Gear stiffener question ??

[Larry DeCamp]

The mission is to improve the shimmy of round gear. Vans drawing proposes a triangular wooden nose on the front of the rod. My question to experienced RVers is, does the oscillation go up and down or front to rear ? If up and down is not the problem, I don,t want to make the gear stiffer. If stabilization is only needed front to rear, that will define a different approach. Comments appreciated.

[RVDan]

Some do the "stiffener" on the front side some on the aft. The stiffener is actually a dampener to help detune the resonant frequency of the gear legs mostly in the fore and aft direction. There are some pre made ones for sale. Others might chime in on how good the pre-made ones are or are not.

[Larry DeCamp]

Thanks for the comment Dan. Kevlar and graphite have been suggested for absorption. The graphite people say it is used extensively for vibration attenuation. So I am just deciding how to apply it for maximum benefit without creating a negative characteristic.

[RVDan]

Actually both are strong and will increase stiffness, but neither work well for dampening. Wood works really well for this.

[vfrazier]

WoodmanRog (on this forum) sells pre-made stiffeners.

We also carry them and will have them at Oshkosh. Visit us at booth 4047, in building D.

http://www.flyboyaccessories.com/RV-...Set-p/2104.htm

[David Paule]

With the energy involved, the damping will be negligible - otherwise the fairings would be hot to the touch after landing since damping absorbs energy.

Of the materials mentioned, the wood works because it has a relatively large moment of inertia. Kevlar works because it has more modulus of elasticity than wood, and is placed at the outer fiber, which tends to add to its effectiveness. Carbon works because of its high modulus of elasticity and it's position, also at the outer fiber.

The added stiffness increases the natural frequency mostly in the fore-aft direction but slightly in the transverse direction too. Separating the natural frequencies of the two directions seems to reduce the likelihood of the vibration.

What I plan to do when I get that far is use Woodman Rog's wooden pieces with some uni carbon, along with the +/- 45 degree glass wrapping over all.

Dave
RV-3B under construction

[RV3bpilot]

I'm not sure how the gear leg oscillates but it does move.
The gear on my aircraft shook so hard that I thought it would tear apart the whole motor mount. Frankly it scared me, this was during the first taxi test. Then I put on wooded gear leg stiffeners per Van's design. The only wooden window trim at our little lumber yard was oak so that is what I used. I never thought about the stiffness, I just wanted the violent shake to go away! I was concerned about the added weight, oak is heavy.. But the end result was awsume. the gear legs still flex and bend but with no shaking.
The wood works great. I can not speak for the other materials because I have no experience with them.

[Larry DeCamp]

I appreciate you all taking the time to help me ! I will update the thread with pics and results as the project proceeds. Larry

[grubbat]

I had the dubious task of removing some wood gear leg stiffeners from a rv6a that we're rotten in places. I imagine they were on there about 15years. That's a fair amount of time but even so. You may want to soak them in some thin slow-curing epoxy to extend their life and reduce moisture wickin. Just a thought.

[jay.pearlman]

I installed the premade stiffeners mentioned above. They were easy to install and saved some time because they are preshaped. I wrapped them in fiberglass with epoxy resin. Having just finished the canopy/windscreen installation with some carbon fiber over the canopy interface, carbon fiber is hard to sand. I find the fiberglass easier to work with. Having said that, I sanded and smoothed the fiberglass winding that went around the wood. I found that using 4 inch tape make the whole process easy.
I am not flying yet, so cannot comment on the performance.