This table is based on Dr. Zahm's experiments and the equation
f = 0·00000778l -0·07v1·85
Where f = skin friction per sq. ft.; l = length of surface; v = velocity in feet per second.
In a biplane model the head resistance is probably from twelve to fourteen times the skin friction; in a racing monoplane from six to eight times.
§ 8. Table I.—(Metals).
| Material | Specific Gravity | Elasticity E[A] | Tenacity per sq. in. |
| Magnesium | 1·74 | 22,000- 32,000 | |
| Magnalium[B] | 2·4-2·57 | 10·2 | |
| Aluminium- Copper[C] | 2·82 | 54,773 | |
| Aluminium | 2·6 | 11·1 | 26,535 |
| Iron | 7·7 (about) | 29 | 54,000 |
| Steel | 7·8 (about) | 32 | 100,000 |
| Brass | 7·8-8·4 | 15 | 17,500 |
| Copper | 8·8 | 36 | 33,000 |
| Mild Steel | 7·8 | 30 | 60,000 |
[A] E in millions of lb. per sq.in.
[B] Magnalium is an alloy of magnesium and aluminium.
[C] Aluminium 94 per cent., copper 6 per cent. (the best percentage), a 6 per cent. alloy thereby doubles the tenacity of pure aluminium with but 5 per cent. increase of density.
§ 9. Table II.—Wind Pressures.
p = kv2.
k coefficient (mean value taken) ·003 (miles per hour) = 0·0016 ft. per second. p = pressure in lb. per sq. ft. v = velocity of wind.