Nose wheel shimmy

[DrTimcat]

Just checking with the forum. I have an ovation that during the last several landings, notice a significant shimmy upon the nose wheel touching down. The last time it shimmied and pulled hard to the left inspire of right rudder force. After slowing, was able to steer and taxi fine. Any ideas?

[DrTimcat]

sorry...inspite of right rudder force

[Guest]

Any recent maintenance on the nose gear or steering controls?

[DrTimcat]

Had a tire and tube replaced several months ago. have had 20-25 T & L since then. Shimmy just started. 

[haymak3r]

Have had this before, though I feel there are multiple reasons/spots this could occur.. If there are worn steering end links, or nose gear bushings, this could be a source of the shimmy. During my first annual, I pointed this out, and we checked the clearance on everything. There was one joint that is super close to not meeting the maximum clearance. I believe it was this one as pointed out in this pic from lasar's site, as it was the first one I had show up in a google image search:

 

We did order a slightly thicker shim for here, and if it continues to progress, I'll replace it during my next annual. One thing that has since solved this, is that on landing as the nose wheel touches down, I continue to keep full after elevator control until I am about to turn off the runway. I have not had the wheel shimmy again since. Again, this may not be your issue, but this has been my experience.

-Chris

[tmo]

At the risk of sounding stupid, did you check the inflation pressure? The wheel might look right when standing still, but be somewhat underinflated - just enough to flex in a weird way upon touchdown.

[Guest]

Tire pressure, loose wheel bearing, lost wheel balance weight, worn or sloppy parts in the nose gear.  You’ll need to jack up the nose to start your investigation.

[87-205SE]

800 hours in a 81 201 flying club Mooney.    800 Hours in my first Mooney a 83 201.   In both of these planes I would point the airplane down the runway (correcting for wind of course) and they flew straight.   I  bough a very low time 87-205 Mooney 2 years ago which I love to death.    Bought it in Seattle and flew it home to Detroit in a day with two fuel stops.  Trues at 165 plus at altitude.   Every takeoff in this plane demands about 5 pounds of force on the bottom of each pedal and tiny corrections  to keeps it straight down the runway.   My only partner actually was trying to keep it straight with brakes as he transitioned from a Tiger although he has significant Mooney time.  After slowing down on takeoff and a screech by myself, he doesn't do that anymore.    I don't think there is any kind of shimmy damper and the "wrench" says we should pull the belly pan and take a look for any kind of "centering springs" or whatever device is used to keep the nosewheel straight, if there is anything, there must be something to add some kind of resistance to nose wheel deflection during takeoff......or is gyroscopic force the only thing out there?     Very low time two owner airplane always immaculately maintained.well appointed and solid.  We deal with it on every takeoff and landing is never an issue.    Anybody help with this issue or is that I just never noticed a sensitive nosewheel on takeoff before?         Thanks   Buds...............Steve 

[Guest]

12 minutes ago, 87-205SE said:

800 hours in a 81 201 flying club Mooney.    800 Hours in my first Mooney a 83 201.   In both of these planes I would point the airplane down the runway (correcting for wind of course) and they flew straight.   I  bough a very low time 87-205 Mooney 2 years ago which I love to death.    Bought it in Seattle and flew it home to Detroit in a day with two fuel stops.  Trues at 165 plus at altitude.   Every takeoff in this plane demands about 5 pounds of force on the bottom of each pedal and tiny corrections  to keeps it straight down the runway.   My only partner actually was trying to keep it straight with brakes as he transitioned from a Tiger although he has significant Mooney time.  After slowing down on takeoff and a screech by myself, he doesn't do that anymore.    I don't think there is any kind of shimmy damper and the "wrench" says we should pull the belly pan and take a look for any kind of "centering springs" or whatever device is used to keep the nosewheel straight, if there is anything, there must be something to add some kind of resistance to nose wheel deflection during takeoff......or is gyroscopic force the only thing out there?     Very low time two owner airplane always immaculately maintained.well appointed and solid.  We deal with it on every takeoff and landing is never an issue.    Anybody help with this issue or is that I just never noticed a sensitive nosewheel on takeoff before?         Thanks   Buds...............Steve 

From the maintenance manual,

[PT20J]

The Mooney doesn't have bungees or nosewheel centering devices like some airplanes -- it's all rigid linkages between the nosewheel and the rudder. A clever articulation of the steering horn centers the nosewheel in the well when retracted. It's really just the caster setting that keeps it going straight. And because it it rigid, the nosewheel won't be centered on touchdown if you're holding rudder for a crosswind. To keep the nosewheel close to center in this case, the amount of steering is restricted and this is what causes it to have a limited turning radius and makes it susceptible to towing damage.

[hypertech]

I fought this when I first bought my plane.  Tracked down and replaced every loose bearing we could find.  Made it better but not perfect.  What finally got rid of it was putting in a Laser rebuilt steering horn.

[takair]

@M20Doc…..I know there is the SB on the older Mooneys for the spacer…..but I also seem to recall that the collar on top is asymmetrical, and if installed upside down can cause the same geometry problems that cause the darty behavior and possible shimmy.  Do these things apply to long bodies?

[Alan Maurer]

I had the same shimmy with my Ovation. It was corrected by Sarasota Avionics by adding few tighter components to the nose wheel gear.

About for hours work and it worked. This was an easy fix.

[Guest]

16 hours ago, takair said:

@M20Doc…..I know there is the SB on the older Mooneys for the spacer…..but I also seem to recall that the collar on top is asymmetrical, and if installed upside down can cause the same geometry problems that cause the darty behavior and possible shimmy.  Do these things apply to long bodies?

 

[DrTimcat]

What happened on my plane was the shaft 720095-17 froze due to corrosion and sheared off. There is a grease fitting that lubricates that shaft but apparently the previous owner was not getting adequate grease in this area and the end sheared off. Fortunately I didn't have a runway incurrence when it finally gave way. Finding the part was difficult because in in my ovation maintenance manual, it doesn't give a part number for the shaft like this manual does. It simply calls it the steering horn assembly. Lazar rebuilds them, but finding the part proved adventurous. It is repaired and will definitely be lubricated in the future.

[Stetson20]

I had a pretty severe shimmy on touchdown today. Did a couple high speed taxi passes and nothing near what I experienced at touchdown. I was probably doing 75kts and touched down a bit firmly, but didn’t bounce. Noticed a flat spot on a newly installed main tire. 
 

Edit:  High speed taxi up to 50kias..
 

Anyone have this happen with a flat spot on the tire? I looked at the nose gear assembly but nothing seemed amiss..