Champ Tailwheel Shimmy - hey, they are all Champs!

[Bob Turner]

We are having a few problems with a GCAA, and maybe with a Decathlon with reported extended gear.

Both have the Scott 3200, adjusted so the kingpin is vertical and tire pressure 50 psi minimum. I know how to make shims and how to bend springs. I also know that tailwheel shimmy is destructive, and I have rebuilt 3200s with some success. I am successfully running an old 3200 on my Decathlon.

The GCAA is driving us nuts. I put my brand new Scott on it last week, and after maybe five successful pattern hours it went nuts. I have not test flown it since then. Its owners don't want to destroy my new tailwheel,so they are getting a new Bushwheel unit this week. I re-bent some new leaf springs to the proper angle, and we will install them at the same time.

The bolt apparently loosened - we should have put a castellated nut on it - but even a loose bolt really shouldn't set up a violent shimmy. Instructors just want to fly, so they keep on keeping on until things get pretty bad. I am trying to stop that, without success.

Anything I should look for other than the above? The 3200 is usually bulletproof when properly maintained. Maybe we should try the ACS tailwheel? I am running two on J3s with great success.

 

[Tangogawd]

I set the kingpin angle to a more negative angle. That way, the kingpin is vertical at full gross and aft CG.

 

[Bob Turner]

We check it with a heavy person in the back. Either vertical or ever so slightly negative.

I am going to suggest to the owners a thorough empennage inspection. There is something wrong -not surprising for an instructional ship.

 

[Tangogawd]

Yeah good, I've found cracks in the tail tubing around the tail spring mounting. Not sure if it would cause much shimmy, if at all, but students are hard on things, so...

 

[Big Ed]

Can't give much perspective, as my sample size is one. But I will say my tailwheel angle is supposedly off kilter, but I get zero shimmy. Rock solid. I bought new tail leaf springs from ACA last spring and they are still sitting on my workbench.