British Super-/Turbocharger Development

[Calum Douglas]

For comparison:

There is too much "noise" between data from totally different engines for this to pick up something like a 5>20% change in fuel economy, I have been attempting to
say this for several posts. The only way to do this is to get two engines which are basically identical and do a with carburettor / with DI.

A good example of this is the DB600, which early versions had carburettors from about 1931>1934 and the first experimental version with D.I. in 1934.

Luckily I have the datasheets for both engines from Daimler-Benz AG corporate archives in Germany, I think this is about as good a comparator basis as is
possible with aero engines of that era (similar will exist for the Jumo210, but I dont think I have the datasheets at hand for that sadly, as the Jumo documents
are less well preserved than Daimler - another mystery for discussion !). These engines also had the same compression-ratio (6.5:1), which is utterly fundamental to
fuel economy.

(DB archive ref "DBAG DB 2MA-121")

Not sure what your German is like, but you must be reasonable if reading the FT documents, but for everyone else "Doppelvergaser" = Twin-Carburettors
and "Einspritz" = Injection (lower pic = DB600 prototype with injection, Upper pic = DB600 prototype with carburettors).





Gain is 17% better economy at full boost and 11% better at max economy with D.I over the
carburettor.

As for Radials and Bristol, Bristol put Direct Injection on the Civil-Centaurus (661) in late 1945, and found it
exceptionally advantageous. (I have the Bristol documents from Rolls-Royce Bristol archives). The best improvments were at high boost, with a
large gain in economy at max boost, and only slight at the lowest boost setting.

0.965 > 0.870 pints/bhp/hr @55.5 " HG boost 2800rpm (10% better economy)
0.540 > 0.536 " " @37" HG Boost 2500rpm (1% better economny

(Point #2 relates to the better fuel economy).

You can see there is no "rule" for the gain you`ll get, and its totally dependant on each individual
engine, its thermal and combustion characteristics. The DB has a min gain of 11%, the centaurus
just 1%, so you can see how if you use a different engine to try to compare DI to Caburettor
or single point injection, you can easily see such differences vanish in the noise. They can only
be seen reliably in data such as these tests where you convert an existing engine which is
otherwise identical from one system to the other.



Now, without just posting my entire book here in this thread just to satisfy you, thats where I`m leaving this matter as closed. If you wish
to carry on with your original views thats totally alright.

 

[Pasoleati]

Very interesting documents! Especially the Centaurus stuff.

 

[Reluctant Poster]

... and R-4360 were so maintenance intensive that only a few trans-Atlantic airlines used them post WW2. The USAF Military Airlift Command was the biggest customer.

No. The R-4360 was a very reliable engine and per primary sources, cooled very well (statement made by a P&W representative during the the Joint Fighter Conference 1944. I strongly recommend Graham White's R-4360 book.

Reliability and maintainability are two different things. The R-4360 did require a high level of maintenance but was also reliable.

 

[Pasoleati]

Do you have some sources for that? Especially its maintenance requirements vs. the R-3350.

 

[Nicknick]

I don't want to start a new battle between Di vs carburator, but I would like to add, that (at least a couple of years ago) the most efficient (41 % efficiency) Otto gazoline engine is the 1.8 L Prius engine. It is a simle design, naturally aspirated and with port fuel ijection, not direct injection. However, its design is not well suited to be transfered to a fighter engine of WW2.

 

[P-STICKNEY]

Reliability and maintainability are two different things. The R-4360 did require a high level of maintenance but was also reliable.

Just some minor stuff. The big C-97 user was Strategic Air Command, with something on them order of 800 KC-97 tankers. Then there are the 350 or so C-119B and C models, and, of course the B-36s.
The R4360 had a high parts count, 56 spark plugs, with their wires, a fistful of magnetos, and a plethora of valves that needed adjusting.
Since an Air Force Mechanic got paid the same as any other airman of the same rank, the USAF could afford it.

 

[HoHun]

Hi Calum,

Basically thats a very longwinded way of saying I agree that in WW2 due to complexity, size, weight and controls problems - a turbo was not at all a means to guaranteed supremacy, although I think the P47 systems were really very good indeed

From reading your book, my impression was that the weakest point of the P-47's power plant was the relatively inefficient compressor design (which generally applied to American superchargers early in the war).

You explicitely point that out in p. 450, though I believe there was an engine-type unrelated statement on supercharger development too which indicated that the turbocharged V-1710 was similarly affected, which I'm unfortunately unable to dig up at the moment.

That has me wondering ... how serious was this deficit? Could the P-47 have been a much leaner aircraft with a more efficient supercharger that could have done with a lot less intercooling, and would the P-38 have lived up to its full potential from the beginning if the US superchargers had been as good as the German ones, or was the difference more subtle than that?

Regards,

Henning (HoHun)