Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/69

Rh particular experimental data, first take any simultaneous known values of H and XX for the curve it is desired to plot. These two values may be those given by the launching data, since at the instant of launching the velocity and angle may be presumed to be known. Next calculate C from equation (14),

where H and 0i are the simultaneous known values as above. Now calculate r from equation (13) thus:—

and repeat this calculation for a series of small increments of H, which must be set out as horizontal lines on the chart.

A trammel is next prepared (Fig. 33), on which these calculated radii are marked off from a fixed tracing point, the extremity of each radius, as marked off, is pierced and indexed with the value of H to which it relates. Thus in Fig. 33 the fixed tracing point is that marked with a cross at the left-hand end of the trammel, and the distances measured off to the points marked 100, 150, etc., are the calculated values for the radius of curvature for the values of H = 100 feet, 150 feet, etc., respectively.

A numerical example of the manner in which a trammel is prepared for any particular curve is as follows:—

Data, $$H_n = 64, H_1 = 36, \cos \Theta_1 = -1.$$

Calculation of constant:—

Radius of curvature:—