The brake rotor and helicopter transmission shafts
Brake HB (TNV) is designed to reduce the time and stop HB transmission units after switching off the engine. It is also used for the entire transmission parked helicopter to prevent unwinding of the support system of the wind.
TITB usually installed on a high-speed shaft of the tail transmission, so that reduced braking torque was the smallest. For example, single-rotor helicopter TNV circuit is put on the drive shaft PB. Support tides brakes with bracket and pads are installed on the case of GR, and the drum brake is attached to the rotating drive shaft flange PB. For better heat and heat dissipation from the surface of the brake drum brakes operate with annular ribs, which gives it additional rigidity.
1, 18 - brake pads; 2 - expander bolt lever; 3 - friction lining; 4 - expander lever; 5 - thrust a finger; 6, 14 - pivot link; 7- bracket; 8 - rod; 5 - the brake drum; 10, 12, 15, 19, 23 - springs; 11 - flange of the tail rotor drive; 13 - the screw; 16 - control cable; 17 - Rivet; 20 - spacer bar; 21 - the adjusting screw; 22 - wing nut
Helicopters coaxial brake mounted on the drive shaft of the fan.
Used drum or disc brakes. Start braking NV made a 25-45% of the nominal frequency of rotation during a 30-45. As the material for the friction linings are widely used plastic with filler - asbestos, barium, brass wire and the like, as a binder - phenol-formaldehyde resin. For brakes, which develops on the surface of the friction temperature up to 100 ° C, the friction material is applied retinax (barium, stabilizing the coefficient of friction).
TREES OF TRANSMISSION
Transmission shafts (BT) is conventionally divided into three groups:
- - The transfer of power from the engine to the gearbox HB (main shaft);
- - The transfer of power to the RV, synchronizing shafts and .t.p. (shafts with low torsional rigidity - spring);
- - A drive of auxiliary units of the power plant helicopter (fans, electric drive units, oil, hydraulic, etc.).
In general, congestion BT define the following types of loads:
- - Torsional (constant and variable) - the main load, determining the geometric parameters of the shafts, couplings;
- - Bending (constant and variable);
- - Longitudinal compression (tension);
- - Vibration load;
- - Temperature.
The static (constant) of the torsional stress is determined by the transmitted torque M variable - torsional vibrations from the engines, gearboxes, IV and PB.
Bending stresses in the BT arise from working joints out of alignment.
Vibratory loads result in an overall reduction in resource elements Tu, in particular the destruction of the bearing intermediate pillars splines wear, etc.
Use flexible couplings, dampers, elastic dampers in the intermediate supports reducing the negative impact of vibration loads.
The temperature change VT elements during operation can cause additional loads. Knowing the temperature field in the zone of operation of BT predicts temperature deformation joints, shafts in general.
Thin-walled hollow shafts made of high-alloyed steels 12H2N4A, 18HN2MA, including electroslag remelting, thermo treated to HRC 32-38, aluminum and titanium alloys, composite materials.
The element can be a threaded shaft on which welling nuts bearings, gear rims, flanges. It is used, as a rule, metric thread increments 1,5 mm angle Profile 60 °. The length of the threaded portion is usually 8-12 mm. For large diameters of shafts (0 100 mm or more), the thread pitch can be increased. Avoid thread shaft in places experiencing alternating bending stresses. Where this is not possible, the thickness of the shaft under the thread increases, taking into account the stress concentration. In such dangerous places thread manufactured with a rounded cavity.
The main shafts are usually carried out without intermediate supports. They consist of 2-x clutches and springs. By mounting misalignment in couplings of shafts with the operation of the helicopter added distortion in the deformation of the attachment GR from external loads (aerodynamic forces on HB, the load in the evolution of the helicopter). One consideration shaft couplings often works in the zone of the heated parts of the engine that must be considered. Connection to the main shaft by means of GR USDA.
Transmission shafts PB transmit power of the engine and are usually of several piers. These shafts are operated at significant movement of the attachment intermediate support relative to their mounting position. Towers couplings chosen based on the maximum operating misalignment for this type of coupling. Knowing the magnitude and direction of movement of individual sections of the shaft specially injected mounting misalignment in couplings, opposite in sign skewed obtainable during operation.
Accessory drive shafts transmit relatively small capacity and carried out both without legs, and with the intermediate supports and several types of couplings. A distinctive feature of the shafts of the group should be regarded as their relative rapidity. Hence - the high demands of balancing shafts.
1 - shaft of the upper screw; 2 - swash plate; 3 - lower screw shaft; 4 - transfer of management swash; 5 - transfer to the management of collective pitch and differential pitch changing; 6 - clutch activation; 7-way clutch; 8 - engine
A promising direction is to obtain a thin-walled, large-diameter shafts, manufactured from steel grades of plastic sheeting using a thick-walled workpiece. The length of the shaft is limited by the capacity of the process equipment.
Increasingly, for the manufacture of rolls used titanium alloys. Shafts of light are obtained, korrozio- persistent, reliable in operation.
Now, when it became widely implemented KM attempts to produce springs from hybrid km (spiral-wound carbon fiber yarns and organovolokna). It is necessary to eliminate the possibility of accidental damage to the drum shaft of composites during installation and operation.
In subcritical shaft diameter and the distance between the supports are selected based on the need to offset out of range.
High critical speed obtained by the use of rigid tubular shafts of large diameter, in the small distances between the bearing supports. Such short tight links of trees in many cases, have to be connected by elastic collars to eliminate the problem of alignment of bearings and shafts (if in the process the support structure can be moved). As a result, the shaft system is complicated, and the weight increases. Constructor sometimes goes to the lower working rotational angular velocity to prevent the onset of the critical mode. In this case, the need to increase the transmitted torque M to save
constant power, and therefore requires even larger shaft sizes and weights.
In the case of a flexible (supercritical) shaft operating angle shaft speed exceed the critical with some margin.
Go through with should take place as quickly aspossibly on condition of excess capacity. To reduce the vibration amplitude of the shaft it is necessary a good balancing. You need to know that the shaft can be balanced only one angular velocity; at other speeds, usually it is unbalanced.
Clutches are set to compensate for angular and linear displacements of the shafts, their connections, turn on and off (freewheel) coupling.
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