1. What is the angle of incidence limiting?
a) Warning indication to the pilot during high angles of incidence
b) The minimum angle of attack that can be measured
c) Keeping angle of incidence under safety limits whilst maneuvering
d) Reducing the error that occurs in an angle of incidence indicator
Explanation: The incidence terms from the airstream sensors can be blended with the pitch rate error terms and the ‘gearings’ (or gain coefficients) of these terms adjusted as higher angles of attack are approached. This enables the angle of incidence to be kept within the safe limits whilst maneuvering at high angles of incidence, i.e., the angle of incidence limiting.
2. The aircraft is a rigid body.
a) True
b) False
Explanation: The aircraft structure is flexible and has a variety of flexural and torsional modes. The frequency of this structural mode is typically between 8 and 15 Hz for a fighter/strike aircraft and 2 to 4 Hz for a large transport aircraft.
3. FCS sensors which sense aircraft motion also sense the structural deflections
a) True
b) False
Explanation: The FCS sensors which sense the aircraft motion also sense the structural deflections and hence couple the structure modes into the control loops. The location of the motion sensors with respect to the nodes and anti-nodes of these structural modes is important.
4. What happens to the phase lag in an actuator as the frequency is increased?
a) Increases
b) Decreases
c) Constant
d) Cannot be determined
Explanation: The response of the actuators at low frequencies is basically that of a low pass (or first-order) filter, but as the frequency increases the lags in the first stage actuation system become dominant. The output/input ratio falls at an increasing rate and the phase lag rapidly increases.
5. What can occur when the control valve travel limits are reached under conditions of large amplitude demands?
a) Stall
b) Structural damage
c) Rate limiting
d) Rate delimiting
Explanation: Rate limiting can occur when the control valve travel limits are reached under conditions of large amplitude demands. The behaviour under rate limiting conditions is non-linear and the onset and the effects are dependent on the amplitude and frequency of the input demand.
6. What is PIO?
a) Pitot indicator
b) Pilot induced oscillations
c) Pressure indicator observed
d) Primary Input/Output
Explanation: Pilot Induced Oscillations are sustained or uncontrollable oscillations resulting from the efforts of the pilot to control the aircraft. They can have catastrophic results in extreme cases
7. Flight control systems comes under the category of _______
a) SISO
b) SIMO
c) MIMO
d) MISO
Explanation: Flight control systems come into the category of multi-input/multi-output (MIMO) closed-loop control systems as control is exerted about three axes and there are six degrees of freedom. The classic control theory approach is very suitable for single input/single output (SISO) closed-loop control systems and some single input/multi-output (SIMO) systems.
8. How does the digital implementation in the FBW system reduce weight?
a) Lightweight materials
b) Fewer components
c) System integration
d) Automated control
Explanation: In a typical Digital FBW system, One computer can control all three axes of control, whereas an analog system requires dedicated hardware for each axis of control. The reduction in hardware weight and volume, due to system integration, is of the order of 5:1 for a system of even modest complexity. The more complex systems could not be implemented economically using analogue technology.
9. Which of the following is not a result of digital implementation?
a) Hardware economy
b) Flexibility in updating
c) More power
d) Built in test capabilities
Explanation: The digital implementation in FBW only affects the control and stability of the aircraft. Power is not, in any way, related to the FBW system.
10. What is it called when the sampled signal is of lower frequency than the original signal?
a) Aliasing
b) Overshoot
c) Steady state error
d) Damping
Explanation: When the sampled signal is of lower frequency than the original signal it is known as aliasing. Aliasing induces data loss and errors. It can be reduced by a process called anti-aliasing.