Question

During a steady-state climb, how must the pilot adjust thrust to maintain the same climb rate if the air density decreases?

Accepted Answer

To maintain a constant steady-state climb rate while air density decreases, a pilot must increase thrust. Air density is the mass of air per unit volume, which naturally decreases as an aircraft climbs to higher altitudes. Thrust is the forward force produced by the engine that overcomes drag, which is the resistance of the air against the aircraft. Lift is the aerodynamic force generated by the wings moving through the air that supports the weight of the aircraft. As air becomes less dense, the air molecules provide less resistance, but they also provide less aerodynamic force for both the wings and the engine. Specifically, for a fixed true airspeed, the engine produces less thrust in thinner air because there is less mass of air entering the intake to be accelerated. Simultaneously, the aerodynamic drag decreases, but the reduction in engine efficiency and the need to maintain the power required to overcome gravity during a climb necessitates an increase in thrust. If the pilot does not increase thrust as density decreases, the aircraft will lose excess power, resulting in a lower rate of climb. Therefore, to sustain the specific rate of climb, the pilot must compensate for the loss of air density by opening the throttle to increase engine output.

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During a steady-state climb, how must the pilot adjust thrust to maintain the same climb rate if the air density decreases?