I got my brushless put on today. It all works fine, but when I get above 3/4 throttle the prop (on a prop saver) starts to make a humming sound. The more throttle I give the louder the hum. Any idea what would be causing this? It sounds like its going to break at WOT.

take a look at this thread

http://www.rcgroups.com/forums/showthread.php?t=414874

summary...balance your prop...oh, and make sure your (banded?) prop saver has enough, and tight enough, bands to hold the prop securely

It would be helpful to know what prop you're using.
If it's a GWS, you're probably trying to spin it too fast causing the blades to flutter, hence the humming sound. The hum is a warning that the blades are about to go ballistic. I've experienced the same thing with GWS props; kinda scary

Yep, its a GWS prop. I hate those things. Its the only prop I could find in a 8x4.3, APC doesn't make that size. Anyone know where I can find a quality 8x4.3 or 8x4 prop?

Definitely check the number of bands holding the prop on. I tried using a prop saver on my latest plane, in turns and high load situations I would hear a similar hum noise, anything above 3/4 throttle as well. I happen to have a collet type adapter with me so I switched to that, same prop. Noise went away. I concluded that the prop saver wasn't holding tight enough, so I have stopped using it on that plane. I figure if I have to band it on there super tight, what is the point, as the more rigid I hold it, the more like not having the prop saver is. YMMV.

Are you using the GWS SF or HD prop?

Not sure, its grey if that helps.

try the hd prop

I've had GWS props that howled like hell's hounds on high rpm cdr motors. From the comments I overheard it certainly got people's attention. I agree with the flutter explaination. The vibration can have different shapes of bending or flexing and the stiffness of the prop saver and the connection to the propsaver can resist some of the vibration 'modes' ('modes' is the engineering term). I cinch my prop savers on tight with nuts and washers, and lash the props on with multiple wraps of a rubberband. It's defeating the purpose of the propsaver, but I can't fly a plane that can compete with the tornado sirens.

if your prop is humming or whistleing its bored. get it a psp or gameboy or portable dvd player to shut it up.... ;p

Check your blade tracking.

One blade may be ahead of or behind the other. Gently bending the offending blade will help.

Maybe it doesn't know the lyrics?

(sorry, could not resist.)

. .

Go with an 8x4 GWS HD, APC E or Graupner Slim or CAM. I have test run all the GWS RS props and viewing them from side-on is interesting (and scary). As they approach their limit of about 40-50,000rpm/diameter, in the larger diameter props especially, the tips bend a LONG way, and the mid-blade section flutters alarmingly - that's where your noise is coming from.

Cheers, Phil

Phil
You've got guts! I hope you had your safety glasses on or better yet a large thick piece of lexan between you and the props when you're testing them.

kern