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Glossary of Terms

9Z Specific Glossary: This incredibly powerful radio has a cluster of features all its own.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

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.

For helis: A 540 stall turn, for example, describes a one and one half revolution spin at the apex of a vertical stall, which results in the helicopter resuming nose forward flight before recovery.

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.

For helis: combining two or more maneuvers into one maneuver. Examples: rolling circle, inverted backwards loop.

3F
Slang abbreviation for flip flop flying. Similar to 3D, but without the finesse.

AFR (Adjustable function rate/high rate)
Adjusts the total travel in each direction of a particular function, such as ailerons. For example, used to adjust total aileron travel whether ailerons are a single servo in channel 1, or two servos set up as flaperons, elevons, or other programming.

ATL
Low-side only trim adjustment. Throttle trims on most radio systems are ATL, allowing the trim to affect only the idle and not the high-speed engine's setttings. NOR (normal) is the other option of trim setting wherein trim movement affects the servo across its entire range of motion.

ATV/EPA
Adjustable travel volume, or end point adjustment. Adjusts the total travel in each direction of servos 1-8 regardless of their control assignment. For example, ATV adjustment to AIL channel will adjust only the servo plugged into channel 1 regardless of any flaperon, elevon, or other programming set-ups.

Aft
Towards the rear. Used such as: "...with an aft center of gravity...."

Aileron Differential
Creating larger upward aileron travel than downward aileron travel to help minimize the model "dragging" the drooped aileron which causes a model to yaw with aileron input.

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.

Ailevators
Twin elevator servos plugged into separate channels used to control elevator with the option to also have the 2 elevator servos act as ailerons in conjunction with the primary ailerons.

air brake (Air only)
Combines elevator, flap, and optionally spoilers to suddenly slow the model for spot landings. May be triggered by throttle position.

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

For helis: The rotor disk is the effective wing, and airfoil refers to the shape of the blades.

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.

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 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.

Auto Shut off
Safety feature which shuts off the transmitter after a set period of time of inactivity to avoid draining the transmitter battery. (Not all transmitters have this feature)

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 Bearing
Servo's output shaft is supported with bearings for increased performance and accuracy.

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.

Battery Fail-safe function
Determines how to regain throttle control after a receiver low battery warning.

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.

Brake flap mixing
A group of 3 mixes, mixing brake flap-to-elevator (F-E), aileron and speed flaps, all individually adjustable.

"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.

Butterfly
Also known as crow. A mix which activates up flaperons and down inner-most flaps for gliding speed control without spoilers or air brakes.

Butterfly-to-elevator mixing
4- and 5-servo gliders only. A preprogrammed mix to deploy elevator to compensate for ballooning caused by butterfly. Adjusted proportionally with the in-flight adjustment of butterfly.

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. Please refer to the swashplate FAQ for further information.

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.

CAMPac
Optional extended data storage module for certain Futaba transmitters.

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

Chandelle
A very steep climbing turn where the airplane makes a 180o 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.

Channel delay (Servo Slow/speed)
A feature within ATV which slows servo operation any time the radio is in the particular condition which has the delay set.

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 NiCd batteries are included.

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.

Collective pitch (Air only)
Used to regulate variable pitch props to slow model and keep engine running in vertical dives and provide maximum torque in model's vertical climbs. Idle trim is used for how high the idle is when in reverse pitch (diving) and the pitch trim finely adjusts the amount of pitch at full throttle to avoid over-propping the engine.

Condition
Separate flight model which has nearly 100% adjustability separate from the basic model set-up.

Condition hold
Holds the actual output to the model in a predefined state, allowing the user to make adjustments to other conditions safely without having the model receive the commands for that condition. For example, condition hold is used by a heli pilot to keep the heli idling safely on the ground while adjustments are made to the throttle hold, idle-up, and inverted conditions. Condition hold is used by an aircraft pilot to keep the aircraft idling safely on the ground while adjustments are made to a condition which requires full throttle, retracts up, smoke on, or other equipment combinations which the modeler wants to adjust but not activate on the ground.

Condition Name
Used to name each flight condition to minimize confusion during set up and use.

Condition Select
Used to select and assign a flight condition to the model currently in use.

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.

Copy condition
Used to copy one condition into another. Often used to duplicate a working base condition into additional conditions to minimize repeating set up steps.

Copy model
Used to duplicate the settings of one model already in memory into a second model memory. Often used to set up 2 similar models, or make a copy of a working model to experiment with new set-ups. Also used to copy models to/from a CAMPac data storage unit or a 32MB CF Card.

Coreless motor
In a conventional servo, the motor has a steel core armature wrapped in wire that spins inside the magnets. In a coreless design, the armature uses a thin wire mesh that forms a cup that spins around the outside of the magnet eliminating the heavy steel core. A coreless motor does not have magnets as standard servo motors do, so they have a smoother, more constant, and stronger action. Regular servo motors have either 3 or 5 magnets (poles) which when the armature is between these, the servo motor is at its weakest.

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.

Cross-trim
Function set-up where the trimmer next to throttle adjusts elevator and the trimmer next to elevator adjusts throttle.

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

DSC = Direct Servo Control
High-end convenience feature which allows control/adjustment of servo function without sending signal through receiver. Requires optional DSC cord (FUTM4250) and DSC-compatible receiver such as R149DP and R113IP.

Dead Stick
Slang term for a landing without engine power. An example: "I ran out of fuel at 50 feet and had to dead stick".

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.

Differential
Uneven movement in each direction of a control surface. Usually used when discussing ailerons or when describing an undesired unevenness in movement of other controls.

Digital
Please see the digital servo web page: http://www.futabarc.com/servos/digitalservos.html

Diode
An electronic component which only allows current to flow one direction. Protects the transmitter against reverse polarity or power surges during charging.

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.

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, air brakes, 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 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 overcontrol.

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.

Elevator trim (2- and 5-servo gliders only)
Two separate offset mixes for the elevator to allow pre-programmed elevator settings, for example, for thermal hunting, penetrating, gliding, etc.

Elevator-to-brake flap mix (5-servo gliders only)
This is a pre-programmed mix from elevator to the brake flaps (small centermost flaps) to increase lift for tighter turns, etc.

Elevator-to-speed flap mix (4-servo gliders only)
This is a pre-programmed mix from elevator to the speed flaps (primary flaps) to increase lift for tighter turns, etc.

Elevator-to-Flap Mixing
Used to apply flaps along with elevators to increase lift, allowing modeler to fly at slower speeds, make tighter loops or turns, etc.

Elevon (Air only)
Used for delta wing and tailless aircraft which have 2 servos operating 2 aileron-like control surfaces as both elevator and aileron.

Empennage
The vertical and horizontal tail surfaces of an airplane.

Engine cut
Also known as throttle kill. Used to safely shut engine off.

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. Please refer to the FAQ for more information. Additionally, battery fail-safe 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. Please refer to the FAQ for more information.

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.

Flap-to-elevator mixing (Air and 2-servo gliders only)
Used to counteract unwanted changes in pitch when flaps are deployed.

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.

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.

Flyback
Decrease in angle held by a servo which is being commanded by an AVCS gyro when the input is released. For example, a rudder servo might be at full deflection when rudder input is held. When the rudder stick is released but the model has not yet turned as far as the AVCS gyro has read your input to tell it to move, the servo will continue to hold input. However, it may "flyback" or decrease the angle at which it is holding slightly. This is perfectly normal.

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 mixture control
Used to command a second servo which adjusts the fuel mixture at the carburetor for different throttle position settings.

Function menu
Used to assign specific features to specific stick, switch, slider and knob positions. For example, flap control can be moved to a switch by simply changing function assignments.

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.

Grease-in
A very smooth, gentle landing without a hint of a bounce.

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.

Gyro sensitivity
Used to create stick priority or activate each rate of a dual rate gyro based on stick position. This preprogrammed mix decreases the gain of the gyro directly proportional to the amount of rudder stick given (or steps the gyro down from high to low rate on dual rate 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.

Hover
To maintain a stationary position in which the model is not climbing, diving, rolling or yawing.

Hovering offset (Heli programming only)
Adjusts the center point of the pitch curves, including the hovering pitch curve, to fine-tune the hovering point when it is not exactly center throttle stick position.

Hovering pitch (Heli programming only)
This is a pre-programmed hovering-type mix which gives an in-flight adjustment to the pitch curve at and around center stick (or the hovering point if that point is not at center throttle stick, then the center-point of this feature is adjusted with the hovering offset command) to give very fine-tuning for easiest hovering.

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

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 others 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.

Inhibit
Makes a feature inactive and unable to be used. When a function is inhibited, it cannot be used even if the assigned switch is moved to the on position. Setting a feature to INH turns off its functionality without losing any settings. Only visible in specific features.

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 "takes in".

Inverted
To fly a model upside-down.

Inverted Flight Control
Activates inverted flight programming for helis, which reverses the direction of the rudder, pitch and elevator servos, and sets up inverted flight pitch high-side and low-side. Inverted programming is used to allow the radio inputs to be identical to upright flight while the model is inverted. Note: this approach to hovering is seldom used. Instead, idle-ups are used and the modeler learns to understand and respond to the controls' reversal in inverted flight.

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".

Lateral Balance
The left-right or side-to-side balance of an airplane. An airplane that is laterally balanced will track better through loops and other maneuvers.

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

Linear Mix
Directly proportional.

Link
Instruction for one mix to obey another. Mixing function which allows multiple mixes to work in conjunction.

Lithium battery
The internal battery in the 9Z which maintains memory when the transmitter battery is removed.

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.

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.

MPH
Speed in Miles Per Hour. Like RPM, MPH is both singular and plural.

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.

Master Mix Mode
Mix option which causes slave channel to operate based on master channel's ATV, not AFR or D/R settings.

Metal gears
Drive gears within a servo which are made of one or multiple metal types. Metal gears tend to wear more rapidly than nylon gears when in the same installation, and so require more frequent service to maintain optimum accuracy; however, metal gears are more durable in the case of severe vibration, flutter, or physical shock.

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.

Futaba module models include TP, TK, TJ, TL, and TK-FSS. For information on which module to use, see 9Z/8U modules, TF modules and aftermarket modules.

Narrow-Band
A radio with a 20 kHz band width. All Futaba radios produced 1992 or later and all Futaba FM and PCM radios ever produced are narrow band. Specific list of Futaba narrow band transmitters.

NiCd = Nickel Cadmium battery
Rechargeable batteries which are typically used as power for radio transmitters and receivers.

Nitro = Nitromethane
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.

Nose Gear
The strut and wheel that's under the nose of some aircraft.

Null
Not assigned or never changed. For example, a mix which has a null switch assignment is always active no matter what switch is moved.

Nylon gears
Drive gears within a servo are made of nylon. Nylon gears show slower wear than metal gears, but are more prone to failure due to severe vibration, flutter, or physical shock to the servo.

PA2 = Pilot Assist
Optional onboard device which uses optical sensors to correct model's orientation to upright.

PCM = Pulse Code Modulation
PCM systems use digitally encoded signals to minimize interference and provide today's most advanced R/C control. Please refer to the PCM 1024 info page and the FAQ for more information.

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.

Pitch to rudder (Heli programming only)
Also known as a revolution mix or a tail rotor mix, counters the torque caused by adding pitch with opposite direction rudder command to keep the helicopter from rotating or revolving as a result of the increased torque. Not required with the use of a heading-hold gyro, which self-counters the torque-caused movement.

Pitch Trim
Offsets the entire heli pitch curve, increasing or decreasing responsiveness proportionally at all points.

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.

Programmable mix (Pmix)
Used to cause specific servo responses to specific inputs separate from the basic control set-ups. For example, used to mix 2 servos to operate in tandem to move a rudder on giant scale aircraft, or to mix smoke activation based upon throttle stick position.

Pull-Pull
A linkage setup using two rods or wires. One is pulled for one direction, the other is pulled for the other.

Push-Pull
A linkage setup using two rods. One rod pushes, while the other pulls.

RPM
How fast something turns. It means Revolutions Per Minute. It is both singular and plural.

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.

Reset (Return to default)
Used to reset timers, also a model submenu used to reset part or all of a specific model's settings.

Resonance
This is the increased vibration (or amplitude of oscillation) of system when acted upon by a force whose frequency is close to or equal to the normal frequency of the system. When the resonance of many parts of a machine are in synch, the whole machine will vibrate at a greater rate and can be damaged. Resonance can cause difficulties in an aircraft, particularly when using a vibration mount with an improperly balanced propeller/spinner.

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 vibration.

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.

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

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.

Rotor direction (Heli programming only)
Sets rotor's rotational direction for proper mixing.

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.

Rudder-to-Aileron
Mix used to counteract undesirable roll which often happens with rudder input, especially in knife edge, also called roll coupling.

Rudder-to-Throttle
This heli mix adds a small amount of throttle to counter the added load on the main gear from increasing the pitch of the tail blades, helping to maintain a constant headspeed during rudder application. (This is a minor effect and is not a critical mix for most helicopters.)

Ruddervator
Ruddervators are on a v-tail. Both of the ruddervators move up and down for pitch control and both move left or right for yaw control.

Rx
Abbreviation for receiver.

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

Seaplane
An airplane that has floats, or pontoons, attached to allow it to land on water.

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 Reversing
Reverses the rotation of a servo with the flip of a switch. Adds ease and flexilibility during installation.

Servo Output Arm
The removable arm or wheel which bolts to the output shaft of a servo and connects to the pushrod.

Servo Reversing
Used to reverse the direction of a servo to ease installation and setup.

Servo Test (Display)
Test feature is used to check for proper servo operation, speed and travel by cycling each servo very slowly. Display feature shows a bar graph indicating movement of each servo. Example: use servo display to plan and test complex radio programming prior to installation into a model to experiment with how best to accomplish a certain goal.

Shot down
A "hit" that results in a crash landing. Sometimes caused by radios miles away.

Slats
Moveable surfaces on the leading edge of the wing that helps 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
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.

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.

Snap Roll Switch
Combines rudder, elevator and aileron movement to cause the aircraft to snap or spin on the flip of a switch.

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.

Speed Flap
The middle control surface on a 6-trailing-edge-surface glider or the inboard control surface on a 4-surface glider.

Spin
A maneuver where at least one wing is stalled and the two wings are operating at very different angles of attack. 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 looks 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 180o.

Spoiler(s)
Control surfaces on the wing that destroy lift. They "spoil" it. They are used on sailplanes 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.

Stabilator
Stabilizer+elevator, also called full-flying tail. Stabilizer incidence controlled by pilot in lieu of an elevator.

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).

Stick setting
Used to assign the specific feature(s) to a particular gimbal's movement.

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.

Swashplate adjustment (Heli programming only)
This feature includes swash-to-throttle mixing, used to add throttle during cyclic commands for constant engine RPM. It also includes swash rotation, used to correct for a model whose set-up has the swash plate shifted a certain angle from the pre-defined swash plate types in the model menu (SWH) or to fine-tune roll or looping maneuvers due to rotor blade phasing differences.

Swashplate type (Heli programming only)
Selects specific helicopter swash plate geometry, such as "CCPM," which uses a 4-servo swash plate set-up. Swash plate rotation can then be adjusted in SWP in the condition menu if your helicopter's specific geometry does not match the positioning of the stock swash types.

Synthesized module/receiver
Allows modeler selection of any U.S. aircraft-legal 72MHz or 50MHz frequency.

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.

Taileron
Stabilator with collective and differential actuation.

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 have the two large wheels in the front, and the small one in the rear. The airplane sits on its tail.

Thermal hunting
Using specific programming set-ups to have the model respond noticeably to the lift of a thermal.

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.

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.

For helis: Aids in setting the hover point, and end points of the throttle in the collective mix.

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.

Throttle hold (Heli programming only)
This is a pre-programmed linear mix with an offset. This mix makes the throttle servo no longer responsive to throttle stick position, and moves the throttle servo to idle. This is used to practice autorotations. NOTE: a helicopter model type pre-assigns a condition specifically to be used for throttle hold or autorotation practice; HOWEVER, it does not assign anything to this condition. Besides activating throttle hold, you will need to create proper pitch curves to allow blade inertia to increase during the drop, and sufficient pitch to bring the helicopter back to a hover and land.

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.

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.

Tricycle Gear
The landing gear arrangement where the airplane has main gear and a nose gear.

Trim follow
Trim combine/separate feature of trim menu. Allows trim adjustments in one condition to affect or not affect other conditions.

Trim menu
Used to memorize current digital trim positions, set trim type, % of trim delay when switching from condition to condition, sound on or off when trimmers used, rate of trim response at 2 different lengths of time held, and having trims affect all conditions or only the current condition. For example, store trim positions to memory once model is perfectly trimmed. Adjust CG and re-fly, re-trim. Amount of trim change caused by adjustment to aircraft is now easily measured. To activate additional features of trim menu, select the specific trimmer and adjust as desired.

Trim offset
Sets an offset or adjustment of trim when switching between conditions. For example, applying up elevator trim when switching from an upright to an inverted flight condition to keep the aircraft flying straight and level.

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.

V-tail model Mixing (Air and all gliders only)
Used on a V-tail model to have 2 servos operate 2 control surfaces as both rudder and elevator.

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.

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.

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).

Wing
The main lifting surface of an airplane.

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 make 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.


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