Airframe Mechanic Flight Control Systems Questions and Answers — Questions and Answers
Question 1: After a minor repair and repainting of an aileron, what procedure is critical to perform to prevent a potentially catastrophic in-flight failure?
- Re-balancing the control surface. (Correct answer)
- Applying a corrosion-inhibiting compound.
- Checking for correct color matching under UV light.
- Measuring the thickness of the new paint layer.
Correct answer: Re-balancing the control surface.
Adding or removing material, such as paint or body filler, can change the weight distribution of a control surface. If the center of gravity shifts aft of the hinge line, it can lead to aerodynamic flutter at high speeds, which is a rapid, uncontrolled oscillation that can destroy the surface and lead to loss of the aircraft. Re-balancing ensures the center of gravity is correctly located relative to the hinge line.
Question 2: A technician is rigging the flight controls of an aircraft and notes that for a left roll command, the left aileron moves 20 degrees up, while the right aileron moves 15 degrees down. What is this design feature called and what is its primary purpose?
- Aileron droop; to increase lift during takeoff.
- Symmetrical travel; to ensure a constant roll rate.
- Differential aileron travel; to counteract adverse yaw. (Correct answer)
- Flaperon mixing; to combine the function of flaps and ailerons.
Correct answer: Differential aileron travel; to counteract adverse yaw.
This is called differential aileron travel. The downward-deflected aileron creates more lift and, as a byproduct, more drag than the upward-deflected aileron. This drag imbalance can cause the aircraft's nose to yaw in the opposite direction of the turn (adverse yaw). By having the up-going aileron travel a greater distance, its drag is increased, helping to equalize the drag on both wings and create a more coordinated turn.
Question 3: Which of the following are all considered primary flight controls?
- Flaps, slats, and spoilers.
- Trim tabs, ailerons, and flaps.
- Ailerons, elevator, and rudder. (Correct answer)
- Spoilers, elevator, and slats.
Correct answer: Ailerons, elevator, and rudder.
Primary flight controls are those required to safely control the aircraft's movement about its three principal axes: pitch, roll, and yaw. The elevator controls pitch (lateral axis), ailerons control roll (longitudinal axis), and the rudder controls yaw (vertical axis). Flaps, slats, spoilers, and trim tabs are considered secondary controls.
Question 4: In a fly-by-wire (FBW) system, what is the primary function of the Flight Control Computer (FCC)?
- To mechanically link the pilot's yoke directly to the control surface actuators.
- To cool the hydraulic fluid that is used to move the control surfaces.
- To serve as a backup instrument display in case of a primary flight display failure.
- To process pilot inputs and sensor data, then command actuators to move control surfaces. (Correct answer)
Correct answer: To process pilot inputs and sensor data, then command actuators to move control surfaces.
In a fly-by-wire system, the mechanical linkages are replaced by an electronic interface. The Flight Control Computer (FCC) is the brain of this system. It receives electrical signals from the pilot's controls, combines this with data from various aircraft sensors (like airspeed, attitude, etc.), and then sends calculated electrical commands to the actuators that move the flight control surfaces.
Question 5: The primary purpose of an elevator trim tab is to:
- Increase the maximum travel range of the elevator.
- Relieve the pilot of the need to maintain constant pressure on the control column. (Correct answer)
- Act as a backup control surface in case the main elevator fails.
- Dampen out high-frequency vibrations to prevent elevator flutter.
Correct answer: Relieve the pilot of the need to maintain constant pressure on the control column.
A trim tab is a small, adjustable surface on the trailing edge of the elevator. By deflecting the trim tab, the pilot creates a small aerodynamic force that holds the main elevator in a position to maintain a desired flight attitude (e.g., level flight, climb, or descent). This allows the pilot to fly 'hands-off' without continuously applying forward or backward pressure on the yoke.
Question 6: A technician must check the tension of a control cable system. Why is it essential to measure the ambient air temperature and use a manufacturer's chart during this procedure?
- The tensiometer's spring is only accurate at a specific calibrated temperature.
- High temperatures can cause the cable's anti-corrosion coating to become too soft for an accurate reading.
- The steel cables and the aluminum airframe have different coefficients of thermal expansion. (Correct answer)
- The chart is needed to convert the tensiometer's reading from pounds to newtons.
Correct answer: The steel cables and the aluminum airframe have different coefficients of thermal expansion.
Aircraft airframes, typically made of aluminum alloys, expand and contract with temperature changes at a different rate than the steel control cables. To ensure the correct cable tension is set for all operating conditions, maintenance manuals provide charts that specify the required tension value based on the ambient temperature at the time of the check.
Airframe Mechanic Flight Control Systems Questions and Answers
After a minor repair and repainting of an aileron, what procedure is critical to perform to prevent a potentially catastrophic in-flight failure?