The GE J-79 turbojet produces a thrust of 10,000lbs at sea level. The inlet diameter is 3.19 ft.
The GE J-79 turbojet produces a thrust of 10,000lbs at sea level. The inlet diameter is 3.19 ft. If an airplane equipped with the J79 is flying at standard sea level with a velocity of 1,000 ft/sec, (a) estimate the jet velocity relative to the airplane, (b) the propulsive efficiency.
(a) \[\dot{m} = \rho AV = 0.0023769\left ( \frac{\pi}{4}\times3.19^{2}\right )\times 1000 = 18.996\, Slug/S = 611.178\, lbm/S\]
\[F_{Thrust} = \dot{m}V_{relative}\]
\[\Rightarrow 10000 = 611.178\times V_{relative}\]
\[V_{relative} = 16.362\, ft/S\]
(b) \[\eta _{p} = \frac{2}{1 + \frac{V_{e}}{V_{a}}}\]
\[V_{e} = V_{rel} + V_{a} = 16.362 + 1000 = 1016.362\, ft/S\]
\[\frac{V_{e}}{V_{a}} = \frac{1016.362}{1000} = 1.016\]
\[\Rightarrow \eta _{p} = \frac{2}{1 + 1.016} = 0.992\]
