Hi Natoquick:

Here's an old NACA test report which investigated the effect of larger than usual stagger in bipes: http://naca.larc.nasa.gov/reports/19...i?page0002.gif

Bipes are, generally speaking, no champs in the lift/drag sweepstakes, but within certain design limitations, particularly within a given wingspan, a bipe could be interesting. Adding a second identical wing to a monoplane may not hurt its lift/drag ratio, assuming that parasite drag in not increased by much, and its lift will be increased by about 90%, permitting it to fly much slower. The thrust required to maintain flight will be higher, but the thrust horsepower will probably be lower, so that the airplane may be able to lift a given load while using less power.

I like to convert bipes to equivalent monoplanes for drag calculations, and a bipe of aspect ratio 8, with normal gap and stagger, will have induced drag about the same as a monoplane with the same wing area, with aspect ratio around 5.5 Two wings of a given design can be built considerably lighter than a single wing of double the area, due to the old square/cube law.

I find that it really pays to be very careful to minimize parasite drag on bipes, by use of sleekly airfoiled cabane and interplane struts. My own design taper-wing bipes have fully cowled engines, and are quite aerodynamically slippery overall, resulting in glide angles roughly the same as those of most monoplanes, and they can turn considerably tighter.

Interesting problem.