Note 24 — Chapter VI · BALANCING THE AERODROME

According to Wellner (“Zeitschrift für Luftschiffahrt,” Beilage, 1893), in a curved surface with 1/12 rise, if the angle of inclination of the chord of the surface be α, and the angle between the direction of resultant air pressure and the normal to the direction of motion be β, then β<α and the soaring speed is

V = √(PK × 1F(α)×cos β)

while the efficiency is

WR = WeightResistance = tan β

The following were derived from experiments in the wind:

α = −3° 0° +3° 6° 9° 12°

F(α) = 0.20 0.80 0.75 0.90 1.00 1.05

Tan β = 0.01 0.02 0.03 0.04 0.10 0.17

so that according to him, a curved surface shows finite soaring speeds when the angle of inclination is 0° or even slightly negative.