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-   -   Rotor size (http://www.Wattflyer.com/forums/showthread.php?t=73224)

Gyrfalcon 02-19-2014 05:21 PM

Rotor size
 
I have 8 inch Rotors on my hex, just wondering what difference it would make with larger rotors, more lift power? shorter battery life? Less agile?
Any advise please. Thanks

JetPlaneFlyer 02-19-2014 06:45 PM

You would get more power and more lift, but unless the motors and ESC are suitably rated you could easily burn something up.

solentlife 02-21-2014 07:39 AM

You can in fact end up with less lift when increasing past the optimum size and pitch. Reason being the motors will only output a maximum power level. That will be absorbed in the prop / rotor. The other factors is the likelihood of over stressing the battery / ESC and or motor... burning them out in fact.

Keep to recc'd prop sizes... there is good reason for that.

Nigel

JetPlaneFlyer 02-21-2014 08:05 AM

Quote:

Originally Posted by solentlife (Post 940586)
Reason being the motors will only output a maximum power level.


Well, actually for electric motors that's not generally the case. They will to a large extent keep producing more and more power and more thrust as you fit larger and larger props. And that's a problem because electric motors are dumb, the dont know their own limits. They will continue to produce more power even when the amount of power causes them to overheat and burn up. This is why a wattmeter is such an important tool when you fly electric.

This is totally different to i.c. (gas/glow) engines. They do have a maximum power that cant be exceeded, and if you fit a prop that's too big on an i.c. engine RPM and power and thrust does indeed drop.

But the advice is the same.. Stick with recommended prop size 'unless' you have a wattmeter and can check that the current (Amps) is not exceeding hardware limits when you fit a larger prop.

Gyrfalcon 02-21-2014 08:25 AM

Props
 
Quote:

Originally Posted by solentlife (Post 940586)
You can in fact end up with less lift when increasing past the optimum size and pitch. Reason being the motors will only output a maximum power level. That will be absorbed in the prop / rotor. The other factors is the likelihood of over stressing the battery / ESC and or motor... burning them out in fact.

Keep to recc'd prop sizes... there is good reason for that.

Nigel

Thanks for info, I think I will leave well alone.

solentlife 02-21-2014 08:27 AM

Hi JPF.... yes I know e- motors will keep increasing until they burn out. I was talking more practical terms.

fhhuber 02-21-2014 10:49 AM

Power (watts input) is not necessarily even proportional to useful thrust produced with an electric motor.

An overloaded motor will attempt to deliver the power demanded, but that just means it will demand more current. If the power demanded is beyond the power the motor can deliver then the excess current just goes to making the motor hot.

Motor efficiency is (power out)/(power in) We start out expecting appx 80% to 90% with 90% being rare. The loss all goes to heat.


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