Far I understand, the supercharger is driven by the engine's crankshaft.
The crankshaft is governed by the governor's set RPM.
However, the same throttle position results in the same boost pressure at say, 2500 or 2700 RPM at the same altitude and same supercharger gear.
What am I missing? Shouldn't 2700 RPM increase boost pressure all else equal?
(my reference is il2:gb yak-1 flight sim)
Do any aircraft piston motors have true superchargers? In aircraft motors "supercharger" is used interchangeably with "turbosupercharger" which is essentially what the modern turbocharger is
Supercharging is just another name for forced induction. The full name of a Turbo is "Turbine Supercharger" then colloquially shortened to turbocharger, then again to turbo. A turbocharger is a supercharger, technically.
All of the old aircraft manuals from when turbo and superchargers were invented call them turbo superchargers for turbine driven ones and just superchargers for belt or chain driven ones.
Some old aircraft were actually twin charged. Some of the aircraft had a small supercharger built right into the engine, and then they added large turbo's as well.
The Merlin had a gear driven supercharger.
Ah, cool, thanks
Superchargers tend to output the same amount of air every rotation. Engines tend to use the same amount of air every rotation.
Thus, RPM cancels out, as the faster the supercharger spins, the more air it produces per second, but the engine uses more air per second as well.
This is true of all supercharged engines, not just aircraft engine and has nothing to do with constant speed props.
Its not quite that simple. Superchargers are not equally efficient at all RPM's. For instance, at higher speeds it will generate more heat and force hotter air into the engine than at lower speeds. Hotter air is less dense and so is countering what the supercharger is trying to do - force lots of air/oxygen into the engine. Also, the supercharger may have valves to prevent it from forcing too much air into the engine - that is another way the boost might not increase if the engine speed increases, everything else being equal.
The engine is spinning faster and removing air from the manifold faster so the supercharger is really just keeping up. The increase in supercharger speed would increase boost pressure all else being equal, but one of the things that would need to be equal is engine speed.
I'm not sure about the Yak-1 specifically, but as someone else mentioned, it's also possible it had what we would now refer to as a turbocharger. All forced induction was called supercharging at the time, it's just that some were specifically "turbosuperchargers".