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Metal Gear Leg Stiffeners

wood vs metal

I'll just throw this out there and see if others agree.

Seems to me the wood are true dampeners and will reduce the shimmy through absorbing the vibration. Whereas the metal stiffeners change the fundamentals of the gear leg; they make the gear stiffer fore and aft, while not doing much up and down.
 
I agree with you
The metal bar stiffens the gear leg more than the wood and encourages the gear to do more bending at the top near the motor mount...just my 0.02
 
I didn't know about or think of the metal bar a few years ago
when I mounted the gear with wood.
If now I think I would try the metal bar, if they didn't work,
remove and go wood or ?
MG
 
Up and down "damping" is not a priority with my installation, it's the fore/aft shimmy that I want to inhibit. The metal stiffeners I use are a subtle change, shimmy can still occur but it occurs with a shorter moment and I can now run more tire pressure without shimmy than I could previously.

I suspect this situation will be unique to particular airframes depending on aircraft weight, wheel/pant mass, tire pressure/balance, gear alignment and phases of the moon. What works for one aircraft may not be the ideal for another. I like the metal stiffeners because they can be easily removed or modified if desired....no fiberglass or bonding needed.
 
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Adel clamps for the stiffeners

I'm probably over thinking this, but I'd rather do that than screw it up. I recently bought an RV 9 and would like to add the stiffeners. I have read this thread several times and am curious about adel sizing. I have gone to Amazon looking for the correct ones and the sizing I am seeing has been either in inches or MM's. In this thread the numbers ginen have been like -12, -18. Are these mm's or a different calibration of sizing that I should be looking for. Thanks Gary
 
Shortfielder said:
I'm probably over thinking this, but I'd rather do that than screw it up. I recently bought an RV 9 and would like to add the stiffeners. I have read this thread several times and am curious about adel sizing. I have gone to Amazon looking for the correct ones and the sizing I am seeing has been either in inches or MM's. In this thread the numbers ginen have been like -12, -18. Are these mm's or a different calibration of sizing that I should be looking for. Thanks Gary
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Those are diameters in 16ths of an inch, so a -12 is 3/4”, a -16 is an inch, and so forth.
 
Well, I started my stiffeners today. I'm a pretty low level fabricator compared to most of you, but I enjoy doing what I can. I cut the aluminum and that went fine. I ordered an assortment of adel clamps from Amazon, and, I'm not comfortable with those. The holes in them are 17/64, and in my mind that is way to big to use the #10 machine screws. I thought about just cutting longer ones down and drilling my own holes but my first attempt didn't go well and the drill bit was snagging on the stainless and twisting it up. And, maybe I just need to drill with less pressure. And, I had another idea of putting the proper size grommets in the holes and using the #10 screws and that did OK, but I'm not sure that is a great idea for long term, although it does cushion the movement some which may not be all bad??? Anyways, just wanted to throw this out there and see what I get for feedback. Are there adel clamps with smaller holes, should I make my own from what I have, or is it possable that the grommets may be OK?
Thanks Gary.
 
Use carbon fibre

Make the stiffener out of carbon fibre. You can buy fibre sheet online and cut into the strips. It's much thinner and fits inside the fairings better. Lighter and works better at doing the job. I made the strips out of differnet thicknesses aluminium and had trouble getting the fairings to fit. I didn't want to remake fairings so went to carbon fiber. They do a better job and weight less as well.
Different thicknesses are available.

Steve
 
The whole idea is stiffness, not cushioning, so avoid soft things in the assembly if you can.

Carbon is a decent idea but it will need to be about as thick and wide as the aluminum. As it is, quasi-isotropic carbon has similar stiffness to aluminum, maybe 8-9 msi modulus compared to about 10 for aluminum. It is less dense, though. The lower modulus suggests that it shouldn't be thinner. Make it as wide as will fit.

I think Steve got lucky. If you can include something like a pre-formed unidirectional shape, running longways, then it can be thinner but it's probably not going to be easy to get bolts or screws reliably in it unless there's some bidirectional fibers in there.

Dave
 
Shortfielder said:
... I thought about just cutting longer ones down and drilling my own holes but my first attempt didn't go well and the drill bit was snagging on the stainless and twisting it up....
Click to expand...

Try using a step drill. Less likely to snag, I think.
But no reason you can't male your own.

Finn
 
My question was more to do with dealing with the hole in the adel clamps. I'll assume they are available with 3/16 holes and look for some different ones. In reading the thread it just mentioned getting clamps from Amazon and that was what I did, but, as usual, there was more to it. Gary
 
Uni directional

Yes, I used multiple layers of uni directional with a single layer of bid on outsides, and one layer between the uni layers. When drilling the holes, clamp some aluminium to both sides, very tightly and use a drill press for a clean hole.

Uni comes in very thin sheets and can be cut with a rotary knife, normally use for cloth fabric.
 
Shortfielder said:
….. from Amazon and that was what I did, but, as usual, there was more to it. Gary
Click to expand...

I will admit that I buy a LOT of stuff through Amazon for my shop - but very rarely does it get installed on (or in) and airplane. You can buy all sorts of metal clamps on the ‘net or at the local Ace, but unless you buy buy them as an aircraft part, they have no specification to meet…such as hole size….

ACS, B&B, WagAero, Wicks - they all list Adel clamps that meet spec.

Paul
 
sibriggs said:
Yes, I used multiple layers of uni directional with a single layer of bid on outsides, and one layer between the uni layers....
Click to expand...

That's the way to do it. That uni is what made it work, plus any additional width you found. And the bid let you put the holes in it. Nice!

Dave
 
Hack!
Two years in (well, almost). Ironflight, how are those stiffeners working out? Any fatigue cracks at the adel 90? Any noticeable shortcomings?
 
scrollF4 said:
Hack!
Two years in (well, almost). Ironflight, how are those stiffeners working out? Any fatigue cracks at the adel 90? Any noticeable shortcomings?
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Ours are fine - no signs of wear. We still have some shimmy at a few speeds, but it’s much reduced from the old wooden things. So far I see no downside to trying the metal ones, and I’ll be planning on doing the same thing with the Rocket.
 
Ironflight said:
Ours are fine - no signs of wear. We still have some shimmy at a few speeds, but it’s much reduced from the old wooden things. So far I see no downside to trying the metal ones, and I’ll be planning on doing the same thing with the Rocket.
Click to expand...

Does the F1 still use titanium gear legs?
 
I now have enough time on the metal stiffeners on the RV-6 to determine their effectiveness. I can run considerably higher tire pressure than previously with minimal gear shimmy in a small speed range. The clamps are holding up just fine.
 
I suppose I'm lucky with my unmodified original short gear legs on the -4 not having the shimmy problem mentioned by many here. I'm curious if the folks with modified legs have logged many landings on back country strips in Idaho, Montana and others with less than smooth runway surfaces. While Atlanta surely was the roughest strip I've had the -4 on, many of the other Idaho interior back country strips give the gear an equally challenging workout. One generous strip that is wide and long and you can see landing traffic is Johnson Creek. It is easy to see the unmodified gear taking up much of the roughness on that runway in how it absorbs the uneven terrain. It appears to my TLAR conditioned eyes, that the stress on the gear is absorbed in the flexing of the leg prior to reaching the engine mount socket. Sort of like a knee joint that can absorb some of the walking action verses one with a locked knee and stiff up to the hips. I guess I'll resort to my other engineering term, "If it ain't broke don't fix it".
 
bjdecker said:
Might want to check with F1Boss about the need for damping -- would hate to see you go through all the effort and it not be needed.
Click to expand...
Wittman believed that the round gear would not fail until some part of the fuselage touched the ground. That has been proven not to be quite true. However the round gear will take an incredible pounding. I beat that gear up unmercifully on my first Tailwind. Routinely landed places some would not land a Super Cub.
The tubular mount on the early RV's is not designed quite like Wittman wanted. That has resulted in the gussets installed on some RV's after cracking of the tubing. Also the RV fuselage portion will not take quite as much stress as a steel tube fuselage.
 
bjdecker said:
Might want to check with F1Boss about the need for damping -- would hate to see you go through all the effort and it not be needed.
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Well Mark contacted me a couple weeks about how to do the metal dampers for a Rocket he’s building…… 😉
 
Ironflight said:
Well Mark contacted me a couple weeks about how to do the metal dampers for a Rocket he’s building…… 😉
Click to expand...
He’d know…I thought the Ti would behave differently than the steel legs and not need the damping (“stiffening “) to ameliorate the shimmying…
 
bjdecker said:
He’d know…I thought the Ti would behave differently than the steel legs and not need the damping (“stiffening “) to ameliorate the shimmying…
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I think the dampening has to do more with the different flexibility for-aft vs up and down. Changing material should not affect this "coupling", just make it occur at a different speed or runway condition. JMHO
 
Ironflight said:
About the only additional information I can give you that wasn’t in the first post was that mine are 25” long. I am pretty sure that if you’re looking to use a two-foot long piece you have handy, 24” would work just as well.

The line of attachment holes is 3/8” in from the edge of the piece. Spacing is where the various clamps are tight on the gear leg. AN3 hardware is used for attachment.

I flew it again yesterday, doing various medium-speed taxied, landings (wheel and three point), and take-offs, and couldn’t induce any shimmy. I’ll want to fly it to different pavements before I declare complete success, but it sure is an improvement over the wood already!

I used to run about 26 psi in the tires to provide some damping - now at 35 for testing, and its fine. I’ll probably take them up to 40 before next flight.

Paul
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Paul I wanted to ask you about this and considering doing this to my RV! One question I have was did you do trial flight with just the stiffeners in without the fairing covers? And if you did fly without the fairing covers were you concerned about alignment so they don’s add any roll effect.
 
J29racer said:
Paul I wanted to ask you about this and considering doing this to my RV! One question I have was did you do trial flight with just the stiffeners in without the fairing covers? And if you did fly without the fairing covers were you concerned about alignment so they don’s add any roll effect.
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No - I didn’t fly it without the fairings - didn’t feel the need to do that, since it wasn’t a planned flight configuration, and the gear leg fairings help hold the upper and lower fairings in place.
 
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