We are ready to install the gear stiffners so I would like to know what kind of recomendations you all have. I have read on the forums to install the fiberglass on the bias which makes sense. Question is do you do it in strips or go all the way from one end to the other covering the complete gear? How many layers? It seems like it will crack and break out any way. Am I right? The wood pieces show the gear is not straight. Do you do it with the weight on or off the gear? If so do you clamp the wood to meet (be flush with) the gear leg? Won't this cause corrosion under the fiberglass? Thanks in advance for your input.
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Too many questions about Gear Stiffners
- Thread starter hudgin
- Start date
Norman CYYJ
Well Known Member
I would not bother with the stiffeners. The last few planes I have not installed them, no difference was found in performance. If you need them install them later, save the labour and weight.
I am also interested in the answer. I am putting the stiffeners on my RV-7A nose gear to help reduce the tendency to oscillate front to back. I have made my stiffeners out of Sitka Spruce and can use glass, carbon fiber or kevlar. I am tempted to use kevlar for the wrap.
Norman CYYJ
Well Known Member
If you use Kevlar do a real neat job of it because it is next to impossible to sand!
Try oak molding a strapping tape for gear shimmy
For the first year or so with my RV-6, I operated with no damping device on the gear legs and, from time to time, experienced rather severe gear shimmy (forward and aft movement of the wheels at roughly 2 or 3 Hz at taxi speeds). Enough shaking to know, ?this is not good?. A change to Michelin tires appeared to help somewhat, but not cure the problem. I also experimented with varying inflation pressure, but I was not persistent enough with the ?test? to establish a best pressure. The fact that the problem would come and go didn?t help matters.
I did, however, have some good success by (literally) taping oak strips to the LE of the legs. To be specific, I visited my local Lowes, selected the most dense length of oak ?? cove molding (roughly the same radius as the steel leg), cut two pieces to 90% the length of the leg(s), then with 1? fiber reinforced strapping tape, bound the wood to the LE of the leg(s). Starting at the top, I just ran the roll of tape down like a candy-cane with a slight overlap with each turn. I used a fair amount of tension and tried to keep the tape smoothly wrapped all the way around. Very inexpensive, and should the need arise to inspect the legs for corrosion, simply remove the old tape and replace it with new. So far after about 2.5 years 200+ hours later, the tape is still looking pretty good and only rarely will the shimmy gremlin reappear. Note, with this size molding, I was able to still slip the fairing over the legs without issue.
For the first year or so with my RV-6, I operated with no damping device on the gear legs and, from time to time, experienced rather severe gear shimmy (forward and aft movement of the wheels at roughly 2 or 3 Hz at taxi speeds). Enough shaking to know, ?this is not good?. A change to Michelin tires appeared to help somewhat, but not cure the problem. I also experimented with varying inflation pressure, but I was not persistent enough with the ?test? to establish a best pressure. The fact that the problem would come and go didn?t help matters.
I did, however, have some good success by (literally) taping oak strips to the LE of the legs. To be specific, I visited my local Lowes, selected the most dense length of oak ?? cove molding (roughly the same radius as the steel leg), cut two pieces to 90% the length of the leg(s), then with 1? fiber reinforced strapping tape, bound the wood to the LE of the leg(s). Starting at the top, I just ran the roll of tape down like a candy-cane with a slight overlap with each turn. I used a fair amount of tension and tried to keep the tape smoothly wrapped all the way around. Very inexpensive, and should the need arise to inspect the legs for corrosion, simply remove the old tape and replace it with new. So far after about 2.5 years 200+ hours later, the tape is still looking pretty good and only rarely will the shimmy gremlin reappear. Note, with this size molding, I was able to still slip the fairing over the legs without issue.
best to wait and add them as you need them
I was at the debating to install on my gear legs and after some research decided not to and wait to see if I will have shimming issue. It is not much of a problem to add them later but if you do, you will never know if you needed them or not and will carry the extra weight all the time.
Well, I started flying about a month ago and have already flown my time off and have not had any issues so far. If you do decide to add them to the front nose gear, be careful as not to do it too much. The front gear leg is tapered in such a way to take the load and if you stiffen it too much, most of the force will go to the engine mount and it could fail there. Vans advises against it unless you have serious shimming on the nose gear.
My 2 cents
Good luck
Mehrdad
I was at the debating to install on my gear legs and after some research decided not to and wait to see if I will have shimming issue. It is not much of a problem to add them later but if you do, you will never know if you needed them or not and will carry the extra weight all the time.
Well, I started flying about a month ago and have already flown my time off and have not had any issues so far. If you do decide to add them to the front nose gear, be careful as not to do it too much. The front gear leg is tapered in such a way to take the load and if you stiffen it too much, most of the force will go to the engine mount and it could fail there. Vans advises against it unless you have serious shimming on the nose gear.
My 2 cents
Good luck
Mehrdad
L.Adamson
Well Known Member
My shimmy experience
When I bought my 6A kit, it was the norm to fiberglass stiffeners to the legs. But I didn't get it flying until last year; and in the meantime, Van's came up with the fiberglass fairings and not installing stiffeners as a standard practice.
So I do have a 6A without stiffeners. On the very first landing, I let the nose down to fast, and got an intense shimmy. I reset the breakout force, and haven't had no further shimmy like that in the near 70 hours that's on the plane now. But I do make it a practice to keep the weight off the nose gear as much as possible. Sometimes, I'll get a slight shimmy while taxiing after landing, and just throttle back to get rid of it. It's just a very small percentage of landings, that it happens. Therefor, I see no reason to add the weight of stiffeners at this time.
L.Adamson --- RV6A
When I bought my 6A kit, it was the norm to fiberglass stiffeners to the legs. But I didn't get it flying until last year; and in the meantime, Van's came up with the fiberglass fairings and not installing stiffeners as a standard practice.
So I do have a 6A without stiffeners. On the very first landing, I let the nose down to fast, and got an intense shimmy. I reset the breakout force, and haven't had no further shimmy like that in the near 70 hours that's on the plane now. But I do make it a practice to keep the weight off the nose gear as much as possible. Sometimes, I'll get a slight shimmy while taxiing after landing, and just throttle back to get rid of it. It's just a very small percentage of landings, that it happens. Therefor, I see no reason to add the weight of stiffeners at this time.
L.Adamson --- RV6A
DRBuilder
Well Known Member
Gear Leg Shimmy
Has anyone else had any experience with this? My -7 will develop a (sometimes) pretty aggressive gear leg shimmy at LOW speeds after a landing. Not during taxi, not during take off, only when on a landing roll out, and only after the tail drops (on a wheel landing) and I am slowing to taxi speeds. I'll need to ride the brakes heavy for a few seconds to stop it, then once it stops, it will taxi fine. I would imagine if it was the tires causing the shimmy due to balancing, it would shimmy at higher speeds and on takeoff as well. How in the world will taping a piece of wood to a solid steel gear leg stop the shimmy? You would think the steel gear leg would be much stronger than a piece of wood??? Any advise from owners who have experienced this would be greatly appreciated. Thanks in advance!
Has anyone else had any experience with this? My -7 will develop a (sometimes) pretty aggressive gear leg shimmy at LOW speeds after a landing. Not during taxi, not during take off, only when on a landing roll out, and only after the tail drops (on a wheel landing) and I am slowing to taxi speeds. I'll need to ride the brakes heavy for a few seconds to stop it, then once it stops, it will taxi fine. I would imagine if it was the tires causing the shimmy due to balancing, it would shimmy at higher speeds and on takeoff as well. How in the world will taping a piece of wood to a solid steel gear leg stop the shimmy? You would think the steel gear leg would be much stronger than a piece of wood??? Any advise from owners who have experienced this would be greatly appreciated. Thanks in advance!
My imagination has failed me more times than I can remember.
I think yours might be failing you. I suggest that you carefully check the tires for roundness. Replace if they are out very much. About .060 absolute max. (Preferably less).
Carefully balance both wheel/tire assemblies.
I bet one of these (or both together) is causing your problem when you hit a speed that excites a natural resonant interaction between the flexibility of the tire and the flexibility of the gear leg (I have seen it before).
In case these things wont solve it,
While you have the wheels off for balancing, check the alignment of the main gear axles to each other. They should have a small amount of toe in.
woodmanrog
Well Known Member
Vans's SK-75 instructions
I saw this post and had to give my two cents worth. Van's plans call for wood gear leg stiffeners for all round main gear legs. The reason for the stiffeners is that on some aircraft the round gearlegs may tend to oscillate in a 360 degree fashion upon taxi or landing. If the aircraft doesn't do this, then there is no reason to install stiffeners. To all those who posted answers on this forum, I ask two questions: What are your tire pressures? Low tire pressure will also eliminate oscillation because it produces more rearward drag on the gear legs. Tire wear increases significantly. Are you landing on grass? Same effect as low tire pressure. The stiffeners only allow the gearlegs to flex from side to side rather than all 360 degrees. The installation calls for 2" fiberglas tape to be spiral wrapped from top to bottom, 2 layers whetted out with epoxy resin. It is not a difficult installation taking perhaps an hour to install on 2 gearlegs. The side benefit is that if you accidentally flare a little high, (I know, we never do this, lol) there is considerably less bounce effect. As most readers on the forums know, I manufacture the stiffeners and have sold them for the past 10 years or so to save about 3-4 hours of building them. I recommend contacting "Antisplat.com" for nose gear stiffeners. Contact: [email protected] for details.
I saw this post and had to give my two cents worth. Van's plans call for wood gear leg stiffeners for all round main gear legs. The reason for the stiffeners is that on some aircraft the round gearlegs may tend to oscillate in a 360 degree fashion upon taxi or landing. If the aircraft doesn't do this, then there is no reason to install stiffeners. To all those who posted answers on this forum, I ask two questions: What are your tire pressures? Low tire pressure will also eliminate oscillation because it produces more rearward drag on the gear legs. Tire wear increases significantly. Are you landing on grass? Same effect as low tire pressure. The stiffeners only allow the gearlegs to flex from side to side rather than all 360 degrees. The installation calls for 2" fiberglas tape to be spiral wrapped from top to bottom, 2 layers whetted out with epoxy resin. It is not a difficult installation taking perhaps an hour to install on 2 gearlegs. The side benefit is that if you accidentally flare a little high, (I know, we never do this, lol) there is considerably less bounce effect. As most readers on the forums know, I manufacture the stiffeners and have sold them for the past 10 years or so to save about 3-4 hours of building them. I recommend contacting "Antisplat.com" for nose gear stiffeners. Contact: [email protected] for details.
One more data point...
When trying to solve a leg shimmy problem, builders should first confirm that all of the different possible causes are not inducing their problem.
Then reduced tire pressure can be used to reduce or eliminate the problem.
If that doesn't work, glassed on leg stiffeners can be used (but I would consider that a last resort)
Data point... all of the Van's Aircraft demonstrator airplanes have no leg stiffeners, and they do not have gear leg shimmy. The wheels are carefully balanced every time the tires are changed.
I solved a severe shimmy problem on my personal airplane by simply replacing the tires and carefully balancing the the wheels.
When trying to solve a leg shimmy problem, builders should first confirm that all of the different possible causes are not inducing their problem.
Then reduced tire pressure can be used to reduce or eliminate the problem.
If that doesn't work, glassed on leg stiffeners can be used (but I would consider that a last resort)
Data point... all of the Van's Aircraft demonstrator airplanes have no leg stiffeners, and they do not have gear leg shimmy. The wheels are carefully balanced every time the tires are changed.
I solved a severe shimmy problem on my personal airplane by simply replacing the tires and carefully balancing the the wheels.
Sam Buchanan
been here awhile
I have found lower tire pressure (24-30 lbs) can reduce gear shimmy. I have not seen increased tire wear as a result of lower pressure (RV-6, thirteen years, 1150 hours).
Balancing is a big deal ....
Not sure if folks realize just how much weight it can take to balance the factory tires. We have a really good balancer on the airport and it took between 6 and 8 the small adhesive weights (sorry don't remember the oz) to get mine to really balance but it made a huge difference. I was shocked but the old hands were not!
I had called Gus at Vans directly about putting on the stiffners and he said not to do it until you had flown off the 25/40 and had done everything else. I took the advice and the balance job solved a reasonably noticable shimmy/shake problem.
Just my .02 but balancing the tires is the first thing to do... stiffeners later if that doens't work.
Bill S
7a GTG (got the grin)
Airplane at Glo-Custom for paint
Not sure if folks realize just how much weight it can take to balance the factory tires. We have a really good balancer on the airport and it took between 6 and 8 the small adhesive weights (sorry don't remember the oz) to get mine to really balance but it made a huge difference. I was shocked but the old hands were not!
I had called Gus at Vans directly about putting on the stiffners and he said not to do it until you had flown off the 25/40 and had done everything else. I took the advice and the balance job solved a reasonably noticable shimmy/shake problem.
Just my .02 but balancing the tires is the first thing to do... stiffeners later if that doens't work.
Bill S
7a GTG (got the grin)
Airplane at Glo-Custom for paint
woodmanrog
Well Known Member
Question about rounding tires
I would like to know if shaving the tires to a more rounded profile is really a necessary item. It would seem to me that every landing must create a flat spot on a tire simply because it goes from 0-50 mph as soon as it touches. I believe there would have to be a certain amont of skidding before the tire actually begins to turn. Input?
Thanks
I would like to know if shaving the tires to a more rounded profile is really a necessary item. It would seem to me that every landing must create a flat spot on a tire simply because it goes from 0-50 mph as soon as it touches. I believe there would have to be a certain amont of skidding before the tire actually begins to turn. Input?
Thanks
Wheel shimmy after landing
I had EXACTLY the same problem as Dennis on my -4. I tried changing the tire pressure up & down to no avail. I put new Goodyear Flight Custom tires on it but no help. I even contemplated putting the gear leg stiffners on it but didn't want the extra weight. This spring doing the annual I took the wheels off to repack the wheel bearings, put them back on when I was done and started tightening the axle nut. I was adjusting it slightly to fit the cotter pin and spinning it to make sure it wasn't too tight. Guess what- I noticed that the right wheel would spin freely about 3/4 of a turn then almost stop. After further investigation I noticed that the brake disc was ever so slightly warped. How it got that way I have no idea. Ordered a new one from Spruce and now it spins freely and shimmy is completely gone.
Worth a look,
Oly
I had EXACTLY the same problem as Dennis on my -4. I tried changing the tire pressure up & down to no avail. I put new Goodyear Flight Custom tires on it but no help. I even contemplated putting the gear leg stiffners on it but didn't want the extra weight. This spring doing the annual I took the wheels off to repack the wheel bearings, put them back on when I was done and started tightening the axle nut. I was adjusting it slightly to fit the cotter pin and spinning it to make sure it wasn't too tight. Guess what- I noticed that the right wheel would spin freely about 3/4 of a turn then almost stop. After further investigation I noticed that the brake disc was ever so slightly warped. How it got that way I have no idea. Ordered a new one from Spruce and now it spins freely and shimmy is completely gone.
Worth a look,
Oly
Stiffeners
I had the shimmy on the right gear leg in my RV-10. I checked toe-in, balance and pressures and finally ended up glassing in oak. About 6 months ago I first tried the strapping tape over a milled piece of oak just like N601SC suggests. This worked great so I ended up glassing it in. Much better now.
I had the shimmy on the right gear leg in my RV-10. I checked toe-in, balance and pressures and finally ended up glassing in oak. About 6 months ago I first tried the strapping tape over a milled piece of oak just like N601SC suggests. This worked great so I ended up glassing it in. Much better now.
RV6airplanePilot
Well Known Member
Video helps
to show results. I see more shimmy on my videos than I expected based on sensation in the seat. So I added stiffeners on the right leg and on the nose leg. I am concerned about the stress caused by the nose stiffener since it has much different geometry than a main leg. But I like the reduced wobble. I am able to baby the nose gear, so I am taking the chance. If your landings are not consistent I would not stiffen the nose leg because it focuses the stress on the small area between the stiffener and the mount. Here is a video that shows before and after. I got my main leg stiffener from Roger (Woodmanrog) and it was very good.
http://www.youtube.com/watch?v=w86kIBn3TcE
Happy landings,
to show results. I see more shimmy on my videos than I expected based on sensation in the seat. So I added stiffeners on the right leg and on the nose leg. I am concerned about the stress caused by the nose stiffener since it has much different geometry than a main leg. But I like the reduced wobble. I am able to baby the nose gear, so I am taking the chance. If your landings are not consistent I would not stiffen the nose leg because it focuses the stress on the small area between the stiffener and the mount. Here is a video that shows before and after. I got my main leg stiffener from Roger (Woodmanrog) and it was very good.
http://www.youtube.com/watch?v=w86kIBn3TcE
Happy landings,
