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Electric Flight Glossary

& discussion of electric flight terms


Part 1 - A to D

by Andrew Gibbs


There are many technical terms and words relating to model aircraft in general, and electric flight in particular. The aim of this detailed glossary is therefore to offer an accurate and detailed yet concise explanation for any of the terms the electric modeller is likely to come across. Let us know if a term you'd like to see covered is not found here!


White Diamond aicraft


This term refers to line drawings showing the subject airplane from three angles; from the side, from above and from in front. Cross sections may also be provided.

This is an abbreviation of Alternating Current. AC is the type of electricity supplied to domestic households, and is so called because, unlike direct current (DC), the direction of the current constantly changes. The output from a brushless ESC may be considered to be AC, and is of course used to supply the motor. See also DC.

Adverse Yaw
When any control is deflected, it will generate drag. This is of particular importance for the ailerons because the down going aileron is a particularly prone to generating drag, and this can cause a phenomena known as adverse yaw. For example, suppose we want to roll the model to the right. A right aileron command will mean the left aileron is lowered and the right one is raised. Because the left hand aileron is going down, it will generate more drag. If the left hand (down-going) aileron produces a large increase in drag compared to the up-going one, an airplane could have a tendency to yaw (nose swinging to one side) to the left - this is the opposite direction to the intended direction of turn. Remedies for adverse yaw are to set the model up with differential aileron, and to use the rudder along with aileron when making a turn.

This is the cross section through a wing. There are many types of aerofoil.

The moveable control surfaces positioned towards the outer edge of a wing. The left and right ailerons operate simultaneously to give control of a model in roll - one goes up, reducing lift while the other goes down to increase lift.

This is the old fashioned term for a propeller. The word is derived from the early concept that a propeller ‘screws’ its way through the air. See also the glossary entry for propeller. Propellers are examined in detail here

Aliphatic resin
A water-based, waterproof adhesive that is suitable for bonding wood such as balsa and ply components. This relatively low cost adhesive is also light in weight and sands better than PVA.

Amps, Ampere
This is the unit of electric current. See the glossary entry for current.

The armature is the name given to the assembly of all moving parts of a brushed DC motor. The armature consists of the motor shaft, the iron laminations, the coils of wire which are wound around it and the commutator. There is no armature in a brushless motor. Brushed motors are discussed in more detail here

electric model aircraft propeller

Propellers used to be called airscrews in the early days of aviation. This prop is attached to John Ranson's fine Tempest.

Electric motor armature speed 600

The armature of a brushed DC electric motor. This example comes from a simple 3-pole motor.


This abbreviation is short for Almost Ready to Fly. It describes many of today's RC electric model aircraft which often require little more than basic assembly and the installation of RC equipment.

Back EMF
Back EMF is the voltage, or electromotive force, generated within a brushed or brushless motor by virtue of its rotation. This voltage opposes the battery voltage, making the effective voltage available to turn the motor lower. Brushless ESCs are able to sense the back EMF and they use this information to control the motor.

BEC (or UBEC, or SBEC)
BEC is short for Battery Eliminator Circuit, often pronounced ‘beck’. A BEC is an electronic device which supplies power for a model’s RC system from the motor battery. The BEC is entirely separate from the motor control circuitry. It eliminates the need for a separate receiver battery, giving rise to its name.

BEC Limitations
All electronic devices, including BECs have operating limits. BECs are rated for a certain voltage, current, or a number of servos that may safely be used. If these limits are exceeded, the BEC may overheat, malfunction and/or shut down. Any of these conditions will of course cause a loss of control, so care must be taken to stay within the rated capability of the BEC.

ESC for electric model airplane

This ESC includes an integrated BEC. Care must be taken not to exceed the current rating of the BEC, otherwise it may well overheat and shut down.

brushless outrunner for electric model aircraft

This Cermark CEM-4220-770 outrunner is rated for 40 Amps continuous. The large holes make it easy to provide a generous flow of cooling air through the motor.

Black wire corrosion
Definition to be added...........

Burst current
The burst current is a measure of how much current a motor can handle for a very limited period of time, for example 15 seconds. Brushless motors tend to be better than brushless motors at handling a high burst current because they do not have brushes which can become pitted at high currents. Some manufacturers specify their burst current for up to 10 or 15 seconds, others up to 60 seconds. Adhere carefully to any such limitations.

In my opinion, if a motor is propped so it will only take full power for a limited period of time it is most definitely 'over-propped', in other words, the propeller is too large. Manufacturers probably like to have this rating as it makes their motors appear more powerful. For normal sport use, I recommend propping a motor only up to the rated maximum continuous current. This avoids the problem of forgetting to throttle back in a timely fashion to avoid excessive heating and possible damage.

C Rating
The 'C' rating of a battery is a way of defining the maximum safe continuous current it can deliver, expressed as a multiple of the battery's capacity in Amp-hours.

A current of 1 Amp may also be expressed as 1,000mA (milliamps). A 1,000mAh (or 1 Ah) battery can therefore supply a current of 1 Amp for one hour. This is known as the 1C current for this battery. Alternatively, this same battery could supply 2 Amps for 30min. This is the 2C current for this particular battery. The battery could also be discharged at 10 Amps which would mean it was empty in 6 min. This would be the 10C current.

Similarly, a 2,200mAh battery can supply 2.2 Amps for one hour. This higher current is the 1C current for this higher capacity battery. The 10C current would be 22 Amps and this would discharge the battery fully in 6 min.

The reason for placing a limit as to the maximum discharge current is because any time a current passes through a resistance (which includes the internal resistance of a battery) heat will be generated. Since excessive heat may cause damage, by limiting the current, the production of heat is also limited.

The C rating of a battery may be exceeded for a brief period, provided the battery is not allowed to become excessively hot. Care should also be taken to limit the discharge current (especially when the cells are approaching a discharged condition) to a value that prevents the battery from dropping below 3 volts per cell e.g. 9.0V for a 3-cell lipo battery. An important point to appreciate is that the voltage of a battery will fall when it is in use, for example when supplying power for a motor.

A canaliser is a small wing-like device sometimes fitted to competition aerobatic models. It comprises a short pylon on top of which a small wing is mounted. A canaliser is typically located just aft of the canopy and its incidence matches that of the wing. Pilots report that adding a properly sized canaliser to a model makes the rudder more effective. Canalisers are most often used on F3A models.

Information on how a canaliser functions is limited, but the device is believed to work by helping to smooth the airflow passing over the top over the model, before it reaches the rudder. The vertical side area of the canaliser's pylon, if significant, may also influence the effectiveness of the rudder.

Canaliser is a French word with the approximate meaning to direct or to channel. The device was invented by top French aerobatic pilot Christophe Paysant Le Roux.


ESC for electric model airplane

The C rating of a battery defines the maximum current it can supply expressed as a multiple of its capacity.

brushless outrunner for electric model aircraft

A canaliser is a small wing-like surface generally fitted aft of the canopy to an aerobatic model.


Cogging is the varying resistance to turning the armature shaft caused by the magnetic field acting on the armature iron. See also the entry for slotted/slotless motors.

Continuous current rating
The continuous current rating of a motor, measured in amps, is a measure of how much current it can safely handle on a continuous basis. The continuous current rating may only be safely sustained if the motor has a sufficient supply of cooling air.

Commutator, commutation
A commutator is a slip ring, or rotary electrical switch, integral to a brushed motor. It performs the functions of switching the current on and off in the various sections of the armature windings, and also of reversing the polarity (direction) of the current in those windings every half a turn. In a brushless motor, the commutation function is carried out by the ESC.

Copper Loss
This term refers to one of the causes of a loss of energy in an electric motor. All conductors such as motor windings have some level of resistance to electric currents. This resistance causes a portion of the electrical energy passing through the wire to be wasted as unwanted heat. This type of resistance is known as copper loss.

A conductor carrying 10 Amps has only 1/4 the copper loss of that same conductor when it carries 20 Amps. So, doubling the current in a motor results in 4 times the heat generated due to copper loss. (In mathematical terms, we can say that the copper loss rises with the square of the current).

commutator for electric model airplane motor

The commutator of a brushed electric motor. The commutator can get quite hot due to brush friction and the electrical resistance between brushes and commutator.

brushless outrunner electric motor for model aeroplane

Brushless motors, identified by 3 wires, do not have a commutator. This function is carried out by the associated ESC instead, without which the motor cannot run.


Current is the word used to describe the quantity of electricity flowing through a wire. To visualise the flow of electricity, it may be likened to water flowing through a pipe. Current is measured in Amperes, often abbreviated to "Amps" or just "A".

In electric flight, it is important to know the current drawn by a particular motor, battery and propeller combination. It is essential that the chosen ESC, battery and motor can all safely handle the current, otherwise components may become damaged.

This is an abbreviation for Direct Current. All batteries produce DC electricity, which flows in one direction only. DC is so called because unlike AC, the direction of the current is constant, like water flowing in a river. DC is used for all model aircraft including brushless types. See also the entries for AC, brushless motors and ESCs.

Differential Aileron
This term refers to ailerons that are set up so that the up-going aileron has more movement than its downwards going counterpart. This helps to combat adverse yaw. Many models will benefit considerably from having differential aileron movement.


Click here for the next part of the glossary


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