Prandtl's interference factor, computed — 0.484 at a fifth of a span

The interference factor σ against the gap between two wings of equal span carrying equal lift, read out of the computed drag through D = (1 + σ)/2 times the monoplane's. It runs from one at no gap — where the two wings are one wing — to zero far apart, where each pays a quarter of the monoplane's drag for its half of the lift and the two together pay a half. At a fifth of a span it is 0.4842, and Prandtl's published chart gives 0.485. That agreement is worth noticing precisely because nothing here was fitted to it.

2 essays call two-wings. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.

It is also the blast radius. Changing two-wings changes every figure listed here at once, and on this site it may change what they assert as well as what they show — which is what has to be rebuilt and looked at before the change is believed.