alleryStart learning →Why must a helicopter pilot never let the rotor slow below a critical angular velocity in flight?
AThe engines cannot restore that spin in time
BThe blades would bend past their safe limit
CThe fuel pump stalls below that spin rate
DThe tail rotor would then spin far too fast
Answer & Solution
Correct answer: A. The engines cannot restore that spin in time
1. Blades that slow too far lose lift, and regaining lift means putting rotational kinetic energy back in.
2. Because of weight limits, helicopter engines are too small to supply lift and replenish that energy at once.
3. So below the critical spin rate the engines cannot restore the rotation in the time available.
4. The rotational kinetic energy must therefore be built up before takeoff and held throughout the flight.
5. One escape is to trade altitude for spin, letting the descent drive the blades back up to speed.
_Source: OpenStax College Physics (CC BY 4.0), Ch 10 "Rotational Motion and Angular Momentum", section 10.4 Rotational Kinetic Energy: Work and Energy Revisited_
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