One of the first maintenance issues I addressed on my Cheetah was nose wheel shimmy. It occurred after touchdown, when lowering the nose wheel to the pavement. It never occured on acceleration prior to rotation for liftoff.

Inspection of the nose tire indicated the pressure was low, so it was adjusted to 21 psi. Inspection of the thread indicated ~5/32″ of thread depth, with even wear around and across the tire, a Goodyear Flight Custom III. No help, the shimmy continued.

Measuring the nose fork friction using a spring scale, as per 32-2-1, Fig. 202, indicated a 6 lb. force was necessary to swing the fork: way below the specification. Tightening the nut to the next available cotter pin hole in the strut assy. resulted in a fork friction of 12 lbs. No help: the shimmy continued.

Next step: disassembly, cleaning, inspection, lubrication and reassembly of the nose wheel fork assembly. Also, the number and order of installed washers and bevel washers (a.k.a. spring disc) were verified with the IPC.

The nose fork friction was adjusted to 24 lbs. This was the lowest force available that was greater than the previous 12 lbs., given the possible positions of cotter pin hole alignment of the nut on the strut. Yes, rotating the nut 30 degrees increased the force from 12 to 24 lbs. Testing: the shimmy continued.

Checking the nose fork friction following testing indicated 20 lbs. of force required for deflection: at the high end and within specification. Still shimmying.

In a post on the Grumman Gang David Fletcher was quoted as recommending an “Aero Trainer 5.00 x 5 Tire” as a solution to the shimmy problem. Installing this tire with a new tube on my nose wheel resulted in a weight reduction from 7.5 lbs. for the Goodyear to 5.5 lbs. for the Aero Trainer. This is enough to require an update to the aircraft’s weight and balance document, as two pounds is not considered a negligible change. Checking the balance of the Aero Trainer tire & wheel assembly on a static balancer indicated no balance weight was needed.

Testing: the shimmy is gone. I can leave the nose wheel on the pavement after touchdown, without lightening the load on it with up elevator. I’m looking forward to someday replacing the mains and gaining 4 more pounds of useful load!

• This topic was modified 8 years, 10 months ago by John Cotter.
• This topic was modified 8 years, 4 months ago by Roscoe Rosché.