109 e3b against spitfire II

[Viper2000]

Originally Posted by TomcatViP

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".

Originally Posted by TomcatViP

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).

Originally Posted by TomcatViP

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.

Originally Posted by TomcatViP

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.

Originally Posted by TomcatViP

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

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...

Originally Posted by TomcatViP

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.

Originally Posted by TomcatViP

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!

Originally Posted by TomcatViP

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]

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

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]

Originally Posted by Kurfürst

..........
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*]

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.

[Kurfürst]

[QUOTE=Blackdog_kt;297896]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..




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

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.