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A&P Mechanic - General > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

What is a freewheeling unit?

A

Helicopter unit that automatically disengages the engine from the main rotor when engine rpm is less the main rotor rpm.

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2
Q

Describe Dissymmetry of Lift?

A

On a helicopter in forward flight, the differential (unequal) lift between the advancing and retreating halves of the rotor blades caused by the different wind flow velocity across each half as a helicopter moves through the air.

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3
Q

How is dissymmetry of lift compensated for in a helicopter?

A

Blade flapping where one blade flaps up and the other blade flaps down is incorporated into helicopter design.

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4
Q

What is Gyroscopic Precession.

A

An inherent quality of rotating bodies, which causes an applied force to be manifested 90o in the direction from the point where the force is applied.

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5
Q

What are wingtip vortices?

A

Circular patterns of air created by the movement of an airfoil through the air when generating lift. Wingtip vortices are caused by the air beneath the wing, which is at higher pressure, flowing over the wingtip and up toward the top of the wing. Also, know as Wake Turblence and can be extremely hazardous to small aircraft.

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6
Q

What is boundary layer?

A

A very thin layer of air lying over the surface of the wing and, for that matter, all other surfaces of the airplane.

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7
Q

What is an airfoil?

A

Any device that creates a force, based on Bernoulli’s principles or Newton’s laws, when air is caused to flow over the surface of the device.

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8
Q

What is the Chord Line?

A

An imaginary straight line running from the wing’s leading edge to its trailing edge.

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9
Q

What is relative wind?

A

The airflow caused by the motion of the aircaft through the air. Relative wind is opposite and parallel to the direction of flight.

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10
Q

What is the angle of attack?

A

The angle between the chord line and the relative wind.

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11
Q

What is Longitudinal Stability?

A

Stability along the lateral axis. Longitudinal stability for an airplane involves the tendency for the nose to pitch up or to pitch down, rotating around the lateral axis, which is measured from wingtip to wingtip.

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12
Q

What is Lateral Stability?

A

Stability around the longitudial axis. Rolling stability or ability of aircraft to return to level flight due to disturbance.

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13
Q

What is Directional Stability?

A

Movement of the airplane around its vertical axis, and the airplane’s ability to not be adversely affected by a force creating a yaw type of motion.

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14
Q

Describe the Lateral Axis of an airplane.

A

A line that runs below the wing, from wingtip to wingtip, passing through the airplane’s center of gravity. Movement around this axis is called pitch, and control around this axis is called Longitudinal Control. The flight control that handles this job is the elevator attached to the horizontal stabilizer or a fully moving horizontal stabilizer.

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15
Q

Describe aircraft Longitudinal Axis.

A

Runs through the middle of the airplane, from nose to tail, passing through the center of gravity. Movement around this axis is known as roll, and control around this axis is called Lateral Control. Movement around this axis is controlled by the ailerons, and on jet transport airplanes, it is aided by surfaces on the wing known as spoilers.

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16
Q

Descibe aircraft Vertical Axis.

A

Runs from top to bottom through the middle of the airplane, passing through the center of gravity. Movement around this axis is known as yaw, and control around this axis is called Directional Control. Movement around this axis is controlled by the rudder.

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17
Q

What are trim tabs?

A

Trim tabs are small movable surfaces that attach to the trailing edge of flight controls. These tabs can be controlled from the flight deck, and their purpose is to create an aerodynamic force that keeps the flight control in a deflected position. Trim tabs moves in opposite direction of flight control.

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18
Q

How is a anti-servo tab used?

A

To reduce the sensitivity, a full length anti-servo tab is installed on the trailing edge of the stabilator. Anit-servo tab moves in the same direction as flight control.

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19
Q

What is a balance tab used for?

A

A balance tab is used to generate a force that assists in the movement of the flight control. Just the opposite of anti-servo tabs, balance tabs move in the opposite direction of the flight control’s trailing edge, providing a force that helps the flight control move.

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20
Q

Describe how a servo tab is used?

A

An adjustable tab attached to the trailing edge of a flight control surface. The tab moves in the opposite direction of the control and aids pilot in moving control.

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21
Q

What is Benoulli’s Principle?

A

An increase in a fluid velocity is offset by a decrease in pressure, e.g., as air passes over an airfoil it’s velocity increases as it flows over the wing and pressures decreases on top of the wing but air is slower below the wing and pressure increases created lift and thereby lifting the airplane.

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22
Q

What is camber?

A

Curvature of an airfloil above and below the chord line surface.

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23
Q

What are Newton’s first, second and third laws?

A
  1. Every object at rest or object in motion remains at that state unless acted upon by another force (inertia).
  2. Acceleration produced in a mass by the addition of force is directly proportional to the force and inversely proportional to the mass.
  3. For every action there is an equal and opposite reaction.
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24
Q

What is the Laminar Layer?

A

Boundary air as it first flows smoothly over the streamedline shape of an airfoil, i.e., nonturbulent air flow.

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25
Q

What is the Turbulent Layer?

A

Boundary Layer as it approaches center of the wing and begins to loose speed because of friction (Boundary Layer becomes thicker and turbulent).

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26
Q

Describe Leading Edge Slots.

A

Ducts that allow air to flow from bottom of wing to top of wing.

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27
Q

What is the purpose of Leading Edge Slots?

A

Assists in preventing Boundary Layer of air from becoming turbulent and separating from wing surface.

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28
Q

What are Vortex Generators?

A

Small airfoil-like surfaces attached to the top of wing’s surface that add energy to the boundary layer preventing airflow separation.

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29
Q

What is upwash?

A

Deflected oncoming air causing it to flow up and over the wing.

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30
Q

What is downwash?

A

Downward deflection of air after it has passed over the wing and is leaving the trailing edge.

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31
Q

Where do aircraft’s axis intersect?

A

Aircraft’s Center of Gravity.

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32
Q

Describe Static Stability.

A

The initial tendency to return to a state of equilibrium when distrubed from that state.

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33
Q

Describe Dynamic Stability.

A

Property of aircraft that causes it, when distrubed from straight and level flight, to develop forces and moments that restore it to original condition of straight and level flight.

34
Q

Describe Positive Static Stability.

A

Condition of stability of an aircraft that causes it, when distriburbed from straight and level flight, to tend to return to straight and level flight.

35
Q

Describe Negative Static Stability.

A

A condition in which an object distrubed from a condition of rest will tend to move further away from its condition of rest.

36
Q

Describe Neutral Static Stabiity.

A

The condition of an object when distrubed from a condition of rest to neither accelerate away or toward its original position.

37
Q

What is Center of Lift (Center of Pressure)?

A

Point where all lifting forces concentrate. It runs wing tip to wing tip.

38
Q

What is Center of Gravity?

A

Point where mass (weight) of an airplane is concentrated.

39
Q

T/F: Typically, for an aircraft to have good longitudinal stability, the CG is located forward of the Center of Lift.

A

True

40
Q

Describe Lateral Stability.

A

Stability along the Longitudial Axis. Movement along the Longitudial Axis is called roll and is conrolled by the ailerons.

41
Q

What is Dihedral?

A

An upward wing angle with respect to the horizontal.

42
Q

What is the advantage of a dihedral wing?

A

Gives an aircraft good lateral stability.

43
Q

What is Dutch Roll?

A

Small amount of oscillation around both the longitudial and lateral axes. Commerical aircraft have a yaw damper to cancel it out.

44
Q

What is Directional Stability?

A

Stability about the vertical axis of an airplane whereby an airplane tends to return, on its own, to flight aligned with relative wind when distrubed. The vertical tail is primary contributor to directional stability causing airplane to align with relative wind.

45
Q

What is Longitudinal Stability?

A

Stability along the Lateral Axis.

46
Q

What is the Lateral Axis of an airplane?

A

Axis running wing tip to wing tip passing through airplanes Center of Gravity. Movement along the lateral axis is called pitch and is controlled by the elevator. Control around this axis is called Longitudial Control.

47
Q

Describe an airplane’s Longitudial Axis?

A

Runs through middle of airplane from nose to tail passing through Center of Gravity. Movement around this axis is called rolled and is controlled by ailerons. Control around this axis is called Lateral Control.

48
Q

Describe airplane’s vertical axis.

A

Runs from top to bottom through the middle of the airplane, passing through the Center of Gravity. Movement around this axis is called yaw and control around this axis is called Directional Control.

49
Q

What is a trim tab?

A

A small auxiliary hinged portion of a movable control surface that can be adjusted during flight to a position resulting in a balance of control forces.

50
Q

Where are trim tabs attached?

A

Trim tabs are attached to the flight control’s trailing edge.

51
Q

What’s an anti-servo tab?

A

An adjustable tab attached to the trailer edge of a stabilator that move in the same direction as the primary control. It is used to make the stabilator less sensitive.

52
Q

Describe a Balance Tab.

A

An auxilliary control mounted to a primary control surface, which automatically moves in opposite direction of the primary control to provide aerodynamic assist in the movement of the control.

53
Q

Describe a Servo Tab.

A

An adjustable tab attached to the trailing edge of a control surface. The tab moves in the opposite direction of control and aids pilot in moving control.

54
Q

Describe a Plain Flap.

A

A wing flap in which a portion of the trailing edge of the wing folds down to increase the camber of the wing without increasing wing area.

55
Q

Describe a Split Flap.

A

Wing flaps in which a portion of either the underside or the trailing edge of the wings splits and folds downward to increase lift and drag. Actually creates more drag than lift.

56
Q

Describe Slotted Flap.

A

A trailing edge wing flap that forms a duct when flap is lowered. Air forced through the duct is held down on the upper surface of the flap allowing more flap extension before airflow separation. Creates additional lift.

57
Q

Describe a Fowler Flap.

A

Wing flap that is lowered by sliding from the trailing edge of wing on a track. Flower flaps modify the shape of the airfoil and increases the area of the wing.

58
Q

What are Leading Edge Slots?

A

Ducts or passages in the leading edge of a wing that allows high pressure air from bottom of wing to flow over top of wing helping to keep boundary layer of air from separating from wing.

59
Q

What are Leading Edge Slats?

A

A moveable auxillary airfoil on the leading edge of a wing. It allows high pressure air below wing to flow over top of wing delaying airflow separation.

60
Q

What is the speed of sound?

A

761 mph on a standard day (59 F).

61
Q

T/F: Speed of sound in air changes with temperature, increasing as temperature increases.

A

True

62
Q

T/F: Critical Mach Number is speed at which shock wave forms.

A

True

63
Q

T/F: Transonic speed is typically between Mach 0.8 and 1.20.

A

True

64
Q

What is Supersonic speed?

A

Speed between Mach 1.20 to 5.0.

65
Q

What is Hypersonic speed?

A

Speed faster than Mach 5.0.

66
Q

Describe how Shock Waves are formed.

A

When airplane’s speed reaches the speed of sound, sound energy (pressure waves) can’t get away from the airplane and it starts to pile up, initially on top of the wing and eventually attaching itself to leading and trailing edge of wing.

67
Q

T/F: A Normal Shock Wave forms ahead of the airfoil approaching the speed of sound (transonic flight) and is perpendicular to path of airfoil.

A

True

68
Q

T/F: Aerodynamic Heating is temperature rise caused by high-speed air flowing over an airfoil.

A

True

69
Q

Describe Oblique Shock Wave.

A

A shock wave attached to the bow and tail of an aircraft flying at a speed greater than the speed of sound.

70
Q

Describe a Fully Articulated Rotar.

A

A rotor that is attached to a helicopter rotor hub in such a way that the pitch angle of each blade can change, and each blade is free to move up and down and back and forth in its plane of rotation.

71
Q

Describe a Rigid Rotor.

A

In rotorcraft, a rotor system permitting blades to feather but not to flap or hunt.

72
Q

Describe Semirigid Rotor.

A

In rotorcraft, a rotor system in which the blades are fixed to the hub but are free to flap and feather.

73
Q

What are the types of Anti-Torque Systems?

A
  1. Tail or Anti-Torque Rotor
  2. Fenestrom (Fan) Tail Rotor
  3. NOTAR (No Tail Rotor)
74
Q

Describe how a anti-torque rotar works.

A

A rotor turning in a plane perpendicular to the main rotor and parallel to the longitudial axis of the fuselage. It is used to counteract the torque of the main rotor.

75
Q

What is Collective Pitch Control?

A

Helicopter control in which pitch of all rotor blades are changed at the same time.

76
Q

Describe Cyclic Pitch Control.

A

Helicopter control in which pitch of blades can be changed on rotation resulting in lateral, forward or backward movement of helicopter.

77
Q

What is Dissymetry of Lift?

A

On a helicopter in forward flight, the advancing blade develops more lift than the retreating blade because of the velocity of the relative wind.

78
Q

T/F: Blade flapping is one method used to compensate for Dissymetry of Lift.

A

True

79
Q

What is Coriolis Effect?

A

Tendency of a rotor blade to increase or decrease its velocity in its plane of rotation when the center of mass moves closes or further from the axis of rotation.

80
Q

What is coning?

A

In rotorcraft, an upward sweep of rotor blades as a result of lift and centrifigal force.

A&P Mechanic - General (2 decks)

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