Principles of Flight - Vocabulary

Vocabulary flashcards based on the Principles of Flight chapter, covering atmospheric properties, fluid dynamics, lapse rates, motion laws, and airfoil aerodynamics.

Atmosphere

An envelope of air that surrounds the Earth and rests upon its surface, composed of $78\%$ nitrogen, $21\%$ oxygen, and $1\%$ other gases.

Viscosity

The property of a fluid that causes it to resist flowing due to the internal adherence of its molecules.

Friction

The resistance that one surface or object encounters when moving over another material in contact with it.

Boundary Layer

The layer of air molecules that adhere to the surface of a wing due to friction, having a relative velocity near zero.

Drag

The combined force resulting from friction and viscosity acting together to resist airflow over a wing.

Pressure

The force applied in a perpendicular direction to the surface of an object, often measured in pounds per square inch (PSI).

Atmospheric Pressure

The force exerted equally in all directions by the weight of the atmosphere, averaging approximately $14.70\,\text{psi}$ or $1,013.2\,\text{mb}$ at standard sea level conditions.

International Standard Atmosphere (ISA)

A worldwide standard reference at sea level defined by a surface temperature of $59\,^{\circ}\text{F}$ ($15\,^{\circ}\text{C}$) and a surface pressure of $29.92\,\text{inHg}$ ($1,013.2\,\text{mb}$).

Standard Temperature Lapse Rate

The rate at which atmospheric temperature decreases with altitude, approximately $3.5\,^{\circ}\text{F}$ ($2\,^{\circ}\text{C}$) per $1,000\,\text{feet}$ up to $36,000\,\text{feet}$.

Standard Pressure Lapse Rate

The rate at which atmospheric pressure decreases with altitude gain, approximately $1\,\text{inHg}$ per $1,000\,\text{feet}$ of altitude up to $10,000\,\text{feet}$.

Pressure Altitude

The height above a standard datum plane (SDP), which is a theoretical level where atmospheric pressure is $29.92\,\text{inHg}$ ($1,013.2\,\text{mb}$).

Density Altitude

Pressure altitude corrected for nonstandard temperature variations, representing the vertical distance above sea level in the standard atmosphere at which a given air density is found.

Relative Humidity

The amount of water vapor contained in the atmosphere expressed as a percentage of the maximum amount of water vapor the air can hold at a given temperature.

Newton's First Law of Motion

Physical law stating that every object persists in its state of rest or uniform motion in a straight line unless compelled to change that state by impressed forces.

Newton's Second Law of Motion

Physical law stating that force is equal to the change in momentum per change in time, expressed as $\text{Force} = \text{mass} \times \text{acceleration}$ for a constant mass.

Newton's Third Law of Motion

Physical law stating that for every action, there is an equal and opposite reaction.

Bernoulli's Principle

Principle stating that as the velocity of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases.

Venturi Tube

A tube with a narrowed throat used to demonstrate Bernoulli's Principle, where fluid speed increases and pressure decreases at the constriction.

Airfoil

A structure designed to obtain a reaction upon its surface from the air through which it moves.

Camber

The curvature of the upper and lower surfaces of an airfoil.

Leading Edge

The rounded front extremity of an airfoil profile facing forward in flight.

Trailing Edge

The narrow, tapered rear extremity of an airfoil profile.

Chord Line

A straight reference line drawn through an airfoil profile connecting the extremities of the leading and trailing edges.

Mean Camber Line

A reference line drawn from the leading edge to the trailing edge of an airfoil that is equidistant at all points from the upper and lower surfaces.

Downwash

The downward backward flow of air from the upper surface of an airfoil that meets the flow from the bottom surface at the trailing edge.

Center of Pressure (CP)

The average point of pressure variation along an airfoil for a given angle of attack, through which aerodynamic force acts.

Tip Vortex

A rotating airflow created at wing tips when high-pressure air below the airfoil flows around the tip toward the low-pressure area on top.