Private Pilot Ground School · Reference
The course vocabulary, in the FAA's own terms. Grows with each lesson. Print it and keep it in your flight bag.
Definitions follow the PHAK (FAA-H-8083-25C) glossary.
| Term | Definition |
|---|---|
| Fuselage | The central body of the airplane. It houses the cabin, and the wings, empennage, landing gear, and powerplant all attach to it. |
| Wing | The surface that produces lift. High-wing airplanes like the Cessna 172 mount it above the cabin, braced by struts. |
| Wing strut | The brace running from the lower fuselage to the underside of each wing, carrying part of the wing's load. |
| Empennage | The entire tail group: vertical stabilizer, rudder, horizontal stabilizer, and elevator. |
| Vertical stabilizer | The fixed upright fin on the tail. It keeps the nose pointed into the relative wind. The rudder hinges to its trailing edge. |
| Rudder | The movable surface hinged to the vertical stabilizer. It yaws the nose left and right. |
| Horizontal stabilizer | The fixed horizontal surface on the tail. The elevator hinges to its trailing edge. |
| Elevator | The movable surface hinged to the horizontal stabilizer. It pitches the nose up and down. |
| Aileron | The movable surface on the outboard trailing edge of each wing. The pair deflects in opposite directions to roll the airplane. |
| Flap | The movable surface on the inboard trailing edge of each wing. Flaps extend downward together to add lift and drag for slower, steeper approaches. |
| Landing gear | The wheels and their supporting structure. Two main wheels plus a nose wheel form tricycle gear. |
| Powerplant | The engine and propeller as a unit. |
| Propeller | The rotating airfoil driven by the engine. It converts engine power into thrust. |
| Cowling | The removable cover around the engine. It streamlines the nose and directs cooling air over the engine. |
| Spinner | The cone-shaped fairing over the propeller hub. |
| Yoke | The control wheel. Turning it deflects the ailerons; pushing and pulling it deflects the elevator. |
| Rudder pedals | Foot controls that deflect the rudder in flight and steer the nose wheel on the ground. |
| Toe brakes | Brakes on the main wheels, applied by pressing the tops of the rudder pedals. Ground use only. |
| Throttle | The black engine-power knob. In for more power, out for less. |
| Mixture control | The red knob that sets the engine's fuel-to-air ratio. Full in is rich; pulled all the way out shuts the engine down. |
| Trim tab | A small hinged tab on the elevator's trailing edge, set by the trim wheel. It holds the elevator in position so the pilot can fly without constant control pressure. |
| Semi-monocoque | Fuselage construction using frames and stringers under a stressed skin, with the skin carrying much of the load. The standard for modern trainers. |
| Truss | Fuselage construction using a welded frame of steel tubes, covered by fabric or thin metal that carries little load. |
| Spar | The main beam inside a wing, running from fuselage toward the tip and carrying most of the wing's bending load. |
| Rib | A cross-sectional former inside the wing that gives it its curved airfoil shape. |
| Cantilever wing | A wing supported entirely by its internal structure, with no external strut. |
| Tricycle gear | Two main wheels plus a steerable nose wheel. The standard trainer arrangement. |
| Conventional gear | Two main wheels plus a tail wheel; a "taildragger." Requires specific training and an endorsement. |
| Firewall | The fire-resistant bulkhead separating the engine compartment from the cabin. |
| Master switch | The red split rocker (BAT/ALT) that powers the electrical system: lights, radios, gauges, and the flap motor on a 172. |
| Ignition switch | The key switch with positions OFF, R, L, BOTH, and START. It selects which magnetos fire and engages the starter. |
| Magneto | An engine-driven generator that produces ignition spark independently of the battery. Airplane engines carry two. |
| Fuel selector | The valve selecting which tank feeds the engine. On a 172: LEFT, RIGHT, or BOTH, with BOTH the normal position. |
| Carburetor heat | A control on carbureted engines that routes warm air to the carburetor to prevent or clear carburetor ice. |
| Term | Definition |
|---|---|
| Lift | The upward aerodynamic force produced as air flows around the wing. It acts perpendicular to the relative wind and opposes weight. |
| Weight | The combined load of the airplane, crew, fuel, and cargo. It acts downward toward the center of the earth, through the center of gravity, and opposes lift. |
| Thrust | The forward force produced by the engine and propeller. It acts parallel to the longitudinal axis and opposes drag. |
| Drag | The rearward force that resists the airplane's movement through the air. It acts parallel to the relative wind and opposes thrust. |
| Relative wind | The direction of airflow with respect to the wing. It is always parallel to, and opposite, the airplane's flight path. |
| Angle of attack (AOA) | The angle between the wing's chord line and the relative wind. The pilot's primary control over how much lift the wing makes at a given speed. |
| Chord line | An imaginary straight line from the leading edge to the trailing edge of the wing's cross section (the airfoil). |
| Airfoil | The cross-sectional shape of a wing: rounded leading edge, sharp trailing edge, usually more curved on top. Any surface with this shape produces lift when air flows around it. |
| Leading edge | The rounded front edge of the airfoil, the first part to meet the oncoming air. |
| Trailing edge | The sharp rear edge of the airfoil, where the upper and lower airflows leave the wing. |
| Camber | The curvature of an airfoil, measured by how far the mean camber line bows away from the chord line. More camber generally means more lift. |
| Downwash | The downward deflection of the airflow leaving a lifting wing. Newton's third law pairs it with the upward force on the wing. |
| Lift coefficient (CL) | The number in the lift equation that captures the airfoil's shape and angle of attack. It rises with AOA until the critical angle, then decreases sharply at the stall. |
| Venturi | A tube with a constriction in the middle. Air speeds up and its pressure drops in the constriction, the cleanest demonstration of Bernoulli's principle. |
| Upwash | The airflow diverted upward at the leading edge, flowing over the wing's upper surface. |
| Center of pressure | The single point through which the total lift force is treated as acting. It moves forward as angle of attack increases and aft as it decreases. |
| Critical angle of attack | The angle of attack where the coefficient of lift peaks (CLmax). Exceed it and the airflow separates from the upper surface: the stall. It is the same angle regardless of airspeed, attitude, or weight. |
| Aspect ratio | Wingspan divided by average chord. Higher aspect ratio means more lift for the same drag; gliders run 10 to 30, trainers 6 to 10. |
| Planform | The shape of the wing viewed from above: elliptical, rectangular, tapered, or a blend. Planform affects efficiency and where the stall begins. |
| Steady (unaccelerated) flight | Flight at constant airspeed and direction, in which the opposing forces sum to zero: lift equals weight and thrust equals drag. |
| Parasite drag | All drag not associated with producing lift: the cost of pushing the airplane through the air. It has three types (form, interference, skin friction) and grows with the square of airspeed. |
| Form drag | The parasite drag due to the airplane's shape and the airflow around it. Streamlining, such as fairings and wheel pants, reduces it. |
| Interference drag | The parasite drag created where two airstreams meet, as at the wing root. Worst at perpendicular junctions; fairings ease it. |
| Skin friction drag | The parasite drag of air rubbing along the airplane's surface. Flush rivets, smooth finishes, and a clean, waxed skin reduce it. |
| Induced drag | The drag that is a byproduct of producing lift. Wingtip vortices tilt the local relative wind downward, leaning the lift vector aft; the rearward component is induced drag. It varies inversely with the square of airspeed, so it dominates in slow flight. |
| Wingtip vortices | The rotating coils of air trailing each wingtip, formed as the pressure difference drives air from below the wing around the tip toward the low pressure above. They cause induced drag and, behind heavy aircraft, hazardous wake turbulence. |
| Lift-to-drag ratio (L/D) | The lift produced compared to the drag it costs, a measure of efficiency. Its peak, L/Dmax, occurs at one angle of attack, where total drag is minimum; best glide speed flies the wing there. |
| Ground effect | The reduction in induced drag within about one wingspan of the surface, where the ground restricts the downwash and wingtip vortices. It makes airplanes float on landing and can let them lift off before they can climb. |
| Stall | The rapid loss of lift when the wing exceeds its critical angle of attack and the airflow separates from the upper surface. It depends on angle, not on any particular airspeed. |
| Stall speed (VS) | The airspeed at which, in a given weight and configuration, the wing reaches its critical angle of attack in steady flight. It rises with weight and load factor and falls with flaps extended. |
| Accelerated stall | A stall that occurs at a higher-than-normal airspeed because increased load factor, as in a steep or abrupt turn, drives the wing to the critical angle sooner. |
| Load factor | The ratio of the lift the wings produce to the airplane's weight, expressed in Gs. It is 1G in steady level flight and rises with bank and abrupt maneuvering. Stall speed increases with the square root of the load factor. |
| Angle of incidence | The angle at which the wing is mounted to the fuselage, between the wing chord line and the airplane's longitudinal axis. It is built in by the designer, unlike angle of attack, which changes in flight. |
| Washout | A built-in twist that sets the wing root at a higher angle of incidence than the tip, so the root reaches the critical angle and stalls first, preserving aileron control. |
| Stall strip | A small metal strip on the inboard leading edge that trips the airflow at high angle of attack, making the wing root stall before the tip. |
| Spin | An aggravated stall with yaw that produces autorotation: the airplane descends rapidly in a corkscrew while rotating about a vertical axis. Both wings are stalled, one more deeply than the other. |
| Autorotation | The self-sustaining rotation of a spin, driven by one wing being more deeply stalled, and so producing less lift and more drag, than the other. |
| Incipient spin | The first phase of a spin, roughly the first turn or two, before the rotation stabilizes. Most inadvertent spins are stopped here. |
| Developed spin | The phase in which a spin's rotation rate, airspeed, and vertical descent have settled and hold roughly steady. |
| Cross-control stall | A stall entered with the controls crossed, aileron one way and rudder the other, as in a skidding turn. It readily drops a wing into a spin and is the classic base-to-final accident. |
| Center of gravity (CG) | The point through which the airplane's entire weight is treated as acting: its balance point. A body free to rotate always turns about its CG, and loading shifts the CG. |
| Stability | The airplane's built-in tendency to return to steady flight after a disturbance. It is mostly a design characteristic, described in static and dynamic parts. |
| Static stability | The airplane's initial tendency the instant it is disturbed: positive (returns toward the original condition), neutral (stays in the new one), or negative (continues away). |
| Dynamic stability | The airplane's response over time as it oscillates around its original state: positive (oscillations damp out), neutral (they hold steady), or negative (they grow). |
| Longitudinal axis | The imaginary line running nose to tail through the CG. Motion about it is roll. |
| Lateral axis | The imaginary line running wingtip to wingtip through the CG. Motion about it is pitch. |
| Vertical axis | The imaginary line running straight up and down through the CG. Motion about it is yaw. |
| Longitudinal stability | Stability in pitch, about the lateral axis. It depends on the CG position relative to the wing's center of lift. |
| Lateral stability | Stability in roll, about the longitudinal axis: the tendency to return to wings-level. Dihedral, keel effect, and sweepback provide it. |
| Directional stability | Stability in yaw, about the vertical axis: the tendency to weathervane the nose into the relative wind. The vertical fin and aft fuselage provide it. |
| Dihedral | The upward angle of the wings seen from the front. It provides lateral stability: after a roll, the resulting sideslip raises the angle of attack on the lower wing and rolls the airplane back to level. |
| Keel effect | The lateral stability a high-wing airplane gets from carrying its weight below the wing, so the fuselage swings back to level like a pendulum. |
| Dutch roll | A combined rolling and yawing oscillation that appears when lateral stability is stronger than directional stability. Unpleasant enough that designers avoid it, favoring mild spiral instability instead. |
| Spiral instability | The tendency, when directional stability is stronger than lateral, for an uncorrected bank to slowly tighten into a descending spiral. It develops gradually and, ignored, can wind into a spiral dive. |
| Limit load factor | The most G an airplane can carry without permanent structural deformation. Beyond it lies the ultimate load, where the structure fails; certification requires a 50 percent margin between the two. |
| Maneuvering speed (VA) | The speed below which a full, abrupt deflection of a single control stalls the wing before the load factor can exceed the limit load. It is lower at lighter weights and does not protect against repeated or combined control inputs. |
| Vg diagram | A chart of the airplane's flight envelope, load factor against airspeed. Curved lines mark the stall limit, horizontal lines the limit load factors, and the right edge the never-exceed speed; safe flight stays inside the enclosed area. |
| Never-exceed speed (VNE) | The redline airspeed beyond which flutter or structural failure can occur. It is the right edge of the Vg diagram. |
| Rate of turn | How fast the airplane's heading changes, in degrees per second. For a given airspeed it increases with bank angle. |
| Radius of turn | The size of the circle the airplane traces in a turn. For a given airspeed it shrinks as bank increases, and for a given bank it grows as airspeed increases. |
| Standard-rate turn | A turn at 3 degrees per second, which completes a 360-degree turn in two minutes. Holding it requires more bank at higher airspeed. |
| Slipstream | The column of air the propeller accelerates rearward, which washes over the fuselage and tail. Because the blades rotate as they push, it leaves the propeller with a rotational twist. |
| Torque reaction | The equal and opposite reaction to the engine turning the propeller. With a clockwise propeller it is a left roll about the longitudinal axis, one of the four left-turning tendencies. |
| Spiraling slipstream | The corkscrew rotation of the propeller slipstream, which wraps around the fuselage and strikes the left side of the vertical fin, yawing the nose left. Strongest at high power and low airspeed. |
| Gyroscopic precession | The property of a spinning disc by which a force applied to its rim takes effect 90 degrees around the rim, in the direction of rotation. Pitching the propeller disc produces a yaw. |
| P-factor | Asymmetric propeller loading at high angle of attack: the descending blade meets the air at a greater angle and speed than the ascending blade, making more thrust and yawing the nose left. Also called asymmetric loading. |
| Term | Definition |
|---|---|
| Reciprocating engine | An engine that converts the back-and-forth motion of pistons in cylinders into rotation of a crankshaft; the standard light-airplane powerplant. |
| Four-stroke cycle | The intake, compression, power, exhaust sequence each cylinder repeats, yielding one power stroke per two crankshaft revolutions. |
| Fixed-pitch propeller | A propeller whose blade angle is set at manufacture; a single compromise between climb and cruise performance. Its power instrument is the tachometer. |
| Constant-speed propeller | A propeller whose governor adjusts blade angle in flight to hold a selected RPM, keeping the engine at an efficient speed. |
| Blade angle | The angle between a propeller blade's chord line and its plane of rotation, decreasing from hub to tip so each station meets the air at a useful angle of attack. |
| Tachometer | The gauge showing crankshaft speed in RPM; on a fixed-pitch installation, the power instrument. |
| Manifold pressure gauge | The gauge showing the pressure of the fuel-air mixture in the intake manifold; the power-setting instrument on constant-speed installations. |
| Carburetor | The induction device that meters fuel into the intake air using the pressure drop in a venturi. |
| Carburetor ice | Ice formed inside the carburetor by fuel vaporization and venturi cooling; most likely below about 70 degrees F in humid air, but possible at outside temperatures as high as 100 degrees F. |
| Fuel injection | An induction system that meters fuel directly to each cylinder's intake port, eliminating carburetor ice and evening the mixture across cylinders. |
| Detonation | Uncontrolled, explosive combustion of the fuel-air charge caused by excessive heat, pressure, or fuel of too low a grade. |
| Preignition | Ignition of the fuel-air charge before the spark, by a hot spot such as a carbon deposit in the cylinder. |