A Amp or Ampere.

Effectively the volume of electricity flowing through a system. Higher amps require larger conductors to carry the load. Amps are one of the killers of electrical and electronic components, but the load can be measured with an Ammeter to check that all is well. Reduce the voltage, reduce the prop size, or increase the gear ratio to reduce the amps.

ARC Almost Ready to Cover

A kit with the fuselage and wings assembled/The ailerons may need to be cut out, and other constructional items may need to be finished before covering.

ARTF Almost Ready To Fly

A kit with the fuselage and wings covered. Expect fitting out to be necessary, and that may also include installing wing fixings.


The assembly formed by the copper wire windings in an electric motor. The armature is part of the rotor in a brushed motor, but stationary in a brushless motor.

Arming Switch

A switch fitted to a speed controller. The switch ONLY isolates the power supply to the radio, and NOT the power from the battery to the controller. A battery connected to a speed controller will continue to drain through the power side of the controller, this is the most effective way to kill a Lithium battery! Arming switches are not normally fitted to OPTO controllers because the radio switch will be used to isolate the receiver power supply. The only real safe way to operate is to connect the flight battery at the start box, fly, and then disconnect the flight battery before entering the pits


British Association of Radio Controlled Soarers. The specialist body for thermal soarers and slope oarers.

BEC Battery Eliminator Circuit

A small circuit found in most Electronic Speed Controllers. A BEC circuit allows power from the drive batteries to operate the receiver, speed controller, and servos. Conventional BEC circuits rely on power from excess voltage being dissipated as heat through the controller heat sinks. The higher the voltage of the drive battery, the fewer servos that can be operated from the BEC circuit. A practical limit for using a conventional BEC circuit is 10 cells or 11,1v Lithium with no more than 4 conventional servos, and in many cases less.


British Electric Flight Association. The specialist body for electric powered model aircraft.


Capacitors absorb and release electric energy very quickly (like a fast acting battery). Capacitors can be used to smooth out the flow of electricity to reduce or prevent arcing at electric motor brushes. Capacitors are also found at the end of most brushless motor controllers to smooth out the flow of electrical energy and reduce potentially damaging voltage spikes.

Clamp Ammeter

Almost all speed controller manufacturers recommend the use of a clamp ammeter for use with brushless speed controllers to avoid the introduction of increased cable length between the battery and controller. Increased cable length between the battery and controller leads to damaging voltage spikes which can damage the controller. The good news is that this tends to happen at the upper end of the controller’s operating range, and it appears to take about 20 to 30 seconds for the protection capacitors to overheat and blow off the end of the board! Make up extension leads using silicon cable for use between the motor and controller, however, the huge blast of air behind an DF (Electric Ducted Fan) unit appears to be sufficient to safely cool the capacitors on the controllers that we use for EDF. The cable must be loose in the ring formed by the jaws of the clamp ammeter, not clamped by the jaws.


Samarium Cobalt magnets are high power magnets which remain stable at high temperatures. Samarium Cobalt magnets are traditionally used in higher quality American motors. The more efficient cobalt motors are packed with magnets.


The copper track that motor brushes run on. The commutator has slots that provide switching of the current between the armature windings. The commutator in a healthy motor is bright shiny copper. A black or burnt armature is a sign of one of the motor brushes either sticking in the brush holder, a weak brush spring, or one of the brushes worn out. A blue commutator is a sign of overheating from overloading the motor. Reduce the current by reducing the voltage, reducing the prop size, or increasing the gear ratio before running the motor again!

EDF Electric Ducted Fan.

An electric motor driving an impeller in a duct, and similar to Ducted Fan, but with far higher erformance when using higher quality motors at 100 to 200 Watts per Pound! (220 to 440 Watts per Kg)

ESC Electronic Speed Controller (now Speed Controller).

A historic term to differentiate between an electronic and mechanical speed controller.

ESC remains a useful abbreviation.


Competition classes for electric powered thermal soarers. BEFA and BARCS use different sets of rules.


A type of competition electric thermal soaring class, normally restricted to using Graupner Speed 00 size electric motors.


International classification for pattern aerobatic models with a maximum wing span of 2m and a maximum length of 2m. Traditionally powered by glow plug engines, top line F3A models are increasing powered by electric power systems using 10 Series Lithium Polymer battery packs.


International classification for muti-task electric powered gliders. The competition includes thermal duration and distance tasks.


International classification for electric powered pylon racing models.

FET Field Effect Transistor

Most modern speed controllers use FETs that limit the current being drawn, but it is not a good idea to use a speed controller as a current limiting device – EVER!

Gold Connector

Normally refers to gold bunch connectors (with a basket type connector). Common sizes are 2mm (for use up to 20A), 3,5A (normally used between brushless motors and controllers), 4mm (normally used for battery connections up to about 90A). There are 5mm and 5,5mm for competition use up to about 150A. Use polarised connectors to avoid reverse connecting speed controllers (one plug and one socket). Beware that not all Gold Connectors are created equal!

HOC Hot Off Charge

Using battery packs immediately after charging, this is desirable with Nickel Metal Hydride battery packs to achieve maximum performance.


An aerobatic electric powered glider which traditionally would use a high power electric system to take the model rapidly to a good height, and then perform aerobatics on the way down. With modern batteries it is possible to perform pattern aerobatics with a hotliner.


A term used to describe a traditional brushless motor with the armature on the outside, and a rotor holding the permanent magnets on the inside.

Li-Po Lithium Polymer

Batteries originally developed for low weight and high capacity in consumer equipment. High discharge cells for 10C and above discharge rates have been developed specifically for use in model applications. The time to land with Lithium Polymer batteries is when the power starts to fall, the next hint that it is time to land will come when the speed controller LVC comes into operation. Reducing the capacity of Lithium Polymer cells to less than 40% capacity can be harmful. Most chargers will not re-charge a pack that has been taken to below 3v per cell for safety reasons. Lithium battery packs prefer to remain cool in use. Store Lithium Polymer battery packs art charged.

LVC Low Voltage Cut-off.

This is an entirely different function to the BEC circuit that may be in a controller. The LVC is programmed into the controller software and may be either set by the user, or automatic. A controller with automatic LVC will detect the start voltage when the drive battery is first connected and change the voltage at which the motor will cut out. The desired LVC is a similar voltage for both Lithium and NiMh battery packs of similar start voltage. It is normal to use hard or sudden motor cut off with powered soarers, and soft or gradual motor cut off with sports, scale and aerobatic models. The motor power reducing is a strong indication that it is time to land!


Neodymium, the highest grade of magnets, and used in traditional European high quality motors. Neodym magnets are produced in different grades.

NiCd Nickel Cadmium

One of the original chemistries used in high discharge rechargeable batteries. Nickel Cadmium is being replaced by Nickel Metal Hydride, but fast charge NiCd have a long service life and can be recharged in a very short time (as little as 20 minutes). NiCd battery packs require a balancing charge initially, and every 12 months. Storing NiCd battery packs fully charged or fully discharged an result in loss of capacity. Store NiCd part charged. Land your model at the end of the day, resist the temptation to charge or discharge your battery pack, and it will actually increase in capacity over time.

NiMh Nickel Metal Hydride

Work by a small number of Chinese chemists has resulted in the latest generation of high discharge Nickel Metal Hydride cells. NiMh cells tend to have a higher capacity thatn similar size Nickel cadmium cells, but take longer to re-charge, typically 40 minutes for fast charge cells. Use NiMh battery packs hot off charge, and keep them warm during use.


OPtical IsOlation between the radio side and power side of an Electronic Speed Controller. OPTO isolation devices were originally used to limit possible interference between the power side and radio side of the speed controller. OPTO controllers are effectively a servo with an electrical rather than mechanical output and must be used with a receiver battery.


A type of brushless electric motor with the armature on the inside, and a rotor holding the magnets on the outside. Almost all outrunner motors designed for model use are of the high torque, low speed LRK design. Low speed in electric motor terms is up to around 10 000 revs. Outrunner is a literal translation of the German Aussenlaufer.

Pattern Aerobatics

Aerobatics perfomed in an imaginary 2 dimensional picture frame in the sky (called the box in F3A aerobatics). Most manoeuvres in pattern aerobatics are historic or current manoeuvres in the F3A aerobatic schedule.

Pattern Ship

Historic term used for a model designed to fly Pattern Aerobatics.

Slope Soarer

A glider designed to soar in the upward moving air approaching a hill. Slope soarers may be gentle flying models or fast aerobatic models. Many slope soaring enthusiasts use electric power assistance to provide height during low wind conditions. Pure (non- powered) slope soarers are more common n UK than in other countries because powered soarers are not normally allowed to be flown from National Trust property.

Switching BEC

A Battery Eliminator Circuit that rapidly switches the power supply so that a lower voltage is produced. This allows quite large voltage drop to be achieved without heat build up. Switching BECs can be stand alone units, and are incorporated in some high quality speed controllers including Jeti SPIN, Kontronik Jazz, and Kontronik Jive. In high current applications it may be preferable to use a receiver battery. All switching BECs MUST be used with a wound ferrite filter between the BEC and the receiver.

Thermal Soarer

A glider designed to have a very shallow glide angle to make best use of thermal lift when flying from a flat field. Most thermal soarers are now launched using electric power, which is then turned off for thermal soaring. The propeller blades fitted to electric thermal soarers fold back to reduce drag.


Thermals are rising pockets or columns of warm air in the sky that a model can fly in to increase the height of the model.

V Volt.

The measurement of the potential difference between a positive and negative electrical contact. Volts are effectively the electrical “pressure”. There are generally fewer losses in a high voltage power system than a low voltage, high amp power system, but stay well within the voltage limit of electronic components!

W Watt.

The metric unit of power. Conveniently Watts are the product of Volts and Amps (Volts multiplied by Amps). The real thing to be aware of is that the proportion of watts lost due to motor inefficiency build up as damaging heat in the motor. Provide adequate cooling and select a motor well up to the job that you intend it to do.


A term coined by Hobby-Lobby to describe a general purpose electric powered soarer that is aerobatic. Many early Hotliner designs would now be considered to be Warmliners.

3D Aerobatics

Aerobatic manoeuvres that are performed in all directions and at all speeds, including manoeuvres performed below normal stalling speed, and not restricted by an imaginary 2 dimensional box.


A competition thermal soaring class developed by Mike Proctor to allow a wide variety of electric powered thermal soarers using different types of battery to compete on equal terms. The class allows 200W of input power for every kg of flying model weight up to a maximum of 400W.