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MODELING
Helicopter modeller. Tips for a modeler
Directory / Radio control equipment Repeated attempts to convert free-flying models of helicopters to radio-controlled ones, as was the case with models of aircraft and gliders, were unsuccessful. This is because models of free-flying helicopters built in asymmetric or coaxial schemes with rotating engines do not have what is called a hull. Simply put, they have neither a nose nor a tail. Therefore, any movement for them, except "up" and "down", has a forward direction. And control of the direction of movement of a helicopter model without a body oriented in space, as well as control of the speed of movement, is impossible without a swashplate. It is not on free-flying and so-called timer helicopters. Let's clarify that a radio-controlled helicopter model is called, which can land at the take-off site. A modern model of this type has almost the same controls as a large helicopter (although some models, like the one described, do not have a collective pitch drive). Almost all models are equipped with gyroscopic stabilization automata (directly connected to the main rotor), the purpose of which is to ensure a constant position of the main rotor rotation plane in case of sharp external disturbances. Here is a brief description and drawings of one of the Japanese models TM-20. Not all technical problems are solved in it in the best way. A designer who wants to explore this unexplored area of technical creativity should be prepared to overcome significant difficulties. In the domestic literature, there are no descriptions of radio-controlled models of helicopters and recommendations for their construction yet. This is a new thing for our modellers, and it is an honor to be a pioneer in a new direction of model technology. Radio-controlled helicopter models are a new class in aeromodelling. The rules of the competition do not yet even define what a helicopter model is, and clear technical requirements have not been developed. The lack of information about such models hinders the development of this class. As a result, unfortunately, we have to state a large gap in it of our athletes.
Fig. 3 There were many attempts to lift a radio-controlled model of a helicopter into the air, but only Vitaly Makeev and Igor Tsibizov, aircraft modelers of the Moscow Aviation Institute, managed to overcome the psychological barrier - the fear of breaking such complex equipment, who set the first All-Union record for flight duration with landing at the take-off site, equal to 6 min 20 With. In another flight, their model flew 2700 m and landed on a pre-designated site. Their mastery of piloting the model did without serious damage. Therefore, the possibility of accident-free development of new technology should be considered proven. There is even an opinion that learning to fly a model helicopter right away is easier than retraining after piloting a model aircraft. But before proceeding with the construction of the model, it is necessary to get acquainted with the features of the scheme, design and the principle of helicopter flight. Let's start with terminology, which will further facilitate our mutual understanding. Helicopter - an aircraft heavier than air, capable of hanging motionlessly, as well as moving in the air at any angle to the horizon. Its lift and thrust are created by one or more rotors driven by a motor. A single-rotor helicopter (Fig. 1) with one (main) main rotor and a tail rotor to compensate for the reaction torque. The tail rotor is also used for yaw control. coaxial helicopter (K-26, Fig. 2) with two rotors located on the same axis and rotating in opposite directions. Helicopter transverse scheme (Fig. 3) with two rotors located on the sides of the fuselage and rotating in opposite directions.Longitudinal helicopter (Fig. 4) with two rotors located at the ends of the fuselage and rotating in opposite directions.
Rotor (main) - a screw that serves to create lift. Swashplate (Fig. 5) - a mechanism that serves to cyclically change the installation angle (pitch) of the rotor blades. Rotor hub - an assembly used to connect the blades to the drive shaft. Horizontal hinge - part of the rotor hub, providing the possibility of flapping motion of the blades. Axial hinge - part of the rotor hub, which allows you to change the angle of installation (pitch) of the blades. Rotor cone - the surface described by the rotor blades.Rotor rotation plane - a plane passing through the rotor hub perpendicular to its axis. Throw Angle - the angle between the axis of the blades and the plane of rotation of the rotor. Mounting angle - the angle between the chord profile hit and the plane of rotation of the rotor. Changing the collective pitch - simultaneous, identical change of installation angles of all blades of all helicopter rotors. hovering - stationary position of the helicopter in the air, when its vertical and horizontal speeds relative to the surrounding air are equal to zero. Autorotation - operating mode of the rotor without power supply from the motor. The rotor in the autorotation mode rotates under the action of the oncoming (from below or from the side) air flow, creating lift and thrust. The term is applied to a helicopter in a flail.In aircraft modeling, for design reasons, single-rotor models of helicopters are most widely used. You need to know the following about the operation of the rotor. The smaller the number of blades, the greater its efficiency. When hovering and when lifting vertically, the rotor of a helicopter works like a propeller. During translational flight, its axis of rotation tilts forward, and it operates in the new airflow mode. As the blades rotate, the lift force causes them to rise, while the centrifugal force prevents them from being thrown up too much, so the rotor disk becomes conical. The aerodynamic characteristics of the helicopter theoretically depend on the shape of the blade. However, the practice of even tests did not reveal this effect to the extent that any definite conclusions could be drawn. But improving the blade surface results in a significant reduction in engine power required to fly. Negative twist to hit by 8-10° gives an increase in thrust by 3-4%. The speed of the blade relative to the air is not the same. It is smaller at the axis of rotation and larger at the end and, moreover, varies depending on the position of the hit in relation to the direction of flight. So, when the propeller rotates, the speed of the hit moving forward is the sum of the speeds of its rotation and the translational movement of the helicopter. For a blade moving backward, the speed will be determined by the difference between the forward speed of the entire machine and its own rotational speed. Due to the slower speed, the backward moving target will also have less lift, or rather would have had less if its angle of attack had not been increased in this case to maintain balance. But it is also impossible to increase this angle too much. The maximum flight speed limit is determined by the value of the true angle of attack of the lagging prey. An increase in the number of revolutions of the rotor with a corresponding decrease in its diameter leads to a deterioration in the hovering characteristics. Significant improvements can be achieved by using profiles with a large value of critical angles of attack, if this does not lead to a significant increase in drag.
The proximity of the ground and the so-called "earth cushion" significantly affect the aerodynamic characteristics of the rotor. But at a distance equal to the diameter of the rotor, this influence can already be neglected. To hover a helicopter without translational speed, 30% more power is required than in level flight at optimum speed. The same phenomenon is observed when climbing. The dynamic ceiling (with translational speed) is always greater than the static ceiling (in hover mode). When the engine stops, the helicopter becomes a gyroplane. In this case, the rotor rotates without power supply as a result of the action of aerodynamic forces. The latter provide the necessary thrust of the rotor and support its rotation. But this transformation depends on many factors. The main one is the direction of blowing the rotor with air flow. During a motor flight, the air flow runs onto the rotor of the helicopter from above, in the autorotation mode - from below. To ensure autorotation, a certain flow velocity (straight or oblique) is required, that is, the helicopter must move relative to it. So, for a safe autorotating landing from the hovering mode, the device must have a headroom of at least 150 m or, in level flight, a forward speed of at least 120 km/h, otherwise an accident is inevitable. These are brief information about the helicopter that an aircraft modeler needs to know.
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Comments on the article: Valentine I agree to talk about the model with the Savonius rotor, both on a helicopter and on a boat: vali.37@mail.ru
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