helicopter autopilot

The inclusion of an autopilot in the helicopter control system is advisable to be performed using the so-called differential scheme, using combined steering assemblies. In this scheme, the latter operate simultaneously both from the signals of the autopilot and from the influence of the pilot. With differential inclusion of steering machines, the control lever, for example the cyclic step handle, can be fixed (or moved by the pilot), while the corresponding control element, regardless of the handle, is deflected by the signals of the autopilot. At the same time, stabilizing control deviations are not transmitted to the handle. At the same time, to quickly change the flight mode or when the autopilot fails, the pilot can always intervene in the control, directly rejecting the control knob.

In the case of differential steering machines powerful tool for improving the safety of the helicopter flight with the autopilot is the limit of their stroke. Normally this course is 10-25% of the full range of deviation management body, resulting in failure of the autopilot easily countered by the intervention of the pilot and control. However, stroke limitation complicates autopilot work as a stabilizer when you change flight modes.

When operating on electronic signals using a three-channel servo handle can perform scheduled flight mode change (change from horizontal flight to climb or descend, and, on the contrary, the gentle turns, etc.).

The choice is determined by the structural scheme of autopilot helicopter appointment. For example, in a structural diagram of an autopilot for vertoleta- crane besides conventional autopilot stabilizing the fuselage deflection angles, it is advisable to set automatic additional devices such as the system damping load on the external load, the stabilization system for a helicopter hovering around the desired point on the ground with Doppler ground speed.

For helicopters with flight weight over 5-7 t set the course of the stabilization system, altitude and flight speed. On heavy helicopters in addition to the above should be considered mandatory installation of automatic control system, which allows to solve the problem is not only the corner, but the trajectory of stabilization, including automatic flight along the path of a given line, automatic approach, etc.

Perhaps the emergence of self-oscillations associated with periodic boosters action. Self-oscillations are caused due to the booster spool displacement movements rocking the control towers and unbalanced sections of control systems fluctuations during vibration, subsidence boosters and autopilot signals generated by vibrations of its sensors and fuselage.

SETTING THE POWER MANAGEMENT SYSTEM hydraulic actuator

Choosing one or another block diagram of an autopilot and thereby defining the need to include it in certain control channels, it is necessary to choose the State in view of their work not only on manual but also on automatic pilot signals.

Power rod GU reproduces mechanical motion control wiring connected to its distributor spool, with multiple power gain obtained by the energy supplied to the fluid.

The required power is determined by the State forces in the longitudinal, lateral and directional control as well as in the management of common HB step.

The constant component of the hinge moment of the blades causes no effort in longitudinal and transverse management, and provides only a constant component of the efforts in the management of collective pitch. The first harmonic provides a permanent part of the effort in the longitudinal and transverse management, and higher harmonics - the variable components of efforts in longitudinal and transverse management and in the management of collective pitch.

The exact definition of hinge moments calculated by the blades difficult. Therefore, the design of the helicopter have to use different methods of assessing approximate values ​​of loads in the management, based on the existing IA extrapolating the results of the flight test data. In the preliminary assessment of State power settings at the stage of conceptual design, you can use the statistics. To do this, it introduces the concept of the specific work GU - product of the efforts developed by State, on its turn, referred to the flight weight.

The maximum force on the output rod of the hydraulic unit is determined by the product of the working pressure on the piston area minus the area of ​​the rod. The speed of movement of the output rod depends on the load, reaching a maximum value at a zero value of the latter. The indicated dependence of the force on the rod on the speed of its movement is called the external, or load characteristic, PG 

Matched thus GU must provide the specified maximum speed of movement of the control at the load of 70% of the load at zero speed GU rod.

In SU-return valves are installed in the pressure supply lines, excluding their "drawdown". The main purpose of these valves - fixing output rods State at the time of transition from the main hydraulic system to duplicate. In addition, check valves prevent arbitrary movement of the output rod under the action of an external load due to the pressure drop in the working GU switching systems.

In the case of a conventional two-stage scheme and the application control circuit GU helicopter design expedient in a combined steering unit operated by a manual control, and signal from the autopilot.

Pumps primary and backup hydraulic actuators are mounted on the main gearbox, which ensures proper operation in the event of engine failure, and the transition to a helicopter autorotation NV mode.

At refusal of the main switching valve system automatically transfers power to the PG backup system.

Power boosters of the first and second stage should be duplicated. If the helicopter can be operated in case of failure of the hydraulic system (with little effort on the control levers on the pivot points), a backup system can not do.

The multi (two- and three-chamber) State each camera is powered independent hydraulic system and the movement of the piston in it is governed by an independent distributor spool (3.8.2, a).

In normal operation, the fluid pressure multichamber SU force on the piston in each chamber are formed on a common stock. Exterior features for multi-GU compared with single-chamber changes to increase surmounted reaction force at the same speed of movement of its output link.

In case of jamming one of the distributing spools of multi-chamber PG, they are connected to each other through decoupling devices (most often spring rods or torsion shafts working on torsion). These devices provide the possibility (with some additional effort) of moving the remaining spools and, therefore, the possibility of controlling the PG. The pressure in the chamber with the jammed spool must be switched off at the crimping signal of the decoupling device. When using multi-chamber PW, the calculation of the required capacities is made for one of its chambers and one hydraulic system. All other chambers and the hydraulic systems supplying them (the number of which is equal to the accepted number of failures for flight) create an excessive (reserve) power of the PG, as well as the mass of the system, determined by the degree of reservation and its scheme.

Helicopters inherent low-frequency vibrations excited by HB, determine the number of special requirements for the hydraulic components. GU helicopter should have a larger dead zone, so as to move the spool caused by vibrations, fit into them. Dead band b of the distribution valve in place of connection of the input depends on the magnitude of the elastic deformations And I support to the State in the direction of the input rod under the action of the maximum operating power. So, for example, Mi-6 D ^ mm to = 0,2, 6 = 0,8; the helicopter

Mi-8 1 A0,17 = mm b = 0,25. As can be seen, the deformation of State supports at maximum operational effort is always less than deadband distributor spool.

The friction forces arising during displacement of the spool must be minimal. The friction of the spool increases significantly with heavy helicopters, due to an increase in spool diameters. To reduce friction forces appropriate to apply the two-stage spools.

When designing SI units, special attention should be paid to the rigidity of their attachment. In case of insufficient stiffness due to State support deformation under the influence of external forces, self-oscillation control at the site of the State may appear. To prevent these self-oscillations in the design should take into account compliance with the directions of action of external forces and possible movement of his power stem from the deformation of the support. The inlet slide valve control rod State should be connected so that the spool is moved by bearing strain

in a direction to the movement of its shaft in the same direction as the action of an external force.

In the kinematic diagram shown in 3.8.3, this correspondence is observed. Indeed, when an external force acts through the output rod 3 to the left, the axis A will move downward due to the deflection of the bracket 4. This will cause the rocking arm 1 to rotate counterclockwise and the movement of the PG 3 rod, as well as the direction of the external force, to the left.