Main rotor diameter
Helicopter rotor(s) diameter. In fact, this parameter primarily determines the dimensions of the machine in the working position; this is especially true for three- and four-bladed models, where the propeller cannot be deployed along the fuselage, reducing the width of the space occupied (although the blades can be folded, which eliminates this drawback). Otherwise, the diameter of the rotor is of secondary importance: it is selected by the manufacturer in such a way as to provide features corresponding to the class of the machine, and it is worth focus primarily on the general purpose and price category of the helicopter, and not the size of the propeller.
Tail rotor diameter
The diameter of the tail rotor in machines of the classical scheme (see below). This parameter is of practical importance only in professional aircraft modeling sports, and even then quite rarely; relevant moments are described in special sources.
Number of channels
The number of control channels provided in the radio-controlled model.
Each such channel is responsible for a separate control function: the operation of the rudder, elevators, etc. For the simplest models, 2 – 3 channels are enough. Full control requires more channels. In advanced models, additional channels may be provided, the total number of which can reach 6 or more.
Stabilization system
The presence in the design of the helicopter
of a stabilization system in the form of a so-called servo axis (flybar) located on the axis of the main rotor (above it or below it). A spun flybar tends to keep the plane of rotation in one position, thus ensuring a stable position for the entire helicopter. This has a positive effect not only on resistance to wind gusts, but also on the quality of control: without a flybar, the helicopter would react too sharply to commands from the remote control, and with a stabilizer, control becomes soft, smooth and accessible even to beginners. On the other hand, the higher the stability, the lower the accuracy and responsiveness of the control; therefore, in professional flight machines, a flybar may be absent — its role in such cases is played by an electronic stabilization system.
Battery capacity
The capacity of the battery supplied with the electric motor model (see "Motor"). Indicated only for variants using branded batteries (see "Battery type"), measured in ampere-hours: 1 Ah corresponds to the capacity at which the battery is capable of delivering a current of 1 A for 1 hour.
The higher the battery capacity, the more time the helicopter can spend in the air, usually. However, the practical time of operation on a charge is largely determined by other characteristics of the machine — dimensions and weight, engine model and power, etc. Therefore, in most cases, this parameter plays a purely reference role, and only helicopters that do not have any significant differences in other characteristics (and even then very approximately) can only be compared in terms of battery capacity.
Battery voltage
Operating voltage of the battery supplied with the helicopter. For models for AA cells (see "Battery type"), this voltage is not indicated — the specification of such cells assumes a common voltage standard, about 1.5 V. In other cases, this data is not particularly important for everyday use, but it may be useful if you you need to pick up a charger, a spare battery or a battery to replace a damaged one, but you don’t have data on the battery model (see below).
Battery model
Model of the original battery (see “Battery type”) for which the helicopter is designed. Most often, such a battery is supplied with the device. Data on the battery model may be needed if it is out of order and needs to be replaced, when looking for a spare battery or when selecting a charger (usually, charging capabilities are already provided in the standard package, but it is possible that a separate device will be required).
Operating time
Operating time of an electric powered helicopter (see "Engine") on one battery charge or on one set of batteries. This parameter is rather conditional and approximate: it is usually indicated for optimal operating conditions, with a uniform low load on the engine (most often for hover mode), and when using replaceable cells — for high quality batteries. Accordingly, in fact, the operating time may differ markedly from that stated in the specifications. Nevertheless, this indicator quite reliably describes the battery life of the car, and different models can be compared according to it.
USB charging
Capable
of charging the helicopter battery from a standard USB port. This function is convenient primarily due to the prevalence of the USB standard: it is used in the vast majority of modern computers and laptops as a data transfer interface, and in portable electronics it is also used as a power source for charging batteries. Thus, a model with this feature can be connected for charging to computer equipment — or to any 220-to-USB network adapter. This is more convenient than using a specialized charger (which can also be lost). However the current power during such charging is relatively low, which is why it is poorly suited for powerful batteries.