Basic Aerodynamics/ Principles of Flight Flashcards

Question

What is density altitude? Hints: 3

Answer 1

1. used for correlating aerodynamic performance in the nonstandard atmosphere 2. the vertical distance above sea level in the standard atmosphere 3. is determined by first finding pressure altitude, and then correcting desnity altitude for nonstandard temperature variations.

Answer 2

1. decrease in air density (less atmospheric pressure) -> High density altitude

Answer 3

affected by changes in altitude, temperature, and humidity

Answer 4

1. Lower elevations, 海拔 (geographic areas or locations that are situated at relatively low altitudes or heights above sea level.) 2. high atmospheric pressure, 3. low temperatures, and low humidity are more indicative of low-density altitude.

Answer 5

Pressure ↓ , Mass ↓ , Density ↓ air is compressed, a greater amount of air can occupy a given volume. the air expands and occupies a greater space At a lower pressure: - the original column of air contains a smaller mass of air. - The density is decreased because density is directly proportional to pressure. - if the pressure is lowered, the density is lowered.

Answer 6

Increasing the temperature of a substance (air become big, mass ↓) → decreases its density decreasing the temperature → increases the density * the density of air varies inversely with temperature.

Answer 7

Water vapour is lighter than air consequently, moist air is lighter than dry air.

Answer 8

Water in Air ↑ (lighter) , Air density ↓ ↑ density altitude (reduction in air density) , ↓ a/c performance As the water content of the air increases, the air becomes less dense, increasing density altitude and decreasing performance.

Answer 9

the amount of water vapor contained in the atmosphere and is expressed as a percentage of the maximum amount of water vapor the air can hold

Answer 10

WARM: *less dense Warm air holds more water vapor, warm and moist (both qualities tend to lighten the air) COLD: *more dense cold air holds less old and dry (both qualities making it heavier the dry air that contains no water vapour has a relative humidity of 0%

Answer 11

Lower → a/c performance will be better

Answer 12

Lift from wing > Gravity opposite direction

Answer 13

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. (external force) forces may add to its motion, slow it down, or change its direction. Body at rest → remains at rest Body in motion →remains in motion

Answer 14

Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration. Force = mass (weight) x acceleration Weight = ma = mg *gravitational acceleration)

Answer 15

For every action, there is an equal and opposite reaction. E.g. the propeller moves and pushes back the air; consequently, the air pushes the propeller (and thus the airplane) in the opposite direction—forward

Answer 16

as the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases. This principle explains what happens to air passing over the curved top of the airplane wing.

Answer 17

The venturi tube has an air inlet that narrows to a throat (constricted point) and an outlet section that increases in diameter toward the rear. The diameter of the outlet is the same as that of the inlet. The mass of air entering the tube must exactly equal the mass exiting the tube. At the constriction, the speed must increase to allow the same amount of air to pass in the same amount of time as in all other parts of the tube. When the air speeds up, the pressure also decreases. Past the constriction, the airflow slows and the pressure increases.

Answer 18

1. Camber difference in the curvatures (called cambers) of the upper and lower surfaces of the airfoil 2. Chord line straight line drawn through the profile connecting the extremities of the leading and trailing edges. 3. Trailing edge 4. Leading edge 5. Mean camber line line is equidistant at all points from the upper and lower surfaces.

Answer 19

a positive pressure lifting action from the air mass below the wing, a negative pressure lifting action from lowered pressure above the wing.

Answer 20

air stream strikes the relatively flat lower surface of a wing or rotor blade when inclined at a small angle to its direction of motion, - the air is forced to rebound downward, causing an upward reaction in positive lift. the air stream striking the upper curved section of the leading edge is deflected upward. Reason: An airfoil is shaped to cause an action on the air, and forces air downward, which provides an equal reaction from the air, forcing the airfoil upward.

Answer 21

airfoil were then inclined so the airflow strikes it at an angle, the air moving over the upper surface would be forced to move faster than the air moving along the bottom of the airfoil. (i.e., as the fluid speed decreases, the pressure must increase). This increased velocity reduces the pressure above the airfoil. Applying Bernoulli’s Principle of Pressure, the increase in the speed of the air across the top of an airfoil produces a drop in pressure.

Answer 22

The downward backward flow from the top surface of an airfoil creates a downwash. a wing shaped to cause an action on the air, and forcing it downward, provides an equal reaction from the air, forcing the wing upward Extra(This downwash meets the flow from the bottom of the airfoil at the trailing edge.) Applying Newton’s third law, the reaction of this downward backward flow results in an upward forward force on the airfoil.

Answer 23

a positive pressure results, particularly at higher angles of attack (As more air particles hit the upper surface)

Answer 24

stagnation point Extra: At some point near the trailing edge, it again reaches a velocity equal to that on the upper surface. (Join back tgt)

Answer 25

Applying Newton’s third law, the reaction of this downward backward flow results in an upward forward force on the airfoil. (Deflection) the pressure differential between the upper and lower surface of the airfoil increases, total lift increases. (i.e., as the fluid speed decreases, the pressure must increase).

Answer 26

1. there are regions along the surface where the pressure is negative, or less than atmospheric, 2. regions where the pressure is positive, or greater than atmospheric. This negative pressure on the upper surface creates a relatively larger force on the wing than is caused by the positive pressure resulting from the air striking the lower wing surface. (Check ch4 pg 8)

Answer 27

center of pressure (CP). Aerodynamic force acts through this CP.

Answer 28

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

Answer 29

since it affects the position of: - air loads imposed on the wing structure in both low and high AOA conditions. - airplane’s aerodynamic balance and controllability are governed by changes in the CP.

Answer 30

As an airfoil moves through air, the airfoil is inclined against the airflow, producing a different flow caused by the airfoil’s relationship to the oncoming air. It causes the air to turn about the object within the air stream. As a result of this change, the velocity about the object changes in both magnitude and direction, in turn resulting in a measurable velocity force and direction.

Answer 31

The high- pressure area on the bottom of an airfoil pushes around the tip to the low-pressure area on the top. 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.

Answer 32

1. Winglets can be added to the tip of an airfoil to reduce this flow. - The winglets act as a dam preventing the vortex from forming. - Winglets can be on the top or bottom of the airfoil. For reference: taper the airfoil tip, reducing the pressure differential and smoothing the airflow around the tip.