Question

According to Newton’s theory, what happens to the lift to drag value with decreasing angle of attack of a flat plate?

(a) Remains same

(b) Increase monotonically

(c) Decreases parabolically

(d) Becomes zero with maximum angle of attack

I had been asked this question at a job interview.

My enquiry is from Time-Marching Technique in section Time-Marching Technique of Aerodynamics

Answer 1

Correct answer is (b) Increase monotonically

To elaborate: The lift/drag ratio for inviscid hypersonic flow over a flat plate is given by:

\(\frac {L}{D}\) = cotα

On plotting the curve, as the angle of attack decreases, L/D ratio monotonically increases. Obviously this is a hypothetical condition as skin friction drag is not incorporated in this.