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So I'm getting into R/C flying and got myself a nice, but pre-owned trainer model. One of the things that need replacing is the propeller, which is a 2-blade nylon 10x8 with too many signs of damage for my liking.

I'd like to stay with a 2-blade 10x8 to not get into any troubles with regard to overloading the motor or ESC. But there's more decisions to be made aside from number of blades, size and pitch.

  • symmetrical vs. undercambered?
  • swept-tipped vs. straight-tipped?
  • nylon vs. wood vs. carbon fiber?

Given that I'm just starting out here, it seems staying with a straight-tipped, symmetrical nylon prop would be the conservative choice. I'm wondering about these things though:

  • since the "collision object" putting the propeller blades at risk the most is the gras you land on, might carbon fiber be more durable, just cutting through it without taking any damage?
  • might wood and carbon sound better than nylon due to being less flexible?
  • might wood and carbon be more efficient than nylon due to being less flexible?
  • how much at-risk for unplanned rapid disassembly from just doing their jobs are these three materials in comparison to one another, a.k.a. what's their lifetime in the best possible case of never colliding with anything but air molecules?
  • what effects does symmetrical vs. undercambered have?
  • what effects does swept-tipped vs. straight tipped have?
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  • $\begingroup$ A lower pitched prop might slow things down. $\endgroup$
    – Eric S
    Commented Sep 20, 2021 at 23:48
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    $\begingroup$ You might get a better answer over at the Drones and Model Aircraft Stack $\endgroup$
    – TomMcW
    Commented Sep 21, 2021 at 0:03
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    $\begingroup$ @PeterKämpf my RC modeling days predates electric motors. Typically we would up the diameter along with dropping pitch. A 10x8 might change to 11x7. Of course landing gear length needs to allow it. 10x8 seems pretty high pitch for a trainer. $\endgroup$
    – Eric S
    Commented Sep 21, 2021 at 4:04
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    $\begingroup$ I’m voting to close this question because it isn't about aviation, as defined in the help center, but belongs on drones.stackexchange.com instead. $\endgroup$
    – Ralph J ♦
    Commented Sep 21, 2021 at 8:38
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    $\begingroup$ @RalphJ While Drones.SE is a better place for this question, I don't think it is necessarily off-topic here. I have however voted to close as needs more focus. $\endgroup$
    – Bianfable
    Commented Sep 21, 2021 at 9:17

2 Answers 2

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Any fixed-pitch propeller has an efficiency that is a function of J = v/nd, where the advance ratio J is itself a function of airspeed v, angular speed n (in turns per second) and prop diameter d. For every pitch value, we have a parabola-like curve that has a maximum. The set of all maxima defines the enveloping curve, and that enveloping curve has itself a maximum.

enter image description here

That maximum of the envelope curve will correspond to the maximum of a given propeller pitch. Having previously defined the diameter and angular speed of your prop, and taking for v the airspeed for best L/D of your airplane, you now have the specs for the prop of highest efficiency...

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From the "been there" file, you may wish to start with wood. In the event of a nose over, breaking the prop first will put much less strain on the motor mounts and the rest of your model.

Also, get a prop balancer at your hobby shop and a rpm meter to check everything out before flying.

While you're at it, feel free to experiment a bit and talk with other flyers about prop choice. Anything from a 10×5 to an 11×7 may be possible. The first number is the prop length, the second is pitch.

Lower pitch, just like in real airplanes, gives better take off and low speed performance, while higher pitch is for more efficient cruising.

A straight wood 10×8 2 blade is a good place to start. Once you get some experience, the next choices will be up to you.

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