Carbon Cub FX-3 Tailwheel shimmy finally resolved

[Neal]

My 2021 FX-3 had the T3 tailwheel with the standard size Aero Classic tire. All worked great but I learned from my CFI that I get my flight reviews from when talking about landing on grass strips that are wet and expressing concern with tearing them up he told me it's not the bushwheels that cause the issue but it's the tailwheel that ends up acting like a plow. With my 2023 FX-3 build I decided to go for a larger tire setup and TK1 was just coming out with their new tailwheel system and as I really like the TK1 Shock Monster main shocks I figured I'd get Tony's new TK1 Shock Monster tailwhee with the 11 inch tire (11x4-5.00).

There have been some growing pains over the last two years in which Tony stepped up on multiple occasions replacing the fork with a newer designed fork due to tire rubbing, and later replacing the shock with a much more customizable setup to control spring rate, caster angle, etc. I have been trying to resolve a shimmy issue since taking delivery of this plane in October of 2023. It has been far too long of "fly adjust, fly adjust, fly adjust" trying anything and everything possible. Tire pressure, caster angle, tight chains, slack chains, different nitrogen pressures, on and on. In the end, I could not resolve it. I read a Facebook post recently of a Carbon Cub SS owner with a baby bushwheel fighting shimmy and about to give up and go back to the Aero Classic tire, I believe he was using the standard leaf spring setup. He was advised by many about landing speeds, on and on all of which like me he was doing...landing in a stall, etc. Some said to wheel land and bring the tail down at low speed. Just craziness...

Well, Trent Palmer has the same TK1 tailwheel setup and I watch his videos closely and never see his tailwheel budge. The difference though is he doesn't have tailwheel steering as I do (rudder horn with spring and link chain). I learned from Tony a few months ago that someone was using his tailwheel with the steering arm without springs/chains connected and he shouldn't have done that but instead remove the steering arm and put in a spacer washer. So I reached out to Tony two weeks ago with my idea. Maybe I'm touching down with the tailwheel tire offset as I'm kicking rudder to keep the nose straight and that's causing the tailwheel tire to react kicking opposite direction and getting into a tailwheel PIO aka shimmy. So I asked Tony about getting a spacer washer to remove my steering arm and give that a try. I also asked for a set of replacement washers that go into the assembly as I had a concern mine were worn out so he included them. I offered to pay for express shipping as he's in CA and I'm in VA and he sent them 2-day but wouldn't let me pay. That's Tony!

Tonight I was able to go flight test the new setup, finally and I'm happy to report 3 landings with no shimmy. And I even kept force on the tailwheel with one of the landings with the stick remaining full back which is something you don't do with a baby bushwheel to combat shimmy I'm told and the tailwheel did not shimmy. So a huge success.

So now I don't have tailwheel steering and I have to admit it is going to take some getting used to. I didn't do so well taxiing out to fly but did far better taxiing back. So we'll see how it goes from here. But there were 3 changes made in this last round of changes: 1) Removed the steering arm, 2) Added 5 degrees of caster so I'm now at 9.7 degrees and 3) new hardware (washers) which allowed a little snugness on the tailwheel pivot assembly to keep it from free castering too easily.

Glad to finally resolve this! I was just about to give up and reinstall my T3 with small tire again.

 

[Cubonaut875]

I'm curious to see how you adapt to Taxiing. Cool solution for sure. In reality when taxiing I seem to use the brakes quite a bit anyway, I'm not sure how effective that tailwheel steering is anyway.

P.S. In case of another pandemic, I see you are well covered with Yellow microfiber towels - I'm headed to Costco this morning!

 

[Neal]

Yes, I am the new microfiber towel distribution center eastern district FYI - I ordered them in bulk from Costco online. Love these towels!

The tailwheel steering vs brakes is interesting. I can typically use just tailwheel steering if I lead the turn and lead the exit of the turn but sometimes add brakes. So yeah, we'll see how things go. I can say before flight wasn't so good, after flight it was effortless and easily controlled. We shall see...

I hate to touch it after so much time in resolving shimmy but I'm curious with the caster angle set and the replaced hardware (4 set of custom washers) and friction on the tailwheel swiveling if I went back to steerable how would it go.

But in further thought, you really have to wonder how much shock you're putting on that rudder horn for steering. Yeah, we have springs and all, but that's still a lot of "trauma" being passed up from the tailwheel. Is that really a good design and thing to use in the end?

I don't have much history on tailwheel steering so I ask...what percentage of tailwheel aircraft out there do you think uses tailwheel steering? I realize (have heard) some have lockable tailwheels. I'm interested in learning more tailwheel history for anyone caring to share.

 

[Waldom]

Most light conventional gear aircraft since the late 1930s use steerable tailwheels. Prior to that, tail skids were predominant. Some tail skids, particularly on heavier aircraft, were steerable, but most were fixed. Few of these airplanes were equipped with brakes. Since almost all runways had sod surfaces, this worked just fine.

I flew a 1941 J-3 with a fixed tail skid and no brakes installed quite a bit and it is surprising how maneuverable the airplane is on the ground with that configuration. In light winds, the airplane could safely operate from paved runways as well. There is a replaceable iron shoe installed on the bottom of most tail skids.

Some larger tailwheel airplanes, such as the Beech 18 and DC-3, have non- steerable, fully castoring tailwheels that are locked for takeoffs and landings as well as long straight taxis. They are steered on the ground using the flight controls and differential braking. [In that order if you are doing it correctly].

I don't have empirical data, but I think it is safe to say to say that over 90 percent of conventional gear aircraft currently flying are equipped with steerable tailwheels.

If you carry hull insurance, it would be interesting to see how your insurance company views the disabling of existing tailwheel steering.

 

[Neal]

If you carry hull insurance, it would be interesting to see how your insurance company views the disabling of existing tailwheel steering.

Interesting thought/question. Didn't think it would even be a consideration. Maybe that's the nudge to try reinstalling the steering arm now that everything else is dialed in. I sure would prefer having tailwheel steering.