PHAK CH 4 (Principles of Flight) Flashcards
Air is a Fluid… What does this mean?
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.
Viscosity
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.
Friction
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. **
Boundary Level
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.
What forces create drag?
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.
Pressure
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)
Instruments that use Atmospheric Pressure
Altimeter, Airspeed Indicator, Vertical Speed Indicator, and Manifold Pressure Gauge
Mass and Weight of Air
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.
Standard Datum Plane for Atmospheric Pressure and Temperature
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)
Standard Temperature Lapse Rate
Standard Pressure Lapse Rate
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
Pressure Altitude and How to Find it
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.
Density Altitude and How it is found
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.
Air Density’s Effect on Aircraft’s Performance
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
Effects of Pressure on Density
Think of COMPRESSION
When density (compression) is decreased, so is pressure, these things are directly proportional at a constant temperature.
Effects of Temperature on Density
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.
Effect of Humidity (Moisture ) on Density
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)
Theories in the Production of Lift
Newton’s Third Law
Bernoulli’s Principle
Magnus Effect
Newton’s Third Law
“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.
Magnus Effect
A rotating object develops lift.
Spinning Basketball, goes father as it falls
Bernoulli’s Principle
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.
Camber of the Wing
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)
Chord Line
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)
Airfoil/Wing works because…?
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
How Do Flaps Work?
Changes the camber of the wing (the curvature of the wing becomes more pronounced) gathers more air creating more lift.
Downward Backwash And Newton’s Third Law
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.
Tip Vortex
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”.
