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The correct choice is (a) it can EXPERIENCE EXCESSIVE flow separation

Explanation: Overall aircraft DESIGN will DECIDE whether the aircraft is STREAMLINED or not. An inadequate and poorly designed aircraft can suffer from drag increment, excessive flow separation etc.

The correct choice is (a) lower tail arm

Easiest EXPLANATION: Tail arm is nothing but the distance between cg of tail to cg of an aircraft, typically. Short and fat fuselage will have shorter tail arm or tail MOMENT arm. SIZE of the fuselage will be REDUCED for such case and as a result of which the tail arm will be reduced.

Right choice is (a) Tightly packed FUSELAGE will not AFFECT MAINTAINABILITY

To explain: Tightly packed fuselage makes it difficult to access some vital components for maintenance. This will affect the maintainability of the aircraft. Wetted area can be reduced by TIGHT packaging or by lowering the fineness RATIO or by both.

Correct answer is (a) REATTACH separated flow

Easiest explanation: VORTEX generator is small BODY placed on surface to reattach the separated flow. A flow flows around the vortex generator, it curls the flow. And as a result of which flow is being forced to SWIRL and to flow reattaches to the surface if it has separated.

The correct choice is (a) HIGHER supersonic wave DRAG

To elaborate: Wave drag is the supersonic phenomena. Wave drag does not exist for incompressible flow. Short and fat fuselage will offer minimization of the wetted AREA. This gives advantage in terms of friction properties. HOWEVER, it suffers from higher wave drag at supersonic speeds.

Correct OPTION is (a) distribution of weight along span as lift distribution

The BEST explanation: Span-LOADING is the distribution of weight along span as lift is distributed. Thrust loading is the RATIO of thrust and weight. Wing loading is weight per area. Power loading is weight of aircraft to the power PRODUCED.

Correct CHOICE is (a) ideal SPAN LOADING

The explanation: Above figure is REPRESENTING the distribution of lift and WEIGHT along the span. It is shown in figure that weight is distributed exactly same as lift along the span. This is ideal condition and termed as ideal span loading.

Correct choice is (a) AREA rule

Best EXPLANATION: Drag divergence Mach number is that Mach number after which drag increases DRASTICALLY. Area rule can be USED to lower the drag up to 50%. By using area rule properly we can improve the drag divergence Mach number.

The CORRECT option is (a) WETTED area

Explanation: Wetted area is considered as ONE of the most powerful aerodynamic tool. Wetted area is nothing but the actual area that will be in contact if fluid is flown over the body. Spar and ribs are STRUCTURAL MEMBERS.

The CORRECT choice is (a) keelson

The explanation is: Keelson is a large beam placed at fuselage bottom. Keelson is structural element through which BENDING loads are carried out. Tail is after section of the aircraft which has primary PURPOSE to provide STABILITY and CONTROL.

Correct option is (b) False

To elaborate: A poorly designed fuselage can lead to drag rise, flow separation etc. As a result of these adverse EFFECTS lift loss will increase. Fuselage is considered as one of the primary drags producing member in an aircraft. Hence, an ADEQUATE DESIGN should be PROVIDED to reduce the lift loss.

Right OPTION is (a) BASE drag is affected by boat tailing

For explanation: Tapering of the base area or aft FUSELAGE SECTION is called boat tailing. Boat tailing will affect base area. As a result of which pressure DISTRIBUTION is affected as well. Hence, as a pressure distribution varies drag due to base area will also change.

Correct answer is (a) area rule

The explanation is: R. whitcomb had DEVELOPED a method to reduce the SUPERSONIC drag. The method is known as area ruling or area rule. In this method overall volume distribution of components are ALTERED in such way that the resultant body should provide less drag.

Right choice is (a) Any unfair REARWARD facing blunt surface

Easiest EXPLANATION: BASE area is nothing but the rearward area of the fuselage. It is any unfair rearward facing blunt surface. Wing area is the PRODUCT of SPAN and chord for rectangular planform. Fuselage cabin will be located at front side of the fuselage.

The correct answer is (a) To reduce drag

Explanation: FUSELAGE is primary drag generating component of aircraft. A lower surface upsweep is provided to reduce drag PENALTY for TYPICAL aircraft. This upsweep will induce vortex flow pattern at the lower surface which can reduce the drag. However, for high SPEED aircraft it should be as low as possible.

Right CHOICE is (a) BENDING

To elaborate: Longerons are structural members of an AIRCRAFT. They are heavy and used to prevent the bending. Longerons are FEWER in numbers and primarily opposes the loads which can result in the bending stress and can cause the bending of structure. Their PLACEMENT should be considered while designing the aircraft.

The correct choice is (a) Wake of a CANARD can stall the engine

For explanation I would say: While designing an aircraft, DESIGNER should not forget about AERODYNAMIC interaction of different components. If a canard is required then the interaction of canard with other components should be considered during LAYOUT. If canard wake enters into the engine it can stall the blades and as a result, engine performance will be reduced as WELL.

Correct answer is (a) PLACING opposite forces NEAR to each other

The best I can explain: To reduce the structural weight it is required that our design should have efficient load paths through which we can effectively CONNECT opposing forces. For a typical aircraft, TWO common forces to be resolved are lift and force. Hence, by locating opposite forces near to each other we can IMPROVE structural considerations of our design.

Right choice is (a) straight and uninterrupted

To explain: A typical transport FUSELAGE will have more numbers of stringers ATTACHED to its STRUCTURE. Stringers are short and light STRUCTURAL elements. They are distributed around fuselage circumference. Stringers should be straight and uninterrupted to minimize the weight as possible and as per our requirement.

The correct answer is (a) True

Explanation: Interaction of various components will affect the aerodynamic design. Wing-fuselage interaction GIVES drag which is known as INTERFERENCE drag. If a design has not CONSIDERED interaction of the various components with each other then it will result in unexpected performance. Wing wake can stall the HORIZONTAL tail, wing downwash will INCREASE AOA seen by tail etc. are examples of interactions between various components.

The correct option is (a) PROVIDE shortest and STRAIGHTEST possible LOAD paths

The best I can explain: In general it is required to locate OPPOSING forces at the same location. We can reducing weight by doing so. However, it is not possible for EVERY scenario. Hence, we need to provide some path through which we can connect these forces. These paths are load paths and by providing shortest and straightest possible load path we can reduce the weight.

Correct choice is (a) True

Explanation: Typically, cutouts will increase the weight of the structure. A cutout provided at the wing carry through box in order to place LANDING GEAR or UNDERCARRIAGE will require larger cutout and will increase LOAD as well. Hence, if possible then we should avoid it.

The correct answer is (a) Typical low wave drag design

The best I can explain: Above DIAGRAM is showing typical low wave drag design of an aircraft. It is called coke-bottling. It is used to improve the wave drag properties by ALTERING the VOLUME DISTRIBUTION. It can be used to reduce drag up to 50%.

The correct choice is (a) 10° – 12°

Easiest explanation: Given, FREE stream velocity V = 120knts. As shown in the figure FUSELAGE has some deviation with free stream. For given speed of FREESTREAM air, a typical fuselage should be ALLOWED up to 12.5° maximum. More than the given limit will affect the drag parameters. Hence, answer would be 10°-12°.

The correct option is (a) lower the fineness ratio

Easiest explanation: Wetted area can be USED to determine the drag PROPERTIES of an aircraft. Fineness ratio is NOTHING but the LENGTH of the FUSELAGE divided by max diameter of the fuselage. Hence, if we lower the fineness ratio then the ratio of length to diameter will reduce which in turn reduces the wetted area.

The correct option is (a) Fuselage can affect aerodynamic efficiency

To explain: Fuselage is primary drag PRODUCING COMPONENT. The overall smoothness and how fuselage is DESIGNED will affect the drag properties of the aircraft. As a RESULT of which fuselage will affect the aerodynamic efficiency of the aircraft as well.

Correct answer is (a) True

Explanation: Area rule is primarily developed to reduce the supersonic wave drag effects. HOWEVER, it is not limited to high SPEED aircrafts only. We can also APPLY same rule to design the civil and COMMERCIAL aircrafts as WELL.

The CORRECT answer is (a) hide the NOZZLE from EXPECTED location of an IR sensor

Easiest explanation: Emissions of hot parts can be reduced by lowering their temperature. We can hide nozzle from the IR detector itself. As a RESULT we can improve the IR detectability.

Right answer is (a) bending beams

The EXPLANATION is: Bending BEAM arrangement is SHOWN in above diagram. This type is combination of the WING BOX and ring frames wing carry through arrangement. Strut braced will rely upon strut and used in slower transport aircraft typically.

Correct choice is (a) 0.1

Easy EXPLANATION: GIVEN, radiant intensity I = 10 W/sr, range R = 10 cm.

Irradiance E is given by,

E = I/R^2 = 10/10^2 = 10/100 = 0.1 W/cm^2.

The correct option is (a) COMMONALITY of parts

For explanation I WOULD say: Commonality of parts will REDUCE the production cost. An increase in FORGINGS will increase cost. Forge and labour REQUIREMENTS will increase the cost as well.

The correct answer is (a) Maintenance of equipment after failure or BREAK down

To elaborate: Corrective maintenance is done after breakdown or failure. Maintenance done before breakdown is CALLED preventive maintenance. SCHEDULED maintenance is similar to preventive.

The CORRECT choice is (a) Forging

For explanation: Forgings are considered as most expensive type of structure. WHENEVER a high load is PASSING through small area might require forgings. Forgings are USED in wing-sweep pivots, landing GEAR struts etc.

The correct CHOICE is (a) True

The EXPLANATION is: Typically, it is ADVISED to not LOCATE fuel tanks under the fuselage. Fuel tanks can increase flames spreading TREMENDOUSLY. Hence, to avoid such a scenario it should not be located below or in the fuselage.

The correct answer is (a) routing tunnels

The best EXPLANATION: To simplify the routing we can provide a routing tunnel. STRUCTURAL break or cut out is based on structural requirements. Cruise lift has no DIRECT effect for GIVEN problem of routing.

The correct answer is (a) Failure MODES and effect analysis

For explanation: FMEA stands for ‘Failure modes and effect analysis ’. Determination of FMEA is ONE of the most important STEP for evaluation of vulnerability of an aircraft. This step is done at later stage during CONCEPTUAL design.

The correct option is (a) Total of detectable emissions and REFLECTIONS

For explanation I would say: Total of detectable and reflections can be called as an IR signature. This signature is used for tracking and DETECTING the aircraft. An aircraft’s IR signature is complex mixture of reflections and EMISSION of various components.

Right ANSWER is (a) Decoy

The EXPLANATION is: A decoy is an off-board system. Decoy is a COUNTERMEASURE that is ejected from and separated away from the aircraft. Decoy will TRY to LURE the missile track away from the aircraft.

Right option is (a) which battle damage can affect individual aircraft components?

To explain: FMEA stand for Failure modes and effect analysis. It is a very IMPORTANT CONSIDERATION in terms of vulnerability of an aircraft. The FMEA CONSIDERS in 2 ways:

i. Which battle damage can affect the individual components?

II. Which damage to each part will affect the other component of an aircraft?

Right CHOICE is (a) avoiding fuel tanks near to the engine

Easy explanation: Fuel tank location can affect the vulnerability of an aircraft. Fuel tanks can catch fire MUCH quickly. HENCE, to IMPROVE vulnerability it is advised to avoid placing fuel tanks near or above the engine or inside the engine.

Right OPTION is (a) effect of struts located below passenger CABIN

Best explanation: Effect of placing strut below passenger cabin is shown in the above diagram. As shown in figure, it strut is placed as shown then, during crash it will increase DAMAGE to passenger. This lowers SAFETY of PASSENGERS and hence, should be avoided to reduce such effects.

Correct choice is (a) Maintenance man-hours per FLIGHT HOUR

Explanation: Reliability and maintainability or R&M are often used together. It is measured in Maintenance man-hours per flight hour (MMH/FH). MMH/FH varies with the TYPE of aircraft. For SMALL aircraft, it is typically less than 1.

Right choice is (a) Large doors should be provided for the avionics system

For explanation I would say: Large should be provided for avionics system as this would ALLOW maintenance engineer to REACH there with ease. Accessibility of PARTS is one of the major requirement and factor which affect overall MAINTAINABILITY of the AIRCRAFT.

The correct choice is (a) proportional to (1/4^4)

For EXPLANATION: Given, Distance d =4m.

Since, no other parameters have mentioned we will directly use the relation between STRENGTH and the distance to FIND required relation.

Typically, RADAR strength is proportional to (1/distance^4) = (1/4^4).

Right option is (a) WING box carrythrough

The best EXPLANATION: Wing box carry through ARRANGEMENT is SHOWN in above diagram. These arrangement is widely used in general aviation and TRANSPORT aircrafts. Here, box is continued from wing through the fuselage as can be seen in the diagram.

The correct choice is (a) TX and Rx

Explanation: A typical radar system CONSISTS of 2 main PRIMARY components; 1. Transmitter TX and 2. Receiver Rx. Transmitter is used to transmit the electromagnetic waves whereas receiver will RECEIVE any INCOMING waves.

The correct OPTION is (a) the amount of EM energy is being RETURNED by an object

Explanation: RCS will directly affect radar DETECTABILITY of the AIRCRAFT. It is the measure of how much EM energy is being returned by an object. If RCS is more then, the object will return more amount of the EM energy and vice-versa.

The correct answer is (a) altering the look angle

Easiest explanation: RCS is BASED on the look angle. By altering look angle we can alter the rcs of an OBJECT. Tail MOMENT arm will AFFECT the stability not the rcs in general. RCS is also REDUCED by using stealth technology.

Right choice is (B) False

The explanation: RCS of an OBJECT can be reduced through number of ways. RAM is one of the available option to reduce rcs of an object. For example, we can reduce rcs by USING stealth TECHNOLOGY, by using sloped surfaced INSTEAD of flat etc. Hence, the given statement that rcs can only be reduced by Ram is not correct.