Principles of Flight - Chapter 4 Vocabulary

Vocabulary flashcards defining fundamental aerodynamic concepts, atmospheric parameters, physical laws, and airfoil terminology from Chapter 4: Principles of Flight.

Atmosphere

An envelope of air that surrounds the Earth and rests upon its surface, composed of $781\%$ nitrogen, $21\%$ oxygen, and $1\%$ other gases.

Viscosity

The property of a fluid that causes it to resist flowing due to the tendency of individual fluid molecules to adhere to each other.

Friction

The resistance that one surface or object encounters when moving over another, causing air molecules to adhere to a wing surface at a microscopic level.

Boundary Layer

The layer of air molecules that adhere to the wing surface because of friction and have a relative velocity near zero.

Drag

The force that resists airflow over a wing, caused by the combined effects of friction and viscosity.

Atmospheric Pressure

The force exerted equally in all directions on bodies within the air due to the weight of the atmosphere, equal to approximately $14.70\,\text{psi}$ or $1,013.2\,\text{mb}$ at sea level under standard conditions.

International Standard Atmosphere (ISA)

A worldwide standard reference established by ICAO where sea level conditions are defined as a temperature of $59\,^\circ\text{F}$ ($15\,^\circ\text{C}$) and a pressure of $29.92\,\text{"Hg}$ ($1,013.2\,\text{mb}$).

Standard Temperature Lapse Rate

The rate at which temperature decreases with altitude in a standard atmosphere, approximately $3.5\,^\circ\text{F}$ or $2\,^\circ\text{C}$ per $1,000\,\text{feet}$ up to $36,000\,\text{feet}$.

Standard Pressure Lapse Rate

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

Pressure Altitude

The height above the Standard Datum Plane (SDP), indicated when the altimeter barometric scale is set to $29.92\,\text{"Hg}$.

Standard Datum Plane (SDP)

A theoretical level where the weight of the atmosphere is $29.92\,\text{"Hg}$ ($1,013.2\,\text{mb}$) as measured by a barometer.

Density Altitude

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

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 forces impressed on it.

Newton's Second Law of Motion

Law stating that force equals mass times acceleration ($F = m \times a$) for a constant mass, or the change in momentum per change in time.

Newton's Third Law of Motion

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 internal pressure within the fluid decreases.

Venturi Tube

A tube with an inlet that narrows to a constricted throat and widens at the outlet, demonstrating Bernoulli's Principle as fluid velocity increases and pressure decreases at the constriction.

Airfoil

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

Camber

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

Leading Edge

The rounded forward end of an airfoil profile that faces forward in flight.

Trailing Edge

The narrow, tapered rear end of an airfoil profile.

Chord Line

A straight reference line drawn directly 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.

Center of Pressure (CP)

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

Downwash

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

Tip Vortex

A rotating airflow generated at the wingtip when high-pressure air beneath the airfoil pushes around the tip to the low-pressure area on top.