Tailwheel Shimmy and Spring Arch

[Steve Pierce]

Put a spacer under the tailpost pad and get on with life. If you ever rebuild it replace the tail spring pad fitting, or remove the rudder, cut that one off and weld a new fitting on using the spring as a fixture of sorts.
100_6759.JPG

[avspecguy]

I had trouble with mine shimmying when I first got it. I'm sure the spring was what was supplied with the univair conversion and the arch was not enough. I took it to a local spring shop and had them add more, matching a template that I made. I was pretty sure the problem would be gone but alas, it did not go away with that mod. Next I tried Maule springs and that helped but did not eliminate it. While problem solving with my IA he suggested that I try more air pressure in the tire. I had been running it at 20 psi whech he felt was not enough. I'm not sure what the recommended pressure is but I've been running it at 40 psi and the problem is GONE! I wonder now if the Maule springs were necessary, but I'm not going to remove them and find out. I like it all just the way it is.

By the way the pad at the tail post on mine is pretty much flush with l the longerons like is shown in one of your pictures.

Happy aviating!
Pat

[Steve Pierce]

I believe the published air pressure for the tailwheel is 45 psi.

[SWolf]

Is the PA-18 ABI still to go to spring or has Univair stepped up there quality in the past few years?

[Gilbert Pierce]

Univair spring is no go. ABW or re-arch.
A fellow Shortwinger contacted me a ot 4 months ago. He got a new Univair spring with less arch than his old one that shimmied. Had the old one re-arched and solved his problem. Univair took the new one back.

[smcnutt]

Univair spring is no go. ABW or re-arch.
A fellow Shortwinger contacted me a ot 4 months ago. He got a new Univair spring with less arch than his old one that shimmied. Had the old one re-arched and solved his problem. Univair took the new one back.

I've heard that for years. Why doesn't Univair fix that? Is it set to the wrong arch for another airplane or do they just not care?

[Gilbert Pierce]

They claim it meets their Piper drawing. I have letters going back to 70’s complaining they don’t have enough arch.

[jeremygerhold]

Is this the one everybody bought?
https://www.airframesalaska.com/PA-1...ngs-s/1893.htm

[Steve Pierce]

Is this the one everybody bought?
https://www.airframesalaska.com/PA-1...ngs-s/1893.htm

Yes it is.

[Shermanj1]

Is this the one everybody bought?
https://www.airframesalaska.com/PA-1...ngs-s/1893.htm

Yes that’s the one. Don’t over think it buy the spring and all your problems will go away.