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.

See all helicopters

The general requirements are:

• - obtaining the assigned flight performance data, sufficient stability and controllability characteristics at the lowest energy costs;
• - sufficient (but not excessive) strength and rigidity of the structure, ensuring the perception of operational loads without residual deformations and the absence of dangerous vibrations;
• - high combat survivability, that is, the ability of the aircraft to continue performing the mission after the impact on it of the enemy's destructive means;
• - reliability of the structure, which depends on its perfection, workmanship, operating conditions;
• - manufacturability of the design, that is, the possibility of extensive mechanization and automation of production processes, the use of high-performance processes (stamping, rolling, welding, etc.), a high degree of standardization of parts and assemblies;
• - the minimum mass of the structure, which is ensured by a rational choice of materials, power circuits, as well as the specification of the existing loads;
• - ease of use, provided by a sufficient number of operational connectors, hatches for inspection and performance of work on equipment, a minimum number of units and systems requiring adjustment, the use of effective controls;
• - maintainability, i.e. the ability to quickly and cheaply restore damaged parts, which is ensured by the interchangeability of the main parts and elements, the widespread use of modular structures;
• - flight safety, ensured by the reliability of technology, good aerodynamic characteristics, the use of special automatics that facilitate piloting, signaling of approaching dangerous flight modes.

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 psychophysiological requirements for LA. Hygienic requirements are reduced to compliance with microclimate standards and limiting the impact of environmental hazards on humans (noise, vibration, temperature, etc.). Anthropometric requirements determine the size of the cabin, command levers of control, their location in accordance with the growth of a person, the length of its limbs, etc. Physiological requirements determine the magnitude of the control effort in accordance with the capabilities of the human body. Psychophysiological requirements characterize the fitness of aircraft, instrumentation to the characteristics 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 take-off and landing, hovering at a given height;
• - ensuring a safe landing in the self-rotation mode of the main rotor (HB) in the event of a power plant failure;
• - permissible vibration level.

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 alignments due to the possibility of redistribution of thrust between NV;
• - good longitudinal stability and controllability.

Longitudinal scheme, however, has some serious drawbacks:

• - a complex and long transmission for transmitting power to the propellers and synchronizing their rotation in order to avoid the collision of the blades;
• - increased vibration level;
• - complex control system;
• - negative influence of the front NV on the operation of the rear one, leading to significant power losses and complication of the design of gearboxes and landing techniques in the NV self-rotation mode; to reduce the harmful effect, the rear HB is located higher than the front.

Dual-rotor helicopters transverse schemes have a number of positive qualities:

• - comfortable streamlined aircraft-type fuselage;
• - Convenience of loading and unloading the cab;
• - Favorable mutual influence of rotors.

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:

• - complex control system;
• - insufficient directional stability;
• - significant vibrations;
• - danger of collision of HB blades rotating in opposite directions;
• - the difficulty of landing in the NV self-rotation mode.

Soviet designers managed to cope with difficulties finishing 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 three-pillar chassis with nose wheel is most common: the main 9 supports are located behind the 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.