RV-6A Strange Nosewheel Situation

Every once in a while while landing, I get a strange nosewheel action. I have tried a number of techniques, but I can't figure out what I am doing wrong or what is going on. Here's the situation.

I come in and flare. Normal landing speed. Actual speed doesn't seem to make much difference as I have tried different speeds. What happens is that when I hold the stick in my gut, and the nose finally comes down on its own, it appears as if the nosewheel is all the way to one side. It vibrates a lot, like it is stuck over to one side. Sometimes, it feels like it is being thrown to one side. I called Van's and they thought I had the friction nut too tight. My old plans called for a break out force of 28 lbs. They suggested 22 lbs. This did not change anything. Keep in mind that I cannot figure out how to make it do this. It just does it some times. Another suggestion I had from a GlassAir guy was that he had a similar problem and raising the tire pressure up cured the problem. I tried that also, and it appears to help some, but not totally.

Has anyone else experienced such a problem or heard of such a situation? If so, I would like any suggestions. It may be my technique, I just don't know. Any help would be appreciated. thanks.

Roger

how about having someone video tape a
bunch of touch and goes until it happens? And if it's loose and the pant slaps violently to one side; you might notice a damaged stop bracket.

Is it lubed enough?

If it's fore aft movement= I heard guys are super gluing dampening sticks on the nose wheel gear just like on the mains.

good luck- let me know what you find.

Less is more, more is less! (Shimmy that is!)

Mine did this on occasion, I ended up with more breakout force than recommended. Don't know the exact number cause my scale ran out at about 30 lbs, probably in the range of 32 to 34 Lbs., but it stopped the shimmy in mine.
You really need to determine the cause and get this stopped as it can cause some real damage to the nose wheel parts.
Good luck!

What pressure are you running in the nose gear tire? Mine (9A) shimmies alittle when I have less than 25PSI, so I run it at 30-35 PSI. Also, if and when it does start to shimmy apply "medium" braking to slow to taxi speed. That seems to stop it right away for me.

Is your nose gear deck angle correct

maybe you need a nose gear stiffener?

nose shimmy

i built, flew, and then sold a 6a to what turned out to be good friends, in time. he would call me for advise, while getting used to his "new' plane. He started to experience what you are going through. I thought it was his landing technique and i would suggest slower touch down speeds, tire pressure, break out force etc etc. eventually he solved the problem with a new tire. seems that the original tire eventually got wore to the place that it started to cause shimmy. New tire, and no more problem.

steve ciha

I found that the specified torque on the axle nut to be too high and caused the breaings to be too tight, causing the nosewheel to grab on touchdown. I modified the mushrooms that hold the inner race of the bearings by staking them with screws. The purpose of the torque on the axle is to prevent the mushrooms from turning. By staking them, you prevent the turning and can now reduce the load on the bearings so the nose wheel spins more freely. This plus maintaining proper tire air pressure, making sure the wheelpant to tire clearance is adequate, and having the 22 lbs. of break out force has cured all my nose gear problems.

Roberta

This is a picture of the wheel bearing mod I did on my 7A. I removed the yoke and tire assembly from the plane. While the wheel was still assembled in the yoke with proper bearing preload, I drilled a hole through the yoke and into the bearing mushrooms. The hole should go into the mushroom about 1/2" and out from the through hole about 1/2". Disassemble and clean any metal debris. It is also a good idea to mark everything right and left so all the holes line up later.

Tap the holes in the mushrooms for an AN3 countersunk screw and drill out the yoke and countersink those holes. reassemble the wheel and bearings and wheel as normal, lining up the holes and inserting the countersunk screws. The wheel pant brackets will prevent the screw from backing out or a large thin flat washer can be used when pants are not installed.

Now that the mushrooms are staked from turning, I was able to reduce the torque on the axle through bolt. This allows the wheel to turn more freely and, consequently, less spinup drag and grab on touchdown.

Worked for me. But you need to make sure you have also eliminated all other nosewheel problems previously mentioned in other posts.

Roberta

Slick

Roberta, you're one bright woman! Really neat trick. Do you also have wood attached to the nosegear?
Regards,

Thanks, Pierre.

No, I didn't do the nosegear stiffener, but I did do the maingear stiffeners.

I'm not the first to incorporate staking of these bearings. Somebody else before me did it and I thought it a good idea.

Roberta

Roberta:

This may be a stupid question (not the first one for me I might add), but why was it necessary to take the fork/wheel assembly off the airplane to do this? Was it so you could drill in in a drillpress? Couldn't this be done freehand?

Thanks!

Good question

I did mine in situ on the 7a, As long as you can keep the drill straight its pretty simple.

Frank 7a 60 hours...Learning IFR in one of these is "interesting".

Frank

Thanks, Roberta

I was having a little trouble envisioning what you were talking about, but with the photo, it is very clear. I hope some others take this to heart, and do some things like this on their planes too. I will do mine next week and try it. It may take some time to find out if it cures the problem, though, since it is an intermittent thing. The first thing I will do is see how tight the wheel is. If it is free, it might not be this. I am guessing/ hoping that this is the answer. Thanks, again.

Roger.

Nose gear redesign

maybe you need a nose gear stiffener?

Click to expand...

A few years back, the nose gear was redesigned, which moved the flex point down on the gear leg, getting it away from the engine mount. Van's did not recommend a stiffener on this new design. While this was done on the -6A gear, I believe the -7A gear to be made the same way. Putting a stiffener on the gear leg may defeat the purpose of the gear redesign, and make a previous problem rear it's ugly head again.
Anyone else remember this?

The mod can certainly be done without removing the fork. It's just easier off. I did use a drill press to ensure nice, straight holes. Removing the fork is very easy when the plane is jacked off the ground.

Roberta

robertahegy said:

The mod can certainly be done without removing the fork. It's just easier off. I did use a drill press to ensure nice, straight holes. Removing the fork is very easy when the plane is jacked off the ground.

Roberta

Click to expand...

I've used this thread to describe "staking" several times to other RV drivers. Good pics Roberta.

With the nose wheel off the ground ( have someone push down on the tail) grab the nose wheel and try to twist it to see if there is play where the gear leg attaches to the motor mount socket. A slightly loose bolt at the top will cause a lot of play at the fork. I check this once a year along with the breakout force.
Good Luck,

Rich Rudolph
RV6A 900 + hrs