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Fig. 2. Air Flow About a Streamline Body Showing an Almost Complete Absence of Turbulence Except at the Extreme Rear Edge. Resistance Is Principally Due to Skin Friction.

Streamline Forms

In poor attempts at streamline form, the flow discontinues its adherence to the body at a point near the tail. The poorer the streamline, and the higher the resistance, the sooner the stream starts to break away from the body and cause a turbulent region. The resistance now becomes partly turbulent and partly frictional, with the resistance increasing rapidly as the percentage of the turbulent region is increased.

The fact that the resistance is due to two factors, makes the resistance of an approximate streamline body very difficult to calculate, as the frictional drag and the turbulent drag do not increase at the same rate for different speeds. The drag due to turbulence varies as V squared while the frictional resistance only varies at the rate of V to the 1.86th power, hence the drag due to turbulence increases much faster with the velocity than the frictional component. If we could foretell the percentage of friction, it would be fairly easy to calculate the total effect, but this percentage is exactly what we do not know. The only sure method is to take the results of a full size test.