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BEML Junior Executive practice questions

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Question 1Defence & Aerospace

In aerospace fastener practice, which material is most commonly specified for aircraft structural bolts that require high strength with good corrosion resistance?

  1. Precipitation-hardening stainless steel such as A286 Correct answer.
  2. Cadmium-plated low-carbon steel
  3. Commercially pure aluminium 1050
  4. Unplated grey cast iron

Explanation

Aerospace structural bolts frequently use precipitation-hardening stainless steels such as A286 because they retain high tensile strength at elevated temperature and resist corrosion without relying on a plated coating. Low-carbon steel and cast iron lack the strength-to-weight ratio needed in airframe joints. Pure aluminium is far too soft for a structural fastener.

Question 2Defence & Aerospace

Which maintenance action is required before an aircraft is returned to service after a hard landing that exceeded the recorded threshold?

  1. A repaint of the lower fuselage skin
  2. Only a walk-around visual check by the line crew
  3. Refuelling to full tanks and re-dispatch
  4. A structural inspection and landing-gear check per the maintenance manual, with sign-off by authorised personnel Correct answer.

Explanation

A hard landing triggers a defined inspection regime in the aircraft maintenance manual, typically covering landing gear, attachments, and nearby structure, and it must be certified by authorised maintenance staff before release. A visual walk-around alone does not satisfy that requirement. Refuelling and repainting have no bearing on structural airworthiness.

Question 3Defence & Aerospace

In a turbojet engine, which station designation conventionally refers to the compressor inlet?

  1. Station 4
  2. Station 8
  3. Station 2 Correct answer.
  4. Station 5

Explanation

Engine station numbering conventionally places station 1 at the inlet lip, station 2 at the compressor face, station 3 at compressor discharge, station 4 at combustor exit, and station 5 at turbine exit. Station 2 therefore marks the compressor inlet. The higher numbers lie downstream in the gas path.

Question 4Defence & Aerospace

Which radar band is most commonly associated with long-range air-surveillance and early-warning sets because of its favourable atmospheric propagation?

  1. W band
  2. V band
  3. L band Correct answer.
  4. Ka band

Explanation

L band offers relatively low atmospheric attenuation and long unambiguous range, which suits long-range surveillance and early-warning radars. Ka, V, and W bands are millimetre-wave regions with much higher attenuation and are used for short-range, high-resolution functions.

Question 5Defence & Aerospace

Which document authorises an aircraft to be dispatched with a known defect deferred under a controlled maintenance procedure?

  1. The minimum equipment list with its associated conditions Correct answer.
  2. The weight and balance schedule
  3. The crew duty roster
  4. The aircraft flight manual performance section

Explanation

The minimum equipment list defines which items may be inoperative for dispatch and under what conditions, so it is the controlling document for deferred defects. The flight manual, weight schedule, and duty roster govern performance, loading, and crewing respectively, not deferral authority.

Question 6Defence & Aerospace

Which property of a solid rocket propellant grain primarily determines the thrust-time profile of the motor?

  1. The burning surface area as it changes during combustion Correct answer.
  2. The electrical resistance of the igniter leads
  3. The mass of the nozzle clamp band
  4. The colour of the inhibitor coating

Explanation

Thrust in a solid motor follows chamber pressure, which depends on the burning surface area exposed at each instant. Grain geometry such as star or tubular configurations is chosen to give progressive, regressive, or neutral thrust profiles. Coating colour, clamp-band mass, and igniter lead resistance do not shape the thrust curve.

Question 7Defence & Aerospace

In aircraft hydraulic systems, what is the primary purpose of an accumulator?

  1. To measure fluid temperature for the cockpit display
  2. To store pressurised fluid for peak demands and damp pressure surges Correct answer.
  3. To cool the fluid by rejecting heat to the airstream
  4. To filter particulate contamination from the fluid

Explanation

A hydraulic accumulator holds fluid under gas pressure so it can supply short-term high flow, smooth pump pulsations, and absorb pressure surges. Filtration, cooling, and temperature measurement are performed by separate components such as filters, heat exchangers, and sensors.

Question 8Defence & Aerospace

Which type of orbit is used by a satellite that must remain continuously visible from a fixed ground region at high latitude?

  1. Geostationary equatorial orbit
  2. Highly inclined elliptical orbit with a long apogee dwell Correct answer.
  3. Low circular equatorial orbit
  4. Sun-synchronous polar orbit at 500 km

Explanation

A highly inclined elliptical orbit such as a Molniya-type orbit spends most of its period near apogee over high latitudes, giving prolonged visibility where geostationary coverage is poor. Geostationary and low equatorial orbits sit near the equator, and a low polar orbit passes overhead only briefly.

Question 9Defence & Aerospace

A gas-turbine engine's compressor pressure ratio is 12 and the intake total pressure is 101 kPa. Ignoring losses, what is the approximate compressor delivery total pressure?

  1. 1212 kPa Correct answer.
  2. 1012 kPa
  3. 113 kPa
  4. 12 kPa

Explanation

Delivery pressure equals intake pressure multiplied by the pressure ratio, so 101 kPa times 12 gives about 1212 kPa. Adding the ratio to the intake value or simply restating the ratio are common errors. The multiplication reflects that pressure ratio is a dimensionless factor, not an increment.

Question 10Defence & Aerospace

During a flight-control rigging check, a pilot reports that the left aileron reaches full deflection before the right. Which condition does this most directly indicate?

  1. An overfilled hydraulic reservoir
  2. A failed static pressure port
  3. A mis-set cabin pressure controller
  4. Incorrect aileron rigging or differential linkage adjustment Correct answer.

Explanation

Asymmetric aileron travel points to rigging or differential linkage adjustment, because the two surfaces should reach their limits in a defined relationship. Static ports, reservoir level, and cabin pressure control do not govern control-surface travel symmetry. The discrepancy must be corrected and functionally checked before release.

Question 11Defence & Aerospace

Which non-destructive test method is best suited to detecting internal voids in a composite aircraft radome?

  1. Eddy current inspection
  2. Through-transmission ultrasonic inspection Correct answer.
  3. Magnetic particle inspection
  4. Dye penetrant inspection

Explanation

Ultrasonic through-transmission detects internal voids and delaminations in composites because sound attenuates or reflects at the defect. Magnetic particle and eddy current methods need conductive or ferromagnetic material, and dye penetrant only finds surface-breaking defects. A radome is non-metallic, so ultrasonic inspection is the appropriate choice.

Question 12Defence & Aerospace

What is the primary function of a missile's inertial measurement unit during the midcourse phase?

  1. To provide continuous position and attitude estimates for guidance without external signals Correct answer.
  2. To detonate the warhead at the correct instant
  3. To cool the seeker detector array
  4. To deploy the aerodynamic control fins

Explanation

The inertial measurement unit integrates accelerometer and gyroscope data to propagate the vehicle's position, velocity, and attitude, enabling guidance when external updates are unavailable or jammed. Warhead fuzing, detector cooling, and fin deployment are handled by separate subsystems.

Question 13Defence & Aerospace

An aircraft flies at a true airspeed of 250 m/s at sea level where the speed of sound is 340 m/s. What is its approximate Mach number?

  1. 1.36
  2. 0.54
  3. 0.74 Correct answer.
  4. 2.50

Explanation

Mach number is true airspeed divided by local speed of sound, so 250 divided by 340 gives about 0.74, which is subsonic. Dividing the speed of sound by the airspeed or ignoring the division entirely produces the other values. The local speed of sound, not a fixed constant, must be used.

Question 14Defence & Aerospace

In avionics data buses, why is ARINC 429 described as a unidirectional protocol?

  1. It permits only one message per flight
  2. It transmits data in only one direction per bus line, so separate lines are needed for each direction Correct answer.
  3. It carries only analogue voltages
  4. It encrypts all transmissions

Explanation

ARINC 429 uses a single transmitter per bus pair, so each line carries data in one direction and two-way exchange requires separate transmit and receive buses. It is a digital protocol, not an analogue or encrypted one, and it supports continuous repeated transmission rather than one message per flight.

Question 15Defence & Aerospace

A pressure altimeter set to the wrong subscale setting will most likely produce which error?

  1. Total loss of the altitude display
  2. An error only when the aircraft is stationary
  3. Random oscillation of the pointer
  4. A steady indication offset proportional to the pressure-setting difference Correct answer.

Explanation

The altimeter computes altitude from static pressure referenced to the selected subscale, so an incorrect setting shifts the whole indication by an amount corresponding to the pressure difference. It does not cause oscillation, blank the display, or depend on the aircraft being stationary. Pilots must cross-check the setting before descent.

Question 16Defence & Aerospace

Which factor most strongly limits the endurance of a battery-powered unmanned aerial vehicle on a surveillance sortie?

  1. The frequency of radio check-ins
  2. The colour scheme of the ground control station
  3. The energy density of the battery relative to payload and airframe mass Correct answer.
  4. The number of operators at the ground station

Explanation

Endurance depends on available energy divided by power required, so battery energy density and the mass it must support dominate. Ground station colour, operator count, and radio check-in frequency do not change the onboard energy budget. Reducing payload mass or improving aerodynamic efficiency extends endurance.

Question 17Defence & Aerospace

In a fly-by-wire system with a normal law that limits bank angle, what happens when the system reverts to direct law?

  1. The engines reduce to idle
  2. All flight-control computers shut down
  3. Control-surface commands map directly to stick input with reduced envelope protection Correct answer.
  4. The aircraft automatically lands

Explanation

Direct law passes pilot inputs to the surfaces with little or no envelope protection, so the crew must observe limits manually. It does not command an automatic landing, shut down the computers, or force idle thrust. Understanding the degradation level is essential for handling qualities.

Question 18Defence & Aerospace

Which mechanism gives a turbofan engine its high propulsive efficiency at subsonic cruise compared with a pure turbojet?

  1. A shorter combustion chamber
  2. A higher exhaust gas temperature in the core
  3. A smaller intake area
  4. A larger mass of air accelerated to a lower velocity through the bypass duct Correct answer.

Explanation

Propulsive efficiency improves when a large mass of air is accelerated modestly rather than a small mass to a very high velocity, which is exactly what the bypass fan achieves. Core temperature, intake area, and combustor length are not the defining reason for the efficiency gain.

Question 19Defence & Aerospace

Which quality characteristic is most important for a fastener used in a vibration-heavy helicopter rotor head?

  1. Bright cosmetic finish
  2. Lowest possible purchase cost
  3. Maximum electrical conductivity
  4. High fatigue strength with resistance to self-loosening Correct answer.

Explanation

Cyclic loading in a rotor head demands fasteners with high fatigue strength and features that resist loosening under vibration, such as appropriate preload and locking provisions. Conductivity, cost, and appearance are secondary to structural integrity in this application.

Question 20Defence & Aerospace

A radar operating at 10 GHz has a free-space wavelength closest to which value?

  1. 3 cm Correct answer.
  2. 30 cm
  3. 0.3 mm
  4. 3 m

Explanation

Wavelength equals the speed of light divided by frequency, so 3 times 10 to the eighth divided by 10 to the tenth gives 0.03 m, or 3 cm. The other values correspond to different frequency decades and would misplace the radar in the wrong band.

Question 21Defence & Aerospace

Why is titanium alloy widely used for critical airframe components despite its cost?

  1. It is the easiest metal to machine by hand
  2. It avoids the need for any surface protection in all environments
  3. It offers high strength-to-weight ratio with good corrosion resistance Correct answer.
  4. It has the lowest melting point of structural metals

Explanation

Titanium combines high strength with low density and forms a stable passive oxide film, which suits weight-critical, corrosion-exposed airframe parts. Its melting point is high rather than low, it is notoriously difficult to machine, and it still needs protection in some environments.

Question 22Defence & Aerospace

A telemetry link shows a sudden drop in received signal strength as an aircraft manoeuvres, with recovery when it returns to level flight. Which explanation is most consistent?

  1. A decrease in the ground station's mains voltage within tolerance
  2. A change in the aircraft's paint scheme
  3. Antenna pattern masking or polarisation mismatch during the manoeuvre Correct answer.
  4. A permanent transmitter failure

Explanation

Manoeuvre-dependent signal loss that recovers in level flight points to antenna pattern masking, shadowing by the airframe, or polarisation mismatch as the geometry changes. A permanent transmitter failure would not recover, and paint or normal mains variation cannot explain the pattern.

Question 23Defence & Aerospace

In a closed-loop flight-control system, adding integral action to the controller primarily achieves which outcome?

  1. Reduction of the system's order
  2. Removal of the need for feedback
  3. Elimination of steady-state error to a constant command Correct answer.
  4. Guaranteed stability margin improvement

Explanation

Integral action accumulates past error and drives steady-state error to zero for a constant reference, but it also adds phase lag and can reduce stability margin if not tuned. It raises, not lowers, system order, and feedback remains essential. Stability is not guaranteed to improve.

Question 24Defence & Aerospace

An aircraft's centre of gravity moves aft beyond the aft limit. What is the most likely consequence?

  1. Reduced static longitudinal stability and possible pitch-up tendency Correct answer.
  2. Improved stall recovery characteristics
  3. Increased longitudinal static stability
  4. No effect on handling if speed is constant

Explanation

As the centre of gravity moves aft, the moment arm between the centre of gravity and the aerodynamic centre shrinks, reducing static margin and degrading longitudinal stability, with a pitch-up tendency in the extreme. Stall recovery worsens rather than improves, and handling is affected regardless of constant speed.

Question 25Defence & Aerospace

A composite skin shows barely visible impact damage. Why is ultrasonic inspection preferred over a simple visual check?

  1. Impact can leave internal delamination and matrix cracking hidden beneath an intact surface Correct answer.
  2. Visual inspection is always more accurate for composites
  3. Ultrasound changes the material's strength
  4. Visual checks cannot be performed on aircraft

Explanation

Low-energy impacts often leave the outer ply intact while delaminations and matrix cracks spread beneath, so surface appearance understates the damage. Ultrasonic methods detect these internal discontinuities. Visual inspection is not more accurate in this case, ultrasound does not alter strength, and visual checks are routine.

Question 26Defence & Aerospace

In a turbojet engine, what is the primary function of the exhaust nozzle?

  1. To compress incoming air before it enters the combustor
  2. To expand hot gases and convert pressure energy into kinetic energy for thrust Correct answer.
  3. To mix fuel with air before combustion
  4. To cool the turbine blades using bypass air

Explanation

The exhaust nozzle accelerates the hot combustion gases by expanding them, converting remaining pressure into velocity and producing thrust. It does not perform fuel mixing, turbine cooling, or compression, which occur in other sections.

Question 27Defence & Aerospace

Which material is most commonly used for the skin of a modern aircraft due to its high strength-to-weight ratio?

  1. Aluminium alloy Correct answer.
  2. Titanium alloy
  3. Stainless steel
  4. Carbon-fibre composite

Explanation

Aluminium alloys, particularly 2024 and 7075, are widely used for aircraft skins because they offer an excellent balance of strength, weight, and cost. While composites and titanium are used in specific areas, aluminium remains the predominant skin material in many airframes.

Question 28Defence & Aerospace

What does the term 'angle of attack' refer to in aircraft aerodynamics?

  1. The angle between the longitudinal axis and the horizontal plane
  2. The angle between the vertical axis and the relative wind
  3. The angle between the wing chord line and the oncoming relative wind Correct answer.
  4. The angle between the wing dihedral and the fuselage centreline

Explanation

Angle of attack is defined as the angle between the wing's chord line and the direction of the relative wind. It directly influences lift and drag and is critical for flight safety.

Question 29Defence & Aerospace

In a missile guidance system, which type of guidance uses a seeker that tracks a target and sends commands to the missile based on the target's position relative to the missile?

  1. Celestial guidance
  2. Homing guidance Correct answer.
  3. Inertial guidance
  4. Command guidance

Explanation

Homing guidance relies on a seeker in the missile that detects and tracks the target, generating steering commands to intercept it. Command guidance uses external tracking and command signals, while inertial and celestial guidance do not involve target tracking.

Question 30Defence & Aerospace

What is the primary purpose of a radar altimeter in a military aircraft?

  1. To provide weather information along the flight path
  2. To determine the aircraft's position relative to navigation beacons
  3. To measure the aircraft's height above the ground using radio waves Correct answer.
  4. To detect and track enemy aircraft at long range

Explanation

A radar altimeter transmits radio waves downward and measures the time for the reflection to return, giving precise height above terrain. It is essential for low-level flight and automatic landing systems.

Question 31Defence & Aerospace

Which of the following is a primary function of a missile's control actuator system?

  1. To store the missile's propellant before launch
  2. To transmit telemetry data to the ground station
  3. To convert electrical commands into mechanical movement of control surfaces Correct answer.
  4. To provide electrical power to the missile's guidance computer

Explanation

Control actuators receive commands from the guidance system and move the missile's fins or thrust vectoring mechanisms to steer the missile. They do not generate power, store propellant, or handle telemetry.

Question 32Defence & Aerospace

In composite materials used in aerospace, what does the term 'prepreg' refer to?

  1. Fibre reinforcement pre-impregnated with a resin matrix Correct answer.
  2. A pre-cured composite panel ready for assembly
  3. A type of adhesive used for bonding metal to composite
  4. A protective coating applied before painting

Explanation

Prepreg is a composite material where the reinforcing fibres are pre-impregnated with a partially cured resin. This ensures consistent resin content and simplifies layup during manufacturing.

Question 33Defence & Aerospace

What is the primary role of a fire control radar in a fighter aircraft?

  1. To provide target detection, tracking, and weapon guidance Correct answer.
  2. To manage communication with ground control
  3. To assist in navigation and terrain avoidance
  4. To monitor engine performance and fuel consumption

Explanation

Fire control radar is designed to detect and track airborne or surface targets and to provide data for aiming weapons. It is distinct from navigation, engine monitoring, or communication systems.

Question 34Defence & Aerospace

A missile's solid rocket motor has a specific impulse of 250 seconds. What does specific impulse represent?

  1. Total impulse divided by burn time
  2. Exhaust velocity divided by gravitational acceleration
  3. Chamber pressure divided by throat area
  4. Thrust per unit weight flow rate of propellant Correct answer.

Explanation

Specific impulse is defined as thrust divided by the weight flow rate of propellant, effectively measuring efficiency. It is often expressed in seconds and equals exhaust velocity divided by gravitational acceleration, but the fundamental definition is thrust per unit weight flow.

Question 35Defence & Aerospace

In aircraft structural design, what is the purpose of a fatigue test on a full-scale airframe?

  1. To determine the number of load cycles the structure can withstand before failure Correct answer.
  2. To measure the ultimate static strength of the structure
  3. To calibrate the flight control system
  4. To verify the aerodynamic shape of the aircraft

Explanation

Fatigue testing applies repeated cyclic loads to simulate service life and identify crack initiation and growth. It is distinct from static strength testing, which loads the structure to failure once.

Question 36Defence & Aerospace

A satellite in low Earth orbit experiences atmospheric drag. What effect does this drag have on its orbit over time?

  1. It has no effect on altitude but decreases velocity
  2. It increases both altitude and velocity
  3. It decreases the orbital altitude and increases the orbital velocity Correct answer.
  4. It increases the orbital altitude and decreases the orbital velocity

Explanation

Drag removes energy from the satellite, causing the orbit to decay to a lower altitude. As the satellite descends, its orbital velocity increases due to conservation of angular momentum and Kepler's laws.

Question 37Defence & Aerospace

In a fly-by-wire flight control system, what is the purpose of the flight control computers' voting logic?

  1. To vote on the pilot's input to ensure it is within limits
  2. To manage the electrical power distribution to the actuators
  3. To determine the optimal flight path for fuel efficiency
  4. To compare outputs from multiple redundant computers and select the most reliable command Correct answer.

Explanation

Voting logic in redundant fly-by-wire systems compares outputs from multiple computers to detect and isolate faults, ensuring that a single failure does not cause loss of control. It does not vote on pilot inputs or manage power.

Question 38Defence & Aerospace

What is the primary advantage of using a strapdown inertial navigation system over a gimballed system in a missile?

  1. It provides higher accuracy at very long ranges
  2. It can operate without any accelerometers
  3. It eliminates mechanical gimbals, reducing size, weight, and complexity Correct answer.
  4. It requires less frequent calibration

Explanation

Strapdown systems mount inertial sensors directly to the vehicle body, removing gimbals and simplifying construction. They are generally smaller, lighter, and more reliable, though they require more complex computation.

Question 39Defence & Aerospace

In a composite aircraft structure, what is the purpose of a lightning protection mesh?

  1. To increase the structural stiffness of the composite
  2. To improve the radar cross-section of the aircraft
  3. To provide electromagnetic shielding for communication antennas
  4. To conduct lightning current away from sensitive electronics and prevent delamination Correct answer.

Explanation

Composite materials are poor conductors, so a metallic mesh (often copper or aluminium) is embedded in the skin to safely conduct lightning currents and protect the structure from damage. It is not primarily for stiffness, antenna shielding, or stealth.

Question 40Defence & Aerospace

A radar transmits a pulse and receives an echo 20 microseconds later. Assuming the speed of light is 3×10^8 m/s, what is the approximate range to the target?

  1. 1,500 metres
  2. 12,000 metres
  3. 6,000 metres
  4. 3,000 metres Correct answer.

Explanation

The total round-trip distance is speed of light multiplied by time: 3×10^8 m/s × 20×10^-6 s = 6,000 m. Since this is round trip, the one-way range is half, i.e., 3,000 m.

Question 41Defence & Aerospace

In a missile's thrust vector control system, what is the function of a jet vane?

  1. To filter particulate matter from the propellant gases
  2. To cool the nozzle throat during firing
  3. To deflect the exhaust plume and generate control moments Correct answer.
  4. To increase the thrust by accelerating the exhaust

Explanation

Jet vanes are aerodynamic surfaces placed in the exhaust stream that can be rotated to deflect the flow and produce side forces for steering. They do not increase thrust, cool the nozzle, or filter particles.

Question 42Defence & Aerospace

Which of the following best describes the term 'radar cross-section' (RCS)?

  1. The area covered by the radar beam on the ground
  2. A measure of how detectable an object is by radar Correct answer.
  3. The physical cross-sectional area of the radar antenna
  4. The frequency bandwidth of the radar signal

Explanation

RCS is a measure of the power reflected by a target back to the radar, indicating its detectability. It is not the antenna area, ground coverage, or bandwidth.

Question 43Defence & Aerospace

In the context of military aircraft, what is the purpose of a terrain-following radar?

  1. To enable automatic low-level flight by measuring terrain clearance and generating climb/dive commands Correct answer.
  2. To assist in air-to-air refuelling by locating the tanker
  3. To provide weather avoidance by detecting storms
  4. To map enemy ground forces for targeting

Explanation

Terrain-following radar scans the terrain ahead and provides signals to the flight control system to maintain a set altitude above ground, allowing high-speed low-level penetration. It is not primarily for targeting, weather, or refuelling.

Question 44Defence & Aerospace

What is the primary reason for using a titanium alloy in the compressor section of a gas turbine engine?

  1. To reduce the cost of manufacturing
  2. To withstand high temperatures while maintaining strength and low weight Correct answer.
  3. To improve the thermal conductivity of the compressor blades
  4. To simplify the machining process

Explanation

Titanium alloys retain strength at elevated temperatures and have low density, making them ideal for compressor blades and discs. They are more expensive and harder to machine than aluminium or steel.

Question 45Defence & Aerospace

In a satellite communication system, what is the purpose of a transponder?

  1. To store data for later transmission
  2. To determine the satellite's attitude
  3. To receive, amplify, and retransmit signals at a different frequency Correct answer.
  4. To generate electrical power from solar energy

Explanation

A transponder receives an uplink signal, amplifies it, and retransmits it on a downlink frequency, often with frequency translation. It does not generate power, determine attitude, or primarily store data.

Question 46Defence & Aerospace

A missile's guidance system uses proportional navigation. What does the guidance law command?

  1. A climb to a higher altitude before diving on the target
  2. A deceleration to match the target's speed
  3. A constant acceleration towards the target
  4. A turn rate proportional to the rate of change of the line-of-sight angle Correct answer.

Explanation

Proportional navigation commands the missile's lateral acceleration to be proportional to the line-of-sight rate, which is an effective way to achieve interception. It does not command constant acceleration, altitude changes, or speed matching.

Question 47Defence & Aerospace

In the context of composite airframe design, what is the significance of the term 'damage tolerance'?

  1. The ability of the structure to retain residual strength in the presence of flaws or damage Correct answer.
  2. The capacity of the structure to absorb radar energy
  3. The resistance of the material to high temperatures
  4. The maximum load the structure can carry without permanent deformation

Explanation

Damage tolerance is a design philosophy ensuring that structures can withstand anticipated damage (e.g., cracks, delamination) without catastrophic failure until repair. It is distinct from static strength, thermal resistance, or stealth.

Question 48Defence & Aerospace

A fighter aircraft is flying at Mach 0.9 at an altitude where the speed of sound is 300 m/s. What is its true airspeed?

  1. 333 m/s
  2. 243 m/s
  3. 300 m/s
  4. 270 m/s Correct answer.

Explanation

True airspeed is Mach number multiplied by the speed of sound: 0.9 × 300 m/s = 270 m/s. The other options result from incorrect multiplication or division.

Question 49Defence & Aerospace

In a radar system, what is the effect of increasing the pulse repetition frequency (PRF) on the maximum unambiguous range?

  1. It doubles the maximum unambiguous range
  2. It decreases the maximum unambiguous range Correct answer.
  3. It increases the maximum unambiguous range
  4. It has no effect on the maximum unambiguous range

Explanation

The maximum unambiguous range is inversely proportional to PRF: R_max = c/(2·PRF). Increasing PRF reduces the time between pulses, so echoes from distant targets may arrive after the next pulse, causing ambiguity.

Question 50Defence & Aerospace

In a missile's inertial measurement unit, what is the purpose of gyroscope bias calibration?

  1. To align the missile's antenna with the ground station
  2. To compensate for magnetic interference from the launch platform
  3. To adjust the accelerometer scale factor
  4. To correct for a constant offset error in the angular rate measurement Correct answer.

Explanation

Gyroscope bias is a constant error in the rate output that, if uncorrected, causes attitude drift. Calibration estimates and subtracts this bias to improve navigation accuracy.