Glossary of Airplane Terms

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3D: Term describing a type of flight pattern, which is characterized by the performance of very specialized aerobatic manuevers below the model's normal stall speed. Examples include torque rolls, 'walk in the park', harriers, hangers, etc.
3F: Slang abbreviation for flip flop flying. Similar to 3D, but without the finesse.
360, 540, etc…: Number describing degrees in an arc. A 360 represents one full turn through an axis. A 360 turn, for example, is a flat turn where the aircraft does not roll its wings but rather just 'slides' through 360 degrees turning on rudder only.
ABC: Aluminum-Brass-Chrome. The components used in the production of non-ringed engines. These engines use an aluminum piston, and a chrome or nickel plated brass sleeve. The engine is harder to turn over and start due to the tight fit between the piston and cylinder. This tight fit is what makes the engine more efficient, and powerful. ABC engines must be run in for best performance.
ABL: Advanced Bimetallic Liner. Specialized form of ABN. Instead of a single-step, single-material plating, the ABL Plating process is based on a layered approach made possible by two OS-developed hard-nickel alloys. The first alloy is used as the bottom (bonding) layer, to fuse the top layer to the brass liner. The second alloy, developed for superior hardness, forms the top layer. Together, they create a barrier that protects the liner against excessive heat and wear.
ABN: Aluminum-Brass-Nickel. The components used in the production of non-ringed engines. These engines use an aluminum piston, and a nickel plated brass sleeve. The engine is harder to turn over and start due to the tight fit between the piston and cylinder. This tight fit is what makes the engine more efficient, and powerful. ABN engines must be run in for best performance.
ARF: Almost Ready to Fly. A prefabricated model.
ATV: Adjustable Travel Volume. Used on many radio transmitters to limit, or extend, maximum throw of a servo. ATV can indicate having a single adjustment which affects both ends of the servo (known as AST) or one adjustment for each end of the servo throw (known as EPA).
Aerobatics: The act of performing 'acrobatic' or stunt manuevers in the air such as loops, rolls, etc. For extensive information on aerobatics, consider purchasing A Look at Aerobatics (GPMZ0220), written by two-time U.S. National IMAC Aerobatic Freestyle Champion, Mike Cross.
Aft: Towards the rear. Used such as: "...with an aft center of gravity....".
After Run Oil: A lubricant designed to displace unburned fuel in the engine after running. The fuel can accelerate corrosion on some engine parts. By using an after run oil, the fuel is displaced, and a protective coating lines sensitive engine parts. This is an inexpensive engine insurance, and promotes long engine life. There are several good after run oils on the market.
Ailerons: Control surfaces usually on the wing, often near the tips. Used to bank the aircraft. They work in opposite directions (when one goes up, the other goes down.) One aileron raising forces air to push that side of the wing down, causing the model to roll in that direction. So, to roll right the right aileron raises. They control the airplane around the roll axis.
Airfoil: The shape of the wing when looking at its profile. Usually a raindrop type shape.
Amphibian: An aircraft that can fly off of water or land. The wheels retract into the hull or floats, depending upon the type of aircraft. An amphibian can land on water and then extend the landing gear to allow it to pull up onto the shore. Many seaplane bases had ramps to allow the airplanes to pull up onto dry land parking areas.
Angle of attack: The angle that the wing penetrates the air. As the angle of attack increases so does lift, up to a point (and drag).
Area: The number of square inches (or feet) of the wing. It's the wingspan multiplied by the wing's chord. The area of a tapered wing is the wingspan multiplied by the average chord.
Aspect Ratio: The wingspan divided by the chord. Aspect ratio is important where a wing's efficiency is concerned. A short aspect ratio (short wings) is better for maneuvering, since it allows a high roll rate. Short wings are also stronger than long wings. Gliders use high-aspect ratio wings (long, skinny wings) because they are more efficient for soaring flight. Example: 10 ft. wingspan with a 1 ft. chord has an aspect ratio of 10.
Axis: The line around which a body rotates.
Ball Link: Connection using a ball, and a link which rotates on the ball. Used to connect the servo to a control surface or lever.
Backlash: Term describing the amount of play between gears, or gear mesh. If too loose, the gear can slip, or strip the teeth. Too tight, and excessive wear is caused.
Barn Door Ailerons: Larger, built up ailerons rather than an aileron from a simple strip of solid wood like some kits have.
Base Load Antenna: A rigid, short antenna mounted to the model. Used to replace the longer receiver antenna.
Binding: What occurs when the friction at a joint is stronger than the linkage.
Blade Balancer: Usually called a 'prop balancer' for aircraft. Used to ensure that the propeller and spinner are equally balanced side-to-side to avoid vibration problems.
Boring holes in the sky: Having fun flying an R/C airplane, without any pre-determined flight pattern.
"Buddy" or Trainer Box: Two similar transmitters that are wired together with a "trainer chord." This is most useful when learning to fly -- it's the same as having dual controls. The instructor can take control by using the "trainer switch" on his transmitter.
CA: Abbreviation for cyanoacrylate. An instant type glue that is available in various viscosities (Thin, Medium, Thick, and Gel). These glues are ideal for the assembly of wood airplanes and other materials. NOTE: Most CA glues will attack foam.
CG: Center of Gravity. For modeling purposes, this is usually considered -- the point at which the airplane balances fore to aft. This point is critical in regards to how the airplane reacts in the air. A tail-heavy plane will be very snappy but generally very unstable and susceptible to more frequent stalls. If the airplane is nose heavy, it will tend to track better and be less sensitive to control inputs, but, will generally drop its nose when the throttle is reduced to idle. This makes the plane more difficult to land since it takes more effort to hold the nose up. A nose heavy airplane will have to come in faster to land safely.
Camber: If you draw a line through the center of the airfoil that's exactly half-way between the top and bottom surface, you get the mean airfoil line. Depending upon the airfoil, it can be straight or curved. This curve is called the "camber" of the airfoil. If it has a lot of curve, the airfoil is said to be "highly-cambered".
Canard: The horizontal surface forward of the wing used to control pitch. It's found on very few aircraft. Also the word used to describe aircraft that have a main wing and a horizontal control surface in the nose...also called, "tail first" aircraft.
Carburetor: The part of the engine which controls the speed or throttle setting and lean/rich mixture via setting of the needle valve.
Center of Pressure: An imaginary point on the chord of an airfoil where the total of all aerodynamic forces are assumed to act.
Centrifugal Force: The force created by a body's tendency to to follow a straight path working against a force which causes it to move in a curve, the resultant force which pulls away from a central axis of rotation.
Chandelle: A very steep climbing turn where the airplane makes a 180° change of direction.
Channel: The frequency number used by the transmitter to send signals to the receiver. If radios transmit on the same frequency, or channel, glitching will occur in the active receiver on that channel. This is due to conflicting signals sent by the two radios. Flying sites should have a frequency control system to ensure that only one radio operates on any given channel at one time. This is usually a board with some type of marker for each channel. If the marker is not available, someone else is using that channel. Do not use your radio unless you are sure you are the only one on the frequency.
Channel: The number of functions your radio can control. Ex: an 8 channel radio has 8 available servo slots used for separate control surfaces or switches. These channels can also be mixed on many radios, for such functions as collective, which increases pitch when throttle is increased.
Charge Jack: The plug receptacle of the switch harness into which the charger is plugged to charge the airborne battery. An expanded scale voltmeter (ESV) can also be plugged into it to check battery voltage between flights. It is advisable to mount the charge jack in an accessible area of the fuselage so an ESV can be used without removing the wing.
Charger: Device used to recharge batteries and usually supplied with the radio if NiCad batteries are included.
Chicken Stick: A hand-held stick used to flip start a model airplane engine.
Chord: The "depth" of the wing, its distance from leading edge to trailing edge. One of the components used to determine wing area. May vary from root to tip.
Clunk: Term used to describe the weighted end of the fuel pickup line in the fuel tank. The purpose of this is to ensure that the fuel pickup is always in the fuel supply, even when inverted
Clutch: The section of the drive train used to engage the gear when throttle is increased, and disengage while engine is at idle. This ensures that the rotor blades can remain at rest while the engine is idling.
Control Surface: Any one of the various moveable portions of the wings, tail surfaces, or canard.
Conventional Gear: The landing gear arrangement where the airplane has a main gear and a tailwheel.
Cowl: The large molded fairing around an engine. It serves two purposes when done right: It helps the airflow go smoothly around the front of the airplane, and also provides a proper path for cooling air around the engine.
Dead Stick: A term used to describe unpowered flight (glide) when the engine quits running.
Dialed In: Slang term for the condition in which the model is set up to fly smoothly and predictably. This is the state where the mechanics and electronics work together to produce the best performance.
Dihedral: The V-shaped bend in the wing. Typically, more dihedral causes more aerodynamic stability in an airplane, and causes the rudder to control both the roll and yaw axis. This is why some trainers and sailplanes require only 3 channels of radio control—i.e., having no ailerons.
Ding: Minor dent or damage to the structure. Also, a nick in a prop. Dinged props must be replaced.
Dorsal Fin: An extension of the vertical fin forward of the main part of the fin, and against the fuselage. On the top, or "dorsal" side of the aircraft.
Down thrust: Downward angle of the engine relative to the centerline of the airplane. Down thrust helps overcome the normal climbing tendency caused by the torque of the engine. Please refer to this FAQ for further information.
Drag: The air resistance to forward motion. Drag can be increased with the use of certain types of devices installed on the aircraft, such as spoilers, airbrakes, or flaps. Old-style aircraft with lots of supporting wires had very large amounts of drag, while modern aircraft such as military jets, have very low drag.
Dual Rates: Radio function used to adjust control sensitivity.
EDF: Electric ducted fan. A battery-powered, fan (rather than exterior propeller) driven model.
Electric Starter: A hand-held electric motor used for starting a model airplane engine. Usually powered by a 12-volt battery.
Elevator: Pitch control. Causes the model to raise or lower its nose, resulting in a climbing or diving response. Moving the elevator down causes the tail to rise, pushing the nose down and causing the model to dive. Moving the elevator up causes the tail to drop, raising the nose in reference to the tail (as if you were sitting in the aircraft).
Empennage: The vertical and horizontal tail surfaces of an airplane.
Engine: The methanol or gasoline fueled power plant used in a model. Two or four-stroke gasoline and glow engines are very popular in aircraft. Four-stroke engines tend to turn higher diameter lower pitch props, and therefore tend to be used in applications requiring more torque and less speed response.
Epoxy: A two-part resin/hardener glue that is extremely strong. It is generally available in 6 and 30-minute formulas. Used for critical points in the aircraft where high strength is necessary.
Expanded Scale Voltmeter (ESV): Device used to read the battery voltage of the on- board battery pack or transmitter battery pack.
Exponential: This radio function allows the modeler to adjust the sensitivity of the control towards the center. This will make the small stick motions very precise, while longer stick movement moves the servo arm at a proportional rate.
FM: Frequency Modulation. This describes the mode of transmission of radio signal from transmitter to receiver.
Failsafe: A PCM function which moves servos to a pre programmed position if transmitter signal is lost or corrupted.
Fairing: A shaped area used to smooth out, streamline, or "fair", the joint between two members of an airplane. A wing fairing joins the wing and fuselage. A landing gear fairing streamlines the landing gear struts, and wheel fairings (wheel "pants") streamline the bulky shape of the wheels.
Field charger: A fast battery charger designed to work from a 12-volt power source, such as a car battery.
"Figure 9": Can be an "official" competition maneuver, or a badly-done loop. When the model flies over the top of a loop and picks up too much speed, the momentum prevents it from maintaining a loop's round shape.
Fin, Vertical Fin: The fixed portion of the vertical tail surface.
Flaps: Hinged control surface located at the trailing edge of the wing inboard of the ailerons. The flaps are lowered to produce more aerodynamic lift from the wing, allowing a slower takeoff and landing speed. Flaps are often found on scale models, but usually not on basic trainers.
Flare: The point during the landing approach in which the pilot gives an increased amount of up elevator to smooth the touchdown of the airplane.
Flight Box: A special box used to hold and transport all equipment used at the flying field.
Flight Pack or Airborne pack: All of the radio equipment installed in the airplane, i.e., Receiver, Servos, Battery, Switch harness.
Floats: Long, canoe-shaped structures that allow an airplane to land on water. They are not a part of the aircraft structure, but suspended below the fuselage on struts. Also called "Pontoons".
Flutter: A phenomenon whereby the elevator or aileron control surface begins to oscillate violently in flight. This can sometimes cause the surface to break away from the aircraft and cause a crash. There are many reasons for this, but the most common are excessive hinge gap or excessive "slop" in the pushrod connections and control horns. If you ever hear a low-pitched buzzing sound, reduce throttle and land immediately.
Flying Boat: The type of aircraft where the fuselage has the lower portion shaped like a power boat. The plane lands on water directly onto the fuselage. There may be small floats suspended from the wings to keep the plane level when it's in the water.
Fore, Forward: Towards the front. Used such as: "...the forward edge of the rib...", or as in: "...with fore and aft movement...."
Frequency Control: The FCC has allowed the 72MHz (72.010 - 72.990) band to be used for R/C aircraft operations. This band is divided up into many different channels in which you can choose a radio system. You should be aware that certain areas have frequencies in which there is pager interference. This is why it is always a wise move to check with your local hobby shop to find out any channels that may be troublesome in the area you wish to fly. The FCC has allowed band 75MHz (75.410 through 75.990) for ground model use only (robots, battlebots, cars, boats), 50MHz (50.800 - 50.980) is allocated only to Amateur HAM license holders for R/C use (and only at 1W maximum power output.)
Fuel: The methanol/nitromethane/lubricant mix used to fuel model engines. A helicopter fuel mix has a higher concentration of lubricant to counter the lack of sufficient airflow over the engine in a hover.
Fuse: Fuselage, main body
Fuselage: The body of an airplane.
Gain: Gyro sensitivity. When too low, the tail will not hold position well. When too high, the surface being dampened by the gyro will tend to wag, or hunt for center.
Gasser: Slang for a model using a gasoline engine as a power plant.
Glitch: Momentary radio problem that never happens unless you are over trees or a swamp.
Glow Fuel: A Methanol based fuel, with a lubricating agent, used in most model engines. Most model fuels also use a percentage of nitromethane.
Glow Heater: This is used to heat the element in a glow plug, and is used when starting the model engine. AKA Ni-Starter.
Glow Plug: This is the plug that is used to help ignite the fuel in a model engine. The combustion of the fuel in the engine keeps the element hot between cycles, thus the glow plug does not need to be regulated or powered while the engine is running.
Ground Effect: The cushion of air that the model rides on when close to the ground. This will decrease the amount of elevator needed to maintain a constant altitude when near the ground/landing.
Gyro: A mechanical or electronic device which helps to stabilize the orientation of the model by sensing rotation, and moving the appropriate servo to compensate. This device can be used on any axis, but is most frequently used on rudder and elevator, typically used to aid in 3D and precision flying.
Header Tank: This is a small fuel tank used in line between the main tank and the carburetor. The purpose of the header tank is to ensure that the fuel fed to the carb is free of bubbles, which can be caused by foaming, or by the clunk falling away from fuel during complex maneuvers.
Heading Hold: This describes a type of Gyro which senses rotation, and maintains direction. This is accomplished by sensing the rate of motion, and the time of motion, then compensating for the distance. While this sounds complicated, the effect is that if you have the model dialed in, and point the nose north, with a heading hold gyro on the yaw axis the model will continue to face north until you command it to yaw. See also Heading Lock. This is not recommended for aircraft use while in flight due to the requirement to use YAW (rudder) command to turn the model. Often used for ground use only for perfect take off and landing runs.
Heading Lock: Slang term for Heading Hold Gyro.
Hit (or to be hit): Sudden radio interference which causes your model to fly in an erratic manner. Most often caused by someone turning on a radio that is on your frequency, but can be caused by other radio sources miles away.
Horizontal Stabilizer: The horizontal tail surface at the back of the fuselage which provides aerodynamic pitch stability to the airplane.
Hot Start: An engine which has been running will tend to remain hot for a short time. During this period, it is possible to restart the engine by turning the crankshaft without the glow plug being plugged in to a glow starter. This is something to be aware of, as it could possibly create an unsafe condition.
Hover: The art of flying without moving. This can also be an illusion, depending on windspeed. For airplanes, this is a 3D manuever also known as a 'hanger'. The aircraft is pointing straight upward, hanging solely on the thrust from the propeller. The model may be drifting horizontally with the wind but should not climb or dive.
Hydraulic Lock: Hydraulic lock happens when the engine becomes flooded with fuel, to the point where the piston cannot compress it in the combustion chamber. This can result in engine damage if the crankshaft is forced through a rotation without relieving the pressure. To cure, remove the glow plug, and pour out the excess fuel.
Immelmann: A maneuver originally used to reverse direction in combat. The airplane noses up and over onto its back. It then rolls upright and continues in the direction opposite to the original direction. It was invented by the World War I German pilot Max Immelmann, whose airplane could perform the maneuver, and other's couldn't. It got him out of a lot of trouble in combat until the Allied aircraft designs caught-up and allowed their planes to perform the maneuver, too.
Incidence: The angle of one portion of a model when compared to another portion of the model. For example, if the stabilizer is perfectly parallel to the ground and the leading edge of the wing points up 2 degrees when compared to the stabilizer, the wing has a 2 degree positive incidence when compared to the stabilizer. Up or down thrust angle are also called engine incidence. Having these 3 measurements in proper relation to one another affects how well the model flies, particularly on vertical lines. An improper engine-to-wing incidence often results in a model which cannot be trimmed on pitch because at higher throttle the engine is pulling the model upward and at lower throttle it is pulling the model downward, or vice versa.
Incidence Meter: Used to measure the angle of attack of an airfoil, can be used to measure blade pitch, or paddle pitch.
Intake: An air inlet on an aircraft. You can have a carburetor intake, cooling intake, air conditioning intake (on full-size aircraft), and so on. Named because it "takes in" air, and because "intake" is a better-sounding word than "takesin".
Inverted: Flying upside down. Note that elevator and rudder seem to work backward from the ground, as elevator, aileron and rudder inputs are all based upon the model's orientation (as if you were sitting inside).
Kit: A Kit describes an unassembled model, arrives as packages of parts which must be assembled, as opposed to an ARF, or Almost Ready to Fly, which is mostly pre assembled.
LE: Leading edge (front)
Landing Gear: The assemblies that include the wheels and the wheel struts. The word "gear" is used in the sense of "equipment", as opposed to the "toothed wheel" meaning of "gear". The British call the landing gear the "undercarriage".
Landing Skid: The rail type landing gear used on some models which have no wheels.
Leading Edge (LE): The very front edge of the wing or stabilizer. This is the edge that hits the air first.
Lean: Refers to carburetor setting. When an engine is run too lean it will overheat, causing damage, and likely an in flight engine failure. Tuning a carburetor is best accomplished by starting rich, and working gradually to the condition which produces maximum power, while allowing a small amount of unburned fuel mixture to lubricate and cool the engine.
Lean Run: This happens when an engine develops a lean condition. Possible causes are improper tuning, improper fuel choice, fuel foaming due to excessive vibration, or a leak developing in the fuel delivery system. The air in the fuel line will cause the engine to run lean.
LG: Landing gear
Loading: a.k.a wing loading. The load placed on the airfoil of a flying machine. In the case of an aircraft, this would be wing loading. Typically found by dividing the weight of the model by the total area of the main wing(s). Note that wing loading is only a good comparison between models of the same size. Larger models appear to have a far higher wing loading while displaying similar flight characteristics.
Loop: A vertical circle in the air. The plane noses up, keeps rotating until it's on its back, and then comes down and around to describe a vertical circle in the air.
Lubricant: The agent used to aid in the reduction of friction between two parts. This term is used for many substances, which in turn are used in many different ways. They are all, however, used to reach the same objective, that being the reduction of wear between parts. In the case of engine fuel, the lubricant is added to the fuel at the factory in many cases. This might be castor, a synthetic, or a blend. The percentage of lubricant required in the fuel will depend on the type of fuel, the engine, and the model requirement.
Main Gear: Also Main Landing Gear. The large, heavy-duty landing gear struts and wheels that support most of the weight of the airplane. They are usually under the wing or under the fuselage near the center of the aircraft. Any other landing gear struts and wheels are noticeably smaller.
Midrange: The power band of an engine between idle and full throttle.
Mixing: Radios with mixing will take two or more controls and mix their output in relation to stick input. The number of channels that can be mixed, and the precision of the mixing curve, or number of curve points, will depend on the transmitter used.
Mixing Arm: A specialized lever which has three or more pivots. The length between pivots will determine the proportion of the mix between two or more linkages.
Mixture: Fuel to air mixture is determined by the needle valve on the engine carburetor.
Motor: Any electric motor used in the model. Examples are the servo motors, which move the servo arms, and thus the control surfaces. There are also kits which use electric motors in place of the engine for quieter, cleaner flight.
MPH: Speed in Miles Per Hour. Like RPM, MPH is both singular and plural. You can go 1 MPH or 100 MPH. You don't go 100 MPH's.
Needle Valve: This is used to tune the fuel to air mixture on the engine carburetor. On most engines, the needle is turned clockwise to lean the mixture, and counterclockwise to richen.
NiCad (or NiCd): Nickel Cadmium battery. Rechargeable batteries which are typically used as power for radio transmitters and receivers.
Nitro: Abbreviation for nitromethane. The addition of nitromethane in fuel provides more power, and a smoother idle, thus making the engine easier to tune. The nitro also makes an engine require more careful tuning, therefore, the amount of nitro added to a fuel results in a tradeoff. Common nitro mixes vary from 0% to 30% and beyond.
Nitromethane: The addition of nitromethane in fuel provides more power, and a smoother idle, thus making the engine easier to tune. The nitro also makes an engine require more careful tuning, however, to avoid overheating. Common nitro mixes range from 0% (FAI fuel) to 30%.
Nose: The front portion of a model's fuselage.
Nose Gear: The strut and wheel that's under the nose of some aircraft.
PCM: Pulse Code Modulation. A modified FM signal used in high end radios. The signal is coded by the transmitter, resulting in a cleaner signal.
PPM: Pulse Position Modulation. Another term for FM.
Peak: This is the point at which a battery will no longer accept a charge, and converts the energy to heat. This is damaging to the battery pack, and potentially hazardous.
Peak Charger: This type of charger will eliminate the guesswork. When the battery has reached peak, the charger reverts to a maintenance charge rate, which will not damage the pack.
Pitch: Describes the fore and aft attitude of the model. (Nose high or low in comparison to the ground.) Controlled by the elevator(s).
Pitch Axis: The airplane axis controlled by the elevator. Pitch is illustrated by holding the airplane at each wingtip. Raising or lowering the nose is the pitch movement. This is how the climb or dive is controlled.
Ply: Plywood
Pontoons: See Floats.
Power Panel: 12-volt distribution panel that provides correct voltage for accessories like glow-plug clips, fuel pumps and electric starters. Usually mounted on a field box and connected to a 12-volt battery.
Prop Balancer: Device designed to aid in the balancing of model airplane propellers.
Pull-Pull: A linkage set up using two rods or wires. One is pulled for one direction, the other is pulled for the other.
Push-Pull: A linkage set up using two rods. One rod pushes, while the other pulls.
Receiver (Rx): The radio unit in the airplane which receives the transmitter signal and relays the control to the servos. This is somewhat similar to the radio you may have in your family automobile, except the radio in the airplane perceives commands from the transmitter, while the radio in your car perceives music from the radio station.
Reflex: If a wing has an airfoil that curves down from the high point, and then curves back up, it's said to be "reflexed". Reflex is the size of that reverse curve.
Resonance: This is the vibration frequency of a rotating or moving object. When the resonance of many parts of a machine are in synch, the whole machine will vibrate at a greater rate. This can cause vibration damage. Resonance can cause difficulties in an aircraft, particularly when using a vibration mount with an improperly balanced propeller/spinner wherein the engine is vibrating at one frequency and the propeller at another.
Retract servo: Specifically used for mechanical retracts. It is a non-proportional servo which only moves 180 degrees. That is to say this servo is either "off" (gear up and fully locked) or "on" (gear down and fully locked). No ATV, EPA, or AST adjustments can be made on these servos because they are not proportional. The linkage must be set up properly to allow this servo to operate at its full range and do its job -- securing your model's landing gear in a gear-up or gear-down position.
Retracts: Short for retractable landing gear. Wheels and struts that fold up into the airplane to get them out of the airstream and present less resistance to the airflow.
Right Thrust: Right yaw angle of the engine relative to the centerline of the airplane. Right thrust helps overcome the normal yaw tendency caused by the torque of the engine. Please refer to this FAQ for further information.
Ringed: An engine which uses a piston with a piston ring. Compare to ABC or ABN. Best used in dusty environments, a ringed engine is less susceptible to damage from contaminants in the fuel/air mixture, but does not provide the higher compression ratio of the ABC/ABN engines.
Roll (maneuver): The airplane keeps the nose pointed in one direction while it rolls over on its back and then upright again.
Roll Axis: The airplane axis controlled by the ailerons. Roll is illustrated by holding the airplane by the nose and tail. Dropping either wingtip is the roll movement. This is used to bank or turn the airplane. Many aircraft are not equipped with ailerons and the Roll and Yaw motions are controlled by the rudder. This is one reason why most trainer aircraft have a larger amount of dihedral.
RPM: Revolutions Per Minute. How fast something turns. It is both singular and plural. An engine can turn one RPM, or 10,000 RPM, NEVER 10,000 RPM's.
Rudder: The moveable portion of the vertical tail surface. The rudder controls the airplane around the yaw axis.
Rx: Abbreviation for receiver.
Seaplane: An airplane that has floats, or pontoons, attached to allow it to land on water.
Servo: The radio component which does the work of moving a control surface.
Servo Output Arm: The removable arm or wheel which bolts to the output shaft of a servo and connects to the pushrod.
Shot down: A "hit" that results in a crash landing. Sometimes caused by radios miles away.
Simulator: A computer program which uses a modified radio transmitter, and a graphic depiction of a model and flying area. This is used to give model pilots a feel for flying, without the risk of a crash. The simulator can be used by the newcomer to learn to take off/hover/forward flight/landings, or by the expert to dial in that new 3D routine without crashing a very expensive 3D model.
Slats: Moveable surfaces on the leading edge of the wing that help airflow in low-speed flight. They enable the wing to fly at lower airspeeds than without them by directing the airflow over the wing and preventing separation of the airflow. Basically, they are retractable slots. All modern jetliners have slats, which open when landing flaps are lowered. Some aircraft intended for very short takeoff and landing have slats that open and close automatically, depending upon airspeed and angle of attack.
Slip: A maneuver where the airplane's controls are used to make the fuselage fly at an angle to the line of flight. This causes a tremendous increase in drag, and allows an airplane without landing flaps to increase its angle of descent without picking up a lot of speed.
Slop: Slop occurs when a control surfaces movement does not move the servo. Common cause is a worn linkage point or poor linkage setup.
Slot: A specially-shaped slot in the wing just behind the leading edge. This directs airflow from below to the top of the wing, and helps low-speed flight by delaying the stall. Because they are permanently-mounted, they do add drag. See also "Slats"
Slow Roll: A very slow version of the roll.
Snap Roll: A type of rolling maneuver that is very quick and violent. It's basically a spin where the flight path is in any direction chosen by the pilot. Improper speed control during a landing approach can also make the model snap over on one wing and enter a spin. Since it's close to the ground, there's not enough room to recover, and a crash results.
Solo: Your first totally unassisted flight that results in a controlled landing.
Span, also "Wingspan": The widest straight-line distance between the two wingtips.
Speed Brakes: Large panels that fold out of the aircraft structure to provide a lot of extra drag to the air. They are not part of the wing structure, but are usually mounted on the fuselage. Military jets most often have speed brakes, which fold out of the fuselage. Some airliners use spoilers as speed brakes when at altitude.
Spin: A maneuver where one wing is stalled and the other is still flying. This causes the airplane to rotate around its middle while it descends at a high rate of speed. When it's done on purpose, it is a precision maneuver, with the pilot trying to get the airplane to rotate an exact number of turns from entry to exit. When it's done accidentally, it can easily result in a crash. Many models crash when the pilot enters an accidental spin too close to the ground. This is caused by improper speed control during the landing approach.
Spinner: The bullet-shaped fairing on the nose of the airplane around the propeller. This smooths the airflow around the propeller hub and also makes the airplane look much better.
Split-S: Basically a reverse Immelmann. The airplane rolls onto its back, and then the nose comes down to finish a 1/2-loop. The direction of flight is changed 180°.
Spoiler(s): Control surfaces on the wing that destroy lift. They "spoil" it. They are used on sail-planes because they can steepen the very flat glide of the aircraft, which makes landings much easier. On full-size aircraft, spoilers are also used to kill lift on landing to make sure the airplane is firmly on the ground. They also add a lot of drag to help with aerodynamic braking.
Stab: Horizontal stabilizer, 'smaller wing'
Stabilizer: A surface which increases the stability of a model. Most aircraft have two stabilizers, the horizontal (stab) and vertical (fin), which are mounted on the tail. The stabilizers help the model overcome the rotational forces caused by the engine.
Stall: When the air flowing over the wing cannot produce enough lift to support the weight of the model, it's called a "stall". This can happen if the modeler flies too slowly, or if the wing is at a too-high angle to the incoming airflow. If the wing is at a too-high angle to the incoming airflow, then it cannot flow over the wing properly to develop lift.
Stall Turn: The maneuver in which the model is flown to a point at which the main wing is vertical, stalls, then is turned about the yaw axis to continue in a nose down attitude, then is returned to horizontal flight.
Strut: Basically this is a supporting member. A wing strut supports the wing, and goes from the fuselage to the wing. Cabane struts are on biplanes, and support the upper wing over the fuselage. A landing gear strut is the portion that holds the wheel assembly to the airplane, and away from the wing or fuselage.
Sub-Trim: This is a trim function on many computer radios, allowing trim function during set-up, and still allowing the full trim function in flight.
Tachometer: An optical sensor designed specifically to count light impulses through a turning propeller and read out the engine RPM.
Taildragger: The nickname of an airplane that sits on its tail with the two main wheels in front and a tailwheel in the rear.
Tailskid: On old World War I type aircraft, or pioneer-type aircraft, there was no tailwheel. A wooden skid was used to support the tail of the airplane. While this helps slow the airplane during landing, it is useless as an aid to steering on the ground. The real aircraft with tailskids had to be maneuvered on the ground by ground crews, who put the tail on a small cart and towed the airplane where they wanted it. For small distances, the tail was picked-up by hand and the airplane pushed into position by the ground crew.
Tailwheel: The small wheel at the tail of the airplane. This is found on the type of airplane that has the two large wheels in the front, and the small one in the rear. The airplane sits on its tail.
TE: Trailing edge (rear)
Throttle: The control that allows the pilot to change the speed of the engine. In a car, the "gas pedal" is actually the throttle control for the car.
Thrust: The forward force provided by the airplane's engine. This is the force that drives the airplane forward.
Torque: The force which tends to cause rotation.
TR: Abbreviation for Torque Roll, a 3D manuever which begins as a hover and the torque of the engine/propeller rotates the model in a counterclockwise direction without any aileron (roll) inputs.
Trainer Airplane: A model designed to be inherently stable and fly at low speeds, to give first-time modelers time to think and react as they learn to fly.
Trailing Edge (TE): The rearmost edge of the wing or stabilizer.
Transmitter (Tx): The hand-held radio controller. This is the unit that sends out the commands that you input.
Tricycle Gear: The landing gear arrangement where the airplane has main gear and a nose gear.
Tx: Abbreviation for transmitter.
Undercamber: This means that the lower surface of the wing has a hollow curve when observed from front to back. A thin wing with a high camber will be undercambered.
Ventral Fin: A small vertical surface on the bottom of the aft fuselage. Usually a long, slim triangle that is narrow at the front, and widens toward the rear. It usually ends at the rudder hinge line.
Washout: The twist in an airfoil which causes less angle of attack at the tips than the root. For airplanes, this increases stability of the model at slow speeds as the wing tips will stall after the center of the wing, avoiding accidental tip stalls.
Weathervane: This describes the tendency to point into the wind. Stabilizers on a model result in its desire to weathervane.
Wheel Pants: The large fairings used to streamline the wheels of an aircraft that has non-retracting, or "fixed" landing gear (so-called because it's "fixed" in place).
Windsock: This can be used to describe a number of devices, all of which give a visual clue to the direction and speed of wind in a given location.
Wing: The main lifting surface of an airplane.
Wing Loading: This is the amount of weight per square foot that has to be overcome to provide lift. It is normally expressed in ounces per square foot. This specification can be easily calculated as follows: If you know the square inches of the wing, simply divide by 144 to obtain square feet. Divide the total weight (in ounces) of the airplane by the wing area (in square feet). This information is valuable when deciding on which airplane to build next. Planes with high wing loading numbers must fly faster to stay in the air. These are generally "performance" airplanes. Conversely, planes with lower numbers do not need as much air flowing around the wing to keep it flying. Trainers are designed to have low wing loading because slow, efficient flight is desired.
Wing Root: The centerline of the wing, where the left and right wing panels are joined.
Winglet: A small vertical surface at the tips of the wings. They help direct the turbulent airflow that all wings have at the tips. They makes the wings more efficient.
Yaw: The nose-left and nose-right movement of the airplane. This is controlled by the rudder.
Yaw Axis: The airplane axis controlled by the rudder. Yaw is illustrated by hanging the airplane level by a wire located at the center of gravity. Left or right movement of the nose is the Yaw movement.
Yaw Rate: The rate of movement about the vertical axis of a model.
Z-Bend: A type of linkage point using a bend in the control rod which resemble a Z.

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