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Old Aug 22, 2012, 03:58 PM
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Joined Aug 2012
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Help!
Stryker propeller

Hi guys!!!
I have built the stryker from spare parts- (which I think alot of people have done)
my question is about the prop. I have an 8 by 6 slo flyer prop on it, and It makes a crazy loud noise when I have it about half throttle...I am worried that the neighbors will start getting upset But the question is if a pusher prop will be better for it, and if it will be more efficient. I just wanted to get some opinions before I bought it.
Thanks!! Wolfgang
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Old Aug 22, 2012, 07:06 PM
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Canada, ON, London
Joined May 2011
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Not sure which Stryker you built (C or Q or ...), but on the Q I had success with the stock 6x6 prop and also Master Airscrew (hobbyking version) 7x5 standard prop with the lettering facing the NOSE of the plane. Key point that - having the lettering facing backwards may work, but the prop will spin backwards to what it was designed to do.

If you mount a normal prop on (facing forward of course) and then make sure the ESC is programmed to spin it the correct direction for thrust. Then you should be okay as long as you consider things like:

- room (ie. the prop isn't going to strike the rudders on the Q when they are deflected (8" prop is pretty tight)

- props' max RPMs ... props are rated for a maximum RPM. If you are spinning it too fast you will risk the prop breaking down and/or at minimum will inject noise. Not a good idea.

- # of cells of your lipo.... related to the RPM above is how many cells / what voltage you're running. 3S and the stock 6x6" is loud, but if you push it to 4S on 6x6 it's _really_ loud. THEN going to 7x5 or 8x? on 3S you get really loud. Also, when one goes from 3S to 4S generally you should consider dropping the prop diameter.

I think the rule of thumb someone told me was 120000 / max RPM ~= max prop diameter.

So if you had:

8" prop, 3S (4.2V x 3 = 12.6V max), and a 1200 kv motor

Your prop RPM would be: 1200kv x 12.6V = 15120

The rule of thumb would say: 120000 / 15120 = 7.94

I can't recall the stock motor spec, but you get the idea.... assuming its near 1200kv then you'd be over the max with 8".

One other thing is that the "slow fly" props are pretty flimsy and inefficient. Flimsy can make for fewer broken props on landing, but less thrust.

Make sure you have properly balanced any prop you use. Vibration can be easily caused by off balance props.

Lastly, make sure you're using a prop nut and NOT a prop saver ;-). Prop savers are a PITA - especially when you get to this much power/speed. If you find a strong enough elastic/o-ring you might as well toss it and get a prop nut anyway because the prop will break with that much elastic ;-).

Hope this is helpful? I'm sure there are others who will / can correct any mistakes in the above. I think I've captured what I've learned over the last couple years ;-).

Good luck and happy flying. I think if you try the MAS 7x5" you'll be more than tickled with the power/performance.

J
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