Turbo Corvair Conversion ..........Hypothetical


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Well-Known Member
Mar 30, 2019
Somerville, TN
I guess it can com down to terminology. Stricly speaking WW might be right - Turbo normalization is defined as maintaining standard atmosphere up to service ceiling. From there on the MAP drops as a normally aspirated engine does. You would start by applying throttle until you reach 30" and as you climb increase the throttle until your service ceiling - or full throttle. If you have a wastegate, it can control this variable to some degree. It will bypass excess exhaust until fully closed. The drawback is that with a fixed pitch prop is screws with your rpms. If your prop is set up for good climb rate at sea level, when you reach the service ceiling the rpms will be much higher due to thinner air. Some props and engine are limited as to high rpms. If you have a cruise prop setup for say...10,000', then your engine will not be able to deliver good takeoff rpms due to the higher pitch and thicker air at sea level. Our installation is a compomise...as all aviation is. We use a prop that is pitched for good cruise at 10,000 - but at a slightly higher rpm than what you would consider normal. This is due to having a shorter prop and an engine that does not suffer from high rpms. So, at 9,500 and 30" MAP we turn the prop about 3400 rpms.
Now at sea level, what we do is slightly boost the engine (up to 36" MAP for now) in order to have the RPMs we are looking for. Now, in our Saberwing, boosting to 35-36" of takeoff is giving us better perfomance than if we were running a normally aspirated 120HP engine. My climb rates are at leaset 500'/min better. WW's point is that to get prop advantage at altitude you would want to boost slightly at seal level.
Now, a controlable prop can give you the advantage of adjusting your MAP and RPM on takeoff and then the prop will adjust to maintain this though its performance range. However you have more complexity and cost involved. We are going to be testing a couple constant speed props soon since our prop hub design allows us to do that. One prop design is also featherable (for a twin later and motor glider soon).
Hope this helps a bit
Bill, I realize this post of yours is over 2 years old, but I wanted to use it to ask you if ever got to a variable pitch prop. Have you considered the AirMaster set-up that the Sling TSi is using? Looks like it should work for what you have in mind. And what I have in mind.

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