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Tunnel vision---landing gear shimmy

Mike S

Mike S

Senior Curmudgeon
For some time now I have experienced the dreaded "shopping cart shimmy" upon landing.

This has been quite intermittent, maybe once in every 10 or so landings.

Most of us have heard or read about the problem, and I would guess that a few of the nosedragger folks may have experienced it.

When this first happened to me, I checked the nose wheel breakout and found it to be a bit light so I snugged up the nut one flat. Seemed to take care of the problem.

When it happened again, I checked the breakout and it seemed to still be good, so I looked at the tire inflation, roundness balance etc. Ended up adding a few PSI, and all seemed fine again------

Now, I need to say that this has only manifested itself on landing roll out after I let the nose wheel down. Classic scenario.

Well, yesterday I had the shakes again, but this time it was while still rolling along with the nose wheel off the runway ---- riding on the mains only as per the recommended technique from Vans. We had 3 on board, so there was a bit of an aft CG shift, and I could keep the nose off just a bit longer, instead of my normal two up landing profile.

Turns out it was a main wheel that was causing the vibration, not the nose wheel.

This time the vibration did did not just shake for a moment and go away, it shook like a wet dog, and then the plane made an instant bee line for the right side of the runway----:eek: Luckily I missed the landing light that was there.

A neighbor who happened to see the entire sequence unfold said the right wheel pant was shaking as I was landing. And then it came loose and tucked under the wheel.

Lets see, one side of the plane rolling happily along, and the other side with a wheel pant jammed under the wheel skidding along-----no wonder we headed off to the dirt.

Luckily I got the plane under control prior to any secondary issues from the swerve-----even kept it mostly on the pavement.

Here is what was left of the wheel pant after going back to pick up the pieces.

P6300003.JPG


P6300005.JPG


And no, there is not a big chunk of fiberglass not in the photo, there is a lot of fiberglass dust still on the runway from being ground into a fine powder under the wheel. Notice the scuffed areas adjacent to the big hole in the nose.

Here is the bracket where the pant used to be attached-------anyone who had built a 10 can attest to the fact that this piece of metal is tough, and not easily bent.

P6300006.JPG


They say confession is good for the soul, and I believe that.

Confession however is not going to fix the plane, that is going to take time work and $$$, which is the entire point of this thread-------dont get tunnel vision when you have something going on that does not seem right.

Perhaps this confession will keep someone else from having a similar problem, or even worse..............

I focused on the nose wheel, as I knew it had to be the problem-----after all, I had read about it many times, and the problem only happened when I let the nose back down on roll out.

In retrospect, I am pretty sure the main wheel was the issue all along, and that the shimmy was speed related, and due to the fact we almost always fly with only the two of us, the speed range just happened to be below where I could keep the nose wheel off------the addition of the third person allowed the plane to stay on the mains only, until the speed dropped down to shimmy range this time.

And just to make matters worse, this happened on the last flight before I planned to start my "annual" inspection prior to OSH.

For those who are thinking that I should have checked the wheel pant for being loose as a part of the preflight------I do, and it was not loose. In fact, the bracket is still mounted tightly.

I hope others can learn from my mistake-----------if you dont find the problem where you "know" it to be, dont get tunnel vision, start looking somewhere else.

Take care, fly safe.
 
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Wow x 2. I'm glad that turned out OK for you and all on board. Hope you still fly her out to Oshkosh.
 
Great job keeping things under control, Mike. The worst part now is fitting a new wheel pant and the endless sanding/filling repetitions that have to happen before you can re-paint. That's just one crummy job.
 
Mike,
I am very sorry for this misfortune but glad everyone is OK. Awesome job handling the plane as I know the runway is not the widest or friendliest.

If you need a camera to mount it under the wing to test/look at the shimmy on each wheel and see at what speed it happens, I have a drift camera that we can quickly mount it some place to check and monitor your landing gear.

Mehrdad
 
scrollF4 said:
Hope you still fly her out to Oshkosh.
Click to expand...

Yep, that is the plan.

Will probably have one naked wheel pant though..........

Already have the new parts ordered, and in addition I am going to install the spacers that Sean makes instead of the factory bushings on the mounting bolts. Should make the wheel pant mounting bracket a bit more stable, I would hope. Also, Sean recommends replacing the elsatic stop nuts with all metal ones due to the head generated by the brake discs--------real no brainer that I should have thought of in the first place.

http://www.planearound.com/TWO-WHEEL-FAIRING-BRACKET-SPACERS-FOR-RV-10-WFSPCR.htm

IMG_0135.jpg
 
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I cannot see the outboard axle extension in the photo. Is it missing or just not visible? Was it the original Vans' part?

Bob
 
Glad it ended up with limited damage. I had a similar situation with my -6a and it was in fact a main wheel balance problem. I think we often blame the nose when the problem is in fact with a main. One thing sure, it appears difficult to tell from the cockpit.
 
leg shake

Mike, On my 8a I had the shake problem on rt. gear leg at 28 mph. Gear leg stiffeners fixed the problem. Ron
 
BobTurner said:
I cannot see the outboard axle extension in the photo. Is it missing or just not visible? Was it the original Vans' part?

Bob
Click to expand...

The extension was the standard Vans part, it was installed to the axle nut with locktite, and cross drilled with a roll pin installed. It broke off, snapped the -3 bolt off flush with the axle nut.

It is there in the second photo, laying on the towel to the left of the pant. Still has the screw and blob of flox "liquid shim" attached to it. If you look closely, you can see the roll pin in the left end of the extension that locked the bolt in place to keep the extension tight on the axle nut.
 
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I have Sean's spacers, nice improvement.
I also put in, at first annual, a thicker (in diameter) aluminum outboard axle extension that has a much larger base, and is less prone to rocking up/down or back and forth. I forget if it still has an AN3, or if it has an AN4, bolt. But I cannot recall from whom I bought it.
 
BobTurner said:
I have Sean's spacers, nice improvement.
Click to expand...
Bob, good to hear that.


BobTurner said:
I also put in, at first annual, a thicker (in diameter) aluminum outboard axle extension that has a much larger base, and is less prone to rocking up/down or back and forth.
Click to expand...

Yes, I think I know the one you are referring to. I actually discussed a different style of spacer with Sean, would be nice it he could make it up.

There is no evidence of my spacer having been loose, no wear marks or fretting on the axle nut-------but I just dont like the looks of the stock setup, even though it seems to have worked just fine until now.
 
To put it nicely, the stock Van's axle extender is junk. I have replaced several of them. I think the aftermarket extenders are a must. The wheel shake is another matter entirely, but the pant would have survived if the extender hadn't broken (unless the screw came out, which I have seen too.

Everybody who is reading and has the stock extenders, please replace them. There are a number of them on the market that do the trick.
 
Sorry to hear Mike

Sorry to hear of your troubles and bad timing indeed just before your OSH trip.
Good job keeping things straight on the runway!

A bit of info:
I just installed new tires and re greased the wheel bearings and installed new brake pads.
I rarely notice any shimmy and if any at all usually on the taxiway.

Upon inspecting my gear leg and wheel installation I found a distinct amount of "play" in the gear leg. With the wheel off the ground of course I found a tiny bit of fore and aft play just enough to notice faint "clunk" as though it had some play in the socket. I found that hard to believe but cannot pinpoint the source oof the problem anywhere else other than the gear leg socket.
I have not opened up the seat bottom to verify my suspicion and since I don't have any shimmy problems did not pursue it any further.
However, those who do have shimmy might want to take a look at the socket
bolt and check for excessive play.

Hope you get'er back together and ready for OSH.
 
I've had tires that are worn but otherwise look ok cause severe shimmy, yours look pretty well used, I would recommend you replace them also.
 
Walt, I was planning on flipping the tire during my inspection, but after the abuse it took skidding across the runway your suggestion might make more sense.

Thanks for pointing that out about wear causing shimmy.
 
Good job Mike. Don't beat yourself up on chasing the wrong issue. If I had a dollar for every time I did that on my plane....well....
 
Mike,
glad that no one got hurt and thanks for sharing. If you mount a gopro at the tail tie down (planearound.com offers a mount) you can see the main wheels and nose wheel very well.
Regards
Mike
 
Mike S said:
For some time now I have experienced the dreaded "shopping cart shimmy" upon landing.

This has been quite intermittent, maybe once in every 10 or so landings.

Most of us have heard or read about the problem, and I would guess that a few of the nosedragger folks may have experienced it.

When this first happened to me, I checked the nose wheel breakout and found it to be a bit light so I snugged up the nut one flat. Seemed to take care of the problem.

When it happened again, I checked the breakout and it seemed to still be good, so I looked at the tire inflation, roundness balance etc. Ended up adding a few PSI, and all seemed fine again------

Now, I need to say that this has only manifested itself on landing roll out after I let the nose wheel down. Classic scenario.

Well, yesterday I had the shakes again, but this time it was while still rolling along with the nose wheel off the runway ---- riding on the mains only as per the recommended technique from Vans. We had 3 on board, so there was a bit of an aft CG shift, and I could keep the nose off just a bit longer, instead of my normal two up landing profile.

Turns out it was a main wheel that was causing the vibration, not the nose wheel.

This time the vibration did did not just shake for a moment and go away, it shook like a wet dog, and then the plane made an instant bee line for the right side of the runway----:eek: Luckily I missed the landing light that was there.

A neighbor who happened to see the entire sequence unfold said the right wheel pant was shaking as I was landing. And then it came loose and tucked under the wheel.

Lets see, one side of the plane rolling happily along, and the other side with a wheel pant jammed under the wheel skidding along-----no wonder we headed off to the dirt.

Luckily I got the plane under control prior to any secondary issues from the swerve-----even kept it mostly on the pavement.

Here is what was left of the wheel pant after going back to pick up the pieces.

P6300003.JPG


P6300005.JPG


And no, there is not a big chunk of fiberglass not in the photo, there is a lot of fiberglass dust still on the runway from being ground into a fine powder under the wheel. Notice the scuffed areas adjacent to the big hole in the nose.

Here is the bracket where the pant used to be attached-------anyone who had built a 10 can attest to the fact that this piece of metal is tough, and not easily bent.

P6300006.JPG


They say confession is good for the soul, and I believe that.

Confession however is not going to fix the plane, that is going to take time work and $$$, which is the entire point of this thread-------dont get tunnel vision when you have something going on that does not seem right.

Perhaps this confession will keep someone else from having a similar problem, or even worse..............

I focused on the nose wheel, as I knew it had to be the problem-----after all, I had read about it many times, and the problem only happened when I let the nose back down on roll out.

In retrospect, I am pretty sure the main wheel was the issue all along, and that the shimmy was speed related, and due to the fact we almost always fly with only the two of us, the speed range just happened to be below where I could keep the nose wheel off------the addition of the third person allowed the plane to stay on the mains only, until the speed dropped down to shimmy range this time.

And just to make matters worse, this happened on the last flight before I planned to start my "annual" inspection prior to OSH.

For those who are thinking that I should have checked the wheel pant for being loose as a part of the preflight------I do, and it was not loose. In fact, the bracket is still mounted tightly. My suspicion is that the wheel balance is the culprit here.

I hope others can learn from my mistake-----------if you dont find the problem where you "know" it to be, dont get tunnel vision, start looking somewhere else.

Take care, fly safe.
Click to expand...

Long term issue for me. Camera mounted on the belly confirmed RH main gear was the culprit 3 or 4 years ago. I have pretty much checked everything mentioned on this thread. I have Seans spacers, Tim Olsons wheel pant mount extenders, checked gear leg torque, checked gear leg play, tried wood stiffeners, always balance the wheels with new tires, have tried many different tire pressures, all to no avail. Mine starts at about 15 knots GS and is gone by18 to 20 knots. Seems worse on deceleration after landing with moderate to heavy braking. I have pretty much given up on finding "the cure" and just work to minimize operating at the offending ground speeds. RV-14 type main gear legs would be sweet!
 
Same here.

dmaib said:
Long term issue for me. Camera mounted on the belly confirmed RH main gear was the culprit 3 or 4 years ago. I have pretty much checked everything mentioned on this thread. I have Seans spacers, Tim Olsons wheel pant mount extenders, checked gear leg torque, checked gear leg play, tried wood stiffeners, always balance the wheels with new tires, have tried many different tire pressures, all to no avail. Mine starts at about 15 knots GS and is gone by18 to 20 knots. Seems worse on deceleration after landing with moderate to heavy braking. I have pretty much given up on finding "the cure" and just work to minimize operating at the offending ground speeds. RV-14 type main gear legs would be sweet!
Click to expand...

It's 16kts for me. Taxi below that and no trouble. The only fix I found was grass, never happens on smooth grass runways:D

I do find it is better with a loaded plane and aft CG.
 
Mike,

Perhaps Anti-Splat's main wheel bearing mod and tire balance may be a good investment. Allan will have the wheels back to you in a heartbeat.

Regards,
 
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On my 6A, I have had the 'Shaking' problem also. Fooling with the nose wheel (break-out, air pressure, etc.) never really did anything to solve the shaking. Only when I would put on new tires on the mains did the shacking go away. And return when the tires would get worn. I contrubute it to out of balance tires.
 
Judging by your tire wear you have a significant amount of toe-in and if you want to get rid of the shake, the wheel alignment will have to be taken care of.
 
I was chasing this problem for a couple years or more. I found the shimmy on taxi around 14-16 kts was the nose wheel. And the shaking on landing was the main gear. The shaking only happens when the wheel pants are installed. I mounted a camera on the belly and did several taxi take-offs and landings. My shaking as everyone describes on landing would start around 32-34 kts and be gone at 36 or so. It was worse the more the airplane was loaded. I Also install Sean's spacers.
I changed tires to retreads and balanced them. I increased air pressure and it was a little better. As tires wore it got worse again. After another year of chasing the problem. I then machined some solid wood gear stiffeners and glued them to the back of the gear legs with Lord adhesive wrapped them with 2 layers 9oz 3 inch tape and epoxy. I purchased new Goodyear flight custom III tires. I also put on the new Matco brakes. All shimmy is gone it has been over 1 year and smooth as silk no matter how I am loaded.
I know Sean Strasburg put the wood stiffeners on before me and I got the dimensions from him to start with. I think he is still shimmy free as well. I will
post some pictures later. Sean if your out there you might throw in your 2 cents. I think some of the gear stiffeners people are using for the 2 place RV's
are not solid enough for the RV-10.

Mike Glad you and your passengers are OK. Good job
 
Judging by your tire wear you have a significant amount of toe-in and if you want to get rid of the shake, the wheel alignment will have to be taken care of.
Click to expand...

Mine looked exactly the same at about 150 hours when I flipped the tires,
now replaced with new ones at 260 hours.

Once the gear legs are drilled into the socket you can no longer adjust it
for toe in or out.
FYI: I had the aftermarket wheel pant spacer installed since new.
I am referring to the extension on the outboard side of the wheel pant.
 
Aerosport1 said:
The shaking only happens when the wheel pants are installed.
Click to expand...

Now, that is an interesting bit of information.

Aerosport1 said:
My shaking as everyone describes on landing would start around 32-34 kts and be gone at 36 or so.
Click to expand...

My shaking was only on landing, never on taxi. It had always happened just after I lost enough speed that I had to let the nose wheel down----with nobody in the rear seat.

This was the first time it shimmied with the nose wheel still up.

Aerosport1 said:
Mike Glad you and your passengers are OK. Good job
Click to expand...

Thanks, all happened so fast there was no way to do anything but let instinct/reactions take over-------luckily I had somehow developed the correct reactions.

Please start a thread about your gear leg stiffeners, and photos if you can. It sounds like this may be something a lot of 10 builders will want to know about.
 
Mike
I never had any shaking except on landing on the main gear either. I had nose wheel shimmy at about 14-16kts but 1 kt difference up or down and it was gone.
 
Balancing surprise

Another data point. I static balance my tires every annual and I'm amazed at how many of those little 1/4 oz weights it takes to balance the mains. It is between 5 and 12 on each tire if I recall. If you haven't done it, you might try adding that to the solution. However, based on my discussions with Sean, it seems that the gear leg stiffeners provided him the most bang for the buck.

Looking at this from an analytical standpoint, I think what we are seeing is a incipient harmonic vibration. The gear legs (or the bearing on the nose wheel) act like tuning forks. Once a perturbation is introduced at the right speed the gear legs "hum". So, in order for this to happen, a perturbation has to be introduced. That could be a tire out of balance, brakes that slip a little, differential surface friction on the landing surface, or many other things. It's analogous to the Vne discussion that Van's put out - you can exceed Vne in smooth air but if you hit a bump it could go to a violent destructive harmonic in a fraction of a second. The violence and ramifications are not of the same amplitude on gear leg vibrations, but the outcome can be pretty unpleasant.

So...you can try to eliminate the perturbations or disturbances (pretty difficult since tires wear, brakes wear, etc) or change the harmonic frequency of the tuning forks/gear legs. The latter is what the stiffeners do and is probably the best solution to the problem.

My $0.02. Can't help but think about the physics, a curse from being an engineer.
 
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douglassmt said:
Looking at this from an analytical standpoint, I think what we are seeing is a incipient harmonic vibration. The gear legs (or the bearing on the nose wheel) act like tuning forks. Once a perturbation is introduced at the right speed the gear legs "hum". So, in order for this to happen, a perturbation has to be introduced. That could be a tire out of balance, brakes that slip a little, differential surface friction on the landing surface, or many other things.
Click to expand...

Yep, agree totally.

Also, remember a couples posts above, Geoff stated he never got the shakes without the wheel pants. Small mass added to the end farthest from the mounting socket-----plus whatever aerodynamic forces the pant generates.
 
During my videos of the gear shake the wheel pants would shake nose up nose down. They did not shake or wobble side to side. Hope this makes sense.

The gear on the RV-10 act like an RC airplane gear made out of music wire. Especially on a tricycle gear RC airplane. Anyone out there that fly's RC has see this
were the gear shakes fore and aft when taking off or landing with a wire gear. Just an example. If wheel pants would be put on it would be more violent like when adding
wheel pants to the 10.

FWIW
 
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Mike S said:
Yep, agree totally.

Also, remember a couples posts above, Geoff stated he never got the shakes without the wheel pants. Small mass added to the end farthest from the mounting socket-----plus whatever aerodynamic forces the pant generates.
Click to expand...

It's worse than that. The wheel pants and mounting system have their own resonant frequency. If you excite that the pants will overshoot then spring back (technical terms -:)) with the amplitude growing until something breaks - as evidenced by the damage to both sides of your pants' mounting hardware.
Beefing up that outboard axle extension will make the system stiffer.

It is clear that some very small things can make a difference. Some have suffered shimmy and cannot seem to eliminate it despite trying lots of things. Others, like myself, have had no problems. I attribute this, in my case, to luck more than mechanical expertise.
 
douglassmt said:
Another data point. I static balance my tires every annual and I'm amazed at how many of those little 1/4 oz weights it takes to balance the mains. It is between 5 and 12 on each tire if I recall. If you haven't done it, you might try adding that to the solution. However, based on my discussions with Sean, it seems that the gear leg stiffeners provided him the most bang for the buck.

Looking at this from an analytical standpoint, I think what we are seeing is a incipient harmonic vibration. The gear legs (or the bearing on the nose wheel) act like tuning forks. Once a perturbation is introduced at the right speed the gear legs "hum". So, in order for this to happen, a perturbation has to be introduced. That could be a tire out of balance, brakes that slip a little, differential surface friction on the landing surface, or many other things. It's analogous to the Vne discussion that Van's put out - you can exceed Vne in smooth air but if you hit a bump it could go to a violent destructive harmonic in a fraction of a second. The violence and ramifications are not of the same amplitude on gear leg vibrations, but the outcome can be pretty unpleasant.

So...you can try to eliminate the perturbations or disturbances (pretty difficult since tires wear, brakes wear, etc) or change the harmonic frequency of the tuning forks/gear legs. The latter is what the stiffeners do and is probably the best solution to the problem.

My $0.02. Can't help but think about the physics, a curse from being an engineer.
Click to expand...

Boy, I think that was the most accurate description of the shake.

I did make stiffeners for my gear made of oak. My shake is gone now since I mounted them. Like Geoff explained, I wrapped mine in fiberglass too. Fairly easy mod and now my passengers ride smooth and not think my plane as an "experimental".:eek:
 
Aerosport1 said:
During my videos of the gear shake the wheel pants would shake nose up nose down. They did not shake or wobble side to side. Hope this makes sense.

The gear on the RV-10 act like an RC airplane gear made out of music wire. Especially on a tricycle gear RC airplane. Anyone out there that fly's RC has see this
were the gear shakes fore and aft when taking off or landing with a wire gear. Just an example. If wheel pants would be put on it would be more violent like when adding
wheel pants to the 10.

FWIW
Click to expand...

I wonder if having a brake disk which was slightly out of true (e.g., grabbing slightly once each wheel revolution) could excite this mode? The excitation frequency would certainly be very speed dependent.
 
I've seen posts in which people talked about drilling a hole in the leg and adding sand to reduce harmonic oscillations to avoid cracking at the weld. Might that be another possibility? Kill two birds with one stone.
 
There is no weld in the gear leg.
It's made of tempered steel, not something you can drill without special equipment or do so before the gear leg is hardened.
 
N427EF said:
There is no weld in the gear leg.
It's made of tempered steel, not something you can drill without special equipment or do so before the gear leg is hardened.
Click to expand...

Well, I am a 7 guy but the 7's have a solid leg tapered down to the axle, then the axle is hollow to accommodate the larger diameter inner bearing race, it is welded on. I don't know how the 10 gear legs are made, but I suspect the same.

It could be possible to fill that cavity with silicone and a steel bar to damp the vibrations. Mass and damping. That is IF that would provide a benefit. no drilling required.

I wonder if there is any VAFer that has access to a 4 post rig that could test the gear.
 
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Wheel shake

The wheel cover is repairable. I just pieced mine back together from last years forced landing. My wheel cover was in 5 pieces and some was missing all together. It was fun making it look like a wheel cover again.
Oh the wheel shake thing can be fixed with wooden gear leg stiffeners, on my first taxi test I thought the wheel and all was going to depart from the aircraft but after I put on the stiffeners it is smooth like silk. As a side note, I did not balance the wheels and the right wheel is even egg shaped to a very noticable degree and still no shake at any speed.
Take your time and enjoy the repairs. Thank you for sharing your adventure.
 
ERushing said:
I've seen posts in which people talked about drilling a hole in the leg and adding sand to reduce harmonic oscillations to avoid cracking at the weld. Might that be another possibility? Kill two birds with one stone.
Click to expand...
I have seen that proposed for the step but not in the gear leg. I would think drilling a hole in the gear leg would make it weak.
 
Folks, first off ---- thanks for the input about the various gear leg dance issues, and a much bigger thanks to those of you who expressed "good job, glad everyone is OK" type thoughts------they are much appreciated.

But, the entire purpose of my starting this thread was to get folks thinking a bit "out of the box" so to speak, when they can not find a problem that they KNOW is there. Thus I posted in the "Safety" forum. Gonna have to try that again.

Guess it is time to move this thread to "RV 10" forum.

Again, thanks for the input, and please keep the good info coming.
 
Two points...

1) Mike's focus on prodding us to think outside the box is absolutely the best part of this thread. We are typically mechanically inclined and tend to get very fixated on break/fix methodologies. It's exactly that mindset that Mike is encouraging us to challenge, and rightly so.

2) Now switching back to the break-fix mindset, it would do us some good to look at the lineage of these gear legs. If I'm not mistaken they're still supplied to Vans by Langair. Harmon Lange got started in this landing gear business as a builder of one of Leeon Davis' wonderful designs, the DA2A. The DA2A exhibits the same kind of transitory gear leg shake, to the point that Leeon added a note in the DA2A builder's handbook to recommend that pilots just accellerate/decelerate through the "shake speed range" as quickly as possible. Some builders stiffened their gear legs with wood and eventually developed cracks in the welds of the gear mounts. Others (I'm in this group) found that running the 5.00-5 tires at about 26psi reduced the shake speed range to a very narrow range of speeds.

I point this out only so we can be aware that gear leg shake on these "Whittman-style" gear legs has been around as long as this style of gear leg has been in existence. While we can fix the shake, or at least move it to a different speed range, Mike's original point should be our big take-away. If something is not right, zoom out and take in the whole picture rather than allowing yourself to get caught inside a little box. Who knows, while outside the box you might just find some other maintenance item that you weren't looking for.
 
Canadian_JOY said:
Two points...

1) Mike's focus on prodding us to think outside the box is absolutely the best part of this thread. We are typically mechanically inclined and tend to get very fixated on break/fix methodologies. It's exactly that mindset that Mike is encouraging us to challenge, and rightly so.
Click to expand...

Thanks Mark, you got it right on the money.

Canadian_JOY said:
Mike's original point should be our big take-away. If something is not right, zoom out and take in the whole picture rather than allowing yourself to get caught inside a little box. Who knows, while outside the box you might just find some other maintenance item that you weren't looking for.
Click to expand...

I really like your "Zoom Out" comment------great metaphor.

I started a new thread to continue this line of thought, see here. http://www.vansairforce.com/community/showthread.php?t=114768
 
Death Wobble

Anyone reading this that has owned a Jeep, I'm sure the first thing that comes to mind is: "Death Wobble"

It's a violent oscillation that feels like the entire front end is going to be ripped off. Need to pretty much come to a complete stop to get the oscillation to stop.

I think Bryant pretty much nailed it; some perturbation is needed to start a oscillation that can be quite violent.

For the Jeep, just about anything can be the source of Death-Wobble: suspension, steering bushings, tires, sway bars, etc... For mine, at about 45mph, hitting a bump could cause it. The "solution" (or band-aid, really) was a bigger steering stabilizer than stock. This dampened an oscillation enough to not become full blown Death-Wobble.

So, there is not a whole lot to an RV landing gear, and I think they are all build a little differently and will oscillate at a different frequency, and the root cause might be in the design and construction of the aircraft.

To suggest a "solution": How about a small shock absorber, that will attach to the upper and lower gear leg? Kind of like replacing the wooden gear stiffener with a shock the size of a lift gate strut.
 
Landing Gear

The correct spelling is Wittman. Steve Wittman designed and patented the flat spring gear around 1935. The round spring gear in the late 40's early 50's. The rights to the flat gear were sold to Cessna in the mid 40's, just before the start of post war production at Cessna.
The round gear was available from several vendors before Harmon Lange. Wittman sold landing gears in the 50's. Harmon Lange started out building landing gears when he was in Wisconsin. Initial sales were almost entirely to Wittman Tailwind builders.
The Wittman round gear does not have an inherent vibration problem. The vibration problems that do occur have a multitude of causes, starting with poor fit in the mounting socket and/or poor fit of the attach bolt.
I have posted many times on this subject. If anyone wants to discuss this further with me, email me at [email protected]
 
Thanks for correcting my spelling, Jim. My typing fingers and brain aren't necessarily well connected! :)

This issues you've mentioned are all real - and as you've suggested, getting the right combination of installation elements is critical to success.
 
Boring video

I shot this video yesterday of my gear to see what they are doing. It includes a long taxi over some different surface, different speeds, takeoff, landing, and another long taxi. There are a couple spots where it starts to shimmy a bit but it doesn't last. I didn't notice anything unusual or severe in the cockpit. I might install stiffeners eventually but it doesn't seem urgent. Be sure to watch it in 1080.

http://youtu.be/KQpRXwEuwzY
 
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First time MLG Shimmy

We landed at KVSF RWY 23, "asphalt good condition", a few days ago. We normally touch down at 60 kias. Just after touch down at 2530 lbs, aft CG, nose wheel kept off, we hit some rough areas of the runway which initiated the oscillation. I knew it was not the fore-aft 14-17 kt oscillation from the nose gear. Knowing what happened with Mike's, I slowed from 55-25 kts as quickly as possible before it let up. It seemed to last forever. Inspected the wheel pants, no damage noted this time and continued on our trip. I knew the other shorter rwy was in "excellent condition", and will take it next time even with a greater crosswind. Still enjoying the heck out of our family hauler.
 
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