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Originally Posted by Jan Carlsson  First, you don't want a propeller doing 4000 rpm due to noise, you will hear it from here to Edmonton, even with smaller diameter it will sound like a hornet (Vespa crabro) And you lose performance also, especially with a pusher working in the wake of fuselage and wings
isn't the wankel's critical RPM in that region too?
if you want good performance go with a PSRU, you need a prop shaft bearing anyway. and you can get a better working propeller.
the nr of blades depends on what you need, to take care of the power, with Power, Speed, RPM, diameter limitations, thickness, and strength as parameters.
Jan |
Thanks Jan, I saw something about this 400RPM problem zone in the Mazda rotaries before. I'll ask on the engine forum.
My thinking on this subject is as follows. I'm looking to see how well I can get away with using direct drive. My plan is to use direct drive at first because it is simple and cheap and I don't care about the efficiency at the beginning. I'll see how well I can make it work with direct drive and if I need to I'll go with a PSRU.
My aircraft project is a very compact pusher so I wouldn't want a prop bigger than 72" no matter what.
With a 72" diameter prop I'll need a PSRU, but what about a 60" prop, that's not tooo much smaller than a 72" and If I can run it at 4000 then I can save a lot of weight.
I'll have to get my propeller book out to calculate the efficiency differences, that will help me decide.
I realize that an engine running at 4000 with four blades will have a higher frequency than one running a 3000 with three blades, but if the tip speeds are the same then the volume should be similar?
I'll ask on the engine forum to see about the 4000 RPM problem area with Mazdas.