Design and operation of a helicopter rotor
In order to fly an airplane or glider, needed lifting force, and this force is created wing. Therefore, the main wing on an airplane is, because eventually entire aircraft can be reduced in the flying wing, the fuselage without, without feathers.
In the role of a helicopter rotor wing plays. Even if the aircraft is nothing else than a rotor, in principle we can name it "Helicopter".
Probably, many in childhood made himself a "helicopter", consisting of only one screw willows, cut from a piece of sheet metal. The starting device for it served as a common thread spool from rotating on the shaft.
However, the role of the main rotor of the helicopter is much more versatile than the role of an airplane wing.
A lifting force is not limited to the appointment of another rotor.
When you look at the helicopter in level flight, you are bound to note that the fuselage nose inclined to the horizon. This turns out to be tilted forward and rotor.
The total aerodynamic force the R, developed by the main rotor and a direction perpendicular to the plane of rotation of all the blades in this case can be broken down into two components: the direction of the vertical lift, which supports the helicopter at a predetermined height, and a force directed along the tangent to the trajectory, P that a helicopter is a traction force. Due to this force helicopter flies forward. Thus, the rotor in forward flight is both a tractor propeller.
However, this is not limited to the role of the main rotor. In contrast to the helicopter aircraft have control surfaces, such as ailerons, trim tabs, and rudders height. Yes, they would have no sense, because during the flight would not be blown on the air flow and therefore could not serve as the management objectives.
After all, we know that in order to change the position of the body, it is necessary to attach an external force. In flight, the helicopter is surrounded by air, so the external force can only be the result of interaction between any parts of the helicopter from the air. In order to force the air there was resistance, the body needs to move with greater speed. When the helicopter is in the air, it does not meet this condition, no portion other than the screw. Therefore, the role of authority control helicopter is also assigned to the main rotor. Acting with the rotary pilot with the help of special devices, which will be discussed in the following sections, achieves a position which is equivalent to changing the plane of rotation of the rotor. At the same time changes its direction and the total aerodynamic force of the propeller and both its components. If the lift is always directed vertically upwards, the second component - tangential to the flight path.
Depending on the angle of the total aerodynamic force is changing not only the direction but also the value of its components. Consequently, the driving rotor pilot can change not only the direction of flight, and flight speed.
For raising or descent of the helicopter pilot also acts on the rotor blades by increasing or decreasing simultaneously by the same amount and the installation angle of all blades.
If the helicopter engine fails, then by reducing the angle of attack of the blades, the pilot puts the rotor in position autorotation (autorotation). Supported by the lifting force generated by the screw on this mode of operation, a helicopter makes a safe gliding descent.
From the above it is clear that for an understanding of the helicopter unit and the flight is necessary to understand first of all the main rotor; to be able to continue to fly a helicopter, the designer must ensure the reliability of especially the rotor.
Pilots, engineers, technicians and mechanics, flying in helicopters and serving them, first of all need to follow the immaculate condition of the rotor.
Thus, the rotor - that's what matters in the helicopter
Mode of operation, a helicopter rotor very much. Each mode has its own helicopter flight mode the rotor. The main helicopter are: propeller mode oblique blasting mode, autorotation mode (avgorotatsiya) and vortex -soltsa mode.
Propeller mode occurs when the vertical lifting or hovering helicopter.
oblique blasting mode occurs during forward flight of the helicopter.
autorotation mode occurs when the engine is disconnected from the main rotor of the helicopter in flight, and the screw is rotated under the action of air stream.
vortex ring mode occurs when reducing helicopter. In this mode, the air flow passing through the rotor swept area downwards again fit to the screw top.
However, in some special cases, such as in propeller mode, its operation is similar to the operation of an aircraft propeller. When the aircraft is on the ground and flies horizontally, it is blown by the propeller rotation plane (axial). When the helicopter is on the ground or hanging in the air rises upwardly, its rotor and is blown by the rotation of the plane (axial). The difference here consists only in the fact that the plane passes through the air jet propeller rotation plane in a horizontal direction, from front to back, while the helicopter - in vertical direction from top to bottom. When this rotor captures air from the top of zone A and drops it by screwing down in the zone. In place of air particles retrieved from the zone A, the particles enter the air from the environment and partly from zone B but is the plane of rotation of the screw.
Before the rotor was driven in rotation, the air over the screw n underneath it in a state of rest With the start of rotation of the screw devices made with the scope of the screw, but located away from it, show the viewer that 0-0 sectional air on -prezhnemu is in a state of relative rest. Its pressure is equal to atmospheric pressure, and velocity. Distance from section 0-0, which has not seen the effect of the screw to the plane of rotation of the screw is a variable that depends on the viscosity of the medium used and the accuracy of our instruments. The more precise the instrument, so it is farther away from the propeller register the presence of the air velocity, the particles of which are fixed to the screw.
If the air was deprived of viscous forces, the action of the screw would affect infinitely far.
In fact, due to the fact that air is a viscous medium, the influence of the screw ceases to be felt even at a distance of tens of meters.
Transferring our devices section of 0-0 closer to the cross section, we will notice a gradual increase in air velocity, inleakage screw. The speed at which the air is coming up to the cross section, called induction, inductive speed. On the basis of the law of conservation of energy the kinetic energy (energy of motion speed) can not be increased without the other did not decrease any kind of energy. Indeed, along with the air velocity increases to u, we see that in this case the air pressure falls r0. This means that an increase in air velocity due to the decrease of pressure. For propeller flow area is compressed and occurs even greater air velocity. It would seem, should have been followed by a further drop in pressure. But just behind the screw increases the pressure to p-2. Is it not contrary to the law of conservation of energy? Yes, contrary, if we do not take into account the fact that the air from the outside (of the propeller) received additional energy (mechanical). Mechanical screw energy is converted into kinetic energy and potential energy of the flow, and increases the speed and pressure of the air at the same time.
In the section immediately behind the propeller device shows us that the air compared with the cross section has the speed and "called rejection rate. And dropping speed is twice the speed of being sucked.
Far beyond the screw in the cross section (theoretically infinite distance), speed and air pressure are restored to their original values. the flow of energy in this case because of the presence of viscous forces scattered in space.
This is the action of the screw in the air, which is a consequence of the application to the screw rotation energy. This action corresponds to the reciprocal action of the air on the screw, which is manifested in the form of traction, which is a component of the total aerodynamic force R on the axis passing through the hub perpendicular to the plane of rotation. If the load cell connected to the screw in stop screw showed a value of zero traction, then with increasing speed traction is more and more increasing. Hovering and vertical lift at all other flight conditions
The magnitude of the thrust generated by the screw, it is possible not only to measure but also to count.
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