elevator balance

Geo · #1 09-10-2007, 12:44 PM

Hi all.
I just fitted my horizontal stabilizer to the fuselage, and then I mounted the elevators to it.
The RIGHT elevator is overbalanced (as it should be), i.e. when I let it go, the counterwight arm goes down and the trailing edge goes up. After finishing it, I will drill out lead weight untils it stays "in trail" as specified in the instructions.
Bu the LEFT elevator is already underbalanced, when I let it go the trailing edge goes down (FYI, I have the electric trim option). So, if I paint it, it will be even more underbalanced. So it looks like I will have to add more weight in the counterweight arm. Any of you has/had the same problem? How did you fix it?
Thanks for any help.
Giovanni

Mike S · #2 09-10-2007, 01:56 PM

Here is one way----old trick from the R/C airplane days.

Tape a small paper cup to the counterbalance (elevator mounted on stab) and add lead shot until it achieves the necessary weight to balance.

Weigh the lead shot, and deduct 1 ounce.

Mix up an ounce of epoxy, mix in the shot, and pour it into the nose of the elevator, now off of the plane again, place the elevator in a nose down position until the epoxy cures.

briand · #3 09-10-2007, 03:00 PM

It doesn't take much weight to make it go the other way. There is a tooling hole just aft of the lead weight. On my left elev. I will add a bolt washer(s) and nut as needed to balance.

FredMagare · #4 09-10-2007, 04:36 PM

I'm not at that point, but keep in mind that the elevators will be tied together! In short, currently one is underbalanced and the other is overbalanced. After painting you may have to do nothing to them.

L.Adamson · #5 09-10-2007, 05:42 PM

Originally, I balanced the elevators seperately, and drilled a lot of lead out of the one, that didn't have the electric trim servo. The one with the trim, balanced rather well.

Then, a few years later, I painted the elevators, and soon saw, that I needed to add all the lead back again.

This time I bolted the two together as a unit, & only added weight back to the one I had previously drilled out. It actually took a bit more, than I initially removed.

In the end, I wish I hadn't removed lead to start with. As to those who fly un-painted, I guess you have to do, what you have to do...

L.Adamson RV6A

DaX · #6 09-11-2007, 06:23 AM

I always thought you were supposed to balance them together as one unit.

WSBuilder · #7 09-11-2007, 08:00 AM

Seems to me that the elevators being coupled together would help dampen, but the long moment (CW to control arm) will allow a divergent resonance (flutter) to form in the one unbalanced control surface.

Who wants to do some Vne experiments for this group?

FredMagare · #8 09-11-2007, 10:11 AM

Quote:

Originally Posted by WSBuilder

Seems to me that the elevators being coupled together would help dampen, but the long moment (CW to control arm) will allow a divergent resonance (flutter) to form in the one unbalanced control surface.

Who wants to do some Vne experiments for this group?

This seems logical and a potential concern. Perhaps you could drill-out the fiberglass wing-tips and simply re-install new C/B weights?

Geo · #9 09-11-2007, 10:24 AM

I just want to add a quick comment.
I strongly believe that the elevators must be balanced separately .
Aerodynamic flutter may be induced in a single unbalanced elevator even if it is joined with another one and the group is balanced.
I learned this lesson years ago when I was rebuilding a long-ez. Burt Rutan was very clear that elevator and aileron balance is critical and must be done on each piece individually. So, this is what I will do.
Thanks to all for your input.

L.Adamson · #10 09-11-2007, 02:10 PM

Quote:

Originally Posted by Geo

I just want to add a quick comment.
I strongly believe that the elevators must be balanced separately .
Aerodynamic flutter may be induced in a single unbalanced elevator even if it is joined with another one and the group is balanced.
I learned this lesson years ago when I was rebuilding a long-ez. Burt Rutan was very clear that elevator and aileron balance is critical and must be done on each piece individually. So, this is what I will do.
Thanks to all for your input.

I've been around these RV matters for around 12 years. I clearly remember elevators being balanced "both" ways, without it being a huge issue.

Personally , I'd like to see some specific information, such as something in an RV building manual, rather that specs for a different design.

Otherwise, this builders forum could spread unwarranted information, that may not apply to RV's.

L.Adamson

edit: after just reading through numerous posting/replies (out of 400) on the Matronics List archives, it appears that it's just fine with Van's to balance these elevators as a unit. Information came from the Van's booth at Oshkosh, as well as over the phone.

There is even info on the ailerons not needing pure balance because of the short wing spans. Just throw in the water pipe weight, and let the ailerons balance each other.