R/C Airplane glossary and terminology

Adam's Park Flyer
R/C Airplanes

R/C Airplane Glossary

Here are a few of the terms that you may find being thrown around at the local hobby shop.

ATL = Adjustable Throttle Limiter: High-end feature which adjusts to bring full servo potential within the limits of bind-free servo travel. Ideal for throttle control, or for more effective braking in gas racing.

ATV/EPA = Adjustable Travel Volume/End Point Adjustment: Allows separate adjustments of maximum servo travel to both sides of neutral. Helps tailor outputs for different control styles.

Ailerons: Hinged control surfaces located on the trailing edge of the wing, one on each side, which provide control of the airplane about the roll axis. The control direction is often confusing to first time modelers. For a right roll or turn, the right hand aileron is moved upward and the left hand aileron downward, and vice versa for a left roll or turn.

Airfoil: The shape of the wing when looking at its profile. Usually a raindrop type shape.

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).

Articulated Rotor: This is borrowed from full sized helicopters, and is a rotor head which allows the blades to flap, drag and feather.

Aspect ratio: The ratio of the wingspan to the wing's chord (depth). For sailplanes this number will be larger than sport planes, which will generally be larger than a "jet" style aircraft.

Autorotation: The ability of a rotary wing aircraft to land safely without engine power. This maneuver uses the stored energy in the rotor blades to produce lift at the end of decent, allowing the model to land safely.

Axis: The line around which a body rotates.

BEC = Battery Eliminator Circuitry: Allows receiver to draw power from a main battery pack, eliminating the need for (and weight of) a receiver battery.

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.

Base Load Antenna: A rigid, short antenna mounted to the model. Used to replace the longer receiver antenna.

Bell and Hiller: Control system used in helicopters. Changes pitch of blades in relation to their position via a swashplate. A flybar with paddles is used to gain responsiveness. The two systems are linked with Control Levers.

Binding: What occurs when the friction at a joint is stronger than the linkage.

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 cord." 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.

CCPM: Cyclic-Collective-Pitch-Mixing. Type of swashplate mixing which requires a radio with CCPM mixing functions. This uses three servos to control the cyclic, while all three work together to raise and lower the swashplate for collective control.

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.

Carburetor: The part of the engine which controls the speed or throttle setting and lean/rich mixture via setting of the needle valve.

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.

Cyclic: Term used for the horizontal controls used to determine the attitude of the helicopter. Also known as elevator and aileron.

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.

Dual Conversion: A type of receiver that converts the incoming frequency through two intermediate stages. This tends to eliminate the type of interference known as "image". With high-precision components, it also allows the receiver to be much more precise in selecting the incoming channel it accepts. This is what helps the receiver to be very narrow-band.

Dual Rates: A switch that can make controls more or less sensitive. Lower rates are better for beginners, who tend to over control.

Elevator: Hinged control surface located at the trailing edge of the horizontal stabilizer, which provides control of the airplane about the pitch axis and causes the airplane to climb or dive. The correct direction of control is to pull the transmitter elevator control stick back, toward the bottom of the transmitter, to move the elevator upward, which causes the airplane to climb, and vice versa to dive.

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 Rate: Offers servo travel that is not directly proportional to stick travel. Control response is milder below half-stick, but becomes increasing stronger as stick travel approaches 100%. Great for aerobatics and trouble situations.

FM: Frequency Modulation. This describes the mode of transmission of radio signal from transmitter to receiver.

Fail Safe: A safety feature which turns a servo to a preset position if the signal is lost or interrupted. Additionally, battery failsafe is a safety feature which brings the throttle servo down to idle as a warning that the receiver battery's voltage is getting dangerously low.

Field charger: A fast battery charger designed to work from a 12-volt power source, such as a car battery.

Flaperons: The movement of two aileron servos, both in the same direction at the same time, acting as flaps.

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.

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.

Frequency Control: The FCC has allowed the 72MHz 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.

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.

Glitch: Momentary radio problem that never happens unless you are over trees or a swamp.

Glow Plug: The heat source for igniting the fuel/air mixture in the engine. When starting the engine a battery is used to heat the filament. After the engine is running, the battery can be removed. The wire filament inside the plug is kept hot by the "explosions" in the engine's cylinder. See next heading and "Idle Bar" plug.

Gyro: A gyro is an electro-mechanical, or electronic device which aids in the control of an R/C model. The gyro senses motion in one axis, and directs the servo to counter that motion. The sensor, which can be a mechanical gyroscope, or an electronic piezo crystal, detects unwanted movement. The gyro then instructs the servo to counter for that motion. At all times, the radio commands will override the gyro command. The level of control the gyro had is adjusted by the GAIN setting.
Mechanical Gyro: uses a mechanical gyroscope (similar to the child's toy) to sense movement.
Piezo Gyro: uses a piezo crystal to sense movement.
Non-Heading-hold vs. heading hold: A standard (nonHH) gyro senses movement and makes an effort to counter that movement as long as it feels it. Therefore, it is NOT going to return the model to the exact heading prior to the movement. Heading Hold (or AVCS) gyros will lock the model into one position, and accurately correct for movement by sensing rate of change and returning at that same rate.
SMM technology: utilizes a microchip to sense movement and provide all readings. Experiences minimal effect from temperature change, commonly known as 'temperature drift' which affects piezo and some mechanical gyros.

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.

Helicopter Radio: A remote control radio system designed specifically for use with helicopter models. The helicopter radio differs from an aircraft radio in a few ways. First, the heli radio needs mixing functions specific to helicopters, and usually a minimum of five channels. Collective mixing for collective pitch helicopters is a necessity. Second is the throttle stick, which is ratcheted in airplane transmitters, will not have the clicking feel on the heli version. This is due to the precise control needed on the heli collective stick to achieve and sustain a controlled hover. The specific radio requirements will vary from user to user, and the parameters used will vary from helicopter to helicopter. Note that many radios produced have both airplane and helicopter programming in a single radio.

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.

Idle Up: This is a setting on the transmitter which limits the throttle minimum. Particularly useful for FFF and 3D stunt flying.

Leading Edge (LE): The very front edge of the wing or stabilizer. This is the edge that hits the air first.

MHz = Megahertz: The unit of radio frequency. 75 MHz are surface frequencies; 72 MHz are air frequencies; 27 MHz and 50 MHz can be used for either ground or air applications. Note: Use of the 50 MHz (ham radio) band requires an FCC license.

Mixing: Allows a single input to control the operation of two or more servos. Simplifies routine flying and allows more involved maneuvers -- great for intermediate-advanced fliers. For example, Flap-to-elevator mixing: Most models will change pitch upon deploying flaps (some will climb; others dive). After test flying the model and determining the direction and amount of elevator throw required to correct for this change, a pilot may set a flap-to-elevator mix to compensate. Once the mix is operating properly, when the modeler gives flap control, the radio automatically also gives the proportional amount of elevator throw, keeping the model flat and straight.

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.

Module: A removable/replacable plug in unit used in most complex computer radios, containing all frequency control equipment, including the crystal and all tuned components. Changing channels or bands on a modular radio requires only changing module. Changing crystals WITHIN a module to change the channel of the module itself is against FCC regulation and is not recommended. To use your transmitter on a different channel you simply purchase another module on that other channel and the radio is now fully properly tuned and safe and easy to use on that other channel as well.

NiCad (or NiCd) = Nickel Cadmium battery: Rechargeable batteries which are typically used as power for radio transmitters and receivers.

Nitro = Nitro methane: A fuel additive which increases a model engine's ability to idle low and improves high speed performance. Ideal nitro content varies from engine to engine. Refer to the engine manufacturer's instructions for best results. Nitro content in fuel is indicated by the percent of the fuel.

PCM = Pulse Code Modulation: PCM systems use digitally encoded signals to minimize interference and provide today's most advanced R/C control.

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 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.

Pitch Curve: The programming function of the radio which aids in setting the hover point, and end points of the blade pitch in the collective mix.

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.

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.

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.
For helis: Keep in mind that a helicopter has many rotating parts, and they all cause resonance. The helicopter will need to be tuned to reduce the amount of resonance, and the vibration caused by resonance. While this can not be eliminated, the vibrations can be tuned individually to reduce the overall vibration of the helicopter.

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.

Revolution Mixing: The function of the radio which mixes throttle to rudder, preventing the rotation of the helicopter during throttle increase or decrease.

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.

Rudder: Hinged control surface located at the trailing edge of the vertical stabilizer, which provides control of the airplane about the Yaw axis and causes the airplane to Yaw left or right. Left rudder movement causes the airplane to Yaw left, and right rudder movement causes it to Yaw right.

Rudder Offset: In radios with idle up functions, this specifies the amount of tail rotor pitch in the different idle up conditions.

SMT = Surface Mount Technology: Ultra light, solid-state components which offer greater vibration resistance and reliability.

Servo: The electro-mechanical device which moves the control surfaces or throttle of the airplane according to commands from the receiver. The radio device which does the physical work inside the airplane.
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.

Slop: Unwanted, excessive free movement in a control system. Often caused by a hole in a servo arm or control horn that is too big for the pushrod wire or clevis pin. This condition allows the control surface to move without transmitter stick movement. Also, see flutter.

Solo: Your first totally unassisted flight that results in a controlled landing.

Stall: What happens when the angle of attack is too great to generate lift regardless of airspeed. (Every airfoil has an angle of attack at which it generates maximum lift -- the airfoil will stall beyond this angle).

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.

Throttle Curve: The programming function of the radio which allows throttle operation to be adjusted to meet the modeler's specific needs at various points along the throttle movement. Particularly useful with 2-stroke engines in providing linear throttle response at the various points of throttle application.

Throttle Hold: A radio function which locks the throttle at a fixed point while a switch is activated. This function is used to hold the throttle in an idle. Useful when starting, as well as for auto rotations.

Torque: The force which tends to cause rotation.

Trailing Edge (TE): The rearmost edge of the wing or stabilizer.

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.

Trainer System: Allows trainer to link radios with a student via a cord, and to instantly take control of student's craft in-flight. The 8U system has special training features available.

Transmitter (Tx): The hand-held radio controller. This is the unit that sends out the commands that you input.

Vertical Fin: The non-moving surface that is perpendicular to the horizontal stabilizer and provides yaw stability. This is the surface to which the rudder attaches.

Washout: An intentional twist in the wing, causing the wing tips to have a lower angle of attack than the wing root. In other words, the trailing edge is higher than the leading edge at the wing tips. Washout helps prevent tip stalls, and helps the "PT" family of trainers recover, hands-off, from unwanted spiral dives.

Wing: The main lifting surface of an airplane.

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.