Airfoil — The shape of the wing, as seen from the end . The three main airfoil types are flat-bottom, semi-symmetrical and symmetrical.

ARF — (Almost-Ready-To-Fly) —An airplane which is largely prebuilt and is usually covered at the factory. May also include an engine or motor.

BHP — Brake Horsepower. A term used to describe an engine’s ability to produce power under controlled circumstances. Commonly used with an RPM measurement to indicate conditions, such as “1.24 BHP @ 13,000 RPM.”

Control Surface — A movable surface on a plane designed to change the plane’s direction. May be used alone, or in combination. See aileron, flaps,rudder, elevator.

Dihedral — The upward angle of the wings, as seen from the nose. Dihedral enhances stability. Trainers tend to have high dihedral, but aerobats have little or none.

Displacement — Refers to the volume of space a piston displaces, and implies an engine’s ability to produce thrust. It may be measured in cubic inches (cu. in) or cubic centimeters (cc), although neither unit may appear. The most popular displacement range in the U.S.A. is .40-size (that is, engines with a displacement of around 0.40 cu. in). However, displacements can range from as little as .049 (for 1/2A kits) up to 7.32 cu. in. for some gas engines.

Elevator — A hinged control surface connected to the back (trailing) edge of the horizontal stabilizer. Moving the elevator makes the plane climb or dive.

Engine — A mechanical device that provides flight power (thrust) by means of internal combustion. The two main types of engines in R/C are the gasoline engine (which burns a gasoline/oil mix) and the more common glow engine (one that burns a nitromethane fuel). Glow types include 2-stroke and 4-stroke engines.

Fin — A slang term for the Vertical Stabilizer.

Finishing — The final stage of building, in which covering and/or paint and trim are applied.

Fixed (Landing) Gear — Landing gear that cannot be moved and remains in take-off/landing position throughout flight. See also Retractable Landing Gear.

Flap — The control surface on a wing closest to the fuselage. Moves up or down, to increase lift or drag.

Flat-Bottom — A wing airfoil that features a flat underside. Typical in trainer airplanes.

Four-Stroke (4-Stroke) Engine — An engine in which the piston travels up and down twice to achieve combustion. Produces more torque (power) than 2-stroke engines of similar size, as well as a more “scale” sound, greater economy and the ability to swing bigger props. Less common than 2-stroke engines, but more often used in large- or giant-scale airplanes. Where engine requirements for a kit are listed, 4-stroke engines are usually the second range listed and marked as such. See also Two-Stroke Engine.

Fuel Tank — The container that holds a plane’s fuel supply.

Fuselage — The long, narrow body of a plane.

Glow Fuel — An alcohol-based fuel which includes nitromethane in the mixture. Glow fuels are often labeled by the percentage of nitromethane included, i.e., 10% nitro, 25% nitro, etc.

Glow Plug — The part of a glow engine which produces the heat needed to ignite glow fuel. Glow plugs provide heat; spark plugs spark ignition in gasoline engines.

Horizontal Stabilizer — The portion of the tail that includes the elevators, which control the plane’s up and down movement.

Kit — An airplane that requires the modeler to do most or all of the building work. Wooden and/or plastic parts on most modern kits are shaped or cut to large degree to minimize work; hardware packages included with planes vary widely in quality and completeness. See also ARF, RTC and RTF.

Landing Gear (Gear) — The wheels and supporting structures on an airplane. The two main types are tricycle and taildragger gear. See also: main gear; mains; tailwheel.

Leading Edge — The front of the wing.

Li-Ion Batteries — Currently one of the most popular types of battery, commonly used in consumer electronics. With one of the best energy-to-weight ratios, this battery dosen't have the problems with batteries such as holding less charge over time and a slow loss of charge when not in use. They can have a shorter lifespan compared to other battery types unless care is taken.

LiPo Batteries — Lithium - polymer (LiPo) batteries are rechargeable batteries which have technologically evolved from lithium ion batteries. The lithium salt electrolyte is held in a solid polymer composite such as polyacrylonitrile. Thus these batteries are less hazardous if mistreated. Furthermore, since no metal battery cell casing is needed, the batteries are lighter with an energy density over 20% higher than that of a Li-Ion battery.

Loop — A basic aerobatic maneuver in which the plane starts from a straight, level path and climbs up, around and over, until it returns to the original flight path.

Main Gear — The two landing gear “legs” located under the wings. Also referred to as mains.

Motor — A mechanical device that creates thrust for flight by using battery power for “fuel.”

NiCd — An abbreviation for NickelCadmium, a type of rechargeable battery. These batteries are generally described by their capacity to store power (measured in milli amps), and/or number of cells, i.e., 1700mAh NiCd, 4-cell, 800mAh NiCd.

NiMH — An abbreviation for Nickel Metal-Hydride. Like NiCds, they are generally described by their storage capacity (mAh) and/or number of cells they include.

Nitro(methane) — The “power” ingredient in glow fuel. Nitro fuel = glow fuel.

On-Board Gear — A term which can have several meanings. In its broadest sense, on-board gear can mean everything in the airplane. More generally, however, on-board gear refers to a more specific group of items, usually including the receiver, receiver NiCd, servos and (in electric models) the motor, motor NiCd, on-off switch or speed control.

Pitch — A term with two different meanings. Pitch (referring to an airplane) is the tendency for its nose to unexpectedly move up or down without pilot input. Pitch (referring to a propeller) measures how far forward the prop will travel in one complete revolution. An 11x7 propeller, for example, is a prop that is 11” in diameter and will pull a plane 7” forward with each revolution. See also roll and yaw.

Power Plant — A slang term for engine, which is sometimes also used in reference to motor.

Prop — Short for Propeller. See below.

Propeller — The whirling device on the plane which turns engine/motor power into thrust. May be carved from wood, or molded from reinforced plastic or nylon.

Pushrods — The rods that connect servos to movable parts of the plane.

Radio — Short for Radio Transmitter. See below.

Radio Transmitter — The part of a radio system that a pilot operates to transmit control signals to a receiver.

Receiver Battery — The radio receiver’s power source.

Receiver — The radio component that receives the transmitter signal and relays its command to the servos.

Retractable (Landing Gear) — Landing gear that can be retracted up into the fuselage and/or wings, for reasons of improving looks, aerodynamics or both. May also be called simply retracts. The alternative to fixed (landing) gear.

Roll — A term with two meanings. A roll is a basic aerobatic maneuver, in which the plane rotates around an imaginary centerline that runs from the center of the prop shaft through the end of the fuselage. However, roll can also be used to describe an unwanted tendency of a plane, i.e., to roll without pilot input. See also pitch and yaw.

rpm — Revolutions Per Minute. Used to describe an engine’s operating range.

RTC — Ready-To-Cover. Describes a plane in which most major sections have been built, preparatory to covering or painting. Surfaces may or may not be factory sanded.

RTF — Ready-To-Fly. A somewhat loose term used to describe a plane which requires very little or no work to prepare for flight. Usually features a significant degree of factory assembly and factory-applied covering. RTFs may also include a transmitter, engine (or motor) and other, smaller items.

Rudder — The hinged part of the vertical stabilizer that moves the plane’s tail to the right and left.

Scale — A term with two meanings. Scale may mean the relationship in size between a model and the original, for instance, “1/12 scale, 1/5 scale, etc.” However, scale can also refer to the model’s trueness to the original’s looks and/or features. Exact scale models are rare; most scale models include at least some design compromises. Exact- (true-, precise-) scale models would be the most authentic, followed by scale, sport-scale and stand-off scale (i.e., “looks more authentic when you stand off a ways”).

"Second" Plane — A plane designed for, or ideal for, pilots who have mastered a trainer. Similarly, “third” plane, good first low-wing plane, etc.

Semi-Symmetrical — A wing airfoil which is neither flat-bottomed nor completely symmetrical.

Servos — The radio components that do the physical work in an airplane, by moving rods that are connected to various parts of the plane.

Span — Short for (wing)span. See also: wingspan.

Stab — Short for stabilizer. See below.

Stabilizer — See Horizontal Stabilizer, Vertical Stabilizer.

Symmetrical — Describes an airfoil which has the same shape on either side of an imaginary horizontal center-line.

Tail — The part of the airplane located on the rear of the fuselage. Includes both the Vertical Stabilizer and Horizontal Stabilizer.

Taildragger (Gear) — Landing gear that includes two main gears (usually located under the wings) and a rear tailwheel attached to the underside of the fuselage. Holds the plane in a nose-up attitude while on the ground. Also used to describe a plane, i.e., “It’s a taildragger I built years ago...”

Trailing Edge — The rear edge of the wing.

Tricycle (Landing) Gear — Landing gear that includes two main gears (usually located under the wings) and a nose wheel. Often found on trainers, it holds the plane roughly level and provides very stable ground handling.

Trim — A term with two meanings. Trim (in relation to finishing) refers to additional decorative elements (graphics, lines, etc) added to an existing finish. Trim (in relation to flying) refers to making mechanical adjustments that will allow the plane to fly predictably and well.

Trim Scheme — The entire range of decorative elements added to a plane for appearance’s sake. This may include covering, paint, lines and designs.

Two-Stroke Engine — The most common type of glow engine, one in which the piston travels up and down once to achieve combustion. Where engine requirements for a plane are listed, the 2-stroke range is usually the first (or only) range listed. See also Four-Stroke Engine.

Vertical Stabilizer — The portion of the tail that provides side-to-side stability. The hinged portion of the vertical stabilizer is called the rudder. Wing —The large, horizontal surface that creates lift (the force that carries a plane into the sky) as it moves through the air.

Wing Area — The surface area of the wings, as measured in square inches or square decameters. General rule: the more wing area, the more lift produced.

Wing Chord — The depth of the wing, from the front (leading) edge to the back (trailing) edge.

Wing Root — The place where the wing joins the fuselage.

Wingspan — The length of the wing, as measured from one wing tip to the other.

Wing Tip — The end of the wing furthest from the fuselage.

Yaw — An undesirable characteristic in airplanes. A plane that yaws is one in which the tail or nose (or both) will make undesirable side-to-side movements away from the desired flight path. See also pitch and roll.

Z-bend — A shape often used to connect a control rod to a servo. So named for the two 90° bends that make it look like a letter “Z.”