Wheel wobble

[rvaitor87]

All;
Could use a helping hand here, Recently I noticed some noise coming from my main wheels, so I removed them and re-packed, then put back on. (Yes, I did do it correctly), after putting it all back together, I did a high speed taxi to test the brakes, and to make sure all was well. At 17kts. I got the worst vibration I have ever experienced. I reduced power, and touched the brakes, after I got below 16kts, it went away. My first thought was, the nuts were not seated right, and there was too much play in the wheels. After checking, everything was as it should be. Put everything back together and try it again, same problem. So I go back and look the whole thing over, this time I leave the pants off. No vibration, this can't be right. Put the pants back on, vibration.

After the last time, someone waiting to take off said that my pants were moving side to side. This was a sudden occurance, as this has never happened before. They are one piece pants that attach to the shaft via a plate. I check all connections, and all is tight, and my rotors are straight.
The only thing I did was re-pack the bearings, and I even checked that again.

Any help will be appreciated.

Mike Bauer
RV-3 N87LB
RV-4 N742MC building

[Kyle Boatright]

Sounds like main gear shimmy, which is pretty common with the RV's with tapered rod landing gear.

My airplane exhibits the characteristic from time to time. The solution seems to be properly balanced, round tires. Not out of balance, herniated, or egg shaped tires. Air pressure also plays a role. Conventional wisdom is that reduced pressures (24 PSI or so) help tame the shimmy, but my best results are at 34-35 PSI.

Does your airplane have the wooden stiffeners on the gear legs? That is a factory recommended fix for shimmy.

[rvaitor87]

Yes we put the wooden dowels on at assy. I usually run about 30 p.s.i. on my tires. maybe I'll try going lower on pressure.

Mike Bauer
Bartow, Fl.

RV-3 N87LB
RV-4 N742MC building

[Marc DeGirolamo]

Originally Posted by rvaitor87

All;

After the last time, someone waiting to take off said that my pants were moving side to side.

Take the wheelpant off, jack the plane up and spin the tire by hand...that will tell you if the tire is out of round.

[rvaitor87]

Done did that too, their round. I don't know, there is something that I am missing here, but I can't see it. It has to be so simple and plain, that I am not seeing it. Maybe I'll try new tires.

Mike Bauer
Bartow, Fl.

RV-3 N87LB
RV-4 N742MC building

[Stu McCurdy]

I used to own and fly an RV-3. It also had significant main gear shimmy at 16-17 knots while taxiing. I reduced it significantly (not completely) by doing the wooden door jam stiffners wrapped in fiberglass on the rear of each main gear and also balancing the wheel pants by placing tire weights in the front of the wheel pants until they hung level through the axle hole then glassed them in. After doing both mods I still had a minor shimmy if I taxiied at that speed.

I eliminated the shimmy by not taxiing faster than the shimmy speed and by always doing wheel landings. It never shimmied with the tailwheel off the ground. So I would touch down in a wheel landing, slowly push the stick forward to keep the tail off the ground, add just a little power to give some aerodynamics to the elevator, and when below about 15 knots slowly let the tail wheel down. After I started using this technique it never shimmied.