Electric helicopter. Drawing, description

MODELING
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Electric helicopter. Tips for a modeller

Modeling

Recently, electric motors have been increasingly used in aviation modeling. This is understandable, their advantage in comparison with internal combustion engines is obvious: ease of start, accuracy of propeller speed control, absence of exhaust gases, low noise level.

Several interesting models of aircraft with electric motors have already been created. The first attempts are being made to apply them to helicopter models.

Engine selection and thrust calculation

The possibility of creating an electric helicopter (Fig. 1) is primarily determined by the specific power of the motor. From light and affordable engines, a series of electric motors from vacuum cleaners can be distinguished, which, with a relatively low weight, develop high power. The smallest of them is used in the "Veterok" electric brush. Its weight is only 430 g, and the power for short-term use can reach 75 W, that is, about 0,1 liters. With. The popular internal combustion engine MK-17 has the same characteristics, however, with three times less weight.

Rice. 1. Drawing of an electric helicopter model (click to enlarge)

When testing "Veterok" with a serial aircraft model propeller Ø 200 mm and a pitch of 100 mm (Fig. 2), it developed a thrust of about 500 g, sufficient to fly an aircraft weighing up to 5 kg. But for a helicopter model, a large power-to-weight ratio is required.

In accordance with the formula of N. E. Zhukovsky, the thrust of the main rotor in the hover mode is:

T = (33,25*N_вDη₀)^2/3,

here: T - thrust, kg; Nv - power, l. With.; D - diameter, m; η is the relative efficiency of the main rotor when operating in place.

Value η₀for the best aircraft model rotors it reaches 0,65-0,7. The power of the electric motor is also spent on the rotation of the tail rotor, fan and losses in the gearbox. We will assume that its share transmitted to the main rotor will be 0,07 liters. With. Choosing its diameter equal to 1,5 m, we determine the thrust:

T= (33,25*0,07*1,5*0,65)^2/3= 1,73 kg.

Thus, for a helicopter model weighing 1,5 kg, the thrust reserve will allow flying not at the "maximum" of the engine. Here we must also take into account the fact that in level flight the required power is less than in hover mode. In addition, during takeoff, the effect of the proximity of the earth will have a positive effect. All this suggests that the electric motor does not have to be operated at maximum speed.

Choosing a Model Schema

At present, in aviation, the main part of helicopters is made according to a single-rotor scheme with a tail rotor, which has become widespread due to its ease of control. Given that the model being created will be manageable, it is best to take just such a scheme as a basis. A possible version of the drawing is shown in Figure 2.

Rice. 2. Power motor "Veterok" (click to enlarge)

For ease of manufacture and balancing, the main and tail rotors are made of two-bladed. When creating any helicopter, serious attention should be paid to stability. In the designed model, it is provided with the help of stabilizing weights, which form a kind of gyroscope. During the operation of the rotor, the weights mounted on the blades tend to maintain the plane of rotation. When it deviates from a predetermined position, a cyclic change in the angles of attack of the blades occurs, due to this, aerodynamic forces arise that return the rotor to its previous position. By changing the plane of rotation of the weights using the swashplate, you can control the flight of the model.

Main gearbox and transmission of rotation to the tail rotor

In order for the main rotor to develop the thrust calculated earlier, it is necessary to correctly select the gear ratio of the gearbox. Accurate calculation requires knowledge of the load characteristics of the engine and the aerodynamic rotor. You can limit yourself to an approximate calculation. Knowing the diameter of the piit, installed during testing on the motor shaft, and the rotor, it is possible to determine the gear ratio of the gearbox by the formula:

i_р= (R_nv/R₀)^5/3,

where R_nv- rotor radius; R₀- the initial radius of the screw on the motor shaft; i_р- gear ratio of the gearbox;

For R_nv= 0,75 m; R₀= 0,1;i_р= 28,8.

Such a gear ratio can be calculated using two or three steps. If a two-stage gearbox is selected, then:

і₁=Z₁/Z₂; the₂=Z₃/Z₄,

where Z is the number of gear teeth of the gearbox. Taking Z₁= 10,Z₂= 100,Z₃= 17,Z₄= 93, get i_р= 28,8. If in practice it is not possible to select gears with a given number of teeth and a deviation of +/-10% from the calculated value occurs, this will not lead to a significant decrease in main rotor thrust.

You should strive to make the gearbox light and at the same time strong enough. To reduce weight, large gears (Z₂= 100 and Z₄= 93) can be made of duralumin or textolite.

The transmission (Fig. 3) to the tail rotor is easiest to do using two pulleys Ø 60-80 mm: the leading one is installed on the intermediate stage of the gearbox, the driven one is on the tail boom. They are connected by a tape made of nylon thread Ø 0,8-1 mm.

Rice. 3. Model transmission diagram (click to enlarge)

Model management

When controlling the model at the first stage, two commands are sufficient: changing the engine speed and controlling the course. The first is done quite simply - with the help of a rheostat included in the power circuit, for example, from the pedal of a sewing machine.

To control the course, it is necessary to change the pitch of the tail rotor. This can be done using a miniature electric motor, for example, type DK-5-19 with a gearbox. The last one is from the timer (auto start for the camera).

After the first successful flights, you can move on to the complexity of aerobatics. To do this, you need to add more . two steering machines to control the swashplate. With their help, the flight "forward-backward", "left-right" is performed.

After mastering the helicopter model, various options for competitions held in the hall are offered, which can be similar to the competitions of real helicopters: flying along the route, landing at a given point, etc.

electric helicopter
Rice. 4. Schematic diagram of the model: M1 - power motor, M2 - control motor, PU - control panel

In conclusion, a few words about safety. First of all, it is necessary to carefully make all connections of current-carrying elements both on the model and on the control panel. In addition, on the latter, be sure to install a fuse (Fig. 4) for a current of 1 A. It is desirable to connect to the network through a transformer. Finally, in preparation for the launch of the machine, it is important to check the reliability of the entire system on the ground. To do this, having tied the helicopter to the base, it is necessary to drive the electric motor in all modes, gradually increasing the rotor speed. Compliance with these elementary requirements will ensure flight safety.

Author: V. Slepkov

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