The location of the blades. A method for reducing loads and vibrations on aircraft with multi-blade propellers with an even number of blades. Tolerances for the relative position of the blades, for the position of the center lines and for the contours of the blades

It has to be based on experimental results or fragmentary information gleaned from various sources. Consider an important issue that arises when creating a windmill - the device of the blades.

How does a simple wind generator work?

There are two types of wind generators:

• horizontal
• vertical

The difference lies in the location of the axis of rotation. The most productive are, reminiscent of their forms of an airplane with a propeller. The screw is the impeller of the windmill, the tail is a wind flow guidance device that automatically turns the axis in the direction of air movement.

When the wind acts on the impeller, a torque is generated that is transmitted to the generator axis. An electric current is excited in its windings, which charges. They, in turn, give charge to the inverter, which changes the parameters of the current and delivers a standard voltage of 220 V 50 Hz to the consumer devices.

There are simpler complexes where consumers are immediately powered from the generator, but such a system is in no way protected from power surges or power outages. The option is used only for lighting or driving pumps that pump water.

What blade shape is optimal?

The main element of a horizontal windmill is an impeller. It most of all resembles a propeller, although it performs completely opposite functions. take on the energy of the air flow, processing it into rotational motion. The efficiency of the impeller and the whole set as a whole directly depends on their configuration.

Horizontal devices have impellers equipped with a large number of blades. Usually there are more than 3. In this matter, there is a dependence of the number of blades on performance. The fact is that with an increase in the number of receiving planes, the power of the impeller decreases, and with a decrease, the sensitivity. Therefore, they choose the "golden mean", taking the average number of blades.

Important! A large number of blades increases the frontal load on the device, creating a tipping force on the base of the mast and a strong axial pressure on the impeller, destroying the generator bearings.

In practice, a large number of different devices have been created, having the shape of an impeller, from simple sectors of a circle, slightly deployed along the radius axis, to complex options with carefully calculated aerodynamics, tested in different conditions. The test results showed that the optimal shape is a model close to the propeller. Such a blade expands somewhat from the center (fairing) of the impeller and gradually tapers towards the end.

The advantage of this type is the uniform distribution of loads on the support bearing, the blade surface and the entire windmill system as a whole. The wind flow acts on all sections with the same force, but if you expand the blade towards the end, you get a fairly long lever that overloads the bearing and breaks out the blades. From this arose such a form, with minor changes used on almost all windmills.

View selection

There are few options or types of blades for horizontal windmills. The reason for this lies in the very design of the impeller - there is simply nowhere to create complex shapes or configurations. Nevertheless, the development of the most successful option is ongoing, today there are several types:

• hard-bladed impellers

Solid blades are made of various materials at once in a certain form, sail blades have a completely different design. The basis is a frame, on which a dense canvas is stretched in such a way that one of the sides is not attached to the frame. It turns out a triangular-shaped blade with one side (from the center to one of the vertices) not fixed to the base.

The current of the wind creates pressure on the sail and gives it an optimal shape for leaving the plane, as a result of which the wheel begins to rotate. The option has an advantage in the mass and weight of the wheel, but needs constant monitoring of the condition of the fabric and the impeller as a whole.

For self-production, improvised materials are usually used. Given the complex profile of the blades, using sheet metal or plastic pipes is a good option.

Blade calculation

In practice, few people calculate the parameters of the blades, since this requires special training and data. Most of the values ​​\u200b\u200bneeded for calculations must first be found, some of them will only be known at all after the windmill is launched. In addition, for most species there is still no mathematical model of rotation, which makes calculations useless.

Most often, the impeller diameter is selected according to the required power, performed according to the table:

As an option, you can use the online calculator, which allows you to get the finished result in seconds, you just need to substitute your own data in the windows of the program.

It should be borne in mind that the calculations of such a device as an impeller will not have sufficient accuracy due to the large number of subtle effects and unknown quantities, therefore, most often, they resort to experimental selection of shape and size.

Material for manufacturing

Before you start work on the creation of the impeller, you need to decide on the material. The choice is made from what is available, or from materials more familiar to the user and available for processing. Requirements for the material for the manufacture of blades:

• strength
• light weight
• ease of processing
• the ability to give the desired shape or the presence of it in the workpiece
• availability

Of all the possible options, several of the most successful were selected empirically. Let's consider them in more detail.

PVC pipes

Use of large diameter PVC sewer pipes allows you to quickly and inexpensively get quite high-quality blades. Plastic is not afraid of exposure to moisture, it is easy to process. The most valuable quality is the presence of an even gutter in the workpiece, it remains only to cut off all that is superfluous correctly.

The ease of manufacture and low cost of the material, combined with the performance of plastic, made PVC pipes the most popular material in the manufacture of homemade windmills. The disadvantages of the material include its fragility at low temperatures.

Aluminum

Aluminum blades are durable, strong and not afraid of any external influences. At the same time, they are heavier than plastic ones and require careful wheel balancing. In addition, working with metal, even as malleable as aluminum, requires skill and the right tool.

The shape of the material also complicates the work - sheet aluminum is most often used, so it is not enough to make blades, you need to give them an appropriate profile, for which you will have to make a special template. Alternatively, you can first bend the sheet along the mandrel, then proceed to marking and cutting parts. In general, the material is more resistant to stress, is not afraid of temperature or weather influences.

Fiberglass

This choice is for professionals. Working with fiberglass is complex, requiring skill and knowledge of many subtleties. The procedure for creating a blade includes several operations:

• making a wooden template, coating its surface with wax, mastic or other material that repels glue
• production of one half of the blade. A layer of epoxy is applied to the surface of the template, on which fiberglass is immediately laid. Then epoxy is applied again (without waiting for the previous layer to dry) and fiberglass again. This creates one half of the blade of the desired thickness.
• the second half of the blade is made in a similar way
• after the glue hardens, the halves are connected with epoxy. The joints are ground, a sleeve is inserted into the end to attach to the hub

The technology is complex, it takes time and the ability to work with materials. In addition, epoxy resin has the unfortunate property of boiling in large volumes, which creates a constant threat to spoil the whole work. Therefore, only experienced and trained users should choose fiberglass.

Wood

Working with wood is fairly familiar to most users, but creating blades is quite a challenge. Not only is the shape of the product itself not simple, but it will also be necessary to make several identical samples indistinguishable from each other.

Solving such a problem is not for everyone. In addition, finished products must be qualitatively protected from moisture, impregnated with drying oil or oil, painted, etc.

Wood has a lot of negative qualities- it is prone to warping, cracking, rotting. Absorbs and easily releases moisture, which changes the mass and balance of the impeller. All these properties make the material not the best choice for a home master, since no one needs unnecessary complications.

Creating blades in stages

Consider the most common option for manufacturing blades. The material used is a PVC pipe with a diameter of about 110-160 mm:

• pieces of pipe are cut along the length of the blades
• a line is drawn along the segment, from which 22 mm are measured in both directions. It turns out 44 mm - the width of one blade
• the same is done from the opposite end
• extreme points on one side of the center line are connected in a straight line. On the second side, a pattern of the shape of the blade is applied
• the blade is cut out, the free end is carefully rounded, the edges are processed with sandpaper or a file
• blades are attached to the hub

The shape of the blades has the following structure:

• end parts are the same in width - 44 mm
• in the middle the width of the blade is 55 mm
• at a distance of 0.15 length, the width of the blade is 88 mm

L fall for a helicopter like rubber for a car. Soft blades smooth out the reactions of the helicopter, make it lazier. Rigid, on the contrary, make the helicopter respond to control without delay. Heavy blades slow down reactions, light ones exacerbate. High profile blades take more energy, while low profile blades are prone to stall when the lift is sharply reduced. When choosing blades, it is worth considering their parameters and choosing the ones that suit your style and experience the most.

When we choose blades, we first of all look at their length, since the length of the blade depends on the class of the helicopter. More often, length refers to the distance from the mounting hole of the blade to its end part. A few manufacturers list the full length of the blade from butt to tip. Fortunately, there are few such cases.
The lift force and the rotational resistance that the blade creates depend on the length. A long blade is able to create more lift, but it takes more energy to rotate. With long blades, the model is more stable when hovering and has more "volatility", i.e. capable of larger maneuvers and performs better autorotation.

Chord (blade width)

An important parameter of the blade, which is most often not indicated at all, and it remains only to measure the chord yourself. The wider the blade, the more lift it can create at the same angles of attack and the sharper the helicopter when controlled by cyclic pitch. A wide blade has a higher rotational resistance and therefore loads the power plant more. When using blades with a wide chord, accurate pitching is important, otherwise you can easily "suffocate" the motor. The largest variation in width is found in blades for helicopters of the 50th class and above.

Length and chord.

Material

The next thing you need to pay attention to is the material from which the blades are made. Today, the most common materials from which helicopter blades are made are carbon fiber and fiberglass. Wooden blades are gradually disappearing from the scene, as they do not have sufficient strength and severely limit the helicopter's flight capabilities. In addition, wooden blades are prone to change shape, which leads to the constant appearance of a "butterfly". Perhaps the least that today is worth agreeing to is fiberglass blades. They do not suffer from shape changes, have sufficient rigidity for light 3D and are perfect for beginner helicopter pilots. Experienced pilots will certainly choose carbon blades as the most rigid ones, allowing the helicopter to perform extreme aerobatics and endowing the helicopter with lightning-fast response to control.

An important parameter is the weight of the blade. Ceteris paribus, a heavier blade will make the helicopter more stable, reduce the speed of control over the cyclic pitch. A heavy blade will add stability and balance and will store more energy in autorotation, making it more comfortable to maneuver. If you are aiming for 3D flight, choose lighter blades.

Blade shape

Straight, trapezoidal. The direct form is more common, the trapezoid is more exotic. The latter allows you to reduce rotational resistance at the cost of reduced recoil.

Blade shape.

Symmetric - the height of the profile is the same at the top and bottom of the blade. Blades with a symmetrical profile are capable of generating lift only at a non-zero pitch. Such blades are the most common among modern helicopters and are used on all models that perform 3D aerobatics.
Semi-symmetrical - the bottom profile of the blade has a lower height. Such blades are capable of generating lift even at zero angles of attack, i.e. They create lift in the same way as an airplane wing does. Such blades are rarely used, usually only on large lance helicopters.

Profile height

The higher the profile, the better it resists stall, but the higher its resistance. Wooden blades usually have a higher profile, but only in order to have sufficient strength.

Profile shape and height.

butt thickness

The thickness of the butt is directly related to the size of the trunnions of your helicopter. If the butt is thicker, then the blade will not fit into the trunnion, if vice versa, it will hang out. Usually within the same class of helicopters, the butt thickness is standard, however, when buying blades, make sure that they fit your helicopter. Some manufacturers supply blades with spacer washers, which can be used if the trunnion seat is larger than the butt thickness. Such washers must be installed in pairs above and below the butt so that the blade is fixed in the center of the trunnion.

Butt thickness.

Mounting hole diameter

The diameter of the hole must match the diameter of the trunnion fixing screw. Like the thickness of the butt, this parameter is standard, however, it is worth checking it before buying blades.

The position of the mounting hole relative to the advancing edge.

Determines how far the advancing edge of the blade protrudes ahead of the trunnion. The rearward offset bore causes the blade to lag behind the trunnion during rotation, making the blades more stable. On the contrary, the offset of the hole to the advancing edge causes the blade to move ahead of the trunnions during rotation, and this position makes the blade less stable.

Mounting hole position.

Blade end shape.

The shape of the end part affects the rotational resistance of the rotor. There are straight, rounded and beveled shapes. The straighter shape creates lift along the entire length of the blade, but also has the most rotational resistance.

Blade end shape.

longitudinal center of gravity.

The position of the center of gravity in the longitudinal direction. The closer the center of gravity is to the tip of the blade, the more stable the blade is and the better it performs autorotation. On the contrary, the displacement of the center of gravity towards the butt makes the blade more maneuverable, but the accumulation of energy by the blade during autorotation suffers.

transverse center of gravity.

The position of the center of gravity across the blade, from the advancing edge to the receding one. Usually they try to place the center of gravity so that during rotation the blade does not lag behind the trunnion and does not protrude forward. A blade with a strongly rearward center of gravity protrudes when the trunnion rotates forward and is therefore more dynamic.

Longitudinal and transverse center of gravity.

Dynamic balancing: protruding/retreating blade.

The parameter depends on the position of the mounting hole, weight, position of the transverse and longitudinal centers of gravity. In general, if a blade rotates forward of the trunnion, then such a blade is more maneuverable and more suitable for 3D flights, but it takes more energy and makes the helicopter not stable enough. If, on the contrary, the blade lags behind the pin during rotation, then such a blade is more stable. If the blade does not lag or protrude, then it is a neutral blade. This blade is the most versatile and is equally well suited for both hover maneuvers and 3D flights.

dynamic balancing.

Night blades.

Night blades with built-in LEDs and a built-in or removable battery are used to complete a helicopter for night flights. Together with the blades, various methods of illuminating the body of the helicopter are used.

Blades with a protective core.

The rod prevents the blade from flying apart in the event of a fall. A very useful safety element, which, unfortunately, is present only in expensive blades from well-known manufacturers. It happens that fragments of blades that are not equipped with such a rod fly up to 10 meters from the place of impact and can lead to injury.

All the most important indicators of a wind wheel, such as speed, power, and speed, depend on the correct angle of installation of the blade. Calculating the angle of installation of a wind turbine blade is quite simple, but it will take some time to understand all this, and so I will start in order.

When the blade is stationary, that is, the wind wheel is standing, the wind runs on it at the angle at which the blade is actually installed to it, but as soon as the blade starts moving, the angle of the wind flow changes. For example, imagine that you are sitting in a car, the wind is blowing right into the side window. As soon as you start moving, as you pick up speed, the wind will already blow obliquely at an angle and into the windshield, and if the speed is very high, then the wind will blow directly into the windshield.

It is the same with the blade, as the rotation speed increases, the real angle of attack of the blade also changes. To calculate this angle, you need to know the speed of the blade. For example, we have a wind of 10m / s, the speed of the screw is Z5, which means the speed of the tip of the blade is five times greater than the wind speed of 5 * 10 = 50m / s.

Now you need to build a right triangle with legs 5 and 50. Next, you need to determine the angle between the hypotenuse and the long leg, for this you need to divide the opposite leg into the adjacent one and we will get the tangent of this angle. 5:50=0.1. In order to derive an angle from this 0.1, we must take the inverse function of the tangent, that is, the arc tangent.

The arc tangent of a number can be calculated in special calculators, or you can use online services, for example >>calculator online. Arctangent 0.1=5.7 degrees. 5.7 degrees is the actual angle of flow on the plane of rotation of the propeller in the speed zone Z5. But since the blade has a different speed along its radius, the real angle of attack will be different, and will be different in each section. For example, in the middle of the blade, the speed is Z2.5, which means the angle of the wind flow is twice as large.

Now we need to know what the true wind is.

The true wind is the one that really presses on the blade and it differs in strength from the one that is approaching the propeller. Any body on which the wind presses, resists it, that is, stops the wind. Imagine snowflakes hitting the glass, on approach they have their initial speed, but approaching the glass they run into a pillow created by the stopped wind. Bumping into this air cushion, snowflakes lose speed and energy. Similarly, on approaching the propeller, resting against it, the wind loses speed and energy. The specific value of losses may be different, but if it is not known, it can be taken as an average equal to about 33%.

Now let's remember the angle of the wind flow that we got above, it is equal to 5.7 degrees. Does it really correspond to the oncoming wind on the blade - No!, since the wind speed is 33% weaker. Then you need to take the wind not 10m/s, but 6.6m/s and everything will fall into place. 6.6m/s*Z5=33, 5:33=0.15, arc tangent 0.15=8.5 degrees. This means that the wind actually runs on the plane of the blade in the speed zone Z5 at an angle of 8.5 degrees.

Further, if the aerodynamic quality of the blade, the polars of the blade, and the wedging angle at which its maximum qualities are manifested are not known, then the wedging angle of the blade can be taken equal to 5 degrees. This means that the blade must be set at an angle of 5 degrees to the actual wind flow on the plane of rotation, then 8.5-5 = 3.5 degrees. It turns out that the angle of the tip of the blade should be set to 3.5 degrees, then with a wind of 10 m / s and a speed of Z5 there will be maximum thrust and blade power, that is, the maximum wind energy utilization factor (KIEV).

The blade also has local speed, and the angle must be calculated separately for each section of the blade. If the tip of the blade is set to speed Z5, then the middle of the blade will be Z2.5.

Under all other conditions, the blade will take much less energy from the wind and, therefore, its KIEV and the power on the shaft will be less. For example, the generator is too powerful and will not allow the blades to reach their speed. Or the wind speed is not the one at which the blade angles were set. Therefore, the blade can be adjusted and manufactured for a certain wind, for example, 5 m/s, then its maximum power will be only at this wind and speed, corresponding to its speed. In order for the blade to work with maximum efficiency in a wide range of winds, it is necessary to have a wind wheel with an adjustable blade angle. The speed of the blades and the degree of braking depend on a bunch of factors, on the thickness of the blade, its width in different areas, on the number of blades, on the fill factor of the area swept by the blades, so actually made homemade blades with rough calculations may behave differently. If you calculated the angles for Z5 speed, this does not mean that the maximum power will be at this speed, for example, if the blades are wide, then the drag will be very large at high speeds and most of the power will be lost on this resistance.

An example of calculating the blades for a specific generator.

Let's say you already have a generator whose power you know. The output power of the generator, and the power consumed by the generator, that is, the efficiency. If the efficiency is not known, then it can be taken equal to 0.5-0.8, that is, roughly speaking, the screw should give the generator twice as much power as the generator produces.

For example, a generator at 180 rpm produces 200 watts/hour of power, and you want to get this power with a wind of 6 m/s. So the screw should take 400 watts from the wind and have 180 rpm. The average KIEV of a three-blade propeller is 0.4 and the speed is Z5. If, for example, a six-bladed propeller, then KIEV will be lower and its speed will also be, approximately KIEV 0.3 and speed Z3.5. More accurate data can only be obtained from specific profiles that have been blown in a wind tunnel, and if there is no blowing data, then only such approximate data can be taken. I also want to note that without load, the screw can accelerate to high speed values, but its power will be much less, and the maximum power will be only at the rated power.

In order for the propeller to take 400 watts, the wind must have an energy of the order of 1000 watts. At 6 m/s, the wind has a power (see other articles on calculating the wind wheel formula) 0.6 * 1 * 6 * 6 * 6 = 129.6 watts per square meter. 129.6 * 8 square meters is equal to 1036.8 watts, the area swept by the blades should be 8 square meters. A propeller with a diameter of 3.2 meters has a swept area of ​​8 m. square. Now we know the diameter of the wind turbine.

Next, you need to find out the speed of the wind turbine. The circumference of the propeller 3.2m is 10m, which means that in one revolution the blades will travel a distance of 10 meters. Now you need to find out the speed of the tips of the blades with a wind of 6m / s and speed Z5, 6 * 5 = 30m / s, that is, in a second the blades will make 30:10 = 3rpm, which is equal to 3 * 60 = 180rpm. From the calculations, it became clear that a wind wheel with a diameter of 3.2 m with a speed of Z5, with a wind of 6 m / s, will have 180 rpm and a shaft power of 400 watts. If the efficiency of the generator is 0.5, then the output will be 200 watts / h electric, if the efficiency of your generator at these speeds is 0.8, then the output will be 320 watts. Also, if the increase in speed of KIEV does not significantly sag, then it is possible that power will increase a little more due to revolutions.

As you know, when the wind speed doubles, its power increases by 8 times, therefore the propeller power will also increase by about 8 times, therefore, the dependence of the output power on the speed should also be quadratic. At 6 m/s, we will have about 250 watts from the generator, and at 10 m/s, the generator should already produce up to 2 kW and, accordingly, load the wind wheel. If the generator turns out to be weak, then the wind wheel will run apart in a strong wind and will spin up to high speeds, hence the strong noise, vibrations and possible destruction of the wind generator. Therefore, the generator must have a power synchronous with the power of the wind turbine.

All these data are of course inverted and have a rather rough calculation, a more accurate calculation can be made independently knowing all the necessary parameters of the generator and knowing the aerodynamic properties of the blade profile used. But for a home windmill, a simple calculation of the installation angles of the blades and the wind turbine as a whole is sufficient. If you have any questions, or you notice gross inaccuracies in my statement of the calculation, then write in the comments below about this to everyone and I will answer all questions. For other materials on the calculation of the blades, see the "VG calculations" section.

Recently, several significant events have taken place in the world of helicopter technology. The American company Kaman Aerospace announced its intention to resume the production of synchropters, Airbus Helicopters promised to develop the first civil helicopter with electric remote control, and the German e-volo - to test an 18-rotor two-seat multicopter. In order not to get confused in all this diversity, we decided to make a brief educational program on the basic schemes of helicopter technology.

For the first time, the idea of ​​an aircraft with a rotor appeared around 400 AD in China, but things did not go beyond the creation of a children's toy. In earnest, engineers took up the creation of a helicopter at the end of the 19th century, and the first vertical flight of a new type of aircraft took place in 1907, just four years after the first flight of the Wright brothers. In 1922, aircraft designer Georgy Botezat tested a quadrocopter helicopter designed for the US Army. It was the first sustainably controlled flight of this type of equipment in history. Botezata's quadcopter managed to fly up to a height of five meters and spent several minutes in flight.

Since then, helicopter technology has undergone many changes. A class of rotary-wing aircraft emerged, which today is divided into five types: autogyro, helicopter, rotorcraft, tiltrotor and X-wing. All of them differ in design, take-off and flight methods, and rotor control. In this material, we decided to talk specifically about helicopters and their main types. At the same time, the classification according to the layout and location of the rotors was taken as the basis, and not the traditional one - according to the type of compensation of the reactive moment of the rotor.

A helicopter is a rotary-wing aircraft in which the lift and propulsion forces are generated by one or more main rotors. Such propellers are parallel to the ground, and their blades are set at a certain angle to the plane of rotation, and the installation angle can vary within a fairly wide range - from zero to 30 degrees. Setting the blades to zero degrees is called idle propeller or feathering. In this case, the rotor does not create lift.

During rotation, the blades capture air and discard it in the opposite direction to the movement of the propeller. As a result, a zone of reduced pressure is created in front of the screw, and an increased one behind it. In the case of a helicopter, this generates lift, which is very similar to the lift generated by a fixed wing of an airplane. The greater the angle of installation of the blades, the greater the lifting force created by the main rotor.

The characteristics of the main rotor are determined by two main parameters - diameter and pitch. The diameter of the propeller determines the takeoff and landing capabilities of the helicopter, as well as partly the amount of lift. The propeller pitch is the imaginary distance that a propeller will travel in an incompressible medium at a certain blade angle in one revolution. The latter parameter affects the lift and rotor speed, which pilots try to keep unchanged for most of the flight, changing only the angle of the blades.

When the helicopter is flying forward and the main rotor is rotating clockwise, the incoming air flow has a stronger effect on the blades on the left side, which increases their efficiency. As a result, the left half of the rotation circle of the propeller creates more lift than the right half, and a heeling moment occurs. To compensate for it, the designers came up with a special system that reduces the angle of installation of the blades on the left and increases it on the right, thus equalizing the lifting force on both sides of the propeller.

In general, the helicopter has several advantages and several disadvantages over the aircraft. The advantages include the possibility of vertical takeoff and landing on platforms, the diameter of which is one and a half times the diameter of the main rotor. At the same time, the helicopter can carry bulky cargo on an external sling. Helicopters are also distinguished by better maneuverability, as they can hang vertically, fly sideways or backwards, and turn in place.

The disadvantages include greater fuel consumption than aircraft, greater infrared visibility due to the hot exhaust of the engine or engines, as well as increased noise. In addition, the helicopter as a whole is more difficult to control due to a number of features. For example, helicopter pilots are familiar with the phenomena of earth resonance, flutter, vortex ring, and the effect of locking the main rotor. These factors can cause the machine to break or fall.

Helicopter equipment of any schemes has an autorotation mode. It belongs to the emergency mode. This means that in the event of a failure, for example, of an engine, the main rotor or propellers are disconnected from the transmission using an overrunning clutch and begin to spin freely by the oncoming air flow, slowing down the fall of the machine from a height. In the autorotation mode, a controlled emergency landing of the helicopter is possible, and the rotating main rotor through the gearbox continues to spin the tail rotor and the generator.

Classic scheme

Of all types of helicopter schemes, the most common today is the classic one. With this scheme, the machine has only one main rotor, which can be driven by one, two or even three engines. This type, for example, includes strike AH-64E Guardian, AH-1Z Viper, Mi-28N, combat transport Mi-24 and Mi-35, transport Mi-26, multipurpose UH-60L Black Hawk and Mi-17, light Bell 407 and Robinson R22.

When the main rotor rotates on helicopters of the classical scheme, a reactive moment arises, due to which the machine body begins to spin in the direction opposite to the rotation of the rotor. To compensate for the moment, a steering device on the tail boom is used. As a rule, this is a tail rotor, but it can also be a fenestron (a screw in an annular fairing) or several air nozzles on the tail boom.

A feature of the classical scheme is cross-links in the control channels, due to the fact that the tail rotor and the carrier are driven by the same engine, as well as the presence of a swashplate and many other subsystems responsible for controlling the power plant and rotors. Cross-coupling means that when you change any parameter of the propeller operation, all the others will also change. For example, with an increase in the rotational speed of the main rotor, the rotational speed of the tail rotor will also increase.

Flight control is carried out by tilting the axis of rotation of the main rotor: forward - the car will fly forward, backward - backward, sideways - sideways. When the axis of rotation is tilted, a driving force will arise and the lifting force will decrease. For this reason, in order to maintain the flight altitude, the pilot must also change the angle of the blades. The direction of flight is set by changing the pitch of the tail rotor: the smaller it is, the less the reaction moment is compensated, and the helicopter turns in the direction opposite to the rotation of the main rotor. And vice versa.

In modern helicopters, in most cases, horizontal flight control is carried out using a swashplate. For example, to move forward, the pilot, using an automatic machine, reduces the angle of installation of the blades for the front half of the plane of rotation of the wing and increases it for the rear. Thus, the rear lift increases, and the front decreases, due to which the tilt of the screw changes and a driving force appears. This flight control scheme is used on all helicopters of almost all types, if they are equipped with a swashplate.

Coaxial scheme

The second most common helicopter scheme is coaxial. There is no tail rotor in it, but there are two rotors - upper and lower. They are located on the same axis and rotate synchronously in opposite directions. Thanks to this solution, the screws compensate for the reactive moment, and the machine itself turns out to be somewhat more stable compared to the classical scheme. In addition, coaxial helicopters have practically no cross-links in the control channels.

The most famous manufacturer of coaxial helicopters is the Russian company Kamov. It produces Ka-27 shipborne multi-purpose helicopters, Ka-52 attack helicopters and Ka-226 transport helicopters. All of them have two screws located on the same axis one under the other. Machines of the coaxial scheme, in contrast to the helicopters of the classical scheme, are capable, for example, of making a funnel, that is, flying around the target in a circle, remaining at the same distance from it. In this case, the bow always remains deployed towards the target. Yaw control is carried out by slowing down one of the rotors.

In general, coaxial helicopters are somewhat easier to control than conventional ones, especially in hover mode. But there are also some peculiarities. For example, when performing a loop in flight, overlapping of the blades of the lower and upper main rotors can occur. In addition, in design and production, the coaxial circuit is more complex and expensive than the classical circuit. In particular, because of the gearbox, which transmits the rotation of the motor shaft to the propellers, as well as the swashplate, which simultaneously sets the angle of the blades on the propellers.

Longitudinal and transverse schemes

The third most popular is the longitudinal layout of the rotors of the helicopter. In this case, the propellers are located parallel to the ground on different axes and spaced apart from each other - one is located above the nose of the helicopter, and the other is above the tail. A typical representative of such a scheme is the American heavy transport helicopter CH-47G Chinook and its modifications. If the propellers are located on the wingtips of the helicopter, then such a scheme is called transverse.

Serial representatives of transverse helicopters do not exist today. In the 1960s and 1970s, the Mil design bureau developed the V-12 heavy cargo helicopter (also known as the Mi-12, although this index is incorrect) of a transverse design. In August 1969, the B-12 prototype set a payload record among helicopters, lifting a load weighing 44.2 tons to a height of 2.2 thousand meters. For comparison, the world's heaviest helicopter Mi-26 (classic scheme) can lift loads weighing up to 20 tons, and the American CH-47F (longitudinal scheme) - weighing up to 12.7 tons.

For longitudinal helicopters, the rotors rotate in opposite directions, but this only partially compensates for the reactive moments, which is why the pilots have to take into account the emerging lateral force that takes the car off course in flight. Movement to the sides is set not only by the tilt of the axis of rotation of the rotors, but also by different angles of installation of the blades, and the yaw is controlled by changing the rotational speed of the rotors. The rear rotor of longitudinal helicopters is always located slightly higher than the front. This is done to exclude mutual influence from their air currents.

In addition, significant vibrations can sometimes occur at certain longitudinal helicopter flight speeds. Finally, longitudinal helicopters are equipped with a complex transmission. For this reason, this arrangement of screws is not very common. But helicopters of the longitudinal scheme are less than other machines subject to the occurrence of a vortex ring. In this case, during the descent, the air currents created by the propeller are reflected upwards from the ground, tightened by the propeller, and again directed downward. In this case, the lifting force of the main rotor decreases sharply, and a change in the rotor speed or an increase in the angle of installation of the blades has practically no effect.

Synchropter

Today, helicopters built according to the synchropter scheme can be attributed to the rarest and most interesting machines from a constructive point of view. Until 2003, only the American company Kaman Aerospace was engaged in their production. In 2017, the company plans to resume production of such machines under the designation K-Max. Synchropters could be classified as transverse helicopters, since the shafts of their two propellers are located on the sides of the hull. However, the axes of rotation of these screws are at an angle to each other, and the planes of rotation intersect.

Synchropters, like coaxial, longitudinal and transverse helicopters, have no tail rotor. The rotors rotate synchronously in opposite directions, and their shafts are connected to each other by a rigid mechanical system. This is guaranteed to prevent the blades from colliding under different modes and flight speeds. Synchropters were first invented by the Germans during the Second World War, but mass production has already been carried out in the USA since 1945 by Kaman.

The flight direction of the synchropter is controlled solely by changing the pitch of the propeller blades. At the same time, due to the intersection of the planes of rotation of the propellers, which means the addition of lift forces in the places of intersection, there is a moment of pitching, that is, lifting the bow. This moment is compensated by the control system. In general, it is believed that the synchropter is easier to control in hover mode and at speeds greater than 60 kilometers per hour.

The advantages of such helicopters include fuel economy due to the rejection of the tail rotor and the possibility of a more compact placement of units. In addition, synchropters are characterized by most of the positive qualities of coaxial helicopters. The disadvantages include the extraordinary complexity of the mechanical rigid connection of the propeller shafts and the control system of the swashplates. In general, this makes the helicopter more expensive than the classical scheme.

multicopter

The development of multicopters began almost simultaneously with the work on the helicopter. It is for this reason that the Botezata quadcopter was the first helicopter to make a controlled takeoff and landing in 1922. Multicopters are machines that usually have an even number of rotors, and there must be more than two. In serial helicopters today, the multicopter scheme is not used, however, it is extremely popular with manufacturers of small unmanned vehicles.

The fact is that multicopters use fixed-pitch propellers, and each of them is driven by its own engine. The reactive moment is compensated by rotating the screws in different directions - half rotates clockwise, and the other half, located diagonally, in the opposite direction. This allows you to abandon the swashplate and, in general, greatly simplify the control of the device.

To take off a multicopter, the rotational speed of all propellers increases equally, to fly to the side, the rotation of the propellers on one half of the device accelerates, and on the other it slows down. The rotation of the multicopter is made by slowing down the rotation, for example, of the propellers turning clockwise or vice versa. Such simplicity of design and control served as the main impetus for the creation of the Botezat quadcopter, but the subsequent invention of the tail rotor and swashplate practically slowed down work on multicopters.

The reason why there are no multicopters designed to transport people today is flight safety. The fact is that, unlike all other helicopters, machines with multiple propellers cannot make an emergency landing in autorotation mode. If all engines fail, the multicopter becomes uncontrollable. However, the probability of such an event is low, but the lack of an autorotation regime is the main obstacle to passing the certification for flight safety.

However, the German company e-volo is currently developing a multicopter with 18 rotors. This helicopter is designed to carry two passengers. It is expected to make its first flight in the next few months. According to the calculations of the designers, the prototype of the machine will be able to stay in the air for no more than half an hour, but this figure is planned to be increased to at least 60 minutes.

It should also be noted that in addition to helicopters with an even number of propellers, there are also multicopter schemes with three and five propellers. They have one of the engines located on the platform deflected to the sides. Thanks to this, the direction of flight is controlled. However, in such a scheme it becomes more difficult to dampen the reactive torque, since two out of three screws or three out of five always rotate in the same direction. To counteract the reactive torque, some of the propellers rotate faster, and this creates an unnecessary lateral force.

speed scheme

Today, the most promising in helicopter technology is the high-speed scheme, which allows helicopters to fly at a significantly higher speed than modern machines can. Most often, such a scheme is called a combined helicopter. Machines of this type are built in a coaxial pattern or with a single propeller, however, they have a small wing that creates additional lift. In addition, helicopters can be equipped with a pusher propeller in the tail section or two puller propellers at the wingtips.

Attack helicopters of the classic AH-64E scheme are capable of speeds up to 293 kilometers per hour, and coaxial Ka-52s - up to 315 kilometers per hour. For comparison, the combined technology demonstrator Airbus Helicopters X3 with two tractor propellers can accelerate to 472 kilometers per hour, and its American competitor with a pusher rotor - Sikorksy X2 - up to 460 kilometers per hour. The promising high-speed reconnaissance helicopter S-97 Raider will be able to fly at speeds up to 440 kilometers per hour.

Strictly speaking, combined helicopters are more likely not to helicopters, but to another type of rotorcraft - rotorcraft. The fact is that the driving force for such machines is created not only and not so much by the rotors, but by pushing or pulling ones. In addition, both the rotors and the wing are responsible for creating lift. And at high flight speeds, a controlled overrunning clutch disconnects the rotors from the transmission and further flight goes in autorotation mode, in which the rotors work, in fact, like an airplane wing.

Currently, several countries of the world are engaged in the development of high-speed helicopters, which in the future will be able to reach speeds of over 600 kilometers per hour. In addition to Sikorsky and Airbus Helicopters, such work is carried out by the Russian Kamov and the Mil design bureau (Ka-90/92 and Mi-X1, respectively), as well as the American Piacesky Aircraft. The new hybrid helicopters will be able to combine the speed of turboprop aircraft and the vertical takeoff and landing inherent in conventional helicopters.

Photo: Official U.S. Navy Page / flickr.com

A centrifugal fan is a mechanical type device that is capable of working with air or gas flows that have a low level of pressure increase. The rotating impeller ensures the movement of air masses. The system of work lies in the fact that the kinetic energy increases the flow pressure, which counteracts all air ducts and dampers.

A centrifugal fan is much more powerful than an axial fan, while it has economical power consumption.

This device allows you to change the direction of the air mass with a slope of 90 degrees. At the same time, during operation, the fans do not create much noise, and due to their reliability, their range of operating conditions is quite wide.

Some Features

I would like to draw attention to the fact that the principle of operation of a centrifugal fan is designed in such a way that it pumps a constant volume of air, and not mass, which allows you to fix the air flow rate. In addition, such models are much more economical than axial counterparts, while the design is simpler.

Scheme of elements of a centrifugal fan: 1 - hub, 2 - main disk, 3 - rotor blades, 4 - front disk, 5 - bladed grate, 6 - housing, 7 - pulley, 8 - bearings, 9 - frame, 10, 11 - flanges .

The automotive industry uses these fans to cool internal combustion engines, which give "use" their energy to such an apparatus. Also, this ventilation device is used to move gas mixtures and materials in ventilation systems.

Can be used as one of the components of heating or cooling systems. This technique is also applicable for the purpose of cleaning and filtering industrial systems.

To ensure the desired level of pressure and flow, a series of fans is usually used. Of course, centrifugal models have higher power, but at the same time remain economical (only 12% of the cost of electricity).

The device of a centrifugal fan consists of an impeller, which is equipped with several rows of blades (fins). In the center is a shaft that runs through the entire body. Air masses enter from the edge where the blades are located, then due to the design they are rotated by 90 degrees, and then, due to centrifugal force, they accelerate even more.

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Types of drive mechanisms

In many ways, the operation of the fan, namely the rotation of the blades, is affected by the type of drive. Currently there are 3 of them:

1. Straight. In this case, the impeller is directly connected to the motor shaft. The speed of the blades will also depend on the speed of rotation of the motor. As a disadvantage of this model, the following are distinguished: if the engine does not have an adjustment of its speed, then the fan will also work in the same mode. But if you take into account that cold air has a higher density, then air conditioning will itself occur faster.
2. Belt. In this type of device, there are pulleys that are located on the motor shaft and impeller. The ratio of the diameters of the pulleys of both elements affect the speed of the blades.
3. Adjustable. Here the speed control is due to the presence of a hydraulic or magnetic clutch. Its location is between the motor and impeller shafts. To make this process easier, such centrifugal fans have automated systems.

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Components of a centrifugal fan

Scheme of impellers of centrifugal fans: a - drum, b - annular, c, d - with conical covering disks, e - single disk, f - diskless.

Like any other technique, the fan will work properly only with the appropriate structural elements.

1. Bearings. Most often, this type of device has oil-filled roller bearings. Some models may have a water cooling system, which is most often used in hot gas service, which prevents overheating of the bearings.
2. Blades and shutters. The main function of dampers is to control gas flows at the inlet and outlet. Some models of centrifugal exhausters may have them on both sides or only on one side - inlet or outlet. The "in" dampers control the amount of gas or air entering, while the "out" dampers resist the airflow that controls the gas. Dampers located at the inlet of the blades help to reduce power consumption.

The plates themselves are located on the wheel hub of the centripetal fan. There are three standard blade arrangements:

• the blades are bent forward;
• the blades are bent back;
• blades are straight.

In the first variant, the blades have blades with a direction along the movement of the wheel. Such fans "do not like" solid impurities in airlift flows. Their main purpose is high flow with low pressure.

The second option is equipped with curved blades against the movement of the wheel. Thus, an aerodynamic channel and a relative cost-effectiveness of the design are achieved. This method is used in working with gaseous consistency flows of low and moderate saturation levels with hard components. As an addition, they have a coating against damage. It is very convenient that such a centrifugal fan has a wide range of speed adjustments. They are much more efficient than models with forward curved or straight blades, although the latter are cheaper.

The third option has blades that expand immediately from the hub. Such models have minimal sensitivity to settling of solid particles on the fan blades, but at the same time they emit a lot of noise during operation. They also have a fast pace of work, low volumes and high pressure levels. Often used for aspiration purposes, in pneumatic systems for transporting materials and in other similar applications.

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Types of centrifugal fans

There are certain standards by which this technique is manufactured. The following types should be distinguished:

1. 1. Aerodynamic wing. Such models are widely used in the field of continuous operations, where high temperatures are constantly present, most often these are injection and exhaust systems. Having a high rate of performance, they are silent.
   2. Reverse curved blades. They have high efficiency. The design of these fans prevents the accumulation of dust and small particles on the blades. It has a sufficiently strong construction, which allows them to be used for areas with high oppression.
   3. Ribs curved backwards. Designed for a large cubic capacity of air masses with a relatively low pressure level.
   4. radial blades. Strong enough, can provide high pressure, but with an average level of efficiency. The rotor guides have a special coating that protects them from erosion. In addition, these models are quite compact in size.
   5. Ribs curved forward. Designed for those cases when you have to work with large volumes of air masses and high pressure is observed. These models also have good erosion resistance. Unlike models of the "rear" type, such units are smaller. This type of impeller has the largest volume flow rate.
   6. Rowing wheel. This device is an open wheel without any casing or casing. It is applicable for rooms where there is a lot of dust, but at the same time, alas, such devices do not have high efficiency. Can be used at high temperatures.