Explore topic-wise InterviewSolutions in .

The CORRECT option is (a) reduce the AURAL signature

The EXPLANATION: By redirecting exhaust stacks away from the GROUND we can reduce the aural signature. We can reduce aural signatures by using MUFFLERS or by providing proper insulation as well.

The correct option is (a) to SUSTAIN DAMAGE, continue flying and RETURN to base

Explanation: VULNERABILITY is the ability of an aircraft which concerns whether the aircraft can sustain damage and continue to fly in order to return to the base. An aircraft can be damaged in number of ways such as through GUN.

Correct choice is (a) The ease with which the aircraft can be fixed

For explanation I would say: Maintainability is defined as the ease with which the aircraft can be repaired or fixed. Vulnerability is related to DAMAGE TAKEN. RCS DETECTION is nothing but RADAR detection.

Correct answer is (a) Higher detectability

To explain I would say: RCS is a MEASURE of how MUCH easier our object van be detected. Higher rcs INDICATE that the object is more detectable to the RADAR and hence, detectability will be more. If rcs are LOW then, it will be less detectable.

The correct choice is (a) flat wrap surfaces

To explain I would say: Flat wrap surface is USED to reduce the EFFORT and cost of the structure. In flat wrapping, we can DIRECTLY wrap a SHEET on our surface. This can significantly LOWER the aircraft production cost.

The correct ANSWER is (a) engine exhaust

Best EXPLANATION: Aircraft noise is PRIMARILY generated due to the engine exhaust. The fuselage, cabin noise are less as COMPARED to the engine exhaust. Lift is an AERODYNAMIC force.

The correct CHOICE is (a) True

The best explanation: Firewalls are used to reduce the effect of FLAMES during hazardous CONDITIONS. FIREWALL will prevent the spread of the flames. Hence, we can improve vulnerability by properly placing and locating the firewall.

Correct choice is (a) Scarfed firewall REDUCES scooping

Easiest explanation: The above DIAGRAM is representing the effect of scarfed firewall. As shown it reduces the scooping. RCS is measurement of RADAR detection. Wetted area will affect aerodynamics of design.

Correct ANSWER is (a) 34380

For explanation I WOULD say: Given, distance d = 2400 feet, LENGTH l=24000 ft.

Visual angles in MINUTES of arcs = 3438*l/d = 3438*24000/2400 = 34380.

The correct ANSWER is (a) dirty blue-grey

Best explanation: For sky BACKGROUND, camouflage paint pattern CONSISTS of dirty blue-grey typically. Apart from this, grey-brown combination is also USED as camouflage paint for the ground background.

Right choice is (a) True

To explain: Radar detection is CRUCIAL and vital CONSIDERATION for a military aircraft. If military aircraft is easily detected by enemy radar then, it can lead to casualties and chaos. If an enemy is not able to detect our military aircraft then, they cannot DEALT much damage and our survivability will increase at such time. There are plenty of reasons among which some has MENTIONED above.

The correct option is (a) Some clearance should be provided between propeller and FUSELAGE

Easy EXPLANATION: Reduction of lift can be achieved by number of WAYS such as AOA reduction, drag increment etc. Thrust at CRUISE will be equal to the drag. Engine exhaust is primary SOURCE of aircraft noise. Hence, the correct statement will be ‘Some clearance should be provided between propeller and fuselage’.

The correct answer is (a) Vulnerable area

To explain: Vulnerable area is KEY parameter of a vulnerability. It is the product of PROBABILITY of an aircraft COMPONENT to be hit and the projected area of that component. RCS concerns with radar DETECTION. IR concerns with IR detectability.

The correct CHOICE is (a) 31ft^2

Easy explanation: Given, part 1: area a1=5ft^2, pk1=1

Part 2: area a2=4ft^2, pk2=0.5

Part 2: area a3=80ft^2, pk3=0.3

Total VULNERABLE area = a1*pk1 + a2*pk2 + a3*pk3 = 5*1 + 4*0.5 + 80*0.3 = 5+2+24 = 31ft^2.

Correct option is (b) False

The BEST I can explain: TYPICALLY, it is not ADVISED to use such arrangements. If this type of arrangement is used then, it may affect the safety of aircraft at the TIME of the crash. Hence, it should be AVOIDED.

The correct choice is (a) radio DETECTION and ranging

To EXPLAIN I WOULD say: RADAR stands for ‘radio detection and ranging’. It is used to detect the aircraft. Radar can be monostatic radar or bistatic BASED on location of TRANSMITTER and receiver. Radar is one of the primary sensors in modern aircrafts.

Right option is (a) True

For explanation: Sun glint will affect the reflections and hence, will affect the IR detection. Sun glint can be reduced by USING SPECIAL paints. These paints will have low IR reflectivity which can IMPROVE the IR detection.

The CORRECT answer is (a) more noise

To explain: in a typical aircraft, engine is primary component which generates higher aural SIGNATURES. SMALL diameter and high exhaust will generate more noise DUE to the EFFECT of air shear layers.

The correct answer is (a) TURBOJET > TURBOFAN > reciprocating engine

For explanation I would say: Engine exhaust aural signatures will be affected by TYPE of engine used. A large diameter propeller with limited tip speed will generate less NOISE as compare to HIGH speed turbojets. Turbofan aural signature is less than that of the turbojet but greater than the reciprocating engine. Hence, the correct order will be Turbojet > turbofan > reciprocating engine.

The CORRECT option is (a) BLADE will not strike anyone if they fly off

The best explanation: As a crashworthiness consideration, positioning of the propeller should be such that the BLADES will not strike anyone in case of failure or emergency. Hence, as a DESIGNER it is our primary role to ensure not only performer but also SAFETY of passengers as well.

The correct choice is (a) typical routing tunnel

The EXPLANATION is: Above figure is showing a typical routing tunnel. An external TYPE is shown in above figure. As shown it is running along the a/c spine. Routing tunnel will help to SIMPLIFY the complexity of routing.

Correct choice is (a) They allow most of the engine to be exposed for maintenance

Easy explanation: Engine DOORS should be such that they allow most of the engine to get exposed during maintenance. This will reduce the EFFORT of removing other components. THEREFORE, it will improve MAINTAINABILITY considerations of the engine.

Right CHOICE is (a) To reduce breakdowns of critical equipment

Easy explanation: Maintenance can be divided into different TYPES. Preventive is one of the type of maintenance. It is done with the GOAL of REDUCING critical equipment breakdown. It is done periodically and very well planned.

Correct choice is (a) Inside fuselage

To ELABORATE: Inside fuselage will eliminate rcs of warheads as they are no longer in the RANGE of radar signals. Locating warheads on wingtips, outside fuselage or below wings will provide some surface AREA through which signal can be returned. HENCE, it will not IMPROVE detectability as an inside fuselage position.

Correct option is (a) CANOPY glint can affect the VISUAL detection of an aircraft

To explain: Canopy glint can affect the visual detection of an aircraft. Weight is not ALWAYS SIMILAR to lift. THRUST is not always same as drag.

Right choice is (a) Drag magnitude

Explanation: Radar detectability is directly affected by how MUCH EM energy is being returned by an object. It is also affected by RCS or radar cross SECTION. RCS depends upon look angle, flat surface, stealth technology ETC. Drag magnitude will not AFFECT radar detection.

The CORRECT option is (a) Engine EXHAUST

To explain I would say: Primary SOURCES for IR detection in an aircraft is engine exhaust. Passenger, cabin crew and fuel tank will play minor ROLE as compared to the engine exhaust. Engine exhaust consists of HOT gases and emissions.

Right choice is (a) aural signature

Easiest explanation: The NOISE generated by an aircraft is called the aural signature of the aircraft. Aural signature or noise is very important for CIVIL as well as military GRADE aircraft. Some aircraft suffers retirement DUE to much higher aural signatures.

The correct option is (a) FLARES

The best I can explain: If we increase ENGINE exhaust temperature then, it will increase the IR detection. As a COUNTERMEASURE for IR detection, most of military a/c are using flares. Flares are used to GENERATE fake IR SIGNATURES.

Correct answer is (a) 512.4K

Explanation: GIVEN, Mach number = 2.0, AMBIENT TEMPERATURE T1 = 305K

Assuming the recover factor as 0.85 and for such CASE,

Recovery temperature T2 = T1*(1+0.17*M^2)

T2 = 305*(1+0.17*2*2) = 305*1.68 = 512.4K.

Right choice is (a) we can use more mufflers

To ELABORATE: Noise by a piston engine exhaust can be REDUCED in a number of ways. ONE of them is by adopting mufflers. Apart from muffler, we can redirect the exhaust in such way that the resulting noise will be MUCH lesser.

Correct answer is (a) INSULATING material

To EXPLAIN: We can use insulating materials to reduce the aural signatures. LOFTING is mathematical MODELING. Drafting is based on DRAWING.

Correct OPTION is (a) We should avoid placing HEAVY items behind or above people

Explanation: Lift is not always same as WEIGHT. Drag is not necessarily to be same as THRUST. Heavy items should be placed as per structural and crashworthiness considerations. Heavy items should not be placed behind or above people or passenger compartment.

The correct answer is (a) 5.71m

The explanation: Given LOCATION of spar = 65% of MAC, distance from t.e. = 2m.

Spar is LOCATED at 65% of chord from l.e. HENCE, from t.e. location of spar = (100% – 65%) of chord = 1-0.65 = 0.35*chord.

From given, 0.35*chord = 2m

Chord = 2/0.35 = 5.71m.

Correct OPTION is (a) 0.25 unit

Explanation: GIVEN, LUMINANCE of A/C L1=10unit, luminance of BACKGROUND L2 = 8unit.

Approximate contras value C = |L1-L2|/L2 = |10-8|/8 = 2/8 = 0.25 unit.

Right answer is (a) 0.2m-0.3m

The explanation: Given chord c = 1m.

Typical range of front SPAR location = 20% to 30% of chord = 20% of 1 to 30% of 1 = 0.2*1 to 0.3*1 = 0.2m-0.3m.

Correct choice is (a) SURFACE current scattering

The explanation: Above figure is illustrating the CONCEPT of surface current scattering. As shown in the figure, some radar energy is incoming to the surface. As radar energy PASSES through the surface some edge scattering can be OBSERVED as shown by the diagram. This scattering effect can affect the radar DETECTION.

Right choice is (a) 12in

To EXPLAIN I WOULD say: GIVEN external DIAMETER = 20in. Radius = 20/2 = 10in.

Approximate radius of passenger compartment = external radius – structural thickness

= 10-4 = 6in

Hence, diameter = 2*6 = 12in.

Correct choice is (a) QUICKLY MIXING exhaust with outside air

To elaborate: Plume EMISSIONS can be reduced by quickly mixing the exhaust of engine with outside air. Emissions from hot parts are reduced by cooling them. Increase in TEMPERATURE will increase emissions and as a result, it will increase IR detection as well.

Correct answer is (a) Typically, in simulated combat we can detect large aircraft quickly than the SMALLER aircraft

To EXPLAIN: Lift is not always the same as WEIGHT. We can detect large aircraft based on its VISUAL parameters. SMALL aircraft can be found by using its color, noise, etc. Hence, the correct option will be in simulated combat we can detect large aircraft quickly than the smaller aircraft. This is primarily due to its size.

The correct choice is (a) Both [A] and [R] are true and [R] is the correct reason for [A]

Explanation: An aircraft will be spending major time in the sky. HENCE, it is required to use lighter COLORS at lower SURFACE as the background lookup angle is sky. It will reduce the contrast of an aircraft with respect to sky and will improve VISUAL detection.

Correct answer is (a) mottled grey GREEN

Easy explanation: For ground background, camouflage PAINT PATTERN consists of mottled grey green typically. APART from this, grey-brown combination is ALSO used as camouflage paint for ground background.