The propulsive efficiency is
- low, with a low mass flow acceleration.
- high, with a low mass flow acceleration.
- high, with a high mass flow acceleration.
Explanation
Propulsive efficiency improves when the jet velocity is only slightly higher than the aircraft speed, meaning the air is given a small acceleration. Accelerating a large mass of air by a small amount wastes little kinetic energy in the wake, so propulsive efficiency is high when mass flow acceleration is low.
ikkyu9 asking:
more mass flow is more thrust, is'nt it.?
Community Comments (2)
E
engAB Posts: 2 06.09.2015 / 16:39
By going back to the Thrust formula you can see that:
T=m(Vo-Vi)
Where Vo is the velocity of the gas at the nozzle, therefore if you increase it you are decreasing A which is acceleration and since they are in direct proportion, the result is reduced propulsive efficency
T=m(Vo-Vi)
Where Vo is the velocity of the gas at the nozzle, therefore if you increase it you are decreasing A which is acceleration and since they are in direct proportion, the result is reduced propulsive efficency
E
engAB Posts: 2 06.09.2015 / 16:43
Correction you are increasing the difference between Vo and Vi which is the gas velocity at the exhaust and at th intake respectivly; by doing so you're increasing A in the formula and by doing so increasing thrust
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