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Break-out force adjustment

R

rightrudder

Well Known Member
I've got 82 hours on my RV-9A so far, and when I came back from my breakfast run this morning I picked up just a hint of shimmy from the nose gear on landing. It was the first time I've experienced this.

So I pulled off the wheel pant and checked the break-out force....15 lb., when it should be 22 lb.

So my question is, should I just tighten the castle nut 1/6 of a turn and reinsert the cotter pin? I'm thinking the break-out force will be well in excess of 22 lb. if I do this.

The alternative would be to drill another hole (at close to 90 degrees from the original hole) in the threaded portion of the nose gear, so I can tighten in increments of 1/12 turn and still secure the cotter pin.

I'm curious as to what others have done, and if you can't get the force at 22 lb., is it better to err on the high side?

BTW, I am LOVING this airplane!!!!
 
It really depends on how high it gets with a 1/6th turn. That is usually what we do. High is better than low. I never drill an extra hole. Just give it one flat and out in a new cotter pin.

Btw, at 16lbs I doubt the shimmy is coming from there. I only get shimmy from breakout force when it is next to nothing for breakout force.
 
Jesse said:
It really depends on how high it gets with a 1/6th turn. That is usually what we do. High is better than low. I never drill an extra hole. Just give it one flat and out in a new cotter pin.

Btw, at 16lbs I doubt the shimmy is coming from there. I only get shimmy from breakout force when it is next to nothing for breakout force.
Click to expand...

All of the Van's Aircraft prototypes have more than one hole.

I agree that higher is better than lower, but there are drawbacks to higher. Higher brake pad wear is one.
If the breakout is set correctly, the majority of ground maneuvering (zero wind) can be done with just rudder.

If the breakout is too low (16 lbs), my experience is that it can definitely result in shimmy, but is dependent on other factors as well. Excessive nose tire pressure will make it much more prone to shimmy.
 
I think I've got a couple of holes in mine. Same with the main gear.

As I recall, there's a bit of a 'gotcha' in the plans if you're not careful. At least the old narrative. I think it mentioned 14 pounds when first fitting things and I think there must have been a notation there to 21 or 22 pounds in final assembly, which I missed.

The thing is: sometime -- rarely, but sometimes -- I think I feel a little shimmy. Sometimes -- most of the time -- I don't.
 
Tire?

What type of tire are you running?

I spent some time trying to resolve a nose wheel shimmy, which included replacing the compresion washers and experimenting with different breakout forces, up to 30lb.

Ultimately I concluded that the shimmy is excited by an out of round tire. However replacing the tire has not been a solution because the new tire is also out of round, out of the box.

My case is a little different because I'm running a very expensive Beringer wheel with a tubeless tire. The wheel is fine but I'm not impressed by the quality of the tubeless tires. If I could wind back the clock I would have bought the antisplat nosewheel with bearing mod and shaved tire.
 
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Thanks for the replies, guys!

Vlad, I promise, more videos to come. I took some footage flying to Bakersfield up the Grapevine, but there were so many fires at the time that visibility was terrible and the video looked awful!! I'll be going to Sedona soon...much better subject matter! Also, I committed to Oshkosh next year; a friend at my airport who's very near finishing his RV-7A wants to go in a flight of (at least) two, so I'm in. :D:D

Great suggestions all around. As for a front tire, I'm running whatever came with the kit...I'll have to check the brand. It could be that with lots of landings and mini-flat spots that it's out of balance now; will check and add balance weights as needed.

I'll try tightening it 1/6 turn and see where the force ends up. Not averse to drilling another hole if necessary.
 
Be sure not to put grease on the 2 Bellville spring washers.i have always torqued mine to a minimum of 23 lbs and checked the tension after working the gear side to side by hand. I don't recommend less tension than Van's states in the plans (23 lbs ).
 
Update: I had to tighten the castle nut a full half -turn to get over 22 lb., so more than I thought. Right now it sits at about 24-25 lb., which is great because it will loosen a bit with use.

I did one landing this morning (meant to do more at my favorite "landing practice" airport in the high desert, but I turned around after getting some nasty turbulence in the Cajon Pass), and it was perfect...no shimmy whatsoever. Even though it's a little tighter than spec, taxiing and turning are easy.

I think break-out force is something I'll check at every 25-hour oil change.
 
I found that after the second setting (the one that you just did) mine has not changed at all in over 8 years. I do check it at each cond. inspection.
 
One other thing to consider... Some of us have solved the shimmy problem by having Anti-Splat Aero upgrade our nosewheel bearings. I had the shimmy problem occur on a regular basis even with the "correct" breakout on my nosewheel. Once I had the Anti-Splat Aero nosewheel bearing mod done about 3 years ago, no shimmy, ever... Just something to think about.

Victor
 
gasman said:
I found that after the second setting (the one that you just did) mine has not changed at all in over 8 years. I do check it at each cond. inspection.
Click to expand...

Good to know. Thanks for the input.

I don't think the shimmy is bearing-related at all. I've got the Matco axle so the taper bearings are pre-loaded, and everything is nice and tight. And so far, in 83 hours' worth of landings, the shimmy has happened just once. I'll update this if I ever get a recurrence.
 
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I had ASA do the bearing and tire tread true up and balance, surprised how much tread they had to remove to make it round, before the new ball bearings, the plane was hard to push around, now I need to chalk it or it will roll out of the hanger on its own.......:D
 
Sounds like you guys have hashed out the break-out pressure thing pretty well, but let me pass along one other thing to check on your nose gear each time you check the break-out. With the tail down, grab the whole nose pant and see if you can wobble it side to side. There have been several cases of this. The gear leg slides up into the engine mount and is secured with one bolt at the top. The hole in the mount can become enlarged and allow the whole gear leg to move a bit resulting in a quarter inch or so at the gear end causing a pretty good shimmy to develop. Depending on how much movement you have (should be none) as to what the required fix might be. Caught early, you can use some Loctite 680 Retaining Compound liberally smeared on the two lobes on the gear leg and slide it back in and tighten the bolt.
 
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