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Basic weather and aerodynamics > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

Define center of pressure

A

The point along the chord line of an airfoil through which all aerodynamic forces are considered to act.

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2
Q

Define airfoil

A

Any surface designed to produce lift when air is passed over it

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3
Q

List two basic types of airfoils

A

Symmetrical

Unsymmetrical/Nonsymmetrical

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4
Q

Define rotational relative wind as applied to an airfoil

A

That flow of air parallel and opposite to the flight path of an airfoil

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5
Q

Define induced flow

A

Downward flow of air through the rotor blades

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6
Q

Define resultant relative wind

A

Rotational relative wind modified by induced flow

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7
Q

How is the angle of incidence measured in a rotary wing aircraft?

A

The angle between a chord of an airfoil and the plane of rotation (tip path plane)

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8
Q

Define angle of attack

A

The angle between the chord and the resultant relative wind

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9
Q

Describe the relationship of lift to resultant relative wind

A

Perpendicular to

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10
Q

Describe the relationship between drag and the resultant relative wind

A

Drag is parallel to and in the same direction of the resultant relative wind

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11
Q

The four types of drag:

A

Induced
Parasite
Profile
Total

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12
Q

Which type of drag increases with airspeed?

A

Parasite drag

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13
Q

Define dissymmetry of lift

A

Differential lift between advancing and retreating halves of the rotor disk

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14
Q

How does the helicopter compensate for dissymmetry of lift?

A

With flapping

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15
Q

How does the pilot correct for blowback?

A

With cyclic feathering

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16
Q

Which forces in the lift equation can the pilot control

A

Coefficient of lift and airspeed

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17
Q

Define blowback

A

Change in the attitude of the rotor system

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18
Q

How does the pilot control dissymmetry of lift?

A

With cyclic feathering

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19
Q

What types of rotor systems are there?

A

Rigid
Semi-rigid
Articulated

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20
Q

Articulated tilts relative to the ________

A

Hub

21
Q

Semi rigid tilts relative to the ________

A

Mast

22
Q

Define centrifugal force

A

outward force produced whenever a body moves in a curved path

23
Q

Define rotor blade coning

A

Upward flexing of the rotor blades

24
Q

Rotor blade coning is a compromise between which two forces?

A

Centrifugal force and lift

25
Q

Define gyroscopic precession

A

When a force is applied to a rotating body it will manifest 90 degrees after application in the direction of rotation.

26
Q

Why is blade twisting necessary?

A

To distribute the lifting force more evenly along the blade.

27
Q

A pedal turn to the right requires _____(less/more) force than a pedal turn to the left

A

Less

28
Q

Define translating tendency

A

Tendency of a single rotor helicopter to drift right while hovering

29
Q

List four methods used to overcome translating tendency in single rotor helicopters

A
  • Rigging the cyclic
  • Tilting the mast
  • Left cyclic
  • Automated flight-control/stabilization augmentation system
30
Q

List the four rotor blade actions

A

Rotation
Flapping
Feathering
Hunting

31
Q

Describe the relationship of the total force to the tip path plane

A

Perpendicular

32
Q

When rotor disk is tilted what are the two components of total force?

A

Lift

Thrust

33
Q

What are the two flight conditions?

A

Balanced/Unbalanced

34
Q

Loss or apparent loss of ground effect is caused by?

A
  • Altitude greater than rotor diameter
  • Trees and bushes
  • Tall grass and uneven terrain
  • Hovering over water
  • Beginning o translational movement
  • Hovering into a wind
35
Q

Define effective rotational lift

A

When the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air

36
Q

Effective translational lift occurs at an airspeed of ______

A

16-24 kts

37
Q

Transverse flow effect is noticeable at an airspeed of_____

A

10-20 kts

38
Q

Define settling with power

A

A condition of powered flight in which the helicopter settles in its own downwash

39
Q

List the three simultaneous conditions required for settling with power

A

Vertical or near vertical descent of at least 300FPM
20%-100% engine power
Slow airspeed less than ETL

40
Q

List the required procedures for settling with power

A

Increase airspeed with cyclic
Reduce collective as altitude permits
Adjust rotor RPM to normal operating range

41
Q

Define autorotation

A

The flight condition during which no engine power is supplied and the main rotor is driven only by the action of the relative wind

42
Q

Describe how a pilot prevents a rotor RPM overspeed during an autorotation with turn

A

Adjusting collective control

43
Q

List of the three contitions required for a dynamic rollover to occur

A

Pivot point
Rolling motion
Exceed a critical angle

44
Q

Dynamic rollover occurs due to a combination of which two factors

A

Physical and human

45
Q

Which control input is required to recover from dynamic rollover on level ground

A

Smooth moderate collective reduction

46
Q

Operating at what speed is most likely to produce retreating blade stall

A

High forward speed

47
Q

Describe the symptoms of retreating blade stall in a single rotor helicopter

A

Abnormal vibration, pitch up of the nose and left roll

48
Q

Describe the recovery procedure from retreating blade stall

A

Reduce collective pitch, regain control of the aircraft, reduce airspeed, increase rotor RPM to normal operating range, minimize maneuvering, and descend to a lower altitude

Basic weather and aerodynamics (4 decks)

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