for the price of rising water temperature (obviously), engine wear etc (hence the restricted usage). The Boost would then consequently drop with rising altitude as per normal - exact figures depending on the given atmospheric conditions. The gain was most noticable down low, I can try to dig out approximate figures if needed.

Almost double boost didn't mean double power mind you, the 3000RPM limit was still to be considered.

What you expect to happen when ''you pull the plug''? At sea level - you can see the boost gauge reading above the +8PSI limit, you can feel and hear the engine working harder, you can see the water temp rising faster, RPM very much depending on the type of propeller used - but your Merlin III is giving you extra 270hp with all consequences.

Hope that helped.

[Crumpp]

Sea Hurricane IC used 16lb boost in combat, but not in 1940.

Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.

The +17PSI is not mentioned in any Spitfire book, this is simply a figure the Merlin III achieved (not safely mind you!)

It has no bearing or relevance. BMW tested the BMW801D2, including flight test of the aircraft, to 2.2 ata but the engine never saw a service rating above 1.65ata.

It is not intellectually honest to make the claim the engine was then capable of 2.2 ata. It was not capable of reliable operation at that boost level and that is reason it did not enter service. Same goes for the Merlin II and III.

If you want to know what an airplane can do, check the latest edition of the Operating Instructions. That is what was approved and in use.

No speculation required!!

[Robo.]

Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.



It has no bearing or relevance. BMW tested the BMW801D2, including flight test of the aircraft, to 2.2 ata but the engine never saw a service rating above 1.65ata.

It is not intellectually honest to make the claim the engine was then capable of 2.2 ata. It was not capable of reliable operation at that boost level and that is reason it did not enter service. Same goes for the Merlin II and III.

If you want to know what an airplane can do, check the latest edition of the Operating Instructions. That is what was approved and in use.

No speculation required!!

The +16PSI on Sea Hurris are irrelevant indeed.

Sir, as stated before, the Spitfire Mk.I was flying at +12PSI Boost. The figure of +16PSI was only mentioned in a reply to TomcatViP regarding the overboosting of early Merlin engines. No one ever said that such a rating should be modelled for Spitfires Mk.I or Hurricanes Mk.I ingame!

We're saying the same thing btw, no need to argue.

[Al Schlageter]

Only after significant modification to handle such pressure, modifications that did not exist in 1940.

So it only took RR maybe 1-2 months to make the significant modification and test the engine at +16lb boost and obtain certification for that boost level. Not bad at all.

[Crumpp]

We're saying the same thing btw, no need to argue.

There is no argument at all. I was trying to help you guys find answers to your questions about these machines.

RR maybe 1-2 months

I don't know as I would have to see the actual timeline. I highly doubt it though.

Changes to aircraft do not generally happen overnight. First the change has to be thoroughly tested because the safety margins are by their very nature very tight in aviation.

Once approved, it can't happen overnight either. The changes have to be disseminated to the folks who will implement them. They need the knowledge to enact the change.

Just as important, the people making those changes need the resources to enact it. That means the manufacturer has to retool or reset the production lines, train employees, and get the new parts made. Making enough for the aircraft in service is just the tip of the iceberg too. You have to have enough replacement parts sitting on the shelves to keep the airplanes in service flying. The standard rule of thumb is one part on the airplane, three replacements on the shelf.

So if you have 25 airplanes, you need 100 parts in total.

Of course once the part is made, it still has to reach the flight line too.

In short, it has to be approved, disseminated, manufactured, and distributed before anyone picks up a screw driver to loosen up the first screw to make the change. On average, that process took ~6months in WWII for most designs. The more technical the change, the longer and vice versa.

Just because a memo says it was approved does not mean it was in operational use from that day forward.

[41Sqn_Banks]

Maybe the +16 lbs were allowed for Sea Hurricane IA that operated from CAM ships (catapult armed merchantman) without the possibility to land - engine life is not a problem in this case.

[Al Schlageter]

Since Sea Hurricanes were in service in Feb 1941, then the +16lb boost Merlins were available in 1940 since it took, according to you, ~6 months.

[Osprey]

So you throw the insults. I respond politely to calm you down and then you add another layer of bullshit ?

Where is your mum that I made an urgent request for some (boosted) slap on your pinky butt ? That also I hev done and was rather good :twisted:

Just to remind you after reading BlkDg post : btw 1940 and 1944 there was Four (4) years of harsh technological development. If they had such boosted Merlin, the MkII would hve been called a MkIX etc.. etc..

WHen dealing with history You need to put things in perspective or you end with acrobatic assumptions such as where we are now.

When dealing with a fleet of airplane at war you need to understand taht factory made does not mean fleet wide or you'll end to say that the F35 is actually in full service just because a couple have just been delivered to an instructor unit (both wings are still on guys ;)) .

And by the way I did alrdy put RR data on the forum. It does not say 17lb at all : 9 lb max op boost at rated alt. And it was in late 1940 early 41 (cant remember).

I would come back latter for the max boost and alt question but I think I (we) hve alrdy discuss this one alrdy. Just remind that that the boost (the supercharger) was not there for max low speed but for increasing the climb rate and maximizing the overall speed at alt. As I hve alrdy said this is not a car tuning. You don't plug the biggest supercharger to get the max peak power.

~S

PS: the FM of the spit is more of a concern for me
PSS : I am (wwe are) not historian(s). Instead of recreating evidences we shld stick to what are the data in the literature. There is enough to discuss on how any data cld impact the FM. Valec as alrdy post a realy good link to source out any perfs


This is really nothing short of an offensive and obtuse post. I am afraid I had to report it.

[Crumpp]

Since Sea Hurricanes were in service in Feb 1941, then the +16lb boost Merlins were available in 1940 since it took, according to you, ~6 months.

Interesting. You are the first source I have seen that makes that claim. Most agree that the prototype Sea Hurricane was flying by Feb 1941.

Most other sources agree that it was not until ~July 1941 that it became operational.

Once the Fleet Air Arm took delivery of the Hurricanes from the RAF, starting with 880 squadron in March 1941 and 804 squadron in April 1941 it then started the mamoth task of shipping the Hurricanes to operational squadrons in all theatres around the world. A large consignment was shipped out in HMS Furious to 807 squadron in Gibraltar on 1 July 1941 (eg V7301 and V7623). Whilst others were shipped to South Africa in SS City of Bombay on 9 January 1942 (eg Z4056). Half a year later further consignments were shipped out on SS Belgian Seaman to Takoradi from Liverpool on 30 June 1942 (eg BP709), and to Simonstown in SS Lt St Lonbert Brie thence to 800 sqn on HMS Indomitable in July 1942 (eg V7416). However, quite a number were lost with the HMS Eagle which sank on 11 August 1942.

http://www.fleetairarmarchive.net/aircraft/hurricane.htm

Sounds kind of like EXACTLY what I told you is typical....

[Seadog]

The first carrier borne Sea Hurricane kill was recorded on July 31 1941, by Sea Hurricanes operating from HMS Furious. The type must have been operational some months sooner with development occurring from mid to late 1940 to early 1941. However, this does not mean that all Sea Hurricanes used 16lb boost right from the beginning. I suspect that the 16lb boost mod was not made until late 1941/early 1942. Brown, in Wings of the Navy, mentions that it was used for the Sea Hurricane IC which had the Hurricane IIC, 4 x 20mm cannon wing, grafted onto a Sea Hurricane IB airframe.

[Al Schlageter]

The squadron formed at Arbroath in January 1941 as a Fleet Fighter squadron with 3 Martlet Is, intended for the still uncompleted HMS Indomitable. The squadron was augmented with 3 Sea Gladiators and 9 Sea Hurricane IAs untill replaced with Sea Hurricane Ibs in July 1941.

The first Sea Hurricanes joined No 880 squadron at Arbroath, Scotland, in January 1941. In July 1941, they joined their aircraft carrier, ‘HMS Furious’.

[Crumpp]

Fleet Air Arm took delivery of the Hurricanes from the RAF, starting with 880 squadron in March 1941 and 804 squadron in April 1941


Sounds like operational trials.

then started the mammoth task of shipping the Hurricanes to operational squadrons

Sounds like General Service adoption.....

[Seadog]

Performance data for Spitfire Mk1 with 12 and 16lb boost:

http://www.spitfireperformance.com/spitfire-I-rae-12lbs.jpg

[TomcatViP]

*Fake (or very highly suspicious) !

pls refer to my earlier post if ever needed regarding power increase Vs speed

[IvanK]

The 12Lb Boost lines and +16Lbs are computed projections of performance I believe. 12lbs we know was available on the MKI. 16Lbs was not available/used in the MKI. I think the first operational use of +16Lbs was on the Spit MKV with Merlin 45

[Al Schlageter]

It does say Boscome (Aeroplane and Armament Experimental Establishment), so I would say it was from testing done there.

The source for the graphic is on the graphic.
http://www.spitfireperformance.com/

[Seadog]

*Fake (or very highly suspicious) !

pls refer to my earlier post if ever needed regarding power increase Vs speed


The 12Lb Boost lines and +16Lbs are computed projections of performance I believe. 12lbs we know was available on the MKI. 16Lbs was not available/used in the MKI. I think the first operational use of +16Lbs was on the Spit MKV with Merlin 45

Here's actual flight data from the Hurricane using 6 and 12lb boost:

http://www.wwiiaircraftperformance.org/hurricane/hurricane-l1717-cal.jpg

Note how closely the performance increases match the previous data for the Spitfire I at 6 and 12lb boost.

I haven't read of the Spitfire I/II using 16lb in combat, but they must have run the Merlin III at 16lb boost to certify it for the Sea Hurricane, and those tests are just as easy to do in a Spitfire with a Merlin III.

[lane]

The following passage from Wing Commander Royce Wilkinson's book is interesting and germane to the discussion.

http://www.wwiiaircraftperformance.org/hurricane/rcw-pg6.jpg

[Blackdog_kt]

Wow, nine aircraft in ten days?

Probably these guys flew quite a lot during those days, let's take a guess and say 3 to 5 sorties per day (depending on distances/time flown), this gives us nine "busted" engines for 30 to 50 sorties total for these 10 days.

Now, divide the amount of engines used up by the sorties and you get a per-sortie engine failure rate of 18% to 30% for going above the limits. In other words, almost one in five to one in three sorties results in a busted engine, not exactly a trivial risk.

Pretty interesting reference there to get a feel of how easy it was to break an engine under operational conditions, thanks for linking it.

[lane]

Pretty interesting reference there to get a feel of how easy it was to break an engine under operational conditions, thanks for linking it.

Sure, no problem. 18 lbs., 3200 rpm clearly exceeded approved limits and as mentioned was hard on the engines. +12 lb., 3000 rpm on the other hand was approved and could be used operationally in emergencies without damage to the engine.

http://www.wwiiaircraftperformance.org/hurricane/151-orb-16feb40.jpg

http://www.wwiiaircraftperformance.org/ap1590b.jpg

[Crumpp]

without damage to the engine.

That is an entry in a Squadron logbook. The man who wrote that is not a technical expert in engines. He is an operator not an engineer.

The engineers clearly disagree with this operator in the instruction under entry number 11 for AP 1590B/J.2-W Merlin II and III Use of +12lbs Boost Pressure - Alterations and Precautions.

Paragraph 11 clearly states:

The use, in an emergency, of this high boost pressure is a definite overload condition on the engine....

[Viper2000]

If however I well understood, the boost cut out was put because this high pressure was damaging to the engine in the long run and therefore its use was limited to real emergency cases.

ABC was introduced in order to prevent pilots from breaking engines by overboosting them below FTH.

I suspect that the cutout was originally provided in case the ABC failed, so that the pilot would still have access to direct throttle control.

The cutout modification was basically a hack which allowed the cutout to function as a combat power detent without extensive modification to the rest of the cockpit.

Later Spitfires didn't have a boost control cutout, but were instead fitted with a gated throttle which allowed the independent setting of the various engine ratings, including the combat rating. They also had double-acting ABC instead of single acting ABC, which meant that the throttle behaviour was a bit different. This is explained in the relevant AP from the period (I forget the number now, but it's been linked to in quite extensively in this forum).

[Viper2000]

Only after significant modification to handle such pressure, modifications that did not exist in 1940. Your document clearly separates it from the earlier Merlin II and III engines.

The Sea Hurricane was a special case; it was used on CAM ships and could not be recovered. The pilot would either parachute out or ditch when he ran out of fuel, as CAM ships had no way of accepting the aeroplane back for landing.

As such, both engine and airframe life were expected to be no more than one sortie, and it was therefore perfectly reasonable to give them a Viking funeral.

[Crumpp]

As such, both engine and airframe life were expected to be no more than one sortie

You know I read that part about one sortie life span. Thanks for pointing that out. Makes perfect sense to put your obsolete motors and so extremely over-boost them in a disposable airplane. Even then I would like to see what the engine was approved for at the boost. I would think it was just to get off the CAT.

Even a disposable fighter is worthless if it cannot fly to a target and fight.

[Viper2000]

You know I read that part about one sortie life span. Thanks for pointing that out. Makes perfect sense to put your obsolete motors and so extremely over-boost them in a disposable airplane. Even then I would like to see what the engine was approved for at the boost. I would think it was just to get off the CAT.

Even a disposable fighter is worthless if it cannot fly to a target and fight.

I don't think they needed the power for takeoff because the "catapult" in this context was a whacking great rocket. (http://en.wikipedia.org/wiki/CAM_ship)

Given the stability & control difficulties associated with using really high powers at low speeds in these aeroplanes, and the obvious risk of engine failure at low speed & altitude off the bow of a ship which probably can't stop or avoid the aeroplane if it ends up in the drink, I would have thought it more likely that the launch was conducted at normal takeoff power.

I think that the extra combat power was primarily intended to be used for a rapid climb to cloudbase in order to intercept/scare off the bomber that was threatening their convoy; in the absence of RADAR, the CAM's fighter was only launched when the enemy was within visual range, and so warning time was strictly limited.

The climb would be unlikely to go higher than cloudbase because the bomber would just cloud-hop home (and probably couldn't hit a ship from any higher anyway, so either way it would be a mission kill); the fighter would be unlikely to give chase because of the obvious navigational challenge of finding their convoy again afterwards in an aeroplane not really equipped for naval navigation (at this time, most Fleet Air Arm aircraft, even the fighters, had a navigator).

For this reason, I suspect that they'd be unlikely to use the extra power for more than a couple of minutes in the sortie; I'm guessing that an early Hurricane with +16 would probably exceed 3000 fpm climb rate, and the cloud base would usually be less than 6000 feet...

[Crumpp]

I don't think they needed the power for takeoff

That low I would think you needed all the power to maintain flight even with a catapult. You only have a few feet until your in the drink.

It would be worth it to accelerate the aircraft quickly to flying speeds and then returning the engine to less catastrophic power levels.

I think that the extra combat power was primarily intended to be used for a rapid climb

You think? I know climbing is the most demanding portion of flight on an engine and it is the time period an engine is most vulnerable to detonation. Such an extreme level of over-boost is begging for detonation in a climb out.

By nature, aircraft engines are high output to weight and very vulnerable to detonation failures. Even with a disposable aircraft, the few minutes climbing in detonation scenario would make the accomplishment of the aircraft's intercept mission unlikely. A normal Hurricane will catch a Condor so I don't see the risk for the reward in it.

Here is a typical aircraft engine failure due to detonation scenario. Here one cylinder begins detonating and the motor makes it another 9 minutes before giving up the ghost.

http://www.to-avionics.com/insight/case.html


Even with modern steam catapults, it is typical to launch at full power with afterburner.

http://www.youtube.com/watch?v=lbbSYb7kDLY

Anyway, it is all speculation until someone comes up with a Sea Hurricane POH!!

[TomcatViP]

BoB museum or the Shuttleworth collection had one I think some years ago in flight condition.

I don't think that CAM ship needed any boosted or special aircraft to be proteced.

Remember that they needed to down reconnaissance Condor that were monitoring the convoy.

I have in memory the story of Hurri being converted from coastal command (and those were not new Hurri) and then moved on teh CAM ship mission.

Also there was only a handful of pilots qualified for that particular exercise (something like 22 - not sure). I read the story of one that did 3 mission (bailing out two time in teh sea and being knocked down once while running to his plane during an alert).

Can't remember the title but as I think he was an ex wingman of Bader, probably the story might be somewhere in Bader story.

Anyway, giving the weary airframe and the dangerous mission with flight in bad weather (when the U-boat were attacking with the Condor coordinating or recognizing the target for the wolf pack) it's un-likely that they played with some tricky eng mods just to gain 20 sec in a climb to cloud base as was alrdy pointed out.

3000ft/min is a huge climb rate. The 109 managed to maintain that one during the war despite her overweight and still was considered one of the best climber at the end.

I am sry to be so contradictory.

Nice to see you back Vip !

[Viper2000]

BoB museum or the Shuttleworth collection had one I think some years ago in flight condition.

I don't think that CAM ship needed any boosted or special aircraft to be proteced.

Remember that they needed to down reconnaissance Condor that were monitoring the convoy.

I have in memory the story of Hurri being converted from coastal command (and those were not new Hurri) and then moved on teh CAM ship mission.

Also there was only a handful of pilots qualified for that particular exercise (something like 22 - not sure). I read the story of one that did 3 mission (bailing out two time in teh sea and being knocked down once while running to his plane during an alert).

Can't remember the title but as I think he was an ex wingman of Bader, probably the story might be somewhere in Bader story.

AFAIK this is a complete list of CAM launches:

http://en.wikipedia.org/wiki/CAM_ship

Anyway, giving the weary airframe and the dangerous mission with flight in bad weather (when the U-boat were attacking with the Condor coordinating or recognizing the target for the wolf pack) it's un-likely that they played with some tricky eng mods just to gain 20 sec in a climb to cloud base as was alrdy pointed out.

3000ft/min is a huge climb rate. The 109 managed to maintain that one during the war despite her overweight and still was considered one of the best climber at the end.

Late war fighters were generally somewhere in the 3500-5000 fpm range. For example, here's some data for the 109G from a source not exactly noted for "blue bias":

http://www.wwiiaircraftperformance.org/me109/me109g-kennblatt-german.html

The P-51 wasn't really known for its climb performance, but its low level ROC in WEP is over 3000 fpm at combat weight for all models at 5000 feet:

http://www.wwiiaircraftperformance.org/mustang/p-51-tactical-chart.jpg

Meanwhile, the mighty Spitfire IX would exceed 3000 fpm at 20,000 feet at +18 psi in 1943:

http://www.spitfireperformance.com/spitfire-IX.html

I am sry to be so contradictory.

Nice to see you back Vip !

Thanks.

[TomcatViP]

Ok I am more in the average climb rate regarding time to 6Km or 20kft

That said 5000ftm seemed impressive to me with a calculated time of 4 min to 20kft witch I hve never heard about ;)

Regarding CAM launches, well you know how stories goes... I hve to dig the book and see.

:-)

[TomcatViP]

Hi guys,

I hve in mind that some of you are waiting for my answer (yeah I am that selfish).

However I took some time to re-read some of my earlier post since I am a newborn on CoD forum in the last couple of days and I am pretty sure that I did alrdy give the arguments you cld be waiting for.

Look, for height , wide open throttle, Supercharging and 2nd thermodynamic principle...

Have fun !

[JtD]

A supercharger that can produce 12lb boost at 10000 feet (~full throttle altitude for a Merlin III) can produce about 17lb boost at sea level. A fairly accurate estimate is really simple maths, just divide boost at altitude by pressure at altitude in atmos, in this case ~0.7.

Doesn't mean the engine can handle it.

Sea Hurricanes modified for 16lb were not throwaway planes, they were primarily used from carriers with the full intend of repeated use and to my knowledge only from 1942 onwards with the 16lb boost.

[TomcatViP]

Ok here we go again

Merlin XX from RR doc WOT at 15000 9lb

What means WOT ? At tht height : max flow = max ro *V

At sea level ro > ro at alt

then ro* V max is LESS (max ur eng can handle)

SO less OT -> less Flow -> less air -> less fuel -> less SHP -> less flywheel rpm (THX mother nature or there will had been a prob) -> less max theo HP

By teh way as I hev alrdy raised soem of your dat (Spitdotcom atc...) are confusing abt HP and SHP as testing was done static without S/C (tht's all abt the source I hve)

As you can see the only way to outsource the most HP of a Merlin in that conditions is to have variable geo (for ex the size of the ducting). It's all abt the Merlin for low alt , the Merlin for med alt and the Merlin for high alt.... Does is sound anything like familiar to you ?

Oh and by the way I didn't mention here the temp raise you'd get in the conversion. But I am sure you'd get enough time for a forum search. Some hve been down to the details more than me (I hve in mind some Crump's posts). Feel free to read them too.

Huh Yeah pls devs give them their 12lb now tht they will be left with 2lb only late Spits when you'll do that 44 add-on :rolleyes:

[Osprey]

Massive arrogance.

[ATAG_Snapper]

Massive arrogance.

I'm still working on the "catch it or go without it".

[TomcatViP]

Ok boys. I am fed up with both of u. I don't know why I keep replying as if the point you raise had any sense.

Seems your not there to debate but only to impose your point of view on the Spitfire trough questionable docs, wall of smokes or even insults and bad mouthing.

Lol figure what ? I did know how it ends. Not because I am that clever but because I hve alrdy seen the movie : you act always the same on this specific debate :cool:.

So argue, raise your point of view, makes this a conversation that we can all share what it seems only you know.

[Jugdriver]

Guys please don’t feed Tomcat. He is the grand wizard of the Spitfire Haters Club and as such has no interest in an honest and good willed discussion on the boost of the Mk 1 Spitfire. His only objective is to dumb down the Spitfire FM as much as possible in this game.

Tomcat the rest of us are fed up with you.

JD
AKA_MattE

[TomcatViP]

Oh Dear..

Forget abt me .. Nobody cares. ARGUE !

btw : I am a Spit aficionados..; The real one. Not the easy mount of some lazy Sim aces

[Osprey]

I think most people are able to make up their own minds what you are.

I would like to thank the real contributors to the thread who supplied solid information on the function and specification of the Merlin of 1940 - very informative.

[TomcatViP]

calm down pls

[Kwiatek]

http://i53.tinypic.com/r0p095.jpg

:P

[IvanK]

Whats the title of this Test document Kwaitek or its AVIA Ref No ?

This does not reflect the In service Boost ratings for the Merlin III. Its unusual in that In service MERLIN III climb rating was + 6.25Lbs boost not as +9 shown here. If its genuine then I believe its a 1 off RAE trial report investigating the feasibility of rating the Merlin to +9Lbs climb in preparation for this rating in the Merlin XII. Merlin XII as fitted to Spitfire MKII had +9 Climb

MERLIN III LIMITS from Spit I Pilots notes
http://img171.imageshack.us/img171/9744/merliniii.jpg

[Kwiatek]

I dont know IvanK - i just found these single document some time ago. But it is clearly for MErlin III testing with 100 octan fuel - data is from 28.02.1940.

Document which you posted is of course for Merlin III with 87 octan fuel only - not for 100 Octan fuel.

Here is for Merlin XII for both 87 and 100 Octan fuel used:

http://i51.tinypic.com/2d1qoo3.jpg

[lane]

IvanK: The Inspection and Test Certificate posted by Kwiatek is taken from Aeroplane and Armament Experimental Establishment’s report on Spitfire II P.7280, Merlin XII - Rotol Constant Speed Airscrew, Comparative Performance Trials, First Part of A.&.A.E.E./692,e dated 27th September, 1940. You will note that the rated power listed matches that of a Merlin XII. I always assumed "Mark III" on the Certificate was a typographical error.

[Kurfürst]

Whats the title of this Test document Kwaitek or its AVIA Ref No ?

This does not reflect the In service Boost ratings for the Merlin III. Its unusual in that In service MERLIN III climb rating was + 6.25Lbs boost not as +9 shown here. If its genuine then I believe its a 1 off RAE trial report investigating the feasibility of rating the Merlin to +9Lbs climb in preparation for this rating in the Merlin XII. Merlin XII as fitted to Spitfire MKII had +9 Climb

My take would be that Kwiatek's paper shows an early rating, valid for the first quarter/half of 1940, with +9 lbs being the initial maximum cleared for generic flying, and +12 only for takeoff when necessary. This seems to be quite typical when introducing higher ratings for an engine.

[IvanK]

IvanK: The Inspection and Test Certificate posted by Kwiatek is taken from Aeroplane and Armament Experimental Establishment’s report on Spitfire II P.7280, Merlin XII - Rotol Constant Speed Airscrew, Comparative Performance Trials, First Part of A.&.A.E.E./692,e dated 27th September, 1940. You will note that the rated power listed matches that of a Merlin XII. I always assumed "Mark III" on the Certificate was a typographical error.


Thanks Lane, I have that report in full. All other pages refer to the engine as Merlin XII. The AVIA ref for this report in the UK National Archives is AVIA 18/1574
I am with you Lane, I think it refers to Merlin XII, the Merlin III looks like a typo on that single page

[Kwiatek]

Hmm interesting so you got IvanK linkl for these report?

I got also such documents for 12 lbs limitation of Merlin III:

http://www.spitfireperformance.com/ap1590b.jpg

http://www.spitfireperformance.com/spit1pn2-a.jpg

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

But i think most know these documents.

[IvanK]

12lbs Boost was available to both the Merlin III and the Merlin XII (running 100 Octane) when Boostcutout was activated. In the case of the Merlin III a couple of mods were also required to allow 12Lbs Boost. This has been debated at length in the forum.

Only the Merlin XII had the +9lbs limit Full throttle. (Boostcutout not activated)
The Merlin III Limit was +6.25Lbs Boost. 9Boostcutout not activated)

I don't have links to the docs. I spent a bunch of time in the UK archives researching and copying them. Pretty much every RAE report is available there.
Bits and pieces of these docs are available online at Spitfire Performance testing and WWII Aircraft performance http://www.wwiiaircraftperformance.org/

[=XIII=Wedge]

Thanks for the information IvanK.

If we could rewind slightly to the opening post question - I know people like to talk about 100 octane and the Merlin XII, but the question was regarding the Spitfire Mk. I and we have 87 octane fuel.

Has anyone tried cutting out the ABC on the deck and then climbing to full throttle altitude?

Is manual boost control even modelled?

[SEE]

Hi See,

I posted the following up in the ATAG thread: This is taken from the game data using kegetys.dll. These are pre_beta so not sure if it's changed since. Basically, the MkI and Ia have 0.002 lbs/sq in extra boost (ie nothing)



From earlier in the thread, it is and it isn't at just 0.002Ibs/sq (according to the extracted game data figures which are shown in Das Attorneys reply).

[TomcatViP]

Just to remind you that the Spit in game as nearly no Drag (hence the boost can't be accurate).

Try the following : bank at 80° and pull the stick until you stall.

I hope you can write with both hands or we won't heard any reply from you soon :cool::grin:

[Osprey]

What on earth are you talking about? Not only is this off topic again but you provide zero evidence in support. Why do you even post? Go away.

Thank you to IvanK and others on posting information.
@Wedge. I think that is worth a try however I find overheat way too severe to complete the task. Maybe a formal attempt at just what you say would be possible though.

[TomcatViP]

Osp you really need a short walk in a park where you could bark at real kitten.

If you put the Spit in a turn at a high bank angle (BA) you'll see easily that the loss of speed is ridiculously low. This a a simple test for E management of any FM. If you don't see what I mean you may have to investigate some G Vs BA charts. I think I did post one some time ago (F16 flight doc)

Hve fun.

[Osprey]

That's not evidence, that's opinion.

And your first sentence, clearly intended as an opening insult, doesn't make any sense in English. You sound like an idiot.

[TomcatViP]

Osp pls let's put an end to that :(