RE: Hangar-9 Sopwith Camel Build Thread
An old builder I knew, now passed, used a simple formula for his multi wings that should work pretty good for standard rectangular staggered wing type biplanes. Set up the plane as near horizontal as you can on a table, and drop a vertical line from the leading edge of the forward wing, usually the top wing, to the table and mark. Then do the same from the trailing edge of the other wing. The distance between the two marks is the total chord of the wing. 25% of that figure is a good place to start flight testing. It can be hung from the top wing. If you want to balance from the bottom wing you need to account for the distance of stagger between the top and the bottom, that is, if the total chord is 20 inches, then the top wing balance should be at (25% of 20 inches) 5 inches back from the leading edge. If the leading edge of the bottom wing is 3 inches behind the LE of the top wing, then the balance point should be 5 minus 3 inches or 2 inches behind the bottom wing LE.
When it was time to balance my Camel, I clamped 2 pieces of 1 by 2 furring strips to a picnic table at fuselage width plus a few inches. Then I slid the plane onto the sticks with the nose toward the table and laid the top wing on the sticks. Flat bottom wing, flat sticks, it sat there nice, no need to worry about it falling fore or aft. Then, from the side, I slid a padded one inch dowel under the wing, across the sticks, and positioned it at the previously marked CG location. At this point, the plane will show a fore or aft (most likely aft with these bipes) tilt, but can't go far because of the sticks. Add weight as needed (or remove it if you can) until the plane sits level. And in the case of the Camel, I MEAN LEVEL! When I got my Camel on the sticks, it showed just a touch of slant rearward. I thought to myself, "hey, that's good to fly!" But I set the 16 ounce lead block on the nose anyway, expecting to see the nose drop and the tail point to the sky, but it simply moved the half inch toward the nose it was lacking. I was astonished! I put the lead in place, and for good measure, I added a 2 ounce heavy hub to the prop shaft. She flew wonderfully! So I took off the heavy hub and she got squirrely fast. This plane does not like even a tiny bit of tail heavy!
Good luck!
Rick