Chapter 31. Glossary

Table of Contents



120 CCPM

A type of CCPM using three servos arranged at equal 120 degrees from each other. The advantage of 120 CCPM is the load of the swashplate is evenly distributed across all three servos resulting in more precise control. 120 CCPM requires a special transmitter ("computer radio") which supports this mode.


A type of CCPM using three servos arranged at 90 degrees to each other (and one spot empty). On an ECO 8/16 using 90 CCPM there is a servo at the left, right, and front positions of the swashplate.

3D flying

A maneuver which requires the constant harmonized input of three or more controls simultaneously during the maneuver.

There is a good discussion of this at


Advancing blade

The rotor blade which is moving into the wind created by helicopter motion, thus increasing its effective airspeed.

See also Retreating blade


Airplane equivalent of left/right cyclic. Although a helicopter can provide cyclic movement in all directions around the mast,not just left/right roll, this can still be a useful concept for pilot orientation.

Airfoil (Aerofoil)

The shape of a wing (or a rotor blade) which produces lift. Different airfoils may be better for different styles of flying.

Angle of Attack

The difference in angle between the direction of the chord of the rotor blades and the direction of the wind.


Almost Ready to Fly. A pre-built helicopter which only requires installation of electronics.

AR Pin

Antirotation pin.

AR Arm

Antirotation arm.


A controlled, unpowered helicopter descent (and landing). A helicopter is a brick with a rotor, so it doesn't glide well when unpowered. The autorotation is the closest to gliding possible. The autorotation consists of a steep descent using negative pitch to keep the rotor blades spinning followed by a slight flaring performed with positive pitch to convert the momentum of the blades into lift to soften the landing.

Autorotation Gear

Autorotation gear. A gear with a one-way bearing so the motor can only drive the main shaft in one rotational direction. Required for performing autorotations.

AR Gear

See Autorotation Gear


Adjustable Travel Volume. This is the amount of servo travel from one servo endpoint to the other. This can be reduced or increased by changing the servo endpoints. This is also used to avoid binding.

See also EPA


All Up Weight. The weight of the heli when ready to fly, including batteries.


Angular Vector Control System. Basically Futaba's own terminology for "heading hold". Their website describes it as "an advanced version of heading hold which doesn't have the temperature related drift problems of most of the older HH gyros."



The play in the mesh between two gears. Too much backlash and the gears can slip or break the teeth, too little backlash can cause excess friction, heat and wear. The common guideline is to allow the thickness of a sheet of paper between gears to achieve the correct amount of backlash.

Ball Link

A connection that allow for adjusting controls using a ball on one end, and a link that "snaps" onto the ball on the other.

Ball-Link Pliers

A special plier made especially for handling ball links. It can quickly remove the ball joint from a ball link without damaging either part. One jaw has a U-shaped cut in it and the other jaw has a small cup on it to hold the ball joint.

Ball Link Pliers

Base Loaded Antenna

A rigid short antenna used to replace the longer wire receiver antenna.


Battery Eliminator Circuit.

On a nitro helicopter, there is a 4.8 volt "receiver pack" that powers the receiver, gyro,and servos. On an electric helicopter, we already have a very large battery which powers the main motor. However, the voltage of this main motor battery pack is typically more than 4.8 volts. So, the BEC will take the voltage of the main battery pack and regulate it down to 4.8 volts to power the receiver, gyro, and servos, This eliminates the need for a separate 4.8 volt receiver pack.

There are two types of BECs: linear BECs and switching BECs.

A linear BEC reduces the main battery voltage to 4.8 volts by applying a resistive load and wasting the excess power as heat. Therefore linear BECs are typically less than 50% efficient and become very warm or hot. A linear BEC will generate more heat (waste more power) as the input voltage rises, so linear BECs should not be used above ~10 volts.

A switching BEC will rapidly pulsing the main battery voltage to create an average voltage of 4.8 volts. This is typically more than 90% efficient an therefore switching BECs will run cooler than a linear BEC. The efficiency of the switching BEC stays fairly constant at higher voltages, so most switching BECs can be used with 35 volts of input or more.

Note: Most BECs are rated for 5 volts of output. The extra 0.2 volts will not harm the electronics equipment. From an electronics point of view, a 5 volt regulator is easier to build than a 4.8 volt regulator since the parts are more easily available, so most BECs output 5 volts instead.

Bell-Hiller Mixer

The seesaw arm on the head of a CCPM helicopter which isolates the height component of the swashplate position and controls the main blade pitch.


A bad condition where the control adjustments can not move as far as the maximum servo travel. This puts extremely high torque on the servo and as well as consuming excessive current and will eventually destroy the servo.


Brushless, usually in the context of brushless motors.

Boom Strike

A type of helicopter crash where the main rotor blade hits the tailboom. This may dent/bend the tail boom and damage the main rotor blades. This is a frequent mistake made by beginners.

Brain Fade

A mental lapse where the person flying the heli, suddenly forgets which way to move the controls, or which control to move at all.

Buddy Box

Two similar transmitters that are wired together with a "trainer cord" or buddy-lead This is most useful when learning to fly, it is the same as having dual controls. The instructor can take over control at any time by using the "trainer switch" on his transmitter.


C-rate (1C, 2C, etc. charging & discharging rate)

This refers to a charging or discharging rate in terms of the capacity of the battery pack. For example, a 2C rate for a 2400 maH battery pack would be 4800 ma or 4.8 amperes. A 1/10 C rate for a 2400 maH battery pack would be 240 milliamperes.

CA Glue

Cyanoacrylate A form of glue, commonly called "super glue" often used in model building. You should treat with extreme caution: always have debonding agent close by, in case your components or parts of your body become bonded in an unanticipated way. Avoid breathing the fumes, as they are toxic.

Collective Pitch Compensator

The assembly with two seesaw arms directly above the swashplate


Cyclic/Collective Pitch Mixing. A type of control system where the swashplate controls both main blade pitch and flybar pitch. The swashplate relative tilt controls the pitch of the flybar as the main rotor rotates, and the absolute height of the swashplate controls the pitch of the main rotor blades.

See also Mechanical Mixing

See also Electronic Mixing

Carbon Fiber

A carbon composite material usually used for rotor blades, helicopter frames, tail booms, and other areas where high strength and light weight are required.

CG, CofG, Center of Gravity

The point at which an object's center of mass appears to be; its balance point


A measure of the number of separate signals that can be handled by a Tx and/or Rx. This usually refers to the number of separate control surfaces or servos/speed controllers a Tx can control, so typically a simple helicopter will need at least four channels.

Coning Angle

Some helicopters like the FP Piccolo are designed so the rotor blades are flexible and will bend upwards in flight. The amount which the blade bends upwards is called the coning angle. The coning effect is good for beginner helicopters because it makes hovering more stable, but is bad for forward flight because it makes the helicopter pitch up which makes forward flight difficult.


Collective Pitch. A helicopter that adjust vertical lift by changing the pitch of the main rotor blades.


Disc Loading

The weight of the helicopter divided by the rotor disc size

Similar to the "wing loading" figure for airplanes. "High disc loading" means the helicopter is heavy for its rotor size, or conversely, the main rotor blades are short for its weight.

Dissymmetry of Lift

The advancing side of the rotor disk moves faster than the retreating side and thus produces more lift. This causes the helicopter to bank in forward flight. This is usually dampened by flapping or seesawing blades.

For further information see Section 23.5.1, “Dissymmetry of lift”


The friction experienced by a object moving through the air.

Dual Rates

A feature of some Tx models which allows you to flip a switch to make the controls more or less sensitive. Usually set as some % of the normal rate.

Dual Conversion

A type of receiver which converts the incoming frequency through two intermediate stages. This type of receiver rejects interference better than single-conversion receivers, but with a size and weight penalty. This type of receiver uses a different crystal than single-conversion receivers.



See also CCPM


Electric Helicopter - hard to figure out, isn't it?

Electronic Mixing

A control system where the radio transmitter controls the mixing between the roll/pitch servos and the main rotor pitch servo. Also called colloquially eCCPM.

See also CCPM

See also eCCPM


EndPoint Adjustment. This is the same as ATV.



Airplane equivalent of fore/aft cyclic The elevator is what pitches a plane forward or back, to dive or climb.


Electronic Speed Control. Basically, the motor controller for brushed and brushless motors.

There are two basic types of ESCs: brushed motor ESCs and brushless motor ESCs.

A brushed motor ESC is basically a switching voltage regulator connected to the motor. It outputs a variable voltage which is proportionally relative to the throttle value. A brushless motor ESC is basically a three-phase AC motor controller. It electrically commutates the three phases of a brushless motor at a frequency proportional to the throttle value.


Electrostatic Discharge. This usually refers to the static electricity which builds up on the tail belt, most often on Logo 10s. Some people have reported "ball lighting" shooting away from Logo 10s on humid days.


A programmable nonlinear response curve associated with a particular transmitter control. This allows either less or more sensitivity near the center of a transmitter joystick. Often useful for beginners to allow better control of helicopter movement.



A default setting for a receiver channel to be used when the transmitter signal is lost, usually associated with PCM receivers. This is useful for airplanes to allow the model to glide when the signal is lost, but is less useful for helicopters.


The rolling motion of a rotor blade along its long axis which changes its angle of attack.

Feathering Shaft

The shaft which allows the blade grips to pivot to change the angle of attack (feather). A flapping head has two feathering shafts (one for each blade) and a see-saw head has one feathering shaft (running through the head)


The metal or CF rod which holds the smaller paddles to the main rotor head

Flybar Paddles

The smaller blades (not the main rotor blades) on the main rotor of a helicopter.


Forward Flight or Fast Forward Flight


Fixed Pitch. Usually refers to a helicopter which has rotor blades at a fixed pitch, and climbs and descends by changing the speed of the main rotor blades. This type of helicopter is more durable and easier to maintain but have some disadvantages such as more sluggish altitude changes and the inability to perform autorotations.


A type of rotor head. (See Section 23.4, “The rotorhead” of Chapter 23, How Helicopters Work )


Mostly used when talking about airplanes and landing. The end of an autorotation maneuver which eliminates the forward motion of the helicopter.



Gyro sensitivity to motion.

See also Section 23.6, “How gyros work”


The slang term which describes a R/C heli that has a motor which runs on gasoline.


Ground Effect. When a helicopter is hovering at less than approximately one rotor length above the ground, the heli will become a little more skittish, as though it is trying to balance on a ball. This is the ground effect. Near the ground your blades produce more lift, but also more turbulence.


Glass fiber (fiberglass) usually in the context of rotor blades.


Momentary uncontrolled operation of control servos or motor speed caused by electronic interference or equipment malfunction. Rearrangement of the electronic components and/or re-routing of wires can often cure this.

Governor, Govenor Mode

A feature of an ESC which will try to keep the motor speed constant despite variable load placed on the motor. This is like the cruise control on a car as it's going up and down hills. Even though the load on the motor is variable as the car goes up and down hills, the cruise control will try to maintain the same speed. The governor mode on an ESC will try to do something similar. Even if the heli is performing wild maneuvers and the load on the main rotor blade is highly variable, it will try to maintain a constant head speed.

If using a governor mode, the throttle curve should not be set to 100%. This is because the governor mode needs a little bit of extra power so it can maintain headspeed. Using the cruise control analogy, if you set the cruise control of a car to its maximum speed the cruise control cannot maintain the maximum speed going up hills. Similarly, if you set the throttle to 100% RPM then the governor mode will not be able to maintain it when the rotor is heavily loaded.

This is why the motor pinion should be selected so the desired headspeed can be achieved at 90 to 95% of the throttle - so the governor mode can work properly.

Ground Resonance

The phenomena that can make a helicopter almost shake itself to bits on the ground, even when it is perfectly balanced in the air. This is more common in seesaw type heads which aren't as dampened as flapping heads, and is also more common on pavement or hard surfaces which don't absorb vibrations.


Glass Reinforced Plastic. A type of plastic material often used in helicopter chassis.


A device used to help stabilize the yaw of a helicopter by adjusting the tail rotor pitch.

Mechanical gyros use a real spinning disk inside a small enclosure measure the yaw due to the torque of the main rotor blades. Solid-state gyros achieve the same measurement without using moving parts, but can still be easily damaged by impact.

Gyroscopic Precession

A tendency of a rotating body to translate an external force into a a new force occuring 90 degrees later in its rotation.


Heading Hold Gyro

A gyro which attempts to "lock" the heading of the gyro and keep the helicopter pointed in the same direction until you choose to turn it via the rudder.

See also Yaw-Rate Gyro


Heading Hold (gyro)

HS Head Speed

The RPM of the main rotor. Most nonmicro helicopters need between 1200-2000 RPM of headspeed to fly. If the headspeed is too low, then the heli will not lift off or will require extra pitch to fly, which will make the heli very unstable. For aerobatics, most people raise their headspeed to about 1800-2000 RPM. Most helicopter rotor hubs are only rated for a maximum of 2000 RPM. If you exceed 2000 RPM, this places excessive stress on the main rotor hub and the heli is likely to throw a blade.


See Wag


Idle-up Mode

A transmitter mode which has a different throttle and pitch curve than the regular mode. For electric helicopters, we normally use the "normal" mode to arm the ESC and spool up the helicopter, and use an idle-up mode with a flat throttle setting for regular flying.

Some transmitters have multiple idle-up modes. For example, the Futaba 9C has idle-up1, idle-up2, and idle-up3 modes. The additional idle-up modes can be programmed for a low headspeed for duration flight, high headspeed with full negative pitch range for aerobatics, etc.

This feature can be used to lock the throttle to a specified value so the throttle stick only controls the collective pitch, which is required for inverted flight.


Jesus Bolt

The bolt which holds the rotor head onto the main rotor shaft.



The no-load RPM per volt of the motor. For example, if a motor is rated at Kv = 3000 and is being run on a 10 cell (12 volt) battery, then the motor will spin at 36,000 rpm. The headspeed can then be calculated by calculating the gear reduction ratio of the pinion/main gear combination. This is very important because a helicopter only flies well in a certain range of headspeed.


Lead/Lag bolt

The bolt which allows the main rotor blades to swing horizontally so it can either lead (swing ahead) or lag (swing behind) the main rotor head.


Local Hobby Shop


A threadlocking adhesive used to ensure screws do not unscrew themselves. Technically, it is an anaerobic adhesive.

Loctite 242 (blue) is removable and used for screws which may require removal later to repair crash damage.

Loctite 262 (red) is permanent and used for screws which will never require removal. If you wish to disassemble parts which have been loctited, then you should weaken the adhesive first by heating the metal parts to about 212F/100C. This can be easily done by touching the metal parts with a hot soldering iron or a hair dryer.


The low-voltage cutoff point of the ESC, if it has one. For a heli, you want an ESC with no or very low LVC

When the battery voltage drops down to the low-voltage cutoff point, the ESC will either stop or throttle down the main motor, which is undesirable for a helicopter. For a heli, you want an ESC with no or very low LVC.



See also Mechanical Mixing

Mechanical Mixing

A type of control system where the roll/pitch and main blade pitch are not mixed at the transmitter but are instead mixed mechanically at the helicopter. JR transmitter manuals refer to this as mCCPM.

See also CCPM

Micro Helicopter

This is a rather subjective term, but in this guide it refers to any helicopter under 800 grams AUW. This includes the Ikarus Piccolos, MS Hornets, Century Hummingbird, Feda, GWS Dragonfly, MIA Housefly, Wes-Technik Helistar LH35, etc.



Hovering or maneuvering with the nose of the helicopter pointed at the pilot. This is a advanced step in the learning stages of flying a helicopter because both roll and pitch controls are reversed relative to the pilot.


Outrunner motor

A motor where the outside of the can rotates. This is also called "rotating can" or "external rotor" by some distributors.



These are the shorter stubby blades on the end of the two rods opposite the rotor blades. These aid in pitching the main rotor blades for quicker responses and less servo stress.


Acronym for Pulse Code Modulation A generic term for digitally encoded data.


Acronym for Pulse Position Modulation. Same as FM. An analog form of encoding data.


A spinning maneuver where the helicopter yaws around the main mast one or more times.

Pitch Meter (or Gauge)

A measuring device used to check the varying pitch settings of your rotor blades and paddles. You need the pitch of the corresponding blades to be very close or they will not track evenly.


A style of helicopter model that derives its name from the appearance of its short fuselage and tail-support boom. This is the usual style for most R/C helicopters, since it is easier to fly and maintain than one with a scale fuselage.

Pusher tail rotor

A tail rotor that pushes air away from the tail boom. Most helicopters including the Corona, ECO 8, Logo 10 use a pusher tail rotor.

See also Tractor tail rotor


Retreating blade

The rotor blade which is moving with the wind created by helicopter motion, thus decreasing its effective airspeed.

See also Advancing blade

Retreating blade stall

A situation in forward flight where the effective airspeed of the retreating blade approaches zero. This can result in loss of helicopter control.

Revo mix/Revo mixing

A mixer which adds a percentage of the main rotor throttle to the tail rotor throttle to prevent the heli from spinning. This is only used with yaw rate (non-heading hold) gyros because the yaw rate gyro only dampens tail movement and cannot maintain the direction of the tail. If using a heading hold gyro, this option should be DISABLED on the transmitter


Radio Frequency Interference. RFI causes little "glitches" in your control and the heli will twitch abruptly in one direction or another and/or the tail may suddenly jerk around.


On an airplane, the vertically hinged plate which controls the course of the airplane. This is equivalent to a helicopter's tail rotor.

Rudder Offset

A transmitter function that lets you specify an additional amount of rudder trim for idle-up modes which usually have a higher RPM or different blade pitch curve and thus different amounts of torque compensation. This function should be inhibited if using a heading hold gyro.


Abbreviation for receiver. The portion of the radio system that is mounted in the helicopter and adjusts the servos and speed controller(s) according to the signals from the Tx.

See also Tx


See-Saw Head

A form of rotor head where the two rotor blades are "connected" through a feathering shaft so that when one pitches up the other pitches down. This makes for a more stable helicopter an a simpler design, but does not handle as well as a flapping head type.

Settling with Power

A dangerous condition when descending during a hover where the helicopter's rotor blades descend into their own downwash. This can cause a crash if not handled properly. Model helicopters have a better power-to-weight ratio than full-size helicopters, so this is usually not a huge problem, however, it does occur.


The amount of "free play" in a control system. A common example of this is a door knob. If you gently twist the doorknob back and forth, you can feel a few degrees of looseness before the internal mechanism engages. These few degrees of looseness is the sloppiness or "slop" in the mechanism. Slop can make the helicopter more unpredictable and less responsive to control input.


Small plates affixed to a helicopter's tail to force the tail to weathervane and improve forward flight characteristics. Helicopters usually have a vertical stabilizer (to prevent the tail rotor from touching the ground) and may have a horizontal stabilizer. Aerobatic models will often have stabilizers with cutouts to reduce the weathervaning effect.


The control mechanism component which mechanically joins the non-rotating control portions to the rotating control portions of the main rotor.


An auxiliary trim adjustment on many transmitter models which allows trim of controls with the joystick trim centered. This allows full trim adjustment while flying.



See Loctite

Throttle Hold (switch)

A switch used to force a zero throttle setting regardless of the throttle stick position or idle-up switch position. This is useful as a safety feature when connecting or disconnecting the battery and also to quickly kill the motor when a helicopter crash is imminent.

Throw a Blade

A slang term describing a main rotor blade detaching from the rotor head and being flung at high speed. This is very, very dangerous.

TL Translational Lift

The extra lift produced by the main rotor when a helicopter is moving horizontally or when hovering in windy conditions. When a helicopter stops moving horizontally it tends to drop, because it loses the extra lift.


Tail rotor

Tractor tail rotor

A tail rotor that pulls air towards the tail boom. The Hummingbird Elite series uses a tractor tail rotor.

See also Pusher tail rotor

Trickle Charge

A continuous charge rate of C/20. This is a safe level for continuous charging of NiCd cells. Cells of other types, such as NiMH and Lipo should NOT be trickle charged.


The path of a rotor blade as it spins. See also Section 12.21, “Blade tracking - CP helicopters”

Training Gear

A landing gear with a wider stance so the likelihood of tipping the helicopter on takeoff or landing is reduced. Often used by beginners while learning to hover and they typically are made of two crossing sticks with whiffle balls on the ends.

Transitional Lift

A corrupted form of translational lift.

See TL Translational Lift


Abbreviation for Transmitter

See also Rx



For a rotor blade, this references the area of the rotor blade where the leading edge has less pitch than the trailing edge. Also, the collective pitch compensator is sometimes referenced as a "washout unit".

See also Collective Pitch Compensator


The tendency of the helicopter to point into the wind like a windsock. The amount of weathervaining is determined by the aerodynamic properties of the helicopter, primarily the size of the vertical stabilizer.


A rhythmic back-and-forth tail movement that will not stop. This may occur with heading hold gyros when the setup is not correct. In this case, the gyro overshoots the correct tail position, so it constantly keeps moving the tail.


Wooden main rotor blades


Yaw-Rate Gyro

A type of gyro which dampens but not eliminates unwanted yaw rotation. If a gust of wind blows the tail of a helicopter with a yaw-rate gyro, the gyro will make the tail rotor 'push back' against the wind to reduce the amount of unwanted tail movement, but since it does not accumulate of total tail movement, it cannot return the tail back to its original position.

See also Heading Hold Gyro



A Z-shaped bend in the wire of a pushrod which is commonly used on airplanes to absorb the impact of crashing. These should not be used in model helicopters because it will create slop in the control system.