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Old Dec 11, 2010, 08:45 PM
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JBuck's Avatar
United States, CA, San Diego
Joined Apr 2007
249 Posts
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Prop size help please

I just built a 36' wingwarrior ESlayer wing.
Himax 2815-300 motor
54amp ESC
2200mah 3s 25c lipo
AUW= 750 grams

Im using a 4.75x4.75 prop. It is probably hitting about 100mph. I want to see if I can get a little more speed out of it. I dont really know that much about prop selecting.

Should I try a larger prop with more pitch with this setup? Smaller prop with more pitch? Any suggestion?

Thank you,
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Old Dec 11, 2010, 09:31 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,153 Posts
in general, increasing diameter will give you more thrust while increasing pitch will give you more speed.

Either way it will increase your amp draw so it's up to you to avoid smoking the system..
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Old Dec 11, 2010, 11:07 PM
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Joined Jan 2010
913 Posts
I just wanted to expand a bit on what Bartricky said:

Increasing diameter will give you more thrust, but will also reduce RPM and therefore will normally cost you speed.

Increasing pitch should give you more speed, but because you lose some thrust it can technically also take away speed if you're trying to get a very draggy plane to an unnaturally high speed.

For your sleek, aerodynamic wing, you'd want to go up in pitch without going up in diameter. Looking at the APC prop list, your only real choice is a 4.75x5.5 Speed 400. Running some numbers through one of the flight calculators, I'd say you're quite close to the limits on your motor to begin with, and that small change might bump you over the edge. For the cost of the prop, it's worth trying if you have a wattmeter, but you may find the only solution is More Power™, which would require a motor change. You can often do very well for high-speed models with a lower Kv running on more voltage to get the RPM back.
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