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PPL Training > PHAK 4: Principles of Flight > Flashcards

PHAK 4: Principles of Flight Flashcards

1
Q

Most of the atmosphere’s oxygen is contained below…

A

35,000 feet

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2
Q

Air is a…

A

Fluid

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3
Q

Fluids take on the shape of…

A

Their containers

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4
Q

What is viscosity?

A

The measure of a fluid’s resistance to flow

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5
Q

What determines how much a fluid resists flow.

A

The way individual molecules of the fluid tend to adhere, or stick, to each other.

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6
Q

Higher viscosity is…

A

Thicker

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7
Q

Lower viscosity is…

A

Thinner

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8
Q

What is friction?

A

The resistance that one surface or object encounters when moving over another.

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9
Q

What is the boundary layer?

A

The thin layer of air that flows directly over a wing’s surface, where air speed changes from zero (at the surface) to the free stream velocity of the surrounding airflow.

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10
Q

What is pressure?

A

The force applied in a perpendicular direction to the surface of an object.

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11
Q

How is pressure often measured?

A

Pounds of force exerted per square inch of an object, or PSI.

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12
Q

An object completely immersed in a fluid will feel…

A

Pressure uniformly around the entire surface of the object.

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13
Q

If the pressure on one surface of the object becomes less than the pressure exerted on the other surfaces, the object will…

A

Move in the direction of the lower pressure.

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14
Q

Which flight instruments are actuated by atmospheric pressure?

A
  • Altimeter
  • Airspeed indicator
  • Vertical speed indicator
  • Manifold pressure gauge
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15
Q

Under standard conditions at sea level, what is the approximate average pressure exerted by the weight of the atmosphere?

A
  • 14.7 psi
  • 1,013.2 mb
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16
Q

The weight of the atmosphere at 18,000 feet is…

A

One-half what it is at sea level.

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17
Q

What is the standard atmosphere at sea level?

A
  • 29.92 “Hg at 59 °F
  • 1013.2 mb at 15 °C
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18
Q

Lapse Rate

A

Change in temperature over altitude.

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19
Q

Standard Temperature Lapse Rate

A

2 °C or 3.5 °F per 1,000 feet
up to 36,000’

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20
Q

What is the temperature from 36,000’ to 80,000’

A

Approximately –65 °F or –55 °C.

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21
Q

What is the standard decrease of Hg with altitude?

A

Approximately 1 “Hg per 1,000 feet up to 10,000’

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22
Q

What does ISA stand for?

A

International Standard Atmosphere

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23
Q

Any temperature or pressure that differs from the standard lapse rates is considered…

A

Nonstandard temperature and pressure.

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24
Q

What does SDP stand for?

A

Standard Datum Plane

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25
Q

What is pressure altitude?

A

The height above an SDP, which is a theoretical level where the weight of the atmosphere is 29.92 “Hg (1,013.2 mb) as measured by a barometer.

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26
Q

The pressure altitude can be determined by one of the following two methods:

A
  1. Setting the barometric scale of the altimeter to 29.92 and reading the indicated altitude.
  2. Applying a correction factor to the indicated altitude according to the reported altimeter setting.
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27
Q

What is density altitude?

A

The vertical distance above sea level in the standard atmosphere at which a given density is to be found.

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28
Q

How do you find density altitude?

A

Pressure altitude corrected for nonstandard temperature.

29
Q

The density of air has significant effects on the aircraft’s performance because as air becomes less dense, it reduces: (3 things)

A
  • Power because the engine takes in less air.
  • Thrust because a propeller is less efficient in thin air.
  • Lift because the thin air exerts less force on the airfoils.
30
Q

As the density of the air increases (lower density altitude), aircraft performance…

A

Increases

31
Q

As air density decreases (higher density altitude), aircraft performance…

A

Decreases

32
Q

Is high density altitude more or less dense?

A

Less dense

33
Q

Is low density altitude more or less dense?

A

More dense

34
Q

What type of altitude does the airplane altimeter display?

A

Pressure Altitude

35
Q

Air density is affected by changes in

A
  • Altitude
  • Temperature
  • Humidity
36
Q

Density varies ______ with pressure and ______ with temperature,

A

directly, inversely

If the pressure is doubled, the density is doubled; if the pressure is lowered, the density is lowered. This statement is true only at a constant temperature.

Increasing the temperature of a substance decreases its density. Conversely, decreasing the temperature increases the density. Thus, the density of air varies inversely with temperature. This statement is true only at a constant pressure.

37
Q

Increasing the temperature of a substance ______ its density.

A

Decreases

38
Q

Decreasing the temperature of a substance ______ its density.

A

Increases

39
Q

In the atmosphere, both temperature and pressure decrease with altitude and have conflicting effects upon density. Which is the more dominant effect?

A

Pressure

40
Q

As the water content of the air increases, the air becomes ______ dense, ______ density altitude and ______ performance.

A

Less, increasing, decreasing

41
Q

What 3 things have a great influence on aircraft performance because of their effect upon density.

A
  • Pressure
  • Temperature
  • Humidity
42
Q

Newton’s First Law:

A

“Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.”

43
Q

Newton’s Second Law:

A

“Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.”

44
Q

Newton’s Third Law:

A

“For every action, there is an equal and opposite reaction.”

45
Q

Bernoulli’s Principle

A

A principle that explains how the pressure of a moving fluid varies with its speed of motion. An increase in the speed of movement causes a decrease in the fluid’s pressure.

46
Q

What is the chord line?

A

An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.

47
Q

An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.

A

Chord line

48
Q

Line drawn from the leading edge to the trailing edge of a wing.
Equidistant at all points from the upper and lower surfaces.

A

Mean camber line

49
Q

Mean camber line

A

Line drawn from the leading edge to the trailing edge of a wing.
Equidistant at all points from the upper and lower surfaces.

50
Q

What is 1?

A

Mean camber line

51
Q

What is 2?

A

Trailing edge

52
Q

What is 3?

A

Leading edge

53
Q

What is 4?

A

Chord line

54
Q

What is 1?

A

Early airfoil

55
Q

What is 2?

A

Later airfoil

56
Q

What is 3?

A

Clark ‘Y’ airfoil
(Subsonic)

57
Q

What is 4?

A

Laminar flow airfoil
(Subsonic)

58
Q

What is 5?

A

Circular arc airfoil
(Supersonic)

59
Q

What is 6?

A

Double wedge airfoil
(Supersonic)

60
Q

Is the velocity of air over the top of an airfoil faster or slower than the bottom?

A

Faster

61
Q

Is the velocity of air under the bottom of an airfoil faster or slower than the top?

A

Slower

62
Q

Is the pressure of air over the top of an airfoil higher or lower than the bottom?

A

Lower

63
Q

Is the pressure of air under the bottom of an airfoil higher or lower than the top?

A

Higher

64
Q

What does CP stand for?

A

Center of Pressure

65
Q

What is the CP?

A

A point along the wing chord line where lift is considered to be concentrated. For this reason, the center of pressure is commonly referred to as the center of lift.

66
Q

At high angles of attack, the CP moves ______, while at low angles of attack the CP moves ______.

A

forward, aft

67
Q

What does an airplanes CP govern?

A

Aerodynamic balance and controllability

68
Q

What is a wing tip vortex?

A

The high pressure area on the bottom of an airfoil pushes around the tip to the low-pressure area on the top. This creates a rotating flow called a tip vortex. The vortex flows behind the airfoil creating a downwash that extends back to the trailing edge of the airfoil. This downwash results in an overall reduction in lift for the affected portion of the airfoil.

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