I bought a 40 size bipe at a swap meet a couple years ago and I've finally gotten around to fixing it up to fly. I have no idea what type of plane this is. This is my first bipe so how to I balance it. Do I use the top wing or flip over the plane and use the bottom to find the CG? Am I still looking for the CG near the main spar?

Thanks

Kevin

Kevin,

It depends on the bipe. Both a Sig Smith miniplane and a Bel Air bipe balance at the leading edge of the bottom wing. Both of these bipes have a stagger wing set. Meaning the top wing is set futher foward than the bottom wing. Do you have a picture of the airplane?

If it has a staggered wing I would start at 1/4 inch before the leading edge of the bottom wing. Make sure you have plenty of available elevator travel. If it is balanced too far forward you might run out of elevator when trying to land.

Jim

for balancing biplanes, you calculate MAC based on the shadow of the wings when the sun is directly above and the airplane is level. Basicly you are ignoring the area of the lower wing that is directly under the upper.

For example, lets say you have a biplane where the upper and lower wings are identical... but the leading edge of the upper is 1 inch forward of the lower. The MAC would be based on adding 1 inch to the upper wing's trailing edge, and ignoring the rest of the lower wing.

From there, you go back to the standard MAC calculation for a monoplane. Just about anything will fly with the CG at 25% MAC (except Canards and flying wings...) and most its safe to go back to 30%.

Now... you don't need to know what airplane it is... you can come up with a starting CG and fly it.

Noseheavy is slggish to respond and requires a high landing speed. Tailheavy will do a 3/4 loop on takeoff... You can almost always deal with how a noseehwavy plane flys. Tailheavy tends to get "rekitted."

Thanks guys! I post a pick tomorrow morning.

http://www.lvrcs.com/content/index.php

Excellent, Thank you

kfowler:

When I did a cut/paste, the site had the cg calculations on the front page. I hope you found it since I went back and tested my post and the site was different.