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Unit 6: Concepts of Stability and Control - Practice Quiz

ASE305 — Flight Mechanics 60 Questions
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1 In flight mechanics, what does aircraft stability primarily describe?

Basic concepts of stability and control Easy
A. The efficiency of the landing gear
B. The ability to produce maximum engine thrust
C. The tendency to maintain or restore an equilibrium condition
D. The capacity to carry a large payload

2 What does aircraft control refer to?

Basic concepts of stability and control Easy
A. The resistance of the structure to bending
B. The engine's ability to maintain constant thrust
C. The pilot's ability to change the aircraft's motion
D. The atmosphere's ability to produce lift

3 An aircraft has positive static stability if, immediately after a disturbance, it tends to:

Static stability Easy
A. Move farther from equilibrium
B. Move back toward equilibrium
C. Remain at the disturbed position
D. Enter a constant-rate turn

4 What is the initial response of a statically neutral aircraft after a small disturbance?

Static stability Easy
A. It remains in the new condition
B. It begins an increasing oscillation
C. It diverges rapidly from equilibrium
D. It returns rapidly to equilibrium

5 Dynamic stability describes an aircraft's response:

Dynamic stability Easy
A. Only during a steady turn
B. At the exact instant of takeoff
C. Over time after a disturbance
D. Only while controls are fixed

6 Which behavior indicates positive dynamic stability?

Dynamic stability Easy
A. Oscillations maintain constant size
B. Oscillations increase with time
C. Oscillations decrease with time
D. Oscillations begin only during landing

7 Longitudinal stability is primarily associated with motion about which aircraft axis?

Longitudinal stability Easy
A. The lateral axis
B. The longitudinal axis
C. The vertical axis
D. The thrust axis

8 Lateral stability is mainly concerned with which motion?

Lateral stability Easy
A. Yawing motion
B. Heaving motion
C. Pitching motion
D. Rolling motion

9 Directional stability is primarily associated with motion about which axis?

Directional stability Easy
A. The lateral axis
B. The wing axis
C. The vertical axis
D. The longitudinal axis

10 In a control-fixed stability analysis, the primary flight controls are assumed to be:

Control-fixed stability Easy
A. Free to move aerodynamically
B. Held at fixed positions
C. Moved continuously by the pilot
D. Removed from the aircraft

11 In a control-free stability analysis, a control surface is allowed to:

Control-free stability Easy
A. Remain mechanically locked
B. Float under aerodynamic forces
C. Rotate the entire tail assembly
D. Produce constant engine thrust

12 What is meant by rudder lock?

Rudder lock Easy
A. The rudder automatically centers during every sideslip
B. The rudder becomes ineffective only at zero airspeed
C. The rudder remains deflected because of aerodynamic hinge moments
D. The rudder is mechanically removed before flight

13 What is the main stability purpose of a dorsal fin?

Dorsal fin Easy
A. To improve directional stability
B. To increase aileron effectiveness
C. To eliminate elevator forces
D. To reduce longitudinal stability

14 In a conventional twin-engine aircraft, failure of one engine initially tends to yaw the aircraft:

One-engine-inoperative condition Easy
A. Toward the failed engine
B. Directly upward
C. Without any preferred direction
D. Toward the operating engine

15 The weathercocking effect tends to turn an aircraft's nose:

Weathercocking effect Easy
A. Toward the relative wind
B. Away from the horizon
C. Toward the lower wing
D. Away from the relative wind

16 During an aileron-induced roll, adverse yaw turns the nose:

Adverse yaw effects Easy
A. Opposite the direction of the intended roll
B. In the direction of the intended roll
C. Upward relative to the horizon
D. Downward relative to the horizon

17 What occurs during aileron reversal?

Aileron reversal Easy
A. The aircraft rolls opposite to the commanded direction
B. The aircraft maintains a constant bank angle
C. The elevator moves opposite to the control input
D. The rudder becomes the primary pitch control

18 A phugoid motion mainly involves a slow exchange between:

Long-period or phugoid motion Easy
A. Lift and structural weight
B. Engine power and fuel mass
C. Rolling and yawing moments
D. Kinetic and potential energy

19 Compared with short-period motion, phugoid motion generally has:

Long-period or phugoid motion Easy
A. A lower frequency and longer period
B. A higher frequency and shorter period
C. No variation in speed or altitude
D. Only rolling and yawing motion

20 Short-period motion is best described as:

Short-period motion Easy
A. A steady lateral motion in roll
B. A gradual change in engine speed
C. A slow directional oscillation in yaw
D. A rapid longitudinal oscillation in pitch

21 An aircraft returns toward its trimmed attitude after a small disturbance but requires unusually large control forces to initiate a maneuver. Which description best fits the aircraft?

Basic concepts of stability and control Medium
A. Stable but not highly controllable
B. Neutrally stable and uncontrollable
C. Dynamically unstable and uncontrollable
D. Unstable but highly controllable

22 For longitudinal static stability, which condition should hold near the trim angle of attack?

Static stability Medium
A.
B.
C.
D.

23 Following a disturbance, an aircraft oscillates about equilibrium with each successive peak becoming larger. How should this response be classified?

Dynamic stability Medium
A. Statically stable and dynamically stable
B. Statically stable and dynamically unstable
C. Statically unstable and dynamically stable
D. Statically neutral and dynamically neutral

24 What is the most likely effect of moving an aircraft's center of gravity aft while keeping it ahead of the neutral point?

Longitudinal stability Medium
A. Static margin increases and pitch response becomes less sensitive
B. Lateral stability increases while static margin remains constant
C. Static margin decreases and pitch response becomes more sensitive
D. Directional stability decreases without changing pitch response

25 An aircraft designer increases the horizontal-tail area without changing its moment arm. What is the primary expected effect?

Longitudinal stability Medium
A. Greater directional static stability
B. Lower lateral control power
C. Greater longitudinal static stability
D. Higher adverse yaw tendency

26 A positively dihedral wing experiences a sideslip with the relative wind coming from the right. What restoring response is expected?

Lateral stability Medium
A. A yawing moment toward the left
B. A rolling moment toward the left
C. A rolling moment toward the right
D. A pitching moment nose upward

27 Using the usual stability-axis sign convention, which derivative indicates positive directional static stability?

Directional stability Medium
A.
B.
C.
D.

28 During a control-fixed longitudinal stability test, what condition is imposed on the elevator?

Control-fixed stability Medium
A. It follows the stabilizer automatically
B. Its hinge moment is held at zero
C. Its deflection is held constant
D. It floats to an equilibrium angle

29 Why is control-free longitudinal stability commonly lower than control-fixed stability?

Control-free stability Medium
A. The free elevator moves the neutral point forward
B. The locked elevator eliminates aerodynamic damping
C. Elevator float increases the wing's lift-curve slope
D. Elevator float reduces the tail's restoring contribution

30 At a large sideslip angle, nonlinear hinge moments drive the rudder toward a high-deflection position and make recovery difficult. This condition is called:

Rudder lock Medium
A. Rudder lock
B. Aileron reversal
C. Spiral divergence
D. Elevator float

31 Why is a dorsal fin often added ahead of the vertical tail on an aircraft that shows poor behavior at large sideslip angles?

Dorsal fin Medium
A. It eliminates induced drag in turns
B. It increases elevator power at low speed
C. It delays directional instability at high sideslip
D. It reduces wing bending during roll

32 On a conventional twin-engine aircraft, the left engine suddenly fails while the right engine continues producing thrust. What is the immediate primary yawing tendency?

One-engine-inoperative condition Medium
A. Pitch downward without yaw
B. Roll right without yaw
C. Yaw toward the operating right engine
D. Yaw toward the failed left engine

33 After the left engine fails on a twin-engine aircraft, which steady control input is primarily required to oppose the resulting yaw?

One-engine-inoperative condition Medium
A. Elevator down
B. Right rudder
C. Symmetric aileron
D. Left rudder

34 A gust creates a sideslip on an aircraft with a large vertical tail located behind the center of gravity. What does the weathercocking effect tend to do?

Weathercocking effect Medium
A. Turn the tail into the relative wind
B. Turn the nose into the relative wind
C. Hold the yaw angle unchanged
D. Create only a pitching response

35 A pilot commands a roll to the right using conventional ailerons. Before rudder correction, which yaw response is typically produced by adverse yaw?

Adverse yaw effects Medium
A. The nose initially yaws left
B. The nose initially yaws right
C. The nose remains directionally fixed
D. The nose pitches sharply upward

36 Which design feature most directly reduces adverse yaw by creating more drag on the wing with the upward-deflected aileron?

Adverse yaw effects Medium
A. Plain flaps
B. Frise ailerons
C. All-moving tails
D. Dorsal fins

37 At high dynamic pressure, a right-roll command twists a flexible wing enough that the aerodynamic twist overwhelms the direct aileron effect. What is the result?

Aileron reversal Medium
A. The aircraft rolls left instead of right
B. The aircraft pitches down instead of rolling
C. The aircraft rolls right at a higher rate
D. The aircraft yaws right without rolling

38 During a lightly damped phugoid oscillation, which energy exchange is most characteristic?

Long-period or phugoid motion Medium
A. Kinetic energy exchanges with gravitational potential energy
B. Lateral energy exchanges with directional energy
C. Engine energy exchanges with rudder hinge energy
D. Rotational energy exchanges with elastic wing energy

39 Which combination best describes the short-period longitudinal mode?

Short-period motion Medium
A. Rapid changes in angle of attack and pitch rate
B. Slow changes in bank angle and heading
C. Slow changes in altitude and airspeed
D. Rapid changes in sideslip and yaw rate

40 A linear aircraft mode has eigenvalues . What response does this mode represent?

Dynamic stability Medium
A. A damped oscillation
B. A divergent oscillation
C. A non-oscillatory divergence
D. A constant-amplitude oscillation

41 An aircraft is trimmed at a forward center-of-gravity position and has , but the elevator reaches its deflection limit before the required lift coefficient is attained during landing. Which conclusion is correct?

Basic concepts of stability and control Hard
A. The aircraft is statically unstable because the elevator cannot generate the required lift
B. The aircraft is statically stable but lacks sufficient control authority for the maneuver
C. The aircraft is neutrally stable because stability and elevator authority cancel each other
D. The aircraft is dynamically unstable because the elevator reaches its deflection limit

42 Near several possible pitch equilibria, the pitching-moment coefficient is , where is an angle-of-attack perturbation. Which statement correctly classifies the equilibria?

Static stability Hard
A. All three equilibria are statically unstable
B. All three equilibria are statically stable
C. is unstable, while are stable
D. is stable, while are unstable

43 A longitudinal mode has eigenvalues , although the aircraft has . How should the motion be classified?

Dynamic stability Hard
A. Statically and dynamically unstable, with a period of about s
B. Statically and dynamically stable, with a period of about s
C. Statically stable but dynamically unstable, with amplitude doubling in about s
D. Statically unstable but dynamically stable, with amplitude halving in about s

44 Neglecting fuselage and propulsion effects, an aircraft has , , , and . If the center of gravity is at , what is the control-fixed static margin?

Longitudinal stability Hard
A. mean aerodynamic chord
B. mean aerodynamic chord
C. mean aerodynamic chord
D. mean aerodynamic chord

45 For an approximate spiral-mode criterion, stability requires . An aircraft has , , , and . What happens if is increased to with all other derivatives fixed?

Lateral stability Hard
A. The spiral mode changes from stable to unstable
B. The spiral mode remains stable with greater damping
C. The spiral mode remains unstable with lower frequency
D. The spiral mode changes from unstable to stable

46 The fuselage contributes and the vertical tail initially contributes . If tail effectiveness is multiplied by a factor , at what value of is directional static stability neutral?

Directional stability Hard
A.
B.
C.
D.

47 An aircraft is initially control-fixed stable. Its center of gravity is moved aft while elevator deflection remains fixed and the aerodynamic derivatives are otherwise unchanged. Which sequence is expected?

Control-fixed stability Hard
A. The static margin decreases and becomes zero at the control-fixed neutral point
B. The static margin increases and becomes zero at the aerodynamic center
C. The control-free neutral point moves aft by the same center-of-gravity shift
D. The elevator hinge moment vanishes before the static margin changes

48 For a freely floating elevator, . Given , , , and , what is with the control free?

Control-free stability Hard
A.
B.
C.
D.

49 With the rudder free, its equilibrium satisfies . What most directly indicates an approach to rudder lock as aerodynamic balance is increased?

Rudder lock Hard
A. approaches zero, causing a very large restoring yawing moment
B. approaches zero, causing a very large free-rudder deflection
C. approaches infinity, causing the pedals to return rapidly
D. approaches zero, causing directional stability to increase

50 A vertical tail provides adequate small-sideslip stability but stalls during large-sideslip engine-out tests. What is the principal benefit of adding a dorsal fin ahead of the vertical tail?

Dorsal fin Hard
A. It increases elevator effectiveness and preserves pitching moment at large incidence
B. It delays directional-surface stall and preserves yawing moment at large sideslip
C. It eliminates vertical-tail side force and reduces all fuselage yawing moments
D. It suppresses wing torsion and delays aileron reversal at high dynamic pressure

51 In an engine-out condition, a small bank toward the operating engine reduces the yawing moment that must be balanced aerodynamically to of its original value. If available rudder moment is proportional to dynamic pressure, how does the minimum control speed change?

One-engine-inoperative condition Hard
A. It remains equal to its original value
B. It decreases to of its original value
C. It decreases to of its original value
D. It increases to of its original value

52 A vertical-fin side force acts behind the center of gravity after a crosswind disturbance. Under the standard convention in which directional stability requires , what is the resulting tendency?

Weathercocking effect Hard
A. The aircraft pitches toward the wind while sideslip remains unchanged
B. The nose yaws away from the relative wind, increasing the sideslip
C. The aircraft rolls into the wind without producing a yawing moment
D. The nose yaws into the relative wind, reducing the sideslip

53 To initiate a right roll with conventional ailerons, the left aileron moves down and the right aileron moves up. If the left-wing drag increase exceeds the right-wing drag change, what initial motion occurs?

Adverse yaw effects Hard
A. The aircraft rolls right and initially yaws right
B. The aircraft rolls left but initially yaws right
C. The aircraft rolls left and initially yaws left
D. The aircraft rolls right but initially yaws left

54 A simplified aeroelastic model gives normalized aileron effectiveness as , where is reversal dynamic pressure. What effectiveness is predicted at ?

Aileron reversal Hard
A. , so the rolling response doubles
B. , so the rolling response reverses
C. , so the rolling response weakens
D. , so the rolling response strengthens

55 Using the approximation for a lightly damped phugoid, estimate its period at with .

Long-period or phugoid motion Hard
A. Approximately
B. Approximately
C. Approximately
D. Approximately

56 For a fixed-thrust aircraft, the local drag slope is at the trim speed. Other damping contributions are small. What is the likely consequence for the phugoid?

Long-period or phugoid motion Hard
A. Its damping must increase because a speed increase always dissipates more energy
B. Its angle of attack diverges rapidly while speed and altitude remain constant
C. Its frequency becomes zero because drag no longer balances aircraft weight
D. Its damping can become negative because a speed increase reduces resisting drag

57 A short-period mode has eigenvalues . Which set of modal properties is closest?

Short-period motion Hard
A. , , and
B. , , and
C. , , and
D. , , and

58 Under conventional short-period approximations, which derivative changes most directly increase natural frequency and damping, respectively?

Short-period motion Hard
A. A more negative and a more negative
B. A more negative and a more negative
C. A more positive and a more positive
D. A more positive and a more positive

59 An aircraft has strong directional stability but weak dihedral effect. After a small bank disturbance, sideslip produces a yawing response faster than the restoring rolling response. Which slow-mode behavior is most plausible?

Lateral stability Hard
A. A pitch divergence despite a stable short-period mode
B. A spiral divergence despite a stable high-frequency Dutch-roll mode
C. A phugoid divergence despite a stable roll-subsidence mode
D. A roll subsidence divergence despite a stable spiral mode

60 A reduced flight-dynamics model has characteristic polynomial . Using the cubic Routh-Hurwitz condition, how is the system classified?

Dynamic stability Hard
A. Marginally stable, with one conjugate pair on the imaginary axis
B. Unstable, with two roots in the right half-plane
C. Unstable, with three roots in the right half-plane
D. Stable, because every polynomial coefficient is positive
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