[donaziza]

Wrote an earlier thread on an RV 8 takeoff vibration I had had, and wanted to update. Thanks to all the guys about balencing tires, flat spots, cold Wx. But especially thanks to moderator Randy Lervold on the re-torquing of the landing gear bolts. This was done and I thought for sure they would accept some tightning, but they all turned out to be perfect. I know I'm preaching to the choir with you builder guys, but if there's any buyers, like me reading this, pay special attention to this last one, ie the re-torquing.

 

[Mike S]

Don, a couple of questions---------

When you re-torqued the LG bolts, did you take the weight off the gear??? This will make a difference.

Have you solved the vibration issue, if so, what was the magic bullet??

Thanks.

 

[donaziza]

Hi Mike, A couple of answers to your question. I wondered the same thing, does the weight need to be off the gear before re-torquing. Two RV 8 guys I know who "built" their planes said no. One of them came down personally, with a jack, and we jacked up one side, then the other, looking for any play. None. Then he put his torque wrench on, and every bolt was at proper torque immediately. So-o-o-o, is the vibration gone? Don't know yet, because I grounded the airplane till all this got done.

(Put in new fuel gages too, still waiting the rerquired 3 or 4 days for the compound to cure.) I had done 5 takeoffs and landings that day. The vibration only happened on takeoff number 4, ie nothing on 5, and then I've been grounded since. So to make a long story short, I don't know yet. But I couldn't let those landing gear bolts go without checking. Any of you moderators reading this?? Does the weight have to be "off" the gear for proper torquing?

 

[Ironflight]

Any of you moderators reading this?? Does the weight have to be "off" the gear for proper torquing?

I don't know if it HAS to be off, but that is how I did mine. The gear flexes a significant amount when it gets unweighted, and this has to react against the attachment point on the fuselage, hence changing the loading on the bolts. Is this significant to the torque value? I haven't calculated it, so can't tell you - but generally, I've done the torque checks when I was doing other Landing gear maintenance, so it was already on jacks.

I frequently get a little shake right after take-off, and just tap the brakes to make it go away - slightly unbalanced wheels/tires I figure, and I just never go to the trouble of balancing them. That is a really fast way of determining if your problem is in the wheel department - just tap the brakes!

Paul

 

[donaziza]

My vibration was quite severe and went away the instant the wheels lifted off. Gosh, now I feel like I've got to get a second jack and try it again with both wheels up. ( We only had one jack, or we would have done this).

 

[Little_Richard]

I would not think jacking it up would help at all

I would think jacking the plane up would not help at all. If I remember correctly, the strap (or bracket or whatever you want to call it) that needs to be retorqued is installed from the bottom. If that is true, then if you jack up the plane to torque the bolts then you are in essence having to tighten those bolts against the weight of the gear leg and wheel assembly. This would work against you in getting the proper torque on those bolts. With the weight of the gear leg and the leverage that is involved we are talking about something close to an extra 40 to 50 pounds that is having to be lifted if the tire is off the ground.

We are talking about the outboard mount bolts aren't we? If not, then just ignore everything I just said...

 

[donaziza]

We torqued every darn one of them. How much torque for each one, I left up to the the builder helper, as he knew. There was 5 on each wheel. I can't be sure by memory in front of my computer, but I think it was 3 towards the outboard, and 2 torwards the inboard. The outboard center was the biggest one, and its nut on the inside, right by the gear towers had a cotter key in it. Don't know if that was a "Vans" or the original builder's idea. I have to get a mirror and try to get inside those gear towers Lervold mentioned, and see if they're cotter keyed also.