Gear leg stiffener install

After operating for almost 2 years, I've come up with a gear leg shimmy, which occurs on both main and nose gear legs. I've been experimenting with all of the usual fixes and have pretty much stopped it, but am unhappy with the close margin from using proper landing technique to which a shimmy can occur. I've decided to go ahead and install the stiffeners on all 3 legs to increase the margin. I've been documenting how each fix affected the shimmy as I've been troubleshooting, including some videos of the legs with each correction and will post a summary later, after installing the stiffeners.

From the vague directions to install, I understand that the stiffeners are epoxied to the leg, then glass wraps used to install. I had pictured this as sort of wrapping the entire wood stiffener in a sort of "ace bandage" style, covering the wood and leg with an overlapping wrap. From an earlier post, Pierre mentioned 4 single bands of wrap for the stiffener to leg. I was hoping that some who installed the stiffeners could give more detail on how they actually applied the cloth wrap, such as cloth weight, number of wraps (bands), how many layers and width of each wrap. If wrapping in bands, I was thinking carbon fiber might be better. I appreciate any input. Pictures would be even better!

I bought the stiffeners from [email protected] and in his instructions for the RV6A, he said Van's no longer recommended the nose gear stiffener. I have not done research into this, but would not install nose gear stiffener anyway, as it would interfer (?) with the Anti-Splat.
I'd like to see some install photos too.
Bob

Attach the stiffeners with either bondo or flox to the metal gearleg, preferably to the aft side. after this sets up, then spiral wrap 2" fiberglas tape from top to bottm and whet it out with epoxy resin. Apply a second spiral wrap over the first and make sure they are snug and totally whetted out. I then advise using peelply over the entire assembly to soak up any extraneous resin. Make sure you do this with the airplane lifted off of the gear so as to simulate an in flight condition. Align the stiffeners just as you will be doing for the gearleg fairings Let this set up overnight and you are good to go.

additional info

Hey Fellas:

Woodman is right, but be sure to wrap the 2" tape at 30 deg min, and wrap the 2nd layer opposite the 1st, using the same 30 deg min.

You can draw some lines on the damper @ 30 deg so you have something to follow.

It's a sloppy job, so plenty of paper on the floor is called for.

Carry on!
Mark

fairings

Will Van's leg fairings fit after the stiffeners are installed?


Glenn

Tires

Tim, did you check your tires for flat spotting?



Hans

If the stiffeners are built according to Van's plan, the fairings fit with no adjustment needed. For those who do not know-the stiffeners also make a great place to mount flat com antennas to. There is a sacrifice to reception but I rountinely could communicate from 60 Nautical miles out side to side and 40 front to back. Gained 3 knots in cruise just by hiding the antennas.

Gear stiffners

I had a pretty good shimmy and ordered the stifffners from Roger. Fortunately a buddy (the one that's on the cover of the Vans 2012 calender) had a spare set of 5.00 X 5 tires so I swapped my tires out with the new ones. After removal I discovered some definate flat spotting on the tires. Landings have had no shimmy since then. I had tried messing with the tire pressure for weeks based on some earlier threads. Sometimes I guess the obvious things aren't so obvious at first.

Ps: Roger was kind enough to send my check back.

Stiffiners

Hi Tim ,
I did the exact thing on my RV4 as I had a bad shimmy. Just used a hardwood, and shaped it to the leg according to the builders manual, and had fiberglass buddy do the work - he wrapped it like a bandage.
This, in combination with having both my wheels professionally balanced got rid of 99% of the shimmy!

Thanks for the replies. As far as checking for flat spots on the tires, I jacked up the wing and rotated the tires and was excited when I found flat spots right away. Later, I realized that of course there are flat spots due to the tire deforming from the weight of the plane. If I check just after landing and taxiing in, no flat spots! After going through all of the tricks, including making spacers for the nose wheel to get the proper bearing pre-load (and actually be able to put the standard torque on the axle nut) and varying tire pressures, etc. I have gotten the shimmy to essentially go away, although sometimes during rollout I get a minor vibration as I transition through an obviously critical speed. This is only for a couple of seconds and is non-existant if I transition quickly through approximately 30 MPH. Always using the proper takeoff and landing technique to keep the nozewheel unloaded as much as possible.

I'm pretty sure the culprit is in the tires, as this is the only real wear in the system and it didn't do this initially. It's about time to change these out and I plan on replacing the worn air-hawks (came with the kit) with Desser Elite retreads. Although everything works OK now, I'm not really satisfied with the small margin to shimmy, so my plan is to put in the stiffeners to increase the margin, not actually to fix a current problem. It's the only sqwalk on the airplane so I want to get rid of it

Also, any opinions on using carbon fiber instead of glass?

trib said:

After operating for almost 2 years, I've come up with a gear leg shimmy, which occurs on both main and nose gear legs.

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If you have gone 2 years without a shimmy, why do you think you need stiffeners?
My 6A had a nose shimmy. I adjusted the nut as instructed...... Gone. My right main had a shimmy Cleveland wheels with felt dust seals. I installed GoodYear flight special II's and ALL shimmy is gone. Tire pressure goes from 40# down to about 20# before I catch it. No shimmy at any pressure. I can tell when the tires need air because it's harder to pull out of the hangar. I also have one leg that was under bent at the factory and has less camber and that has not effected the quality of my landings.

If you had the shimmy from the start and used good tires and good control on your bearing and seal drag...... then I would say add the wood brace. But I don't think that you need it Yet.

trib said:

Also, any opinions on using carbon fiber instead of glass?

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I would think CF is not as desirable since it is much stiffer then fiberglass and might not help with the flexibility that it needs. Also, since it acts as a dissimilar metal, in case your powder coat rubs off, there is a greater chance for corrosion.

I was actually thinking of if it can be wrapped with a webbing so if it ever needs removal (either for inspection or other reasons) it can be done much easier?

I understand the carbon fiber is much stiffer, I'm not sure about the acting as a dissimilar metal. My understanding is that carbon is about the most inert material there is. Galvanic corrosion between dissimilar metals doesn't seem to be applicable, in that plain carbon fiber is not a metal and would not corrode or induce corrosion. Am I missing something here? THe stiffness and durability were the issues I was hoping to find out about. Primarily is anyone has used carbon fiber in this application as I think it is so much stronger (and way cooler looking ). If there isn't anyone who has any experience using it here, then I'll just stick with the glass wrap. I'm always interested in the learning experience, so if you have knowledge of the corrosion potential here I'm glad to hear it.

Gasman, as far as needing the stiffeners, I can get by without them, but I'm not happy with the near margin to the shimmy and want to install these to increase it. It's only a little of my time and pretty inexpensive, so I am choosing to do this. I can't think of any negative repercussions, other than I might miss a couple of hours of flight time during the installation. It may just be to satisfy my need to tinker.

As always- I appreciate the feedback here. DR, I'm a little late in sending in my funds this year, but will get to it as this is the best bang for the buck I know of!

I know two builders, that wrapped the nose leg with carbon fiber. One has been flying for 3 1/2 years with no problem. The other, is about a year.

L.Adamson

trib said:

I understand the carbon fiber is much stiffer, I'm not sure about the acting as a dissimilar metal. My understanding is that carbon is about the most inert material there is. Galvanic corrosion between dissimilar metals doesn't seem to be applicable, in that plain carbon fiber is not a metal and would not corrode or induce corrosion.

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I don't know the chemistery, but the earlier Bombardier Challenger aircraft screwed carbon flooroards directly to the milled aluminum floor beams. A little moisture from rain, galley spills, or cleaning the carpets is all to took. Many of the repairs went well into the hundreds of thousands with weeks of downtime. The fix was to epoxy paint the new beams and install a rubber gasket so they didn't touch each other. If you think about it - What are carbon/zinc batteries full of?

Many newer corporate aircraft have carbon boards to save weight, but have some method to keep them from touching. I have even seen ones with a layer of fiberglass or other fabric such as kevlar bonded to the surface that contacts the aluminum.

One aircraft I am familiar with came out with carbon engine pylon boards held down with $8 each titanium screws to save weight. After drilling out all the corroded ones the change was made to steel. (CRES if memory serves). Solved the problem.

Chemically, carbon (and carbon fiber) behaves as a metal and when in direct contact with another metal (and moisture) will result in galvanic corrosion. If you wrap the gear leg with it and you ever break through the powder coat so they can be in direct contact, you will have corrosion.

airguy said:

Chemically, carbon (and carbon fiber) behaves as a metal and when in direct contact with another metal (and moisture) will result in galvanic corrosion. If you wrap the gear leg with it and you ever break through the powder coat so they can be in direct contact, you will have corrosion.

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And, it will depend on moisture, and possibly other factors. Dissimilar metals. corrode at different rates, according to the conditions. For instance,...... copper, aluminum, and galvanized sheet metal, don't usually do well, when in contact with each other. But when pressed together with force, such as in air conditioning coils; they can last for many years, with minimal corrosion.

L.Adamson

L.Adamson said:

But when pressed together with force, such as in air conditioning coils; they can last for many years, with minimal corrosion.

L.Adamson

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If you can have them in contact with each other with no air gap for liquids (electrolyte) to penetrate, then you can't form a cell. Without a galvanic cell you can't have corrosion. The cell requires electrical contact between two dissimilar metals, plus an electrolyte in contact with both metals. Break the electrical contact, or remove the electrolyte, and you've broken the cell.

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