Question

What is the value of specific air range where the lift to drag ratio is 10, weight is 50000N, efficiency is 85% and specific fuel consumption is 7.43 kg/kW-hr?

(a) 3000km

(b) 4000 km

(c) 1000km

(d) 5000km

The question was posed to me in an interview for job.

This intriguing question comes from Range and Endurance for Aircraft with Power Producing Engines topic in portion Cruising Performance of Aircraft Performance

Answer 1

The correct answer is (b) 4000 km

Easy explanation: The answer is 4000km. Given \(\frac{L}{D}\)=10, W=50,000kg, η=85%, C=4.25×10^-5kg/kW-hr. From the equation SAR=\(\frac{\eta}{C}\frac{L}{D}\frac{1}{W}\). On substituting the values we get SAR= \(\frac{0.85}{4.25 \times 10^{-8}}\)*10*\(\frac{1}{50000}\).

On solving above equation we get SAR=4000 km.