Having started out in RC helis not too long ago myself, I thought it might be helpful to beginners visiting my blog to have a list of terms and their definitions.Since I compiled these myself, mostly from memory, there may be some mistakes or inaccuracies. If you’d like something added, or see something that needs to be corrected, let me know!

Aileron:
On an aircraft, the control surface that influences movement of the aircraft along it’s roll axis. While a helicopter lacks true ailerons, the pitch of the main rotors is manipulated in such a way as to have the same effect.

Antenna Tube:
A small-diameter plastic tube used to route the receiver’s antenna so as to keep it from getting tangled or fouled.

Anti-Rotation Bracket:
A bracket mounted on the model’s airframe that engages a pin on the swashplate to keep it from spinning freely.

Autorotation or Auto:
A procedure by which a helicopter is able to continue to fly controllably in the event the motor fails. The collective pitch of the main rotors is manipulated in such a way that the airflow moving through them causes them to rotate (much like a windmill), thereby generating lift. Using autorotation, it is possible to make a controlled descent and landing with a helicopter that has lost main engine power.

Balance Charger or Balancer:
In a multiple-celled battery pack, it is possible for the individual cells to develop differences in their charge levels. Since Lithium Polymer (LiPo) batteries are very sensitive to overcharging, it’s important that their cells be kept at or very near equal  levels when charging. A balancer does this by monitoring the individual cell voltages in a pack through a connector on the pack (called a balance tap) and adjusting their rate of charge accordingly. When such a balancer is built in to a charger, the charger is known as a Balance Charger or Balancing Charger.

Ball Link:
A semi-spherical connection point for control linkages used widely in RC helicopters. Ball links mate to a socket end on a link rod and offer a wider range of movement than a regular linkage. This makes them ideal for things such as swash plates, which must move in several axes at once.

Bearing Block:
A plastic or metal block which mounts inside a model helicopter’s frame which holds the main bearings that support the main rotor shaft.

BEC:
Battery Eliminator Circuit. This electronic device is found on electric-powered models and supplies power to the receiver and servos from the main battery, thus negating the use of a separate receiver battery and thereby saving weight. Usually, these are equipped with built-in voltage regulation circuitry to convert the main battery’s voltage to a level compatible with the receiver and servos.

Blade Balancer:
A device by which the main or tail rotor blades are balanced. Unbalanced blades can cause severe vibrations in a helicopter, and even make it dangerous.

Blade Grip:
A molded plastic or machined metal part that connects the blades to the rotor head. The  grips are bolted to the head by way of the feathering shaft, and the blades are bolted into the grips. A ball link is attached to the grip and a linkage is connected to it to allow the pitch of the blade to be changed. Every blade has one grip at its root.

Blade Holder:
Usually made out of foam, a blade holder slides over the folded main rotor blades where they meet and secures them by clipping to the tail boom.

Bog:
A condition by which too much pitch (positive or negative) is induced on a rotor, causing the motor to slow down due to increased drag. More common on electric helicopters, bogging is usually a symptom of either an underpowered model, or poor collective management. Bogging is sometimes accompanied by a sound known as “blade farting”, “chuffing”, or “woofing”.

Brushed:
A type of electric motor employing a rotating armature (also called a ‘rotor’) that gets its power through a set of small contacts called “brushes”. These brushes remain stationary and ride on a portion of the rotating armature called the “commutator”. Since these brushes come into physical contact with the commutator, the brushes induce friction and wear, eventually requiring replacement. A brushed motor has two power leads and is operated by varying the voltage supplied to the motor to regulate the motor’s speed.

Brushless:
A type of electric motor that employs a stationary armature around (or within) which the magnets move. Since the power wires connect to the stationary portion of the motor, brushes are not required, and no friction or drag is thus induced by them. Brushless motors generally last longer than brushed, and give better performance. A brushless motor typically has three power leads, where a brushed motor will have only two. A brushless motor is controlled by sending a chain of pulses or the appropriate timing to the motor.

C Rating:
The maximum safe amount of current that can be drawn from a battery is the amperage rating of the battery times its C rating. For example, If you have an 11.1v battery rated at 2100 mAH (Milliamp-hours) and a 20C rating, you can safely put a maximum load of 2100 x 20 = 42000 mAh or 42 amps on that battery continuously until it is fully discharged. Exceeding the C rating of a battery can damage it, and in the case of a LiPo, can cause it to puff or catch fire.

CA:
Cyanoacrylate Adhesive, sometimes known as super glue. This type of adhesive is known as an “anaerobic” adhesive, which means that it works in the absence of air. It will glue most things instantly, thought there are different types that work in slightly different manners and bond at different speeds. Generally, all types of CA will bond your fingers (or any other body parts) together instantaneously. Usually, a “de-bonder” made of acetone is used to disconnect you from yourself should this happen.
Canopy:
In aircraft terms, the covering over a cockpit. In RC heli terms, it’s a lightweight plastic, fiberglass, or composite shell attached to the front of a “pod-and-boom” type of helicopter. Covering just the forward portion of the heli, and such things as the batteries, electronics and avionics, a canopy generally does not cover the whole frame of the model.

CCPM:
Collective Cyclic Pitch Mixing. This is a method of flight control employed by modern RC helicopter models and radios. In a CCPM helicopter, three servos are connected to the swash plate, either directly or through a linkage system and work directly to move it. In a mechanical CCPM helicopter, the pitch servo moves a linkage that physically moves the  elevator and aileron servos (not just the arms, the WHOLE servo) when collective input is given. With an eCCPM helicopter, all servos remain stationary and their movement is electronically mixed within the transmitter to achieve the same results.

Chaos:
An advanced “3D” helicopter maneuver in which the pilot executes a series of stationary flips and pirouettes timed so that the helicopter appears to be totally out of control. A VERY difficult maneuver.

Circuit:
Flying a model in the classic “racetrack” pattern, basically a large circle or oval. Circuits can be performed upright, inverted, forward, reverse, and even rolling, or any combination of the above.

Clutch:
A mechanical device installed on the engine of a nitro or gas powered helicopter that connects the engine’s output to the main rotor gear train. The clutch will allow slippage at low RPM to keep the engine running at idle while the blades are stopped, and will grip more tightly as RPM is increased, thereby transferring engine motion to the main rotors.

Collective Pitch:
A control method of a helicopter by which the pitch of all main rotor blades is varied in unison or “collectively”, thereby imparting lift changes in the rotor disc to facilitate ascent or descent along the helicopter’s vertical axis. It’s basically what allows a helicopter to lift straight up off the ground, hover, and land straight down. In RC helicopters, the collective pitch is generally linked to the throttle control and both are controlled by the same stick at the same time. SEE ALSO: “Curve, Pitch”

Curve, Pitch:
The Pitch Curve is a setting in the radio that controls how much collective pitch is imparted to the rotor disc in relation to the position of the throttle stick. The transmitter uses its on-board computer to “mix” the throttle and collective channels together, based on how the curves are set up.

Curve, Throttle:
Similar to the Pitch Curve, the Throttle Curve regulates the amount of power the engine or motor is given based on the position of the throttle stick on the transmitter. The throttle curve can be anything from a “flat curve” which indicates a constant throttle setting no matter where the stick is, to a “linear curve” in which throttle position is directly proportional to the position of the stick.

Cyclic Pitch:
A control method by which the pitch of the main rotor disc is varied at different points around its circumference. Pitch is varied at different points to change both the attitude of the helicopter and the direction of it’s flight. On “Mode 2” controllers (standard setup in the US), cyclic is controlled by the right-hand stick. This stick controls both the aileron and elevator servos of the helicopter, and the transmitter’s computer mixes the inputs to get the desired motion of the swash.

Dual Rates:
The property of modern computer-controlled RC transmitters by which the total throw of any servo can be adjusted. High rate gives more control surface deflection for a given stick movement whereas low rate gives less. The amount can be adjusted, generally per servo and toggled between high and low with a switch. Some radios combine all dual rates to a single switch, while some give a separate switch for each servo. High rates generally give a more nimble feeling to an aircraft, while low rates make the model more docile, but reduce overall maneuverability.

Elevator:
The surface of an aircraft that controls the pitch attitude of the entire aircraft (not to be confused with the collective pitch, which refers to the pitch attitude of the rotor blades themselves). The pitch axis of the aircraft extends from the left side of the aircraft to the right, along the center of gravity. On Mode 2 transmitters, the elevator is assigned to the right stick.

ESC:
Electronic Speed Controller. The esc is an electronic component that connects to the throttle channel of the receiver on an electric-powered model. The device receives inputs from the receiver and thus controls the motor it’s attached to. A brushed speed controller has two wires, one positive and one negative, and works by varying the voltage that it supplies to the motor. A brushless esc has three motor wires and sends a pulse train to the motor which then moves accordingly. These pulses are timed in such a way as to precisely control the motor’s RPM and other functions. An esc must be rated high enough to handle the maximum amount of amperage expected to be drawn by the motor at any given time.

Exponential, or Expo:
The property of a modern radio control transmitter by which the amount of servo movement is varied with regards to the position of the control stick. Total throw is constant, but amount of throw can be varied such that a small stick movement produces very little servo movement, but moving the stick to its limit produces a larger proportional movement of the servo. Expo is used to tame “twitchy” or sensitive aircraft and help with precision flying.

Feathering Shaft:
The part of two-bladed RC helicopter that connects the blade grips together in the head. The feathering shaft allows the blade grips to rotate along their center axis, thereby allowing the pitch of the individual blades to be varied independently. The feathering shaft is not rigidly attached to the head, but allowed to “float”, which has the effect os allowing the blades a minimal amount of “flap”, which assists with forward flight and wind handling. The movement of the feathering shaft within the head is buffered by rubber bushings called head dampers.

FF, or FFF:
Forward Flight or Fast Forward Flight, respectively.

Figure Eight:
A maneuver where the aircraft describes a path through the air resembling that of the number eight. Much like circuits, with an RC helicopter a figure eight can be flown in a standard, nose-first pattern, with a constant heading, or even with flips and rolls along the path. It can be flown in upright, inverted, forward or reverse or any combination of these. One of the first aerobatic maneuvers most new pilots learn how to do, a flat, constant-heading figure eight helps develop finer control and tail management.

Flip:
A maneuver in which the helicopter is rotated around its pitch axis. If not otherwise moving when this maneuver is performed, it is referred to as a stationary flip, and the goal is to rotate the model 360 degrees (or more) with no change in altitude. When the maneuver begins with the nose of the aircraft coming up, it is a “backflip”; when the nose drops at the start, it is a “front flip”.

Flybar:
A component of the helicopter’s main rotor system that acts to stabilize that system and make it more controllable. Used on two-bladed main rotors only, the flybar is a metal rod that is mounted perpendicular to the main blades, and either above or below them, with a short airfoil (or paddle) on each end. The flybar passes through the mast-mounted “seesaw” and through the linkages attached to it, is responsible for the pitch changes imparted to the main rotor blades. It does this by converting aerodynamic forces from the spinning airfoils into angular forces which act on the main rotor blade grips. The flybar also employs both angular momentum and aerodynamic force to help stabilize the  main rotor blades. Newer electronic stabilization systems which allow the elimination of the flybar are becoming more affordable. SEE ALSO: Flybarless

Flybarless:
Generally referring to a two-bladed rotor system that does not have a flybar to help  stabilize it. Helicopter rotor systems having more than two blades are all flybarless. Since the flybar is absent, a flybarless rotor system usually needs a series of additional gyros and an additional mixer to help stabilize the head and make it flyable. While it is possible to fly a flybarless head without these extra gyros and mixers, it is VERY difficult. The benefit of a flybarless two-bladed head is increased maneuverability and lower rotating mass, which means more power to the rotors. Flybarless rotor heads with more than two blades are very useful for scale models.

Frame:
Made of materials such as plastic, aluminum, fiberglass, or carbon fiber, the frame is just that: the framework that the rest of the helicopter is built on. All major component assemblies attach to the frame, which holds everything together. Note that this is not generally referred to in RC heli modeling as the “fuselage”, a term that is reserved for a complete outer shell used on scale models or on FAI F3c competition models.

Funnel:
A maneuver in which the helicopter is oriented tail-down, and the rotates about its roll axis. In a true funnel, the tip of the tail remains stationary while the nose describes a circle.

Fuselage, or Fuse:
In RC helicopter parlance, the term fuselage refers to the outer body shell attached to a scale model or an F3C competition model. Generally made of fiberglass, they can also be made of other materials, such as balsa, plastic, carbon fiber, or other materials.

Glow Plug:
A small plug installed in the head of a nitro-burning model engine that facilitates combustion. The plug has an element consisting of a platinum coated nichrome wire that glows hot when connected to a battery for starting purposes. Once the engine has started, the battery is removed and the heat of compression and combustion keeps the element hot. This, coupled with catalytic action of the platinum coating, maintains the combustion source as the engine runs.

Glow Starter:
The device attached to a glow plug when starting a nitro burning model engine. Some have a built in battery as a source of power, while some are wired clips that attach to an external battery or power panel on a flight box.

Governor:
A device connected inline with a nitro heli’s throttle servo and the receiver, the governor has a sensor on the engine and is used to regulate the RPM of the engine. The desired RPM is set on the unit before flight, and the governor monitors engine parameters such as actual RPM and temperature, then adjusts the throttle setting accordingly to give a constant head speed.

Gyro:
The gyro is a small electronic device that is connected between the receiver and the tail servo. The gyro contains an accelerometer and senses rotational (yaw) movement of the helicopter and adjusts the pitch of the tail rotors to compensate and keep the tail steady. The first RC helicopters did not have gyros and relied solely on pilot input to keep the tail of the craft steady. When main rotor RPM changed, the tail would swing in one direction or the other. The gyro was developed to counteract this tendency and make the pilot’s workload easier. Modern gyros operate in one of two modes: rate mode and heading hold mode. SEE ALSO: Rate Mode, Heading Hold Mode

Gyro Gain:
Put simply, the sensitivity of the gyro. A gyro with gain set too high will “wag” the tail, while a gyro with too low gain will tend to drift from side to side. Some gyros have a gain adjustment on the gyro itself, and some are adjustable from the transmitter. Newer gyros are computer programmable and the gain is among the settings you can program.

Gyro Mixer:
Used for flybarless helicopters, helis with more than one main rotor (such as a tandem-rotor heli) and helis with more than two main rotor blades, a gyro mixer takes inputs from one or more secondary gyros and feeds them to the receiver to help stabilize the model on its pitch and roll axes.

Head:
The central block of the rotor assembly that the main rotors are attached to. The entire rotating assembly of the rotor, minus the blades and flybar is also sometimes referred to collectively as the head.

Head Button:
A small disk of plastic or metal that’s mounted to the top of the head block that adds a finished appearance to the rotor assembly. Sometimes used by impatient pilots (like me) to slow down the rotor after landing.

Head Dampers:
Rubber o-rings or bushings in the head block that dampen the movement of the feathering shaft, and through it, the main rotors. Dampers absorb vibration and allow a small bit of flex in the rotor.

Heading Hold:
A mode of gyro operation whereby the gyro actively attempts to resist ANY yaw axis movement by adjusting the tail rotor’s pitch. This is the easiest mode to fly and is thus the most common. Heading hold gyros are generally more expensive than rate-mode only gyros.

Hover:
A helicopter hovers when it remains laterally and vertically stationary above one point on the ground (or water as the case may be). A hover can be upright, or inverted, and can be any of a number of different orientations with relation to the pilot. For example, nose-in hovering is when the helicopter hovers with its nose pointed directly at the pilot.

Idle Up Mode:
A flight mode programmed into the transmitter that employs different pre-programmed curve sets to govern the behavior of a model. Idle Up Mode is generally characterized by a linear pitch curve (low stick=full negative pitch, high stick=full positive pitch) mixed to a flat (constant) or v-shaped throttle curve. Since flying in Idle Up Mode flight affords the pilot with full negative pitch capability, this is the mode that must be used for inverted flight and most aerobatics. SEE ALSO: Normal Mode.

Inrunner:
A type of brushless motor that closely resembles the operation of a brushed motor in that the outer “can” of the motor stays stationary, while the central shaft of the motor spins.

Inverted:
Upside-Down

Jesus Bolt:
In full-sale helis, this is what pilots refer to the main bolt connecting the rotor head to the mast. Named this because if this bolt comes off, you’re on your way to meet Jesus. On RC helicopters, the Jesus bolt threads perpendicularly into the bottom end of the main shaft and bolts the main gear to it, thus holding the whole assembly in the model.

Klunk:
A fuel pick-up tube generally mounted inside a fuel tank that has its end weighted so as to always move to the bottom of the tank, no matter what orientation the tank is in. The klunk is used to prevent fuel starvation of the engine during aerobatic maneuvers.

KV Rating:
For a brushless electric motor, the KV rating tells how many RPM that motor will turn per volt supplied to it. For example, if you have an 11.1v battery powering a 3500KV motor, your motor’s top RPM will be 3500 X 11.1 = 38,850 RPM.

Linkage, Linkage Rod:
Any stiff bar connecting a servo horn to its associated control surface or intermediate control, such as a bellcrank.

LiPo:
A battery chemistry known as Lithium Polymer. The electrolyte in a LiPo battery is a polymerized form of lithium. LiPo cells have a nominal voltage of 3.7v per cell. LiPo batteries offer very high power output per gram of weight, but are somewhat costly and very intolerant of mistreatment. Overcharging or over-discharging a LiPo battery will destroy it, sometimes spectacularly (think big, smoky fireballs). LiPos have become the cell chemistry of choice for the flying RC hobbies.

Main Shaft:
Sometimes called the mast, this is the central shaft that makes up the rotor assembly. At one end is the main gear, and at the other is the head block and rotor blades. In between these, along the shaft rides the swash plate and mixing block.

Main Gear:
This is the large, horizontal gear attached to the bottom of the main shaft and driven by the motor. This gear will also contain a one-way bearing to facilitate autorotations, and a  smaller, secondary gear or pulley for driving the tail rotor. The ratio of the number of teeth on the main gear to the number of teeth on the pinion will determine the helicopter’s headspeed for a given motor RPM. SEE ALSO: Pinion, One-Way Bearing.

Mixing (radio):
In radio terms, the process of combining two or more channels into one, combined movement. In a helicopter, it’s often necessary to mix multiple channels so that multiple servos each move a certain amount to obtain the right movement of control surfaces. Some radios have “program mixing” in which you can specify that when one servo moves to a set position or past a certain point, another servo begins to move automatically.

Mixing Arms:
The small levers built into the rotor assembly that are positioned by the straight vertical movement of the swash plate and server to combine cyclic inputs with pitch inputs. For example, to maintain forward flight at a constant altitude, the rotor disc must be tilted slightly forward by using a slight bit of down elevator, but to keep from losing altitude, the collective pitch of the entire disc must be increased at the same time. The mixer arms combine the appropriate amounts of both cyclic and collective to allow this to happen.

Motor Mount:
The bracket that allows the motor or engine to be connected to the frame.

Muffler:
A cylindrical device fitted to the exhaust port of an internal combustion engine that utilizes tuned back pressure waves to both increase engine efficiency and reduce sound output. mufflers are sometimes fitted with a nipple that is connected back to the fuel tank via fuel tubing and thus pressurizes it for better fuel delivery.

Nitro:
Also known as “glow fuel”, nitro is a model fuel that is made chiefly of methanol (alcohol), nitromethane, and natural or synthetic oil. The percentage of nitromethane content will determine how quickly the mixture burns and will give more power. Helicopter engines usually give the best performance if run on 15% to 30% nitro.

Normal Mode:
A flight mode programmed into the transmitter that employs different pre-programmed curve sets to govern the behavior of a model. Normal mode is characterized by a linear throttle curve (full down stick=idle, full up still=wide open throttle) mixed to a non-linear pitch curve (generally 0 degrees pitch at half stick). Normal mode is used for spinning up a model for takeoff and for spooling down after landing. Some pilots do not even leave the ground in normal mode, preferring to fly in Idle Up constantly. SEE ALSO: Idle Up Mode.

One-Way Bearing:
The central bearing in the main gear assembly, the one-way bearing allows the main gear (and the tail drive gear/pulley) To spin freely in the event of engine or motor cut-off. When under power, the one-way bearing locks the gears together so they spin as one. This allows the main rotors to spin freely during autorotation and as allows them to drive the tail rotor so control is maintained throughout the auto.

Outrunner:
A type of brushless motor in which the main shaft is attached to the outer “can” of the motor and the “can” spins the shaft.

Paddles:

The small blade-like airfoils at the ends of the flybar that add force to the flybar and assist with pitch changes of the main rotor blades.

Pinion:
The small gear attached to the output shaft of the motor or engine that engages the larger main gear. The ratio of the number of pinion teeth to the number of teeth on the main gear determine the model’s head speed at a given RPM.

Pirouette or Piro:
A maneuver by in which the helicopter spins around its yaw axis. Not an overly complex maneuver by itself, piros add additional layers of complexity to many other maneuvers.

Pitch:
The angle of a surface or body in relation to the oncoming airflow. For a rotor, the pitch is measured in degrees positive or degree negative. By varying the pitch of the rotor for a given axis, be it elevator (pitch axis) or aileron(roll axis… see cyclic pitch), the attitude of the entire aircraft can be manipulated. By varying the pitch of the entire rotor disc equally (see collective pitch), the helicopter can be made to ascend or descend vertically.

Pitch Gauge:
A measuring tool used to determine the pitch of the rotor blades. A pitch gauge is used to set the amount of pitch the blades are set to at minimum, neutral, and maximum stick inputs, as well as to determine if both blades are equal.

Puff:
The behavior exhibited by a Lithium Polymer cell or pack that has been overcharged, over-discharged, abused, or has just decided it’s done working and wants to die. The cells start to produce gas, and since the electrolyte is a polymer, it can’t re-absorb this gas. the cells are contained within a pliable metal foil packet rather than a rigid can, and thus the gas pressure inside causes them to swell up, or puff.

Rate Mode:
A gyro operating mode in which the gyro attempts to hold the rate of yaw below a certain level. A rate mode gyro will not necessarily keep the helicopter’s tail from drifting, but in sensing sudden changes in yaw moment (generally caused by collective or throttle changes), it dampens the yaw of the helicopter. The first gyros were rate mode gyros, and use less sophisticated electronics than heading-hold gyros. Therefore, they are less expensive. Due to their lower level of sophistication, they are also harder to fly than heading hold gyros. Most heading hold gyros can be made to operate in “rate” mode by lowering the gain setting.

Receiver:
The model-mounted component of a radio control system that receives radio-wave carried control signals from the transmitter and sends appropriate control impulses to the servos and other connected control equipment to facilitate the remote control of the model.

Rotor (main):
The assembly of parts mounted on a helicopter that is responsible for generating lift and controlling most aspects of both how the helicopter flies, and its attitude in the air (some of this responsibility and control is shared by the tail rotor). Basically, the rotor assembly is a rotating wing, moving through the air while it’s associated aircraft is stationary relative to this wing motion.

Rotor (tail):
A smaller, vertically mounted rotor attached to the end of the tailboom whose purpose is to both counteract the torque of the main rotor and to control the helicopter’s position in the yaw axis. The tail rotor is either a fixed pitch (on micro helis) blade on an electric motor, or is a variable pitch unit equipped with two blade grips, a central hub, and a linkage by which to vary the pitch of the blades. Driven either by shaft (see torque tube) or a belt (see tail belt), the tail rotor is coupled to the main rotor and spins in relation to it. The pitch is varied by control inputs sent to the gyro and then to the tail servo and the pitch is varied which causes movement around the yaw axis. Full-scale helicopters (and some models!) are equipped with other types of tail rotors, such as forced-jet air or semi-enclosed, many-bladed fan units (like the Fenestron).
Rudder:
A name sometimes given to the control of the tail. “Giving rudder input” is the same as causing the tail of the helicopter to move in a particular direction (and consequently, the nose to move in the opposite direction). The rudder channel on Mode 2 transmitters is located on the left stick. Most heli pilots learn to fly by moving the rudder in such a way as to influence the nose to move in the intended direction. This is called “flying the nose” of the aircraft. For example, as I fly, I may want the helicopter to turn to the left. This requires the nose to move left, so I feed in right rudder, which moves the tail right but moves the nose left. I feed inputs to the tail based on where I want the nose to go.

Seesaw:
A cage-like part of the rotor assembly that is connected directly to the flybar and is also connected to the mixer arms through linkages. The seesaw is the pivot point for the flybar and based on how it’s engineered, the seesaw’s movement is mechanically reduced and fed to the main rotor blades thorough the mixing arms.

Servo:
A shortened form of the word “servomotor”, a servo is a small motor that is connected to a control device so as to transfer the commands of the control unit to a remote location. In radio control systems, the servos attach to the receiver and through linkages, to the control surfaces of the model. Signals are received and translated by the receiver and are then sent to the servos as pulses, which cause the servos to move and actuate their associated control surface.

Servo Horn:
A small nylon or plastic arm or wheel that attaches to the output shaft of a servo, the purpose of which is to connect the servo to whatever control linkage necessary. There are usually holes at different points on a servo arm to facilitate adjustments in control surface deflection (the amount the surface moves in relation to the servo) and leverage.

Skids:
The long bars attached to the bottom of the landing gear on some helicopters.

Spindle:
See: Feathering Shaft

Starter:
A small handheld motor with an aluminum cup attached to the output shaft, into which may be installed a rubber cup or a long, hexagonal metal shaft. This is used for turning over an internal combustion engine and starting it. Can be used for gasoline engines, but the more commonly have pull starters. Mainly used for nitro engines. To use with most modern helis, the long hexagonal shaft attachment is used and is slipped into a matching hole in the end of the motor’s crankshaft. A glow starter is attached to the glow plug and the starter is triggered, spinning the crankshaft and (hopefully) starting the engine.

Swash Plate:
A circular disk that sits near the base of the main rotor shaft and transfers the control inputs up to the rotating control linkages of the rotor assembly, the swash plate is the primary control point of a helicopter. The swash plate is usually made up of two halves. The top half rotates with the rotor, while the bottom half does not. Due to the use of a semi-spherical bearing in the center, the swash plate is free to tilt in response to control inputs, and transfers those inputs through the linkages to the rotor blades.

Tail Belt:
A long, narrow cogged rubber belt that connects the tail rotor drive gear to the main gear.

Tail Case:
A plastic or metal casing mounted at the end of the tail boom that houses the tail rotor drive gears and spindle.

Tail Fin:
A plastic or fiberglass fin, usually mounted on the tail case that extends downwards from the tail boom. The primary purpose of the tail fin is to help protect the spinning tail rotor from striking the ground. A secondary purpose of the tail fin is to help stabilize the tail of the helicopter during fast forward flight.

Tail Boom:
A hollow carbon fiber or aluminum tube that extends out from the rear of the frame and holds the tail case and tail rotor assemblies.

Threadlocker:
A liquid or semi-liquid compound that, when applied to the threads of a screw or bolt, helps to prevent that screw or bolt from loosening. Commonly referred to by the trademark name “Loctite”, threadlocker comes in different strengths for different applications. These different compounds are identified by their color. Blue threadlocker is the most commonly used type for RC helicopters.

Torque Tube:
An alternate means of driving a tail rotor. Rather than a belt, a torque tube equipped helicopter uses an aluminum tube mounted on the inside of the tail boom with gearsets on each end to drive the tail rotor. Torque tubes generate less drag on the motor than a belt and is more durable in normal operation. A torque tube system is less tolerant of boom strikes and tends to strip out gears in a crash.

Transmitter:
The part of the radio control system that the pilot holds in his or her hands. Manipulating  the control sticks and switches causes the transmitter to send radio signals to the receiver in the model, which are then translated into control signals.