PHAK CH 4 (Principles of Flight)

Question 1

Air is a Fluid… What does this mean?

Answer 1

Fluids take the shape of their container. Fluids do not resist deformation when even the smallest stress is applied or the resist is only slightly, this is known as VISCOSITY. Fluids also have the ability to flow, and will expand to fill the available volume of its container.

Question 2

Viscosity

Answer 2

The property of a fluid that causes it to resist flowing.
Air has LOW viscosity and flows EASILY
But! It does resist flow just slightly.

Question 3

Friction

Answer 3

Friction is the resistance that one surface or object encounters when moving over another object. **the surface of a wing at a microscopic level has a certain level of roughness, which has a certain roughness that causes friction with the air traveling over it, and slows down the velocity of that air. **

Question 4

Boundary Level

Answer 4

Molecules of air pass over the surface of the wing and actually adhere (stick, or cling) to the surface because of friction. The layer of molecules that adheres to the wings surface is referred to as the BOUNDARY LEVEL.

Question 5

What forces create drag?

Answer 5

Friction causes the boundary layer of the air to adhere to the wing, further resistance to the airflow is caused by viscosity (the tendency of the air to stick to itself) these two forces create drag.

Question 6

Pressure

Answer 6

Is the force applied in a perpendicular direction to the surface of an object (measured in PSI). The nature of air feels pressure in all uniformly around the entire surface. ***if the pressure on one surface of the object becomes less than the pressure exerted on the other surfaces, the object will move in the direction of the lower pressure. (Think Jello)

Question 7

Instruments that use Atmospheric Pressure

Answer 7

Altimeter, Airspeed Indicator, Vertical Speed Indicator, and Manifold Pressure Gauge

Question 8

Mass and Weight of Air

Answer 8

Air has mass, and is affected by the attraction of gravity. Therefore is has weight, and thus has force. Since air is a fluid substance the force is exerted equally in all directions.

Question 9

Standard Datum Plane for Atmospheric Pressure and Temperature

Answer 9

Standard Datum Plane ( a standard measurement for an adjustable variable): the pressure of the atmosphere varies with time and location, thus a standard reference was developed.

The standard datum plane Temperature is set at 59F or 15C, and Standard Pressure is 29.92 inches of mercury or 1013.2 mb (millibars)

Question 10

Standard Temperature Lapse Rate
Standard Pressure Lapse Rate

Answer 10

3.5F or 2C per 1,000ft up (until 36,000 ft)

Pressure decrease -1Hg (inches of mercury) per 1,000 ft of altitude (up to 10,000ft)

ANYTHING ELSE IS CONSIDERED NON STANDARD
ALL AIRCRAFT INSTRUMENTS ARE CALIBRATED FOR THE STANDARD ATMOSPHERE

Question 11

Pressure Altitude and How to Find it

Answer 11

Pressure Altitude is the height ABOVE the standard datum plane

It is found by setting the altimeter to 29.92 and reading the indicated altitude shown or applying the correction factor to the indicated altitude based off to the current recorded altimeter setting.

Question 12

Density Altitude and How it is found

Answer 12

Density Altitude is a PERFORMANCE determiner in NONSTANDARD ATMOSPHERIC conditions.
(How the airplane flies in the current atmosphere)

Calculate Pressure Altitude first then correct for non standard temperature conditions.

Question 13

Air Density’s Effect on Aircraft’s Performance

Answer 13

As air becomes LESS DENSE it reduces: THIN AIR

Power (engine takes in less air)
Thrust (Prop moves less air)
Lift (Thin air exerts less air on the wings)

*the HIGHER the density altitude, the LESS DENSE the air
HIGH DA the more Stupid your PLANe

Question 14

Effects of Pressure on Density

Answer 14

Think of COMPRESSION

When density (compression) is decreased, so is pressure, these things are directly proportional at a constant temperature.

Question 15

Effects of Temperature on Density

Answer 15

Increasing the Temperature, Lowers Density Think Ice to Water
Decreasing the Temperature, Raises Density Think Water to Ice

Density varies inversely with Temperature, this statement is only true at a constant pressure.

Question 16

Effect of Humidity (Moisture ) on Density

Answer 16

Water Vapor is Lighter than Air, thusly WET AIR is LIGHTER than DRY AIR. THINK CLOUDS
As WATER content INCREASES, the air becomes LESS DENSE.

HUMIDITY: refers to the amount of water vapor contained in the atmosphere and it is expressed as a percentage of the maximum amount of water vapor the air can hold.

WARM AIR (less dense) hold MORE (more space) Water Vapor, than cold air.
Which is why warm and humid tend to go together.

Humidity ALONE is NOT considered an important factor in calculating density altitude and aircraft performance, but is a contributing factor. (Also if you live in Alabama)

Question 17

Theories in the Production of Lift

Answer 17

Newton’s Third Law
Bernoulli’s Principle
Magnus Effect

Question 18

Newton’s Third Law

Answer 18

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

As the Propeller moves and pushes back the air, thusly the air pushes the Propeller in the Opposite Direction i.e. Forward.

Question 19

Magnus Effect

Answer 19

A rotating object develops lift.
Spinning Basketball, goes father as it falls

Question 20

Bernoulli’s Principle

Answer 20

A study of how a fluid moves in a vacuum (air is a fluid)

That as the VELOCITY of a moving fluid increases, the PRESSURE within the fluid DECREASE

So…. As the wing moves through the air, the flow of air across the curved TOP surface increase in velocity (travels a greater distance, at the same time) creating a LOWER PRESSURE area on TOP.

Question 21

Camber of the Wing

Answer 21

the curvature/shape of the wing
Notice there is a difference in the curvatures (called cambers) of the upper and lower surfaces of the airfoil.

The camber of the upper surface is more pronounced than that of the lower surface, which is usually somewhat flat

Shallow Tear Drop Shape:
Leading Edge: front (more pronounced, round)
Trailing Edge: back (tapered, and narrowed)

Question 22

Chord Line

Answer 22

Chord line or Reference Line: a straight line drawn through the profile in half connecting the leading and trailing edges (runs through the wing and Splits it in half perpendicularly)

Question 23

Airfoil/Wing works because…?

Answer 23

It takes advantage of aerodynamic physics laws: creates two actions from the air mass: a positive pressure lifting action from the mass below the wing, and the negative lifting action from lowered pressure above the wing. velocity is higher above the wing= lower pressure

Question 24

How Do Flaps Work?

Answer 24

Changes the camber of the wing (the curvature of the wing becomes more pronounced) gathers more air creating more lift.

Question 25

Downward Backwash And Newton’s Third Law

Answer 25

The downward backward force of air from the top surface of the wing/airfoil creates a downwash, Newton’s Third Law thus means this would create a reverse upwards forwards force on the airfoil.

Question 26

Tip Vortex

Answer 26

The high pressure area on the bottom of an airfoil pushes around the tip to the low pressure area on the top. Thus the air rotates around the tip creating a “tip vortex”.