The wheels of the helicopter landing gear
From the condition of stability while taxiing on the wheel main landing should account for about 70% weight of the helicopter. The design process is determined (relative to the helicopter's center of gravity) takeaway main landing gear wheels racks b and bow (front) or rear (back) and rack. Thus selected chassis base with.
Removal of the main landing gear wheels is determined from the condition of non-tipping on the tail of the helicopter in the parking lot with an angle 15 °. To transport helicopter quantity b should be such that the machine is not tipping when loading through the rear hatch. This problem can also be solved by the use of outriggers from the bottom of the fuselage.
Track Chassis affects protivokapotazhny angle y and the characteristics of the "earthly" resonance. The use of special chassis shock absorbers and dampers VSH can successfully combat the phenomenon of "earthly" resonance practically all the possible values of the track helicopter landing gear.
When HB helicopter generates lift the pressing force of the helicopter to the ground is reduced. The helicopter may tip about an axis passing through the nose wheel and one main landing gear, and can slide on the site.
For those cases when the helicopter is on a firm, smooth ground, considering the conditions of equilibrium, excluding its
tipping and slipping. On uneven ground, the wheels may rest against an obstacle, the lateral movement of the helicopter is difficult. It is also difficult on the court with the soft ground, the wheels are deeply immersed in it, or when a slight lateral movement of the wheel is formed of earth roller, stopping the helicopter.
(The value of the thrust at which the helicopter continues to work on the land) permissible grounds tilt angles are determined from the conditions of slipping and depend little on the track chassis and the height of the helicopter center of gravity location.
By lowering the coefficient of friction / permissible angles
area bank sharply reduced. If the landing and takeoff of the helicopter slip can be prevented by increasing / or by putting a pad under the wheels, the range of permissible angles site expands.
In single-rotor helicopters permissible angle of heel pad left and right differ significantly. Critical corners area in which the helicopter tips over, decrease with increasing traction NV. If the selected track of the main landing gear legs with a nose strut tilt angle does not provide a helicopter balance, then move on to a four-post rack.
Equilibrium helicopter given special attention when it is based on ships. When roll angles of the landing pad can reach 10 ° or more.
After determining the basic chassis parameters are the selection of the tires of the wheels in the catalog of aircraft wheels (70% to take into account of the actual load on parking gear wheel in the normal weight of the helicopter).
SPECIFICATIONS PNEUMATIC WHEELS CHASSIS
It consists of pneumatic tires and tubes. Used and tubeless pneumatics. To increase the strength, hardness and wear resistance tires performed layered. The outer layer (tread) is made of vulcanized rubber on the outer surface it has a profiled pattern (recesses) to create resistance to lateral sliding. The interior of the tire (the cord) is composed of many layers of rubber-coated threads without a duck and is made of cotton, synthetic or metal high-strength fibers.
Normal load from the ground to the pneumatic action is balanced mostly excess air pressure inside it. Excess pressure on the contact area is formed by flattening pneumatics. Elements of the tire, next to the ground, bent and compressed, its other areas of work in tension.
The greatest bending stiffness are arched pneumatics.
In the selection of wheels for helicopters operated on unpaved runways, counted cross-claim on the ground
- - The ability to get a move on and the movement on the airfield without the formation of a deep rut.
Permeability is characterized by soil strength, the size of the irregularities to be overcome, the resistance coefficient and depth of the track formed by the motion on the ground landing gear (wheels, Polozkov et al.). The drag coefficient at movement on the ground is directly dependent on the depth gauge, and the latter depends on the tire pressure and their size. At low speeds the movement of the helicopter the higher the tire pressure, the deeper track. At the same time increased and the adhesion strength of pneumatics with the ground is reduced.
To ensure the patency of the wet ground tire pressure should not be higher than 0,3-0,35 MPa and 0,5-0,6 MPa for the dry soil.
The depth gauge, which is formed on the surface of the runway ground when moving at low speed, is calculated by the formula
If the depth gauge is exceeded, take the following measures to improve the patency:
- Increase the number of wheels (reduced P st) ',
- Increase the size of the wheels;
- Reduce the tire pressure.
Permeability can be improved by a wheeled chassis in combination with the ski. Partly ski mounted parallel to the plane of the wheel, it improves the permeability of the helicopter and can be used as an additional brake on unpaved airfield. When operating the helicopter at the ski dry soils can be removed.
Energy and loading characteristics of strength and energy pneumatics chassis wheels
The difference between the dynamic pneumatic compression obtained when landing, and "static" (slow) compression varies with the load rate, which, in turn, depends on the parameters and pneumatic cushioning. dynamic loading force exceeds static ua 7-10%. Typically, in the absence of experimental data on the influence of the loading rate at work are static pneumatic pneumatic compression curve.
Most pneumatic service is in a parking compression. To ensure the durability of pneumatic taken 8ST much less 8P <0. Normally $ item = (0,2-0,4) 5 0 n.
When determining the position of the wheel or wheels in relation to other parts (for example, a cylinder, sleeve or poluvilki) must take into account factors such as the adhesion of dirt and raznashivanie tire.
Setting the wheels on the chassis should provide the opportunity to survey the state of the main sites of attachment and the brake system. When using pneumatic sizes are increased by approximately 4% of the diameter and 2-3% in width. We can not allow not only touch, but also a small gap between the tire and any relevant part of the rack.
Main undercarriage wheels have to be sure to brake. Apply shoe, chamber and disc brakes.
to brake the wheels and their system requirements:
- Simultaneity and similarity of braking the wheels in order to avoid a reversal of the helicopter;
- Smooth operation, ie, a gradual increase in the frictional forces;
- The possibility of rapid braking and the brake (braking time full - 1,5 s release - 1,5 c);
- The possibility of a separate braking wheels.
Chamber rim brakes are stacked on the periphery of the pads. Rim with pads pressed against the rubber ring cam disk by being supplied with air or liquid chamber. Pads are moved in the radial direction and pressed against the entire circumference of the brake drum wheel.
Compared with the brake drum provides intimate uniform contact pad to the drum. Therefore, a more effective brake chamber, and braking torque does not depend on the direction of rotation of the wheels. However, the brake chamber has a reduced throttle response, because it requires a certain time (1,0-1,5 s) to fill the chamber with liquid or air.
Disc brake works by incorporating a friction clutch. When applying fluid pressure to the cylinder block the pistons against the resistance of the return spring, the pressure plate is moved. He presses the wheels fixed to the rotating, and the wheel is braked. Disc brake braking torque is independent of the direction of rotation of the wheel, their reliability is higher than the brake chamber. Disc brakes have smaller dimensions (in comparison with drum brakes and chamber) with the same energy consumption and efficiency, which simplifies placing a brake on the wheel.
For shipboard helicopters brake wheel landing gear plays an important role in ensuring the stability of his position on the flight deck. Braking with the principle of gradual increase in braking force is not acceptable. For example, the brake can be applied running in the thrust: by the mechanical spring pressure sector gear engages a crown wheel rigidly connected with the hub, preventing its rotation. The brake is released when applying hydraulic pressure. In addition to the ship's helicopters is necessary to fulfill the requirements of the constancy of braking torque as in the movement of the helicopter forward and backward under the influence of ship pitching. These requirements are satisfied chamber and disc brakes.
wheel weight can be reduced by design and technological solutions. Tubeless pneumatic lighter than conventional and gradually replacing them. series alloys used for the manufacture of wheels: magnesium, aluminum, titanium.
Drum brakes replaced by more compact - disc. The use of self-lubricating bearings reduces maintenance costs and weight of the chassis hinge assemblies.
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