Engine Vibrations
 

I have an OS95AX with a pretty bad vibration at lower RPMs. When it's close to idle speed, the vibrations are very noticeable, especially around the vertical stabalizer. But at any from mid range to wide open throttle, the vibrations are no longer present. I've already checked all the screws/bolts on the mount and firewall and everything is tight. I've also tried a few different props and I also balance all my props. Any thoughts?

The other thing I've noticed is that if I spin the prop in reverse (clockwise when looking from the front), at the compression point but before it turns over there is a slight metalic click or pinging like sound. Is this normal?

RE: Engine Vibrations
 

DenverJayhawk, I'm hesitant to offer you any useful advise on the off chance that you might be a Denver Broncos fan. I'm going to give you the benefit of the doubt in the hope that you have the good sense to revile the Broncos like all right thinking people should!

A slight click at the top of the stroke is normal as the connecting rod changes direction. This clicking/pinging effect should subside once the engine is thoroughly broken in. I also suspect the vibration that you're experiencing may also be due to insufficient break in/run time on a fairly new engine.

You might try balancing whatever spinner you're using with your propeller; an unbalanced spinner can cause just as much of a shake as an unbalanced propeller. You could also simply try to replace your spinner with a safety nut and see if that improves the low speed vibration.

I believe, however, you won't find any significant balance issues with your spinner, either. Your O.S. Max .95 AX most likely will require a couple of gallons of fuel to be run through it while flying to smooth out the vibration at idle speeds and to reduce/eliminate that click/ping sound you're getting at the top of the cylinder stroke. Fly the engine fast and not too rich and it should settle in nicely as you continue to fly it.

Alarming amounts of vibration is often reported with larger glow engines when the engine is new. There isn't anything about your description that indicates a problem other than an engine that needs more run time to finish breaking in.

Good luck and good flying!

RE: Engine Vibrations
 

I would think that a vibration at low RPM's is more the engine than the prop or spinner. Doesn't an imbalance there show up at higher RPM's or at an RPM that is more resonating than it would be at lower RPM's? Just wondering here because I'm not exactly sure.

I do know that if you are using a "soft mount", it will vibrate like crazy at low RPM's, but settle out at higher RPM's.

CGr.

RE: Engine Vibrations
 

Where do you fly and will you be there this weekend? even with the snow, I will be there (cherry creek dam state park) sunday and probably monday.
dan

RE: Engine Vibrations
 

Welcome to the world of 'harmonic vibrations and frequency resonance'! Remember playing with a jump rope when you were a kid? Each kid on an end could shake the rope end up and down to either make the 'waves' in the rope get larger or cancel out midpoint. This is a simple excercise to demonstrate what is happening with the tail of your aircraft at certain engine rpm's. Using softmounts just changes the resonant frequency needed to vibrate the tail. Be sure and balance your propellor/ spinner combination 'properly'. There are threads elsewhere to demonstrate this. Make sure the tail structures are adequately glued/ braced. Too bad there aren't any inline 6- cylinder or 3- rotor wankel type model airplane engines!

RE: Engine Vibrations
 

DenverJayhawk,

It seems that your model is reaching a resonace vibration at lower RPMs, and there is no much more to do about it than modifying the natural vibration of your engine-model.
If the vertical tail shakes more, then your main vibrations may be in a horizontal direction.

Try changing the position of the propeller respect to the shaft, and also try a propeller of different weight (lighter would be better, I believe).

Best luck!

RE: Engine Vibrations
 

Thanks for the suggestions. I'm using a safety spinner nut instead of a cone-spinner. I also had an SK90 engine on this model before the OS and it also had the same vibrations in the tail. Maybe it's just something with this model (Big Stik 60)? I was worried that something might be loose internally in the OS Engine. But doesn't sound like you guys think that would be the problem.

I called TowerHobbies where I bought the OS engine. They said it's under warranty and I can send it in for testing/evaluvation/repair. Do you think it's worth doing?