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An un-supercharged Kestrel was good for 635hp at sea level at 2900rpm from 1297 cu in (21.25 L) BMEP of 66.85 ?
Moderately supercharged Kestrel was good for 730hp at 5,250 ft at 2900rpm and using 2 5/8lbs of boost. BMEP of 76.8 ?
The problem with alcohol as a fuel is that it needs different amount of air.
Ethanol has about 62% of the BTUs per pound that gasoline does.
Ethanol has a 9.00 Stoichiometric Air Fuel Ratio. So you need about 50% more Ethanol per pound of air.
The Higher compression used may be a result of the higher "octane" rating of the blend. They had already set up the engine to use this blend for performance reasons. Not to stretch gasoline supplies.
Alcohol was rather popular in the 1920s and 30s for racing cars and record setting aircraft and racing planes.
My own beliefs are that the Italians knew what they were doing with Fiat A.30 and the 23% ethanol fuel. They set up the engine to take advantage of the fuel. There was no trick to unlock more power with a slightly different blend.
I will note that there were a number of WW I and later engines that were set up to use only part throttle at take-off/low alludes even without superchargers and only made full power at higher altitudes were the throttles could be fully opened. Many engines were not allowed to use full rpm for take-off.
Just like the data plate. Take-off was done at 2600rpm but power at altitude was at 2750rpm.
Kestrel engines were built with 6.0 compression ratio when supercharged and 7.0 compression ratio supercharged. Unsupercharged Kestrels in 1938 were good for 560hp 2375rpm fpr take-off, 585hp at 2500rpm "international" rating and a mere 635hp at 2900rpm at sea level. 13% increase in power for a 22% increase in RPM? piston ring drag/friction much have been a a bitch.
A lot of inconsistencies on both sides.
And yes, I wonder if this Fiat A.30 RA was able to sustain full throttle operation at sea level - I think the answer is NO, in fact ! This would explain why the loss of power at 3.000 m. in this normally aspirated engine is only 50 hp..
Actually high compression ratio was common way of compensating for lack of supercharger.And probably the high CR of engine (8:1) doesn't allow it, neither.
The BMW IIIa was with the 'triple throttle'. Used also on one of the versions of the fighter Fokker D.VII.Actually high compression ratio was common way of compensating for lack of supercharger.
However it required, for safety sake, special gated throttles to prevent the pilot/s from fulling opening the throttle at low altitude which would wreck the the engine.
Germans were doing this in WW I. One engine/airplane had three slots in the throttle and the throttle handle was moved to the appropriate slot/gate as the aircraft climbed and descended, Plane was a 2 seater (?) and didn't climb/dive like a single seater. It allowed for high compression with the low octane fuel of the time but full throttle was only at high altitudes.