Aircraft Design - Airfoil and Geometry Selection Quiz(MCQ)

1 .

We are using the airfoil in the aircraft as _____

A)

it is not a streamline body

B)

it is easy to make than rectangular

C)

it is a streamline shape which provides better aerodynamics

D)

it is a random shape can be changed to rectangular as well

Correct Answer : it is a streamline shape which provides better aerodynamics

Explanation : Airfoil is a streamlined body which provides much smoother flow than non-streamlined body. Airfoil is designed in such a way that it can provide better aerodynamics than any other shape. Hence, in aircraft we use airfoils.

2 .

Which of these is not part of an airfoil?

A)

Leading edge

B)

Fins

C)

Chord

D)

Camber

Correct Answer : Leading edge

Explanation : Fins are extended surfaces which are used to improve heat transfer. Leading edge is foremost part of an airfoil. Camber is curve of an airfoil.

3 .

Pitching moment co-efficient for an airfoil is given by _____

A)

lift*area

B)

drag*area

C)

lift/dynamic moment

D)

section pitching moment/dynamic pitching moment

Correct Answer : section pitching moment/dynamic pitching moment

Explanation : Lift*area will give moment. Drag*area will also provide moment but will be less. The ratio of sectional pitching moment and dynamic pitching moment is called pitching moment co-efficient.

4 .

An airfoil is subjected to the flow with temperature of 288.16K and flow is ideal. The velocity at the leading edge is ____

A)

0m/s

B)

16.882m/s

C)

250m/s

D)

288.16m/s

Correct Answer : 0m/s

Explanation : Given, temperature T=288.16K
For idle flow, at leading edge flow is brought to rest isentropically.
Hence, velocity at leading edge = velocity of flow at the impact to leading edge = 0m/s.

5 .

The cross-sectional shape of wing is called _____

A)

circle

B)

airfoil

C)

chord

D)

camber

Correct Answer : airfoil

Explanation : Wings are designed with airfoil cross-section. Engine inlets are typically circular in cross-sections. Camber and chord are parameters of an airfoil.

6 .

An aerofoil is operating with flow velocity of 100m/s. Aerofoil is symmetric and is at 0° AOA. Determine lift produced by this aerofoil.

A)

0 N

B)

10.5 N

C)

50 N

D)

100N

Correct Answer : 0 N

Explanation : Lift is an upward force produced by pressure difference.
Given, velocity V=100m/s, AOA = 0°.
For symmetric airfoil at 0° AOA pressure will be same as upper and lower surface.
Hence, lift = 0N.

7 .

Consider a NACA 2812 airfoil. It is operating with flow velocity of 900m/s with chord of 1m. What should be the maximum thickness of this airfoil?

A)

28.12m

B)

0.9m

C)

0.12m

D)

0m

Correct Answer : 0.12m

Explanation : NACA-4 digit series is used to define certain airfoil characteristics.
Here, velocity = 900 m/s, chord = 1m
From NACA-4 digit,
Maximum thickness = last two digits in percent of chord=12% of chord = 0.12*1 = 0.12m.

8 .

Find location of aerodynamic centre from leading edge if, chord is 10m and airfoil has flow velocity of 0.2 M.

A)

0.2 m

B)

2.5 m

C)

5 m

D)

10 m

Correct Answer : 2.5 m

Explanation : Given, velocity = 0.2M = 0.2*340 = 68m/s
Chord = 10m
Given velocity is less than the sonic speed.
Hence, location of aerodynamic center is = 25% of chord = 0.25*10 = 2.5m from leading edge.

9 .

A symmetric airfoil is operating with flow velocity of 350m/s. The lift produced by the airfoil is 21 N at 0.008 rad AOA. If chord is c m then, what will be the pressure difference across the airfoil?

A)

21 Pa

B)

21c N

C)

21/c Pa

D)

21c/2 N

Correct Answer : 21/c Pa

Explanation : Given, symmetric airfoil
Flow velocity V=350m/s, Lift L=21N, AOA = 0.008rad
Chord = c m, Span of airfoil = 1 unit
Pressure difference = Lift/Area of airfoil
= 21/c*1 = 21/c Pa.

10 .

If an airfoil has lift of 200 N at 10° AOA, then what is induced drag produced by airfoil at that AOA?

A)

0

B)

0 N

C)

100

D)

100 N

Correct Answer : 0 N

Explanation : Given, Lift=200N, AOA = 10°
Here, airfoil is mentioned which is 2D shape.
For an airfoil Induced drag Di = 0N.

11 .

If an airfoil is operating at Mach 1.1, then it is working in _____

A)

transonic range

B)

subsonic range

C)

hypersonic range

D)

supersonic range

Correct Answer : transonic range

Explanation : Based on mach number flow can be subsonic, supersonic, transonic or hypersonic. If flow mach number is <0.8 then it is subsonic. If flow mach number is >0.8 but <1.2 then, it is transonic. If flow mach number is in the range of 1.2-5.0 then, it is supersonic. If flow mach number is <5.0 then, it is hypersonic.

12 .

Which of the following is not an application of an airfoil?

A)

To provide lift

B)

To provide lift co-efficient

C)

To provide streamlined flow

D)

To provide thrust for acceleration

Correct Answer : To provide thrust for acceleration

Explanation : In an aircraft, engines are used to provide thrust for acceleration. Airfoil is used to provide lift, to improve certain flow characteristics. Streamlined flow is also produced by an airfoil.

13 .

What is represented by ‘?’ in following diagram of an airfoil?
Aircraft-Design

A)

Thickness

B)

Chord

C)

Trailing edge

D)

Leading edge

Correct Answer : Thickness

Explaination : Thickness is distance between upper and lower surface of the airfoil. Leading and trailing edge are foremost and most rear parts of airfoil. Thickness will be different at each section of an airfoil.

14 .

NACA stands for _____

A)

National Advisory Committee for Aero models

B)

National Advisory Committee for Arithmetic

C)

National Advisory Committee for Aeronautics

D)

National Authorized Committee for Aeronautics

Correct Answer : National Advisory Committee for Aeronautics

Explanation : NACA is a National Advisory Committee for Aeronautics. NACA airfoils are simple to adopt. NACA series is used to identify the airfoil.

15 .

Determine the value for maximum camber for NACA1235 airfoil. Given chord is 1m.

A)

0m

B)

0.01m

C)

0.02m

D)

0.021

Correct Answer : 0.01m

Explanation : Given, NACA 4 digit airfoil as NACA 1235.
Chord c=1m.
Based on NACA 4 digit, first digit is the maximum camber in hundreds of chord.
Hence, maximum camber for NACA 1235 = 0.01*chord = 0.01*1 = 0.01m.

16 .

A thin airfoil is defined as NACA 0009 is at ? = 5°. What is the value of lift curve slope?

A)

0.4 per degree

B)

2? per rad

C)

2? per degree

D)

4 per degree

Correct Answer : 2? per rad

Explaination : Given, NACA0009 airfoil,
AOA ? = 5°
As mentioned the airfoil is thin. Hence, thin airfoil theory can be used.
According to thin airfoil theory, for thin airfoil,
Lift curve slope = 2π 1/rad = 0.11 1/degree.

17 .

The straight line joining L.E. and T.E. of an airfoil is _______

A)

radii

B)

camber

C)

camber line

D)

chord line

Correct Answer : chord line

Explanation : Chord line is defined as the straight line which connects the leading and trailing edge of an airfoil. Camber line or mean camber line is line passing from locus of mid points. Almost every parameter is defined with respect to chord.

18 .

Pressure on the upper surface is _________

A)

lower than lower surface

B)

always same

C)

higher than lower surface

D)

always 30.25 times lower surface

Correct Answer : lower than lower surface

Explanation : Pressure on the upper surface of an airfoil is lower than that of the lower surface. This will provide pressure difference which will generate lift force. Pressure will be the same if AOA is 0° in case of symmetric airfoil.

19 .

Laminar bucket is region where ____

A)

turbulent is produced

B)

lift is reduced drastically

C)

flow remains laminar

D)

drag increases drastically

Correct Answer : flow remains laminar

Explanation : Laminar bucket is phenomena of laminar airfoils. It is the region where flow remains laminar. This laminar flow is very important as it decreases drag and thus improves overall performance. However, for such airfoils Reynolds number is very important consideration. Following diagram shows laminar bucket for a typical laminar airfoil.

20 .

If I want to locate my minimum pressure at 0.5 of chord c then ________

A)

NACA 0009

B)

NACA 6512

C)

NACA 65211

D)

NACA 652132

Correct Answer : NACA 652132

Explanation : NACA series is used to identify airfoils as per our requirement. NACA -4 and -5 digit series are not used to provide a minimum pressure point. NACA 6 digit series is used for such operations.

21 .

Location of aerodynamic centre for low speed airfoil is ______

A)

at half of chord

B)

at quarter chord point

C)

there is no such place

D)

at quarter chord from leading edge

Correct Answer : at quarter chord point

Explanation : Aerodynamic center is that point at which pitching moment curve slope becomes zero. Hence, it is the point at where pitching moment is almost independent of AOA. For, low speed airfoils it is located at 25% of chord from leading edge.

22 .

A NACA 22104 airfoil is operating at AOA = 3°. The lift-coefficient at this AOA is 0.15. Determine the value of angle of attack at designed lift co-efficient.

A)

4.36°

B)

4.36rad

C)

0.05°

D)

0.05 rad

Correct Answer : 4.36°

Explaination : Given NACA 22104 airfoil.
AOA = 3°, Cl = 0.15 at 3°
Based on NACA -5 digit series design Cl = first digit*0.15 = 2*0.15 = 0.3
Now, for thin airfoil lift curve slope = 0.11 per degree
0.11 = (design Cl – Cl at 3°) / (AOA –3°)
0.11 = (0.3-0.15) / (AOA -3°)
0.11*(AOA -3°) = 0.15
Hence, at designed Cl, AOA = (0.15/0.11) + 3° = 4.36°.

23 .

The maximum lift co-efficient for NACA 19584 (chord=2.5m) airfoil is_______

A)

0.15

B)

0.15N

C)

0.3N

D)

0.315

Correct Answer : 0.15

Explanation : Given, NACA 13250 airfoil
Based on NACA -5 digit series, designed lift co-efficient = first digit*0.15 = 1*0.15 = 0.15.

24 .

What will be the location of maximum camber for NACA 13250 with chord length of 2m?

A)

0.32 from leading edge

B)

0.32 from trailing edge

C)

0.32m from trailing edge

D)

0.32m from leading edge

Correct Answer : 0.32m from leading edge

Explanation : Given, NACA 13250 airfoil
Based on NACA -5 digit series, location of maximum camber = (second and third digit)/2 in hundredth of chord from leading edge
= (32/2) * 0.01 * chord = (32/2)*0.01*2 = 0.32m from leading edge.

25 .

Let’s consider we need to design supersonic aircraft then, which type of airfoil should be adopted?

A)

Bluff shape

B)

Thicker airfoil

C)

Supersonic airfoil

D)

Symmetric airfoil

Correct Answer : Supersonic airfoil

Explanation : Supersonic aircraft needs to fly at much higher speed. Hence, supersonic airfoils are used to provide required velocity. Thicker airfoils cannot generate required amount of flow characteristics such as critical mach number.

26 .

A cambered airfoil is operating with 200N of lift. The velocity of the flow is 500m/s. Determine lift-induced drag by this camber airfoil.

A)

0

B)

0N

C)

0.5

D)

1

Correct Answer : 0N

Explanation : Given, Lift=200N, velocity = 500m/s.
For cambered airfoil the downwash angle = 0°. Hence, there will be no downwash acting on the flow.
Hence, there will be no induced drag. Hence, for any airfoil induced drag = 0N.

27 .

A 3D airfoil is called ________

A)

airfoil

B)

wing

C)

engine

D)

lofting

Correct Answer : wing

Explanation : Wing is generated by elongating an airfoil. Airfoil is 2D shape. Engine is main source of power. Lofting is skin modelling.

28 .

A twin turboprop engine is flying with 120m/s. Wing of the aircraft has span of 2m and lift co-efficient as 0.15 with aspect ratio as 9.2. Find the lift produced by the wing.

A)

120 N

B)

574.18 N

C)

574.18

D)

620 N

Correct Answer : 574.18 N

Explanation : Given, a twin turboprop
Velocity V = 120m/s, CL = 0.15, Aspect ratio = 9.2, span b=2m
Aspect ratio = b*b/S
9.2 = 2*2/s
S = 0.434m2
Now, lift is given by,
L = (1/2)*ρ*V2*S*CL = 0.5* 1.225*120*120*0.434*0.15 = 574.18N.

29 .

Which type of wing planform is shown below?

A)

Delta wing

B)

Elliptic wing

C)

Rectangular wing

D)

Tapered wing

Correct Answer : Tapered wing

Explaination : Tapered wings have finite value of taper ratio. In taper wing root and tip chord will have different values of chord. Elliptic wings are of elliptic shape. Rectangular wing has taper ratio of unity which shows a rectangular profile.

30 .

A jet fighter is operating at Mach number of 1.4. Wing chord is 1m then, find the location of aerodynamic centre.

A)

0.4m

B)

0.4

C)

0.8m

D)

0.8

Correct Answer : 0.4m

Explanation : Given, jet fighter aircraft which is cruising at Mach 1.4.
For such high speed aircraft, location of the aerodynamic center is given by,
Location of aerodynamic center = 40% of chord = 40% of 1 = 0.4*1 = 0.4m.

31 .

If a sailplane is to be designed then, the aspect ratio of the sailplane will be ______

A)

same as military aircraft

B)

lower than military aircraft

C)

higher than military aircraft

D)

exactly half of the military aircraft

Correct Answer : higher than military aircraft

Explanation : Sailplanes are different from military aircrafts. Sailplanes are designed to glide through air. For such requirements, it will require higher lift capability which can be provided by using higher aspect ratio wings than military aircrafts.

32 .

A typical wing has aspect ratio of 7 and span of 2m. If taper ratio T = 0.2 then, find the value of root chord.

A)

0.4761m

B)

0.61m

C)

0.71cm

D)

0.81m

Correct Answer : 0.4761m

Explanation : Given, span = 2m, aspect ratio = 7 and taper ratio T = 0.2
The root chord is given by,
Croot = 2*S / (b*(1+T))
Here, S is not given but aspect ratio is given.
Aspect ratio AR = Span square / S = 2*2 / S
7 = 4/ S
S = 0.5714 m2
Hence, Croot = 2*S / (b*(1+T))
= 2*0.5714 / (2*(1+0.2)) = 0.4761m.

33 .

Wing aspect ratio is defined as _____

A)

span square

B)

span square plus reference area

C)

span square divided by reference area

D)

span square multiplied by reference area

Correct Answer : span square divided by reference area

Explanation : Aspect ratio of wing gives relation between span of wing and wing reference area. It is defined as the ratio of span square to the reference or planform area. Higher aspect ratio wings will be long with less area.

34 .

Wing planform is affected by _____

A)

sweep only

B)

taper ratio only

C)

aspect ratio only

D)

aspect ratio, sweep angle, taper ratio

Correct Answer : aspect ratio, sweep angle, taper ratio

Explanation : Wing planform is shape of the wing when viewed from top. Aspect ratio will affect span and area. Overall planform will be affected by aspect ratio, taper ratio, sweep etc.

35 .

For high aspect ratio strength of the wing tip vortex is low.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

Explanation : Wing tip of high aspect ratio wing is far from root as compared to low aspect ratio wing. The wing affected by higher ratio will be less and the strength of tip vortex will be less as well.

36 .

If aspect ratio of wing is 8 and S=0.1m2 then, what will be the span of wing?

A)

0.89

B)

0.89m

C)

0.89cm

D)

0.89inch

Correct Answer : 0.89m

Explanation : Given, wing Aspect ratio AR=8, S=0.1m2
Aspect ratio = span square/ reference area
8 = span square / 0.1
Span square = 8*0.1 = 0.8
Hence, span = 0.89m.

37 .

Excessive dihedral can produce _____

A)

pitch

B)

dutch roll

C)

thrust

D)

deflection at nose

Correct Answer : dutch roll

Explanation : Dihedral is upward deflection of wing. It is used to provide roll stability. If excessive dihedral is provided then, it will lead to dutch roll; continuous side to side motion involving yaw and roll.

38 .

What is the function of wing twist?

A)

To provide lofting

B)

To reduce lift by tail

C)

To improve stall characteristics at tip

D)

To increase engine thrust

Correct Answer : To improve stall characteristics at tip

Explanation : Wing twist is used to delay the stall at tip typically. Wing twist can be used to rearrange the lift distribution of the wing. Lofting is skin modelling.

39 .

If root chord is 2m and tip chord is 0.9m then, find taper ratio.

A)

0.25

B)

0.45

C)

0.55

D)

0.65

Correct Answer : 0.45

Explanation : Taper ratio is defined as,
Taper ratio = tip chord/root chord = 0.9/2 = 0.45.

40 .

The ratio of tip and root chord is called ____

A)

slope

B)

sweep

C)

aspect ratio

D)

taper ratio

Correct Answer : taper ratio

Explanation : Taper ratio is the ratio of tip chord of wing to root chord of the wing. Aspect ratio is square of span divided by area. Sweep is angle between wing and fuselage reference line.

41 .

Wing sweep is used to ______

A)

increase critical mach number

B)

increase lofting

C)

increase drafting

D)

decrease critical mach number

Correct Answer : increase critical mach number

Explanation : If wing is at some finite angle from fuselage reference line then it is called wing is sweep by that much degree. Main function of sweep is to increase critical mach number. Lofting is skin modelling and drafting is drawing phenomena.

42 .

Which of the following is correct in accordance to diagram?

A)

Aspect ratio of 1 is highest

B)

Aspect ratio of 2 is maximum

C)

Aspect ratio of 3 is maximum

D)

Similar aspect ratio

Correct Answer : Aspect ratio of 1 is highest

Explaination : High aspect ratio will give higher value of maximum lift coefficient. As shown in figure for -1, maximum lift coefficient is highest and hence, aspect ratio of 1 will be highest. Similarly for -3 it is lowest and hence, aspect ratio of 3 will be minimum.

43 .

An aircraft with elliptic wing planform has parasite drag coefficient as 0.6. Lift coefficient of wing is 0.25 and aspect ratio is 7.5. If induced drag co-efficient is 0.0235 then, find total drag coefficient for the wing.

A)

0.0235

B)

0.6

C)

0.5235

D)

0.06235

Correct Answer : 0.06235

Explaination : Given, parasite drag co-efficient = 0.6, induced drag coefficient = 0.0235
Total drag coefficient = Parasitic drag coefficient + induced drag coefficient = 0.6+0.0235 = 0.06235.

44 .

Typically tail provides ______

A)

stability

B)

control

C)

stability and control

D)

accelerating force

Correct Answer : stability and control

Explanation : Typically tail is used to provide stability and control. Accelerating force will be provided from engines. One of the main function of the tail is to provide enough stability and controllability to make aircraft fly smoother at the time of any disturbance.

45 .

Which tail profile is shown in below diagram?

A)

T – tail

B)

H – tail

C)

Cruciform tail

D)

Conventional tail

Correct Answer : Cruciform tail

Explaination : Cruciform tail viewed from front will look like a ‘plus’ as shown in figure. T – tail will look like letter T and similarly H tail has shape of letter H.

46 .

Why dorsal fins are used?

A)

Provides lift to fly

B)

Similar to horizontal tail

C)

To reduce tail-effectiveness at high slide slip angle

D)

To improve tail-effectiveness at high slide slip angle

Correct Answer : To improve tail-effectiveness at high slide slip angle

Explanation : Dorsal fins are small attachments at the vertical tail. Dorsal fins are used for improving tail effectiveness at high slide slip angle. Dorsal fins are not similar to horizontal tail. Lift is primarily provided by wings.

47 .

Which control surface is primarily used for spin recovery?

A)

Flap

B)

Rudder

C)

Aileron

D)

Elevator

Correct Answer : Rudder

Explanation : During spin aircrafts is not stable. Aircraft performs unstable yaw motion. For stabilizing such event adequate amount of rudder control is required. Flaps are used to increase lift and drag.

48 .

Elevator provides control for ______

A)

roll

B)

yawing

C)

yaw-roll

D)

pitching moment

Correct Answer : pitching moment

Explanation : Elevator is one of the primary control surfaces of an aircraft. The elevator is located at the horizontal tail. Elevator is responsible for pitching motion to provide required nose up or down moment.

49 .

What is the use of V type tail?

A)

To produce thrust

B)

To increase wetted area

C)

To reduce wetted area

D)

To prevent adverse yaw roll

Correct Answer : To reduce wetted area

Explanation : V tail arrangement is used to combine horizontal and vertical tail. It combines in such way that the wetted area reduces. However, it generates adverse yaw roll motion. To prevent such effect inverted V tail can be used.

50 .

The inverted V-tail is used to ______

A)

to reduce adverse yaw-roll

B)

to increase lift

C)

to increase thrust

D)

to provide adverse yaw-roll

Correct Answer : to reduce adverse yaw-roll

Explanation : Inverted V tail arrangement is used to prevent the adverse yaw roll motion. Lift can be increased by flaps. Thrust is increased by an engine.

51 .

Which of the following is not part of tail?

A)

Aileron

B)

Rudder

C)

Elevator

D)

Horizontal stabilizer

Correct Answer : Aileron

Explanation : Aileron is part of the wing. Rudder is part of vertical tail. Elevator is part of the horizontal tail. Horizontal tail is also called Horizontal stabilizer.