• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Prop overspeed? - sudden vibration


Active member
Hello... Newbie here, but longtime FT watcher.

My son and I are finally getting into scratch building, and built our first power pod last night! Yay, he's so excited! We're basically using the guts from an Ares P-51; Park 370 motor, 18A ESC, 600mA 3C battery, I think (new to this). Everything ran smooth until we put the prop on (8x4.3 slowfly). It runs great up to about 80% throttle, and then it has a sudden vibration. I tested the prop, and the tips were slightly out of alignment, so I installed a new prop. Same thing... Is this overspeed? Am I using too small a prop? I think the ones I bought are the same as the 2 bladed prop provided with the P-51 kit, so I'm not sure why it would be a problem. Please help!

Also, what is the best plane swappable for my son to start out with? He's used to flying park flyers (Cub-S).



New member
Did you balance the props before trying them on the motor?
Check out this article ways to balance your props
What you describe sounds like badly balanced props. This is bad because the vibration can tear the motor out of the mount during flight, leading to a busted motor and a busted aircraft.
Also running the prop at full speed while holding the aircraft stationary applies a lot of stress to the blades and can warp them, try not to do that too much.
Last edited:
I would also second checking to make sure they are balanced properly.

A well balanced prop no matter what speed will not induce vibrations.

A unbalanced prop will eventually find that resonance spike where the unbalance weight shakes uncontrollably.

Foam Addict

Squirrel member
Actually that's not exactly true. Slow fly props do have an RPM limit where they will flutter and make a loud humming noise. Unbalance does make it worse, but this point will be reached eventually. You can try balancing the prop, if that doesn't solve the problem I'd recommend switching to a stiffer prop


Cardboard Boy
I had a problem with a 6x4 prop where it would make a loud metallic noise when in a dive, when we tried it on a more powerful setup it made the same and I figured the blade tips were probably going transsonic/supersonic. Probably not your problem but that was fun and scary.


Old and Bold RC PILOT
By all means ensure that your prop is balanced, but also do not forget to check if the motor does not have a bent shaft. On some motors the shaft is so long that the shaft can be bent in a heavy "Nose in" landing while the remainder of the aircraft is undamaged. With a bent motor shaft the prop will never run "true" and makes all sorts of noises at full throttle.

If you have fitted a "Prop saver" remove it as the "O" rings can allow a prop to move around and create nasty noises.