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I've been reading about these remarkable engines from WW2. I'm curious:

-has anyone ever tried an inverted V layout in an F1 or other racing car?

-why were the Germans able to use fuel injection technology but not the Allies?

-how did the fuel injection work on the early engines without computers, pneumatics? like the early Corvettes?

-what is the advantage of a fluid coupling of the supercharger?

tuj wrote:-why were the Germans able to use fuel injection technology but not the Allies?
-how did the fuel injection work on the early engines without computers, pneumatics? like the early Corvettes?

this Bosch-type injection worked like a diesel's only more easily due to the much lower injection pressure needed

the Allies installed DI when useful eg in the Wright 3350 as in the B-29, partly to avoid mixture distribution problems
but many Allied engines eg RR used higher boost, and fueled into the supercharger for charge cooling and reduced supercharging work
(note to self : postwar many of the 12000 military Turbo-Compound versions of the 3350 seem to have fueled this way)
the fabled negative g (really, low +g) benefits of DI were promptly realised by the As with mods to carbs, then came ''injector carbs'

the DI injected very early and slowly, ie completely the opposite of our current interest in DI
though Allied analyses agreed that it allowed higher CR etc in some engines, at least with poor fuel

the supercharger needed to compress much more, ie to rotate faster, with altitude
fluid drive can help do this nicely
the Allies used a 2 speed gear or a turbo
or often had no speed change and throttled the air before the supercharger as needed (to avoid overboost at low altitude)

the supercharger needed to compress much more, ie to rotate faster, with altitude
fluid drive can help do this nicely

In this regard, can a positive displacement supercharger work over a larger rev-range? I'm thinking of a rumor I heard about 10 years ago that Mazda was thinking about a fluid-coupled SC for the Renesis 13b wankel engine.

tuj wrote:

the supercharger needed to compress much more, ie to rotate faster, with altitude
fluid drive can help do this nicely

In this regard, can a positive displacement supercharger work over a larger rev-range? I'm thinking of a rumor I heard about 10 years ago that Mazda was thinking about a fluid-coupled SC for the Renesis 13b wankel engine.

a positive displacement supercharger is less efficient at the pressure ratios of interest to aviation (also bigger etc)
but, very crudely, its delivery is proportional to rpm and the centrifugal supercharger delivery is proportional to rpm squared
sometimes road cars have used belt-driven centrifugals?? eg Paxtons in 60s Studebakers ? and other earlier US cars ?
but the positive displacement is better suited to being driven this way

The D-B fluid drive supercharger gave a variable ratio - as required for altitude compensation.
Not as efficient as multi-stage/turbo set-ups, but ok with a big mill in a small airframe (Bf 109).

The Germans did not pursue such high boost levels as used in the R-R V12s, but generally ran higher comp ratios,
- for cruise fuel efficiency, & due to octane limitations.

The fluid drive allowed a side-mount S-C, giving space for a moteur-cannon to be fitted in the V,
& also avoided some shock/harmonics loadings which could affect geared/clutched mechanical units.

When ramping up production numbers - the elegant/expensive rolling element bearing crankshaft
was replaced by plain bearings, which initially gave some dramas.

Think about the ideal crankshaft thrust line location for a propeller aircraft vs a racing car..
The inverted V was perhaps not really worth the extra design effort - in terms of results achieved.

The D-B V12s were also licenced for production in Italy & Japan..

J.A.W. wrote:The D-B fluid drive supercharger gave a variable ratio - as required for altitude compensation.
.... The inverted V was perhaps not really worth the extra design effort - in terms of results achieved.

sincere question - what was the variation and how was it achieved ?
(was there no involvement of automatic throttling in boost regulation ?)

the pilot view for landing eg a 109 would have been non-existent with an upright DB engine
the Buchon has an upright engine, but that's smaller

these WW2 engines all have design features that have only appeared in F1 in recent decades
very squat pistons (high wrist pins) and very close bore centres for compactness and very deep crankcase/sump structures
the DB crankcase design seems very demanding of its foundry work

Think about the ideal crankshaft thrust line location for a propeller aircraft vs a racing car.

Thanks for your observations. I have thought about this and could the issue not be solved by a clever 'vertical' gearbox? Certainly similar to the reduction drive gears.

Do you happen to know if the CoG is lower with an inverted V? I would think with the valve trains located low, it might be? Also, if you were allowed to mount the intake under the car, that would possibly create a vacuum effect that could be taken advantage of without resorting to fans and such. Perhaps you could also take a cue from today's Merc engine and put the compressor-ERS-turbine assembly under the V?

tuj wrote:Do you happen to know if the CoG is lower with an inverted V? I would think with the valve trains located low, it might be? Also, if you were allowed to mount the intake under the car, that would possibly create a vacuum effect that could be taken advantage of without resorting to fans and such. Perhaps you could also take a cue from today's Merc engine and put the compressor-ERS-turbine assembly under the V?

While the heads are at the bottom some of the heaviest structures and components are at the top - ie the crank and crank case.

Mounting the intake under the car would, possibly cause problems due to foreign object injestion. I doubt the suction effect would be sufficient and you miss out on the ram effect.

Tommy Cookers wrote: sincere question - what was the variation and how was it achieved ?
(was there no involvement of automatic throttling in boost regulation ?)

This period 'Flight' article gives a straightforward technical description of the machinations..

http://www.wwiiaircraftperformance.org/ ... 7Nov40.pdf

good post ! - thanks for that

Tommy Cookers wrote:good post ! - thanks for that

Seconded.

Thanks chaps..

& here is a fairly scathing US report on Kawasaki's efforts to build D-B 600 series mills..

http://www.wwiiaircraftperformance.org/ ... ort-39.pdf

They note attempts to improve supercharging ( inc' provision of ADI) but criticise Kawasaki's
apparent failure to match D-B in casting quality control/machining of fundamental components..

..D-B skills in this area being something - even the rather parochial Brit examiner - readily conceded..

The allied aircraft engine designers could certainly have employed mechanical DI fuel injection systems on their engines, but they did not feel the added complication and lower reliability of the systems was worth the benefits. The requirements placed on German fighters/interceptors was far different than those placed on US fighters/escorts.

The job of a performance engine, in a racing machine or fighter plane, is to provide
sufficient reliable power to enable the pilot to get his machine to defeat the opposition..

The Germans wasted time & resources on high-tech stuff, most of which never amounted to much,
while failing to match/beat the best opposition..

& were too slow in improvements to their machines to keep pace, let alone an edge..

..it was the Merlin Mustang swarming over Berlin that killed them..

As W & T-C rightly noted, the Brits were impressed by German injection tech,
& even used it on the Crecy, but were able to utilize cheaper/simpler/effective alternatives..
( Not that they could've mass produced such exactingly accurate injection units so well - anyhow..)