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Those not familiar with aircraft design or operation may not understand some of the terminology used within this site. We hope that this section, which defines some common terms and symbols, will be useful.


Symbol Description Units Definition
AIAA American Institute of Aeronautics & Astronautics - -
AN/APG Unknown - Designation for radar systems
c Chord length ft Characteristic length of an airfoil.
C D Coefficient of drag - Measure of the total drag of the aircraft
C D0 Parasite drag coefficient - Measure of the drag due to the aircraft shape
C Di Induced drag coefficient - Measure of the drag caused by lift
CEP Circular Error Probable - Defines how likely a bomb is to reach its target
CG Center of Gravity ft Point where the aircraft is balanced
C L Coefficient of lift - Measure of the lift produced by the aircraft
C M Pitching moment coefficient - Measure of the pitching moment about the aerodynamic center
D Drag lb Force pushing against aircraft motion
DGPS Differential Global Positioning System - System allowing precise navigation and position data anywhere on Earth
EW Electronic Warfare - -
FBW Fly-by-wire - Flight surfaces controlled electronically rather than mechanically
FLIR Forward Looking Infrared - System using infrared (heat) sensors to image an area
g Acceleration due to gravity or "g's" ft/s Defines how much load a structure can take before failing
GBU Guided Bomb Unit - Bomb guided by advanced targeting system
GPS Global Positioning System - see DGPS
GTOW Gross Takeoff Weight lb Weight of aircraft at takeoff including fuel and payload
IFF Identification Friend or Foe
System used to identify friendly or enemy aircraft
IMU Inertial Measurement Unit - -
INS Inertial Navigation System - Very accurate navigation device
IRS Infrared Signature - Measure of the heat signature of an object which can be viewed with IR sensors
JDAM Joint Direct Attack Munitions - Second generation of advanced bombs
KEAS Knots equivalent airspeed knots Ground equivalent airspeed
L Lift lb Upward force on aircraft opposing gravity
LE Leading edge - Forward surface of wing
M Mach number - Multiple of the speed of sound at a given altitude
m Meter - -
M cr Critical Mach number - Mach number at which shocks begin to form
n Load factor g Number of g's experienced by the aircraft
NM Nautical mile - Standard distance measurement used in aviation, equals 6,280 ft
OEI One Engine Inoperative - -
R/C Rate of climb ft/min Rate at which altitude is gained
RAM Radar Absorbant Materials - Advanced materials which absorb radar waves
RCS Radar Cross Section - Measure of how much radar a shape reflects
RFP Request for Proposal - Industry term indicating a need for a design
SFC Specific Fuel Consumption lbmass fuel / hr / lb force thrust Measure of the fuel needed per pound of thrust, or a measure of fuel efficiency
S ref Reference area ft Measure of wing area used to determine aerodynamic characteristics
T Thrust lb Force opposing drag which propels aircraft forward
t/c Thickness to chord ratio - Ratio of airfoil thickness to chord (length)
UCAV Uninhabited Combat Aerial Vehicle - Politically correct term for new class of unmanned combat aircraft
V Freestream velocity ft/s The speed of the air flowing past the aircraft
V A Corner or maneuvering speed ft/s or KEAS Minimum speed at which aircraft can maneuver without stalling
V C Maximum level cruise speed at sea level ft/s or KEAS Maximum level speed at which aircraft can fly
V D Design dive speed ft/s or KEAS Maximum speed aircraft can reach in a dive
VHF Very High Frequency - Radio band used for communications
V S Stall speed
ft/s or KEAS
Speed at which the wing will stall (i.e. lose lift)

Other Terminology:

  • afterburning: Process of burning fuel in a pipe aft of the turbine in a jet engine to increase thrust and speed.

  • aileron: Control surface located on the outboard section of the wings that deflect up or down to increase or decrease the lift produced by each wing and produce a rolling motion.

  • airfoil: Shape defined by the cross-section of wing or aero surface.

  • angle of attack: Angle at which the airstream meets the wing.

  • aspect ratio: Ratio of the square of the wingspan to the wing reference area.

  • avionics: Aviation electronics.

  • camber: The curvature of an airfoil or wing as viewed from the side.

  • ceiling: A maximum altitude.

  • egress: Exit.

  • flap: Control surface located on the inner portion of a wing that extends outward and deflects downward to increase the camber and lift of the wing.

  • ingress: Entrance.

  • knots: Measure of velocity in nautical miles per hour.

  • longerons: Fuselage structural members.

  • low observables: Materials designed to make an aircraft harder to detect by radar, IR, or other sensors.

  • pitch: Up and down motion of the aircraft nose.

  • planform: A two-dimensional aircraft or wing shape as viewed from above.

  • range: Maximum distance aircraft can travel without refueling.

  • roll: Up and down motion of wing tips.

  • rudder: Control surface located on the vertical tail that defects from side to side to change the sideforce on the aircraft and cause the nose to turn right or left.

  • sawtooth: Notch in the leading or trailing edge of a wing.

  • signature: Radar/IR/electromagnetic "fingerprint" left by an aircraft.

  • stall: As the wing angle of attack increases, the wing generates more lift until a maximum is reached. After this point, the wing is said to stall because it rapidly loses lift.

  • sweepback: Angle of wing inclination with respect to the fuselage.

  • thrust vectoring: System that deflects the engine thrust in different directions to make the aircraft more maneverable.

  • turbofan: Gas turbine engine in which a large diameter fan in a short duct generates thrust.

  • turbojet: Gas turbine engine in which the exhaust gases generate thrust.

  • turboprop: Gas turbine engine in which exhaust gases are used to turn a propeller.

  • yaw: Side to side motion of aircraft nose.

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