Aeronautical Terms

100-Hour Inspection

An inspection, identical in scope to an annual inspection. Must be conducted every 100 hours of flight on aircraft of under 12,500 pounds that are used for hire.

Absolute Altitude

The vertical distance of an airplane above the terrain, or above ground level (AGL).

Absolute Ceiling

The altitude at which a climb is no longer possible.

Acceleration

Force involved in overcoming inertia, and which may be defined as a change in velocity per unit of time.

Accessories

Components that are used with an engine, but are not a part of the engine itself. Units such as magnetos, carburetors, generators, and fuel pumps are commonly installed engine accessories.

Adjustable Stabilizer

A stabilizer that can be adjusted in flight to trim the airplane, thereby allowing the airplane to fly hands-off at any given airspeed.

Adjustable-pitch propeller

A propeller with blades whose pitch can be adjusted on the ground with the engine not running, but which cannot be adjusted in flight. Also referred to as a ground adjustable propeller. Sometimes also used to refer to constant-speed propellers that are adjustable in flight.

Adverse Loaded CG Check

A weight and balance check to determine that no condition of legal loading of an aircraft can move the CG outside of its allowable limits.

Adverse Yaw

A condition of flight in which the nose of an airplane tends to yaw toward the outside of the turn. This is caused by the higher induced drag on the outside wing, which is also producing more lift. Induced drag is a by-product of the lift associated with the outside wing.

Aerodynamic Ceiling

The point (altitude) at which, as the indicated airspeed decreases with altitude, it progressively merges with the low speed buffet boundary where pre-stall buffet occurs for the airplane at a load factor of 1.0 G.

Aerodynamic coefficients

Non-dimensional coefficients for aerodynamic forces and moments.

Aerodynamics

The science of the action of air on an object, and with the motion of air on other gases. Aerodynamics deals with the production of lift by the aircraft, the relative wind, and the atmosphere.

Ailerons

Primary flight control surfaces mounted on the trailing edge of an airplane wing, near the tip. Ailerons control roll about the longitudinal axis.

Air Start

The act or instance of starting an aircraft’s engine while in flight, especially a jet engine after flameout.

Aircraft

A device that is used, or intended to be used, for flight.

Aircraft engine

An engine that is used or intended to be used for propelling aircraft. It includes turbosuperchargers, appurtenances, and accessories necessary for its functioning, but does not include propellers.

Aircraft Logbooks

Journals containing a record of total operating time, repairs, alterations or inspections performed, and all Airworthiness Directive (AD) notes complied with. A maintenance logbook should be kept for the airframe, each engine, and each propeller.

Aircraft Specifications

Documentation containing the pertinent specifications for aircraft certificated under the CARs.

Airfoil

An airfoil is any surface, such as a wing, propeller, rudder, or even a trim tab, which provides aerodynamic force when it interacts with a moving stream of air.

Airframe

The fuselage, booms, nacelles, cowlings, fairings, airfoil surfaces (including rotors but excluding propellers and rotating airfoils of engines), and landing gear of an aircraft and their accessories and controls.

Airplane

An engine-driven, fixed-wing aircraft heavier than air that is supported in flight by the dynamic reaction of air against its wings.

Airplane Flight Manual (AFM)

A document developed by the airplane manufacturer and approved by the Federal Aviation Administration (FAA). It is specific to a particular make and model airplane by serial number and it contains operating procedures and limitations.

Airplane Owner/ Information Manual

A document developed by the airplane manufacturer containing general information about the make and model of an airplane. The airplane owner’s manual is not FAA-approved and is not specific to a particular serial numbered airplane. This manual is not kept current, and therefore cannot be substituted for the AFM/POH.

Airworthiness

A condition in which the aircraft conforms to its type certificated design including supplemental type certificates, and field approved alterations. The aircraft must also be in a condition for safe flight as determined by annual, 100 hour, preflight and any other required inspections.

Airworthiness Certificate

A certificate issued by the FAA to all aircraft that have been proven to meet the minimum standards set down by the Code of Federal Regulations.

Airworthiness Directive

A regulatory notice sent out by the FAA to the registered owner of an aircraft informing the owner of a condition that prevents the aircraft from continuing to meet its conditions for airworthiness. Airworthiness Directives (AD notes) must be complied with within the required time limit, and the fact of compliance, the date of compliance, and the method of compliance must be recorded in the aircraft’s maintenance records.

Alternate Air

A device which opens, either automatically or manually, to allow induction airflow to continue should the primary induction air opening become blocked.

Alternate Static Source

A manual port that when opened allows the pitot static instruments to sense static pressure from an alternate location should the primary static port become blocked.

Alternate static source valve

A valve in the instrument static air system that supplies reference air pressure to the altimeter, airspeed indicator, and vertical speed indicator if the normal static pickup should become clogged or iced over.

Alternator/Generator

A device that uses engine power to generate electrical power.

Altimeter

A flight instrument that indicates altitude by sensing pressure changes.

Altitude Engine

A reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.

Angle Of Attack

The acute angle between the chord line of the airfoil and the direction of the relative wind.

Angle Of Incidence

The angle formed by the chord line of the wing and a line parallel to the longitudinal axis of the airplane.

Anhedral

A downward slant from root to tip of an aircraft’s wing or horizontal tail surface.

Annual Inspection

A complete inspection of an aircraft and engine, required by the Code of Federal Regulations, to be accomplished every 12 calendar months on all certificated aircraft. Only an A&P technician holding an Inspection Authorization can conduct an annual inspection.

Anti-ice

Preventing the accumulation of ice on an aircraft structure via a system designed for that purpose.

Anti-Icing

The prevention of the formation of ice on a surface. Ice may be prevented by using heat or by covering the surface with a chemical that prevents water from reaching the surface. Anti-icing should not be confused with deicing, which is the removal of ice after it has formed on the surface.

Antiservo tab

An adjustable tab attached to the trailing edge of a stabilator that moves in the same direction as the primary control. It is used to make the stabilator less sensitive.

Appliance

Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory, including communications equipment, that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine, or propeller.

Approved Type Certificate

A certificate of approval issued by the FAA for the design of an aircraft, engine, or propeller.

Arm

(GAMA) The horizontal distance from the reference datum to the center of gravity (CG) of an item. The algebraic sign is plus (+) if measured aft of the datum or to the right side of the center line when considering a lateral calculation. The algebraic sign is minus (-) if measured forward of the datum or the left side of the center line when considering a lateral calculation.

Aspect ratio

Span of a wing divided by its average chord.

Asymmetric thrust

Also known as P-factor. A tendency for an aircraft to yaw to the left due to the descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind.The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller.

Attitude

The position of an aircraft as determined by the relationship of its axes and a reference, usually the earth’s horizon.

Attitude Indicator

An instrument which uses an artificial horizon and miniature airplane to depict the position of the airplane in relation to the true horizon. The attitude indicator senses roll pitch, which is the up and down as well as movement of the airplane’s nose.

Autopilot

An automatic flight control system which keeps an aircraft in level flight or on a set course. Automatic pilots can be directed by the pilot, or they may be coupled to a radio navigation signal.

Axes Of An Aircraft

Three imaginary lines that pass through an aircraft’s center of gravity. The axes can be considered as imaginary axles around which the aircraft turns. The three axes pass through the center of gravity at 90°angles to each other. The axis from nose to tail is the longitudinal axis, the axis that passes from wingtip to wingtip is the lateral axis, and the axis that passes vertically through the center of gravity is the vertical axis.

Back Side Of The Power Curve

Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.

Balance tab

An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control. Sometimes referred to as a servo tab.

Balanced Laterally

Balanced in such a way that the wings tend to remain level.

Ballast

A weight installed or carried in an aircraft to move the center of gravity to a location within its allowable limits.

Balloon

The result of a too aggressive flare during landing causing the aircraft to climb.

Basic Empty Weight

(GAMA) Standard empty weight plus optional equipment.

Basic Empty Weight (GAMA)

Basic empty weight includes the standard empty weight plus optional and special equipment that has been installed.

Basic Operating Index

The moment of the airplane at its basic operating weight divided by the appropriate reduction factor.

Basic Operating Weight (BOW)

The empty weight of the aircraft plus the weight of the required crew, their baggage and other standard item such as meals and potable water.

Best Angle Of Climb (Vx)

The speed at which the aircraft will produce the most gain in altitude in a given distance.

Best Glide

The airspeed in which the aircraft glides the furthest for the least altitude lost when in non-powered flight.

Best Rate Of Climb (Vy)

The speed at which the aircraft will produce the most gain in altitude in the least amount of time.

Bilge Area

The lowest part of an aircraft structure in which water and contaminants collect.

Biplanes

Airplanes with two sets of wings.

Blade Face

The flat portion of a propeller blade, resembling the bottom portion of an airfoil.

Boost Pump

An electrically driven fuel pump, usually of the centrifugal type, located in one of the fuel tanks. It is used to provide fuel to the engine for starting and providing fuel pressure in the event of failure of the engine driven pump. It also pressurizes the fuel lines to prevent vapor lock.

Brake horsepower

The power delivered at the propeller shaft (main drive or main output) of an aircraft engine.

Buffeting

The beating of an aerodynamic structure or surface by unsteady flow, gusts, etc.; the irregular shaking or oscillation of a vehicle component owing to turbulent air or separated flow.

Bus Bar

An electrical power distribution point to which several circuits may be connected. It is often a solid metal strip having a number of terminals installed on it.

Bus Tie

A switch that connects two or more bus bars. It is usually used when one generator fails and power is lost to its bus. By closing the switch, the operating generator powers both busses.

Butt (or buttock) Line Zero

A line through the symmetrical center of an aircraft from nose to tail. It serves as the datum for measuring the arms used to determine the lateral CG. Lateral moments that cause the aircraft to rotate clockwise are positive (+) , and those that cause it to rotate counterclockwise are negative (-).

Cabin Pressurization

A condition where pressurized air is forced into the cabin simulating pressure conditions at a much lower altitude and increasing the aircraft occupants comfort.

Calibrated Airspeed (CAS)

Indicated airspeed corrected for installation error and instrument error. Although manufacturers attempt to keep airspeed errors to a minimum, it is not possible to eliminate all errors throughout the airspeed operating range. At certain airspeeds and with certain flap settings, the installation and instrument errors may total several knots. This error is generally greatest at low airspeeds. In the cruising and higher airspeed ranges, indicated airspeed and calibrated airspeed are approximately the same. Refer to the airspeed calibration chart to correct for possible airspeed errors.

Camber

The camber of an airfoil is the characteristic curve of its upper and lower surfaces. The upper camber is more pronounced, while the lower camber is comparatively flat. This causes the velocity of the airflow immediately above the wing to be much higher than that below the wing.

Cambered

CAMs

The manuals containing the certification rules under the Civil Air Regulations.

Canard

A horizontal surface mounted ahead of the main wing to provide longitudinal stability and control. It may be a fixed, movable, or variable geometry surface, with or without control surfaces.

Canard configuration

A configuration in which the span of the forward wings is substantially less than that of the main wing.

Cantilever

A wing designed to carry loads without external struts.

Carburetor

1. Pressure: A hydromechanical device employing a closed feed system from the fuel pump to the discharge nozzle. It meters fuel through fixed jets according to the mass airflow through the throttle body and discharges it under a positive pressure. Pressure carburetors are distinctly different from float-type carburetors, as they do not incorporate a vented float chamber or suction pickup from a discharge nozzle located in the venturi tube. 2. Float-type: Consists essentially of a main air passage through which the engine draws its supply of air, a mechanism to control the quantity of fuel discharged in relation to the flow of air, and a means of regulating the quantity of fuel/air mixture delivered to the engine cylinders.

Carburetor Ice

Ice that forms inside the carburetor due to the temperature drop caused by the vaporization of the fuel. Induction system icing is an operational hazard because it can cut off the flow of the fuel/air charge or vary the fuel/air ratio.

Center of Gravity (CG)

(GAMA) The point at which an airplane would balance if suspended. Its distance from the reference datum is determined by dividing the total moment by the total weight of the airplane. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. It may be expressed in percent of MAC (mean aerodynamic cord) or in inches from the reference Center of Lift. The location along the chord line of an airfoil at which all the lift forces produced by the airfoil are considered to be concentrated.

Center of gravity limits

The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.

Center of gravity range

The distance between the forward and aft CG limits indicated on pertinent airplane specifications.

Center of pressure

A point along the wing chord line where lift is considered to be concentrated. For this reason, the center of pressure is commonly referred to as the center of lift.

Center-Of-Gravity Limits

The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent airplane specifications.

Center-Of-Gravity Range

The distance between the forward and aft CG limits indicated on pertinent airplane specifications.

Centroid

The distance in inches aft of the datum of the center of a compartment or a fuel tank for weight and balance purposes.

CG

Center Of Gravity.

CG Arm

(GAMA) The arm obtained by adding the airplane’s individual moments and dividing the sum by the total weight.

CG Limits

(GAMA) The extreme center of gravity locations within which the aircraft must be operated at a given weight. These limits are indicated on pertinent FAA aircraft type certificate data sheets, specifications, or weight and balance records.

CG Limits Envelope

An enclosed area on a graph of the airplane loaded weight and the CG location. If lines drawn from the weight and CG cross within this envelope, the airplane is properly loaded.

CG Moment Envelope

An enclosed area on a graph of the airplane loaded weight and loaded moment. If lines drawn from the weight and loaded moment cross within this envelope, the airplane is properly loaded.

Chord

A straight-line distance across a wing from leading edge to trailing edge.

Chord Line

An imaginary straight line drawn through an airfoil from the leading edge to the trailing edge.

Circuit Breaker

A circuit-protecting device that opens the circuit in case of excess current flow. A circuit breakers differs from a fuse in that it can be reset without having to be replaced.

Climb Gradient

The ratio between distance traveled and altitude gained.

Coefficient Of Lift

See Lift Coefficient.

Coffin Corner

The flight regime where any increase in airspeed will induce high speed mach buffet and any decrease in airspeed will induce low speed mach buffet.

Combustion Chamber

The section of the engine into which fuel is injected and burned.

Complex Aircraft

An aircraft with retractable landing gear, flaps, and a controllable-pitch propeller, or is turbine powered.

Compression Ratio

1. In a reciprocating engine, the ratio of the volume of an engine cylinder with the piston at the bottom center to the volume with the piston at top center. 2. In a turbine engine, the ratio of the pressure of the air at the discharge to the pressure of air at the inlet.

Configuration

This is a general term, which normally refers to the position of the landing gear and flaps.

Consensus standard

For the purpose of certificating light-sport aircraft, an industry-developed consensus standard that applies to aircraft design, production, and airworthiness. It includes, but is not limited to, standards for aircraft design and performance, required equipment, manufacturer quality assurance systems, production acceptance test procedures, operating instructions, maintenance and inspection procedures, identification and recording of major repairs and major alterations, and continued airworthiness.

Constant Speed Propeller

A controllable pitch propeller whose pitch is automatically varied in flight by a governor to maintain a constant r.p.m. in spite of varying air loads.

Control pressures

The amount of physical exertion on the control column necessary to achieve the desired attitude.

Controllability

A measure of the response of an aircraft relative to the pilot’s flight control inputs.

Controllable Pitch Propeller

A propeller in which the blade angle can be changed during flight by a control in the cockpit.

Conventional Landing Gear

Landing gear employing a third rear-mounted wheel. These airplanes are also sometimes referred to as tailwheel airplanes.

Coordinated Flight

Application of all appropriate flight and power controls to prevent slipping or skidding in any flight condition.

Coupled ailerons and rudder

Rudder and ailerons are connected with interconnected springs in order to counteract adverse yaw. Can be overridden if it becomes necessary to slip the aircraft.

Cowl Flaps

Devices arranged around certain air-cooled engine cowlings which may be opened or closed to regulate the flow of air around the engine.

Crab

A flight condition in which the nose of the airplane is pointed into the wind a sufficient amount to counteract a crosswind and maintain a desired track over the ground.

Crazing

Small fractures in aircraft windshields and windows caused from being exposed to the ultraviolet rays of the sun and temperature extremes.

Critical Altitude

The maximum altitude under standard atmospheric conditions at which a turbocharged engine can produce its rated horsepower.

Critical Angle Of Attack

The angle of attack at which a wing stalls regardless of airspeed, flight attitude, or weight.

Critical Engine

The engine whose failure has the most adverse effect on directional control.

Current induction

An electrical current being induced into, or generated in, any conductor that is crossed by lines of flux from any magnet.

Current Limiter

A device that limits the generator output to a level within that rated by the generator manufacturer.

Datum (Reference Datum)

An imaginary vertical plane or line from which all measurements of moment arm are taken. The datum is established by the manufacturer. Once the datum has been selected, all moment arms the location of CG range are measured from this point.

Deicer Boots

Inflatable rubber boots attached to the leading edge of an airfoil. They can be sequentially inflated and deflated to break away ice that has formed over their surface.

Deicing

Removing ice after it has formed.

Delamination

The separation of layers.

Delta ∆

This symbol, ∆, means a change in something. ∆CG means a change in the center of gravity location.

Detonation

The sudden release of heat energy from fuel in an aircraft engine caused by the fuel-air mixture reaching its critical pressure and temperature. Detonation occurs as a violent explosion rather than a smooth burning process.

Differential Ailerons

Control surface rigged such that the aileron moving up moves a greater distance than the aileron moving down. The up aileron produces extra parasite drag to compensate for the additional induced drag caused by the down aileron. This balancing of the drag forces helps minimize adverse yaw.

Diffusion

Reducing the velocity of air causing the pressure to increase.

Dihedral

The positive acute angle between the lateral axis of an airplane and a line through the center of a wing or horizontal stabilizer. Dihedral contributes to the lateral stability of an airplane.

Directional Stability

Stability about the vertical axis of an aircraft, whereby an aircraft tends to return, on its own, to flight aligned with the relative wind when disturbed from that equilibrium state. The vertical tail is the primary contributor to directional stability, causing an airplane in flight to align with the relative wind.

Downwash

Air deflected perpendicular to the motion of the airfoil.

Drag

An aerodynamic force on a body acting parallel and opposite to the relative wind. The resistance of the atmosphere to the relative motion of an aircraft. Drag opposes thrust and limits the speed of the airplane.

Drag Curve

A visual representation of the amount of drag of an aircraft at various airspeeds.

Dutch Roll

A combination of rolling and yawing oscillations that normally occurs when the dihedral effects of an aircraft are more powerful than the directional stability. Usually dynamically stable but objectionable in an airplane because of the oscillatory nature.

Dynamic Hydroplaning

A condition that exists when landing on a surface with standing water deeper than the tread depth of the tires. When the brakes are applied, there is a possibility that the brake will lock up and the tire will ride on the surface of the water, much like a water ski. When the tires are hydroplaning, directional control and braking action are virtually impossible. An effective anti-skid system can minimize the effects of hydroplaning.

Dynamic Load

The actual weight of the aircraft multiplied by the load factor, or the increase in weight caused by acceleration.

Dynamic Stability

The property of an aircraft that causes it, when disturbed from straight-and level flight, to develop forces or moments that restore the original condition of straight and level.

EGT

Exhaust Gas Temperature.

Electrical Bus

A Bus Bar. An electrical power distribution point to which several circuits may be connected. It is often a solid metal strip having a number of terminals installed on it.

Electrohydraulic

Hydraulic control which is electrically actuated.

Elevator

The horizontal, movable primary control surface in the tail section, or empennage, of an airplane. The elevator is hinged to the trailing edge of the fixed horizontal stabilizer.

Empennage

The section of the airplane that consists of the vertical stabilizer, the horizontal stabilizer, and the associated control surfaces.

Empty Weight

The weight of the airframe, engines, all permanently installed equipment, and unusable fuel. Depending upon the part of the federal regulations under which the aircraft was certificated, either the undrainable oil or full reservoir of oil is included.

Empty-weight Center of Gravity (EWCG)

This is the center of gravity of the aircraft in the empty condition, containing only the items specified in the aircraft empty weight. This CG is an essential part of the weight and balance record of the aircraft.

Empty-weight Center of Gravity Range

The distance between the allowable forward and aft empty-weight CG limits.

Engine Pressure Ratio (EPR)

The ratio of turbine discharge pressure divided by compressor inlet pressure that is used as an indication of the amount of thrust being developed by a turbine engine.

Environmental Systems

In an aircraft, the systems, including the supplemental oxygen systems, air conditioning systems, heaters, and pressurization systems, which make it possible for an occupant to function at high altitude.

EPR

Engine Pressure Ratio.

Equilibrium

A condition that exists within a body when the sum of the moments of all of the forces acting on the body is equal to zero. In aerodynamics, equilibrium is when all opposing forces acting on an aircraft are balanced (steady, unaccelerated flight conditions).

Equipment List

A list of items approved by the FAA for installation in a particular aircraft. The list includes the name, part number, weight, and arm of the component. Installation or removal of an item in the equipment list is considered to be a minor alteration.

Exhaust

The rear opening of a turbine engine exhaust duct. The nozzle acts as an orifice, the size of which determines the density and velocity of the gases as they emerge from the engine.

Exhaust Gas Temperature (EGT)

The temperature of the exhaust gases as they leave the cylinders of a reciprocating engine or the turbine section of a turbine engine.

Exhaust Manifold

The part of the engine that collects exhaust gases leaving the cylinders.

Explosive decompression

A change in cabin pressure faster than the lungs can decompress. Lung damage is possible.

External load

A load that is carried, or extends, outside of the aircraft fuselage.

External-load attaching

Means the structural components used to attach an external load to an aircraft, including external-load containers, the backup structure at the attachment points, and any quick-release device used to jettison the external load.

Feathering Propeller (Feathered)

A controllable pitch propeller with a pitch range sufficient to allow the blades to be turned parallel to the line of flight to reduce drag and prevent further damage to an engine that has been shut down after a malfunction.

Fire resistant

(1) With respect to sheet or structural members, the capacity to withstand the heat associated with fire at least as well as aluminum alloy in dimensions appropriate for the purpose for which they are used; and
(2) With respect to fluid-carrying lines, fluid system parts, wiring, air ducts, fittings, and powerplant controls, the capacity to perform the intended functions under the heat and other conditions likely to occur when there is a fire at the place concerned.

Fireproof

(1) With respect to materials and parts used to confine fire in a designated fire zone, the capacity to withstand at least as well as steel in dimensions appropriate for the purpose for which they are used, the heat produced when there is a severe fire of extended duration in that zone; and
(2) With respect to other materials and parts, the capacity to withstand the heat associated with fire at least as well as steel in dimensions appropriate for the purpose for which they are used.

Fixed-Pitch Propellers

Propellers with fixed blade angles. Fixed-pitch propellers are designed as climb propellers, cruise propellers, or standard propellers.

Flame resistant

Not susceptible to combustion to the point of propagating a flame, beyond safe limits, after the ignition source is removed.

Flap extended speed

The highest speed permissible with wing flaps in a prescribed extended position.

Flaps

Hinged portion of the trailing edge between the ailerons and fuselage. In some aircraft, ailerons and flaps are interconnected to produce full-span “flaperons.” In either case, flaps change the lift and drag on the wing.

Flash resistant

Not susceptible to burning violently when ignited.

Flat Pitch

A propeller configuration when the blade chord is aligned with the direction of rotation.

Flight Idle

Engine speed, usually in the 70-80 percent range, for minimum flight thrust.

Force (F)

The energy applied to an object that attempts to cause the object to change its direction, speed, or motion. In aerodynamics, it is expressed as F, T (thrust), L (lift), W (weight), or D (drag), usually in pounds.

Form Drag

The part of parasite drag on a body resulting from the integrated effect of the static pressure acting normal to its surface resolved in the drag direction.

Forward wing

A forward lifting surface of a canard configuration or tandem-wing configuration airplane. The surface may be a fixed, movable, or variable geometry surface, with or without control surfaces.

Friction Drag

The part of parasitic drag on a body resulting from viscous shearing stresses over its wetted surface.

Frise-Type Aileron

Aileron having the nose portion projecting ahead of the hinge line. When the trailing edge of the aileron moves up, the nose projects below the wing’s lower surface and produces some parasite drag, decreasing the amount of adverse yaw.

Fuel Control Unit

The fuel-metering device used on a turbine engine that meters the proper quantity of fuel to be fed into the burners of the engine. It integrates the parameters of inlet air temperature, compressor speed, compressor discharge pressure, and exhaust gas temperature with the position of the cockpit power control lever.

Fuel Efficiency

Defined as the amount of fuel used to produce a specific thrust or horsepower divided by the total potential power contained in the same amount of fuel.

Fuel Heaters

A radiator-like device which has fuel passing through the core. A heat exchange occurs to keep the fuel temperature above the freezing point of water so that entrained water does not form ice crystals, which could block fuel flow.

Fuel Injection

A fuel metering system used on some aircraft reciprocating engines in which a constant flow of fuel is fed to injection nozzles in the heads of all cylinders just outside of the intake valve. It differs from sequential fuel injection in which a timed charge of high-pressure fuel is sprayed directly into the combustion chamber of the cylinder.

Fuel Load

The expendable part of the load of the airplane. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.

Fuel Tank Sump

A sampling port in the lowest part of the fuel tank that the pilot can utilize to check for contaminants in the fuel.

Fulcrum

The point about which a lever balances.

Fuselage

The section of the airplane that consists of the cabin and/or cockpit, containing seats for the occupants and the controls for the airplane.

Glide Ratio

The ratio between distance traveled and altitude lost during non-powered flight.

Glidepath

The path of an aircraft relative to the ground while approaching a landing.

Governing Range

The range of pitch a propeller governor can control during flight.

Governor

A control which limits the maximum rotational speed of a device.

Gross Weight

The total weight of a fully loaded aircraft including the fuel, oil, crew, passengers, and cargo.

Ground Adjustable Trim Tab

A metal trim tab on a control surface that is not adjustable in flight. Bent in one direction or another while on the ground to apply trim forces to the control surface.

Gyroscopic Precession

An inherent quality of rotating bodies, which causes an applied force to be manifested 90º in the direction of rotation from the point where the force is applied.

Hand Propping

Starting an engine by rotating the propeller by hand.

High Performance Aircraft

An aircraft with an engine of more than 200 horsepower.

Horsepower

The term, originated by inventor James Watt, means the amount of work a horse could do in one second. One horsepower equals 550 foot-pounds per second, or 33,000 foot-pounds per minute.

Hydraulics

The branch of science that deals with the transmission of power by incompressible fluids under pressure.

Hydroplaning

Impact Ice

Ice that forms on the wings and control surfaces or on the carburetor heat valve, the walls of the air scoop, or the carburetor units during flight. Impact ice collecting on the metering elements of the carburetor may upset fuel metering or stop carburetor fuel flow.

Inclinometer

An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.

Index Point

A location specified by the aircraft manufacturer from which arms used in weight and balance computations are measured. Arms measured from the index point are called index arms.

Induced Drag

That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed.

Induction icing

A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.

Induction Manifold

The part of the engine that distributes intake air to the cylinders.

Inertia

The opposition which a body offers to a change of motion.

Integral Fuel Tank

A portion of the aircraft structure, usually a wing, which is sealed off and used as a fuel tank. When a wing is used as an integral fuel tank, it is called a “wet wing.”

Intercooler

A device used to reduce the temperature of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.

Interference drag

Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.

Internal Combustion Engines

An engine that produces power as a result of expanding hot gases from the combustion of fuel and air within the engine itself. A steam engine where coal is burned to heat up water inside the engine is an example of an external combustion engine.

Inverter

An electrical device that changes DC to AC power.

Jet Powered Airplane

An aircraft powered by a turbojet or turbofan engine.

Landing gear extended speed

The maximum speed at which an aircraft can be safely flown with the landing gear extended.

Landing gear operating speed

The maximum speed at which the landing gear can be safely extended or retracted.

Landing Weight

The takeoff weight of an aircraft less the fuel burned and/or dumped en route.

Lateral Axis

An imaginary line passing through the center of gravity of an airplane and extending across the airplane from wingtip to wingtip.

Lateral Offset Moment

The moment, in lb-in, of a force that tends to rotate a helicopter about its longitudinal axis. The lateral offset moment is the product of the weight of the object and its distance from butt line zero. Lateral offset moments that tend to rotate the aircraft clockwise are positive, and those that tend to rotate it counterclockwise are negative.

Lateral Stability (Rolling)

The stability about the longitudinal axis of an aircraft. Rolling stability or the ability of an airplane to return to level flight due to a disturbance that causes one of the wings to drop.

Lead-Acid Battery

A commonly used secondary cell having lead as its negative plate and lead peroxide as its positive plate. Sulfuric acid and water serve as the electrolyte.

Leading Edge

The part of an airfoil that meets the airflow first.

Leading Edge Devices

High lift devices which are found on the leading edge of the airfoil. The most common types are fixed slots, movable slats, and leading edge flaps.

Leading Edge Flap

A portion of the leading edge of an airplane wing that folds downward to increase the camber, lift, and drag of the wing. The leading-edge flaps are extended for takeoffs and landings to increase the amount of aerodynamic lift that is produced at any given airspeed.

Lean of Peak

A mixture setting where the mixture was leaned from the full-rich fuel flow position to lean of peak exhaust gas temperature (EGT).

LEMAC

Leading Edge of the Mean Aerodynamic Chord.

Licensed Empty Weight

The empty weight that consists of the airframe, engine(s), unusable fuel, and undrainable oil plus standard and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization.

Lift

One of the four main forces acting on an aircraft. On a fixed-wing aircraft, an upward force created by the effect of airflow as it passes over and under the wing.

Lift Coefficient

A coefficient representing the lift of a given airfoil. Lift coefficient is obtained by dividing the lift by the free-stream dynamic pressure and the representative area under consideration.

Lift/Drag Ratio

The efficiency of an airfoil section. It is the ratio of the coefficient of lift to the coefficient of drag for any given angle of attack.

Limit Load Factor

Amount of stress, or load factor, that an aircraft can withstand before structural damage or failure occurs.

Load Cell

A component in an electronic weighing system that is placed between the jack and the jack pad on the aircraft. The load cell contains strain gauges whose resistance changes with the weight on the cell.

Load Factor

The ratio of the load supported by the airplane’s wings to the actual weight of the aircraft and its contents. Also referred to as G-loading.

Loading Graph

A graph of load weight and load moment indexes. Diagonal lines for each item relate the weight to the moment index without having to use mathematics.

Loading Schedule

A method for calculating and documenting aircraft weight and balance prior to taxiing, to ensure the aircraft will remain within all required weight and balance limitations throughout the flight.

Loadmeter

A type of ammeter installed between the generator output and the main bus in an aircraft electrical system.

Longitudinal Axis

An imaginary line through an aircraft from nose to tail, passing through its center of gravity.

Longitudinal Balance

Balance around the pitch, or lateral, axis.

Longitudinal stability (pitching)

Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement.

LOP

Lean of Peak

MAC

Mean Aerodynamic Chord.

Magnetic Compass

A device for determining direction measured from magnetic north.

Magneto

A self-contained, engine-driven unit that supplies electrical current to the spark plugs; completely independent of the airplane’s electrical system. Normally there are two magnetos per engine.

Magnus effect

Lifting force produced when a rotating cylinder produces a pressure differential. This is the same effect that makes a baseball curve or a golf ball slice.

Main Gear

The wheels of an aircraft’s landing gear that supports the major part of the aircraft’s weight.

Maintenance

Inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.

Major alteration

An alteration not listed in the aircraft, aircraft engine, or propeller specifications—
(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations.

Major repair

A repair:
(1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or
(2) That is not done according to accepted practices or cannot be done by elementary operations.

Maneuverability

Ability of an aircraft to change directions along a flightpath and withstand the stresses imposed upon it.

Maneuvering Speed (Va)

The maximum speed where full, abrupt control movement can be used without overstressing the airframe.

Manifold absolute pressure

The absolute pressure of the fuel/air mixture within the intake manifold, usually indicated in inches of mercury.

Manifold Pressure (MP)

The absolute pressure of the fuel/air mixture within the intake manifold, usually indicated in inches of mercury.

Maximum Allowable Takeoff Power

The maximum power an engine is allowed to develop for a limited period of time; usually about one minute.

Maximum Landing Weight

The greatest weight that an airplane normally is allowed to have at landing.

Maximum Ramp Weight

The total weight of a loaded aircraft, including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and runup operations. Ramp weight may also be referred to as taxi weight.

Maximum Takeoff Weight

(GAMA) Maximum weight approved for the start of the takeoff run.

Maximum Weight

The maximum authorized weight of the aircraft and all of its equipment as specified in the Type Certificate Data Sheets (TCDS) for the aircraft.

Maximum Zero Fuel Weight

The maximum authorized weight of an aircraft without fuel. This is the total weight for a particular flight less the fuel. It includes the aircraft and everything that will be carried on the flight except the weight of the fuel.

Mean aerodynamic chord (MAC)

The average distance from the leading edge to the trailing edge of the wing.

METO Horsepower (maximum except takeoff)

The maximum power allowed to be continuously produced by an engine. Takeoff power is usually limited to a given amount of time, such as 1 minute or 5 minutes.

Minimum Controllable Airspeed

An airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in an immediate stall.

Minimum drag

The point on the total drag curve where the lift-to-drag ratio is the greatest. At this speed, total drag is minimized.

Minimum Fuel

The amount of fuel necessary for one- half hour of operation at the rated maximum-continuous power setting of the engine, which, for weight and balance purposes, is 1/12 gallon per maximum-except-takeoff (METO) horse-power. It is the maximum amount of fuel that could be used in weight and balance computations when low fuel might adversely affect the most critical balance conditions. To determine the weight of the minimum fuel in pounds, divide the METO horsepower by two.

Minor alteration

An alteration other than a major alteration.

Minor repair

A repair other than a major repair.

Mixture

The ratio of fuel to air entering the engine’s cylinders.

Moment

The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (lb-in). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.

Moment Arm

The distance from a datum to the applied force.

Moment Index

The moment (weight times arm) divided by a reduction factor such as 100 or 1,000 to make the number smaller and reduce the chance of mathematical errors in computing the center of gravity.

Moment Limits vs Weight Envelope

An enclosed area on a graph of three parameters. The diagonal line representing the moment/100 crosses the horizontal line representing the weight at the vertical line representing the CG location in inches aft of the datum. When the lines cross inside the envelope, the aircraft is loaded within its weight and CG limits.

Monocoque

A shell-like fuselage design in which the stressed outer skin is used to support the majority of imposed stresses. Monocoque fuselage design may include bulkheads but not stringers.

Monoplanes

Airplanes with a single set of wings.

Movable Slat

A movable auxiliary airfoil on the leading edge of a wing. It is closed in normal flight but extends at high angles of attack. This allows air to continue flowing over the top of the wing and delays airflow separation.

Nacelle

A streamlined enclosure on an aircraft in which an engine is mounted. On multiengine propeller-driven airplanes, the nacelle is normally mounted on the leading edge of the wing.

Negative Static Stability

The initial tendency of an aircraft to continue away from the original state of equilibrium after being disturbed.

Net Weight

The weight of the aircraft less the weight of any chocks or other devices used to hold the aircraft on the scales.

Neutral Static Stability

The initial tendency of an aircraft to remain in a new condition after its equilibrium has been disturbed.

Nickel-Cadmium Battery (NiCad)

A battery made up of alkaline secondary cells. The positive plates are nickel hydroxide, the negative plates are cadmium hydroxide, and potassium hydroxide is used as the electrolyte.

Normal Category

An airplane that has a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for non-acrobatic operation.

Normalizing (Turbonormalizing)

A turbocharger that maintains sea level pressure in the induction manifold at altitude.

Octane

The rating system of aviation gasoline with regard to its anti-detonating qualities.

Overboost

A condition in which a reciprocating engine has exceeded the maximum manifold pressure allowed by the manufacturer. Can cause damage to engine components.

Overspeed

A condition in which an engine has produced more r.p.m. than the manufacturer recommends, or a condition in which the actual engine speed is higher than the desired engine speed as set on the propeller control.

Overtemp

A condition in which a device has reached a temperature above that approved by the manufacturer or any exhaust temperature that exceeds the maximum allowable for a given operating condition or time limit. Can cause internal damage to an engine.

Overtorque

A condition in which an engine has produced more torque (power) than the manufacturer recommends, or a condition in a turboprop or turboshaft engine where the engine power has exceeded the maximum allowable for a given operating condition or time limit. Can cause internal damage to an engine.

P-Factor

A tendency for an aircraft to yaw to the left due to the for descending propeller blade on the right producing more thrust than the ascending blade on the left. This occurs when the aircraft’s longitudinal axis is in a climbing attitude in relation to the relative wind. The P-factor would be to the right if the aircraft had a counterclockwise rotating propeller.

Parasite Drag

That part of total drag created by the design or shape of airplane parts. Parasite drag increases with an increase in airspeed.

Payload

(GAMA) Weight of occupants, cargo, and baggage.

Permanent Ballast (fixed ballast)

A weight permanently installed in an aircraft to bring its center of gravity into allowable limits. Permanent ballast is part of the aircraft empty weight.

Phugoid oscillations

Long-period oscillations of an aircraft around its lateral axis. It is a slow change in pitch accompanied by equally slow changes in airspeed. Angle of attack remains constant, and the pilot often corrects for phugoid oscillations without even being aware of them.

Pilot’s Operating Handbook (POH)

An FAA-approved document published by the airframe manufacturer that lists the operating conditions for a particular model of aircraft and its engine(s).

Piston Engine

A reciprocating engine.

Pivotal Altitude

A specific altitude at which, when an airplane turns at a given groundspeed, a projecting of the sighting reference line to a selected point on the ground will appear to pivot on that point.

Planform

The shape or form of a wing as viewed from above. It may be long and tapered, short and rectangular, or various other shapes.

Porpoising

Oscillating around the lateral axis of the aircraft during landing.

Position Lights

Lights on an aircraft consisting of a red light on the left wing, a green light on the right wing, and a white light on the tail. CFRs require that these lights be displayed in flight from sunset to sunrise.

Positive Static Stability

The initial tendency to return to a state of equilibrium when disturbed from that state.

Potable Water

Water carried in an aircraft for the purpose of drinking.

Power

Implies work rate or units of work per unit of time, and as such, it is a function of the speed at which the force is developed. The term “power required” is generally associated with reciprocating engines.

Power Distribution Bus

A Bus Bar. An electrical power distribution point to which several circuits may be connected. It is often a solid metal strip having a number of terminals installed on it.

Power Lever

The cockpit lever connected to the fuel control unit scheduling fuel flow to the combustion chambers of a turbine engine.

Powerplant

A complete engine and propeller combination with accessories.

Practical Slip Limit

The maximum slip an aircraft is capable of performing due to rudder travel limits.

Precession

The tilting or turning of a gyro in response to deflective forces causing slow drifting and erroneous indications in gyroscopic instruments.

Preignition

Ignition occurring in the cylinder before the time of normal ignition. Preignition is often caused by a local hot spot in the combustion chamber igniting the fuel/air mixture.

Preventive maintenance

Simple or minor preservative operations and the replacement of small standard parts not involving complex assembly operation as listed in 14 CFR part 43, appendix A. Certificated pilots may perform preventive maintenance on any aircraft that is owned or operated by them provided that the aircraft is not used in air carrier service.

Profile Drag

The total of the skin friction drag and form drag for a two-dimensional airfoil section.

Propeller

A device for propelling an aircraft that, when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane of rotation. It includes the control components normally supplied by its manufacturer.

Propeller Blade Angle

The angle between the propeller chord and the propeller plane of rotation.

Propeller Lever

The control on a free power turbine turboprop that controls propeller speed and the selection for propeller feathering.

Propeller Slipstream

The volume of air accelerated behind a propeller producing thrust.

Propeller Synchronization

A condition in which all of the propellers have their pitch automatically adjusted to maintain a constant r.p.m. among all of the engines of a multiengine aircraft.

Ramp Weight

The total weight of the aircraft while on the ramp. It differs from takeoff weight by the weight of the fuel that will be consumed in taxiing to the point of takeoff.

Reciprocating Engine

An engine that converts the heat energy from burning fuel into the reciprocating movement of the pistons. This movement is converted into a rotary motion by the connecting rods and crankshaft.

Reduction Factor

A number, usually 100 or 1,000 by which a moment is divided to produce a smaller number that is less likely to cause mathematical errors when computing the center of gravity.

Reduction Gear

The gear arrangement in an aircraft engine that allows the engine to turn at a faster speed than the propeller.

Reference Datum

(GAMA) An imaginary vertical plane from which all horizontal distances are measured for balance purpose.

Region Of Reverse Command

Flight regime in which flight at a higher airspeed requires a lower power setting and a lower airspeed requires a higher power setting in order to maintain altitude.

Registration Certificate

A State and Federal certificate that documents aircraft ownership.

Relative Wind

The direction of the airflow with respect to the wing. If a wing moves forward horizontally, the relative wind moves backward horizontally. Relative wind is parallel to and opposite the flightpath of the airplane.

Residual Fuel

Fuel that remains trapped in the system after draining the fuel from the aircraft with the aircraft in level flight attitude. The weight of this residual fuel is counted as part of the empty weight of the aircraft.

Rigging

The final adjustment and alignment of an aircraft and its flight control system that provides the proper aerodynamic characteristics.

Roll

The motion of the aircraft about the longitudinal axis. It is controlled by the ailerons.

Rudder

The movable primary control surface mounted on the trailing edge of the vertical fin of an airplane. Movement of the rudder rotates the airplane about its vertical axis.

Ruddervator

A pair of control surfaces on the tail of an aircraft arranged in the form of a V. These surfaces, when moved together by the control wheel, serve as elevators, and when moved differentially by the rudder pedals, serve as a rudder.

Safety (Squat) Switch

An electrical switch mounted on one of the landing gear struts. It is used to sense when the weight of the aircraft is on the wheels.

Sea level engine

A reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.

Semimonocoque

A fuselage design that includes a substructure of bulkheads and/or formers, along with stringers, to support flight loads and stresses imposed on the fuselage.

Service Ceiling

The maximum density altitude where the best rate-of-climb airspeed will produce a 100 feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.

Servo

A motor or other form of actuator which receives a small signal from the control device and exerts a large force to accomplish the desired work.

Servo Tab

An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.

Skin friction drag

Drag generated between air molecules and the solid surface of the aircraft.

Small airplane

An airplane of 12,500 pounds or less maximum certificated takeoff weight.

Special fuel consumption

The amount of fuel in pounds per hour consumed or required by an engine per brake horsepower or per pound of thrust.

Specific Fuel Consumption

Number of pounds of fuel consumed in 1 hour to produce 1 HP.

Speed Brakes

A control system that extends from the airplane structure into the airstream to produce drag and slow the airplane.

Speed Instability

A condition in the region of reverse command where a disturbance that causes the airspeed to decrease causes total drag to increase, which in turn, causes the airspeed to decrease further.

Spiral Instability

A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.

Spiraling Slipstream

The slipstream of a propeller-driven airplane rotates around the airplane. This slipstream strikes the left side of the vertical fin, causing the airplane to yaw slightly. Vertical stabilizer offset is sometimes used by aircraft designers to counteract this tendency.

Split Shaft Turbine Engine

See Free Power Turbine Engine.

Spoilers

High-drag devices that can be raised into the air flowing over an airfoil, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed. Spoilers are also used to shorten the ground roll after landing.

Stabilator

A single-piece horizontal tail surface on an airplane that pivots around a central hinge point. A stabilator serves the purposes of both the horizontal stabilizer and the elevator.

Stability

The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flightpath. It is primarily an airplane design characteristic.

Stall Strips

A spoiler attached to the inboard leading edge of some wings to cause the center section of the wing to stall before the tips. This assures lateral control throughout the stall.

Standard Empty Weight (GAMA)

This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane; including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.

Standard weights

Weights established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available.

Starter/Generator

A combined unit used on turbine engines. The device acts as a starter for rotating the engine, and after running, internal circuits are shifted to convert the device into a generator.

Static Load

The load imposed on an aircraft structure due to the weight of the aircraft and its contents.

Static Stability

The initial tendency an aircraft displays when disturbed from a state of equilibrium.

Station

A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.

Stress Risers

A scratch, groove, rivet hole, forging defect or other structural discontinuity that causes a concentration of stress.

Structural Station

This is a location in the aircraft, such as a bulkhead, which is identified by a number designating its distance in inches or percent MAC from the datum. The datum is, therefore, identified as station zero. The stations and arms are identical. An item located at station +50 would have an arm of 50 inches.

Subsonic

Speed below the speed of sound.

Suction relief valve

A relief valve in an instrument vacuum system required to maintain the correct low pressure inside the instrument case for the proper operation of the gyros.

Supercharger

An engine or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.

Supersonic

Speed above the speed of sound.

Supplemental Type Certificate (STC)

A certificate authorizing an alteration to an airframe, engine, or component that has been granted an Approved Type Certificate.

Swept Wing

A wing planform in which the tips of the wing are farther back than the wing root.

Synchro

A device used to transmit indications of angular movement or position from one location to another.

T-Tail

An aircraft with the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T.

Tailwheel Aircraft

See Conventional landing Gear.

Takeoff Weight

The weight of an aircraft just before beginning the takeoff roll. It is the ramp weight less the weight of the fuel burned during start and taxi.

Tandem wing configuration

A configuration having two wings of similar span, mounted in tandem.

Tare Weight

The weight of any chocks or devices that are used to hold an aircraft on the scales when it is weighed. The tare weight must be subtracted from the scale reading to get the net weight of the aircraft.

TEMAC

Trailing Edge of the Mean Aerodynamic Chord.

Temporary Ballast

Weights that can be carried in a cargo compartment of an aircraft to move the location of CG for a specific flight condition. Temporary ballast must be removed when the aircraft is weighed.

Throttle

The valve in a carburetor or fuel control unit that determines the amount of fuel-air mixture that is fed to the engine.

Thrust

The force which imparts a change in the velocity of a mass. This force is measured in pounds but has no element of time or rate. The term, thrust required, is generally associated with jet engines. A forward force which propels the airplane through the air.

Thrust Line

An imaginary line passing through the center of the propeller hub, perpendicular to the plane of the propeller rotation.

Tire Cord

Woven metal wire laminated into the tire to provide extra strength. A tire showing any cord must be replaced prior to any further flight.

Torching

The burning of fuel at the end of an exhaust pipe or stack of a reciprocating aircraft engine, the result of an excessive richness in the fuel air mixture.

Torque

(1) A resistance to turning or twisting.
(2) Forces that produce a twisting or rotating motion.
(3) In an airplane, the tendency of the aircraft to turn (roll) in the opposite direction of rotation of the engine and propeller.
(4) In helicopters with a single, main rotor system, the tendency of the helicopter to turn in the opposite direction of the main rotor rotation.

Torque Meter

An indicator used on some large reciprocating engines or on turboprop engines to indicate the amount of torque the engine is producing.

Torque Sensor

See Torque Meter.

Total drag

The sum of the parasite drag and induced drag.

Trailing Edge

The portion of the airfoil where the airflow over the upper surface rejoins the lower surface airflow.

Transponder

The airborne portion of the secondary surveillance radar system. The transponder emits a reply when queried by a radar facility.

Tricycle Gear

Landing gear employing a third wheel located on the nose of the aircraft.

Trim Tab

A small auxiliary hinged portion of a movable control surface that can be adjusted during flight to a position resulting in a balance of control forces.

True Airspeed (TAS)

Calibrated airspeed corrected for altitude and nonstandard temperature. Because air density decreases with an increase in altitude, an airplane has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure. Therefore, for a given calibrated airspeed, true airspeed increases as altitude increases; or for a given true airspeed, calibrated airspeed decreases as altitude increases.

Truss

A fuselage design made up of supporting structural members that resist deformation by applied loads. The truss-type fuselage is constructed of steel or aluminum tubing. Strength and rigidity is achieved by welding the tubing together into a series of triangular shapes, called trusses.

TSO

Technical Standard Order

Turbocharger

An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system.

Turbulence

An occurrence in which a flow of fluid is unsteady.

Type Certificate Data Sheets (TCDS)

The official specifications issued by the FAA for an aircraft, engine, or propeller.

Ultimate load factor

In stress analysis, the load that causes physical breakdown in an aircraft or aircraft component during a strength test, or the load that according to computations, should cause such a breakdown.

Undrainable Oil

Oil that does not drain from an engine lubricating system when the aircraft is in the normal ground attitude and the drain valve is left open. The weight of the undrainable oil is part of the empty weight of the aircraft.

Unusable Fuel

Fuel that cannot be consumed by the engine. This fuel is considered part of the empty weight of the aircraft.

Usable Fuel

(GAMA) Fuel available for flight planning.

Useful Load

The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only.

Utility Category

An airplane that has a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for limited acrobatic operation.

V-Bars

The flight director displays on the attitude indicator that provide control guidance to the pilot.

V-G Diagram

A chart that relates velocity to load factor. It is valid only for a specific weight, configuration, and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds.

V-Speeds

Designated speeds for a specific flight condition.

V-Tail

A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers.

Va

The design maneuvering speed. This is the “rough air” speed and the maximum speed for abrupt maneuvers. If during flight, rough air or severe turbulence is encountered, reduce the airspeed to maneuvering speed or less to minimize stress on the airplane structure. It is important to consider weight when referencing this speed. For example, VA may be 100 knots when an airplane is heavily loaded, but only 90 knots when the load is light.

Vapor lock

A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporise due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude.

Vector

A force vector is a graphic representation of a force and shows both the magnitude and direction of the force.

Velocity

The speed or rate of movement in a certain direction.

Vertical Axis

An imaginary line passing vertically through the center of gravity of an aircraft. The vertical axis is called the z-axis or the yaw axis.

Vertical Stability

Stability about an aircraft’s vertical axis. Also called yawing or directional stability.

Vfe

The maximum speed with the flaps extended. The upper limit of the white arc.

Vfo

The maximum speed that the flaps can be extended or retracted.

Vle

Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended.

Vlo

Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear.

Vlof

Lift-off speed. The speed at which the aircraft departs the runway during takeoff.

Vmd

Minimum drag speed.

Vmo

Maximum operating speed expressed in knots.

Vne

Never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator.

Vno

Maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc.

Vp

Minimum dynamic hydroplaning speed. The minimum speed required to start dynamic hydroplaning.

Vr

Rotation speed. The speed that the pilot begins rotating the aircraft prior to lift-off.

Vs1

Stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc.

Vso

Stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc.

Vx

Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle.

Vy

Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time.

Waste Gate

A controllable valve in the tailpipe of an aircraft reciprocating engine equipped with a turbocharger. The valve is controlled to vary the amount of exhaust gases forced through the turbocharger turbine.

Weight

A measure of the heaviness of an object. The force by which a body is attracted toward the center of the Earth (or another celestial body) by gravity. Weight is equal to the mass of the body times the local value of gravitational acceleration. One of the four main forces acting on an aircraft. Equivalent to the actual weight of the aircraft. It acts downward through the aircraft’s center of gravity toward the center of the Earth. Weight opposes lift.

Weight And Balance

The aircraft is said to be in weight and balance when the gross weight of the aircraft is under the max gross weight, and the center of gravity is within limits and will remain in limits for the duration of the flight.

Windmilling

When the air moving through a propeller creates the rotational energy.

Wing

Airfoil attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight.

Wing Area

The total surface of the wing (square feet), which includes control surfaces and may include wing area covered by the fuselage (main body of the airplane), and engine nacelles.

Wing Chord

A straight-line distance across a wing from leading edge to trailing edge.

Wing Span

The maximum distance from wingtip to wingtip.

Wing Tank Liner

A liner for aircraft fuel tanks which limits the amount of fuel that can be spilled in the event of a crash.

Wing Twist

A design feature incorporated into some wings to improve aileron control effectiveness at high angles of attack during an approach to a stall.

Winglet or tip fin

An out-of-plane surface extending from a lifting surface. The surface may or may not have control surfaces.

Wingtip Vortices

The rapidly rotating air that spills over an airplane’s wings during flight. The intensity of the turbulence depends on the airplane’s weight, speed, and configuration. It is also referred to as wake turbulence. Vortices from heavy aircraft may be extremely hazardous to small aircraft.

Yaw

Rotation about the vertical axis of an aircraft.

Yaw String

A string on the nose or windshield of an aircraft in view of the pilot that indicates any slipping or skidding of the aircraft.

Zero Fuel Weight

The weight of the aircraft to include all useful load except fuel.

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