Which condition describes the effect of reduced downwash on the elevator due to reduced power?

• A. Elevator effectiveness is reduced
• B. Elevator effectiveness is increased
• C. Elevator becomes irrelevant
• D. Tailplane stalls

Answer: (A)

Elevator effectiveness is determined by how much a given elevator deflection changes the tail’s angle of attack, which is the elevator deflection minus the downwash coming from the wing. When power is reduced, the aircraft slows down, so to maintain lift the wing must operate at a higher angle of attack. That increases the lift produced by the wing, which in turn increases the downwash reaching the tail. More downwash means the tail is being blown downward more, so a change you make with the elevator produces a smaller change in the tail’s angle of attack. In short, reduced power leads to more downwash and therefore reduced elevator effectiveness. The other possibilities don’t fit the effect described: increased effectiveness would occur if downwash decreased; tailplane stalls or the elevator becoming irrelevant aren’t the immediate outcome of simply reducing power in this context.