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Nosewheel shimmy?

Ed_Wischmeyer

Well Known Member
Really? On an RV-9A?

Has happened twice in the last month, never in the preceding six years.

Vibration stopped after two cycles, both times. Moderate intensity.

Both landings probably had exceptionally gentle nosewheel touchdown.

Condition inspection was two months ago, but the only thing done to the nosewheel was to grease the fitting on the fork.

Nosewheel is a sealed unit. Tire pressure looks good visually.

And, of course, leaving for Oshkosh next week, good Lord willing and the thunderheads don't rise...
 
Im sure you checked the breakout force but I found mine had reduced in force after about 80 hours. I have the AntiSplat Lip Skid and that made it a bit more of a pain to tighten but it worked.

Good luck on it.
 
Five things to check: 1) breakout force. 2) tire pressure (gauge, not an eyeball check). 3)Wheel bearing preload correct. 4) nose wheel fork grease ok (don’t want sticky turning action). 5) static wheel/tire balance ok (at least not way out out of balance).
 
Shimmy

My nosewheel shimmy turned out to be a shimmy in the mains. Didn’t realize it until I taxied at high speed with the nose up. :)

Barring that: Maybe the grease worked its way in over the last two months and loosened your breakout force?
 
Barring that: Maybe the grease worked its way in over the last two months and loosened your breakout force?

If it is grease that went too far, can that be fixed by tightening things up or does that require disassembly and cleaning?
 
You could try tightening, but sometimes grease and oil get between the washers, and you may have better luck disassembling and cleaning it..
 
Ed, I just helped A friend fix this exact issue. Jack the nose wheel up and check that the tire is true by rotating it slowly and seeing if it has an oblong shape to it. Once we balanced his nose wheel that fixed the shimmy.
 
Nose tire pressure was 25, way low, two months after condition inspection by a new AI. Ran the tire inflator, still 25. Then the pressure gauge broke in two. (!) now it’s inflated to 50. While we’re at it, checking the mains. Wheel pants look nice, but…

Embarrassed, yes, but rather embarrassed than hours of work.
 
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shimmy

If these procedures do not correct problem consider replacement of the bell washers, available from Vans.
 
Landing today gave nosewheel shimmy. Again. Went back tonight and measured tire pressure: 28, down from 50. I'll order a new tube tomorrow and get it installed while I'm at Oshkosh. (I don't park at KOSH).

Hopefully, these guys will get it right. At my home airport, they botched the job and had to order another tube. Long story...
 
Landing today gave nosewheel shimmy. Again. Went back tonight and measured tire pressure: 28, down from 50. I'll order a new tube tomorrow and get it installed while I'm at Oshkosh. (I don't park at KOSH).

Hopefully, these guys will get it right. At my home airport, they botched the job and had to order another tube. Long story...

Did you recheck the breakout force? A fish scale works, I use a luggage scale that holds the peak reading. Check to the left and to the right.
 
Five things to check: 1) breakout force. 2) tire pressure (gauge, not an eyeball check). 3)Wheel bearing preload correct. 4) nose wheel fork grease ok (don’t want sticky turning action). 5) static wheel/tire balance ok (at least not way out out of balance).
Hi, I want to make it clear I am not a builder, so please forgive any ignorance in my query that may seem obvious to an experienced builder. I am having significant nosewheel shimmy upon landing in my 7A as of late. I won't claim my landing technique may not be at least part of the problem, however this shimmy has become more pronounced as of late and I do try to keep the back pressure on landing. (I also keep back pressure on the stick during taxi, and don't seem to have a shimmy issue, even at speed) I've been through the forum and haven't seen many references to the shimmy damper, and what the 'breakout force' refers to, but I am assuming this is the force required to move the nose gear left/right when the nose gear is off of the ground. Can you tell me what this force should be? I have a sealed bearing and the wheel seems to rotate freely, and the tire pressure is at 35lbs. Any help you could provide would be very much appreciated. Thanks
 
The spec is 26 pounds.
But having that number and not knowing how to properly measurement it is of no value. I strongly suggest you get a copy of the plans. They are invaluable for maintaining and repairing your RV. You can get a digital copy for your model for only $10 from fans. Not being a builder it would take you a little bit of digging through them to find the information but I think that would be a good education process for being an owner of an RV.
 
Breakout force and rolling resistance of the front Tire are key. Also important is to verify the bolt holding the nose gear onto the engine mount is tights and not oval. If those 3 things are correct I have never seen a shimmy issue.
 
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