Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/354

§ 220 § 220. Power Expended in Flight (continued).—It has been shown that, neglecting body resistance, the power per unit weight requires to increase directly as the velocity. Table XVI. gives the calculated indicated horsepower per 100 ''lbs. weight'' for velocities ranging from 15 to 100 feet per second, the Table also being figured for the thrust horse-power for velocities from 30 to 200 feet per second. The value taken for the total efficiency is the same as employed in calculating column (4) of the preceding Table, i.e., 75 $$\times$$ 66.6 per cent. = 50 per cent., so that the velocities for a given horse-power value are in the ratio of 2 : 1.

The calculation has been made for values of $$\gamma$$ extending from 6 degrees to 12 degrees, as in the preceding Table; experiment would appear to show that 10 degrees is as low a value of $$\gamma$$ as can be obtained under practical conditions; it is, however, possible that with increased experience lower values may be obtained. An aerodrome whose $$\gamma$$ is greater than 12 degrees is certainly of inefficient design.

If we take account of body resistance, we know that the total resistance is greater the higher the velocity, for the body