Superchargers are what's known as positive air displacement devices, they turn at a given speed and each revolution displace 'X' amount of air. That's fine when at sea level but when you go up into thinner air then the volume that is displaced is reduced accordingly (because the air's thinner) so you might have say 8psi of boost at sea level but that might be reduced to 2 psi of boost at 5000 feet (whatever). Also note under load a supercharger can not produce more psi than the driven speed allows.
A Turbocharger relies on exhaust pressure that is usually in excess of what's needed to spin the turbines so if you have 8psi at sea level, the exhaust has enough excess energy to continue to speed up the turbo's turbine to continue to maintain that 8psi at 5000 feet (whatever).
Also under load and even at low rpm, the exhaust pressure is still increased by greater cylinder pressures to provide high levels of boost that a supercharger can not as it's limited by the driven rpm.
Just a suggestion but for these reasons you might consider changing to a turbocharged version that is far more suited for flying, possibly the supercharged's internals are the same.
If at all possible could you weigh and display?
I understand how a supercharger works. WWII fighters were equipped with various supercharger/turbo-superchargers. Some had some type of mechanical drive while some were exhaust driven.
Depending on the pulley I end up with, I expect about 260hp at WOT.
Any replies not directly related to the combination I am building serves no purpose on this thread.
I've been reading some of the posts in the different blogs on this wonderful creation where we have the opportunity to express ourselves. I've read how some individuals are trying to pare down any amount of miniscule weight from an engine in order to get it to a weight consistent for the airframe they have chosen. Designers of a particular airframe had an engine in mind for that application that weighed a specific amount. Instead of falling in love with a specific engine, why not try to find one with the proper weight and potential. I also have been following the direct drive groups. I understand the reasoning of saving the weight and cost of a PSRU, but when you introduce the various complexities of inverting an engine not designed for that purpose, the monies one could have saved are evaporated. The BMW in the WWII ME-109 was designed from the ground up as an inverted packaged. My point is that the V8's, V6's, and four cylinder engines all work in their normal positions and if you factor in a PSRU from the begining you will know if a particular engine FWF weight is viable with your intended airframe.
Most WW2 planes used centrifugal superchargers, more closely related to the Turbo - not positive displacement Rootes type superchargers as the LSJ does.
The centrifugal blower has the same issues though, it is related to engine speed, not engine needs.
... at sea level.
At 5000 feet it will be 220hp and at 10,000 feet it will be 180hp, a fact of physics that can not be changed unless you have the ability to de-couple the blower from the engine and increase it's speed to compensate for the altitude change ... A turbocharger does this automatically.
... and the reason I suggest a turbo to overcome this issue is not because I am talking "one on one" with you, but because this is an open forum topic that thousands of forum visitors are reading of who some might choose to follow a different LSJ path to you and informing people that the choice of a turbo to maintain boost pressure at altitude is very relevant and very on topic to this thread.
If you do not wish for posts like mine to appear debating or questioning your choices then there is a closed section where you can control what is posted ... Member Project Logs
Interesting project none ever the less, good luck with it all.
To get a super charger to work low rpm and still make power at altitude you will have to over drive it and blow off the extra that will waste a lot of the energy used to drive the supercharger and the reason ww2 superchargers were 2 speeds. To test this on a dyno you will need a way lower the local air pressure around the intake.
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