t Figure 8.4 shows a drag polar plot of a glider, with C₁/CD and C2/C3 superimposed as func-

ons of the lift coefficient.

For a given weight, W, wing area, S and altitude, h (this determines the density), by selecting a

range of values for angle of attack, it is possible to compute: C₁/CD, C/C, V and RD. The corre-

sponding performance data are shown in Table 8.1.

The glider selected for this example is a relatively poor one by modern standards. Its lowest flight

path angles are high compared to those achievable with modern gliders. Trimmed lift-to-drag ratios

of 40.0 to 50.0 have already been achieved, yielding descent angles as low as 1.2 degrees! Despite

this, the reader is asked to verify that the approximations of Eqns (8.22) - (8.24) are quite good!

The performance results of Table 8.1 are plotted in Figure 8.5. The reader is asked to check out

the significance of the points labeled A, B and C in Figures 8.4 and 8.5. These very important points

are discussed next.