September 19, 2010
The ailerons and elevators must be balanced with counterweights to make the controls feel light and to prevent flutter. This page will cover adding a counterweight to the ailerons.
You need a couple of 4' lengths of 3/4" x .035" aluminum (6061) tube, about 10 lbs of fine lead shot (available from gun shops as shotgun reloading materials), a small postal scale, and some fiberglass resin.
According to the 2005 Bearhawk Patrol newsletter, fabric and paint weighs approx. .10 lbs per square foot. According to my calculations, the fabric and paint that will be put on the aileron will weight approx. 1.6 lbs. Note: If you put the paint on light (like you should) it may weigh a bit less. If you put on one of those smooth high gloss paint jobs where you can't see the fabric weave, it will be a bit heavier. But generally 1.6 lbs will be added to the aileron.
Here is my set up for figuring out how much weight we will need to balance
First, the empty 3/4" tube was placed in the holes in the nose ribs of the aileron, measured and cut to the correct length to fit the center area between the hinge pockets. It was then reinstalled in the aileron:
Next the aileron was hung from the ceiling by strings tied to the hinge bolts.
Also, a lightweight 1 quart mixing bucket was hung from the rivet holes that
will eventually secure the aluminum counterbalance tube in place:
Next we need a weight to simulate the weight of the fabric. As previously
stated, I needed 1.6 lbs. Searching around the shop, I weighed several
items and finally found that my favorite bucking bar weighs 1 lb, 10 oz..
The bucking bar was placed on the aileron at it's geographical center
(9 3/8" from the nose):
Next, I poured lead shot into the paint mixing bucket until the aileron balanced on the hinge bolts:
You need a partner to help hold the aileron level while you pour the lead shot.
The lead shot required to balance the aileron was weighed and came out to 4 1/2 lbs.
Here is my set-up for putting the lead shot and fiberglass resin into the
aluminum tube. The tube was placed vertically and taped to the table
legs to keep it from tipping:
The bottom of the tube was sealed with some tape and placed onto the floor..
Here are the needed materials. The lead shot, some fiberglass resin
and some Acetone (not shown):
About 6oz. of the resin was mixed with the hardener and then thinned about 25% with the Acetone. Work fast as you only have about 5 to 10 minutes working time with the resin. Pour a little resin in first, trying to pour it in a stream right down the center of the tube. Now pour in about 1/4 of the lead shot, pour in 1 oz of resin, another 1/4 of the lead, 1 oz of the resin, etc. until the tube is full of lead. next drizzle the resin in slowly until no more will fit.
In my case, I still had about 6 oz of the lead remaining that would not fit into the tube. I figure the resin will weigh something so that should help.
Now leave it alone for 24 hours and let the resin cure. Once it was fully cured, I weighed the tube (filled with shot and resin) and it came out to 4 lbs. 4oz. This is a little lighter than the 4 lbs. 8 oz. needed, but is close enough that I'm going to wait until the aileron is actually covered to see if it's balanced or not. If I need more, I can always add another tube with lead to the aileron between the end and the hinge pocket.
Once the resin had cured, the tube was placed into the aileron:
All that is left to do is to match drill the existing aileron nose skin holes into the tube, and secure it in place with 1/8" stainless steel pull rivets.
Come back later for more. This page last updated on 09/21/10.
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