SIFT Principles of Helicopter Flight Questions and Answers 2

Question 1

What is 'translational lift' in helicopter aerodynamics?

Accepted Answer

The extra lift generated when forward airspeed improves rotor efficiency at around 16-24 knots

Answer

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.

Question 2

What is 'autorotation' in helicopter flight?

Accepted Answer

An unpowered descent where aerodynamic forces keep the rotor spinning to enable a safe landing

Answer

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.

Question 3

What causes 'torque roll' tendency in a single-rotor helicopter?

Accepted Answer

The main rotor's reaction torque trying to rotate the fuselage opposite to the rotor

Answer

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.

Question 4

What is 'retreating blade stall' and when does it occur?

Accepted Answer

Stall of the retreating blade at high forward airspeeds when it cannot generate sufficient lift

Answer

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.

Question 5

What is 'effective translational lift (ETL)' and how does it affect hover performance?

Accepted Answer

The speed at which a helicopter achieves maximum efficiency, approximately 16-24 knots, improving hover-out-of-ground-effect capability

Answer

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.

SIFT Exam Practice Test

SIFT Exam Practice Test

SIFT Principles of Helicopter Flight Questions and Answers 2