Discussion
A jet aircraft is initially flying steady and level at its maximum endurance condition. For the aircraft to fly steady and level, but faster at the same altitude, the pilot should
Answer: C
The pilot should increase thrust and reduce angle of attack.
For a jet, fuel flow is roughly proportional to thrust, so maximum endurance is flown at minimum drag, the speed of maximum L/D. Flying faster than that speed raises the drag, so steady flight at the higher speed needs more thrust.
Lift must still equal weight: \(W = \frac{1}{2}\rho V^{2}SC_{L}\). At the same altitude, a higher V needs a smaller \(C_{L}\), that is, a smaller angle of attack.
More thrust alone, with the same angle of attack, would give more lift than weight as the speed rose, so the aircraft would climb. Increasing the angle of attack makes that worse. Reducing the angle of attack alone loses lift without the thrust to hold the higher speed, so the aircraft would descend.
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