Airspeed measurements can be made by measuring the vortex’s _______

A)
Vorticity
B)
Strength
C)
Frequency
D)
Direction

Correct Answer :   Frequency


Explanation : A vortex sensor measures vortices shed by fluid flow over a deliberately-inserted obstruction. The frequency of vortices is proportional to the airspeed. This method has been used in helicopters and in ground vehicle fire control systems.