Nose wheel tire cupping.

[Michael Rath]

I have put 40 hours on my comanche 250 since I bought it this summer. I have picked up a little nose wheel shimmy and I noticed that the nose tire is showing a little cupping in the tread. Air pressure is right on. I looked in the logs and I noticed the previous owner had replaced the wheel and nose tire during the last annual. Anyone else had this problem before? The nose wheel was also changed to the smaller tire. Not sure of the size without going out and looking.

I am probably going to have to get it up on jacks and see if I have anything loose. Just wondering if anyone had a good place to start.

[N3322G]

Michael,

In general, if something was working before and it doesn't work now, I look at the last thing changed - since the Comanche is new to you - it puts you in a tough position - any chance the previous owner might share background with you? I've also read that not all Comanche tires take the same inflation so you might also verify that aspect. IIRC there's a nose tire that takes different inflation than a main on the same aircraft - my twin happens to take 42 psi for all tires. If this is a different tire size, does it take the same inflation - don't know but might be worth checking. If this were a car tire, cupping usually means lack of proper inflation - may or may not be the case here due to the tire size issue you mentioned.

Might be more than one issue. I know twin's can legally put a smaller nose tire on with appropriate paperwork - don't know about singles. Have you looked at the service manual online here for legal tire specs? http://www.comancheflyer.com/NS/index_serv_manuals.php

Also, I've heard a LOT of positive feedback on Bill Creech's book available here http://www.comancheflyer.com/NS/buy-mer ... .php#03-12

In addition, the shimmey dampner does wear out after awhile and can be replaced by Air Parts of Lock Haven Product - I've done this and am happy with the results. If you call them, tell George and Bill I said Hi. http://www.airpartsoflockhaven.com/

Hope this helps.

[Michael Rath]

Thanks Pat,

I will talk to the previous owner and see if he had the same problems. I talked with webco today and they said they would start with the shimmy damper. I have the original dampner and I am sure it is weak at best. They told me how to check it and that you can get one from airparts. They are up to $790 now (ouch!).

It does have the STC for the 15 600x6 on the nose and it does take less pressure than the mains.

This might be related or add to the problem, I have a little brake shimmy when applying the brakes. I am also planning on changing out the brake pads and brake rotors. I have the three hole rotors that are bolted on. Does anyone have a part # handy for those rotors and pads? I would like to get them ordered before I get home next week.

[Ray B]

In less your in love with the small nose tire look I'd try putting the full size 6:00x6 back on before I'd plunk down $790 for the dampener. That's all that was required to stop the shimmy on a friends 250 plus it went a bit faster. My 6:00x6 nose tire is still going strong with close to 400 hours in the last two years .-------P.S. I bought a good used shimmy dampener off e-bay for $50 last year when the new price was still down at the $500 mark! I've seen two more pop up since then. Might be worth while to put one on the shelf in case the time comes when it's needed. Ray B

[Andrew Foster]

I would also check the bushings on the steering yoke. We had a similar issue. Replaced the shimmy dampner with the Air Parts STC replacement. Little if any change. Changed the bushings in the sterring yoke so it mated with the bellcrank much tighter. This elimanted the shimmy we had during takeoff and landing. I'll look up the page number in the service manual. Page 2a14 in the parts maunal, # 15, these are bushings of various sizes, webco has them.

[Michael Rath]

I will check out eBay but the newest used one out there will still be 40 years old. If the damper is bad I don't think it would matter what size tire you run would it?

I have the Wow cowl so I don't think the bigger tire would make much difference on the speed.


I will have to jack it up and check to see how tight everything is. Could be a combination of things. I will take a look at that when I get back home.

[md11flyer]

Michael:

I would start out by balancing the wheel/tire combination. Sounds like the balance is out... maybe a lost wheel weight?
or maybe was never balanced. I had a huge wheel weight on my nose wheel on my airplane.. well huge in reference to the actual weight of the wheel/tire combo...
anyway when I swapped out the regular size tire for the smaller STC'd tire the wheel/tire combo didn't require any wheel weights.
So even though you match up the red dot on the tire to align with the valve stem of the tube.. you still can have a relatively big balance problem as was my case with the original size tire.
And let me tell you you will notice it if it is not balanced with a definite shimmy in the nose wheel.

Anyway before spending money on the other stuff, see if it is balanced first.

Happy Holidays,

Gary

[Michael Rath]

Thanks Gary,

I will start with the wheel balance and while I have it up on jacks I will check for play I any of the bushings. I won't replace the dampner until it is my last option.

I also see that aircraft door seals has a STC to refil the MATCO dampners. Anyone ever use that STC?

[Kristin Winter]

Aircraft Spruce sells the same kit. I would certainly try it before dropping huge coin on a new one.

[Michael Rath]

Thought I would post an update on my uneven nose tire wear and shimmy problems. I might have the part names screwed up so anyone feel free to correct me. After a little inspection we found that the steering arm (in pictures) was badly worn and its bushings were shot. I was told that when one side is touching the nose gear bushing, the other side should only have 1/16" gap between the steering arm and the steering bushing. I had almost a 1/4"due to the wear. This is why the airplane wandered so bad during taxi and I think it added to the shimmy problem because there was so much play in the system.

I sent the steering arm in and had it rebuilt, replaced all the bolts and bushings in the steering arm, dampner and nose scissors. I also replaced the nose wheel tire and had it dynamically balanced.

It is like a new airplane, no play in they system and no signs of shimmy.

[N3322G]

Thanks for posting Michael, we can all learn from this.

[Zach Grant L1011jock]

And there is the demonstration of why it is important that the rollers turn, and are properly lubricated on a regular basis! Thanks for sharing your experience on this.
Zach

[John Wedge]

Michael, thanks for the update and photos. I had been wondering what the end result of your investigation had come to as your problem was one I expect to probably encounter some time in the future and I like to try to know ahead of time based on others experiences / actions.
Would you tell us where you sent it to for rebuild and cost?
Thanks.
John

[Michael Rath]

I sent the steering arm into Webco. John was great to deal with and really took care of me.

The cost of the steering arm repair was around $200 and I spent another $200 for all the new bolts and bushings mentioned earlier in the post. I also had the rollers rebuilt. One side was good and the other was repaired.

I spent another $200 on a new Goodyear flight custom III nose tire and tube.

It was money well spent. It really made a world of difference on how the airplane handles on the ground.

[John Wedge]

Thanks for info.
John