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1998 RV6A - What is wrong with my nosewheel???

D

dalemaher

Active Member
Hi,

I have a nosewheel shake / shimmy that seems to be getting worse despite efforts to reverse it!

Here is a landing video which shows significant vertical shimmy (no horizontal that I can detect). The motion starts basically as the wheel makes contact with the runway, with the worse of it at about 14 seconds in as I am slowing from 25-20 knots.


I have:
- brand new tire
- sent the wheel to Antisplat Aero for the bearing mod, wheel balancing, and shaping of the tire
- torqued the axle and inflated to Antisplat's specs
- replaced the nosegear attach nut / bolt at the engine mount (no detectable wear in the attachment hole)
- breakout force 28lbs

I had a good talk with Al from Antisplat about this and he was not able to shed any new light based on my description. fWhen I received the wheel back from Antisplat, it did get a little better for a while, but now it is getting much worse to the point that the deceleration shimmy is now a front end shudder.

Any advice appreciated!
 
You could add a nose gear stiffener, usually wood. My 9A nose gear has a resonant shimmy at exactly 17 knots taxi speed - disappears at 16 or 18 but reliably will shimmy at 17. I call that my "taxi too fast" alarm.
 
Another vote for the wood nose gearleg stiffner. Did mine many moons ago. Notably I don't have those on my main gear legs.
 
I didn't see what tire pressure you are running. When I had the nose at 40 PSI I would get a shimmy like that. Reduced to 35 and it has mostly gone away. 40 mains, 35 nose seems to be a good balance for my 6A.
 
paulsmeds said:
I didn't see what tire pressure you are running. When I had the nose at 40 PSI I would get a shimmy like that. Reduced to 35 and it has mostly gone away. 40 mains, 35 nose seems to be a good balance for my 6A.
Click to expand...
I've tried nosewheel pressure all over the place! After talking with Al at Antisplat Aero, he recommended 50psi, which is what it is set to now. My mains are 35
 
Unweight the nose (Weight on tail) and make sure the nose gear strut is rotationally solid in the strut socket. It’s a well-known weak spot in the -A model design and the subject of numerous threads here over the years. Review this thread and determine that this isn’t your problem. The shimmy on my 12 year-old RV-9A was due to the slop-in-the-strut-bolt problem. I solved it with help from as long-time RV-6A builder who had the same well-known nose gear problem 20 years ago and we fixed my problem the same way he fixed his all that time ago.

Nose Gear Lessons Learned

Given the recently reported nose gear leg bolt failure, a few of us “VAFers” have concluded that the time has come to summarize “Nose Gear Lessons Learned” at least from our personal perspectives and in the interest of safety for our fellow VAF RV-A builders and fliers. We are talking about...
vansairforce.net
 
Last edited:
Perhaps this might alleviate your issue:

antisplataero.com

The Nose Job 2 - AntiSplatAero

THE NOSE JOB TWO – ADVANCED NOSE GEAR PROTECTION At Anti-Splat-Aero, we are excited to introduce The Nose Job Two, a highly requested variation of our original nose gear reinforcement system. This updated design provides the same level of protection while fitting under the stock Van’s fairing...
antisplataero.com antisplataero.com
 
Update...

After taking Al's advice from Antisplat Aero, and Carl's advice from above, I did a circuit with the GoPro pointing at the mains...


Crazy amount of shimmy in the left main (maybe some in the right as well) while decelerating 25-20 knots (roughly 18 seconds in). I showed an AME friend of mine who said "tires". I changed the left main to a new spare tire I have, did another circuit, and absolutely no change!

Would a balancing solve this much shimmy / shutter or should I be looking elsewhere. This has gotten progressively worse only for the past couple of months. So relatively suddenly.
 
Balancing should always be the first step, along with checking for roundness of tire when rotated (place something next to the tire and rotate while jacked off the ground to observe that the gap from the object stays relatively constant).

There is a slight fore/aft shimmy in the nose wheel. Does it rotate freely?
 
What tire pressure are your mains at? I had main gear shimmy (originally suspected it was the nose wheel) that went away when I dropped the mains to 30psi.
 
dalemaher said:
Update...

After taking Al's advice from Antisplat Aero, and Carl's advice from above, I did a circuit with the GoPro pointing at the mains...


Crazy amount of shimmy in the left main (maybe some in the right as well) while decelerating 25-20 knots (roughly 18 seconds in). I showed an AME friend of mine who said "tires". I changed the left main to a new spare tire I have, did another circuit, and absolutely no change!

Would a balancing solve this much shimmy / shutter or should I be looking elsewhere. This has gotten progressively worse only for the past couple of months. So relatively suddenly.
Click to expand...
Switch wheels/tires left and right. See if it follows that tire. Go back to inflation pressure you used before. Last, have you hit anything or run through any potholes with that left main? I’m sure it’s the camera, but it “looks” toed out.
 
If my tire pressure is over 30 I get main gear shimmy as I get slow on roll out. As Scott said, check to see if your nose wheel spins freely. I trimmed one of the lips off the double lip seals to reduce drag on the wheel spinning (used a razor blade).

Do you have a spacer between the bearings on the nose wheel?
 
Are your belleville washers installed correctly? If not the breakout force will go way down very quickly.
 
The troubleshooting continues. To answer above posts, I will try switching tires left to right, the nosewheel does spin relatively freely (mostly due to the sealed bearings - no longer have tapered bearings), and washers installed correctly.

The wheelpants are off...going to try from there. If no change, I will try switching tires, tighten the wheel nut, ensure wheelpant support on securely etc...
 
blaplante said:
Another vote for the wood nose gearleg stiffner. Did mine many moons ago. Notably I don't have those on my main gear legs.
Click to expand...

dalemaher said:
Update...

After taking Al's advice from Antisplat Aero, and Carl's advice from above, I did a circuit with the GoPro pointing at the mains...


Crazy amount of shimmy in the left main (maybe some in the right as well) while decelerating 25-20 knots (roughly 18 seconds in). I showed an AME friend of mine who said "tires". I changed the left main to a new spare tire I have, did another circuit, and absolutely no change!

Would a balancing solve this much shimmy / shutter or should I be looking elsewhere. This has gotten progressively worse only for the past couple of months. So relatively suddenly.
Click to expand...
I just solved my vibration problem. I added wood stiffeners. Fiberglassed them to the legs and then fiberglass wrapped them it stopped all vibration on our 6A.
 
dalemaher said:
Hi,

I have a nosewheel shake / shimmy that seems to be getting worse despite efforts to reverse it!

Here is a landing video which shows significant vertical shimmy (no horizontal that I can detect). The motion starts basically as the wheel makes contact with the runway, with the worse of it at about 14 seconds in as I am slowing from 25-20 knots.


I have:
- brand new tire
- sent the wheel to Antisplat Aero for the bearing mod, wheel balancing, and shaping of the tire
- torqued the axle and inflated to Antisplat's specs
- replaced the nosegear attach nut / bolt at the engine mount (no detectable wear in the attachment hole)
- breakout force 28lbs

I had a good talk with Al from Antisplat about this and he was not able to shed any new light based on my description. fWhen I received the wheel back from Antisplat, it did get a little better for a while, but now it is getting much worse to the point that the deceleration shimmy is now a front end shudder.

Any advice appreciated!
Click to expand...
I had the same problem with my 6A. I checked the breakout force and within specs. Then I lubed the nosewheel at the zero fitting and lo and behold the force about zero. Retorqued the bolt to spec and its been fine ever since! The lack of lube was giving me a false reading! Hope this helps. PS I run the tire at 40-45 psi
 
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