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The CORRECT ANSWER is (a) True

For explanation I would say: Fiber optic cables carries a digitally modulated light intensity signal. IT has no necessity to be made of an conductor as the only CONDITION for light to pass through is an opaque medium. Optical fibers are always made with an insulating material as they OFFER less EMI.

The CORRECT answer is (d) wavelength division multiplexing

The explanation: Fibre optic DATA transmission USE ‘wavelength division’ multiplexing whereby a SINGLE fibre can be used to transmit SEVERAL channels of information as coded light pulses of different wavelengths (or colours) simultaneously. The individual data channels are then recovered from the optically mixed data by passing the light signal through wavelength selective passive optical filters which are tuned to the respective wavelengths. WDM has a very high integrity as the multiplexed channels are effectively optically isolated.

Right answer is (b) Heavy compared to normal wires

Easy explanation: Fiber optics weigh comparatively very low than normal wires. Wires REQUIRE shielding from EMI which ALSO adds up to the overall weight of the connectivity SYSTEM. They also offer high speed data transfer and are relatively costly.

The correct option is (c) Screened enclosure around the CONNECTOR

Explanation: The wires from the cable connectors and the EM filters are housed within a screened enclosure around the connector known as an ‘EMC vault’ so that there is no aperture for EMI radiation to ENTER the box. The wires connecting different electrical EQUIPMENT are the most affected by EMI.

The correct choice is (b) Ability to survive in the vicinity of nuclear explosion

Easy explanation: Vicinity to a nuclear explosion and consequent emission of gamma RADIATION and an EMP of very high electric field strength. Military avionic equipment is specially designed to survive up to a certain (classified) level of these EFFECTS. This attribute is REFERRED to as ‘nuclear hardness’ and is achieved by the design of the circuits, use of nuclear HARD components, CIRCUMVENTION techniques and very efficient electromagnetic screening.

The CORRECT answer is (b) False

The explanation is: In addition to high data rates in the optical transmission medium, ANOTHER important ADVANTAGE is its ability to survive EMI. FIBER optics have very less interference by EMI and are used in AIRCRAFT mainly for this reason.

Right choice is (b) Electromagnetic compatibility

For explanation: EMC or Electromagnetic compatibility is the ability of the aircraft equipment to withstand HIGH levels of EMI. This is a necessary condition as many cases have occurred of aircraft experiencing SEVERE transients in the automatic FLIGHT control SYSTEM placing the aircraft temporarily out of control whilst overflying high power radar/radio transmitters. This has been due to the susceptibility of the flight control system analogue ELECTRONICS to EMI because of inadequate electro-magnetic screening.

Correct answer is (a) Electromagnetic pulse

Easiest EXPLANATION: An EMP, ABBREVIATED as Electromagnetic pulse is a SUDDEN change in the magnitude of an electrical field(a pulse) with strengths of hundreds of volts per meter. It occurs in a very WIDE range of electromagnetic RADIATION spectrum and can damage any electrical equipment in its vicinity.

The correct CHOICE is (d) Bad weather

Easy explanation: One of the COMMON modes of failure in the Fly-By-Wire system is EMI. Since the whole aircraft runs on ELECTRICITY, Electromagnetic Interference heavily affects the FBW system. It is caused by lightning strikes and in regions of high power RADIO or RADAR.

The correct CHOICE is (d) Processing this signal does not REQUIRE any electrical device

Easiest explanation: Passive optical sensors offers PARTICULAR advantages as these sensors are not affected by EMI. Passive optical sensors are defined as sensors which do not require electrical supplies or any electronic processing at the sensor, the output of the sensor being an optical signal which is modulated by the quantity being MEASURED. The processing of this optical signal is carried out by a separate electronic unit which is fully screened from EMI, the only connection between the sensor and the electronic unit being an optical fibre CABLE.

Correct choice is (B) Staleness

Easiest explanation: Data staleness OCCURS when a channel is delayed by, say, one iteration,before comparison with OTHERS. To overcome this problem it is necessary to have some form of time SYNCHRONISATION of the COMPUTER iteration periods.

The correct option is (d) Not affected by electromagnetic interference

Explanation: Very LARGE reductions in the weight of cabling are ACHIEVED by the USE of multiplexed data transmission and data bus networks. HIGH integrity data transmission can be achieved with very COMPREHENSIVE self checking and data validation capabilities. However, they are heavily affected by electromagnetic interference.

Correct OPTION is (a) Time synchronisation

For EXPLANATION I WOULD say: Data staleness PROBLEM it is necessary to have some form of time synchronisation of the computer iteration periods. This iteration period synchronisation is GENERALLY implemented through software.

The correct answer is (d) Sampling at more than double the frequency of the original signal

To EXPLAIN I WOULD say: Aliasing occurs when the sampling rate is lower than the frequency of the original signal. The NYQUIST THEOREM STATES that the sampling rate should be more than twice the frequency of the original signal to avoid aliasing.

The CORRECT choice is (a) Aliasing

To explain: 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.

Right option is (C) More power

The explanation is: 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.

Right answer is (c) System integration

For 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.

The correct answer is (c) BIRD strike

The best explanation: The type of failure which can affect all systems at the same time is termed a Common Mode Failure. Examples of common mode failures are the Lightning strike, Electro-magnetic INTERFERENCE, Fire/explosion/battle DAMAGE, INCORRECT maintenance, Common design errors – e.g., software.

The correct option is (a) Computer

Explanation: The signal from the lane passes through the voter and consolidator for cross COMPARISON of signals. These signals are then PASSED on to the computer which applies CONTROL LAWS and calculates the amount of deflection required by the actuator. The signal passes through another set of voter and consolidator for errors before PASSING to on to the actuator.

Correct choice is (c) Monitored duplex system

To explain: A monitored system USES SIGNAL monitors to identify ERROR in the signal. If an error is identified the MAIN signal is disconnected and the next channel takes over. Since there are two channels in the above system it is a monitored duplex system.

Correct answer is (c) When 2 channels FAIL none is disconnected

The EXPLANATION is: When two channels fail and are not disconnected, two good channels VERSUS two failed HARD over channels so that the CONTROL surface does not move resulting in a ‘fail passive’ situation. When one channel fails and is not disconnected, the other three good channels overrides the failed one.

The correct CHOICE is (b) Monitored triplex

To EXPLAIN: The incorporation of a monitoring system to check the correct functioning of a channel to a very high confidence level can also enable a failed channel to be identified and disconnected and this leads to an ALTERNATIVE failure survival configuration KNOWN as ‘monitored triplex’. A monitored triplex configuration comprises three totally independent parallel channels with each channel monitored by a dissimilar system to DETECT a failure.

Correct answer is (a) System with 4channels

Explanation: A well ESTABLISHED redundant system COMPRISES four TOTALLY independent CHANNELS of sensors and computers in a parallel arrangement to GIVE the required failure survival capability – such a configuration is referred to as a quadruplex system.

Correct option is (d) Mean Time Between Failures

Easiest explanation: MTBF is abbreviated as Mean Time Between Failures. It is the PREDICTED time between two inherent failures of a system. The mean time between failures, or MTBF, of a single CHANNEL FBW system is in the region of 3,000 hours. The FBW system must THUS possess redundancy with multiple PARALLEL channels so that it is able to survive at least two failures if these very low FAILURE probability figures are to be met.

The correct option is (c) MIMO

Easy 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.

Right ANSWER is (b) Pilot induced oscillations

To EXPLAIN: 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.

The correct ANSWER is (c) Rate limiting

To explain I WOULD SAY: 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.

Right choice is (a) INCREASES

The best 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.

Right OPTION is (a) True

The 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.

Right answer is (b) False

To explain: 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.

Correct choice is (c) Keeping angle of INCIDENCE under safety limits whilst maneuvering

Easiest 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.

Right option is (a) Damage from bird strikes and local airflow disturbance

Explanation: Although the angle of incidence indicator can provide motion feedback sensor information the major shortcomings of using them are damage from bird STRIKE as they are mounted EXTERNAL to an aircraft and effect of the local airflow AROUND the fuselage cause variations in MEASURED values.

Correct answer is (d) 50,000 to 100,000 hrs

For EXPLANATION I would say: Solid state RATE gyros are very reliable sensors with an MTBF in the REGION of 50,000 to 100,000 hours – ‘FIT and FORGET’ devices. Also, they are mounted internally and suffer less damage from the environment.

Correct choice is (d) One PLUS DERIVATIVE error controller

The best I can explain: A phase advance controller is usually KNOWN as phase advance controller with a transfer function.

The control term is filtered to limit the increase in gain at high frequencies and smooth the differentiation PROCESS which amplifies any NOISE present in the error signal.

The correct option is (a) LOW STEADY state error

Easiest explanation: INTEGRAL of error control eliminates steady-state errors and reduces the following lag. The integral of error term increases the LOOP gain at low frequencies up to theoretically infinite gain at dc so that there are zero steady-state errors due to out of trim external moments or forces acting on the aircraft.

The correct option is (d) Value of k is constant with altitude and AIRSPEED

The explanation: As the altitude and airspeed are varied, the magnitude of hinge MOMENT in the control surface varies. This RAISES the need to vary GAIN K with change in FLIGHT conditions.

Correct answer is (b) Pilot input angle

To elaborate: Pitch RATE command law is given by

 ηD = K(θi − GQQ)

 where ηD is the TAILPLANE demand angle; θi is the pilot’s input command; Q is the pitch rate; K is the forward loop gain, and Gq is the pitch rate gearing.

Correct answer is (a) Algorithms relating pilots STICK and control surface

The best explanation: The term ‘control LAWS’ is used to DEFINE the algorithms relating the control surface demand to the pilot’s stick command and the various motion sensor signals and the AIRCRAFT height, SPEED and Mach number.

Correct OPTION is (b) Improves control

The best explanation: 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.

Right CHOICE is (a) Rate gyro

The explanation: 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.

The correct choice is (B) Autopilot provides FBW commands of roll, pitch, and yaw

The explanation is: 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.

Correct ANSWER is (a) True

To EXPLAIN I would say: 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.

The correct choice is (a) True

Explanation: 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.

The correct option is (B) ACTS as a low pass filter on the stick movement

Easiest explanation: 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.

Correct choice is (C) FBW INCEPTOR

Explanation: 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.