BigBirdBlue

I'm trying to figure out what is an ideal prop size for an engine, knowing the engines average max power output across its powerband. I'm not caring about looking at the engine's rpm range, I'm assuming it doesn't matter for this case. What would be the best way to estimate the best prop size knowing the eninge power output and flying speed range? I know a larger diameter prop theoretically gives more thrust for a given power output but this probably has limitations in the real world. And how do you match a prop pitch to your flying speed because a prop induces a much higher airspeed than the plane's airspeed. Anyone know a way to approach this problem? thanks

Edit: This was a jumbled mess of words so I just simplified it to the theoretical approach

scale only 4 me

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You wanting what we think works for your motor? tell us what is the motor?

or a long debated theoretical discussion? because that's sure to follow.

da Rock

Almost every model airplane motor/engine lists it's specs and one of them is recommended props. Obvious right?

So if you don't have a model airplane motor, or one that's too cheap to provide specs, figure out the closest match that has proper documentation and start with that info. For example, if it's a glow engine you have, look at Tower's website and click through the OS engines by displacement. Match that and read what prop OS recommends. If you're wondering what prop for a cheap Chinese brushless motor, look at the Rimfire motor listings and go from there.

If you are working with a brushless, it is safer to check it's rpm with a tach and it's power demands with a meter. Because of their propensity to quite happily burn themselves up when overloaded without giving a hint they're pulling too much juice, it's smarter to use a couple of tools, neither of which are expensive.

da Rock

BTW, look around for charts that list prop by power range. Notice there aren't any?

Model airplane prop pitch ratings are WAG values. Wild Ass Guess values. In fact they aren't of any more value than what they are: WAGes. The mfg's have no clue what weight and drag model we're going to hang them on. They also have no clue what our choice of power will be either.

If you're going to use a brushless motor, look for the eCalc app and plug in what you know about your motor. It'll save you a lot of time answering questions everyone who tries to help you will have to ask in order to even give WAGes.