SIFT Aircraft Components and Controls 4 — Questions and Answers
Question 1: What is the primary purpose of an aircraft's vertical stabilizer?
- Generate upward lift to offset weight
- Provide directional (yaw) stability about the vertical axis (Correct answer)
- Support the horizontal stabilizer structure
- Control roll during steep turns
Correct answer: Provide directional (yaw) stability about the vertical axis
The vertical stabilizer provides weathervane-like yaw stability, keeping the aircraft aligned with the relative wind and resisting unwanted yaw movements.
Question 2: During autorotation in a helicopter, which component supplies energy to keep the rotor turning?
- The engine drives the rotor at reduced power
- The stored inertia of the rotor and upward airflow through the rotor disk (Correct answer)
- The tail rotor transfers energy to the main rotor
- The collective is raised to add pitch energy
Correct answer: The stored inertia of the rotor and upward airflow through the rotor disk
In autorotation, rising air through the rotor disk (and initially rotor inertia) drives the rotor blades, providing lift for a controlled descent without engine power.
Question 3: What is the function of the 'feathering hinge' (or pitch change bearing) in a helicopter rotor blade?
- Allows the blade to move fore and aft (lead-lag) in the plane of rotation
- Allows the blade to rotate about its spanwise axis to change pitch angle (Correct answer)
- Connects the blade to the swashplate horn
- Dampens vibrations between the blade and hub
Correct answer: Allows the blade to rotate about its spanwise axis to change pitch angle
The feathering hinge (pitch change bearing) allows each rotor blade to rotate about its spanwise axis, changing its angle of attack in response to cyclic and collective inputs.
Question 4: On a fixed-wing aircraft, what is the function of the 'elevator'?
- Controls roll by differential deflection
- Controls pitch by deflecting the horizontal tail surface (Correct answer)
- Controls yaw through the vertical tail
- Provides additional lift during low-speed flight
Correct answer: Controls pitch by deflecting the horizontal tail surface
The elevator is the movable portion of the horizontal stabilizer that deflects up or down to pitch the nose of the aircraft up or down.
Question 5: What is 'translational lift' in helicopter flight?
- Lift generated by the tail rotor during forward flight
- The increased efficiency and lift gained as the helicopter transitions from hover to forward flight (Correct answer)
- Extra lift created by lowering the collective rapidly
- The lift differential between the advancing and retreating blades
Correct answer: The increased efficiency and lift gained as the helicopter transitions from hover to forward flight
Translational lift occurs as the helicopter moves forward and the rotor exits its own downwash, gaining more efficient airflow through the disk and a noticeable increase in lift.
Question 6: In a fully articulated rotor system, the 'lead-lag hinge' is designed to:
- Allow blades to flap up and down
- Allow blades to move fore and aft in the plane of rotation to absorb Coriolis forces (Correct answer)
- Change the pitch of the blade
- Lock the rotor during engine startup
Correct answer: Allow blades to move fore and aft in the plane of rotation to absorb Coriolis forces
The lead-lag (drag) hinge allows rotor blades to move slightly fore and aft in their plane of rotation, absorbing the Coriolis effect that occurs as blades flap.
Question 7: What is the purpose of 'winglets' on a fixed-wing aircraft?
- Increase the aircraft's maximum speed
- Reduce induced drag by limiting wingtip vortices (Correct answer)
- Provide roll control at low speeds
- Support external fuel tanks
Correct answer: Reduce induced drag by limiting wingtip vortices
Winglets are vertical extensions at the wingtip that reduce the strength of wingtip vortices, decreasing induced drag and improving fuel efficiency.
SIFT Aircraft Components and Controls 4
What is the primary purpose of an aircraft's vertical stabilizer?