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Directional control helicopter
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Directional control helicopter

Directional control helicopter

 

Command directional control lever are the foot controller. KKS directional control is determined by field layout considerations.

On a single-screw helicopter with a mechanically driven HB, the track control is carried out with the aid of a RW placed at the end of the tail fuselage beam. The RV balances the torque HB and creates a control torque relative to the vertical axis. The PW pitch varies over a large range (approximately -10 ° to + 25 °). The torque of the HB (determined by the value of the common pitch) varies depending on the flight mode: from the maximum on the hover mode and climb to the minimum on the autorotation mode. The consequence of this is a large range of balancing positions of the track control pedals. On the hovering mode, the pitch of the RV is close to the maximum (especially at high altitude), at autorotation mode - to minimum, at cruising speed - to zero.

Usually helicopter power management GU collective pitch PB installed on the main gearbox housing. In this case, substantially increasing the length of the power wiring from the control rod mechanism to force State change the collective pitch PB. Installation of the power PG on the body of the intermediate gear heavy helicopter minimizes the length of the power of the control circuit.

In twin screw helicopter HB schemes have the opposite direction of rotation for the mutual balancing of torques. Directional control helicopter longitudinal differential circuit achieved HB cyclic variation in the transverse direction and transverse to the helicopter circuit - differential cyclic pitch variation in the longitudinal direction. Directional control of the helicopter coaxial achieved differential change in the collective pitch IIB.

Foot controller connected to the loading mechanism and an exemplary device of the type of the cyclic control stick. Electrical work loading mechanism foot control can be performed by pressing the trigger on the toe, which are mounted on the support sites pedals. Electrical Wiring inclusion mechanism is performed in such a way that when accidentally pressed simultaneously both gashetok electric mechanism was not included.

The ranges of the cyclic and collective pitch NV, as well as step PB calculated from the need for effective management and inventory control in flight on a different alignment and different flight. The length of the control levers is determined in accordance with the recommendations developed on the basis of experience in the design and operation of helicopters.

 

The choice of parameters of elements of control wiring

 

The elements include traction wires, cables, levers, sectors, rocking rollers, bearings and guides.

Depending on the layout conditions, weight, stiffness, and other factors on the helicopters used one of the three main types of manual postings:

- Rigid, in which signals are transmitted to the control surfaces using the reciprocating movement of the tubular rod working on compression and tension;

- Flexible at which signals are transmitted by means of the reciprocating movement of ropes running only in tension. Flexible wiring must consist of two branches (forward and return);

- Rotational - kind of hard wiring, in which signals are transmitted reversible rotary movements

tubular rod - shafts, and the deviation of the actuators is performed via screw converters rotational motion into linear.

Frequently used combinations of different kinds of wiring. Usually, a combination of hard (reciprocating) and cable entries.

Friction and backlash in the wiring

Friction in the wiring should be minimal. A significant influence on the management also provides the friction in the control spool State. The smaller this value is, the better control of the helicopter.

Friction in the distributor spool State should always be slightly less than the initial friction and the compressive force of the loading mechanism in the control system. If the friction in the spool exceeds this amount (which, for example, happens when clogged plunger assembly of the spool), then spontaneously driving control knob when the autopilot. It interferes with the normal control of the helicopter and removed, usually by replacing PG.

The control system does not have to be nearly backlash. This means that the design of the control wiring should be used in all the joints bearings made of high accuracy classes, and strive to reduce the amount of these compounds.

Reduction of these connections is achieved by using roller guides for control rods installed on straight sections of a sufficiently long mechanical wiring. The length of the rods is thus increased without losing their stability to 2 m, instead of the maximum possible length of 1,3 m, which occurs in conventional wiring with pull rods and rockers. At the same time, when using such guides, it is necessary to take into account the elastic deformations of the fuselage of the helicopter in order to avoid jamming the control rods. When calculating the backlash of the hinge joints, it is assumed that the radial play in the hinge bolts does not appear due to the friction created when they are tightened.

Counting the play in the joints of mechanical wiring given to the control lever, is produced by the empirical formula

A backlash is small. Significantly more in control wiring elastic deformations of the non-linear nature. The definition of these deformations by calculation difficult, with a force on the handle before they make N 30 3,5-5 mm.

Some free wheeling on the control handle is also formed by the dead zone spools State. This should be considered in the design of the mechanical elements of control wiring and choice of strokes State. The gear ratio control system is selected so as to not exceed the free wheeling 3 mm.

With a large number of joints in the wiring it is advisable to increase the stroke control to the specific value of backlashes and elastic deformations in it was less. In addition, the control system must produce irreversible weight balancer wiring. Knob, although centered boot springs in any position, should be exempt from moments arising from unbalanced elements mechanical wiring.

Characteristics of loading mechanism

When irreversible management efforts on arms control are not available. Download the cyclic control stick and the foot control is performed by special springs with so-called device. This device allows you to change the amount of force on the handle and foot control optional pilot, also used the system, which consists of electric machines or electromagnetic brake clutch. In the "avtotrimmirovaniya" removing loads from the handle is carried out simultaneously on the pitch and roll by pressing a button on the control handle.

Selecting Performance loading mechanism handles or pedals to a large extent determined by the level of friction in the control system. The friction on the control handle depends largely on the efforts, the need to move the spool State. In the case of the helicopter included a differential steering machines autopilot requirements gradient efforts should be different.

When the steering gear must deviate only spool State and not the control knob. Therefore, the total force of friction F in the wiring to control the steering of the machine and effort stratgirovaniya loading mechanism to exceed the force on the spool State. Based on this condition, characteristic of the loading mechanism should have a "step" - preload.

Pq value of the step is selected so that it exceeds the level of friction in the spool with a certain margin, depending on the hydrodynamic forces on the spool. Roughly P 0, reduced to the control handle is 12-20 N for longitudinal control and 9-15 N for the cross.

For helicopters with irreversible State control system where the effort on the handle P when it created only deviation from the loading mechanism can significantly reduce the area is not centered by creating a large gradient in the load P 0

a small section of a course at a neutral position of the handle and less - on the rest of the course.

The band width is taken from the calculation that the "break" of the characteristic occurs at the point PQ = 1,2Рт. The maximum permissible values ​​of the non-centering zone for longitudinal and lateral control can be adopted on the basis of statistical data on the operation of helicopters of various classes. For medium and heavy helicopters, the variation in the values ​​of these zones is explained by an excessively large force on the spool of heavy duty helicopters. If the spool force is reduced by using a two-stage spool device or a two-stage control system, these values ​​can be assumed to be the same for these classes of helicopters.

Helicopters can fly in an emergency without the State should have a strong spring loading.

In some cases, instead of downloading the directional control pedal spring mechanisms of the auto trim they are loaded into the control system established by a special hydraulic damper. This solves two problems.

  • 1. The damper provides stabilization of speed of automatic moving of pedals at work from signals of an autopilot (so-called "distillation" mode). "Distillation" occurs when, under the action of signals in the autopilot channel, the movement of the rod of the steering machine to the extreme position relative to the autopilot cylinder is not enough. Under the action of the stops, a mechanical connection is opened between the movement of the rod of the steering machine and the distribution spool. In this case, the slide remains ajar, allowing the actuating rod to move together with the head of the steering unit and the pedals until the change in the course of the helicopter stops the signal to the autopilot. Pedals will be rejected in a new position, corresponding to a balancing deviation for this flight mode.

"Distillation" pedal occurs stable low speed provided by a specially profiled slide valve or by applying the damper pedal. The main body of the head of the steering unit set limit switches are designed to switch off the magnetic clutch pedal spring load at the start of the regime, "distillation". The limit switches are activated by pressing their stops.

In order to ensure safety in case of failure of the autopilot steering unit allows the pilot and in the "distillation" pedal to move in the right direction, ie, "Overpower" the action

autopilot. This is due to the pre-compressed spring in the installation stops. At the "overriding" the pilot must attach to the pedal force, where the spring is fully obozhmetsya and pedal arm moves the distribution spool in the position corresponding to the movement of the pedals.

  • 2. The hydraulic damper prevents too abrupt movement of the pedals at the pilot transitional flight regimes. A warning is not justified the need for normal piloting a helicopter is a sharp increase in the movement of the pedal force on the foot of the pilot signal and lighting of the bulb. At the same time in an emergency, such as autorotation, the pilot can quickly move the pedals, overcoming the threshold limit forces the reloading valve damper.

Restricting the velocity of the pedals, and consequently the rate of change of thrust PB can significantly reduce the variable part of the forces acting on the tail rotor powertrain.

To prevent the pedals from sticking at any scuffing hydraulic damper has the ability to turn it off.

This is achieved by removing the pressure in the supply line and valve actuation ringing. The friction of the damper rod is chosen in such a way as to protect the work of a differential inclusion with the autopilot fixed pedals.

When irreversible booster Mr running on the axis of rotation the collective pitch lever set a special friction device with mechanical or hydraulic release that allows the pilot to establish and fix the lever in any position.

For the clutch requires that when disinhibition on the rotation axis of the control lever remains some friction, in which the amount of friction in the harness would exceed approximately twice the magnitude of the friction distributor spool MG. Violation of this condition leads to driving and "twitch" collective pitch lever when it is displaced.

Hard wiring

For each posting, depending on the transmitted forces there is an optimal length of the rods on the straights, where the mass of wiring turns out lower (typically of the order of length of 1200-1500 mm).

In the event of the command lever from the neutral position may be undesirable nonlinearity and changing gear ratios in the wiring. To prevent this it is necessary to strive to angles in the neutral position between the axes of the levers and are connected to rocking rods them were equal 90 °, lever arms and magnitude chosen so that their deviations do not exceed ± 30-35 °.

Traction disposed between the rotating plate AP and the lever pivot axis (QLU) of each blade should be adjustable,

To compensate for linear deformations helicopter design in hard wiring apply compensation mechanisms and rocking, and rope - regulatory mechanisms tension cables. To balance the inclined control rods installed counterweights.

Selection of the type of connecting elements (wires) mainly depends on its length. On helicopters whose distance from the controls in the cockpit to the State is small, it is advisable to perform a mechanical hard wiring, ie using rods and rockers.

Experience design shows that the hard wiring to irreversible Gu Long 15 m above and to the number of joints to do more 40 inappropriate. In such a long cable to the control stick feels excessive friction exceeding 20-30 II, there are illegal clearances and elastic deformations.

To eliminate the jamming in the joints connecting rods with rocking at their installation and deformation frame from loading the helicopter in flight between the plug and the ear connection provides clearance and ear tip mounted Swivel rod bearing.

Mechanical traction wire made of aluminum alloy tubes with crimped ends, which are screwed into the tips. Hard links move guide rollers or suspended on a shaker. Brackets guide rollers and rockers are made of magnesium alloys by casting or forging.

Rockers run punched control of magnesium and aluminum alloys. The flammable compartments, as well as in the power unit wiring traction control performed welded steel.

Tie rods should have a minimum weight and not lose in compression resistance (general and local). With a total loss of stability in the range of applicability of the Euler critical stress is given by.

External periodic forces can cause in the control rods the forced oscillations. The forms (tone) of oscillations of the hinged fixed rod of the control wiring are harmonic, damped and increasing. When the frequencies of the forced and natural oscillations coincide, a resonance occurs, which can cause the rods to break. Forced oscillations thus determine the dynamic strength of the thrust. To eliminate vibration, it is necessary to select the natural frequency of the oscillations of the rods as far as possible from the frequencies of the disturbing forces. The natural oscillation frequency of the thrust with hinged ends at axial load is determined by the formula.

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