Vibration after lift off

[seagull]

How I balance mine;
I have a 24" axle, (steel rod), that I put horizontally in the shop vise. With the wheel on the axle I spin it up with a die grinder and a 2" rubber wheel. I watch the vibration through all speeds at it winds down. With the wheel 12" out on the axle small imbalances are very noticeable. I use 2" patches of duct tape stacked and stuck to the tread to balance it and remove the vibrations. When I find the right amount and spot I weigh the stack and multiple x 3. Then use that amount of stick on tire weight on the inside of the rim. I remove the original tire weight foam tape and replace it with Scotch 411 tape, the grey stuff, it does not come off easily.

To clarify, I put the weight on the "outside" of the wheel on the surface facing the axle. Centrifugal force works to make the weight stick better.

[dbhill916]

Originally Posted by rvbuilder2002

I would caution other RV owners against using this technique to balance aircraft tires.

The reason we liberally coat the surface of the tube and the inside of the tire with talc is for it to act as a lubricant because the tube is always moving slightly from the flexing of the tire. The RV-12 is a light airplane. Because of that we run rather lower pressure in the nose tire compared to most airplanes so that can potentially make the situation even worse.

Even the smallest amount of movement of the tube against the sharp corners of the typical wheel weight is going to, at the very least, cause a major inconvenience at some point, and possibly worse.

Thanks for the input. Will definitely look at an alternative.

[Mike Howard]

Follow up information on strange vibration.
I performed a test take off today with the stick full back. The nose lifted off very quickly with little or no nose wheel spin up. [b]No vibration, problem solved? maybe?[b]
This still doesn't explain why the vibration stops immediately after I reduce the throttle with a normal take off technique. Throttle position shouldn't have any impact on vibration caused by an unbalanced tire.
Also why did the vibration only start after I installed the new nose gear leg and fork? I didn't change the tire or wheel and it wasn't a problem before I installed the new pars.

[Mike S]

Originally Posted by Mike Howard

Also why did the vibration only start after I installed the new nose gear leg and fork? I didn't change the tire or wheel and it wasn't a problem before I installed the new pars.

This is a new "system" and probably has different vibration frequency.

Professor Horton could explain it most likely.

[rk2436]

I bit the bullet and bought some Michelin Pilot tires. I'm done with those cheap POS Aero Classics. No more vibrations and they make the nicest chirp too!!

[RFSchaller]

I bought a motorcycle tire balance rig from Harbor Freight. It’s a rod with two conical pieces that when pushed together clamp the wheel on either side at the bore for the axle. The rod then acts like an axle and rests on two bearings so the heavy spot rotates to the bottom, and you can add weights until the wheel doesn’t rotate due to a heavy spot. I’ve found that you can balance really bad tires even on the aircraft axles and get a marked improvement.

[RickSolana]

You might have mentioned this, but did you check the nose fork break out force?

[sblack]

Originally Posted by Mike Howard

Follow up information on strange vibration.
Throttle position shouldn't have any impact on vibration caused by an unbalanced tire..

I have to disagree with this. Things resonate when they get vibrated at a specific frequency, or multiple of that frequency. It is possible that as you throttle back your engine goes through some specific rpm as it slows down that interacts with the fork.

If you have a wheel out of balance on your car it doesn’t necessarily get worse as you go faster. It will get bad at a certain speed and be fine above or below that speed.

Gear shimmy and resonance issues are very common and tricky to fix on many types of airplanes. Nosewheel shimmy on cessnas is common. It will break the engine mount. Tailwheel shimmy will damage structure as well. Lots of modern fighter aircraft have had nosewheel shimmy issues. In the airliner world they do exhaustive testing on the runway to identify any potential issues by hitting a shimmy plate at different speeds with nose and main gears, which is just a means of exciting vibration. It is a tricky thing. It would not surprise me at all to find that there is an interaction with the nosewheel fork and engine rpm. So not impossible at all.

[Hotscam]

I have the exact same problem since replacement of the nose leg.
The wheel is balanced and never had any vibration with the old leg.
It starts full throttle take off at about 2-300 feet @70 kts for 2-3 seconds.
Throttle back stops it immediately.

It seems related to a different stiffness of the leg.

[Slightlyabnormal]

Any further thoughts on the cause of this?
I have it too. Not every flight but on some of them a few seconds after lift off I get the vibration then it is gone as quickly. New nose gear.
Per the seller my break out force is lower than the instructions, I haven’t checked it yet, unsure how much lower.