7.23 A 1:3 scale model of a torpedo is tested in a wind tunnel to determine the drag force. The prototype operates in water at 28m/s.

It has a diameter of 533mm and is 6.7m long. The maximum wind tunnel speed is 110 m/s but the air pressure can be varied. The air temperature is constant at 20 C. Determine the air pressure in the wind tunnel necessary to achieve a dynamically similar test. At these conditions, the drag force on the model is measured as 618 N.

Determine the drag force expected on the full-scale torpedo.