Requirements for helicopters
To the helicopter had a high performance characteristics and has been an effective means of transport, convenient to operate, it must meet several requirements. These requirements can be divided into common to all aircraft (LA), and special, depending on the purpose and characteristics of combat use.
The general requirements are:
- - Obtaining the designated flight performance data of sufficient stability and controllability of energy at the lowest cost;
- - Adequate (but not excessive) strength and rigidity to ensure the perception of operating loads without permanent deformation and no hazardous vibrations;
- - High combat survivability, t. E. The ability of the aircraft to continue the job after exposure to damaging of the enemy;
- - Reliability of the design, which depends on its excellence, manufacturing quality, operating conditions;
- - Manufacturability design, t. E. The possibility of a broad mechanization and automation of production processes, the use of high-performance processes (stamping, rolling, welding, and so on. P.), A high degree of standardization of parts and components;
- - The minimum mass of the structure, which ensures the rational choice of materials, power circuits, as well as clarification of the existing load;
- - Ease of use, provides sufficient performance connectors, hatches for inspection and performance of works on the technique, the minimum number of components and systems that require adjustment, the use of effective means of control;
- - Maintainability, t. E. The ability to quickly and cheaply repair damaged parts, which ensures interchangeability of major parts and components, extensive use of modular structures;
- - Flight safety, provides a reliable technology, good aerodynamics, the use of special automation to facilitate the piloting, signaling the approach of a dangerous flight regimes.
Many of these requirements are contradictory. During the design of helicopters going to overcome these contradictions by adopting compromise solutions or developing new constructions.
Due to the increasing complexity of aviation technology and increased demands on the level of safety has significantly increased the importance of ergonomic requirements for JTA. Ergonomic requirements are reduced to LA fitness, his cab, command control levers, instrumentation and other equipment to the physiological and psychological possibilities of man for the most effective use of both aircraft and pilot. In this respect, it is important to the proper distribution of functions between JIA and automatic pilot.
Ergonomic requirements include hygienic, anthropometric, physiological and physiological requirements for L A. Hygiene requirements are reduced to the norms of microclimate and limit exposure to harmful environmental factors on human (noise, vibration, temperature, and so on. d.). Anthropometric requirements determine the dimensions of the cockpit, command levers, their location in accordance with the growth of man, his long limbs and so on. etc. Physiological requirements set values of the control effort, in accordance with the possibilities of the human body. Psychophysiological fitness requirements characterize LA instrumentation to the peculiarities of the human senses.
In addition to the above general requirements for helicopters special requirements, reflecting the specificity of their design, flight mode, ways to create lift, management and so on.
The special requirements include:
- - Providing vertical takeoff and landing, hovering at a predetermined height;
- - Ensuring the safe landing mode, autorotation rotor (HB) in case of failure of the power plant;
- - Acceptable level of vibration.
In the development of a military helicopter to his special requirements defined by its purpose and the conditions of combat use of so-called tactical and technical requirements (TTT). They define the performance characteristics necessary for the effective performance of their combat tasks: maximum speed, range, ceiling, payload, the crew, the necessary equipment and weapons. TTT developed taking into account the current level of science-and- technology and the immediate prospects of their development.
Classification helicopters design features
Helicopter called LA, which lift and thrust for forward flight the blades are rotating one or more of HB. Unlike an airplane wing blades HB hildren are streamlined incident flow not only in forward flight, but when working on-site. This provides the opportunity to hang motionless helicopter, take off and land vertically.
In the origin and development of helicopters it has been tested a number of different schemes, from simple to complex composite aircraft. As a result, they were pushed back unsuccessful and identify viable scheme helicopters currently in use.
The main criterion for distinction of these schemes is considered to be the number and location of the rotor. By the number of helicopters HB can be single-rotor, twin-screw and mnogovintovymi. Modern helicopters are built only for Twin and single screw schemes.
Single-rotor design has a relatively low weight, maximum simplicity of design and control systems. However, to balance the reactive torque of the HB helicopter tail rotor necessary, consume up to 10% engine power. It is mounted on a long boom, increasing the size and weight of the helicopter, a danger for the staff.
A disadvantage of single-rotor helicopter is also a narrow range of permissible center of gravity because of its balancing is possible provided that the center of mass is located near the axis of the shaft HB.
HB helicopters twin screw rotating in opposite directions, so their reactive moments cancel each other without additional power losses.
Helicopters longitudinal schemes are most common among twin screw helicopter due to a number of advantages:
- - Large comfortable fuselage;
- - A relatively wide range of permissible center of gravity due to the possibility of redistribution between traction NV;
- - Good longitudinal stability and control.
Longitudinal scheme, however, has some serious drawbacks:
- - A complex and long transmission for transmitting power to the screws and synchronize their rotation in order to avoid collision of the blades;
- - Increased level of vibrations;
- - A complex system of management;
- - The negative impact on the work front HB rear, resulting in a significant loss of power and complexity of design and technology gear mode, autorotation landing on HB; to reduce the harmful effects of the rear HB is located above the front.
Dual-rotor helicopters transverse schemes have a number of positive qualities:
- - Handy streamlined fuselage of the aircraft type;
- - Ease of loading and unloading of the cabin;
- - Favorable mutual influence of the rotor.
A serious drawback is the need for cross-circuit special design to accommodate the screws, which has more drag and weight. To reduce drag, this structure can be formed as a wing.
The disadvantages of the transverse scheme should also include a narrow range of center of gravity and the need for long transmission synchronization NV, the difficulty of providing stability and controllability.
Two-screw coaxial-rotor helicopters have the least size. HB helicopter coaxial arranged one above the other and do not require synchronization of rotation, which greatly simplifies and facilitates the transmission. Aerodynamic symmetry scheme simplifies the piloting and aiming.
However, coaxial scheme has certain disadvantages:
- - A complex system of management;
- - Lack of directional stability;
- - Significant vibration;
- - Risk of collision HB blades rotating in opposite directions;
- - The complexity of the regime of autorotation landing NV.
Soviet designers managed to cope with difficultiesfinishing helicopters experienced such a scheme, and they are commercially available.
In twin screw helicopter crossed-screw axis HB located on the sides of the fuselage and angled outward. In view of the power losses associated with slope HB, and a very complex system management, such a scheme is not widespread.
Airspeed any schemes helicopters limited by the conditions of flow HB. With increasing airspeed end portions of the blades are influenced by the compressibility of the air and fall into a regime of flow separation that leads to strong vibrations and sharp increase in power consumption. Therefore, the maximum level speed of conventional helicopters is less than 320-340 km / h.
To further increase the speed of flight is necessary to relieve the HB. For this purpose, a helicopter wing set.
Additional thrust in the direction of flight of the helicopter can be created propeller (pulling or pushing) or turbojet. The speed of the aircraft can reach a combined 500 km / h and above. Despite the complexity of construction, combination circuit helicopters are promising.
Currently, the most widespread in our country and around the world have helicopters, made of single-rotor scheme with the tail rotor.
The main parts of the helicopter, their purpose and layout
In the development of the helicopter there was a very definite image of a modern helicopter.
The main part of the helicopter fuselage is adapted to accommodate cargo, crew and equipment, fuel, and so on. N. Moreover, it is the power base to which are mounted all the other parts of the helicopter and the load is transmitted from them. The fuselage is reinforced by a thin-walled construction. The central part of the fuselage is usually a truck cabin, Bow - cabin crew.
The tail end 8 and 6 beams are an extension of the fuselage and are designed to accommodate the tail rotor and tail of the helicopter.
On the ceiling of the central panel of the fuselage mounted engines 1 (usually two gas turbine engine), the output shafts of which are connected to the main gearbox.
Main gearbox distributes power coming from the engine, between the units of the helicopter. The main consumer of engine power is HB mounted on the shaft of the main gearbox. It is intended for thrust needed for flight of the helicopter, as well as for longitudinal and lateral control.
The main parts of HB are 2 hub and attached blades 3, directly creating lift.
When you rotate the helicopter HB reactive torque acts seeking to expand it in the opposite direction. To balance this moment is the tail rotor 5. It is driven by the main gearbox via the shafts and gears. In addition, the tail rotor is used for directional control of the helicopter.
The chassis provides the fleecing of the helicopter at the parking lot and walk on the earth's surface, as well as reduced loads during landing.
The most widespread scheme is the three-bearing chassis with nose wheel: the main support situated behind 9the center of gravity of the helicopter, 12-front under the forward fuselage. On high-speed helicopter chassis can be cleaned in flight.
Plumage is intended to enhance the stability of the helicopter. It consists of a stabilizer and fin 7, the role usually played by a specially profiled end bar.
The layout of twin-screw coaxial helicopter is compact due to the smaller diameter screws and the lack of the tail rotor and tail-end beams. However, coaxial HB increases the height of the helicopter, and the lack of directional stability requires the installation of a powerful vertical tail.
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