SIFT Aircraft Components and Controls Questions and Answers 2 — Questions and Answers
Question 1: What is the primary purpose of the collective pitch control in a helicopter?
- To control the tail rotor thrust
- To simultaneously change the pitch angle of all main rotor blades (Correct answer)
- To control the cyclic pitch for directional movement
- To adjust engine throttle automatically
Correct answer: To simultaneously change the pitch angle of all main rotor blades
The collective pitch control raises or lowers the pitch angle of all main rotor blades simultaneously, changing the total lift generated and controlling altitude.
The collective pitch control changes the pitch angle of all main rotor blades at the same time and by the same amount. Raising the collective increases blade pitch across all blades simultaneously, generating more lift and causing the helicopter to climb. It is operated with the left hand by the pilot.
Question 2: What does the term 'semi-monocoque' refer to in aircraft construction?
- A fuselage structure using only an outer skin with no internal framework
- A fuselage structure where the skin shares stress loads with internal framework (Correct answer)
- A wing design using composite materials only
- A landing gear type with semi-rigid shock absorbers
Correct answer: A fuselage structure where the skin shares stress loads with internal framework
Semi-monocoque construction uses a combination of an outer skin and internal structural members (frames, bulkheads, stringers) that share the stress loads.
In semi-monocoque construction, the outer skin is reinforced by longerons, stringers, frames, and bulkheads that help carry structural loads. This is the standard construction method for most modern aircraft fuselages because it provides a strong, lightweight structure.
Question 3: What is the function of the anti-torque pedals in a helicopter?
- Control engine power output
- Control the pitch of the main rotor blades
- Control the pitch of the tail rotor blades to counteract torque (Correct answer)
- Activate the wheel brakes during landing
Correct answer: Control the pitch of the tail rotor blades to counteract torque
Anti-torque pedals control the pitch angle of the tail rotor blades, which adjusts the thrust that counteracts main rotor torque and controls yaw direction.
By Newton's third law, the main rotor torque causes the fuselage to spin in the opposite direction. The tail rotor produces a sideways thrust to counteract this. The anti-torque pedals change tail rotor blade pitch to increase or decrease this thrust, allowing the pilot to control yaw (left-right rotation).
Question 4: What component in a helicopter transmission system allows the rotor to continue spinning when the engine fails?
- The centrifugal clutch
- The freewheeling unit (one-way clutch) (Correct answer)
- The synchronizing shaft
- The governor
Correct answer: The freewheeling unit (one-way clutch)
The freewheeling unit, or one-way clutch, disengages the engine from the rotor when engine RPM drops below rotor RPM, allowing autorotation.
The freewheeling unit permits the rotor to rotate faster than the engine or to rotate independently. During an engine failure, the rotor's inertia and aerodynamic forces keep it spinning in autorotation. Without this unit, the seized engine would stop the rotor instantly.
Question 5: What is the purpose of the horizontal stabilizer on a helicopter?
- To provide lift for forward flight
- To prevent the tail rotor from producing too much thrust
- To provide aerodynamic stability and reduce pitch oscillations (Correct answer)
- To control altitude via collective movement
Correct answer: To provide aerodynamic stability and reduce pitch oscillations
The horizontal stabilizer provides aerodynamic stability by countering the tendency of the nose to pitch up or down, reducing oscillations in forward flight.
As helicopter speed increases, the fuselage can develop pitching tendencies. The horizontal stabilizer provides a stabilizing moment that resists nose-up pitching caused by rotor disc tilting and fuselage aerodynamics. It improves handling qualities in forward flight.
Question 6: What does 'chord' refer to in relation to rotor blades or wings?
- The distance from rotor hub to blade tip
- The imaginary straight line from the leading edge to the trailing edge (Correct answer)
- The angle between the blade and the horizontal plane
- The thickness of the blade at its widest point
Correct answer: The imaginary straight line from the leading edge to the trailing edge
The chord is the imaginary straight line drawn from the leading edge to the trailing edge of an airfoil, used as a reference for measuring angles of attack.
The chord line is a geometric reference that runs straight from the leading edge to the trailing edge of an airfoil. Angle of attack is measured between the chord line and the relative wind. Chord length affects how lift is distributed along the blade span.
SIFT Aircraft Components and Controls Questions and Answers 2
What is the primary purpose of the collective pitch control in a helicopter?