Rebalancing elevators after paint

Paul Eastham · #1 10-31-2008, 01:04 PM

Hey everyone, I hope to pick up my 9A from the paint shop pretty soon, and am trying to prepare for what I will need to do to get it back in the air.

I know the answer will vary depending on paint job and elevator size, but roughly how much weight did you all have to re-add to your elevator counterweights to get them back into balance?

I had to drill out my counterweights pretty aggressively, so I have plenty of spots to add weight. I also have lots of lead scrap and shavings left over. If the adjustment is small, I was thinking about rolling up some of the shavings, packing them into the holes in the counterweight, then epoxying in place. If a big adjustment is needed, I'm not sure what to do.

2nd question: did anyone bother rebalancing the rudder? I can't access those weights, not sure where I would add weight...

N55CU · #2 10-31-2008, 01:12 PM

Hi Paul, I flew my RV-7 home yesterday after picking it up from GLO (beautiful job on the paint-could not be happier) and do not see a need to do any further balancing. Don't see any value in trying to balance the rudder.
Randy Utsey
N55CU
RV-7 150 hrs
Charlotte, N.C.

Mel · #3 10-31-2008, 01:25 PM

The elevators and the rudder need to be rebalanced after paint. The most common procedure is to leave the surfaces "overbalanced" slightly before paint. An over balance is not as bed as under balance. If you had them balanced before paint, you really need to balance them again. And the rudder sees the exact same forces as the elevator, so it should be done also.

plehrke · #4 10-31-2008, 01:27 PM

It should not take very much to rebalance. Do not remember exactly but I believe it was only a couple washers worth of weight. (of coarse your results may vary based on how far from the hingeline you are adding the weight).

Remember that statically balancing the elevator is not for flying forces. Just because it did not feel like you needed it does not mean you do not need to get it balanced. Having an unbalanced elevator will reduce your Vne. If it is unbalanced you will experience flutter at a lower speed then if you have it balanced.

Paul Eastham · #5 10-31-2008, 01:32 PM

Quote:

Originally Posted by plehrke

It should not take very much to rebalance. Do not remember exactly but I believe it was only a couple washers worth of weight. (of coarse your results may vary based on how far from the hingeline you are adding the weight).

How are you balancing within a few washers' worth of precision? The drag from the bearing is way more than that (I have to do it *on* the airplane in order to balance them as a single unit -- one counterweight was too small, the other too big)

DaX · #6 10-31-2008, 02:27 PM

OT, but Paul - be sure to post pictures of the paintjob. I read your entire build, and even though I'm building a -7, it is/was/has been helpful!

kentb · #7 10-31-2008, 03:06 PM

I need about 1/2 lb in each elevator after painting. I drilled 1/4 hole in the nose rib. I mixed fiberglass resin and added lead shot (as in shotgun reloading supplies from GI Joes). I poked it through the hole and made sure the the nose of the elevator was down so that it would harden at the tip.

Good luck.

Kent

Kevin Horton · #8 10-31-2008, 03:22 PM

Quote:

Originally Posted by Paul Eastham

How are you balancing within a few washers' worth of precision? The drag from the bearing is way more than that (I have to do it *on* the airplane in order to balance them as a single unit -- one counterweight was too small, the other too big)

Keep in mind that if you balance them as a unit torsional stiffness of the connection between the elevators comes into play. The flutter speed will be lower than it would be if each elevator was balanced individually.

Paul Eastham · #9 10-31-2008, 04:21 PM

Thanks for the replies. Sounds like this won't be a totally trivial project...too bad it has to happen a ways away from home.

Maybe with the added paint weight, I'll be able to balance each elevator separately (and if not, I guess i can bolt them together, off of the airplane).

I'll come equipped with lead shot, epoxy, and a drill. And some tape to cover the holes with until I get back to the nest.

rvbuilder2002 · #10 11-01-2008, 11:11 AM

Quote:

Originally Posted by Paul Eastham

Thanks for the replies. Sounds like this won't be a totally trivial project...too bad it has to happen a ways away from home.

Maybe with the added paint weight, I'll be able to balance each elevator separately (and if not, I guess i can bolt them together, off of the airplane).

I'll come equipped with lead shot, epoxy, and a drill. And some tape to cover the holes with until I get back to the nest.

Paul,
As long as you can stay well within the airspeed indicator green arc range, you would be fine to just fly the airplane home and do the rebalance there (unless the painter some how put on a horrendous amount of paint).

As Mel said, slightly over balanced is not a real bad thing which is why the weights are supplied with more than enough mass (in most cases) to do a proper balance job. It is much better if builders wait until after painting to drill out weight instead of having to add it back afterwards.