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Electric Flight Glossary

& discussion of electric flight terms


Part 4 - R to Z

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 discussed here!


White Diamond by Andrew Gibbs


Receiver battery
The receiver battery is a separate battery used to supply power to the receiver and servos in a model airplane. For an electric powered model, a receiver battery is not required if power is supplied via a BEC from the main flight battery.

Resistance is the term given to opposition to current. Using the analogy of water flowing through a hosepipe, resistance may be represented by a restriction in the pipe. The hose itself will provide some resistance to the flow; the longer the hose, and the smaller it is, the greater the resistance will be. The same holds true for electrical wire; the longer this is, and the smaller the cross-section of the wire, the greater the resistance to electrical current. Resistance is measured in Ohms.

Motors, ESCs and batteries all have electrical resistance, and therefore all generate a noticeable heat in use, especially in high power set-ups. The heat is generated when a current is made to flow through a resistance.

brushed and brushless electric motors for model airplanes

Electrical resistance causes heat to be generated in electric flight components such as motors, ESCs and batteries.

small brushless electric motor for RC aircraft

The rotor of a brushless motor consists of all the rotating parts. For the outrunner, this means the case with the attached magnets plus of course the propeller shaft.

The rotor is the name given to the moving components of a brushless electric motor. In an outrunner, the rotor consists of the case to which the magnets are attached. The rotor of an inrunner comprises the shaft and the magnets which are attached to it.

RPM/V or RPM per Volt
See the entry for Kv

Receiver, Rx
Rx is an abbreviation for receiver. The receiver decodes the transmitter signal detected by the receiver’s own aerial, and sends the required commands to the servos.

servo for RC airplane

The position of the servo output disc will follow transmitter commands, allowing a model to be accurately controlled.

receiver rx for model airplane

The receiver detects the transmitter's signals, and passes its commands to the servos.

A servo is an electro-mechanical device used to operate a model’s control surface. The servo takes a command from the receiver, amplifies it and powers a small highly geared electric motor to move an output arm. The servo also contains a feedback potentiometer so it ‘knows’ when it has reached the required position.

Shock Flyer, shocky
This is the generic name given to small, highly aerobatic indoor models typically made from Depron or other foam. The name probably came about because the models were almost shocking to witness when they first appeared late in 2003. Since then the genre has been developed and it is now a popular form of indoor RC flying.

Slotted / Slotless Motors
A brushless motor in which the windings are wrapped around “teeth” in the stator is known as a slotted motor. The windings may also be wrapped completely over the stator ring. Motors built in this manner are known as slotless motors.

An easy way to tell the difference between a slotted and a slotless motor is to turn the motor shaft. A slotted motor’s rotor poles are magnetically attracted to the “teeth” on the stator plates. You’ll feel a detent, slip, detent in the shaft as it turns, this is known as cogging. A slotless motor doesn’t have teeth, so there’s nothing for the magnets to pull on, thus no cogging.

spinner and propeller of an electric model aircraft

The spinner streamlines the front of the model. Visually, it is a very significant part of any scale model.

suppression capacitor of a brushed motor

This brushed motor is fitted with suppression capacitors to reduce the amount of radio interference radiated by the motor.

The spinner is the cone-like fairing fitted to the propeller. For scale models, it is important that the spinner is of the correct profile, otherwise the impression that the model is a miniature version of the real thing is spoiled.

The wing of an model aeroplane is angled at a few degrees to the the oncoming air in normal, level flight. The angle at which the wing operates is called the angle of attack. The angle of attack will vary depending on the flight conditions. Consider the case of an model flying at different speeds, but maintaining level flight. At cruise speed the wing will be at a low angle of attack, perhaps 3 degrees or so. As the airspeed is reduced, the angle of attack must be increased so that the wing can continue to produce lift equal to the weight of the model. At low speed, the wing will be angled at perhaps 12 degrees or more.

If the model is slowed still further, the angle of attack will increase even more, until at some point the majority of airflow over the upper surface of the wing will start to break away, and the wing will be unable to produce lift equal to the weight of the model. In this condition, the wing is said to be stalled, and the wing has reached its critical angle of attack.The critical angle of attack is typically around 15 degrees.

Stator ring
This is another name given to a flux ring. See the entry for flux ring.

Suppression capacitor
Suppression capacitors are fitted across the motor terminals of brushed motors to reduce the radiated electrical noise (interference) from the motor. The electrical noise from a brushed motor is generated at the interface between the brushes and the commutator. Suppression capacitors are not used with brushless motors.


Explanation to be added

Tip stall
When a wing reaches its critical angle of attack, it will stall. However, not all parts of the wing will stall at the same time. When a wing stalls, the wing tip may tend to stall before the inboard part. This is known as a 'tip stall'. The more heavily tapered a wing is, the more likely it is that the wing will stall at the tip first.

Torque is the name given to a turning, or twisting force. Torque is defined as a force multiplied by a radius (distance). Torque therefore has to be defined in terms of both of these units, for example ounce-inches when defining a relatively small force, or pound-feet for larger forces.

An example of a relatively low value of torque could be a servo which might have a torque of 80 ounce-inches. This means the servo can develop a torque equivalent to an 80 ounce force at a radius of 1 inch (80 x 1 = 80) or a 160 ounce force at half an inch (160x0.5 = 80). As we can see, the torque is expressed taking into account the distance and the force. We can’t define a torque using only one of the units.

Another practical example of torque is when using a wrench to tighten a propeller nut. For example, we might apply a force of 10lbs. If our hand gripped the wrench at a distance of 6 inches from the nut, the torque applied would 5 pound feet (10 x 0.5 = 5).

The propeller generates a force called thrust which drives a model forward. There are two types of thrust; static thrust and dynamic thrust. Static thrust is the thrust we can feel the propeller generating when the model is stationary. Conversely, dynamic thrust is the thrust which the prop generates with the model at flying speed.

Unless the model is in a zero airspeed condition, such as when hovering, dynamic thrust is the only value of importance. Static thrust may easily be measured by means of a force measurement device such as a simple spring balance. Unfortunately, measuring the static thrust of propellers tells us literally nothing about the likely flying performance of a model. However, thrust measurements for EDF models do have some use. Unfortunately, without a wind tunnel dynamic thrust is impossible to measure.

You can find much more useful information about props in More Than Motors, available here

This refers to the number of times the windings are wound around the armature of a brushed motor, or the equivalent in a brushless motor. A single wind would be once around the shaped armature, two winds twice and so on. Varying the number of turns of wire in the coils varies the magnetic field, and therefore also the motor’s characteristics.

A greater number of turns can yield stronger magnetic fields, however space inside a motor is always at a premium, so all else being equal, to achieve a greater number of turns, thinner wire must be used. Thinner wire has a greater resistance and therefore a limited ability to carry a high current. The motor’s designer must therefore make compromises to attempt to achieve the desired motor characteristics.

A motor made with a high number of turns (winds) will generally have a higher torque and a low kv (low rpm per volt). It will also have higher copper losses because of the higher resistance of the winding wire than motors with lower turns and larger winding wires. Similarly, motors with a small number of winds are characterised by higher rpm and lower torque.

Motors for electric RC applications are often partially identified by the number of turns, or winds making up the wraps of each coil. However, this single piece of information is of limited use when choosing a motor for an electric power system.

Transmitter, Tx
The transmitter is the device used to send signals to the model's receiver. The receiver decodes the signals and sends a command to the servos. Tx is an abbreviation for transmitter.


This is the unit of electrical potential. Volts are the electrical equivalent of pressure in a hosepipe – it is the pressure that causes the water to flow. Without pressure, no water will flow, and hence, there will be no current. Voltage is measured in Volts, abbreviated to "V". The symbol for voltage in equations is also "V".

Watts are a measure of electrical power. Electrical power is found by multiplying Voltage and Current:

Power = Volts x Amps. (For example, 1W = 1V x 1A)

Motors are rated for a maximum current at a maximum voltage. It is therefore simple to find the Wattage (power consumption) of a motor if we know these ratings. For example, a motor intended to operate on 10 Volts and rated at 12 Amps would be capable of consuming 10 x 12 Watts – 120 W.

See also the glossary entry for ‘power’.

You can find more useful information about electricity in Mastering Motors, available here

Winds is another name given to the number of turns of wire within an electric motor. See the entry ‘turns’.

Wing loading
The wing loading of a model is found by dividing the model's weight by its wing area. Traditionally, wing loading for models is expressed in ounces per square foot, or oz/sq ft. There are 144 square inches in one square foot.

A model weighing 12 ounces which has 144 square inches (1 square foot) of wing area would have a wing loading of 12 ounces per square foot. Similarly a model with a weight of 60 ounces and 360 square inches (2.5 square feet) has a wing loading of 25 oz/sq ft.

The larger the model, the higher the wing loading may be for acceptable flight performance. Almost all of the models featured in the articles section all have wing loadings given.

WOT is an abbreviation for Wide Open Throttle, i.e. the full power condition. Of course, it’s only carbureted internal combustion engines that have a throttle as such, but the term WOT is still a useful term of reference to use with electric flight, denoting the full power condition.

This is an abbreviation for weather, and is often used by full size pilots.



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