Principles of Helicopter Flight Questions and Answers Flashcards
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What is 'translational lift' in helicopter aerodynamics?
Answer: The extra lift generated when forward airspeed improves rotor efficiency at around 16-24 knots
Translational lift is the improvement in rotor efficiency and increase in lift that occurs when the helicopter moves at approximately 16-24 knots forward and leaves its own rotor downwash behind.
What is 'autorotation' in helicopter flight?
Answer: An unpowered descent where aerodynamic forces keep the rotor spinning to enable a safe landing
Autorotation is the emergency procedure where, following engine failure, the rotor is disengaged from the engine and kept spinning by aerodynamic forces during descent, allowing a safe landing.
What causes 'torque roll' tendency in a single-rotor helicopter?
Answer: The main rotor's reaction torque trying to rotate the fuselage opposite to the rotor
By Newton's Third Law, if the engine torques the main rotor clockwise, the rotor torques the fuselage counterclockwise. This tendency is countered by the tail rotor.
What is 'retreating blade stall' and when does it occur?
Answer: Stall of the retreating blade at high forward airspeeds when it cannot generate sufficient lift
At high forward airspeeds, the retreating blade's lower airspeed relative to the air may require such a high angle of attack to match lift that it stalls, causing loss of control.
What is 'effective translational lift (ETL)' and how does it affect hover performance?
Answer: The speed at which a helicopter achieves maximum efficiency, approximately 16-24 knots, improving hover-out-of-ground-effect capability
ETL (also called translational lift) occurs at approximately 16-24 knots, where rotor efficiency improves significantly as the helicopter transitions from hovering downwash to cleaner incoming air.
What is 'density altitude' and how does it affect helicopter performance?
Answer: Pressure altitude corrected for temperature, representing air density; high density altitude reduces helicopter performance
Density altitude is pressure altitude corrected for non-standard temperature. High temperature, low pressure, and high humidity all increase density altitude, reducing rotor efficiency and engine power.