Question

The mass flow of air through a turbojet engine in flight is 0.5slug/sec, and the jet exhaust velocity is 1,000 f/sec. The flight velocity is 180 knots, and neglecting the mass of the fuel burned, find the magnitude of the gross thrust in lbf

Answer 1

The gross thrust produced by the turbojet engine, when accounting for the given mass flow rate and jet exhaust velocity, and converting flight velocity to the same units, is calculated to be 348.0971 lbf.

Step-by-step explanation:

To calculate the gross thrust produced by the turbojet engine, we use the basic thrust equation for a jet engine, which is a product of the mass flow rate of the air through the engine (δm/δt) and the difference in velocity between the jet exhaust and the flight velocity (Ve - V0).

Given:

• Mass flow rate of air (δm/δt) = 0.5 slug/sec
• Jet exhaust velocity (Ve) = 1000 ft/s
• Flight velocity (V0) = 180 knots

First, convert the flight velocity from knots to feet per second (ft/s). There are 1.68781 feet per second in a knot:

180 knots * 1.68781 ft/s per knot = 303.8058 ft/s

Now, apply the thrust equation:

Thrust (F) = (δm/δt) * (Ve - V0)

Thrust (F) = 0.5 slug/sec * (1000 ft/s - 303.8058 ft/s)

Thrust (F) = 0.5 slug/sec * 696.1942 ft/s

Thrust (F) = 348.0971 slug*ft/s2

In the English system, one slug*ft/s2 is equivalent to one pound-force (lbf). Therefore, the gross thrust is:

348.0971 lbf