Question

Which of the following is the correct performance equation for power-producing engines?

(a) ηV=PD

(b) ηD=PV

(c) ηP=VD

(d) V=ηPD

I got this question in a job interview.

The query is from Range and Endurance for Aircraft with Power Producing Engines in division Cruising Performance of Aircraft Performance

Answer 1

The correct option is (c) ηP=VD

To explain I would say: The correct equation for performance equation is ηP=VD where ŋ is propeller efficiency, P is drag power, D is drag and V is velocity. In a power-producing engine the shaft power is produced as well as propulsive thrust produced by the propeller which is converted into power.