This set of Aircraft Design Quiz focuses on “Configuration Layout – Aerodynamic Considerations-2”.
1. Why do we provide upsweep to the lower surface at aft fuselage?
a) To reduce drag
b) To increase drag
c) To increase lift
d) To maximize 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.
2. What is the base area of the fuselage?
a) Any unfair rearward facing blunt surface
b) Forward facing surface
c) Wing area
d) Fuselage cabin area only
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.
3. Which of the following is correct?
a) Base drag is affected by boat tailing
b) Base drag is not affected by boat tailing
c) Wing area is always same for every mission
d) Fuselage should be circular in shape always
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.
4. Which of the following is correct?
a) Wake of a canard can stall the engine
b) Wake will increase engine efficiency
c) Wake will increase engine thrust
d) Wake will increase engine performance
Explanation: 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.
Explanation: 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%.
6. Supersonic wave drag can be reduced by using ____________
a) area rule
b) drag ruling
c) lift augmentation
d) drag augmentation
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.
7. Interaction of components will not affect aerodynamic design of fuselage.
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.
8. Vortex generator is used to ____________
a) reattach separated flow
b) increase volume
c) increase surface area
d) separate 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.
9. Area rule can be used for high speed aircraft only.
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.
10. Drag divergence Mach number will increase by using _______________
a) area rule
b) increment in total volume
c) increase in drag
d) drag increment at maximum area
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.
Sanfoundry Global Education & Learning Series – Aircraft Design.
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