Question

Evaluate required scale factor if ratio of weight of the rubber engine and the actual selected engine is 0.8.

(a) 0.8164

(b) 0.012

(c) 6.2

(d) 1

This question was addressed to me in an interview.

Question is taken from Propulsion topic in section Propulsion and Fuel System Integration of Aircraft Design

Answer 1

Right option is (a) 0.8164

Best explanation: Given, ratio of rubber engine weight (w) and actual engine weight (W) = 0.8

Now, weight of the rubber engine is given by, w = W * SF^1.1

Hence, SF^1.1 = w/W = 0.8

1.1*ln (SF) = ln0.8 = -0.223

Hence, ln (SF) = -0.223/1.1 = -0.2028

Hence, SF = e^-0.2028 = 0.8164.