In other words, if a curve be constructed whose abscissae represent extensions, and ordinates the corresponding weights, it will show a reverse curvature, one portion being concave toward the axis of abscissae, the other convex. [19] The following table taken from “Experiments in Aerodynamics,” p. 107, gives the data for soaring of 30×4.8 inch planes, weight 500 grammes. -------+-----------------------+-----------------+--------------------+ | | | Weight with planes | | Soaring speed | Work expended | of like form that | Angle | ‹V›. | per minute. | 1 horse-power will | with | | |drive through the | horizon| | |air at velocity ‹V›.| α. +-----------+-----------+---------+-------+----------+---------+ | Metres | Feet |Kilogram-| Foot- | Kilo- | Pounds. | |per second.|per second.| metres. |pounds.| grammes. | | -------+-----------+-----------+---------+-------+----------+---------+ 45° | 11.2 | 36.7 | 336 | 2,434 | 6.8 | 15 | 30 | 10.6 | 34.8 | 175 | 1,268 | 13.0 | 29 | 15 | 11.2 | 36.7 | 86 | 623 | 26.5 | 58 | 10 | 12.4 | 40.7 | 65 | 474 | 34.8 | 77 | 5 | 15.2 | 49.8 | 41 | 297 | 55.5 | 122 | 2 | 20.0 | 65.6 | 24 | 174 | 95.0 | 209 | -------+-----------+-----------+---------+-------+----------+---------+ The relations shown in the above table hold true only in case of planes supporting about 1.1 pounds to each square foot of sustaining area. For a different proportion of area to weight, other conditions would obtain. [20] This pressure per unit of area varies with the area itself, but in a degree which is negligible for our immediate purpose. [21] See “Internal Work of the Wind”; also Revue de L’Aeronautique, 3^e Livraison, 1893. [22] More recent experiments under my direction by Mr. Huffaker give similar results, but confirm my earlier and cruder observations that the curve, used alone, for small angles, is much more unstable than the plane. [23] As stated in the Preface, Part III has not yet been prepared for publication. [24] 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› = √(‹P›/‹K›×(1/(‹F›(α)×cos β))) while the efficiency is ‹W›/‹R› = Weight/Resistance = 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