FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsHard
During a hovering takeoff, a helicopter's left skid becomes momentarily caught on uneven terrain, causing the aircraft to begin rolling about that skid contact point. If the roll angle exceeds the helicopter's critical rollover angle before the pilot can correct it, what will happen?
- AThe main rotor will automatically flap to counteract the roll
- BThe tail rotor will provide enough thrust to right the aircraft
- CIncreasing collective pitch will stop the roll
- DThe helicopter will roll over even with full corrective cyclic applied
Show answer & explanationAnswer & explanation
Correct answer: D. The helicopter will roll over even with full corrective cyclic applied
Dynamic rollover occurs when one skid or wheel acts as a pivot point and the fuselage rolls about it. Beyond the critical angle, the moment produced by rotor thrust and gravity exceeds the moment that cyclic control can counteract, and rollover becomes unstoppable regardless of cyclic input. Prevention requires recognizing the onset and applying corrective cyclic before reaching the critical angle.
Why the other options are wrong
- A. Blade flapping does not correct a fuselage roll about a ground pivot point.
- B. Tail rotor thrust has no significant effect on lateral rollover about a skid pivot.
- C. Increasing collective actually increases rotor thrust and worsens the rolling moment.
Dynamic Rollover
A tendency for a helicopter to roll over when one skid or wheel is on the ground and acts as a pivot point, if bank angle exceeds a critical angle.
- Occurs during takeoff/landing when a skid/wheel is a fixed pivot
- Beyond critical angle, cyclic cannot stop the roll
- Prevented by smooth, coordinated liftoffs and avoiding sideward loads on skids
Memory trick: Past the point of no return, cyclic can't turn the tide.