Question

Which of the following is the correct equation for the Prandtl-Glauert factor?

(a) β=\(\sqrt{1-M^2}\)

(b) β=\(\sqrt{1-M}\)

(c) β=\(\sqrt{M^2-1}\)

(d) β=\(\sqrt{1+M^2}\)

The question was asked by my school teacher while I was bunking the class.

The origin of the question is Minimum Drag Speed in division Aircraft Force Systems and the Equations of Motion of Aircraft Performance

Answer 1

Right choice is (a) β=\(\sqrt{1-M^2}\)

To explain: The correct equation for the Prandtl-Glauert factor is β=\(\sqrt{1-M^2}\) where β is Prandtl-Glauert factor and M is mach number. This Prandtl-Glauert factor equation is applicable only in cases of subsonic airflow i.e. M<1.