On a plane aerofoil.
N = P(2 sin α/1 + sin2 α)
| Inclination. | Ratio Lift to Drift. |
| 1° | 58·3:1 |
| 2° | 29·2:1 |
| 3° | 19·3:1 |
| 4° | 14·3:1 |
| 5° | 11·4:1 |
| 6° | 9·5:1 |
| 7° | 8·0:1 |
| 8° | 7·0:1 |
| 9° | 6·3:1 |
| 10° | 5·7:1 |
P = 2kd AV2 sin α.
A useful formula for a single plane surface. P = pressure supporting the plane in pounds per square foot, k a constant = 0·003 in miles per hour, d = the density of the air.
A = the area of the plane, V relative velocity of translation through the air, and α the angle of flight.
Transposing we have
AV2 = P/(2kd sin α)
If P and α are constants; then AV2 = a constant or area is inversely as velocity squared. Increase of velocity meaning diminished supporting surface (and so far as supporting surface goes), diminished resistance and skin friction. It must be remembered, however, that while the work of sustentation diminishes with the speed, the work of penetration varies as the cube of the speed.
§ 13. Table V.—Timber.