Vibration after lift off

[Mike Howard]

I have developed a strange engine vibration that occurs approximately 3 to 5 seconds after I lift off while at full throttle. The vibration started just after I replaced my nose gear leg and fork. I do not believe that it is related to an out of balance nose wheel because it does not happen until more that 5 seconds after the nose wheel lifts off.
Here is the strange part the vibration goes away completely if I pull the throttle back to about 50% for a second or two and then push it back in for full throttle. The vibration does not occur for the remainder of the flight for any throttle position.
I have checked the lower engine mounts where the new gear leg clamps to the firewall. I thought that the nuts might have bottomed on the bolt so I added a washer under the nut. The problem seems a little less but it is still there.
Anny ideas?

[BlndRvtr]

Could it be a harmonic set up by the new NG leg, fork and wheel assembly? More specifically, is it related to nose wheel tire rotation. As the tire stops spinning, the harmonic subsides? A camera aimed at the nose gear could be revealing.

George

[kritsher]

I'd check the breakaway force on the nose wheel.

[bobg56]

You probably do this put I'll suggest it anyway, my RV12 has vibration after lift off but its the main wheels spinning, I apply the brakes and it stops.

[cajunwings]

Sounds like the tire/wheel balance and it’s worse when the weight is off and it’s spinning down. Make a takeoff, don’t touch anything and see if it stops in the same time frame. Tire balancing might be needed.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

[Dgamble]

I get this too but it seems to occur more often after a touch & go than a normal takeoff. The only difference between the two is that the nosewheel is probably turning faster after the touch & go than it is after a normal takeoff.

My normal takeoff is stick full back until the nosewheel lifts, then just hold that attitude until it flies itself off the runway. That keeps the speed down for the nosewheel.

I bought the motorcycle wheel balancer from Harbor Freight and did find the nosewheel to be out of balance. I just live with it now because I don’t trust modern wheel weights that are held on (barely) with double-sided tape, and they don’t seem to be made out of lead anymore, so you have to use more of them.

[cajunwings]

Originally Posted by Dgamble

I get this too but it seems to occur more often after a touch & go than a normal takeoff. The only difference between the two is that the nosewheel is probably turning faster after the touch & go than it is after a normal takeoff.

My normal takeoff is stick full back until the nosewheel lifts, then just hold that attitude until it flies itself off the runway. That keeps the speed down for the nosewheel.

I bought the motorcycle wheel balancer from Harbor Freight and did find the nosewheel to be out of balance. I just live with it now because I don’t trust modern wheel weights that are held on (barely) with double-sided tape, and they don’t seem to be made out of lead anymore, so you have to use more of them.

I balance my aircraft tires. Remove the double sided tape (belt sander or whatever) and use silicone or proseal to hold them on. Works great.

Don B

[dbhill916]

I was pretty sure that vibration as described by the OP was from my front tire spinning down because I could do a "wheelie" touch-n-go and have no vibration at all on climb out.

Ditto for Dave G's comments --On his advice, I bought the same tire balancer from Harbor Freight.

I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them. Works great. No vibration on regular take offs or wheelies.

[Greg Arehart]

Originally Posted by dbhill916

I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them. Works great. No vibration on regular take offs or wheelies.

I would suggest that this may cause you issues down the road (so to speak) rubbing the tube. I balance my wheels similarly, but use pieces of old inner tube rather than anything rigid or with sharp edges. Less weight than metal weights but more flexible.

[rvbuilder2002]

Originally Posted by dbhill916

I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them.

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.