Flat wing

Summing induced drag with profile drag , we shall receive expression for polar:

. (4.13)

Fig. 4.15. Dependence of profile drag on lifting force

It can be assumed that the profile drag does not depend on a lift coefficient . In this case we shall write down , where - the wing drag coefficient at (in this case it coincides to ). It is necessary to note that in general the profile drag rather changes by especially at large values of or , it is approximately proportional to (Fig. 4.15); in some cases this change is taken into account in parameter :

, (4.14)

Where ; for high-aspect-ratio wings and , ).

Fig. 4.16. Flat wing polar

The last polar writing (4.14) - the most general form, which is fair for any aerodynamic shapes if not to decipher parameters and . Parameter has the name of a polar pull-off coefficient. Obviously, that in general . Wing profile drag do not depends on and polars for wings of various aspect ratio are look like it is shown on a fig. 4.16. As it was spoken earlier, the induced drag decreases with increasing of aspect ratio , and consequently the drag for a wing of infinite aspect ratio (airfoil) will be equal to profile drag or .

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