Engine noises normal?

[kgh31386]

When my plane is sitting there idling with the prop spinning...it sounds like there's a vibration/rough running sound. But once it powers up to full throttle it's fine. Also on a few passes I think I heard a little bit of a vibration. Also question, is it bad to spin the prop at all by hand with no throttle? The plane flies fine and will still go pretty high...do loops, etc. but I'm just curious about the sound. And one last question, if I ever have to replace my motor. How hard is it. I see it just screws in, but what about the wires, how do you go about hooking up the new motor?

[SCC]

My motor sounded rough at low RPM.

Replacing the motor is simple. Unplug the wires, mine needed a good tug to seperate. Undo the four screws that hold the gearbox and motor to the firewall. Now if you look at the back of the gearbox you will see two screws holding your motor. Once these are removed the motor is free. These two screws should be checked, they can vibrate loose.

Vibration could be caused by the two screws being loose or an unbalaced prop.

Spinning the prop by hand when the plane is switched off no problem.
When the plane is armed i personally don't put my fingers anywhere near the prop.

[flydiver]

Just because a prop is new doesn't mean it's balanced. Worst prop I've ever seen in my life was a brand new Cub prop. Generally though an unbalanced prop will get worse with more RPM's.

The gears are pretty rough. You can help them a little with a DRY lube (no oil, grease, WD-40, etc.). I use a spray on dry lube that leaves a white thin powder behind. Little is needed.

Be honest now-did you dork the motor? That makes the question different.

fly

[kgh31386]

Nah it's sounded like this since a I got it a couple of weeks ago. I've clipped the prop on the ground before when I landed. That plane loves to bounces as soon as you touch the ground....UNLESS you land it jusssst right which is pretty easy unless the wind gets at it. But my girlfriend did crash it in the grass which broke my prop and cracked the cowl. I taped the inside of the cowl and replaced the prop and it still flies fine.

[flydiver]

Gearboxes are noisy, one of the reasons some people prefer direct drive outrunners. The cub has a kind of growling whine at idle increasing to a whiny racket at throttle.
I would do SCC's suggestion on checking the engine mounts and screws. After a crash of any sort a good check is not wasted effort. Taking out a cowling and prop is not entirely benign.

I have a buddy that keeps insisting that his landings just are NOT THAT BAD when he rips off his highly reinforced landing gear. Uh huh.....

fly

[cvrcmember]

Ha! Yah, my cub does that too it's pretty much normal unless you upgrade the motor.