Definitions Flashcards
Airfoil
A structure, piece, or body originally likened to a foil or leaf in being wide and thin and designed to obtain a useful reaction upon itself in its motion through the air. An airfoil may be no more than a flat plate, but usually it has a cross section carefully contoured in accordance with its intended application or function. Airfoils are applied to aircraft, missiles, or other aerial vehicles or projectiles to develop lift (as a wing), for stability (as a fin), for control (as an elevator), and for thrust or propulsion (as a propeller blade). Certain airfoils combine some of these functions.
Absolute Altitude
The aircraft’s height above the terrain directly beneath the aircraft, measured in feet above ground level (AGL). Absolute altitude is found by subtracting the terrain elevation from the true altitude.
Absolute Ceiling
The maximum altitude above sea level in a standard atmosphere that an airplane can maintain level flight.
Accelerated Spin
A spin in which the control stick is not held in the full aft position. An accelerated spin is characterized by steeper pitch attitudes and higher spin rates.
Accelerated Stall
A stall in which the load factor is greater than one, as in a pullout. Usually more violent and disorienting than a normal stall.
Accelerated Stall Line
A curved line describing the number of g’s that can be generated at a given indicated airspeed as a function of CLMAX angle of attack for a particular airfoil. Also called line of maximum lift.
Acceleration
A change in the velocity of a body with respect to magnitude or direction, or both.
Accelerometer
An instrument that measures one or more components of the acceleration of a vehicle.
Adverse Pressure Gradient
A pressure gradient of increasing static pressure in the direction of airflow.
Adverse Yaw
Yaw in the opposite direction of aileron roll input.
Aerodynamic Balance
The feature of a control surface that reduces the magnitude of the aerodynamic moment around the hingeline. See shielded horn.
Aerodynamic Braking
A technique for slowing an airplane to a speed suitable for frictional braking. Aerodynamic braking is accomplished by increasing the surface area exposed to the relative wind in order to increase parasite drag, primarily by holding the nose of the airplane in the landing attitude.
Aerodynamic Center (AC)
The point along the chordline of an airfoil where all changes in aerodynamic force effectively take place. It is normally located at the point of 25% chord.
Aerodynamic Force (AF)
A force acting on an airfoil that is the result of air pressure and friction distribution over the surface of the airfoil.
Aerodynamics
The science that studies the motion of gaseous fluid flows, and of their actions against and around bodies, and of the forces acting on bodies within that flow.
Aerodynamic Twist
Form of wing tailoring that employs a decrease in camber and/or relative thickness from wing root to wingtip. The wing root is more positively cambered and/or thicker (relative to the chord) than the tip, resulting in a root first stall pattern. Also called section variation.
Aileron
A movable control surface, attached to the wing of an airplane, used to produce a rolling moment around the longitudinal axis by creating unequal lifting forces on opposite sides of an airplane.
Aileron Reversal
Reversal of the control effect usually produced by an aileron, caused by a moment around the aerodynamic center twisting the wing and changing its angle of attack.
Aircraft (A/C)
Any device used or intended to be used for flight in the air.
Airflow
A flow or stream of air. A rate of flow measured by mass per unit time.
Airfoil
A streamlined shape designed to produce lift as it moves through the air.
Airframe
The structural components of an airplane including the framework and skin of such parts as the fuselage, wings, empennage, landing gear, and engine mounts.
Airplane
An engine driven, heavier-than-air, fixed-wing aircraft that is supported by the dynamic reaction of airflow over its wings.
Altimeter
Any instrument for measuring altitude. An instrument similar to an aneroid barometer that uses the change of atmospheric pressure with altitude to indicate the approximate elevation above a given reference.
Altitude
The height of a point, measured from a reference plane, such as mean sea level.
Ambient
Pertaining to the air or air conditions around a flying aircraft but undisturbed or unaffected by it.
Aneroid Barometer
An instrument for measuring the pressure of the atmosphere which operates on the principle of having changing atmospheric pressure bend a metallic surface which, in turn, moves a pointer across a scale graduated in units of pressure.
Angle of attack (AOA, α)
The angle formed between the relative wind and the chordline of the airfoil.
Angle of bank (AOB, φ)
The angle between the horizon and the lateral axis of an aircraft. The angle of lateral displacement (roll) of an aircraft, especially in making a turn.
Angle of climb (AOC, γ)
The angle between the horizon and the flightpath of a climbing aircraft.
Angle of descent (γ)
The angle between the horizon and the flightpath of a descending aircraft.
Angle of incidence
The angle between the airplane’s longitudinal axis and the chordline of its wing. The root chord is commonly chosen to measure the angle of incidence. For rotary wing aircraft, Angle of incidence is the angle between the blade chord line and the plane of rotation of the rotor system. It is a mechanical angle rather than an aerodynamic angle.
Angular acceleration
Rate of change of angular velocity.
Anhedral angle
A negative dihedral angle. Also called cathedral angle.
Approach
A specified flightpath and associated altitudes to be flown in preparation for a landing, especially a published instrument approach.
Artificial feel
A method of simulating, altering, or otherwise enhancing the feedback or control feel that is transmitted to the cockpit controls by the forces acting on the control surfaces.
Aspect ratio (AR)
The ratio of the wingspan to the average chord.
Attitude
The orientation of an aircraft as determined by the relationship between its axes and some reference line or plane. Usually refers to nose attitude or pitch attitude.
Automatic slot
High lift device that consists of a movable vane attached to the leading edge of the wing that moves away from the body of the wing to allow airflow from below the wing to reach the upper surface and reenergize the boundary layer, delaying boundary layer separation. See slat.
Autorotation
During powered flight, the rotor drag is overcome with engine power. When the engine fails, or is deliberately disengaged from the rotor system, some other force must be used to sustain rotor RPM so controlled flight can be continued to the ground. This force is generated by adjusting the collective pitch to allow a controlled descent. Airflow during helicopter descent provides the energy to overcome blade drag and turn the rotor. When the helicopter is descending in this manner, it is said to be in a state of autorotation.
Three Regions of Vertical Autorotation:
The driven region, also called the propeller region, is nearest to the blade tips and normally consists of about 30 percent of the radius. The total aerodynamic force in this region is inclined slightly behind the rotating axis. This results in a drag force which tends to slow the rotation fo the blade.
The driving region or autorotative region, normally lies between about 25 to 70 percent of the blade radius. Total aerodynamic force in this region is inclined slightly forward of the axis of rotation. This inclination supplies thrust which tends to accelerate the rotation of the blade.
The stall region includes the inboard 25 percent of the blade radius. It operates above the stall angle of attack and causes drag which tends to slow the rotation of the blade.
Average ** Chord**
The geometric average of every chord from the wing root to the
wingtip. Also called mean geometric chord.
Axis
A reference line passing through a
body, around which the body rotates.
Axis System
A set of three mutually perpendicular axes, intersecting at the
center of gravity of an aircraft, around which the motions, moments, and forces
of roll, pitch, and yaw are measured.
Bank
The position or attitude of an aircraft
when its lateral axis is inclined from the
horizontal.
Bernoulli’s Equation
In aerodynamics, a law or theorem stating that in a flow of
incompressible fluid, the sum of the static pressure and the dynamic pressure along
a streamline is constant if gravity and frictional effects are disregarded.
Boundary Layer
The layer of airflow over the surface of an airfoil, which shows
local airflow retardation caused by viscosity. The boundary layer is very thin at the leading edge of an airfoil (about 1
mm) and grows in thickness as it moves over a body. It is composed of laminar flow and turbulent flow.
Boundary Layer Control (BLC)
The control of the airflow within the boundary layer in
order to prevent its separation at high angles of attack. See also slot and slat.
Buffeting
The beating, shaking, or
oscillation of an aircraft’s structure or
surfaces by an unsteady flow, gusts,
turbulence, etc.
Cabin
Compartment of an aircraft in which
passengers, troops, or cargo are loaded.
Calibrated Airspeed (CAS)
Indicated airspeed corrected for instrument error.
Calibrated Altitude
Indicated altitude corrected for instrument error.
Camber
The curvature of the mean line of
an airfoil from leading edge to trailing
edge; the amount of this curvature.
Cantilever
A beam or object supported only
at or near one end, or one point; without
external bracing.
Cathedral
See anhedral.
Center of Gravity (CG)
The point at which
the weight of an object is considered to
be concentrated.
Chord
A measure of the chordline from the
leading edge to the trailing edge of an
airfoil. The chord may vary in length from
the wingtip to wing root. The root chord,
CR, is the chord at the wing centerline and
the tip chord, CT, is measured at the
wingtip.
Chordline
An infinitely long, straight line
drawn through the leading and trailing
edges of an airfoil.hordline
Chordwise Flow
Airflow perpendicular to the
leading edge of an airfoil; airflow along
the chord of an airfoil. Since chordwise
flow is accelerated over a wing, it
produces lift.
Cockpit
Compartment of an aircraft in which
the flight crew, especially the pilot(s), are
located. The cockpit is where the aircraft
is controlled from.
Coefficient of Aerodynamic Force (CF)
The dimensionless portion of the aerodynamic
force that is a function of angle of attack,
camber, aspect ratio, compressibility, and
viscosity.
Coefficient of Drag (CD)
The dimensionless portion of the total drag on an airfoil that
is dependent on the same variables that affect CF.
Coefficient of Friction (μ)
A dimensionless number whose value depends primarily
on the type of material and condition of
the two surfaces that are in contact.
Coefficient of Lift (CL)
The dimensionless portion of the total lift on an airfoil that is
dependent on the same variables that affect CF.
Compressibility
The property of a substance that allows its density to
increase as pressure increases.
Compressible Flow
Flow at speeds sufficiently high that density changes in the fluid can no longer be neglected.
Compressible flow describes the behavior of fluids that experience significant variations in density.
Constant-Speed Propeller
A propeller designed to maintain engine speed at a
constant RPM, automatically increasing
or decreasing pitch as engine speed
tends to increase or decrease.
Continuity Equation
ρ1A1V1 = ρ2A2V2.
Principle of physics that states that for
fluids, the mass flow rate has the same
value at every position along a closed
tube.
Control Feel
The feel or impression of the
stability and control of an aircraft that a
pilot receives through the cockpit controls,
either from aerodynamic forces acting on
the control surfaces or from devices
simulating these aerodynamic forces.
Control Force
A force, either aerodynamic
or pilot induced, acting on a control
surface.
Control Horn
A short lever or rigid post
attached to a control surface, to which a
control cable, wire, line, or rod is attached.
Controllability
The capability of an aircraft
to respond to control inputs, especially in
direction or attitude.
The driven region, also called the propeller region, is nearest to the blade tips and normally consists of about 30 percent of the radius. The total aerodynamic force in this region is inclined slightly behind the rotating axis. This results in a drag force which tends to slow the rotation fo the blade.
The driving region or autorotative region, normally lies between about 25 to 70 percent of the blade radius. Total aerodynamic force in this region is inclined slightly forward of the axis of rotation. This inclination supplies thrust which tends to accelerate the rotation of the blade.
The stall region includes the inboard 25 percent of the blade radius. It operates above the stall angle of attack and causes drag which tends to slow the rotation of the blade.
Three Regions of Vertical Autorotation:
