Avionics Interview Questions and Answers on “Fly-By-Wire Technology – 2”.
1. What type of system is classified as “Direct electric link system”?
a) Systems with parallel wire connection
b) System with serial wire connection
c) System with motion sensor feedback
d) System without motion sensor feedback
Answer: d
Clarification: A FBW system by definition has to have a motion feedback system. Without these, the system is considered as “Direct electric system”. The information from these sensors is used to automatically stabilize the aircraft.
2. What does FBW use to scale the control surface deflection according to the aircraft’s airspeed and height?
a) Air Data Computer
b) Flight Management System
c) Flight Control Computer
d) Autopilot system
Answer: a
Clarification: FBW uses an Air Data System to scale the control surface deflection according to the aircraft’s airspeed and height variations. The need for air data information on the airspeed and height is to compensate for the very wide variation in the control surface effectiveness over the aircraft’s flight envelope of height and speed combinations. The Air Data Computer provides various information available from the airstream such as airspeed, altitude, and angle of attack.
3. What is the incidence angle in the yaw plane called?
a) Side slip angle
b) Yaw angle
c) Crossflow angle
d) Angle of crosswind
Answer: a
Clarification: The angle of incidence in the yaw plane is known as the side slip angle. It is the angle between the direction the aircraft is travelling and the direction its nose is pointing. When the side slip angle is high the aircraft is not in a coordinated turn and hence is flying inefficiently.
4. Why does an FBW system use a smaller tail area?
a) Bigger tails are harder to move as they produce larger wing loads
b) Actively controls the tail thus making up for the reduced stability due to lesser area
c) Tail does not contribute much to stability and its area can thus be reduced effectively
d) To reduce weight and drag but at a cost of natural stability
Answer: d
Clarification: The reason for using reduced tail area is to reduce weight, drag and to increase overall performance, But at a cost of reduced natural stability. A FBW makes up for the reduced stability by actively controlling the tailplane and rudder using accurate motion feedback sensors and actuators.
5. An aircraft is negatively stable when ______
a) its tailplane produces negative lift (downwards)
b) its tailplane produces positive lift (upwards)
c) its tailplane does not produce lift
d) it is flying inverted
Answer: b
Clarification: An aircraft is said to be negatively stable when its tailplane produces positive
lift. The tail of an aircraft without an FBW system must always produce negative lift to maintain stability and to keep the nose up. Since it produces negative lift, it actually acts in the direction of weight reducing aerodynamic efficiency. In an FBW equipped aircraft a positive lift producing tail can be used by using flight control computers and motion sensors to main stability at all times.
6. A highly stable aircraft is not easily maneuverable.
a) True
b) False
Answer: a
Clarification: An aircraft is said to be stable when the aerodynamic forces on the aircraft are equal to thrust produced and the weight of the aircraft. Such a condition is called steady level flight. A highly stable aircraft will return to its initial stable position even if disturbed. Maneuverability is the rate of pitch, roll, and yaw an aircraft can execute without failing. Roll, pitch, and yaw are basically disturbances and a stable aircraft will try to resist the change from its initial position.
7. A FBW control stick is referred as _______
a) FBW joystick
b) FBW control pad
c) FBW inceptor
d) FBW analog stick
Answer: c
Clarification: A FBW control stick is referred to as FBW inceptor. An inceptor by definition is a device that converts the pilot’s control inputs into electrical signals. There are two types of inceptors- active and passive.
8. Why are dampers an essential element in FBW inceptors?
a) Control aircraft stability by damping forces
b) Acts as a low pass filter on the stick movement
c) Provides accurate deflections
d) To prevent aircraft to carry out critical maneuvers
Answer: b
Clarification: Without the damper, the stick would be considerably under damped because of the low friction in the mechanism and the significant mass of the hand grip. It provides a smooth feel to the stick movement; the spring–mass–damper combination acting as a low pass filter on the stick movement. These characteristics are carefully tailored to meet the consensus of pilot approval.
9. FBW has the power to reject pilot inputs in extreme situations.
a) True
b) False
Answer: a
Clarification: FBW system automatically limits the pilot’s commands to ensure it does not enter unacceptable altitude or approach stall. A number of aircraft are lost in a year due to flying too close to their maneuver limits and the very high workload in the event of a subsequent emergency. This system makes a significant contribution to flight safety.
10. What is the relation between autopilot and FBW?
a) FBW provides autopilot commands for roll, pitch, and yaw
b) Autopilot provides FBW commands of roll, pitch, and yaw
c) Autopilot is a part of FBW system
d) Autopilot is not related to FBW
Answer: b
Clarification: The autopilot is like an artificial pilot system which flies the aircraft under a set of constraints. It provides steering commands such as roll, pitch and yaw rates to the FBW system. FBW system ensures that response to the autopilot commands is fast and well damped, providing smooth control of aircraft in autopilot modes.
11. Fill the missing block in the roll rate command system.
a) Rate gyro
b) Flight control computer
c) Display
d) Autopilot
Answer: a
Clarification: The missing block is in a feedback loop, typically it consists of a motion sensor. Here the motion sensor used is a rate gyro. The signal from the rate gyro is subtracted from pilot’s input so that the error in deflection is corrected.
12. Why is FBW essential in stealth aircraft?
a) FBW system damps radar energy
b) Improves control
c) Reduces engine noise
d) Disturbs tracking techniques used by missiles
Answer: b
Clarification: Stealth configurations and requirements can conflict with aerodynamics requirements and FBW flight control is essential to give acceptable control and safe handling across the flight envelope. An example of such is the American fighter F -117, nicknamed “Nighthawk”. It is almost impossible to fly this aircraft without feedback FBW system.
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