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RC Helicopter Terms Glossary


Use this handy glossary of remote-controlled helicopter terms if you hear something about RC helicopters and don’t know what it means.


– A –

12V starter – An electric motor used to start RC helicopterengines.

2.4 Ghz – A radio frequency used by spread spectrum radio systems.

3D – A RC helicopter which can maneuver in 3 dimensions freely (I.E an RC helicopter which can hover upside down).

72 Mhz – A frequency band used by RC aircraft in North America. 72 Mhz radios are gradually being replaced with spread spectrum (2.4 Ghz) technology.

– B –

Batteries – An array of electro chemical cells used for the storage of electricity. Each cell is a device which can convert chemical energy directly into electricity (the flow of electrons). Each cell has two terminals (positive and negative) connected to a pair of internal electrodes suspended in an electrolyte. A battery is composed of multiple cells.

Brushed Motor – An internally commutated electric motor, which runs off DC (direct current) power.

Brushless motor – An electric motor which uses an electric control system instead of brushes. Brushless motors are more efficient, more reliable, and last longer than brushed motors. Brushless motors are frequently used in CD ROM drives.

Buddy Box – A dummy radio transmitter used by a student pilot, linked to a real radio transmitter used by the instructor. This allows the student to control the RC helicopter, while the instructor can take control if the student loses control.

– C –

Carburetor – The carburetor mixes fuel with air. It then sends this mixture to the cylinder, where it is burned.

Center of Gravity – The point on any object where the gravitational forces are balanced (balance point).

Coaxial – An RC helicopter design which uses two main rotors, placed on top of each other. There appears to be only one axial, but the main axial is actually composed of two axials, one inside the other. This design is frequently used in small inexpensive RC helicopters.

Collective – The collective is a control function on the RC helicopter where the swashplate moves upwards or downwards evenly. This increases or decreases the pitch of the rotor blades collectively (at the same time). The change in pitch will cause the helicopter to rise or descend.

Conventional Design – Conventional RC helicopters use one main rotor to generate lift, and a smaller tail rotor mounted at the end of the fuselage to control yaw.

Crash – An unplanned and sudden landing, usually resulting in damage to the RC helicopter.

Cyclic – Cyclic pitch is used to control the RC helicopters pitch (orientation). When the cyclic is used, the swashplate tilts, changing the pitch of the rotor blades cyclically. This “bends” the rotor disc in one direction, and the resulting change in thrust will move the RC helicopter in that direction.

– D –

Drag – Drag is the force which resists the movement of a solid object in a fluid or gas (air). Drag is the opposite of thrust, and can be reduced by using a streamlined fuselage.

– E –

Electric – Electric power is becoming more popular amount RC helicopter enthusiasts. Electric power is quiet, clean, and can deliver just as much power as a comparable gas or nitro engine.

Engine – An engine burns fuel to turn a shaft, directly converting stored chemical energy into kinetic energy (motion). Engines can be either gas or glow, with gas being favored among larger models.

Engine break in – If your engine is new, run a few tanks of fuel through it before you fly for the first time. The manufacturer will provide a manual explaining how to do this. If you can, perform the break in with the engine attached to a work bench, and a propeller installed.

– F –

Field charger – A battery charger that can be run off of a 12 volt field battery.

Fixed pitch RC Helicopter – An RC helicopter that does not change the pitch of it’s rotor blades.

FM – Frequency Modulated.Modern RC helicopters use either an FM radio system, or the newer spread spectrum technology.

Four forces of flight – Thrust, weight, lift and drag. In order to fly, the thrust must exceed the drag and the lift must exceed the weight.

Fuel – Can be either gas or nitro. Nitro engines burn a blend of nitromethenol and castor oil, while gas engines burn gasoline.

– G –

Gas – Gasoline. Only the largest fuel powered RC helicopters use gasoline as a power source. Most small and mid size helicopters use nitro fuel or electricity.

Glow Driver – A small electric plug which heats the glow plug during engine start up

Glow plug – A part of the engine which burns nitro fuel by a catylitic reaction. The glow plug needs to be heated with a glow driver to start the engine.

Ground Effect – When the helicopter hovers close to the ground (less than one rotor diameter), the downwash from the rotor blades creates a high pressure bubble of air. Flight performance is changed when the helicopter is close to the ground, requiring the pilot to pay extra attention.

Gyro – A gyroscope is a device which maintains it’s orientation in space. When installed in an RC helicopter, the gyroscope eliminates any unwanted movement of the tail (yaw). There are two kinds of gyroscope available: rate, and heading hold. Read the article on RC helicopter gyros to learn more.

Gyro Gain – Gyro gain is the sensitivity of the RC helicopter gyroscope. A high gyro gain will resist tail motion, while a low gyro gain will allow it. Use a high gyro gain when learning how to fly RC helicopters, and a low gyro gain when performing aerobatics.

Gyroscopic Precession – Any spinning object acts as a gyroscope, including the main rotors of the RC helicopter. The rotors spin, but any pitch change will only take effect until approximately 90 degrees from the point where the change was applied.

– H –

Heat Sink Head – RC helicopter engines come with large heat sink head. This is important, because the engine is not exposed to the airstream. The heat sink head radiates the heat generated by the engine.

Hover – A helicopter hovers when it is at rest relative to the ground while flying.

– I –

Infra Red – The red portion of the invisible electromagnetic spectrum. Infrared light is sometimes used to control cheap micro electric RC helicopters.

Instructions – The single most important part of any RC helicopter, whether its a kit, ARF, or RTF. Also, the most frequently ignored / misused.

Instructor – A more experienced RC helicopter pilot, who teaches student pilots how to fly their RC helicopters safely.

– L –

Landing Skid – Landing gear for an RC helicopter (what the RC helicopter rests on when landed)

Lead Acid – A type of battery used in cars and flight boxes, due to it’s large capacity. These batteries are very heavy, so they are not used in RC helicopters or other RC models. Usually, they are avaiable in various capacities, all at 12 volts.

Lift – The upwards force acting on an RC helicopter (or any RC aircraft). This is the force which keeps the RC helicopter flying. Lift is generated by a difference in atmospheric pressure between the top and bottom rotor blades, causing a downward flow of air, resulting in an upwards propulsive effect.

Lipo – Lithium polymer battery. These batteries are very light, and have a huge capacity. Because of this, they have almost entirly replaced NiCd or NiMh batteries in RC helicopters. They have a volitile chemistry, so they must be supervised when charging or discharging. Unlike NiCd or NiMh batteries, they cannot be completely discharged. If the voltage of each cell in the battery pack drops below 3 volts, the pack will be destroyed.

Loop – An aerobatic maneuvre, performed by causing the RC helicopter to travel 360 degrees in a verticle motion.

– M –

Memory Effect – Does not actually exist. This “effect” is the illusion of a battery pack losing capacity due to over discharge or over charge. The memory effect actually consists of two separate effects: Cell aging, and voltage depression. Voltage depression is caused by the buildup of crystals inside each cell. This increases the internal resistance of the cell and leads to a rapid decrease in voltage. Cell aging works in the same way, except that it occurs gradually over time. These two effects are the reason that rechargable batteries wear out. Most prevalent in NiCd batteries, it can be repaired to some extent by discharging each cell to near its minimum voltage, and then fully charging the battery pack. Prevent damage to your battery packs by not over charging or discharging below the minimum capacity.

Micro RC Helicopter – Used interchangably with Mini RC Helicopter, ususally meaning a small, inexpensive, 2 channel RC helicopter.

Mid Air Collision – A mid air collision between two RC helicopters or other aircraft. A mid air collision usually results in the destruction of both aircraft involved. It is very hard to determine who is at fault after a mid air collision, so it is generally best when pilots take their own losses.

Mini RC Helicopter – See micro RC helicopter.

Mixture – Refers to the amount of fuel and air in being burned in the engine. Adjust the mixture by using the needle valve, so that the engine runs smoothly.

Mode 1 – Mode 1 RC transmitters are commonly used in the United States. On a mode 1 transmitter, throttle and the tail rotor are controlled with the left stick, while the cyclic and elevator functions are controlled using the right stick.

Mode 2 – Mode 2 transmitters control cyclic and elevator with the left stick, and throttle and tail rotor with the right stick.

Motor – An electric motor is a device which uses the relationship between electricity and magnitism to turn a shaft and do work. Electric motors can be either brushed, or brushless.

– N –

NiCd – Nickel Cadmium. This is a type of rechargable battery . These batteries are becoming less popular due to voltage depression , which increases the internal resistance of the battery when it is over charged or over discharged.

NiMH – Nickel Metal Hydride. This is a type of rechargable battery, which is frequently used in radio equipment. NiMh batteries do not suffer from voltage depression to the same extent as NiCds. This makes them a great choice for RC cars, which can discharge a pack rapidly.

– P –

Pitch – Pitch has two definitions:

  1. The tilt of the RC helicopters rotor blades – can be fixed or cyclic collective.
  2. The attitude of the helicopter itself (the vertical tilt of the nose)

Pod AndBoom – A typical RC helicopter design, consisting of a canopy section (pod) and a tail rotor mounted at the end of a long rod (boom). This design is common with high performance, 3d models and beginner trainer models.

PCM – Pulse code modulation. PCM works exactly like PPM, except that the initial pulse is coded. After receiving the initial pulse, the receiver will only respond to signals with a properly coded timing pulse. This helps eliminate interference, but it can be

PPM – Pulse proportional mode. FM radios can send an initial timing pulse to the receiver. This pulse notifies the receiver that the transmitter is going to send more signals, in the form of additional pulses. Each channel of control receives one pulse containing position information for the servo. A higher pulse rate will increase servo responsiveness.

– Q –

Quad Rotor – A quad rotor helicopter uses four separate rotors to fly. Quad rotor helicopters are fixed pitch, and maneuver by using differential thrust.

– R –

Radio – A control system used in RC helicopters, which uses radio waves to communicate between the transmitter and reciever.

RC – Short for radio control. A Radio control aircraft uses radio waves to control it’s flight functions. Radio waves are long wavelength electromagnetic radiation, occurring in the radio wave region of the electromagnetic spectrum.

RC Aerial Photography – The act of taking pictures from the air.

RC Heli – An abbreviation of RC helicopter

RC Helicopter – A remote controlled aircraft which uses horizontally oriented rotors to produce lift.

RC helicopter kit – A RC helicopter kit contains the parts needed to build the RC helicopter, and a set of instructions. A radio and engine are not included, so you will need to purchase them separately.

Repairs – Repairs to an RC helicopter need to be performed whenever it becomes damaged. Here is an article about RC helicopter repairs.

Roll – An aerobatic maneuver performed by rolling the RC helicopter on its side, through 360 degrees. Roll can also refer to any rotation about the horizontal axis of the helicopter.

Rotors – The main rotor(s) is a pair of thin wings placed on top of a spinning shaft. Moving these rotors through the air generates lift. The tail rotor works in the same way, but it is oriented differently and is smaller.

– S –

Scale – An RC Helicopter which has been built to look exactly like a real, full scale helicopter.

Semi Scale – An RC Helicopter whose design has been inspired by a real helicopter, but is not an exact small scale copy.

Servo – Servos are small electronic devices responsible for moving the different control surfaces of an RC helicopter. Servos come in several varieties, including:

Standard Servos – – Standard servos use an analogue amplifier and a cored motor. These are great general purpose servos, but they lack the precision and lifetime of higher quality core less and digital servos. Some standard servos use ball bearings to support their output shaft, which greatly increases their precision.

Coreless Servos – – Coreless servos are like standard servos, except that they use a higher quality coreless motor. They have a better torque and resolution than standard servos.

Digital Serovs – – Digital servos have a digital amplifier and use coreless motors. This gives them an incredible resolution (precision of movement).

Simulator – An rc flight simulator is a program which runs on a personal computer, and simulates RC aircraft flight. The FMS (flying model simulator) is one of the best free simulators avaiable.

Sport – A sport RC helicopter can be used as a trainer, or perform aerobatic maneuvers.

Spread Spectrum – A spread spectrum radio system operates on the 2.4 gigahertz band, and actively scans for open channels before establishing communication with the RC helicopter. Spread spectrum technology is becoming more popular, because it eliminates any possibility of radio interference between models.

Swashplate – The swashplate is a device which transforms linear motion from the servo arms, to the rotational motion required by the rotor blades.

– T –

Tail Rotor – The tail rotor is a smaller rotor mounted at the end of the tail of the RC helicopter. The tail rotor is oriented at 90 degrees to the helicopter fuselage, so it can control the yaw.

Tail Rotor Compensation – Whenever the throttle or collective is increased, the tail will turn. Tail rotor compensation automatically increases the speed of the tail rotor to compensate for this.

Throttle – The throttle is the control function responsible for controlling the speed of the engine.

Throttle Cut – This function will turn off the engine, by reducing the throttle to idle cut off.

Thrust – The force caused by the movement of the RC helicopter rotors. In order to move forward, thrust must be greater than drag.

Training gear – Training gear can be attached to an RC helicopter to help stabilize it while learning how to fly. You can make training gear using ping pong balls and stiff wire.

Transitional Lift – The additional lift obtained from the increased efficiency of the main rotor blades while horizontal. The increased lift is caused by the increased airflow over the rotor blades, and increases with the speed of the RC helicopter.

Transmitter – The transmitter relays the pilots commands to the RC aircraft, by sending radio waves.

– U –

UAV – Unmanned aerial vehicle. Usually, this term refers to an unmanned aircraft with a sophisticated auto pilot.

– W –

Weight – The weight is the effect of gravity on the RC helicopter. In order to fly, thrust must overcome weight.

– Y –

Yaw – The side to side motion of the nose of the RC helicopters nose. Yaw is usually controlled with the tail rotor, but some coaxial RC helicopters control yaw by varying the speed of their top and bottom rotors.

by Danny Stefanov

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