Distance between wings for biplane?
 

How far apart should the wings of a biplane be to avoid aerodynamic interference? I am thinking about adding a lower wing to a high wing design to decrease wing loading for better 3D performance. Wing span will be 48 inches.

RE: Distance between wings for biplane?
 

It's a largely sliding scale sort of thing. Common practice called for 1 to 1.5 times the chord but racing planes sometimes used as little as .7 to .8 of the max chord. Certainly at less than .7 bad things will become much more possible.

RE: Distance between wings for biplane?
 

I wrote a long message a few mins ago telling about all the design parameters for bipes, but there was a posting error and I lost the message.

The long and short of it was:

Gap/Span is the important number, the bigger the better. You dont want to stagger the wings (can create unstable stall behavior, bad for a 3D model) and you want them to have the same angle of attack. You also want them to be the same length.

Otherwise, its a 3D aerobatic model, aerodynamics don't really matter much. Go with what looks right.

RE: Distance between wings for biplane?
 

Oh yeah, one other thing. The aerodynamic center of a biplane is farther forward than a monoplane. Instead of being at 25% of the chord like a monoplane, it's more like 23%. So you will likely have to move your CG a bit forward to maintain static pitch stability.