Aircraft Design - Stability, Control, and Handling Qualities Quiz(MCQ)

1 .

Longitudinal stability means _________

A)

stability about pitching axis

B)

stability about lateral axis

C)

stability about yawing axis

D)

stability about negative yawing axis

Correct Answer : stability about pitching axis

Explanation : Longitudinal stability means stability about pitching axis. Pitch up or pitch down moments will be included in this type of stability. Stability about yawing axis is called directional stability and similarly stability about lateral axis is called Lateral stability.

2 .

For pitching moment coefficient diagram shown below which one will have positive trim AOA?

A)

Aircraft 1

B)

Aircraft 2

C)

Aircraft 3

D)

Aircraft 3 and Curve 2 both

Correct Answer : Aircraft 1

Explanation : Pitching moment coefficient curve is shown for 3 different configurations. To trim at positive AOA, value of zero lift pitching moment coefficient Cm0 should be positive. As can be seen in the diagram aircraft 1 has positive value of Cm0. Hence, aircraft 1 will result in trim at positive AOA.

3 .

A wing alone arrangement has wing lift curve slope of 2.65 per rad. Find slope of pitching moment coefficient. Given Xcg = 0.3.

A)

0.0035 per degree

B)

0.025 per degree

C)

0.03 per rad

D)

45 per rad

Correct Answer : 0.025 per degree

Explanation : Considering ideal location of aerodynamic centre i.e. Xac = 0.25
Slope of pitching moment curve = (wing lift curve slope*[Xcg-Xac])
= (2.56[0.3-0.25])
= 0.1325 per rad = 0.00253 per degree.

4 .

Aircraft is said to be statically stable if _______

A)

it has more thrust than drag

B)

it has more lift than weight always

C)

it has tendency to return to equilibrium state with the help of pilot�s input

D)

it has initial tendency to come back to its original equilibrium condition after being disturbed

Correct Answer : it has initial tendency to come back to its original equilibrium condition after being disturbed

Explanation : An aircraft or an object is said to be statically stable if and only if it has initial tendency to return to its original equilibrium position after being disturbed. Lift is not always greater than the weight. At cruise it will be equal to weight of the aircraft.

5 .

How can we say that the aircraft has initial tendency to return to its original equilibrium position after being disturbed?

A)

If lift is same as weight always

B)

If thrust loading is always unity

C)

If aircraft generates some restoring force or/and moment without any external help

D)

If restoring force is not generated to oppose the disturbance

Correct Answer : If aircraft generates some restoring force or/and moment without any external help

Explanation : If some disturbance is given to the aircraft and aircraft has initial tendency to generate some restoring force or/and moments without any external means then, we say that the aircraft has initial tendency to return to its original equilibrium position after being disturbed. Hence, it has static stability.

6 .

Object shown in the following diagram can be considered as _________

A)

statically stable

B)

neutrally stable

C)

statically unstable

D)

stability can’t be guessed from diagram

Correct Answer : statically stable

Explaination : A typical illustration of stability criteria is shown in the diagram. As shown in the figure, if ball is disturbed from equilibrium position it will return to its original equilibrium position. It has an initial tendency to return to the equilibrium position. Hence, the above diagram is illustrating the concept of statically stable object.

7 .

If aircraft continues to go farther away from equilibrium position after being disturbed then, the aircraft is called _______

A)

stable

B)

unstable

C)

statically stable

D)

neutrally stable

Correct Answer : unstable

Explaination : If after being disturbed from the equilibrium position, aircraft tends to go further away from the original equilibrium position then it is said that the aircraft is not stable or it is Unstable. It will be called neutrally stable if it attains new equilibrium position however it is not mentioned in the question so the correct answer will be unstable.

8 .

Which of the aircraft will be statically stable based on following diagram?

A)

aircraft number 1

B)

aircraft number 2

C)

aircraft number 3

D)

same static stability for all 3 aircrafts

Correct Answer : aircraft number 1

Explaination : As shown in the diagram typical pitching moment coefficient curve is represented. Aircraft number 1 will be statically stable. As can be observed in the diagram if aircraft number 1 is disturbed by some forces; let’s consider some upward direction gust is encountered. At such conditions it will generate negative pitching moment to oppose the upward deflection and hence, it has initial tendency to return to the original equilibrium position. Therefore it is statically stable.

9 .

Following diagram represents _____

A)

drag polar

B)

lift curve slope

C)

pitching moment diagram for stable aircraft

D)

pitching moment coefficient diagram of unstable aircraft

Correct Answer : pitching moment coefficient diagram of unstable aircraft

Explaination : As shown in the diagram typical pitching moment coefficient curve is shown. As shown it is used to provide relationship between pitching moment coefficient and angle of attack. Given diagram is illustrating the concept of statically unstable aircraft. Lift curve is related to lift and AOA.

10 .

An aircraft wing is experiencing AOA of 5°. If downwash due to wing is 2.6° then, how much angle is being seen by tail of the aircraft?

A)

1.23°

B)

2.4°

C)

4.5°

D)

6.7°

Correct Answer : 2.4°

Explaination : Tail AOA = wing AOA – downwash angle = 5°-2.6° = 2.4°.

11 .

Canard will provide longitudinal static stability.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : True

Explanation : Canards are typically used to provide longitudinal instability. Canards are located at the forward section of the aircraft. They are located ahead of the CG of aircraft typically. Hence, if some disturbance is given then, it will not have initial tendency to return to its original equilibrium position. Hence, it will not provide static stability.

12 .

Which of the following is correct to trim an aircraft at positive AOA?

A)

Cm0 > 0

B)

Cm0 < 0

C)

Cm0 will not affect positive trim AOA

D)

Every value of cm0 will trim at positive AOA

Correct Answer :

Explaination : To trim an aircraft at positive AOA, it is required that aircraft has positive value of zero lift moment coefficient. Hence, to trim aircraft at a positive angle of attack, aircraft should be designed with Cm0 positive i.e., Cm0>0. Negative value of Cm0 will not allow the aircraft to trim at positive AOA.

13 .

If CM0 is -0.052 and lift coefficient at zero angle CL0 is 0.92 then, find CMac. Consider rectangular wing.

A)

0.98

B)

-0.282

C)

2.5

D)

7.89

Correct Answer : -0.282

Explanation : CMac = CM0 +CL0*[Xcg-Xac]
For a typical rectangle wing, Xcg-Xac =0.25.
Hence, CMac = CM0 + CL0*0.25 = -0.052+0.95*0.25 = -0.282.

14 .

A rectangular wing has chord of 2m. Fond neutral point for this wing.

A)

50 cm

B)

189 cm

C)

267 m

D)

290 cm

Correct Answer : 50 cm

Explanation : For rectangular wing, Location of neutral point = chord/4 = 2/4 = 0.5m = 50cm.

15 .

Determine required static margin if lift curve slope is 6.5 per rad and pitching moment coefficient slope as -0.58 per rad.

A)

0.89

B)

8.9%

C)

8.403

D)

78%

Correct Answer : 8.9%

Explanation : Static Margin = – (moment coefficient slope/lift curve slope)
= -(-0.58/6.5) = 0.089 = 0.089*100% = 8.9%.

16 .

Following diagram represents _______

A)

lift curve

B)

drag polar

C)

typical roll stability concept

D)

typical longitudinal stability

Correct Answer : typical roll stability concept

Explaination : Above diagram is illustrating the concept of roll stability. Typical lateral stability criteria can be observed in the diagram. Longitudinal stability is represented by using pitching moment curve. Lift curve will be used to provide relationship between lift and angle of attack. Drag polar will correlate drag and lift.

17 .

Rolling moment will influence ______

A)

pitch axis stability

B)

longitudinal stability

C)

pitching stability only

D)

aircraft lateral stability

Correct Answer : aircraft lateral stability

Explanation : Rolling moment will influence the aircraft lateral stability. It also affects the yawing and therefore directional stability of the aircraft. Longitudinal stability is used for pitching moment.

18 .

Which is the minimum requirement for pure directional stability?

A)

Negative lift curve slope

B)

Positive zero lift pitching moment coefficient

C)

Slope of yawing moment curve positive

D)

Negative pitching moment coefficient curve slope

Correct Answer : Slope of yawing moment curve positive

Explanation : An aircraft is said to be in directional stability if the yawing moment curve slope is positive. Negative pitching moment coefficient curve slope is minimum criteria for longitudinal static stability. Positive value of zero lift pitching moment coefficient will be used to design an aircraft to trim at positive AOA.

19 .

Determine the value of rudder deflection δr for an aircraft which is flying in north with the velocity of 60.5 m/s under the crosswind of 5m/s from east to west with Cnβ=0.02/deg and Cnδr = -0.045/deg, where sideslip angle β is -4.72°.

A)

-2.09°

B)

-4.5°

C)

-4.74°

D)

3.5°

Correct Answer : -2.09°

Explaination : Given, North velocity n = 60.5m/s, East to west velocity e = 5m/s.
Now, rudder deflection δr = – [Cnβ/ Cnδr]*β = -[0.02/-0.045]*(-4.72) = -2.09°.

20 .

Determine the net velocity if sideslip angle is 3.8 degree and [v] = 4.2 unit.

A)

63.23 unit

B)

100 unit

C)

100.23 unit

D)

102.623 unit

Correct Answer : 63.23 unit

Explanation : Net velocity V = v*sine (sideslip) = 4.2*sine (3.8°) = 63.23 unit.

21 .

Find resultant velocity if [u, v, w] = [80, 2, 4.5]. Consider steady level flight.

A)

80.151

B)

90

C)

10.52

D)

100.159

Correct Answer : 80.151

Explanation : Resultant Velocity V = [u²+v²+w²] ^0.5 = 80.1521.

22 .

Stability about yawing axis is called as _________

A)

lateral stability

B)

directional stability

C)

longitudinal stability

D)

pitching moment stability

Correct Answer : directional stability

Explanation : Directional stability of the aircraft is defined as the stability about the yawing axis. In typical aircraft yaw and rolling both will be produced by deflecting the rudder. Stability about rolling moment is called lateral stability.

23 .

Yawing moment is positive if ________

A)

if nose pitches up

B)

if nose pitches down

C)

right wing comes forward

D)

right wing goes back

Correct Answer : right wing goes back

Explanation : Yawing moment is said to be positive by sign convention if right wing goes back and vice versa. If nose pitches up then it is a positive pitching moment and similarly if nose pitches down it is called negative pitching moment as per the sign convention is considered.

24 .

Stability about roll axis is called _________

A)

elevator control

B)

directional stability

C)

lateral stability

D)

longitudinal stability

Correct Answer : lateral stability

Explanation : Stability about the rolling is termed as lateral stability. Lateral and directional stability are closely coupled. When we deflect only aileron it will generate rolling as well as it will also cause the aircraft to yaw. Longitudinal stability is Stability about pitching moment. Elevator is used for such purposes.

25 .

Stick free stability permits ________

A)

fixed rigid body

B)

lift and drag ratio

C)

elevator to float

D)

elevator to be fixed

Correct Answer : elevator to float

Explanation : In stick free, we allow elevator to float as angle of attack or relative wind changes. In stick fixed we will deflect elevator at some angle and then fix it at that angle. Stick free stability depends upon number of factors such as hinge moment etc.

26 .

Stick fixed and stick free are similar.

A)

True

B)

False

C)

Can Not Say

D)

None of the above

Correct Answer : False

Explanation : No, stick free and stick fixed are not similar. Floating of elevator is permitted in stick free however, in stick fixed elevator is not permitted to float. In stick fixed, some desired elevator deflection is given as required. At that position, elevator is fixed and not allowed to float.

27 .

Stick force is function of ________

A)

hinge moment

B)

lofting

C)

fuel air ratio

D)

pressure ratio of inlet

Correct Answer : hinge moment

Explanation : Stick force is function of hinge moment. Lofting is a mathematical modelling used to define different cross section or geometry. Fuel air ratio is related to aircraft engine. Pressure ratio of inlet will be dependent of the type of inlet.

28 .

Which of the following is correct for hinge moment?

A)

Lifting property of the airfoil is same as a sphere

B)

Hinge moment is not dependent on the tail angle

C)

Downwash is used to reduces angle of attack at tail

D)

Hinge moment coefficient is function of tail angle of attack

Correct Answer : Hinge moment coefficient is function of tail angle of attack

Explanation : Hinge moment coefficient is function of number of factors such as tail angle of attack, tail setting angle, etc. Due to downwash the angle of attack at tail will be more. Lifting property of an airfoil and sphere will be different. Airfoil is 2d shape and sphere is 3d shape.

29 .

Negative stick force gradient is used to provide _________

A)

thrust

B)

speed stability

C)

gliding ratio

D)

propulsive force

Correct Answer : speed stability

Explanation : Negative stick force gradient is used to provide speed stability. Thrust is a propulsive force. Thrust is generated by aircraft engine. Propulsive force is a typical force which is responsible for driving the aircraft or a system in forward direction typically. Gliding ratio is related to glider.

30 .

Hinge moment coefficient depends upon ________

A)

Only tail angle

B)

Only wing angle

C)

Lift to drag ratio of fuselage

D)

Tail AOA, elevator deflection, etc

Correct Answer : Tail AOA, elevator deflection, etc

Explanation : Hinge moment coefficient depends upon number of factors such as elevator deflection, angle of attack at tail, tail setting angle etc. Lift to drag ratio is defined as aerodynamic efficiency of the aircraft. Fuselage is primary drag producing member of the aircraft. Lift to drag ratio of the fuselage will be less.

31 .

Stick fixed neutral point is defined at 40% of chord. Choose appropriate location of Stick free neutral point.

A)

0.39

B)

0.5

C)

0.65

D)

0.8

Correct Answer : 0.39

Explanation : Typically, stick free neutral point is located at 2-5% ahead of stick fixed neutral point.
Stick free neutral point = 2 to 5 % ahead of stick fixed = 0.02*0.4 to 0.05*0.4 ahead of stick fixed = 0.008 to 0.1 ahead of stick fixed neutral point
Hence, neutral point location of stick free = 0.4-(0.008 to 0.1) = 0.392 to 0.39.
Hence, Correct answer from the given options Will be 0.39.

32 .

Damping ratio is defined as _________

A)

lift to drag

B)

thrust to weight

C)

damping coefficient divided by critical damping coefficient

D)

weight to power

Correct Answer : damping coefficient divided by critical damping coefficient

Explanation : Damping ratio is defined as ratio of damping coefficient to the critical damping coefficient. Lift to drag ratio is used to provide information about aerodynamics of the aircraft. It is often termed as aerodynamic efficiency. Thrust to weight ratio is called Thrust loading.

33 .

An aircraft is consider to be over damped. What will be the appropriate value for damping ratio?

A)

0.001

B)

0.04

C)

0.1

D)

1.45

Correct Answer : 1.45

Explanation : For overdamped system, value of damping ratio is greater than 1.
Hence, among the given options, 1.45 is correct answer as it is > 1.

34 .

If damping ratio is unity then, system is ________

A)

over damped

B)

critically damped

C)

high lift device

D)

thrust augmented

Correct Answer : critically damped

Explanation : Damping ratio is defined as damping coefficient divided by critical damping coefficient. If damping ratio is unity then, the damping coefficient is equal to the critical damping coefficient. Hence, for such scenario system is said to be critically damped.

35 .

Find critical damping coefficient if damping ratio is 0.5 and damping coefficient is 1.1.

A)

2.2

B)

4.1

C)

4.9

D)

5.2

Correct Answer : 2.2

Explanation : Critical damping coefficient damping coefficient/ damping ratio 1.1/0.5 = 2.2.

36 .

Which of the following is an example of longitudinal mode?

A)

Dutch

B)

Lateral

C)

Phugoid

D)

Aileron

Correct Answer : Phugoid

Explanation : Phugoid mode is an example of longitudinal mode. Dutch and lateral mode are not example of longitudinal mode. Aileron is known as primary control surface. Aileron is used to control the aircraft rolling moment.

37 .

Which of the following is not the type of aircraft dynamic mode?

A)

Phugoid

B)

Flap

C)

Dutch roll

D)

Lateral mode

Correct Answer : Flap

Explanation : Flap is a high lift device. Flap is used to increase lift produced by the wing. Flaps are used to increase camber and overall surface area of the wing. This results in increased lift. Dutch roll, phugoid, lateral mode etc. are typical aircraft dynamic modes.