Nose gear fork swivel action -- should the disc springs rotate with it???

[roee]

Putting the nose gear fork on the gear leg for the first time (with the disc springs, flat washer, and nut as specified) I noticed the following peculiarity: When I swivel the fork, the disc springs rotate with it. That doesn't seem right, does it?

To elaborate a bit: I would have thought that when the fork swivels, the disc springs should remain stationary, and there would be a "bearing surface" where the top disc spring contacts the brass bushing of the fork. Instead, the disc springs rotate with the fork, and so the "bearing surface" is where the bottom disc spring contacts the flat washer. Again, that just doesn't seem right. I'm not worried about the disc spring cutting into the flat washer, which is easily replaceable. But I would worry that over time the rotating disc springs might cut grooves into the gear leg, which wouldn't be good...

Please respond with experience and insight:

Do your disc springs rotate with the fork, or do they remain stationary?

Do you know if the design intent is for the disc springs to rotate or not?

(I will also call and ask Van's about this on Monday, but I'd sure also like to hear from the group)

Thanks,
-Roee

[Mike S]

http://en.wikipedia.org/wiki/Belleville_washer

Search old threads for this, I have seen it before-----

Have you already set the break out force???

[Walt]

If they were designed to remain stationary they would have to be keyed to the axle.

[roee]

Originally Posted by Mike S

Search old threads for this, I have seen it before-----

I searched. Didn't find any other thread dealing with this issue. Do you have a link?

Originally Posted by Mike S

Have you already set the break out force???

Yes. Breakout force is set per specifications, 22 lb.

Originally Posted by Walt

If they were designed to remain stationary they would have to be keyed to the axle.

You're right that there is no keying mechanism there to positively keep them from rotating. But that doesn't mean they are meant to rotate.

The effective bearing surface -- the contact surface where adjacent parts will rotate against each other -- will be the contact surface that has the least friction of all the contact surfaces, and therefore will be the first to allow relative movement when force is applied.

There are four possible candidates here (listed from top to bottom):
1) the contact surface between the top Belleville washer and the brass bushing of the fork
2) the contact surface between the two Belleville washers
3) the contact surface between the bottom Belleville washer and the flat washer
4) the contact surface between the flat washer and the nut

I would have expected it to be number 1, but evidently in my case it is number 3. So the question is: is that supposed to be the case, or is there something wrong with my setup?

[terrykohler]

There are four possible candidates here (listed from top to bottom):
1) the contact surface between the top Belleville washer and the brass bushing of the fork
2) the contact surface between the two Belleville washers
3) the contact surface between the bottom Belleville washer and the flat washer
4) the contact surface between the flat washer and the nut

I would have expected it to be number 1, but evidently in my case it is number 3. So the question is: is that supposed to be the case, or is there something wrong with my setup?
__________
Roee:
1. You probably wouldn't want a hardened steel spring rotating against the soft bushing.
2. Make certain the two bellevilles are positioned correctly. If they're stacked up with the profile the same, the spring force will be 2X what you'd see if they are aligned opposed. The latter will give you greater travel.
4. In many fastener applications, you'd like to see relative motion between a hardened nut and hardened washer-this typically allows greater clamping force for a given torque. You're not looking for clamping force here.
3. This is probably most desirable, since both the bellville and flat washer are hardened, likely producing the lowest coefficient of friction and the least possible wear or galling situation.
Terry, CFI
RV-9A N323TP

[AlexPeterson]

In observing several of these, the rotation seems to go all the way to the nut. Of course, the nut is limited by the cotter pin, but if one observes closely, it can often be noted that the nut is turning slightly back and forth (hitting the cotter pin).

This is not a surprising result, since the radius upon which the friction is acting is minimum at that point. I.e., if the coefficients of friction are essentially the same between all members of the stack, one would expect the relative rotation at the point where it is acting on the smallest diameter.

I did not like the nut constantly beating on the cotter pin, so I found a 1-1/4"-16 threaded split collar. I use this instead of the castle nut.

Unfortunately, I do not know where I got this (I or a friend bought two of them, and neither of us remembers where). I have done a lot of searching, and cannot find a manufacturer who sells one with that size thread.

If I had the cotter pin, I'd replace it at every annual as a precaution.

[868RM]

With some effort you can pin that washer. You will need a milling machine and some carbide tooling. ( I put a .125 dia. roll pin through gear leg ) McMaster Carr has a washer to put next to the bronze hat bushing that is .135 thick. With proper fitting you can end up more than .030 wear before the pin will hit the spring washer. My plane is under construction but nose wheel breakout is very consistent . Hope this helps. PM me if you want more info. Ron

[roee]

Just to close the loop here: I spoke with Van's tech support about this issue. They indicated that this is normal and not a problem. They recommend keeping all parts in the stack-up well greased to minimize galling. Also, to inspect the washers periodically (I'll probably do this at annual) and replace as needed. In their experience, the washers do wear over time, but they haven't seen any scoring of the gear leg.

Thanks again to all who replied.