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  #1  
Old 03-26-2012, 08:47 AM
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woodmanrog woodmanrog is offline
 
Join Date: May 2005
Location: Florida
Posts: 444
Default Nose wheel shimmy adventure

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.
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  #2  
Old 03-26-2012, 09:18 AM
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Exclamation

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.
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  #3  
Old 03-26-2012, 09:19 AM
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N42AH N42AH is offline
 
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Default 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.
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  #4  
Old 03-27-2012, 07:56 AM
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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
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  #5  
Old 03-27-2012, 08:28 AM
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Quote:
Originally Posted by woodmanrog View Post
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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Last edited by DanH : 03-27-2012 at 08:30 AM.
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  #6  
Old 03-27-2012, 09:46 AM
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Quote:
Originally Posted by DanH View Post
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...
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  #7  
Old 03-27-2012, 08:00 PM
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Quote:
Originally Posted by woodmanrog View Post
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.
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  #8  
Old 04-07-2012, 09:06 AM
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Janekom Janekom is online now
 
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Default 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.
As in both in the same orientation.
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  #9  
Old 04-08-2012, 08:36 PM
RetiredRacer RetiredRacer is offline
 
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Quote:
Originally Posted by woodmanrog View Post
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.
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  #10  
Old 04-09-2012, 08:37 AM
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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.
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