Aircraft Design - Aerodynamics Quiz(MCQ)

1 .

Wave drag is produced due to ________

A)

incompressible flow

B)

shock wave formation

C)

fluid is not compressible

D)

flow separation of incompressible flow

Correct Answer : shock wave formation

Explanation : Wave drag is primarily result of shock wave formation. Shock waves are very thin layer across which we can observe drastic change in the flow properties. Across shock, pressure and temperature will increase drastically. This sudden change in pressure results in the wave drag.

2 .

The location of separation point will depend on _______

A)

body weight

B)

mass of body

C)

only on body length

D)

curvature of the body

Correct Answer : curvature of the body

Explanation : Curvature of the body will affect the location of separation point.

3 .

What is interference drag?

A)

Skin friction drag

B)

Lift induced drag

C)

Drag due to weight of the aircraft only

D)

Drag produced by interaction of different components

Correct Answer : Drag produced by interaction of different components

Explanation : Drag produced due to interaction between various components is termed as interference drag. Skin friction drag is due to viscosity effects. Skin friction is one of the parameters which affects aerodynamic heating. Lift induced drag is result of vortices and downwash.

4 .

If I want to design an aircraft which primary flies in a low speed region then, which type of drag shouldn't be considered?

A)

Wave drag

B)

Parasite drag

C)

Induced drag

D)

Form drag only

Correct Answer : Wave drag

Explanation : Wave drag is drag produced at high speeds. At supersonic or near supersonic speed due to shock formation, the wave drag is produced. Hence, for low speed aircrafts, the wave drag is not a key parameter.

5 .

Aerodynamic forces are generated due to _________

A)

twisting of beam

B)

shear effects only

C)

shear and pressure force acting on body

D)

only pressure forces

Correct Answer : shear and pressure force acting on body

Explanation : Shear force and pressure force are most fundamental cause which generates aerodynamic forces. Shear forces typically seen as resisting forces which results in friction. Pressure force or pressure gradient will generate forces as well.

6 .

For ideal flow, total pressure along streamline will be _____

A)

increases

B)

constant

C)

decreases

D)

always decreases by half

Correct Answer : constant

Explanation : Bernoulli’s theorem is one of the fundamental principles in fluid dynamics and mechanics. It stats total pressure along streamline will be constant. Total pressure is sum of static pressure and dynamic pressure.

7 .

For an incompressible flow, if local area velocity decreases then, the dynamic pressure will ________

A)

increase

B)

decrease

C)

constant

D)

independent of velocity

Correct Answer : decrease

Explanation : Dynamic pressure is defined as the product of density and square of velocity and 0.5. It is pressure exerted by fluid due to motion and the fluid flow. As mentioned, dynamic pressure is proportional to square of velocity and hence, if velocity decreases then, the value of corresponding dynamic pressure is reduced as well.

8 .

Consider an incompressible flow. If static pressure increases then, the local freestream velocity ______

A)

increase

B)

decreases

C)

remains same

D)

insufficient data

Correct Answer : decreases

Explanation : If static pressure is increased then the corresponding value of the dynamic pressure should decrease. Bernoulli’s has provided better understanding of pressure acting on the aircraft.

9 .

How do you define the lift coefficient?

A)

Lift to drag

B)

Thrust to weight

C)

Wing lift to weight of aircraft

D)

Ratio of aerodynamic lift to the dynamic lift

Correct Answer : Ratio of aerodynamic lift to the dynamic lift

Explanation : Lift coefficient is defined as aerodynamic lift divided by Dynamic lift. Dynamic lift is defined as product of dynamic pressure and reference area. Lift coefficient of airfoil and wing will be different.

10 .

If an aircraft as pitching moment of 10 Nm and dynamic pitching moment is about 8.25Nm. Find the moment coefficient Cm.

A)

1.21

B)

0.0921

C)

3.4

D)

5.67

Correct Answer : 1.21

Explanation : Moment coefficient Cm = pitching moment / dynamic pitching moment
Cm = 10/8.25 = 1.21.

11 .

For a symmetrical airfoil drag coefficient at zero lift is 0.05 and induced drag coefficient is 0.0025. Find the total drag coefficient.

A)

52.5

B)

5.25

C)

0.0525

D)

0.45

Correct Answer : 0.0525

Explanation : Total drag coefficient = drag coefficient at zero lift + induced drag coefficient
= 0.05+0.0025 = 0.0525.

12 .

Following diagram represents ________

A)

typical drag polar

B)

wing lift curve

C)

thrust required for wing

D)

drag polar for non-symmetric wing

Correct Answer : typical drag polar

Explaination : The above diagram is illustrating a typical schematic diagram of airfoil drag polar. Drag polar is nothing but a graph which shows variation of drag coefficient with respect to lift coefficient. Wing lift curve is used to show lift variation.

13 .

Following diagram represents ______

A)

cambered wing drag polar

B)

drag polar of an airfoil

C)

cambered airfoil drag polar

D)

symmetric wing drag polar

Correct Answer : cambered wing drag polar

Explaination : Above diagram is showing typical drag polar for cambered wing. Drag polar will be different for different types of wing. Drag polar is graphical representation of drag characteristics. It shows relationship between drag coefficient and lift coefficient typically.

14 .

Cambered wing has minimum drag coefficient of 0.05 and constant K of 0.023. If CL is 0.8 then find the value of CD. Given minimum drag occurs at CL of 0.1.

A)

61.2

B)

6.1

C)

0.6721

D)

0.06127

Correct Answer : 0.06127

Explaination : Given, minimum drag coefficient CD_min = 0.05, constant K of 0.023, CL is 0.8 and minimum drag occurs at CL of 0.1. Hence, CL_mindrag = 0.1.
Now, CD is given by,
CD = CD_min + K*(CL – CL_mindrag)²
= 0.05+0.023*(0.8-0.1)²
= 0.06127.

15 .

Following diagram represents _________

A)

uncambered airfoil

B)

uncambered wing lift curve

C)

cambered airfoil lift curve

D)

cambered wing lift curve slope

Correct Answer : uncambered wing lift curve

Explaination : A typical diagram of lift curve is illustrated in above figure. The diagram is applicable to uncambered wing. Airfoil lift curve will be different from wing. Typically, lift coefficient of airfoil is greater than the wing.

16 .

Following diagram represents _________

A)

drag polar

B)

thrust loading

C)

cambered wing lift curve

D)

power loading

Correct Answer : cambered wing lift curve

Explaination : A typical, lift curve is shown for Cambered airfoil. As shown in the diagram, camber wing with cambered airfoils will produce lift at small angle. Drag polar is used to provide information about drag characteristics. Thrust loading is defined as ratio of weight to thrust.

17 .

Following diagram represents _____

A)

drag polar

B)

wing loading chart

C)

thrust required minimum

D)

lift curve slope vs mach number

Correct Answer : lift curve slope vs mach number

Explaination : The above diagram is showing a typical variation between lift curve and Mach number. Drag polar is nothing but the drag variation with lift or angle of attack. It is used to estimate drag properties of airfoil and wing. Wing loading is defined as the ratio of weight to the reference area.

18 .

Following diagram represents _________

A)

rudder

B)

plain flap

C)

spoiler

D)

aileron

Correct Answer : plain flap

Explaination : Flap is a high lift device. Flap is used to increase lift produced by wing during landing and takeoff. Aileron is used to bank the aircraft. Rudder provides yawing motion to the aircraft. Spoiler is used to provide additional drag during landing.

19 .

A subsonic aircraft wing has aspect ratio of 8. Now we have been asked to provide winglet to this wing. Evaluate approximate value of effective aspect ratio of winglet is considered.

A)

4.89

B)

9.6

C)

23

D)

34

Correct Answer : 9.6

Explaination : Approximate effective aspect ratio = 1.2*Wing aspect ratio
= 1.2*8 = 9.6.

20 .

A supersonic 2D airfoil has Mach number of 1.5. Find Lift curve slope of the airfoil.

A)

0.062 per degree

B)

0.062 per rad

C)

12.56 per degree

D)

24 per degree

Correct Answer : 0.062 per degree

Explanation : Given, mach number M = 1.5
2D lift curve slope = 4 / (M² – 1)^0.5
= 4 / (1.5² – 1)^0.5 = 3.57 per rad = 3.57/57.3 = 0.062 per degree.

21 .

At same value of maximum lift AOA, lift coefficient of Cambered wing is _________

A)

lower than uncambered wing

B)

higher than uncambered wing

C)

same as cambered airfoil always

D)

not dependent on camber

Correct Answer : higher than uncambered wing

Explanation : Lift coefficient at maximum lift AOA for a cambered wing is higher than that of the uncambered wing. At maximum lift AOA, value of lift coefficient will be maximum as well. Further increase in angle will reduce the amount of lift generated by wing.

22 .

A 2D airfoil is operating at 0.6M. Find the approximate value of lift curve slope in per rad.

A)

1.9

B)

2.3

C)

3.87

D)

7.85

Correct Answer : 7.85

Explanation : Given, mach number M = 0.6
2D lift curve slope = 2*π / (1-M²)^0.5
= 2*π / (1-0.6²)^0.5 = 7.85 per rad.

23 .

Which of the following is a method for estimating the potato drag?

A)

Weight only

B)

Mach number

C)

Conceptual design

D)

Equivalent skin friction method

Correct Answer : Equivalent skin friction method

Explanation : Equivalent skin friction method is one of the typical method used to estimate parasite drag. Mach number is defined as the ratio of the speed of object to the speed of sound. Weight is force due to gravity.

24 .

Equivalent skin friction coefficient may include _______

A)

only wave drag

B)

only thrust loading

C)

skin friction and separation drag

D)

only skin friction drag

Correct Answer : skin friction and separation drag

Explanation : Equivalent skin friction coefficient includes both skin friction and separation drag. Wave drag is supersonic phenomenon. Wave drag occurs when aircraft is traveling with speeds greater than the speed of sound. Thrust loading is defined as the ratio of the thrust and weight.

25 .

To get initial estimation of the parasite drag, aircraft wetted area can be multiplied by _____

A)

lift

B)

weight

C)

wing span

D)

equivalent skin friction coefficient

Correct Answer : equivalent skin friction coefficient

Explanation : Initial estimation of parasite drag can be obtained by multiplying equivalent skin friction coefficient with wetted area of aircraft. Lift and weight will be in opposite direction to each other. Wing span is a typically length of the aircraft.

26 .

Which of the following is correct for nacelle form factor (FF)?

A)

FF = 1+(0.35/f)

B)

FF = 1*(0.35/f)

C)

FF = 1/(0.35/f)

D)

FF = 1-(0.35/f)

Correct Answer : FF = 1+(0.35/f)

Explanation : Form factor will be different for different components of an aircraft. For nacelle, form factor can be estimated as follows: Form factor FF = 1 + (0.35/f). Where, f = length/maximum diameter = fineness ratio.

27 .

Flat plate skin friction coefficient depends upon __________

A)

weight of the aircraft

B)

mach number only

C)

reynolds number only

D)

mach number, reynolds number etc

Correct Answer : mach number only

Explanation : Flat plate skin friction coefficient depends upon number of factors including Mach number, Reynolds number, type of flow etc. Mach number is used to provide information about speed of the object with respect to the speed of sound.

28 .

Determine the initial estimation of parasite drag coefficient if, equivalent skin friction coefficient is 0.004 and ratio of wetted area to the reference area is 0.8.

A)

0.0032

B)

0.04

C)

1.2

D)

4.2

Correct Answer : 0.0032

Explaination : Parasite drag coefficient = equivalent skin friction coefficient*area ratio
= 0.004*0.8 = 0.0032.

29 .

Consider equivalent skin friction coefficient as 0.0025 and Swet/Sref = 0.6. Evaluate parasite drag.

A)

02.34

B)

1.23

C)

0.0015

D)

0.000025

Correct Answer : 0.0015

Explanation : Parasite drag = equivalent skin friction coefficient*(Swet/Sref)
= 0.0025*0.6 = 0.0015.

30 .

Find the approximate value of wetted area Swet for given reference area of Sref=20 unit and parasite drag coefficient of 0.0028. Consider equivalent skin friction coefficient Cf as 0.003.

A)

12 unit

B)

18.67 unit

C)

20 unit

D)

65 unit

Correct Answer : 18.67 unit

Explaination : Wetted area Swet = Parasite drag coefficient*Sref/Cf
= 0.0028*20/0.003 = 18.67 unit.