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There are CW & CCW propellers specific for moltirotor and other propellers as the following APC E style, distributed as propeller specific for planes.

enter image description here

I'm wondering if such plane propellers mounted on quadcopter:

  • a) works correctly;
  • b) works correctly with some adaption to mount upside down the pair for CCW;
  • c) works correctly but with noticeable loss of performances/efficiency compared to proper CW/CCW propellers;
  • d) they would impact significantly the performances and they shouldn't be used for multirotor at all;

Thanks in advance.

EDIT

To clarify why I have mentioned turning it upside down. I was considering the fact the propeller thin "blade-like" side when the propeller rotate on clock-wise motor cut through the air but in case it is mounted on a motor rotating in CCW the "dull" side would be used instead and this is clearly inefficient, but, if the propeller is turned upside down on the CCW motor, the thin blade like side would be the side that cut through the air. So it's unclear to me why the air flow design shouldn't be if not equally efficient at least better than using a CW APC normally mounted on CCW rotating motor.

enter image description here

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2 Answers 2

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The multirotor APC propellers were introduced because APC had a very limited CCW range. They also tend to have lower pitches than their aircraft propellers.

Apart from those two things, there's very little difference. If you can find a CW/CCW pair with the pitch and diameter that suit your multirotor, it should work just as well as the 'multirotor' propellers. Similarly, 'multirotor' propellers are handy for planes with two electric motors, allowing you to have contra-rotating props.

Note that you can't turn CW prop into a CCW prop by mounting it upside down. It will still blow in the same direction, just at about half the efficiency.

Another minor difference is that 'multirotor' propellers don't include the set of shaft adapter rings. You need to order these separately (or reuse some of the spares you have from flying planes).

I should add that APC 'multirotor' propellers are designed for slow, long-duration multirotors. They don't have propellers suitable for FPV race drones.

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  • $\begingroup$ The problem is that some propeller sizes are hard to find in CW/CCW version and are sold as CW only. I was thinking about reverse the one mounted on CCW due to the fact the blade side would cut through the air in the direction of rotation turning them upside down, otherwise with normal mounting would be used the dull side using a CW propeller on CCW motor to "cut through the air". $\endgroup$
    – AndreaF
    Nov 3, 2022 at 17:17
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    $\begingroup$ @AndreaF, no chance. The point is not so much the shape of the leading edge, but the pitch angle of the blade. If you just spin a CW prop in the wrong direction (CCW), it will push the air 'backwards' (up for your picture), but poorly due to sub-optimal shape. If you turn the prop upside down (and still spin it CCW from the point of view of aircraft), it will do the same (push the air up), but will do it efficiently. There is no way to make a CCW prop from CW. $\endgroup$
    – Zeus
    Nov 4, 2022 at 3:10
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There are two major reasons why aircraft and multirotor propellers differ

Airflow profile

An airplane is always moving forward, it almost never has to generate static thrust. An airplane propeller is designed with this in mind and is efficient when moving through clean air. A multirotor propeller has the exact opposite airflow profile. Most of the time, it is moving very slowly or not at all, and is generating static thrust to keep the aircraft airborne. The blade profile is therefore significantly different to minimize blade stall characteristics and be efficient in this operating mode. Racing/FPV quadcopter propellers are also pushed at much higher RPMs than an equivalent airplane propeller, especially in the static thrust case. This requires a different airflow profile

Weight/rotational inertia

An airplane rarel changes throttle position, and if it does, the throttle does not need to be changed right now but at some point in the near future, for whatever reason. Active braking is not employed (usually, folding propellers/motorgliders are an exception, but it's still not for responsiveness) and algorithms to accelerate the propeller up to speed uickly at the cost of efficiency are a waste. I'm happy to wait 1/4 second (electronically an extremely long time) for my airplane to spool up, even in an emergency stall condition.

Multirotors change their speed 4-8 thousand times per second (betaflight's 8k PIDloop with DSHOT600). When the motor is demanded to change speed, it is to do so right now, because another command is coming in 1/8000th of a second. Whether that be speeding up or slowing down, it needs to be changed for the sake of the stability of the aircraft.

The major contributing factor to this is the rotational inertia of the rotating mass (motor bell, magnets, propeller). Aircraft propellers are thicker at the root and are optimized for airfoil efficiency, at the expense of a lot of rotational inertia. A multirotor propeller is quite the opposite in that it is very light, is (mostly) optimized for rotational inertia, and is also generally made of a different material to handle smashing into concrete at 100km/hr (aside).

History

Historically, "Slowfly" aircraft propellers (GWS was the big brand here) were the first to be used in multirotors. Their blade shape, while not optimized for rotational inertia, is very good for generating thrust statically/at low speeds. They are not made to be spun fast (I'll show you scars to prove it), but this was before the age of ludicrously high RPMs on mini quads. They are also light as they are often put on lightweight, slow flying aircraft, as they were designed to.

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  • $\begingroup$ in ecalc simulation for quadcopter I get best result with APC E compared to SF props. Is this just an error? $\endgroup$
    – AndreaF
    Nov 17, 2022 at 1:01
  • $\begingroup$ It's unlikely the simulation takes into account a) the turbulent airflow produced by static thrust and b) the poor handling characteristics due to the added weight. It's possible that it would in fact be a better prop for your setup (APC E is a very good propeller), however that wouldn't be a cut and dry "always use APC E" $\endgroup$ Nov 17, 2022 at 12:21

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