Gear leg Stiffners

[redhawk]

I have to replace my gear leg stiffners on my 3B, and wondering what the consensus is for the type of wood to use? I’ve made them years ago out of oak for my -4, but see some folks are using poplar which is not much harder or denser than pine…
It’s impossible to find the right size/shape of oak trim board anymore, so guess I’ll have to mill them out of a solid oak piece now using my table saw…

 

[PilotjohnS]

Metal

I, and many others, have gone to metal plate and adel clamps for the gear leg stiffeners. There is a thread on this on the site.
I have 120 hours on my stiffeners and no ill effects; working great.

 

[PaulvS]

Oregon pine

I'm going to mill mine out of Oregon Pine ie Douglas Fir using table saw and router table. It is strong and lighter than hardwoods and seems a better choice than Poplar, which appears a bit soft and fibrous and the boards at the store were warped.

 

[Sam Buchanan]

Another good field report of excellent service from the metal stiffeners on my RV-6. I didn't want to bond stiffeners to the gear legs and possible create a good environment for corrosion. The metal clamps and stiffeners can be quickly removed or modified if needed.

 

[RV8JD]

Fiberglass/Carbon Fiber

"Hitt7A" used a fiberglass/carbon fiber stiffener with success on a -7A. His detailed post on how he did it:

https://vansairforce.net/community/showthread.php?t=186409​

 

[Steve Ashby]

What is the thickness of your gear leg stiffener?

Sam,
Do you recall the thickness of your gear leg stiffeners? Do you think .090 will do the trick?
Thanks!
Steve Ashby

 

[Dan 57]

Many moons ago I used hazel... epoxied to the front of the legs, then covered by 3 layers of carbon bid, then applied the shaped foam to the rear of the legs, and finally wrapped them with 3 layers of bid fibreglass.

Quite some work, so would probably go for the metal stiffeners method nowadays, the more so for the availability of fibreglass fairings.

 

[Sam Buchanan]

Sam,
Do you recall the thickness of your gear leg stiffeners? Do you think .090 will do the trick?
Thanks!
Steve Ashby

Steve, I don't recall what I used, probably something I had nearby. But 0.090 should work fine. I have the Rocket gear fairings which are a bit larger than some versions, you'll need to customize the stiffeners to fit inside your fairings. One advantage of the metal option is that you can modify it easily if you want to try a different stiffener material.

This thread from last year has good details about fabbing the clamps you'll need.

https://vansairforce.net/community/showthread.php?t=211524&highlight=stiffener

 

[redhawk]

Gear leg stiffners

Think I’m going to try the metal and clamps option …
Here’s a question: It sounds like the favorite size of the aluminum piece is 1/8” x 1.5”. Would it make sense to add another strip (maybe 3/4” wide) alongside the 1.5” strip just to add extra stability ?

 

[Sam Buchanan]

Think I’m going to try the metal and clamps option …
Here’s a question: It sounds like the favorite size of the aluminum piece is 1/8” x 1.5”. Would it make sense to add another strip (maybe 3/4” wide) alongside the 1.5” strip just to add extra stability ?

Probably the only way to answer your question is to try the single stiffener first to see it it works the way you wish. It'll be easy to add another stiffener later if needed.

I (shadetree engineer with TLAR certification) suspect the point of the stiffeners is to change the natural frequency of the gear leg to a point that doesn't drop into the speed range where we normally taxi. In my case the stiffer legs resulted in the shimmy moving to a higher ground speed which meant I didn't have shimmy at the speed I use for taxiing to the runway. I can also run higher tire pressure than before without inducing shimmy at taxi speed. I suspect each airframe will react differently, the metal option makes it much easier to customize than bonding stiffeners to the legs.

 

[PilotjohnS]

Just me

Probably the only way to answer your question is to try the single stiffener first to see it it works the way you wish. It'll be easy to add another stiffener later if needed.

I (shade-tree engineer with TLAR certification) suspect the point of the stiffeners is to change the natural frequency of the gear leg to a point that doesn't drop into the speed range where we normally taxi. In my case the stiffer legs resulted in the shimmy moving to a higher ground speed which meant I didn't have shimmy at the speed I use for taxiing to the runway. I can also run higher tire pressure than before without inducing shimmy at taxi speed. I suspect each airframe will react differently, the metal option makes it much easier to customize than bonding stiffeners to the legs.

Well my TLAR certificate is from the University of hard Knocks, I think the metal stiffeners changes the coupling factor, so that the up and down (perpendicular the stiffener) is much easier than the fore and aft, so the up and down doesn't couple to the fore and aft. Whatever it is, it works very well for me. JMHO

 

[David Paule]

Redhawk, if you do add a strip, it should ideally be at the aft edge of the stiffener. That will be furthest away from the steel leg, which is what you want to increase the moment of inertia.

John, you figured it out! I'm pretty sure that's what's going on. The numbers (moment of inertia fore-aft compared to vertical) support it.

If anyone goes to the trouble of calculating these, don't forget to include the modulus of elasticity.

Dave

 

[Sam Buchanan]

Redhawk, if you do add a strip, it should ideally be at the aft edge of the stiffener. That will be furthest away from the steel leg, which is what you want to increase the moment of inertia.

John, you figured it out! I'm pretty sure that's what's going on. The numbers (moment of inertia fore-aft compared to vertical) support it.

If anyone goes to the trouble of calculating these, don't forget to include the modulus of elasticity.

Dave

The chord of the gear fairing will dictate the max size of the stiffener, I suspect the RV-3 fairing is petite. The stiffener I have probably wouldn't fit inside a legacy RV-6 fairing.

I would have brought up modulus of elasticity, moment of inertia, and fore/aft coupling but didn't want the engineers to feel like I was talking over their head.....

 

[jrs14855]

gear

For the Wittman Tailwind I think I used 3/16 or maybe even 1/4" 2024. I removed the pad from the clamps and reshaped the clamps so the aluminum is captured between the ends of the clamps. Removal of the pads was because of clearance issues with my fairings.
Initially I had some remaining shimmy but when I reversed the tire for uneven wear the shimmy went away. Only on the left side. The right side never shimmied. Goodyear II tires. My landing gear is 13/16" at the small diameters. I think most of the RV's are 7/8" When I first encountered the shimmy I could see the aft end of the wheel pant moving at least 1" in each direction.
I also tried balancing the wheel pants with zero results. I removed the weight.