3 ms·

Constant speed propellers are more efficient than fixed pitch; in order to keep the propeller rpm in the optimal point you have to adjust the engine gas control

Constant speed propellers are more efficient than fixed pitch; in order to keep the propeller rpm in the optimal point you have to adjust the engine gas control and the propeller pitch, not extremely complicated but not simple enough to be allowed for light sport planes - it is considered too complex for that. If you play with the propeller pitch, the force on the engine will make it change the rpm; if you change the engine rpm to the optimal of your propeller, you don't always have the best pitch, so you adjust it and this will impact the rpm. With an electrical motor the power delivery is much more robust, so you can adjust the pitch and then set the motor to the desired rpm and that's it.

mannykannot 7y ago
> you can adjust the pitch and then set the motor to the desired rpm and that's it. Normal operation of a constant-speed propeller involves setting the desired rpm via the pitch control, and then adjusting the power, via the throttle, according to your purpose (such as level cruise at a specific IAS, or climb at maximum sustainable power), with the propeller govenor maintaining the chosen rpm via pitch changes, and I do not see how electric power changes this relationship. I understand that electric power might simplify making a sort of FADEC for electric airplanes (so that there is only one power control), and that constant-speed propellers could eke out more duration from the batteries, but now you are adding the cost and complexity of a constant-speed prop. I am not sure that it would be justified in a light airplane having a cruise speed not much higher than its best climb speed.
- AdrianB1 7y ago
  Yes, for some light airplanes a constant speed propeller is not required, but if it is simple enough and you get sizable benefits (even 10% more range), then why not? There are many planes in Europe that have the cruise speed much higher than the best climb speed. The best climb speed is around 100-120 km/h for light planes, while several plane models have the cruise speed over 200 km/h, up to 250 km/h. I am not aware of any plane with cruise speed below 200 km/h to use constant speed propellers, they have fixed pitch propellers, but the faster ones have in-flight adjustable pitch. I personally flew 7-8 different models of planes, only one with adjustable pitch, but they were all in the LSA class and const-speed is not used there.

mannykannot 7y ago

> you can adjust the pitch and then set the motor to the desired rpm and that's it. Normal operation of a constant-speed propeller involves setting the desired rpm via the pitch control, and then adjusting the power, via the throttle, according to your purpose (such as level cruise at a specific IAS, or climb at maximum sustainable power), with the propeller govenor maintaining the chosen rpm via pitch changes, and I do not see how electric power changes this relationship. I understand that electric power might simplify making a sort of FADEC for electric airplanes (so that there is only one power control), and that constant-speed propellers could eke out more duration from the batteries, but now you are adding the cost and complexity of a constant-speed prop. I am not sure that it would be justified in a light airplane having a cruise speed not much higher than its best climb speed.

AdrianB1 7y ago
Yes, for some light airplanes a constant speed propeller is not required, but if it is simple enough and you get sizable benefits (even 10% more range), then why not? There are many planes in Europe that have the cruise speed much higher than the best climb speed. The best climb speed is around 100-120 km/h for light planes, while several plane models have the cruise speed over 200 km/h, up to 250 km/h. I am not aware of any plane with cruise speed below 200 km/h to use constant speed propellers, they have fixed pitch propellers, but the faster ones have in-flight adjustable pitch. I personally flew 7-8 different models of planes, only one with adjustable pitch, but they were all in the LSA class and const-speed is not used there.