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Nose wheel shimmy adventure

woodmanrog

Well Known Member
Upon landing at X01 on Saturday, I experienced shimmy so bad I thought I had a flat tire. Observers told me the nose gear was oscillating about 90 degress from side to side. WOW,. This had never happened before. I flew home and made sure that the nose gear didn't touch down until it had to on its own. RE: Lots of back stick landing as I normally do. No vibration. I taxied back to the hanger very slowly with no abnormal vibration. Upon examination Sunday, I found that oil had somehow gotten between the Bellville washers and reduced the breakout force to 12 pounds. My partner explained to me I had the perfect storm come together. 1 Lubricant where there is supposed to be dry contact. 2. A tire that had become worn and was most likely out of balance. 3. Landing and putting the nose gear down at a higher than normal speed due to needing as short a rollout as possible. As I said this was very surprising as I had just done the conditional inspection and everything looked normal and the breakout force seemed correct with the gauge. What I neglected to do was disassemble the entire tire and fork mechanism at the inspection. I also measured the breakout force with the wheel and tire in place using the axle hole in the wheel pant. Not a good idea in retrospect. Anyway, alls well that ends well. New tire and tube, cleaning and drying everything that should be.
 
I'm not sure that the Bellville washers should be dry.

The exact same system in my Tiger is specified to be greased - AeroShell 22 or equivalent - every 100 hrs/annual. Just set the breakout force after greasing.
 
Anti Splat Bearing Replacement

Do yourself a favor and get your nose wheel reworked by Allen at AntiSplat. IMHO it is almost as good as sliced bread. I had mine done and the last time I flew, doing some testing, I was able to keep my nose wheel on the ground at over 60 MPH and it was as smooth as a baby's butt. The same held true with landing. No shimmy, bounce wiggle etc. Previously I had to be very careful just like you. I am still cautious about weight on the nose wheel, don't want to push my luck. Observers had told me it was jumping all over the place when taxiing at 10 MPH.
 
Az,
the Bellville washers should be applied in a dry state. The fork is greased to provide lubricated movement. The Bellville's only apply the correct resistance to movement.
Thanks,
Woodman
 
Az, the Bellville washers should be applied in a dry state. The fork is greased to provide lubricated movement. The Bellville's only apply the correct resistance to movement. Thanks, Woodman

Dry will result in a considerable delta between static and dynamic friction. Put another way, the measured breakout force to begin rotation from rest will be much higher than the force required to keep it rotating once it begins to move. This is not a good setup for a damper, and damping is the whole purpose for the belleville application. The best dampers have no delta between static and dynamic. Greased bellevilles will get closer to that optimum, although being a surface friction device they can't reach zero delta.

Greased bellevilles will require a higher clamp force. I don't know if the standard RV nose gear stack will allow enough.

Keeping them dry is unrealistic anyway. Absent dedicated seals, lubricants creep.

Good call Gil.
 
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Dry will result in a considerable delta between static and dynamic friction. Put another way, the measured breakout force to begin rotation from rest will be much higher than the force required to keep it rotating once it begins to move. This is not a good setup for a damper, and damping is the whole purpose for the belleville application. The best dampers have no delta between static and dynamic. Greased bellevilles will get closer to that optimum, although being a surface friction device they can't reach zero delta.

Greased bellevilles will require a higher clamp force. I don't know if the standard RV nose gear stack will allow enough.

Keeping them dry is unrealistic anyway. Absent dedicated seals, lubricants creep.

Good call Gil.

Thanks Dan,

There is over 35 years of operational history on the Grummans with the Maintenance Manual saying to keep them greased...:)
 
Az,
the Bellville washers should be applied in a dry state. The fork is greased to provide lubricated movement. The Bellville's only apply the correct resistance to movement.
Thanks,
Woodman

I've kept mine greased for 10 years, and have never had to adjust the breakout force. Dry would be problematic sooner or later.
 
And please check the installation of the Belville washer

Recently had a shimmy develop on our 10 and found that my building partner had put it in the wrong way. :eek:
As in both in the same orientation.
 
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Upon landing at X01 on Saturday, I experienced shimmy so bad I thought I had a flat tire. Observers told me the nose gear was oscillating about 90 degress from side to side. WOW,. This had never happened before. I flew home and made sure that the nose gear didn't touch down until it had to on its own. RE: Lots of back stick landing as I normally do. No vibration. I taxied back to the hanger very slowly with no abnormal vibration. Upon examination Sunday, I found that oil had somehow gotten between the Bellville washers and reduced the breakout force to 12 pounds. My partner explained to me I had the perfect storm come together. 1 Lubricant where there is supposed to be dry contact. 2. A tire that had become worn and was most likely out of balance. 3. Landing and putting the nose gear down at a higher than normal speed due to needing as short a rollout as possible. As I said this was very surprising as I had just done the conditional inspection and everything looked normal and the breakout force seemed correct with the gauge. What I neglected to do was disassemble the entire tire and fork mechanism at the inspection. I also measured the breakout force with the wheel and tire in place using the axle hole in the wheel pant. Not a good idea in retrospect. Anyway, alls well that ends well. New tire and tube, cleaning and drying everything that should be.

OK, this is exactly what I had happen and in the same circumstances, on my way back from NatFly on the week end. Your post is like I wrote it (except for finding oil on inspection, as I haven't checked it yet and my tire is almost new). I have just started doing my annual inspection but haven't got to the undercarriage yet, as I'm waiting on the new brake pads.

I would be very interested in anything further you may find.
 
We flew Saturday with everything buttoned up and all was well. I am wondering if the Belleville washers on a Grumman are the same as on and RV. I have not been able to locate anything from Van's that says to lubricate between the washers. I do have a problem with the idea of having to torque them to an almost flat position if they have lube in order to get the proper breakout resistance. Just FYI, I did my breakout force without the wheel installed. Another side note, I just found out about an axle from Matco that replaces the original spacer system and allows the nose wheel to rotate more freely without the spacers turning the wheel bearings. I just ordered one and will comment after I have it installed.
 
We flew Saturday with everything buttoned up and all was well. I am wondering if the Belleville washers on a Grumman are the same as on and RV. I have not been able to locate anything from Van's that says to lubricate between the washers. I do have a problem with the idea of having to torque them to an almost flat position if they have lube in order to get the proper breakout resistance. Just FYI, I did my breakout force without the wheel installed. Another side note, I just found out about an axle from Matco that replaces the original spacer system and allows the nose wheel to rotate more freely without the spacers turning the wheel bearings. I just ordered one and will comment after I have it installed.

Mine have been torqued that way for over 400 hours with no problem and has stayed in spec.
 
Moving parts

We flew Saturday with everything buttoned up and all was well. I am wondering if the Belleville washers on a Grumman are the same as on and RV. I have not been able to locate anything from Van's that says to lubricate between the washers. I do have a problem with the idea of having to torque them to an almost flat position if they have lube in order to get the proper breakout resistance. Just FYI, I did my breakout force without the wheel installed. Another side note, I just found out about an axle from Matco that replaces the original spacer system and allows the nose wheel to rotate more freely without the spacers turning the wheel bearings. I just ordered one and will comment after I have it installed.

Bellville washers can be used statically to provide a pre-load, but in the RV (and Grumman) case they are moving parts.

If used dry, I bet something is wearing out - check the surfaces that your bellville washers bear against, I would guess they are starting to show wear areas...

The Grummans use 4 belville washers but of a smaller diameter - a -10 size bolt. I haven't got one to inspect but I seem to recall they each are about 1/16 to 3/32 inch thick.
 
OK! Gil may have made a statement that showed I wasn't clear in my original post. When I was explaining the oil intrusion I meant that it had seeped BETWEEN the two Bellville's. This allowed the washers to rotate against one another. As far as wear, I didn't see anything excessive on the top or bottom surfaces. When I install the new axle, I will again take a close look.
Thanks,
Woodman
 
Perhaps this is just our 9A, but I would expect it to be true of many others. We have oil from the engine (hey, it is a Lyc!) drip down the fiberglass fairing covering the front gear leg. Mostly this is a problem with the front wheel pant--it can look a little ugly. Keeping the Bellvilles dry would be impossible! Oil will seep in between them, so we have always torqued them in the lubed condition. Never had a shimmy, and my partner is an ex-Cessna pilot...

Bob
 
another data point

Did the nosewheel yoke upgrade a couple years ago. The dry belleville washers had some rust between them, so I greased them sparingly when re-assembling. I had to torque them flat to get 20 lbs. breakout!
When doing my annual a few days ago, tested them again, and it was pretty even at 15 lbs in each direction...but as I've seen ( felt?) no shimmy, I am not going to torque the heck out of them to try to get 22 lbs on the scale.
 
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When dry, there's a larger variation of friction while operating, from one time to another, than there is when lubricated. Put another way, the lubricated installation is more consistent, once it's adjusted appropriately.

Dave
 
Do yourself a favor and get your nose wheel reworked by Allen at AntiSplat. IMHO it is almost as good as sliced bread. I had mine done and the last time I flew, doing some testing, I was able to keep my nose wheel on the ground at over 60 MPH and it was as smooth as a baby's butt. The same held true with landing. No shimmy, bounce wiggle etc. Previously I had to be very careful just like you. I am still cautious about weight on the nose wheel, don't want to push my luck. Observers had told me it was jumping all over the place when taxiing at 10 MPH.


Steve, what exactly does Allen do to "rework" the nose wheel?
 
Steve, what exactly does Allen do to "rework" the nose wheel?

I think the topic is discussed in this thread. http://www.vansairforce.com/community/showthread.php?t=85219

Summary: Bearings replaced with permanent bearings, wheel balanced, tire shaved to be circular.

I'm looking forward to hearing some "before and after" experiences with this modification. I have nose wheel shimmy decelerating through 35 knots or so on landing.
 
Upon landing at X01 on Saturday, I experienced shimmy so bad I thought I had a flat tire. Observers told me the nose gear was oscillating about 90 degress from side to side. WOW,. This had never happened before. I flew home and made sure that the nose gear didn't touch down until it had to on its own. RE: Lots of back stick landing as I normally do. No vibration. I taxied back to the hanger very slowly with no abnormal vibration. Upon examination Sunday, I found that oil had somehow gotten between the Bellville washers and reduced the breakout force to 12 pounds. My partner explained to me I had the perfect storm come together. 1 Lubricant where there is supposed to be dry contact. 2. A tire that had become worn and was most likely out of balance. 3. Landing and putting the nose gear down at a higher than normal speed due to needing as short a rollout as possible. As I said this was very surprising as I had just done the conditional inspection and everything looked normal and the breakout force seemed correct with the gauge. What I neglected to do was disassemble the entire tire and fork mechanism at the inspection. I also measured the breakout force with the wheel and tire in place using the axle hole in the wheel pant. Not a good idea in retrospect. Anyway, alls well that ends well. New tire and tube, cleaning and drying everything that should be.

Have you found anything else that may have caused this, or any further to add?

Thanks

Bob
 
Bob,
After the cleanup and retorquing the breakout force I have not had any more problems. I recently changed the the axle to the Matco type and found another significant improvement as the wheel now turns much freer than the original Vans spacers would allow. Had I known about it sooner, I would have invested in the Anti-Splat reworking of the nosegear. I had already purchased the Matco axle before I knew about this terrific mod by Anti-Splat.
 
I haven't had this happen again, but then I have only been landing on grass strips. I normally hold the front wheel off until the elevators wont hold it off any longer. But like you, when it happened to me I dropped the front down as soon as I touched down so I could start braking to get off the runway as there were other traffic on final.
I have a Grove front wheel on mine which has a similar set-up to the Matco (spins freely). But to me it seems it could be a out of balance thing because of the massive RPM the little wheel would have been doing when I dropped it down.
I'm getting the Antisplatt mod done so I haven't checked the break out or checked to see if mine has any oil present yet.
I'll let you know if I find anything when I do it.

Bob
 
Nose Wheel Rework

They remove the roller bearings and put a sealed ball bearing pack in there, redo the race and then balance the tire.

Suggest you ask Allen exactly what the process involves.

MAde all the difference for my shimmy problems.

Steve, what exactly does Allen do to "rework" the nose wheel?
 
Check out Anti-Splatt's website for the video of the front wheel mod. Pretty impressive. Since I had already purchased the Matco axle, I didn't want to spend another $200.
 
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