TOTAL AIRPLANE DRAG

The foregoing material has considered the separate sources of drag that contribute to the total drag of an airplane. Adding these together, let us now

Thus the drag is composed of two parts: the parasite drag, which varies directly with V2, and the induced drag, which varies inversely with V2. The drag has a minimum value when the parasite, and induced drag are equal. This minimum value is easily determined from Equation 4.58 and is equal to

and occurs at a velocity equal to

(4.60)

Observe that the minimum drag is independent of density and depends on the span loading instead of the wing loading.

D, Dmi„, and can be combined and expressed in a general manner as

The first term on the right-hand side of Equation 4.61 represents the parasite drag; the second term is proportional to the induced drag. Both of these terms and the total drag ratio are presented in Figure 4.52.