New Shimmy

[VetRepp]

I  have an 2006 Ovation2. On Landing today upon rollout  - braking (I was slowed down to probably @ 30-40kts when I started to brake) I got a moderately severe Nosewheel shimmy. I let off brakes and Shimmy stopped. It braked smoothly and evenly - did not pull to either side. The landing was smooth.  When stopped and taxiing there was no shimmy. Take Off was w/o issue.

The shimmy was bad enough that I don't feel comfortable flying it until I know why. There is nothing obvious with any of the gear. The Hockey pucks were replaced on the mains at last annual @ 3 mo ago. The tires were replaced 2 annuals ago and Hi speed balanced. Tire pressure is normal. The brakes have also been recently done. I never brake hard (I usually use full runway to slow since I pay for the brakes)

I Plan on doing a Hi speed Taxi  up to Rotation speed then stopping when I can get back to airport in a couple days. Talked briefly to my A&P, He thought a Hi speed Taxi was a good Idea, but he didn't  have good possibilities'.

Any Thoughts on causes, or what I should look or test for would be greatly appreciated.

 

Thanks

Roger

[PMcClure]

When was last service (greasing) of the nose gear?

 

[N201MKTurbo]

Put it up on jacks and see how much play you have in the truss bushing by moving it for and aft. Move it like it is turning and see how much slop you have in the steering horn. You will have to have someone hold the rudder or peddles or just look under at the steering horn to see how much slop you have. If they are excessively loose you will need to fix them.

[Guest]

Although it does not specifically effect your plane, the concept is the same.  See SB M20-202 concerning nose wheel castor angles, the numbers for your plane will be in the maintenance manual.

Clarence

[N201MKTurbo]

When My old plane had a shimmy problem, I found that if I tapped one of the rudder peddles kind of hard it would stop the shimmy. Also a bit of elevator pressure would sometimes stop it.

Not a fix, but something to get you by until you get it fixed.

[Loogie]

FYI, high speed taxi tests are responsible for a lot of bad things. A Long list of bad things...trying to find problems or duplicate an event during a high speed taxi can lead to a myriad of other issues.  I would try and find the problem in a hangar, with the plane jacked up first. If there is a problem a good mechanic will find it. Just a thought...

[VetRepp]

Thanks to all the replies, I think I will forego the Hi speed taxi afterall and just put it up on jacks.

2 hours ago, PMcClure said:

When was last service (greasing) of the nose gear?

It was greased at annual and there is still abundant grease in the fittings

 

2 hours ago, N201MKTurbo said:

Put it up on jacks and see how much play you have in the truss bushing by moving it for and aft. Move it like it is turning and see how much slop you have in the steering horn. You will have to have someone hold the rudder or peddles or just look under at the steering horn to see how much slop you have. If they are excessively loose you will need to fix them.

The movement was checked at the last annual (3 mo. ago)  - But I think this more likely the issue. It just seemed strange to occur at relatively hi speed albeit modest braking and then stopped when I let off the brakes.

Thanks again for all replies.

Roger

[carusoam]

It may help to familiarize yourself with the worn parts related to Mooney nose wheels.  I don't suspect Long Bodies to be any different than short ones...

Dmax wrote a paper and titled it 'the eight second ride’.  The time a bull rider is expected to stay on the beast....

He explains what to look for and how to measure it.  LASAR probably has the parts...

Doing a high speed (fill in the blank)......with an expected problem, doesn't sound logical to an engineer.

maybe you might find it does something worse.  A lot worse...  The airplane designers and mechanics have put a lot of work into these things.  They have tests for anything that can wear or needs adjustment without leaving the ground.

Best regard,

-a-

[N201MKTurbo]

Just now, VetRepp said:

 It just seemed strange to occur at relatively hi speed albeit modest braking and then stopped when I let off the brakes.

 

The braking will compress the pucks and change the castor, which seemed to excite the shimmy in your case. It seems counter intuitive because the compression will increase the castor and make it more stable. When my old plane was all sloppy it did the same thing.

[bradp]

On June 8, 2016 at 8:57 PM, N201MKTurbo said:

The braking will compress the pucks and change the castor, which seemed to excite the shimmy in your case. It seems counter intuitive because the compression will increase the castor and make it more stable. When my old plane was all sloppy it did the same thing.

Sounds like a bad shopping cart wheel.  

[Marauder]

I'm following this thread since the shop called me earlier this week and indicated a component was badly worn on my nose wheel. I told them that I had no directional control issues with the plane and they were really surprised. They are replacing the part in question. It is not the nose truss but something behind it. Anyone have an idea what it is? I am going to ask to look at the part.

[mooniac15u]

Shimmy problems seem to typically be nose gear issues but in this case the problem occurs when braking so it seems like a brake problem on one of the mains could potentially be the source of the issue. Is it possible you have a warped brake disc on one side?

[jhbehrens]

I experienced the 'eight second ride' a week ago in an S - exactly as Don Maxwell describes. We checked nose gear rigging and found the nose wheel was about an inch too far forward. The procedure to measure this is described in the article as well as in the maintenance manual. You level the airplane on jacks. The stabilizer will beat about shoulder height. Then you hang a plumb line over the trunnion and it should be roughly on the centre of the nose wheel axis. I my case it was 1" back. That can cause severe issues on roll-out. No idea why I never noticed before.

Check you have the spacer installed on top of the shock discs as per the SB or attached drawing. We reversed the collar (it had an off-centre hole) so there is more metal between the bolt and the discs and that pushed the wheel back to where it should be. There are also two different sized collars - you could swap the -005 for the -007 model to get a similar effect.

Nose Gear Assembly.pdf

Edited June 12, 2016 by jhbehrens