better? more or less breakout force

andrew phillips · #1 04-10-2009, 03:55 PM

After 70hrs my nose-wheel breakout force is quite a bit less than original. If I leave the nut where it is then I have less than the specified force. If I turn the nut to the next location for a cotter pin I have more than the specified force. Without drilling a new hole through the axle, which is better? Which causes less wheel shimmy?

rvbuilder2002 · #2 04-10-2009, 04:07 PM

Quote:

Originally Posted by andrew phillips

After 70hrs my nose-wheel breakout force is quite a bit less than original. If I leave the nut where it is then I have less than the specified force. If I turn the nut to the next location for a cotter pin I have more than the specified force. Without drilling a new hole through the axle, which is better? Which causes less wheel shimmy?

It usually needs to be adjusted a couple of times when new while it breaks in so I would go for a little more as long as it is not excessive.

Bob Axsom · #3 04-11-2009, 01:59 AM

Don't hesitate to go to the next higher notch. Even it doesn't settle in some more the one notch higher will not cause a problem. you really need the specified breakout force as a minimum.

Bob Axsom

guccidude1 · #4 04-11-2009, 08:30 AM

You can also add a thin washer under the axle nut to give you more breakout force using the same cotter pin hole. It's one of those "if you can't raise the drawbridge, lower the river things". Dan.

jetjok · #5 04-11-2009, 10:17 AM

Quote:

Originally Posted by guccidude1

You can also add a thin washer under the axle nut to give you more breakout force using the same cotter pin hole. It's one of those "if you can't raise the drawbridge, lower the river things". Dan.

Exactly! Or, remove the existing washer for one that has a greater thickness. There are many ways to "get there" and you do not have to settle for out of tolerance "break out" tensions.
Good Luck!

Lionclaw · #6 04-11-2009, 10:22 AM

This thread has perfect timing! I'm just getting ready to drill the hole for my pin. Should I set the breakout force a few pounds higher in anticipation of it loosening up?

rvbuilder2002 · #7 04-11-2009, 11:32 AM

Quote:

Originally Posted by Lionclaw

This thread has perfect timing! I'm just getting ready to drill the hole for my pin. Should I set the breakout force a few pounds higher in anticipation of it loosening up?

No...a small amount of turn on the nut makes quite a bit of change once the initial adjustment is set, so you can generally use the same cotter pin hole. You should try and get it close to the specified value, if you get it much tighter it requires a lot more break usage to manuver
It is just something that has to be checked occasionally when the airplane is new. After you have 100 hrs or so it usually never changes anymore.

Bob Axsom · #8 04-12-2009, 10:26 AM

If you let the breakout force get low the nose gear is very prone to oscillation that is so violent you will think the nose tire has blown out and your thoughts turn to the next level in the landing scenario - limiting damage. The oscillations do not stop until the airplane completely stops moving. The washers are not common flat washers and stacking unknown shim washers in nosegear assembly to line up the hole in the nose strut with the exact notch in the nut that will give you the precise breakout force as measured with an uncalibrated fish scale, pulling at an angle that you hope is normal to the strut tire plane at an approximate distance from the pivot point is just silly. Going over the target breakout force is not an operational problem beyond the possible increase in brake wear when you need to turn and start moving from a standing still situation as mentioned by Scott McDaniels. I have had mine up well over 23 lbs specified for my RV-6A and it is not a problem. As scott says it gets lower with use in the early life of operations. I set mine as close as I could get it in the initial build and the initial flights were fine. The first time it went into the oscillation I had no knowledge about the "settling in" breakout force reduction that is characteristic of this assembly. When I went through rechecking everything I found the and found the breakout force was down in the mid teens. I checked it every so often after that and at every annual condition inspection. A couple more times during first 100 hours or so I had to tighten the nut. Since then as Scott says, the breakout force has held steady.

Bob Axsom

andrew phillips · #9 04-12-2009, 10:58 AM

I thought I had blown a tire on a couple of landings but then when I stopped there was no damage. My partner was flying the plane and on a landing another pilot radioed him to say that something was wrong with the nose gear. He described is like a "motorcycle tank slapper". That is exactly what is was. I tightened the nut and also changed to the new Matco axle. So far so good.

flyboy1963 · #10 06-22-2009, 09:08 AM

thanks for the info, but I am curious how accurately we can possibly set this.
Obviously 'stiff' is good.
I set mine on the bench to about 30 lbs.
After install, and weight on the gear for a week, it is now about 12 lbs.
All this must be affected by the temperature, and lubricant on the washers etc. If no lube is used, they will rust and seize, I would think.
I was going to pre-drill 2 sets of holes in the gear leg, but didn't want to weaken it.
Why not drill an extra hole in the nut, halfway between the slots? This would have negligible effect on the nut strength. Shimming sounds good also, except for more disassembly required, and finding the right washer is tough.

comments?