These days, a helicopter is the most versatile aircraft. In many countries it is called " helicopter", which was formed from two Greek words, translated meaning "spiral" and "wing". A helicopter, hovering in one place for a long time, can then fly in any direction, without even making a turn. And he also does not need special runways, because he is able to take off vertically without a “run” and make a vertical landing without a “run”. Thanks to this, helicopters are widely used for transport to hard-to-reach places, for firefighting, sanitary and rescue work.

The main difference between a helicopter and an airplane is that it takes off without acceleration and rises up in a vertical position. The helicopter does not have wings, but instead has a large propeller located on the roof and a small propeller on the tail. The main advantage of a helicopter is maneuverability. It can hover in the air for a long time and, in addition, fly in reverse. To land, the helicopter does not require an airfield: it can land on any flat area, even high in the mountains.

At the beginning of the twentieth century, the Frenchman P. Cornu was the first in the world to fly a helicopter. He managed to fly to a height of 150 centimeters, that is, he hung in his invention somewhere at the chest level of an adult man. Then this flight lasted only 20 seconds. Paul Cornu decided that the height was too high, and he was taking a lot of risks, so subsequently he soared upward only with a safety net - on a leash.

The main design element that makes a helicopter take off and then soar through the skies is its large propeller. It constantly scoops up air with its blades, which is why the helicopter flies. At the same time, the tail rotor prevents the body of this flying bird from turning in the opposite direction of rotation of the main rotor. This helicopter design was invented in the 1940s by a Russian engineer.

When the main rotor of a helicopter rotates, a reaction force arises, spinning it in the opposite direction. Depending on the method of balancing this force, there are single-rotor and twin-rotor helicopters. In single-rotor helicopters, the reaction force is eliminated by an auxiliary tail rotor, and in twin-rotor helicopters, due to the fact that the rotors rotate in opposite directions.

Types of helicopters.

The main purpose of attack helicopters is to defeat enemy ground targets. These are the best military helicopters, which is why such machines are also called attack helicopters. Their weapons consist of guided anti-tank and aircraft missiles, heavy machine guns and small-caliber guns.

An attack helicopter can destroy a huge amount of enemy equipment and manpower in one battle. The Eurocopter Tiger attack helicopter is in service with the armies of France, Spain, Germany and Australia.

The Russian Ka-50 helicopter is considered one of the most maneuverable attack helicopters in the world. It is widely known in the world under the nickname Black Shark. This helicopter is equipped with two large propellers, and its tail is like an airplane. The Black Shark helicopter performs the most complex aerobatic maneuvers and is capable of hovering in the air for up to 12 hours. Thanks to modern automation, the Ka-50 is controlled by only one pilot.

In 1983, the AN-64 Apache attack helicopter was created in the US state of Arizona. Its armament included an automatic rapid-fire cannon and 16 guided anti-tank missiles. The Apache helicopter can reach speeds of up to three hundred kilometers per hour and fly at an altitude of 6 kilometers. This helicopter maneuvers perfectly both in pitch darkness and during the worst weather conditions. The Apache helicopter is still the main helicopter used by the US Army today.

A transport helicopter can be used to transport both passengers and cargo. Other types of helicopters include a special rescue helicopter and a light two-seat research helicopter.

.

Main rotor of a helicopter: one or more (usually two) main rotors are used for flight. Its blades (up to 8 pieces) act like airplane wings and, when rotating, create the necessary lifting force. At first, the blades were made of metal, and since the late fifties of the last century they have been made of fiberglass.

The auxiliary rotor serves to eliminate the reaction force that spins the helicopter in the opposite direction when the main rotor rotates. Sometimes, instead of a propeller, a jet nozzle can be installed on the tail boom. Helicopter engine A drives the main and auxiliary screws to rotate. This is usually a piston or jet engine.

Pilot in the cockpit V there is a control rudder (steering wheel), which is turned by the pilot to fly in the direction he needs. The rudder changes the inclination of the propeller blades; during flight, one part of the circle that the propeller describes will be lowered lower than the other, and the helicopter will fly in that direction.

The fuselage includes the cockpit, passenger or cargo compartment, and engine compartment. Chassis - since a helicopter does not need to “jog” for takeoff and landing, very often the wheeled chassis is replaced with more convenient skis.

FEDERAL AGENCY FOR EDUCATION

STATE EDUCATIONAL INSTITUTION OF ADDITIONAL PROFESSIONAL EDUCATION

INSTITUTE OF MANAGEMENT AND INNOVATION OF THE AVIATION INDUSTRY

V.V. Angelica

HELICOPTER DESIGN

Rostov-on-Don

UDC 629.7 (075)

D 81

D 81 Dudnik V.V. Helicopter design. – Rostov n/d: Publishing house IUI AP, 2005. – 158 p.

ISBN 5-94596-015-2

The textbook outlines: the composition, purpose, structure and process of designing the main units and systems; structural-power and kinematic diagrams of units, designs of parts and units of units.

For students of the professional retraining program in the direction of “Helicopter Engineering”, as well as for practitioners.

Published by decision of the editorial and publishing council of the Institute of Management and Innovation

aviation industry

Scientific editor:

Doctor of Technical Sciences, Professor I.V. Boguslavsky

ISBN 5-94596-015-2

© Dudnik V.V., 2005 © Publishing House IUI AP, 2005

INTRODUCTION

IN These days it is difficult to imagine humanity without aircraft. A worthy place among aircraft is occupied by helicopters - heavier-than-air aircraft that use a main rotor to move in the air. Since helicopter manufacturing is a relatively young field of activity, there is an active change in the design and manufacturing technology of units. In recent years, innovations such as supercritical transmission shafts, active noise and vibration dampers, multi-closed blade spars, monocoque fuselages, tail boom ridges and a number of others have begun to be used. Unfortunately, Russia, for a number of reasons, has lagged behind in the application of some innovations. In accordance with this, it is necessary to strive to make maximum use of the experience accumulated in the global helicopter industry.

IN This textbook attempts to fill the gaps in the coverage of modern technologies, so they are given a little more attention.

Chapters 5 and 8 were written jointly with Oleinik Nikolai Ivanovich.

1. GENERAL INFORMATION ABOUT HELICOPTERS

1.1. Helicopter classification

IN Currently, several dozen types of helicopters are produced in the world. They have different purposes, sizes and characteristics, but the main criterion for classifying a helicopter is its take-off weight. There are several opinions about weight classification. Often it is established by legislative acts of a particular state. Thus, in Russian civil aviation, helicopters are divided into four classes depending on their maximum take-off weight.

1st class – 10t or more,

2nd class – from 5 to 10t,

3 class - from 2 to 5t,

4th grade – up to 2t.

In practice, helicopters are often divided into ultra-light, light, medium, and heavy. Here is one of the division options.

Up to 700kg – ultra-light; 700-5000kg – light; 5000-15000kg – average;

over 15000kg – heavy.

The heaviest helicopter in the world was the Soviet Mi-12 helicopter (105t), and among production vehicles - the Mi-26 (56t).

Standing somewhat apart from this series are unmanned helicopters used for reconnaissance, environmental monitoring and agricultural processing, the take-off weight of which ranges from 80 to 1000 kg.

In addition, helicopters are classified by purpose as:

passenger; combat; transport; agricultural;

search and rescue and others.

The presence of engines on board allows aircraft to be classified by the number of engines - one, two and three engines, and by type - piston and gas turbine.

Another important characteristic is the helicopter layout. The helicopter design determines the method of balancing the reaction torque of the main rotor. Currently, single and double-screw schemes are used. Three and even four-screw designs developed in the Soviet Union and the United States have not found widespread use.

Single-rotor design - assumes the presence of one main rotor and a device that compensates the reactive moment of the main rotor. The tail rotor is usually used as a device for compensating the reactive torque, but in some cases other mechanisms are also used (Figure 1a, b).

The twin-rotor design assumes the presence of two rotors that rotate in different directions. The reactive moments of such screws are mutually compensated. In turn, twin-rotor helicopters, based on the location of the rotors, can have:

∙ coaxial scheme - counter-rotating rotors are located one above the other (Figure 1c);

∙ longitudinal scheme - screws synchronized with each other are placed one in front of the other with a small overlap zone (Figure 1d);

∙ transverse diagram - the propellers are located to the right and left of the fuselage (Figure 1d);

∙ scheme with intersecting screws - two axes of rotation are inclined at an angle to each other (Figure 1e).

IN Currently, Kamov and Mil helicopters predominate in Russia. The first helicopters of our own design appeared at the Kazan Helicopter Plant. Attempts to develop light helicopters are being made in Ukraine. The main European helicopter manufacturers are consortia - Eurocopter, consisting of the French corporation Eurocopter Franz and the German Eurocopter Deutschland and AgustaWestland, consisting of the Italian company

Pania Agusta and English Westland. Boeing, Sikorsky and Bell corporations are the largest in the USA. Companies from Poland and South Africa have been very active in this sector of the market in recent years. Companies from countries such as the USA, Belgium, Italy, and Canada successfully operate in the class of ultra-light helicopters. Japanese firms Yamaha and Fuji are actively promoting unmanned agricultural helicopters.

In addition, it should be noted that on the North American continent other rotary-wing aircraft - single- and double-seat gyroplanes - are very popular. Several companies are involved in their production.

The vast majority of helicopter manufacturers in the world use a single-rotor design. Aircraft built according to these principles are created by the Mil company. Coaxial is used on Kamov helicopters and on some foreign unmanned aerial vehicles. The transverse design is currently used only on Bell tiltrotor aircraft, developed independently and in cooperation with the Agusta company. The longitudinal design is used by Boeing transport helicopters. The scheme with crossed screws is very complex and is used only by Kaman (USA).

1.2. Making helicopters

The process of creating a new helicopter or modifying an existing one is quite complex and consists of several stages (Figure 2). To make a decision to start designing a helicopter or modification, a “critical” mass of requirements must accumulate. These requirements are developed by various services:

∙ engineering - based on an analysis of the developments of other companies and our own research works prepared for implementation;

∙ marketing - based on an analysis of current and future market needs;

∙ operation - based on an analysis of comments and suggestions from operating organizations;

∙ stylist (designer) - based on an analysis of current design trends, in order to create an attractive appearance of the helicopter.

Figure 1. Various rotor layouts.

a – single-rotor configuration with a tail rotor (Mi-28 helicopter, Russia), b – single-rotor configuration with the NOTAR system (MD500, USA), c – coaxial (Ka-50, Russia), d – longitudinal (CH-47, USA) , d – transverse (BA609, USA-Italy), f – diagram with intersecting screws (K-MAX, USA).

Requirements are often in conflict with each other, so after analyzing their importance, urgency and cost, a compromise option is developed that best suits all services. On its basis, preliminary design is carried out, during which aerodynamic and other calculations are performed, the general geometry and equipment composition are determined, decisions are made on the most important technical solutions, and the layout of the aircraft is developed. After completing the preliminary work, detailed design is carried out. At this stage, three-dimensional models of parts, assemblies and assemblies are developed, their strength calculations are performed, on the basis of which a decision is made to lighten or strengthen structural elements. Based on the final three-dimensional model, working documentation is drawn up. Given the high degree of computerization of aviation production, sometimes manufacturers use a simplified documentation system in which, for example, a drawing of a part shows a general view, but does not have dimensional data. Consumers of such a drawing can always obtain the necessary information from the developed computer model located on the corporate network. The design results are transferred to production, where first a prototype is manufactured, and then a real helicopter. If the modification of the aircraft does not involve significant changes, the stage of manufacturing a prototype may be absent.

Flight and static tests confirm the correctness of the calculations. It should be noted that each stage following design leads to a partial change in the design due to the elimination of identified deficiencies. The result of all this work is a certificate authorizing the operation of the aircraft in a particular country in the world. In order to receive a certificate, the aircraft must comply with the airworthiness standards in force in the given territory. As a rule, there are separate rules for civil and

military helicopters. These documents regulate the indicators that the entire device or its individual units must satisfy. For example, it is indicated how much wind the helicopter must withstand in a particular mode.

Figure 2. Simplified diagram of the helicopter creation process.

duration of flight or what noise level it cannot exceed depending on the take-off weight. A significant part of the standards are strength standards. They are considering various options for loading the device in flight, during takeoff and landing, while parking and moving around the airfield. Accordingly, all cases are divided into flight, landing and ground.

Today, people have invented many different types of technology that can not only move along roads, but also fly. Planes, helicopters and other aircraft made it possible to explore the airspace. Helicopter engines, which were required for the normal operation of the corresponding machines, are highly powerful.

General description of the device

Currently, there are two types of such units. The first type is piston engines or the second type is air-breathing engines. In addition, a rocket engine can also act as a helicopter engine. However, it is usually not used as the main one, but is briefly included in the operation of the machine when additional power is needed, for example, during landing or takeoff.

Previously, they were often used for installation on helicopters. They had a single-shaft design, but they began to be quite strongly replaced by other types of equipment. This became especially noticeable on multi-engine helicopters. In this type of technology, the most widely used are twin-shaft turboprop helicopter engines with a so-called free turbine.

Twin-shaft units

A distinctive feature of such devices was that the turbocharger did not have a direct mechanical connection with the main rotor. The use of twin-shaft turboprop units was considered quite effective, since they made it possible to make full use of the helicopter's power structure. The thing is that in this case, the rotation speed of the main rotor of the equipment did not depend on the rotation speed of the turbocharger, this in turn made it possible to select the optimal frequency for each flight mode separately. In other words, the twin-shaft turboprop helicopter engine ensured efficient and reliable operation of the power plant.

Jet propeller drive

Helicopters also use jet propeller drive. In this case, the circumferential force will be applied directly to the propeller blades themselves, without using a heavy and complex mechanical transmission that would force the entire propeller to rotate. To create such a circumferential force, either autonomous jet engines are used, which are located on the rotor blades, or resort to the outflow of gas (compressed air). In this case, the gas will exit through special nozzle holes, which are located at the end of each blade.

As for the economical operation of a reactive drive, here it will be inferior to a mechanical one. If you choose the most economical option only among jet devices, then the best is a turbojet engine, which is located on the propeller blades. However, constructively creating such a device turned out to be too difficult, which is why such devices did not receive widespread practical use. Because of this, helicopter engine factories did not begin mass production.

The first models of turboshaft devices

The first turboshaft engines were created back in the 60-70s. It should be mentioned that at that time such equipment fully met all the needs of not only civil aviation, but also military aviation. Such units were able to provide parity, and in some cases, superiority over the inventions of competitors. The most mass production of turboshaft helicopter engines was achieved through the assembly of the TV3-117 model. It is worth noting that this device had several different modifications.

In addition to it, the D-136 model also received good distribution. Before the release of these two models, the D-25V and TV2-117 were produced, but at that time they could no longer compete with the new engines, and therefore their production was stopped. However, it is fair to say that quite a lot of them were produced, and they are still installed on those types of air transport that were released quite a long time ago.

Equipment gradation

In the mid-80s, a need arose to unify the design of a helicopter engine. To solve the problem, it was decided to bring all turboshaft and turboprop engines available at that time to a common size range. This proposal was accepted at the government level, and therefore a division into 4 categories arose.

The first category is devices with a capacity of 400 hp. s., second - 800 l. s., third - 1600 l. With. and the fourth - 3200 l. With. In addition, the creation of two more models of helicopter gas turbine engine was authorized. Their power was 250 hp. With. (0 category) and 6000 l. With. (category 5). In addition, it was assumed that each category of these devices would be capable of generating power by 15-25%.

Further development

In order to fully ensure the development and construction of new models, CIAM conducted quite extensive research work. This made it possible to obtain a scientific and technical basis (NTR), along which the development of this area will proceed.

This NTZ indicated that the operating principle of future generations of helicopter engines should be based on the simple principle of the Brayton thermodynamic cycle. In this case, the development and construction of new units will be promising. As for the design of the new models, they should have a single-shaft gas generator, and a power turbine with a forward output of the power shaft through this gas generator. In addition, the design must also include a built-in gearbox.

In accordance with all the requirements of the scientific and technical background, work began at the Omsk Design Bureau on the production of such a helicopter engine model as the TV GDT TV-0-100, the power of this device was supposed to be 720 hp. s., and it was decided to use it on a machine such as the Ka-126. However, in the 90s, all work was stopped, despite the fact that at that time the device was quite advanced, and also had the ability to boost power to indicators such as 800-850 hp. With.

Production at OJSC Rybinsk Motors

At the same time, Rybinsk Motors OJSC was fine-tuning such an engine model as the TV GDT RD-600V. The power of the device was 1300 liters. s., and they planned to use it for such a type of helicopter as the Ka-60. The gas generator for such a unit was made according to a fairly compact design, which included a four-stage centrifugal compressor. It had 3 axial stages and 1 centrifugal stage. The rotation speed provided by such a unit reached 6000 rpm. An excellent addition was that such an engine was additionally equipped with protection from dust and dirt, as well as from the ingress of other foreign objects. This type of engine has undergone many different tests, and its final certification was completed in 2001.

Further, it is worth noting that in parallel with the refinement of this engine, specialists worked on the creation of the TVD-1500B turboprop engine, which was planned to be used on An-38 model helicopters. The power of this model is only 100 hp. With. higher and thus amounted to 1400 l. With. As for the gas generator, its layout and equipment were the same as on the RD-600V model. During their development, creation and configuration, it was planned that they would form the basis for a family of engines such as turboshafts and turboprops.

Motorcycle with helicopter engine

Today, the production of various types of equipment has advanced quite widely. This is true for almost all industries, including motorcycle manufacturing. Each manufacturer always tried to make its new model more unique and original than its competitors. Because of this desire, Marine Turbine Technologies recently released the first motorcycle that was powered by a helicopter engine. Naturally, this change greatly affected both the structural part of the machine and its technical characteristics.

Equipment parameters

Naturally, the characteristics of a motorcycle that has a helicopter engine at its disposal also has unique technical parameters. In addition to the fact that such an innovation made it possible to accelerate the motorcycle to an almost unimaginable 400 km/h, there are other properties that are also worth paying attention to.

Firstly, the fuel tank volume of this model is 34 liters. Secondly, the weight of the equipment has increased quite significantly and amounts to 208.7 kg. The power of this motorcycle is 320 horsepower. The maximum possible speed that could be achieved on such a vehicle is 420 km/h, and the size of its rims is 17 inches. The last thing worth mentioning is that the operation of the helicopter engine greatly affected the acceleration process, which is why the equipment reaches its limit in a matter of seconds.

The first such creation that Marine Turbine Technologies showed to the world was called Y2K. Here we can add that the exact acceleration time to 100 km/h takes only one and a half seconds.

To summarize all of the above, we can say that the industry for creating helicopter engines has come a long way, and the current development of technology has made it possible to use products even in equipment such as motorcycles.

A helicopter is a rotary-wing aircraft in which the required lift force is created by one or more screws or propellers driven by engines.

An airplane flies due to increased air pressure under its wings and lower air pressure below them. The helicopter uses the same principle: the role of the wing is played by a rotor with blades.

Rotating, the main rotor creates a large lifting force. This rotation also creates a rotational or reactive moment, which tends to spin the fuselage of the helicopter itself in the opposite direction. In order to somehow compensate for this reactive moment, as a rule, an additional tail rotor is used in a vertical position. If the tail rotor has the form of a fan mounted in a vertical tail unit, it is usually called a fenestron.

In all cases, the main rotor of helicopters has a swash plate, which is designed to ensure a change in the position of the center of pressure of the rotor itself for flight control (the exception here is for schemes in which there are three or more main rotor mechanisms).

In the event that there is only one drive rotor, it is mandatory to have a device to dampen the torque of this rotor (usually a tail rotor or fenestron, much less often jet devices and others). In schemes with several propellers, the torque is often compensated by ordinary counter-rotation of the existing rotors. If the propeller rotates thanks to jet engines installed directly on the propeller blades themselves, the torque, in general, is almost completely unnoticeable and can easily be compensated by aerodynamic rudders.

To better relieve the load on the main rotor mechanism and the rotor itself at high speeds, the helicopter can be equipped with a fairly powerful and well-developed wing, which will provide directional stability. Plumage can also be used for the same purpose.

Another method for compensating reactive moments in a helicopter is to install two rotors, which will rotate in opposite directions and located on a common axis (coaxially). Then the second rotor will be called an aerodynamically symmetrical coaxial rotor (this option, for example, can be seen on the Russian Ka-50 helicopter). It should be noted that helicopters with this design have lower efficiency compared to single-rotor designs due to interference of the helicopter rotors. This became the reason for the use of such flying devices in cramped spatial conditions, for example, in carrier-based aircraft.

The helicopter engine is used to rotate the main rotor. If a helicopter has several main rotors, then they can be driven by one common engine or each by a separate engine, but so that the rotation of the rotors is strictly synchronized.

The purpose of an engine on a helicopter differs from the purpose of an engine on an airplane, gyroplane, or airship, since in the first case it rotates the main rotor, through which it creates both thrust and lift, in other cases it rotates the tractor rotor, creating only thrust. the reaction force of a gas jet (on a jet aircraft), which also provides only thrust.

If a helicopter is equipped with a piston engine, then its design must take into account a number of features inherent to the helicopter.

A helicopter can fly in the absence of forward speed, that is, hang motionless relative to the air. In this case, there is no airflow and cooling of the engine, water radiator and oil cooler, as a result of which the engine may overheat and fail. Therefore, on a helicopter it is more expedient to use an air-cooled engine rather than a water-cooled one, since the latter does not need a heavy and bulky liquid cooling system, which would require very large cooling surfaces on a helicopter.

An air-cooled engine, usually installed on a helicopter in a tunnel, must have a drive for a forced-air fan, which provides cooling to the engine during hovering and level flight, when the speed is relatively low.

An oil cooler is installed in the same tunnel. The temperature of the engine and oil can be adjusted by changing the size of the inlet or outlet openings of the tunnel using movable dampers controlled from the cockpit manually or automatically.

An aircraft piston engine typically has a rated speed of about 2000 rpm. It is clear that the full number of engine revolutions cannot be transferred to the propeller, since in this case the tip speeds of the blades will be so high that they will cause a high-speed stall. For these reasons, the M number at the ends of the blades should be no more than 0.7-0.8. In addition, with high centrifugal forces, the main rotor would be of heavy construction.

Let's calculate the maximum permissible revolutions of a rotor with a diameter of 12 m, at which the number M of the ends of the blades does not exceed 0.7 for a flight altitude of 5000 m at a flight speed of 180 km/h,

So, a helicopter engine must have a gearbox with a high degree of reduction.

On an airplane, the engine is always rigidly connected to the propeller. A durable, small-diameter all-metal propeller easily withstands the jerks that accompany the start of a piston engine, when it suddenly picks up several hundred revolutions. A helicopter rotor, having a large diameter, masses far spaced from the axis of rotation, and therefore a large moment of inertia, is not designed for sudden variable loads in the plane of rotation; When starting, damage to the blades may occur due to starting jerks.

Therefore, it is necessary that at the time of launch the helicopter’s main rotor is disconnected from the engine, i.e., the engine must be started idle, without load. This is usually done by introducing friction and cam clutches into the engine design.

Before starting the engine, the clutches must be turned off, and the rotation of the engine shaft is not transmitted to the main rotor.

However, without load, the engine can develop very high speeds (spin), which will cause its destruction. Therefore, when starting, before the clutches are engaged, you cannot fully open the engine carburetor throttle and exceed the set speed.

When the engine is already running, it is necessary to connect it to the main rotor using a friction clutch.

A hydraulic coupling consisting of several metal discs coated with a material with a high coefficient of friction can serve as a friction clutch. Some of the disks are connected to the engine gearbox shaft, and the intermediate disks are connected to the main shaft drive to the main rotor. As long as the disks are not compressed, they rotate freely relative to each other. The compression of the discs is carried out by a piston. Supplying high pressure oil under the piston causes the piston to move and gradually compress the discs. In this case, the torque from the engine is transmitted to the propeller gradually, smoothly unwinding the propeller.

The revolution counters installed in the cockpit show the engine and propeller revolutions. When the engine and propeller speeds are equal, this means that the hydraulic clutch discs are pressed tightly against each other and the clutch can be considered to be connected as a rigid clutch. At this moment, the dog clutch can be engaged smoothly (without jerking).

Finally, to ensure the possibility of self-rotation, the main rotor must be automatically disconnected from the engine. As long as the engine is running and turning the propeller, the dog clutch is engaged. If the engine fails, its speed quickly decreases, but the main rotor continues to rotate for some time by inertia at the same number of revolutions; at this moment the dog clutch disengages.

The main rotor, disconnected from the engine, can then continue to rotate in a self-rotating mode.

Flight in self-rotation mode for training purposes is carried out with the engine turned off or with the engine running; in the latter case, its speed is reduced so much that the propeller (taking into account the reduction) makes a greater number of revolutions than the engine crankshaft.

After the helicopter lands, the engine speed is first reduced, the clutch is disengaged, and then the engine stops. When parking the helicopter, the propeller must always be braked, otherwise it may begin to rotate due to gusts of wind.

The power of a helicopter engine is spent on overcoming the resistance of the main rotor rotation, on the rotation of the tail rotor (6-8%), on the rotation of the fan (4-6%) and on overcoming losses in the transmission (5-7%).

Thus, the main rotor does not use all the engine power, but only part of it. The propeller's use of engine power is accounted for by a coefficient that shows how much of the engine power the rotor uses. The higher this coefficient, the more advanced the helicopter design. Typically = 0.8, i.e. the propeller uses 80% of the engine power:

The power of a piston engine depends on the weight charge of the air drawn into the cylinders, or on the density of the surrounding air. Due to the fact that the density of the surrounding air decreases with increasing altitude, the engine power also constantly decreases. Such an engine is called a low-altitude engine. With an increase to a height of 5000-6000 m, the power of such an engine is approximately halved.

In order for the engine power not only to decrease, but even to increase up to a certain altitude, a supercharger is installed on the air suction line into the engine, increasing the density of the intake air. Due to the supercharger, the engine power increases up to a certain altitude, called the design altitude, and then decreases in the same way as in a low-altitude engine.

The supercharger is driven into rotation from the engine crankshaft. If there are two speeds in the transmission from the crankshaft to the supercharger, and when the second speed is turned on, the speed of the supercharger increases, then with an increase in height it is possible to provide an increase in power twice. Such an engine already has two design heights.

Helicopters, as a rule, have engines with superchargers.