Tailwheel shimmy

[n3833v]

When I needed to get clear of the bracket, I used blocks with carpet padding.

John

[Lee]

I just purchased a new set of tailwheel springs and chains ... I am going back to the "old"/original tension type. It is a Scott 3200 kit ... I was a little surprised at how "stout" the springs are. I am going to go over the tailwheel and take it apart ... I am suspicious of the pawl and I am also going to replace the leaf springs ... something I intended to do anyway. Fun 'n games! R/Lee

[tshort]

I just replaced the springs on mine, too - went from compression springs to the Scott replacement from spruce (can't believe I got a whole set of airplane parts for 19$!)
So far they are great. I feel like steering is a little more positive and I haven't broken any more clips or lost tailwheel steering operating off grass (this was an ongoing problem with the compression springs...)

Thomas

[phantomphixer]

I also had compression springs on my 170 when I bought it. Bad mistake. During last annual, while inspecting thru the top of the horiz stab insp hole(fwd rh slightly tucked under the vert stab) discovered bulkhead pulley, the one with the cable going to the tail wheel had pulled thru the bulkhead. Had to pull the vert and horiz to repair and still had to get a little guy instide the tail cone to assist. Not a difficult repair just an access problem. You might want to check this area very carefully. My 2 cents worth.

[GAHorn]

I also had compression springs on my 170 when I bought it. Bad mistake. During last annual, while inspecting thru the top of the horiz stab insp hole(fwd rh slightly tucked under the vert stab) discovered bulkhead pulley, the one with the cable going to the tail wheel had pulled thru the bulkhead. Had to pull the vert and horiz to repair and still had to get a little guy instide the tail cone to assist. Not a difficult repair just an access problem. You might want to check this area very carefully. My 2 cents worth.

Yep,..to the uninitiated compression springs seem like a good idea... until something like that happens.
It's been argued to me that the compression springs are "FAA" approved, etc.... but the thing to remember is that just because a part is "approved" for generic or specific use, is not the same thing as approval for installation on a particular airplane model. And in many cases, small parts like chains and springs are routinely swapped out/around on airplanes with not-so-much as a logbook entry being made.

[Lee]

I am going out to NQA tomorrow for some maintenance work ... I went ahead and bought a new set of leaf springs, a new pawl ("just in case"), and the aforementioned tension-type tailwheel springs and chains (Scott kit) as well as an F&M oil filter. I also decided to replace all the spark plugs. BAS pull handles and new ignition harness next project. I really appreciate the comments and advice ... helps a bunch! Thanks ... Regards, Lee (N1967C)

[GAHorn]

Lee, it's possibly the "pawl" ...but more likely it's the "pawl spring" that's broken. Does your tailwheel swivel more easily in one direction than the other? That's a common indicator of broken pawl spring.
(The spring is flat spring-stock, shaped like one/half of a hexagon...the ends bearing against the depression within the pawl. This keeps the pawl oriented towards a centered tailwheel.)

[Lee]

Actually, as near as I can tell, the tailwheel swivels with the same force left and right. I moved the control arms on the tailwheel left and right ( movement was less than one inch for and aft) ... it was this apparent play that led me to believe the pawl might be broken or damaged. (The replacement pawl has not been opened ... will return if not needed) I will know more later after I get the tail off the ground. Quick question while I am it, two really: 1) I bought a new set of leaf springs ... George said to put a radius on the first leaf spring above the main leaf spring ... any reason not to put a slight radius on all of them? I think George said the idea was to preclude stress risers, 2) What kind of tool(s) do you all use to set the gap on spark plugs? I have seen two different types, wildly apart in price and also a tool that is used to open the gap up. (I am using Champion REM40Es) Any thoughts would be appreciated. Thanks! R/Lee (Have to hit the rack ... got called out at 01 this morning to do an out and back to Chicago ... long story short, but, thought it was 06! Then, got caught up in Pres. Bush's arrival here in Memphis ... my eyeballs are a little uncaged right now ... long night!)

[GAHorn]

I'd suggest you open up a new topic on the spark plugs question...or there'll end up a non-searchable, non-readable topic about spark plug service in a subject thread about tailwheel shimmy.

[JTS]

Lee,
Hopefully you don't find the problem that I'll describe, but check it out anyway when your tailwheel is disassembled. I had the same symptom that I think you have, where the steering arms moved independantly of the wheel (while the tailwheel is centered). It turned out that the steering arm assembly's center hub came loose from the outside hub/thrust surface that the arms attach to (yes, it is two pieces). The outside portion would rotate while the pawl spring held the inner portion steady. I had to replace the arm assembly. I took the opportunity to put a 3214T arm on to beef up the steering a little.(not much difference in price compared to the 3214 at the time). Incidentally, my Scott 3200 tailwheel was only a few years old when this occured. Good luck, and hopefully it only requires a simple repair/remedy.

Jody

[Lee]

Hi, Jody ... thanks for the information ... I hope to find out what is going on with the tailwheel Saturday. I have looked at Spruce and Wag-Aero and did not see the 3214T you mentioned. Is it possible to weld the arms back to the center hub? R/Lee

[JTS]

Hi Lee,
It seems that Alaskan Bushwheel has adopted the Scott 3200 tailwheel line and the replacement parts also, so just go to thier section on Spruce's site (Or Chief Aircraft Parts) and you'll find the 3214T steering arm part there. If you require a new steering arm and your wondering which one to get, just do a forum discussion search on Scott tailwheel steering arms (3214 vs. 3214T) and decide from there.
Regarding the possibility of welding the inner hub to the outer, if that's the problem, I guess anything's possible and you can discuss the options with your mechanic. Personally, I viewed this part as a precision component, and when found defective I chose to replace it. But hopefully it's a non-issue for you. Best of luck.

Jody

[Lee]

Thanks, Jody ... funny thing ... unless my eyes deceive me, the standard Scott steering arm has a slight bend in the arms ... mine look more like the bent up arms on the Alaskan ... 3214T? I'll know more later and let you all know what I found out. Interesting discussion on this issue in the Tailwheel forum ... similar sentiments. More later, R/Lee

[Lee]

I was out at the hangar until ealry this morning working on the the tailwheel (disasembled and removed excess grease ... ) and replacing the compression springs and old chains for the new chains and springs in the Scott tailwheel kit ... test flew this afternoon ... everything worked as advertised ... nary a shimmy and solid steering on the ground. I think the response with the tension springs is as good as with the compression. Previous note about slack in the chains where before there was none due, I think, to the shimmy stretching the links. I have a slight amount of slack now but, when I jacked the tail up, I noticed the chains were snug. Tailwheel leaf springs next. Thanks for all the help ... I very much appreciate it! Regards, Lee

[GAHorn]

With your new mainspring installed, you might need to readjust your chains to achieve the proper tension. They should be "just" tight at 2,000 lbs. aircraft wt. with the tail on the ground. The tension springs allow for the wheel to settle downward in flight. (Yes the 3200 steering arms have a slight upward bend to them normally. The 3200T has 90-degree upturned ends.)