Over Compressed Engines Video

The Salmson R9 (water cooled radial) of 1917 had an additional air intake valve that opened at high altitude to compensate for low air pressure at altitude. It's covered in the book "Engines of Russian Combat Aircraft" by Vladimir Kotelnikov (in Russian). The R9's manual says: "The carburetors adjusted during engine testing do not require adjustment. However, for the sole purpose of saving fuel, for long raids at high altitudes we have equipped the heaters with an additional air inlet valve 10774." I am not sure if other engine (or carburetor) manufacturers were doing something similar.

Hi Greg Like pretty much all of your work, I enjoyed your over-compressed engines video, especially how BMW used a clever dual carburetor arrangement to get the power at altitude. You offer an excellent combination of storytelling with a serious aviation technical mindset. However, I have a totally unrelated issue which I wonder if you have already discussed, might perhaps consider discussing. Lately Dronescapes has uploaded 'lost interviews' about Frank Whittle and Hans von Ohain's contributions to the invention of the gas turbine aircraft engine. Their conclusion seems to be that Whittle invented it and von Ohain was shown Whittle's design prior to patenting his and that he more or less copied it. They claim that von Ohain admitted as much in his biography "Elegance in Flight", a copy of which I just ordered. While that might be possible, I had always understood that these two had independently developed the jet engine. I wonder if some semblance of truth be established? To say the HeS 3B was a copy of the WU or other Whittle design would surely mean having to compare the design of the engine that powered the Heinkel He-178 to Whillte's WU and perhaps how von Ohain's engine evolved from the hydrogen test model to the HeS-3A and HeS-3B. Was there a hint of sudden design changes more along the line of Whittle's ideas? I've looked around but have not found good illustrations of these. Clearly the jet engine is a major milestone in the development of aviation. Was the first one to fly a copy of another which flew first merely because Ernst Heinkel had greater vision than the British Air Ministry or because Whittle's rival AA Griffith (who may have arguably proposed the first aircraft gas turbine in a 1926 paper) had a personal interest in getting his own ideas into the air? I wonder if this might be a topic that would interest you?

I think I cover all of that in a video. I'm using the term NACA used.

Pan, yes, I would say so, although a turbo normalized engine can make it's full power through a wider altitude range.

Your description of "knock" is that of detonation. Actual knock occurs after ignition, in the end-gas ahead of the flame front when there's a spontaneous ignition of the mixture due to the rising temperature/pressure ahead of the flame front. That can result in high speed gas movement, notably across the top of the piston. When sufficiently severe, it strips the boundary layer of gas that protects the metal from the very, very hot flame, resulting in damage to the piston. Very light knock conditions (referred to as pinging) that leave sufficient boundary layer intact but the induced vibrations can eventually cause damage/accelerated wear. Retarding the ignition timing resolves many knock situations as the later the ignition, the greater the speed of the piston (up to about 3/4 mid-stroke) and the available volume into which the burning gases can expand. i.e. the pressure/temperature in the end gas is not as high and spontaneous ignition is less likely. While retarding the ignition reduces propensity to knock, it also reduces BMEP and BSFC (i.e. efficiency). The optimum is to operate the engine at "incipient knock", which is a strategy chosen for many automotive engines, aided by one or more knock sensors that are effectively microphones with frequency filters and a time window (relative to TDC) in which knock would be a bad thing.

So the theory behind the overcompressed engine is similar to a turbo-normalized aircraft engine, yes?

Thank you for the suggestion Greg, that was a great movie.

“Should’ve been me”. First movie at a drive IIRC😎

Super interesting video. What to you think of the movie "The Blue Max"? I like that one a lot.