Radio-controlled helicopter

Bell-Hiller Rotor Head Design

For a long time, it was not possible to create a radio-controlled model of a helicopter. Until April 1970, the best of the attempts ended in flights lasting up to a dozen seconds. A real breakthrough is due to the German engineer Schluter. He used a two-blade rotor with a cyclic change in the pitch of the blades and stabilizing blades. At the heart of the rotor lay a cardan head with a transverse through-spoke, at the ends of which control blades were fixed. The scheme was called Bell-Hiller. Since then, no fundamental innovations in radio-controlled helicopter models have been made, except for the development of electronic stabilization systems that allow the use of simpler bearing rotors without stabilizing blades.

Powerplant

As a power plant, 2-stroke glow engines of internal combustion (hereinafter ICE ) or brushless electric motors in conjunction with lithium-polymer batteries are usually used. The electrical version is currently more common due to the ease of use and the relative cheapness of the installation. Also, helicopters install gasoline and gas turbine engines on the RU.

With glowing ICE

ICE (working on a mixture of nitromethane , methanol and castor / synthetic oil ) helicopters are divided into classes, depending on engine size:

• 30 class, engine displacement 0.30 cu. inches (5.5 cm³)
• 50 class, engine displacement 0.50 cu. inches (8.2 cm³)
• 60 class, engine displacement of 0.6 cubic meters. inches (10 cm³)
• 90 class, engine displacement of 0.9 cubic meters. inches (15 cm³)

The larger the engine capacity, the longer the blades it can spin, therefore the model itself is larger. The flight time of such helicopters is from 7 to 14 minutes, depending on the engine capacity, tuning and piloting style.

With gasoline ICEs

Helicopters with a gasoline power plant are a pretty good replacement for a hot-air ICE, pluses include:

• Lower fuel consumption.
• The cheapness of gasoline (about 20 times cheaper) relative to the fuel for glowing internal combustion engines.
• The relative "cleanliness" of the exhaust (the helicopter and its equipment remains clean enough after flying).
• High flight duration.

The disadvantages include:

• Large sizes: helicopters with gasoline ICE are class 90 models due to the large size of the installation.
• Not very large thrust-to-weight ratio : the gasoline engine is much heavier than the glow engine, and the increase in power is not so great. So with the size of class 90, the model is pretty sluggish.
• The complexity of the design as a whole and, often, the need to alter the frame to install the engine.

A large number of minuses more than cover these advantages, so models with gasoline ICE did not find such wide popularity among modelers.

With electric motors

For a long time, electric helicopters were mainly used indoors because of their small size and lack of exhaust. Then came the large models of electric helicopters designed to fly in open spaces and perform complex maneuvers. ICE helicopters can also be equipped with an electric motor using special kits (whales) or manually.

The smallest RC electric helicopter in the world is Silverlit Nano Falcon ^[4] (it should be noted that this helicopter is controlled by infrared radiation, not radio waves).

There are helicopter classes:

• 100: blade length of the main rotor 70-190 mm, flight weight of the model 50-150 grams;
• 250: the length of the main rotor blade is 200-210 mm, the flight weight of the model is 250-350 grams;
• 400: the length of the main rotor blade is 230-250 mm, the flight weight of the model is 300-500 grams;
• 450: the length of the main rotor blade is 290-350 mm, the flight weight of the model is 800-1200 grams;
• 500: the length of the main rotor blade is 420-450 mm, the flight weight of the model is 1700-2200 grams;
• 550 (30th grade): the length of the main rotor blade is 550-570 mm, the flight weight of the model is 2500-3500 grams;
• 600 (50th grade): the length of the main rotor blade is 600-620 mm, the flight weight of the model is 3300-4000 grams;
• 700 (60th grade): blade length of the main rotor 690-720 mm, flight weight of the model> 4000 grams;

With gas turbine engines

In helicopter models, turbojet engines can also be used. In general, the device is quite simple: the air flow from the turbine enters the impeller of the screw, which in turn transmits torque to the main rotor. But the problem is that for the turbine to work properly, you need to install a large number of expensive electronics to control the fuel supply, temperature, speed and throttle. In view of these facts, turbines are used very rarely in helicopters, and mainly in replica models, to create greater realism.

According to the mechanical control scheme

There are several basic designs of helicopter RPs, characterized by stability or maneuverability. Maneuverability provides more opportunities for the performance of complex aerobatics, but adds to the complexity of management.

• Classic design (main rotor + tail rotor) with collective pitch control.
• Classic design (main rotor + tail rotor) without collective pitch control.
• Coaxial scheme : a pair of multidirectional rotors on the same axis. This type of model has much greater stability compared to the classical scheme, which makes the model ideal for beginners and / or flying indoors. But this scheme has disadvantages:
  • most of these models have a fixed pitch, which greatly simplifies the model, but worsens the course control of the model
  • the impossibility of flying outdoors in windy weather.
• Multi-rotor scheme ( multicopter ) : the multi- rotor scheme (in the jargon of modellers - “multicopter”) is gaining more and more popularity when creating self-stabilizing micro-helicopters and micro-helicopters with autopilot, and most often, a quadrocopter is a circuit with four screws located at the ends of the axisymmetry. In this case, both scheme X and + are used. In addition to quadrocopters, schemes with 3, 6, 8 rays are used. Each beam can be installed as one or two screws.
• Others (e.g. longitudinal pattern: two multidirectional rotors).

Control Equipment

Due to the complexity of mechanical control, helicopter transmitters must have a channel mixing function, for example: “curve” step / gas.

Transmitter prices range from $ 100 to $ 2,000. The most famous manufacturers of radio equipment: JR, Spektrum, Futaba, Hitec, Sanwa (also known as "Airtronics" in North America). More budget Turnigy.

Modulation

Transmitters emit an FM signal in two types of modulation.

PPM is cheaper than PCM, and is mainly used in low-cost helicopter models. The high probability of interference does not allow the installation of such equipment on large models due to the high risk in case of interference. High-end transmitters provide both PCM and PPM modulation for greater compatibility with a large number of receivers.

PCM

Pulse-code modulation - a scheme in which the desired position for each servo is transmitted as an encoded number. Manufacturers use their own method of encoding this number with different number of bits and accuracy. JR uses Z-PCM (10 bits, 512 values) then S-PCM (11 bits, 1024 values).

PPM

Pulse-position modulation is a scheme in which a certain pulse width is transmitted for each position of the servo machine.

Spread spectrum

Spectrum extension methods - a system based on changing the frequency in the 2.4 GHz channel, instead of using different frequencies in the megahertz range, this system does not use only one frequency, but changes it throughout the flight.

Management

The control equipment makes it possible to change the collective pitch and the flow of the air-fuel mixture into the engine (through the so-called curves in the graphs, a tutor can also be used to control the throttle), the collective pitch and the pitch of the tail rotor. Such equipment allows a radio-controlled helicopter to perform all the maneuvers that a real helicopter is capable of, such as hovering and flying with its tail forward, as well as a huge number of maneuvers that conventional helicopters are not capable of.

So-called servomotors ( servos or just servos) are responsible for controlling the helicopter itself. Servos are connected to the plates of the rotor swash plate (1-4 pcs), responsible for the collective and cyclic pitch of the rotor (or screws); and tail rotor (1 pc).

RC helicopter has zero intrinsic stability along the course axis. To solve this problem, electronic piezo gyroscopes are used. Based on the signal received from the gyroscope, the electronics damps the angular displacements of the model around the course axis ^[5] . Thus, without a command to change course from the control panel, the helicopter either does not change course or sets the tail boom according to the actual flight of the model. The gyroscope is connected to the servo-machine controlling the pitch of the tail rotor in the classic circuit or to the “ V-tail ” mixer of both engines in the coaxial circuit. In micromodels of the classical scheme, the gyroscope controls the rotor speed.

For the most part, the helicopter model device is similar to full-size helicopters. The market, however, offers a wide variety of simplified options. Models may vary in the number of control channels:

2-channel . It is controlled by changing the rotor speed (s) and rotation around its own axis. The latter is realized either by changing the rotor speed of the tail rotor, or (in a coaxial circuit ) by changing the rotational speed of one (or both) of the rotors. The model is balanced so that when flying, it moves forward at a low speed along the course.

3 channels . Unlike 2-channel models, the ability to control pitch is added. It is realized either by a swashplate or by a small special screw located on a beam and directed upwards.

4 channels . Unlike 3-channel models, the ability to control roll is added. Pitch and roll channels are controlled by a swashplate (for example, E-sky Lama ).

5 channels . Unlike 4-channel models, the ability to control the collective pitch of the rotor is added. The tail boom is controlled by changing the pitch of the tail rotor.

6 channels . Unlike 5-channel models, the ability to control the gyro sensitivity is added.

7-9 channels . More than six channels require aerobatic helicopter models. Typically, one channel is required to control the carburetor needle (adjusting the mixture) and a pair of channels to control the tutor. The latter is required to maintain the given rotor speed regardless of the step value. To perform most aerobatics, it is more convenient to maintain constant rotor speed, since when changing speed, the reaction to the step-gas knob noticeably changes. The teller, measuring the speed of the main rotor, controls the throttle so that the speed remains unchanged.

Regardless of the above, radio-controlled helicopters may have additional control channels that are not directly related to flight control, functions (cleaning / landing gear , searchlights , lights, cameras, etc.). These channels are usually discrete.

The most popular radio-controlled helicopters usually have 4 or more channels:

• Ailerons ( Roll - Cyclic step );
• Elevator ( Pitch - Cyclic step);
• Rudder (Yaw);
• Collective Step / Throttle (Step / Gas).

To perform complex aerobatics, you must configure a special mode "idle". In this mode, the step range starts at its maximum negative step and ends at the maximum positive (usually from −10 ° to + 10 °). On the other hand, the gas curve is adjusted so that in the extreme positions of the step / gas knob, the damper is open to maximum, and in the center, the damper is open to its minimum required value. This setting allows you to change the direction of thrust created by the main rotor in order to be able to pilot the model in an inverted state.

In the case of cyclic pitch and yaw, pilots usually do not apply any changes when switching from normal flight mode to idle mode. If necessary, modern control equipment allows you to change and adjust them to your style of piloting.

One of the beginner’s auxiliary equipment is the training chassis. It usually consists of four carbon or metal rods with plastic balls at the ends on one side. The opposite sides of the rods are connected through a special coupling, forming a cross-shaped component, the center of which is located under the centers of mass of the model and is fixed on the model's skis either with special latches, or, upon failure, with plastic mounting ties. There is an option of attaching two rods to each other in pairs, and then they cross them crosswise to the skis. In this design, “slippers” have a less negative effect on the controllability of the model and nevertheless reduce the likelihood of model breakdowns during a hard landing or fall. As noted earlier, T. Sh. Negatively affects the flight characteristics of the model and is used only at the first steps or in the development of new first flight figures (pancakes and eights in a position other than tail to themselves).

Additional avionics include:

• FPV (First Person View) - a set of transceiver equipment for flights actually by video. It includes an onboard camera and a transmitter installed on board, as well as a receiver and monitor mounted on the ground. The monitor in most cases is in the form of glasses or a mask worn on the face of the pilot. Management is not carried out by visual observation of the model from the side, but by the side camera. In addition, you can install a unit that gives telemetry to the pilot screen: horizon, angle of attack, coordinates, azimuth, speed, altitude, on-board voltage, current, etc.
• Online Position Recorders
• Equipment for the sound signal when the batteries are low or search for a model that has fallen in tall grass.
• Entertainment systems that drop objects on board to entertain the audience watching the flights.

Typically, in the manufacture of a helicopter, the following materials are used: plastic , aluminum , fiberglass and carbon . The blades are made of wood , fiberglass and carbon fiber. Models are sold in a semi-assembled state (ARF, Almost Ready to Fly, almost ready to fly) and in the form of self-assembly kits (Kit), also in a fully assembled and fully equipped with electronics (RTF, Ready to Fly, ready to fly). Also, some helicopters are delivered in assembled condition, but without control equipment (BNF, Bind and fly, “plug and fly”).

As a rule, a helicopter model device is similar to full-size helicopters. The design of a helicopter model requires more accurate execution than an airplane model, due to the presence of vibrations that affect handling.

In addition to everything, the small size and weight of the helicopter's RC make the control of the model, especially the cyclic step, super-maneuverable and redundant. For these reasons, on helicopter models do not use the usual (simpler) Bell swashplate control system, instead use the Bell-Hiller mixing system, which uses the so-called. servo axis (flybar). This design has excellent Hiller system stability and Bell system speed.

Some models use the Bell system, it is commonly called a flybarless system, in such models it is necessary to use electronic stabilization systems that electronically replace the mechanical servo axis. Examples of such systems: V-bar, SK360, etc.

There are also RC helicopters (mainly the first classic-style helicopters for beginners with a fixed pitch FP, that is, RC helicopters of a classic circuit without collective pitch control) that are equipped only with a Hiller system, for example, an Esky Honey Bee FP helicopter. A clean Hiller control system, one in which the skew plate is connected to the flybar and the flybar in turn controls the pitch of the blades. The result is a very stable helicopter, practically approaching in stability to the RC helicopters of the coaxial scheme, at the same time less wind-fearing, which however lacks the purity and direct control capabilities of the Bell system.

RC helicopters are used not only for aerobatics or copy flight, but also for other purposes: video and photo shooting from a height, observation of terrain, etc. (see, for example, ZALA 421-06 ). Some manufacturers offer helicopter models specially designed for this purpose. For the convenience of panoramic shooting and shooting from a height on such helicopters, a HD video / photo camera is installed. And the control buttons display control buttons. Such helicopters have been widely used in cinema and amateur extreme shooting. Also appeared helicopters with a camera and a screen on the control panel - it is possible to control such models without raising your eyes from the transmitter.

• Quadcopter
• Radio model control equipment
• Unmanned aerial vehicle
• Rc car
• RC airplane

• RC Helicopter Wiki - A wiki dedicated to RC helicopters
• Dedicated Encyclopedia For Electric RC Flight
• A comprehensive R / C Helicopter links directory
• A complete description of the operating principles behind the flybar and Hiller / Bell-Hiller style rotor heads
• Fixed Pitch Vs Collective Pitch RC Helicopters
• RCHeli.dk A useful resource if you are thinking about starting on flying RC helicopter, with a pilot locator and a field locator. And a personal blog about flying
• India based discussion site for RC Helicopters
• Radio Controlled Helicopters Buying Guide - Radio Controlled Machines
• RC Heli Talk - A forum dedicated to electric rc helicopter, grat place for beginners and advance fliers to get help.
• RC Heli Club - MAAC sanctioned RC heli club dedicated to RC helicopters for professional and beginner pilots located in Edmonton, Alberta Canada.
• - Set up a training helicopter. Author: Sean Kitchen with the additions of aarc Translation: aarc.
• 3D aerobatics on the T-rex 600