Wave drag of a nose part

Wave drag

At first we shall consider a wave drag. This is drag of pressure, therefore it is determined by known distribution of the factor of pressure along lateral surface of the body of revolution

. (13.5)

It is convenient to present the factor of wave drag as a sum of drag coefficients of pressure of the nose and rear parts (the cylindrical part does not create the wave drag)

(13.6)

If considered body differs from a body of revolution then factor of wave drag includes an additional addend

, (13.7)

where - sum of wave drags of various sources. Such sources of an additional wave drag of the fuselage can be: canopy, lateral and ventral air intakes, coupled nozzles in the rear part and so on.

Fig. 13.1. Drag of pressure of a nose of the body of revolution

The nose drag of pressure of the body of revolution substantially depends on flow mode.

At subsonic speeds there is a reduced pressure on some sites of a surface, owing to that the sucking force can appear, and the drag can be negative. At supersonic speeds pressure is increased on the nose surface, due to that drag of pressure appears (Fig. 13.1).

For calculation of the wave drag at simple engineering method exists - method of local cones (Fig. 13.2).

Fig. 13.2.

Let's write down ratios

, , .

The factor of pressure on the ray which is going out from cone top has constant value and is determined by the ratio

, (13.8)

from here

. (13.9)

It is possible to define size of by known value of the factor of pressure integrating its analytically or numerically. In particular, for the conical shape of nose:

; . (13.10)

For the parabolic nose:

. (13.11)

Generally will depend on the nose shape. If the head fuselage part has bluntness or air intake, its drag coefficient varies in comparison with fuselage without bluntness or air intake. At bluntness, as a rule, increases drag of the head part. Besides, flow rate coefficient through the air intake provides the essential influence onto character of flow about nose of the body of revolution with a channel. In this case, drag of the fuselage is increased on some size called as additional drag of the air intake.

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