Nose Wheel Vibration

[crxcte]

Anyone experience a front nose wheel vibration right after lift off until the gear is put up?  I had my shock disks changed and never notice it before. 

 

Thanks

ctr

[GeorgePerry]

The first thing I would check is the steering horn and truss to make sure everything is tight.  There should be little or no play in your nosewheel assembly.  The next thing I would check is the tire.  If it's been sitting for a long period of time it could have developed a perminent flat spot and might need replacing.  Both can be easily checked by lifting the nosewheel off the ground.

[Kwixdraw]

You may want to check the setup of your nose gear too, if it was changed from the original type pucks to the lord type and the shock absorber removed. I believe others have cured this problem with rigging adjustments.

[crxcte]

Was not the original pucks just replacement of the lord shock disks.  There is a little play as in side to side in the steering horn.  Tire is fairly new and the plane is flown at least once every 2 weeks.  No vibration occurs until lift off then it stops after the gear is raised.

[Sven]

Could it be an unbalanced tire? Can tires that small be unbalanced?

[Kwixdraw]

See the "landings gone wild" post, it has the link to Don Maxwells publications where he explains the SB on the nose gear and how to check the rigging. I suspect it is just on the margin and the shimmy is when the weight comes off the gear and makes the trail just a bit too verticle to stay stable.  The short body Jeeps do this too if you lift them and the caster gets too steep on the steering swivels.

[crxcte]

Thanks for the info.  I'll check Maxwell's site on the nose rigging.

[Alan Fox]

This is very common , The collar that holds the stacks into the nose wheel truss is either upside down , or there was a shim left out , If the stack is too long , there is not enough caster to keep the nosewheel from shimmying , This can get real bad to the point of losing steering control of the aircraft , When I converted my donuts from goodyears to lords I had this problem , Flipping the collar so the the half of the collar that is longer to the bolt hole (the hole is off center a few thousandths ) is facing the truss and stack stopped mine from shimmying , and my airplane is a b model , so no shimmy damper either , I couldnt believe this fixed it....

[crxcte]

I see, the collar may of been upside down.  Looked like it was symmetrical.  I will check, thanks.  

[Sven]

N74795, Thanks so much for your explanation of the shimmy. Our 20D has been really bad since I started flying it and I thought this was just the way Mooneys were made. So, if I'm understanding what you said correctly the collar definitely has an up and down because the hole is slightly off "center." But I am a little dense in understanding which way is up from your explanation. I'm attaching a diagram with the placement of the hole being exaggerated. Can you tell me if it's A or B? I'm thinking you're saying it's B but I want to make double-sure before I put it all together this week. Just looking at the collar you can't really tell there's a difference. Thanks so much for your help.

-Sven

[carusoam]

Sven,

Quick heads-up.  Your attached image is not coming through for me...

I think images that are .jpg in nature post easiest...

-a-

[crxcte]

From the other Mooneys on the field it look like image B is correct.  I'm going to need to a tool to move mine around to verify.  Your images are viewable on my PC.  The side that goes to the bottom would be the dirty/rusty side.

[Sven]

The image is a JPG but I'll change something and give it another try. I'm a Mac so that might be the problem, too.

[carusoam]

I'm a PC, and I am still unable.....

-a-

[Sven]

Let's try this GIF.

[carusoam]

I can see the images......

-a-

[conom06d]

I have this problem a bit but i have no idea what to do to fix as im lost in what youre all talking about switching or what those pics show. What do i tell my mechanic to be the problem or to be done to remedy it?

[Sven]

I'll be putting up a separate post called "Nose Wheel Vibration Solved" in an hour or so. I had an amazing experience with the folks at LASAR you need to know.

 

-Sven

[conom06d]

ok thanks sven! They are based near clearlake area right?

[Sven]

Yep. Lampson is 1O2. It's a great airport and there's a place to eat there with odd hours. Some days it gets really warm there so pay attention to density altitude. As a student I did a fast touch and go there in August once and it was close to 9,000 ft. I think the temp had to be 190° in the shade.

[carusoam]

Sven,

Unable to read the follow up post.  Nose wheel vibration solved....

Did you cut and paste from a word processor?  I am blocked out from reading it.  Some other people will be blocked also, but not everyone.

maybe you could re launch?

Best regards,

-a-

[Sven]

Let me know if you can see this. Sorry. I didn't know copy-paste from a word processor was an issue. I did use a microsoft product. Maybe that was the issue. Here is the post:

 

Like many other Mooney drivers, we’ve been experiencing some problems with nose wheel instability and understood that this is just the way the Mooney works. Yesterday I found out this is absolutely not true and found out the reason why from the folks who discovered the problem in 1977.

My partners and I own a very rare fixed-gear Mooney M20D, which is basically an M20C. We’ve owned it for a little over two years and have been working closely with our very kind A&P to address 15 years of neglect in a harsh outdoor coastal environment.  Each year we tackle a big new project based on the triage skills of our mechanic. This year we tackled the gear.

It turns out our shock disks had not been changed in 20 years. So we took the gear off and decided to sandblast all the rust and grime and put on a new coat of paint. Yesterday, something happened I place in the “guardian angel” category. The first paint job didn’t work (bad paint). So I stripped the paint off and started over. I reached for the small collar that holds the shock disks in tension at the top of the stack. I was about to rub off a little rust with a brass brush but could not find it. So, I reached for the steel wool. As I rubbed the top rim of the collar a strand of wool got wedged in a very small crack that before this, went completely unnoticed. I grabbed my reading glasses and discovered this crack went through the entire collar. As I held it up I could also see the collar was bent. This part was destined to be placed back on the plane. There’s no way I could do that so I called my friends at LASAR and explained my situation. And here’s where the good stuff begins.

I talked with Dan who is the “know everything” guy. During our conversation he asked me if we’ve been having problems with taxiing, take offs and landings. You betcha we have. In fact, a couple months ago the plane shot left and blew a tire on touchdown. I almost went into the rhubarb and took out a runway light. I couldn’t explain what happened. It felt like it was in a rut and no matter what I did the plane was going left. He told me the problem was that collar.

Back in the mid-late 70’s LASAR was getting complaints about nose wheel instability. They discovered that the collar was not tall enough. This created a situation where the centerline of the nose wheel was aft of the datum. Basically, it’s trying to push a backward shopping cart wheel forward. Impossible, right? The nose wheel wants to make a 180° turn to be stable. That’s the shimmy we’ve been experiencing taxiing and the source of the squirrely take offs and landings. The fact that our shock disks were outdated made the situation even worse. The straighter the nose gear stands, the more forward of the datum the nose wheel is. I was carrying 4 adults which placed my CG further aft making it very bad. That’s three strikes against me.

LASAR was reporting these findings to Mooney but they weren’t listening. Then he said there were three accidents that got the FAA’s attention. Mooney listened and the FAA issued service bulletin #202. LASAR fixed the problem by putting special washers under the collar which caused the nose wheel to move aft of the centerline where it belonged.

Dan told me he suspects that when I had the blowout the nose wheel was cocked to the left and when it touched, it was so far left that it shot me over. I was even giving it a slight amount of right rudder before touchdown due to a small crosswind. He said if I had not caught that crack on the collar, I was headed for certain disaster. The new collar places the bolt center hole a full 1/8-inch higher. He said that a variance as small as 1/32 can cause the shimmy.

So, thanks to bad paint, steel wool, reading glasses and Dan at LASAR, we will have a safer Mooney. I know this explanation was long but it helped me to know the engineering behind the problem. Pushing a pivoting wheel backward is a recipe for disaster and I narrowly avoided that scenario.

The only way you’re going to see that collar is to take off that collar. You can do it without the tool by jacking up the plane and putting the weight on the nose. You’ll need to rent the tool to put it back on, however.

I hope this helps any fellow Money drivers out there with similar issues. I really hope this helps someone else avoid an accident. If our runway wasn’t 150 ft wide, those fixed-gear Moneys would be even more rare.

 
-Sven

[carusoam]

Perfectly visible.  Thanks for sharing your situation and solution.

Have you seen Jezzie's photos of before and after paint on the landing gear bits and pieces?

http://www.mooneyspace.com/index.cfm?action=gallery&userGallery=1429

-a-

[Sven]

Yeah. Ours looks exactly like his did. I just finished the last of the priming today. Even green they look great. We also had to delaminate a flap during this annual because of a delaminating aluminum block. Once the flap is back together I'll be posting some photos as well. Our Mooney is up on jacks and because it's a fixed-gear, we've never seen what it would look like if we could put the gear up. It's very tempting to have it converted but the guy we bought it from made us promise never to do that and he refused to give us the kit. I'm anxious to get back in the air and shoot some "normal" landings and taxi without the wobble.