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gear shake revisited

Tony Spicer

Well Known Member
For some background on the gear shake issue, have a look here:

http://www.vansairforce.com/community/showthread.php?t=40349&highlight=gear+shake

After fighting gear shake for two years, I finally bit the bullet and added dampeners. Balancing, tire pressures as low as 18 psi, checking tire runout, barking at the moon, nothing worked permanently. Taxiing at 17 knots and things started to shake. Only way to stop it was to come to a complete stop. The dampeners stopped it. None, nada, zip. Same with Fred Bauer and his -3.

Fred's:

http://picasaweb.google.com/airspeedzero/N313RVVansRV3BSN11366FredBauerJr#5319921373556714082

http://picasaweb.google.com/airspeedzero/N313RVVansRV3BSN11366FredBauerJr#5319921410848024466

Mine:

http://picasaweb.google.com/tonyboytoo/RV3BMiscellaneous#5446251840017694466

http://picasaweb.google.com/tonyboytoo/RV3BMiscellaneous#5445895114546404962

Bottom line- put the darn things on during the build.

Tony
 
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My theory is that gear shake is a resonance of the undercarriage legs which occurs at different speeds in different RV-3s due to slight variations in construction. If the type of wood used as a stiffener is changed then the resonant frequency of the undercarriage leg will change because of the different natural resonant frequencies of the woods used, causing the gear shake to occur at a different speed. The ideal speed which greatest resonance occurs should be one that is higher than the no wind ground speed at which the plane takes off or lands.

Please note this is only my theory and I am willing to be corrected.
 
Island,
I believe you are correct with your observation that various building irregularities affect the gear shake.
I believe the gear legs as supplied by Van's are not stiff enough to overcome all of the different aircraft builds, BUT ------------ adding stiffness to the gear legs by adding the wood stiffners does.

Don't even try to think this through, ADD THE WOOD STIFFNERS.:)
 
So, Tony and Fred. What type of wood?
Also, I mentioned when this subject came up last time, that I had installed a set of Desser Monster retreads and they seemed to have mostly eliminated the problem. After many moons and well over 100 landings, for the most part, I have very limited amounts of shimmy. The sidewalls are so stout that air-pressure doesn't seem to matter either.

Bill Newkirk
N283RV
 
I had the same problem on an RV-3 I built 20 years ago. The leg stiffeners did the trick. I put them on an RV-6 and 7 during the build.

The first ones I made. The last ones I bought from Roger at Turtlewood Designs. www.turtlewooddesigns.com

Worked great.
 
Island,
I believe you are correct with your observation that various building irregularities affect the gear shake.
I believe the gear legs as supplied by Van's are not stiff enough to overcome all of the different aircraft builds, BUT ------------ adding stiffness to the gear legs by adding the wood stiffeners does.

Don't even try to think this through, ADD THE WOOD STIFFENERS.:)

Hi Fred,

I do intend to fit the stiffeners and made that decision after reading Randy Levold's experiences with gear shake without stiffeners fitted. I too would be interested in what type of wood to use for the best results, ie no gear shake. Would a stiffener made of wood laminations be better?

On another note, I think your RV-3 is as they say in the RAF "Absolutely Spiffing". So much so, I have provided a link to your photo album on my build site. Do you fly your 3 much with the open cockpit option?
 
Wood type noted in the photos. Dimensions in my photos. Lowes sells clear pine in 1/2" thickness. If you're going full length, one 4" x 36" board will do one leg. Split diagonally, bevel leading edges, glue together, cut to size, put a fresh 80 grit belt on the sander, hook up the shop vac and have at it. Mine are 1" thick at the big end and taper to gear diameter at the little end. A small bottle jack from Harbor Freight placed just inboard of the gear leg on the engine mount will take the bow out of the leg.

Tony
 
Do 8As need these?

Pardon the stupid question, but do you need stiffeners for 8A gear legs?
Thanks,
 
RV-6 - Haven't needed them yet

I made but haven't fitted the wooden gear leg Stiffeners/Dampeners on my RV-6. So far I have well over 100 grass and and black top landings and haven't experienced any vibration or shimmy during take-off, landing or taxiing so I plan to leave them off.

Jim Sharkey
RV-6 - almost out of Phase 1 :)
 
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Island,

Yes, we fly around with the open cockpit quite often but not at high cruise and we need some modifications (see my pics and explanation on Picasa) to be able to enjoy it more.
At Oshkosh last year we purchased a really good helmet with built-in noise canceling and we have a heated seat so we can enjoy the open cockpit experience.

Fred
 
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Still need some guidance

OK Campers, I just gotta know. Am I going to need these dampners on an
8A (tricycle gear). I am not building an 8 with the spring steel gear but an 8A with the tubular steel rod gear. Any 8A drivers out there with the scoop?
 
Since the 8A does have the same style round rod whittman style gear, it may be needed. You could always add them during your build, or leave them off until you fly it to figure out if they are needed. They don't really add much weight, so it may be easier to add them during the initial build.

I have talked with some people that needed them and others that did not. Some even only needed it for one leg.

Each plane has it's subtle differences, so each will have different characteristics.
 
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