Tailwheel steering malfunction

[Dave Dollarhide]

We were about 30mph on the landing roll in my RV-4...friend in the back, when it started left. Right rudder was not working, right brake was not bringing it back very quickly, due to the aft CG. We were headed for the ditch on the side of the runway, but as we slowed, the correction finally took hold and we managed to only whack a runway light with the left flap, with minor damage.

What the **** had just happened, ran through my mind. Tailwheel steering had worked to the left and not to the right, giving a ratchet effect. In the "ride the bicycle" mode, every time I moved the rudder a little left, the tailwheel did the proper thing, but to the right...nothing.

Back on the ramp, I pulled the tailwheel assembly apart and found the spring loaded key gummed up with grease and dirt. It was not fully engaging the slot in the steering bar. Due to slight differences in tolerance, it was catching the slot to the left, but not to the right. It was a minor mechanical issue, with major impact.

I cleaned up the shaft and flushed the spring and key with WD-40. I had been using wheel bearing grease, and did again on the shaft, but this time, I oiled the key and spring area with 30W motor oil. It's working fine now, but it's one of those minor details to pay attention to.

The next day, at a local RV fly in, a friend was familiar with the problem said to only use motor oil on the tailwheel shaft, pulling it apart for re-lub every 6 mo. or so. He further stated that newer assemblies don't have the zerk fitting, since grease can gum up the works, especially on sod runway operations. Also, there is the fact that grease never really gets to the shaft properly using the zerk fitting anyway.

I'm probably "Johnny come Lately" on this issue, but wanted to get this version of tailwheel steering problems on the forum.

Dave Dollarhide

[dan]

Had the tailwheel steering go on me twice so far. Here's the deal:



The "key" wears and actually builds up little burrs on the corners that can prevent it from sliding in and out of the slot properly. You might think it's just "gunk" and grime in there, but mic the key and you'll see what I mean. In the crappy photo above, the little burrs on the corners caused the key to "widen" inadvertently and jam up. The result was that the key would get forced into the slot as the horn turned on it, and then the spring didn't have enough force to overcome the friction of the now very close tolerance fit in the slot.

In fact, when I took it apart, the key refused to come out regardless of degreaser spray and cleaning it up. Fortunately the slot is open on the other side of the shaft and I could poke something in there to force the key out.

A quick rub on the Scotch Brite wheel polishes these burrs right out (go light, just enough to square off the corners) and it's back to 100% for another 400 landings or so.

Any time you have your tailwheel apart, do yourself a favor and check for these "corner burrs." If you don't, then you may be in for a surprise sometime on landing.

)_( Dan
RV-7 N714D (725 hours)
http://www.rvproject.com

[Bob Martin]

I agree 100% with Dan and ditto his comments.....
my -6 did exactly the same thing and my hangarmates did too.

We bought new full swivel tailwheel assemblies and converted from the original design, non full swivel and chains to the full swivel with steering link and love it......but when they came from Vans with no zerk fitting I asked Vans why and they said the grease would not travel up and down the shaft, so just service it very 25 hours!!
sorry, but I'm too lazy and like to fly too much, so I had a machine shop mill a groove on the inside up and down to let the grease move along the shaft.
But......that didn't keep the burring problem from happening.
I read with interest about the motor oil for lubing.
Fly Safe
and know thy airplane.
Love this forum.
Bob Martin

[Bob Martin]

Additionally, we didn't have any landing problems when we found ours burred, but noticed the steering arm had crossed over to the wrong side and looked funny. The burred pin wouldn't extend and it let the wheel castor around to the other side. I now see we were LUCKY......thanks for the heads up!
Bob Martin

[CFI1513840]

I remember reading about this before on Dan's web site. It's not something that I'm looking forward to when I'm flying my 7. Would it help to use hardened steel keys?

[Kyle Boatright]

A hardened steel key wouldn't be a *great* solution. You want the key to be the part that wears, not the rest of the assembly, because the key is much easier to replace than the parts it wears against.

[Sam Buchanan]

It's not something that I'm looking forward to when I'm flying my 7. Would it help to use hardened steel keys?

This isn't something to spend a lot of time worrying over. Just inspect the pin each time you service the tailwheel at the condition inspection and you shouldn't have any surprises. The time the pin froze up on my RV-6 I was able to tell the swivel mechanism was getting a little sticky during preflight inspections and while pushing the plane around the gas pump. As others have stated, a minute or so with a piece of sandpaper was all it took to fix the problem.

On a related note, one of our local RV-4 pilots had the aftermarket tailwheel steering link on his plane break recently. He didn't know the link had broken on the preceding takeoff until he started taxiing to parking at a pancake breakfast. The landing was without incident and he subsequently flew the plane home and landed at his grass strip after removing the link. The taildragger RVs are pretty docile even without the normal tail steering.

Sam Buchanan (RV-6, 700 hrs)

[John_RV4]

I just finished installing my fs tw. I replaced the tailspring also since the original is not compatible.

I taxied the plane around and am somewhat taken aback by the ground handling. The steering is generally looser than it was but the real thing that has me a bit concerned is this: When I lock the brake on one side and spin the plane around, the swivel works fine. However, when I want to stop the turn, I have do it with brake since there's no rudder connect. The catch is that it seems to take a lot of rolling straight ahead for the tailwheel to straighten itself out. I can't really tell how to make it re-engage nor can I feel it click in like some do.

I taxied over some bumps and felt the tailweel break free. Didn't expect that. I guess I'm concerned that if I were given a "no delay" takeoff, I might take off with the wheel cocked at an angle. I sure wouldn't want to land with no tailwheel steering.

Anyway, I decided not to fly it, although I desperately wanted too :-(
Anybody else a little uncomfortable with this setup ?

Thanks

John

[KirkGrovesRV8]

Just as another data point, A friend of mine nickle plated my whole tailspring and tailwheel fork assembly and at the same time coated the inside of the tailwheel fork with a industrial coating called "Rulon" I believe, don't hold me to that name. It is a heavy duty coating used in very big and heavy machines(like earth movers) he told me it is a self lubricating substance and the more it wears the more it protects. Now I only have a little over 85hrs on the plane but I have pulled the tailwheel twice just to check and you can't even tell that there has been any wear at all, none on the key and none on the inner surface of the tailwheel fork.
Anyway just another thing to consider..

[tin man]

John RV4
If you keep your tires a little on the soft side (25lbs) you can pull the tire right off the rim by locking up one brake and spinning the airplane. Ask me how I know...... Airshow 400 miles from home, tire went flat grounding the wheelpant to the tarmac. No tube to replace. Not fun,
Tom
RV3 2000 +