Reading the great Secret Horsepower Race book, they mention that a swirl throttle avoids the pumping losses which occur when the engine is trying to suck air in past a partly closed butterfly valve.
Most people don’t watch long videos but the start of this video describes it
I wonder about the relevance to our GA engines…
Peter wrote:
I wonder about the relevance to our GA engines…
Not likely, since you need a radial compressor, constant speed (engine driven) supercharger to make any sense. Very interesting video. Had no idea they used a “swirl throttle” before the supercharger, and interesting how a supercharger (radial compressor) works in a setting like this.
The FW-190 had no DB engine though 
They had the BMW 801 radial engine, except the -D version which had a Junkers Jumo.
Have to add. There have been several (failed) development of two stroke diesel engines for GA. A two stroke diesel in general requires charged air to be able to work at all. This can be done in the “normal” two stroke manner, but this complicates oil distribution. A two stroke diesel therefore typically have a separate supercharger, usually a constant displacements thing. A constant displacement supercharger wont work well in this setting (as explained in the video), but it’s still needed to get air into the engine. This means you also need a second supercharger, or a turbocharger. This gets very complicated. The cost and weight is one thing, but the sheer complexity of the system as a whole must become a nightmare IMO. Certainly doable, but it doesn’t sound like the best way to get a simple, reliable, light and cost efficient GA engine to me.
There must be a way to make an engine do less power than throttling the air intake and making it suck really hard against the restriction…
I believe some of the early rotary engines on WW1-era aircraft were unthrottled and thus operated at WOT the whole time.
If you wanted reduced power (e.g. for descent and landing) then you blipped the mag switches off and on.
Peter wrote:
There must be a way to make an engine do less power than throttling the air intake and making it suck really hard against the restriction…
Running LOP and regulating power with the mixture control. Of course you would need very well balanced intakes/injectors.
Peter wrote:
There must be a way to make an engine do less power than throttling the air intake and making it suck really hard against the restriction…
Substitute gasoline with diesel. A diesel always run at WOT
Airborne_Again wrote:
Running LOP and regulating power with the mixture control. Of course you would need very well balanced intakes/injectors.
If you run LOP WOT at a low power setting, balancing is less important. I did it at FL120 or so on a carburetted O-360 with carb heat on, and it ran smoothly.
How do diesels do it?
No throttle?
Graham wrote:
If you wanted reduced power (e.g. for descent and landing) then you blipped the mag switches off and on.
So one was basically ejecting unburnt fuel? Funny.
Peter wrote:
How do diesels do it?No throttle?
By changing the mixture! Diesels are always fuel-injected and power is controlled by the amount of fuel injected in the cylinders.
