On biplanes, the airflow around one wing interferes with the airflow around the other. One effect is that that the top wing, usually ahead of the lower, directs air downward which reduces the effective angle of incidence of the lower wing. Bipes are usually designed with a couple degrees more incidence on the lower wing relative to the top wing. Another effect of the airflow interference is an increase in drag, and reduction of lift. Instead of relying on actual total wing area, one should consider 83% of actual wing area to be the effective wing area. This means the effective wing loading of a bipe is higher than what would be calculated based on actual total area. More power is good, if the loading does not get too high . High loading on a bipe means a glide like a brick.