Glossary of Terms

Autorotation - A way of 'gliding' a helicopter safely back to the ground without engine power. To achieve this you need to be able to set the main rotor blades to a negative pitch.

CCPM - Cyclic/Collective Pitch Management - a computer controlled system where three or four servos are used to control the collective pitch and cyclic controls on a helicopter. Each servo controls one part of the swashplate and the computer works out what position the servos need to be in to achieve the correct swashplate movements. This system is complicated but more precise and is typically the system used on larger, more expensive machines.

Collective Pitch - See Pitch

Cyclic Controls - Those controls which affect the helicopters attitude in two directions namely rolling left and right (known as the aileron control) and moving the nose up and down (known as the elevator control). Confusingly, on an aeroplane, the elevator is said to control the 'pitch' of the aircraft. For this reason, with model helicopters we simply refer to the elevator so that it is not confused with the pitch of the main rotor blades.

Dual Conversion - A type of receiver in which the signal from the transmitter is filtered twice (instead of once) and thus suffers less from radio interference.

Flight Mode - Some manufacturers refer to their transmitters being in different flight modes, e.g. Normal (for hovering), Idle Up or Stunt (for aerobatics) and Hold (for practising autorotations amongst other things). Each flight mode is selected by means of a switch and allows the pilot to select different throttle and pitch curves to suit the type of flying he is doing. In some cases, it can also determine other settings such as the gyro gain.

Flybar - Also known as the control rotor, the flybar is partially responsible for the cyclic control of the helicopter, the rest of this control coming directly from the swashplate. These two control methods - direct (the Bell system) and flybar (the Hiller system) - complement one another on many radio control helicopters offering a good compromise between responsiveness and stability. The degree to which each system affects the cyclic controls is defined by the mechanical ratio designed into the mixing arms on the flybar seesaw.

Gain - The degree to which a gyro will attempt to correct an un-commanded change in yaw. If you set the gain too low the tail of the helicopter will not maintain its heading well - if you set it too high the tail will wag from side to side.

Gyro Sense - The setting in your gyro which tells its circuitry which way it should move the servo to correct errors in the yaw attitude of the helicopter. If this is set incorrectly, the helicopter will spin uncontrollably at take-off. It will do this because as soon as an error is detected it will attempt to correct it the wrong way. It picks up this error and again tries to correct it. This is a cumulative problem and happens so quickly that it is impossible to control.

Governor - With IC models, this is a separate unit that plugs into the throttle channel that allows the pilot to determine the head speed electronically rather than by using a throttle curve.

Head Speed - The rotational speed of the main rotor assembly - in other words how many times the head goes round every minute.

Heading Hold - A gyro mode in which the gyro will not only resist un-commanded changes in direction (yaw) but correct them as well. Some gyros are capable of both heading hold and normal modes.

Idle Up - Sometimes known as Stunt; Idle Up is a term that refers to a group of settings on your transmitter which enable the helicopter to perform aerobatic manoeuvres such as flying upside down. One of the most notable features of Idle Up is that it allows you to set the transmitter so that the throttle control is high when the throttle stick is low.

Normal Mode - (sometimes called Standard Mode) - usually refers to one of two things - either the basic transmitter mode which is used for taking off and doing hovering manoeuvres or the gyro mode which does not hold its heading - see Heading Hold.

Optical Tachometer - A gadget for measuring head speed consisting of a box with a hole through which you view the rotor disk of the helicopter. There is a moving vane inside the box which creates a 'waggon wheel' effect on the image of the helicopter. You adjust the speed of the vanes and when the blades appear to stop you read off the head speed on a digital readout.

  • Typical view through an optical tachometerTypical view through an optical tachometer

PCM - Pulse Coded Modulation - This is a better and normally a more expensive system than PPM and offers a function called 'failsafe' which allows the pilot to program the receiver with a set of default servo positions in case of radio failure. Want to know more? Take a look here.

Pitch - Correctly called Collective Pitch; with helicopters this normally refers to the angle of the main rotor blades. Positive pitch creates lift. (Negative pitch creates lift if you are flying upside down.)

PPM - Pulse Position Modulation - Want to know more? Take a look here.

Rate Gyro - A rate gyro is one which controls the helicopter's rate of yaw and will set it depending on the pilot's rudder control. This is distinct from older type of gyro where the pilot effectively just controls the pitch of the tail rotor blades and the gyro endeavours to prevent the models from any yaw at all. In a sense, with these older style gyros the pilot was always 'fighting' the gyro. This is a subtle but very important difference and the introduction of rate gyros has made certain manoeuvres much smoother and easier to control.

Rotor Disk - An illusion, this is the transparent disk which appears to be formed when the rotor blades are rotating quickly.

Sense - See Gyro Sense

Standard Mode - See Normal Mode.

Swashplate - A device on a helicopter which connects the static non-rotating controls to the ones which rotate with the rotor blades. The swashplate always controls the cyclic controls and, on some types of helicopter, also plays a part in controlling the collective pitch.

Throttle Hold - A feature which is activated by a switch on the transmitter and which sets the throttle either to zero/near zero (on electric helicopters) or to a tick-over setting (on glow-powered models). It does this irrespective of the position of the throttle/collective pitch stick and does not directly affect the pitch unless the transmitter has a separate pitch curve for throttle hold. Typically the feature is used to practise autorotations but is also a useful safety feature which can, for example, be engaged when carrying the model to the take-off spot. It is also a useful means of recovering from a tail rotor/gyro failure during flight which, by removing the torque from the engine/motor will prevent the helicopter from spinning uncontrollably and enable the pilot to autorotate safely to the ground.

Tracking - This refers to the degree to which the two blades on the main rotor are set at the same angle. If they are the same then the blades will rotate in the same plane and in flight the rotors will appear to form a single disk. If they are not at the same angle, then the two blades will not rotate in the same plane and in flight the rotor disk will appear to be split into two.

Transmitter Mode - The type of transmitter you have. If your throttle stick (the one that doesn't spring back to the centre when you move it forwards and backwards) is on the right-hand side you have a Mode 1 transmitter. If it's on the left-hand side your transmitter is Mode 2 (this is the most common type). For more details, see this article.

Yaw - A change in direction of motion of the aircraft which causes the nose to move either left or right.

Yoke - (Typically) the device which controls the pitch of the tail rotor blades, also known as the tail pitch slider or the Tail Rotor Control Assembly.