Helicopter Glossary

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 maneuvers 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.

A return to top

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.

Activating (Arming) Switch
An external switch that prevents the electric motor from accidentally turning on.

Adjustable Function Rate (AFR)
Similar to ATV, AFR allows end point adjustment independent of Dual Rate or Exponential settings.

Adjustable Travel Volume (ATV)
End Point Adjustment, ATV you can independently preset the maximum travel of a servo on either side of neutral.

Adverse Yaw
Some airplanes, especially high-wing airplanes with flat-bottom airfoils, have a tendency to yaw in the opposite direction of the bank. This is most common when flying at low speeds with high angles. Adjusting the ailerons can help reduce the yaw.

Aerodynamics
Science of air in motion.

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.

Aileron Extension
The Aileron Extension (also known as a servo extension) is a cable with connectors on either end which goes between the receiver and a servo. This allows the servo to be placed at a greater distance from the receiver than the cable that comes on the servo will allow. It also permits easier removal of a wing when the servo that controls the aileron is mounted in the wing and the receiver is in the fuselage (which is usually the case).

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 Bleed Screw
Screw for adjusting the amount of air allowed to bleed into the carburetor during idle

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.

AM
AM, or Ampilitude Modulation, was the primary means of modulation in R/C until recently. The control information is transmitted by varying the amplitude of the signal.

AMA
The Academy Of Model Aeronautics. The official national body for model aviation in the United States. The official national body for model aviation in the United States. AMA sanctions more than a thousand model competitions throughout the country each year, and certifies official model flying records on a national and international level.

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).

Antenna
The telescoping tube that transmits the signal.

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.

ARF
Almost Ready to Fly, a model airplane that can be put together with a minimal amount of time.

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.

ATS, Revolution Mixing, or Anti Torque Compensation
This is " Automatic Tail System". This refers to the radio mixing in a certain amount of tail rotor when the throttle / pitch is increased or decreased.

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.

B return to top

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

Backplate
Cover over the rear of the crankcase of an engine.

Ballast
Ballast is extra weight added to a glider to help it penetrate better in windy weather or to increase its speed. Ballast is usually added in tubes in the inner portion of the wings or in the fuselage at the center of gravity.

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 Cycling
To fully charge and discharge a battery to erase battery memory.

Battery Meter
The device used to monitor the strength of the transmitter batteries

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.

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

C return to top

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.

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.

Capacity
The maximum amount of energy a battery can store.

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

Center Line
An imaginary line drawn through the center of the aircraft from the nose through the tail.

Center of Gravity (CG)
Balancing point of an aircraft.

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.

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 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.

Clevis
The clevis connects the wire end of the pushrod to the control horn of the control surface. A small clip, the clevis has fine threads so that you can adjust the length of the pushrod.

Clunk
Located in the fuel tank, a clunk is weighted and ensures that the intake line has a steady supply of fuel.

Collective Pitch
This is the ability to vary the main blade pitch when the throttle is increased or decreased.

Computer Radio
By using the advanced programming functions of the transmitter, you can adjust the airplane without changing any mechanical structures.

Constant Drive Tail
This is a special autorotation clutch that will always drive the tail rotor even when the engine is off or in "Hold".

Control Horn
This arm connects the control surface to the clevis and pushrod.

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.

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.

Covering
The covering of an aircraft is the skin which is applied to the airframe, closing it in. It is commonly a fabric or plastic film which is heat applied with an iron. Plastic covering, once applied, gives a durable, shiny finish and requires no further treatment. Fabric covering usually requires a layer of paint to finish it and make it resistant to the exhaust of the engine.

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.

Crankcase
Main body of the engine

Critical Angle of Attack
The angle of attack at which smooth airflow over the top of the wing stops.

Crow Mixing
Primarily used in gliders for spoiler action by mixing the flaps and ailerons. It is necessary for the ailerons to be using separate servos, plugged into separate channels and the flap servo to be independent of both aileron channels. Upon applying Crow Mixing, the flaps go down while both ailerons go up.

Crucifix Tail
Crucifix refers to a stabilizer that is mounted part way up the fin. This is a compromise between the conventional tail and the T-tail combining some of the advantages of both.

Crystal
The device that sets the radio frequency of the transmission

Cylinder
The section of the crankcase where combustion takes place

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

D return to top

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.

Differential Ailerons
This type of mixing is accomplished by having separate servos on each aileron, plugging one into the aileron channel and the other into another unused channel. The two channels can be programmed to both operate from the aileron control stick, however the travel volume for each aileron may be adjusted separately giving more deflection in one direction (usually up) than in the other.

Dihedral
The degree of angle (V-shaped bend) at which the wings intersect the plane is called dihedral. More dihedral gives an airplane more aerodynamic stability. trainer planes with large dihedral dispense with ailerons and use only the rudder to control the roll and yaw.

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

Direction of Flight
The relative direction of the wing in relation to still air

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, 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 Aileron Extension or Y-Harness
The Y-Harness is a cable which plugs into a single channel in a receiver and two servos. This allows both servos to be operated from the same channel.

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 (D/R)
Dual Rate allows the modeller to choose between two different control sensitivities. With the dual rate switch in the "OFF" position, 100% servo throw is available for maximum control response. In some more sophisticated systems this "OFF" position may be adjusted to provide anywhere from 30% to 120% of normal full throw. In the "ON" position, servo throw is reduced and the control response is effectively desensitized. The amount of throw in the Dual Rate "ON" position is usually adjustable from 30% to 100% of total servo movement. The modeller can tailor the sensitivity of his model to his own preferences.

E return to top

Electric Starter
This is the small motor commonly used to start the airplane's engine.

Electrolyte
A caustic material found in batteries.

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 Mixing
Mixes the Elevator and Aileron functions, especially useful for delta-wing models where the elevator and ailerons are the same control surfaces. Each surface is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the elevator channel), the surfaces will act as both ailerons and elevator, depending on the position of the controls.

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.

Empennage
The vertical and horizontal tail surfaces of an airplane.

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
Exponential Rate is where the servo movement is not directly proportional to the amount of control stick movement. Over the first half of the stick travel, the servo moves less than the stick. this makes control response milder and smooths out level flight and normal flight maneuvers. Over the extreme half of the stick travel, the servo gradually catches up with the stick throw, achieving 100% servo travel at full stick throw for aerobatics or trouble situations.

F return to top

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

Fail Safe (FS)
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.

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.

Flapperon Mixing
Mixes the Flap and Aileron functions so that when each aileron is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the flap channel), the surfaces will act as both ailerons and flaps, depending on the position of the controls.

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.

Flat Bottom
A Flat Bottom Wing is when the lower surface of the wing is primarily flat between the leading and trailing edges. This type of wing has high lift and is common on trainer type aircraft.

Flex Cable
A flex cable is a special type of pushrod which is very flexible and can bend around corners even more easily than a flexible pushrod. These are generally made with a metal cable running inside a plastic tube and are popular in controlling the engine throttle.

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 Stab
A flying stab is where the stabilizer/elevator is one complete unit which all moves to control the aircraft in pitch.

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.

FM
FM, or Frequency Modulation, is now the common method and is less prone to interference than AM. Information is transmitted by varying the frequency of the signal.

Foam Rubber
Material that is used to dampen the airplane's vibrations and protect the airplane's battery and receiver.

Four Way Wrench
Combination wrench with sizes to fit glow plug, prop nut, etc.

Fore, Forward
Towards the front. Used such as "...the forward edge of the rib...", or as in "...with fore and aft movement...."

Frequency Flag
The frequency flag is a marker that is mounted on your transmitter to indicate what frequency your system is operating on to alert other modelers so as not to cause interference.

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 Bulb
Rubber bulb used to transfer fuel to model tank

Fuel Overflow Line (Vent)
This line pressures the fuel tank and provides an even fuel flow to the engine. It also functions as an overflow line when the fuel tank is full.

Fuel Pickup Line
This line connects the fuel tank to the carburetor, usually with a clunk on the tank end to keep the fuel flowing while the aircraft is in flight. Fuselage. The main body of an airplane.

Fuselage
The body of an airplane.

G return to top

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.

Gimbal (or Stick)
The device that allows the user to input desired control movements into the transmitter

Glide Ratio
The glide ratio is defined as the distance travelled in a horizontal direction compared with the vertical distance dropped on a normal glide. A 10 to 1 glide ratio means that the aircraft would loose one foot of altitude for every ten feet of distance traveled.

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.

H return to top

Handle
The device for carrying the transmitter

Harness
A device consisting of wires, switches, and a fuse that connects a motor to a battery.

Head
The component which forms the end of the compression chamber of the engine

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.

HEC
High Efficiency Clock. High motor pulse frequency, giving very fine control of motor speed, and saving current in the part-load range. Produces longer running times and reduces the thermal load on the motor.

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.

High Wing
This term describes an airplane that has its wings mounted on the top of the fuselage.

Hinge
The hinges are the moving blades on the control surface that allow you to control the airplane's movement. All hinges must be glued properly and securely to prevent the airplane from crashing.

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.

Hovering Pitch
This is the amount of pitch you will need to hover the helicopter. On average this is about 5 degrees. Most helicopter radio's will have a knob on the transmitter to vary the amount of pitch at the present hovering stick position.

Hovering Throttle
This is the amount of throttle you will need to hover the helicopter. On average this is about 50% throttle. Most helicopter radio's will have a knob on the transmitter to vary the amout of throttle at the present hovering stick position.

I return to top

J return to top

K return to top

L return to top

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

Lmmelmann
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.

Lntake
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".

Lnverted
This is when the helicopter is inverted and the funtions of the Pitch, Elevator, Rudder can be reversed by the use of the "Inver" switch or the pilot can do it him or her self at the sticks. This is refered to as "Switchless" inverted.

Lnverted 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.

L/D
Lift divided by drag expressed as a ratio. Essentially the same as a glide ratio. Think of L/D as a glide slope, then, for a given amount of distance the sailplane moves forward, it drops a certain amount.

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.

Long Stroke
The stroke of an engine refers to the distance the piston travels from top to bottom. In a Long Stroke engine this distance is a bit longer than on the standard engine making the engine a bit stronger in torque and operation lower RPM. Quite often an engine is "Long Stroke" if the stroke distance is greater than the diameter of the piston.

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.

M return to top

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.

mAh (Milliamp Hour)
A measure of a battery's capacity. The larger the number of milliamp's the longer the battery cell will last.

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.

Main Landing Gear
The wheel and gear assembly the airplane uses to land. It is attached to the bottom of the fuselage.

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.

Minimum Sink
The speed at which a sailplane loses altitude most slowly. Usually expressed in feet per minute.

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.

Mode I
The control stick configuration with the rudder and elevator being controlled by the left stick while the right stick controls the throttle and ailerons.

Mode II
The control stick configuration with the ailerons and elevator being controlled by the right stick while the left stick controls the rudder and throttle.

Mode III
The control stick configuration with the rudder and elevator being controlled by the right stick while the left stick controls the ailerons and throttle.

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.

Mounting Lug
The section of the crankcase used to mount the engine to the airplane

Muffler
This device muffles engine noise and increases the back pressure from the engine's exhaust stack, which can improve the airplane's performance at low speeds. Mufflers are usually required by R/C Clubs.

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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.

Needle Valve
This mechanism within the carburetor adjusts the fuel mixture and throttle. Refer to your engine's manufacturer instructions for directions on how to adjust the needle valve.

NiCad (or 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.

Noise Traps
A Noise Trap is a small electronic device which is wired into a long servo extension to reduce radio interference and to boost the control signal going to the servo. These are recommended for use where long servo leads are necessary.

NORRCA
National Organization for Racing Radio Controlled Autos.

Nose Gear
The part of the landing gear that is attached to the nose of the fuselage. The nose gear is usually connected to the rudder servo to help you steer the airplane on the ground.

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.

O return to top

OPTO
Galvanic separation, blocks interference from the motor current circuit, prevents it reaching the receiver.

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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.

PCO
Low-voltage protection, gives safely margin when using BEC in model aircraft. PCO cuts off the motor (the main power consumer) in good time, to reserve sufficient battery capacity for a safe landing.

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.

Peak Detection
Usually refers to a type of battery charger that automatically shuts off when a battery is fully charged.

Penetrate
To make progress against the wind.

Pitch
Degree of nose up or nose down from level to the horizon.

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

Polyhedral
Polyhedral refers to the multiple angle wing panels make with the horizontal. A wing with polyhedral has more than two wing panels and the angle of the wing changes at each joint.

POR - Power On Reset
Safety circuit; controller does not start working until the throttle stick is set to "off". Prevents the motor bursting into life unexpectedly; an important safety aspect for all modelers.

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 shaft
The main crankshaft which transfers the power of the engine to the propeller

PPM
Pulse Position Modulation. Another term for FM.

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.

Pushrod
The rigid mechanism that transfers movement from the servo to the control surface.

Pushrod Connectors
The pushrod connector is another means by which a pushrod may be connected to a servo. The connector is mounted onto a servo arm and the pushrod wire is secured by means of a set screw.

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R return to top

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.

Relative Wind
Direction that the air molecules strike the lead-ing edge of the wing.

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 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.

ROAR
Radio Operated Auto Racing. National body to standardize and sanction R/C car and truck racing.

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.

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.

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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 Control Arms
Servo Control Arms are the plastic output horns which are mounted to the output shaft on your servos. These come in various sizes and styles for different control applications. Most servos will come with an assortment of arms so you can customize to your own specific control needs.

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 set up.

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.

Slipper Clutch
This is another special unit that is attached to the autorotation clutch will let the main blades turn the tail rotor when the engine is off or in "Hold". The difference between this and a "Constant Drive Clutch" is that this one will "Slip" a little so the tail rotor while spinning will not load the main rotors as much while in the "Hold" funtion doing a "Autorotation".

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 Button
This feature is found on more complex radios and is used to perform a snap roll maneuver by simply pressing one button. The function is usually programmable to give a combination of rudder, elevator and aileron control.

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 Control
An electronic device that functions as a throttle for an electric motor. A speed control controls the speed or rpm of an electric motor.

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.

Stabilizer
The Stabilizer is the fixed horizontal surface at the rear of an aircraft. It provides pitch stability for the aircraft.

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).

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.

Switch Harness
This switch is commonly located on the fuselage and governs the on/off mechanism for the flight pace. Tachometer. A device the measures the engine's RPM (rotations per minute) by counting light impulses that pass through the spinning propeller.

Symmetrical Wing
A Symmetrical Wing airfoil is curved on the bottom to the same degree as it is on the top. If a line was drawn from the center of the leading edge to the center of the trailing edge the upper and lower halves of the airfoil would be symmetrical. This is ideal for aerobatic aircraft and most lift is created by the angle of incidence of the wing to the flight path.

T return to top

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
Rising body of hot air that can take a sailplane to a great height.

Thread Locker
A liquid that solidifies; used to prevent screws from loosening due to vibration.

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 Stop Screw
Screw for setting the lower limit of the throttle movement

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.

Torque Rods
Inserted into ailerons, these rigid wire rods run along the wings' trailing edge, then bend downward and connect to the pushrods.

Tow-hook
The tow-hook is a small metal hook mounted on the bottom of the glider fuselage at approximately the center of gravity and to which the hi-start or winch is connected.

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 Lever
Slides used to adjust control surfaces during flight.

Tx
Abbreviation for transmitter.

U return to top

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 return to top

V-Tail
A V-Tail is a special tail surface configuration where the horizontal stabilizers and elevators are mounted at an angle between 30 and 45 degrees in a V-shape and the vertical fin is eliminated entirely. The stabilizers provide stability in both pitch and yaw while the moveable surfaces provide directional control in both pitch and yaw.

V-Tail Mixing
Used when there is a V-Tail on the aircraft rather than the conventional elevator and rudder. Each control surface of the V is connected to a separate servo. Operating the elevator control stick will move both surfaces up for back stick or both surfaces down for forward stick. Moving the rudder control stick left will move the left surface of the V down and the right surface up. Moving the rudder control stick to the right will move the left surface of the V up and the right surface down.

Variable Trace Rate (VTR)
This radio function is similar to exponential except it uses two linear responses to determine the servo sensitivity on the first and second half of the control stick movements.

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 Stabilizer
The vertical surface of the tail gives the airplane stability while in flight.

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.

W return to top

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 Collar
The round retaining piece that anchors wheels in place on the axle.

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
Because wings provide the primary lift force on an airplane, adjustments to the wings affect the airplane's movements while in flight.

Wing Area
The Wing Area is the total surface area of the wing of the aircraft, usually calculated by the wingspan times 7the wing chord, although more complex calculations are used on unconventional wing plans.

Wing Chord
The Wing Chord of an aircraft is distance from the front or "leading edge" of a wing to the back or "trailing edge".

Wing Loading
Wing loading is the weight of the aircraft divided by the wing area. It is designated ounces per square foot.

Wing Seating Tape
Wing seating tape is mounted on the fuselage wing saddle where the removeable wing fits and isolates the wing from vibration as well as to form a seal to keep exhaust gases from entering the structure.

Wing Span
The maximum distance from wingtip to wingtip.

Wing Tip
The very outer end of a wing.

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.

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Y return to top

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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Z-Bend
The wire ends of pushrods have Z-shaped bends, which attach to the servo.