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.
The following formulæ proposed by Mr. Chas. M. Manly show how the center of pressure may be moved any desired distance either forward or backward without in any way affecting the center of gravity, and by merely moving the front and rear wings the same amounts but in opposite directions, the total movement of each wing being in either case five times the amount that is desired to move the mean CP1, and the direction of movement of the front wing determining the direction of movement of CP1.
In Figure 7, CPfw and CPrw are the centers of pressure of the front and rear wings respectively; the weights of the wings, which are assumed to be equal and concentrated at their centers of figure, are represented by w, w, and a is the distance of the center of pressure in either wing from its center of figure. The original mean center of pressure of the aerodrome is CP1, W is the weight of the aerodrome, supposed to be concentrated at CG1, while m is the distance from CPrw to CG1.