Correct Answer : 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.
Correct Answer : 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.
Correct Answer : lower the fineness ratio
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.
Correct Answer : Higher supersonic wave drag
Explanation : 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 Answer : 10° – 12°
Explaination : 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°.
Correct Answer : Both [A] and [R] are true but [R] is not the correct reason for [A]
Explaination : A good aerodynamic design of a fuselage will maintain smooth longitudinal contour to reduce the drag and other similar effects. This can be achieved by using longitudinal control lines. Smooth fuselage with lesser discontinuity will reduce the drag and as a result of which aerodynamic efficiency will improve. Hence, [A] and [R] both correct however, [R] is not correct reason.
Correct Answer : lower tail arm
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.
Correct Answer : 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.
Correct Answer : Any unfair rearward facing blunt surface
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.
Correct Answer : Typical low wave drag design
Explaination : 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%.
Correct Answer : area rule
Explanation : 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.
Correct Answer : reattach separated flow
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.
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.
Correct Answer : Structural elements by virtue of which opposing forces are connected
Explanation : Load path is nothing but the elements by virtue of which opposing forces are connected. Typically, a good structural arrangement will have efficient load path. By providing appropriate load path, we can improve our design based on structural considerations.
Correct Answer : placing opposite forces near to each other
Explanation : 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.
Correct Answer : distribution of weight along span as lift distribution
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 Answer : provide shortest and straightest possible load paths
Explanation : 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 Answer : ideal span loading
Explaination : 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 Answer : wing box carrythrough
Explaination : 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.
Correct Answer : ring frames
Explaination : A typical ring frames arrangement is shown in above diagram. In this type of wing carry through, large and heavy bulkheads are used. These bulkheads are used to oppose the bending. This type is mostly used by modern fighters.
Correct Answer : bending beams
Explaination : 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 Answer : 12in
Explanation : Given external diameter = 20in. Radius = 20/2 = 10in.Approximate radius of passenger compartment = external radius – structural thickness= 10-4 = 6inHence, diameter = 2*6 = 12in.
Correct Answer :
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 Answer : straight and uninterrupted
Explanation : 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.
Correct Answer : keelson
Explanation : 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 Answer : bending
Explanation : 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.
Correct Answer : radio detection and ranging
Explanation : 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.
Correct Answer : 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.
Correct Answer : proportional to (1/4?)
Explaination : 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?) = (1/4?).
Correct Answer : radar cross section
Explanation : RCS is acronym of ‘radar cross section’. RCS of an aircraft will directly impact the radar detectability of the aircraft. RCS is usually measured in decibel square meters or dBsm.
Correct Answer : Surface current scattering
Explaination : 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.
Correct Answer : Inside fuselage
Explanation : 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 Answer : providing some slope to flat surface
Explanation : Flat surfaces offer highest rcs possible. Now, to reduce it we can provide some slope to flat side of the surface. This will reduce the amount of EMW being returned by the flat side. If we increase the flat side length then, it will not reduce rcs of the flat surface.
Correct Answer : 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.
Correct Answer : altering the look angle
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.
Correct Answer : 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.
Correct Answer : hide the nozzle from expected location of an IR sensor
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.
Correct Answer : Decoy
Explanation : 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.
Correct Answer : quickly mixing exhaust with outside air
Explanation : 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 : flares
Explanation : 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 : False
Explanation : IR is an electromagnetic wave. An infrared radiation is not visible to a human named eye. Any bay which has warmth will generate infrared radiation. Aircraft will emit infrared radiation.
Correct Answer : Irradiance
Explanation : Typically, all it detector will respond to irradiance. Irradiance is area density of the power. Hence, an infrared detector will respond to the density of the radiant power. RCS is measure of radar detection.
Correct Answer : Total of detectable emissions and reflections
Explanation : 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.
Correct Answer : Engine exhaust
Explanation : 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.
Correct Answer : 512.4K
Explanation : Given, Mach number = 2.0, ambient temperature T1 = 305KAssuming the recover factor as 0.85 and for such case,Recovery temperature T2 = T1*(1+0.17*M²)T2 = 305*(1+0.17*2*2) = 305*1.68 = 512.4K.
Correct Answer : 0.25 unit
Explaination : 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.
Correct Answer : 34380
Explaination : Given, distance d = 2400 feet, length l=24000 ft.Visual angles in minutes of arcs = 3438*l/d = 3438*24000/2400 = 34380.
Correct Answer : increase detectability
Explanation : Contrast between two parts of an aircraft will increase visual detectability. Higher contrast makes it easy to be seen visually. We can reduce contrast so that we can improve visual detection of the aircraft.
Correct Answer : A/C size, color, etc
Explanation : Visual detection is affected by size, color etc. How much wider or longer or big is my aircraft? Will affect its visual detection. Color of my aircraft with respect to background will affect visual detection as well.
Correct Answer : camouflage pattern
Explaination : By using a red color pattern we are making our aircraft to look more vibrant which will increase its chances of detection. Camouflage patterns can be used in order to reduce background contrast.
Correct Answer : mottled grey green
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.
Correct Answer : dirty blue-grey
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.
Correct Answer : Both [A] and [R] are true and [R] is the correct reason for [A]
Explaination : 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 : By using chevron nozzle
Explanation : Chevron nozzle is used to reduce the engine exhaust aural signatures. Chevron nozzle accompanies saw tooth pattern at the trailing edge. High velocity jet will produce more noise due to air shear layer effects.
Correct Answer : reduce the aural signature
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.
Correct Answer : insulating material
Explanation : We can use insulating materials to reduce the aural signatures. Lofting is mathematical modeling. Drafting is based on drawing.
Correct Answer : aural signature
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.
Correct Answer : engine exhaust
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.
Correct Answer : more noise
Explanation : 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.
Correct Answer : Turbojet > turbofan > reciprocating engine
Explaination : 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.
Correct Answer : we can use more mufflers
Explanation : 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 : redundant components
Explanation : Redundant components in simple words are additional components which can be used at the time of emergencies or failure of the component. For example, redundant of hydraulic system, electric system, etc. can improve survivability. Hence, by using redundant component we can improve the vulnerability of our design.
Correct Answer : avoiding fuel tanks near to the engine
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.
Correct Answer : Failure modes and effect analysis
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.
Correct Answer : 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 Answer : Vulnerable area
Explanation : 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.
Correct Answer : blade will not strike anyone if they fly off
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.
Correct Answer : 31ft231ft2
Explaination : Given, part 1: area a1=5ft2, pk1=1Part 2: area a2=4ft2, pk2=0.5Part 2: area a3=80ft2, pk3=0.3Total vulnerable area = a1*pk1 + a2*pk2 + a3*pk3 = 5*1 + 4*0.5 + 80*0.3 = 5+2+24 = 31ft2
Correct Answer : Capability of structure to protect against impacts and crash loads
Explanation : Capability of structure to protect against impacts and crash loads can be termed as crashworthiness design. Whether the aircraft will stay in cruise or not this will be decided by operating environment.
Correct Answer : Scarfed firewall reduces scooping
Explaination : 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 : increment in crash load due to firewall scooping
Explaination : Above diagram is showing scooping effect. As shown in the figure, because of the scooping crash loads has increased. Wing loading will be used to size the aircraft. Based on mission and type of aircraft we can size our design by using wing loading concepts.
Correct Answer : they wouldn’t rip open fuel tanks at the time of crash
Explanation : Gears should be placed such that they would not rip open fuel tank at the time of crash. Location should be selected by considering crashworthiness as well. If location is not adequate then, it will damage to crashworthiness properties of our design.
Correct Answer : commonality of parts
Explanation : 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.
Correct Answer : poor production break design
Explaination : A good designer will consider the location of sub-assembly breaks. They will try to avoid placing components across these breaks. If it is not considered then, it will cause problems during production such as shown in the above figure. Here, the landing gear is across production break.
Correct Answer : weight, size, material, etc
Explanation : Aircraft production cost is based on its weight, material used, its size and volume etc. Production cost is affected by number of processes, sub-assembly etc. Only weight is not responsible for cost.
Correct Answer : flat wrap surfaces
Explanation : 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.
Correct Answer : Forging
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.
Correct Answer : routing tunnels
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.
Correct Answer : typical routing tunnel
Explaination : 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 Answer : The ease with which the aircraft can be fixed
Explanation : 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 : 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.
Correct Answer : Accessibility
Explanation : Maintainability will be affected by accessibility. Survival is characteristic of vulnerability consideration. RCS is a term used in radar detection. Vulnerability is based on combat damage.
Correct Answer : They allow most of the engine to be exposed for maintenance
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.
Correct Answer : Maintenance done before breakdown of component
Explanation : When maintenance is done at given pre-defined period of time, before breakdown then it is called preventive maintenance. It has goal to reduce breakdown of components. Unscheduled is not done at pre-defined time.
Correct Answer : Maintenance of equipment after failure or break down
Explanation : Corrective maintenance is done after breakdown or failure. Maintenance done before breakdown is called preventive maintenance. Scheduled maintenance is similar to preventive.
Correct Answer : Requirements of removing number of major structural elements
Explanation : Easily accessible and reachable parts are primary requirement of maintainability considerations. Accessibility directly affects the effort and maintainability of an aircraft. If a design requires removal of major structural elements to access the component then, it is considered as the worst design based on maintainability.
Correct Answer : To reduce breakdowns of critical equipment
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.
