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Design and operation of a helicopter rotor

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 to change the position of the body, an external force must be applied to it. In flight, the helicopter is surrounded by air, so the external force can only be the result of the interaction of any parts of the helicopter with the air environment. In order for an air resistance force to arise, the body must move at a higher speed. When the helicopter is hanging in the air, then this condition is not met by any part of it, except for the screw. Therefore, the role of the helicopter control body is also entrusted to the rotor. Acting the handle of control, the pilot with the help of special devices, which will be discussed in the following chapters, achieves a position that is equivalent to a change in the plane of rotation of the rotor. At the same time, the complete aerodynamic force of the propeller and both its components change its direction. And if the lifting force is always directed vertically upwards, the second component is tangent 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, for example, in the propeller mode, its operation is similar to that of an aircraft propeller. When the aircraft is on the ground or flying horizontally, its screw is blown from the side of the plane of rotation (along the axis). When the helicopter is on the ground, hangs in the air or rises vertically upwards, its main rotor is also blown from the side of the plane of rotation (along the axis). The difference in this case is only THAT, the air jets pass through the plane of rotation of the screw in the horizontal direction, from the front to the back, whereas in the helicopter - in the vertical direction, from top to bottom. In this case, the carrier screw grasps air from zone A from above and throws it, spinning it down, into the zone. Air particles, taken from zone A, are replaced by particles of air from the environment and partly from zone B, but already outside the plane of rotation of the screw.

Before the rotor was rotated, the air above the screw and underneath it was at rest. With the beginning of the screw rotation, the instruments introduced from the area of ​​the screw, but far from it, will show the observer that in the section 0-0, air through Is still in a state of relative rest. Its pressure is equal to atmospheric, and speed. The distance from the cross section of 0-0, where no effect of the screw is yet observed, is the magnitude of the variable to the plane of rotation of the screw, which depends on the viscosity of the medium and the accuracy of the instruments used by us. The more accurate the device, the further it will record from the screw from the presence of air velocity, the particles of which will be directed 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.

Carrying our instruments out of section 0-0 all the way closer to the section, we will notice a gradual increase in the air speed, sucked by the screw. The speed that air has when approaching the section is called the inductive speed of suction. On the basis of the law of conservation of energy, the kinetic energy (the energy of the speed of motion) can not increase without decreasing another kind of energy. And indeed, along with the increase in the air velocity to w, we notice that the air pressure p0 is falling at the same time. This means that the increase in air velocity was due to a decrease in pressure. Behind the screw the cross section of the flow is compressed and an even greater increase in the air velocity occurs. It would seem that a further drop in pressure should follow. However, immediately after the screw, the pressure rises to p-2. Does this not contradict the law of conservation of energy? Yes, it contradicts if we do not take into account the fact that air from the outside (from the screw) received additional energy (mechanical). The mechanical energy of the propeller, converted into the kinetic and potential energy of the flow, increases both the speed and pressure of the air simultaneously.

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.

"The main ones for the helicopter are: propeller mode, oblique blowing mode, self-rotation mode (autorotation) and" vortex ring "mode.

Not tired of copying from books on aerodynamics. What insanity is "oblique blowing mode", "axial blowing" mode.
There is one law and one mode - the law Zhukovsky education wing lift. In flight, the airflow impinges on a leading edge of the blade rather than the screw. Whatever azimuth blade was not, it is still a stream runs onto its edge. All.
And talk about all sorts of blowing forget. If the flow will pass through the screw top, then thrust NV that? It should fall. Simple addition of the thrust vector and the resulting flow. I do not want to argue and take your time. Scientists, academics review the last helicopter aerodynamics. All that is now taught buduyuschim helicopter pilots are not borne out in practice.

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