Theme 13. drag coefficient of a fuselage

Section 2. Aerodynamics of body of revolution

Drag of body of revolution can be presented as several components. On the one hand, the drag can be presented as pressure drag and friction drag. The pressure drag is caused by forces of pressure which act along perpendicular to the body surface. The friction drag is caused by forces which act along tangent to the body surface.

At flow about the body of revolution with a blunt base, behind which there is no jet stream from the engine, the drag from pressure on the blunt base occurs in addition.

On the other hand, the drag is divided into drag which is not connected with lifting force, and induced drag connected with presence of lift. In this case, the drag coefficient at small angle of attack can be presented as

, (13.1)

where - drag coefficient at zero lift, - induced drag, which is determined similarly to low-aspect-ratio wing

, (13.2)

where - relative factor of sucking force, if to neglect it, then the factor of a polar pull-off will be equal .

Generally drag coefficient at zero lift is equal

, (13.3)

where - factor of profile drag; - factor of a wave drag; - factor of base drag.

At subsonic speeds the drag consists of drag of friction in and drag of pressure in . At transonic and supersonic speeds the drag of pressure in times exceeds drag of friction (due to occurrence of wave drag).

At the wave drag is equal to zero .

The critical Mach number of the body of revolution depends on its aspect ratio and aspect ratio of its nose

. (13.4)

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