SIFT Aircraft Components and Controls 5 — Questions and Answers
Question 1: What happens to the tail rotor's anti-torque requirement when main rotor pitch (collective) is increased?
- It decreases because less engine power is used
- It increases because more engine torque is needed to drive the rotor at higher pitch (Correct answer)
- It remains unchanged since tail rotor RPM is fixed
- It reverses direction to assist the main rotor
Correct answer: It increases because more engine torque is needed to drive the rotor at higher pitch
Increasing collective requires more engine torque to maintain rotor RPM, which increases the torque reaction the tail rotor must counteract.
Question 2: The 'T-tail' configuration on a fixed-wing aircraft places the horizontal stabilizer:
- Ahead of the wing (canard position)
- At the base of the vertical stabilizer
- At the top of the vertical stabilizer (Correct answer)
- Under the fuselage for low-drag
Correct answer: At the top of the vertical stabilizer
A T-tail mounts the horizontal stabilizer at the top of the vertical fin, keeping it out of the wing's disturbed wake but creating risk of deep stall.
Question 3: What is the primary purpose of a 'mixing unit' (or mixing lever) in a helicopter flight control system?
- Mixes fuel and air in the carburetor
- Prevents collective pitch inputs from affecting the aircraft's trim when cyclic is applied
- Prevents a cyclic input from also changing overall (collective) blade pitch (Correct answer)
- Coordinates rudder and aileron inputs automatically
Correct answer: Prevents a cyclic input from also changing overall (collective) blade pitch
The mixing unit mechanically separates cyclic and collective inputs so that moving the cyclic doesn't inadvertently change the average (collective) pitch of all blades.
Question 4: What is 'adverse yaw' in a fixed-wing aircraft?
- Yaw induced by engine torque at full power
- The tendency of the aircraft to yaw toward the lowered (rising) aileron during a roll input (Correct answer)
- Yaw caused by asymmetric thrust in multi-engine aircraft
- The nose-down pitch that occurs when flaps are deployed
Correct answer: The tendency of the aircraft to yaw toward the lowered (rising) aileron during a roll input
Adverse yaw occurs because the down-going aileron (on the rising wing) generates more drag than the up-going aileron, pulling the nose toward the rising wing instead of the direction of roll.
Question 5: In a tandem-rotor helicopter (e.g., CH-47 Chinook), how is torque typically counteracted?
- By a conventional tail rotor
- By the two rotors spinning in opposite directions, canceling each other's torque (Correct answer)
- By differential collective pitch on a single rotor
- By vectored exhaust nozzles
Correct answer: By the two rotors spinning in opposite directions, canceling each other's torque
Tandem-rotor helicopters use two counter-rotating rotors whose torques cancel each other out, eliminating the need for a tail rotor.
Question 6: What is the function of 'ground spoilers' (also called lift dumpers) that deploy automatically on touchdown?
- Reduce bounce by limiting residual lift so wheel brakes are more effective (Correct answer)
- Extend the trailing edge flaps for go-around performance
- Increase engine reverse thrust during rollout
- Protect the gear from hard landings by absorbing vertical loads
Correct answer: Reduce bounce by limiting residual lift so wheel brakes are more effective
Ground spoilers destroy remaining wing lift upon touchdown, transferring the aircraft's full weight to the wheels immediately so that brakes and tires can decelerate the aircraft most effectively.
Question 7: Which primary control input would a helicopter pilot use to initiate a left pedal turn while in a hover?
- Left cyclic
- Left collective
- Left anti-torque pedal (Correct answer)
- Right anti-torque pedal
Correct answer: Left anti-torque pedal
Pushing the left anti-torque pedal increases tail rotor thrust, which yaws the nose of the helicopter to the left while in a hover.
SIFT Aircraft Components and Controls 5
What happens to the tail rotor's anti-torque requirement when main rotor pitch (collective) is increased?