By the type of landing gear, aircraft are classified into. Aircraft classification by purpose

Aircraft classification
depending on the functions they perform

The purpose of aircraft is determined mainly by the design of its individual fragments, general assembly, equipment used on the aircraft, as well as flight, weight and geometric properties. The site notes that basically there are two large groups of aircraft - military and civil.

Military aircraft are involved in air strikes against various military targets, manpower and equipment, as well as enemy communications. Air strikes are delivered both in the rear of the opposing side and in the front-line zone. In addition, military aircraft serve to protect their manpower and facilities from air strikes, as well as to transport troops and equipment, cargo and landing forces. Sometimes military aircraft are used in reconnaissance and for communication "with their own". Military aircraft, in turn, are divided by purpose into several types - bombers, fighters, fighter-bombers, reconnaissance aircraft, military transport and auxiliary aircraft.

Bombers inflict bomb strikes on the most important enemy targets, as well as on communication centers and places where the greatest amount of manpower and equipment is observed. Basically, the action of the bomber takes place in the rear. Fighters serve to repel enemy air strikes. They are subdivided into escort fighters (protecting their bombers from air strikes), front-line fighters (protecting their troops over the battlefield and not far from the front line), interceptor fighters (intercepting and destroying enemy bombers). Fighter bombers are equipped with bombs, missiles and cannons. They take part in delivering strikes in the forward zone and in the near rear, and destroy the enemy's air army.

Military transport aircraft are used when it is necessary to transfer cargo, equipment and troops. Reconnaissance aircraft conduct reconnaissance in the rear of the opposite side, and auxiliary aircraft carry out liaison, correction, sanitary and other functions.

Unlike the military, civil aircraft work in the field of transportation of goods, mail, passengers, and are also used in some sectors of the national economy. They can be divided into several types, also depending on the purpose. Passenger planes are used to move passengers, various baggage, and mail.... They come in trunk lines as well as local lines. The site notes that the split depends on the number of passengers, the range of air travel, and the size of the runways. Trunk lines are subdivided into short, medium and long-distance ones, and carry out transportation at a distance from one to eleven thousand kilometers. Local planes include heavy, medium and light aircraft and can carry from fifty-five (maximum) to eight (minimum) people.

Civil aircraft are also cargo aircraft, they are used to transport goods of various volumes and gravity. Special aircraft are used in agricultural, medical and polar aviation. In addition, there are aircraft that take part in geological exploration, to ensure the safety of forests (from fires, for example), and even for aerial photography. For the training of pilots, there are special training aircraft - they are of initial training and transitional. There are only two seats in the aircraft of initial training, they are quite easy to learn and technique, they are used for pilots who have sat down "at the helm" for the first time. Transition aircraft serve to train already experienced pilots to fly production aircraft already in use on various airlines.

In addition to the purpose, there is also a definition of aircraft according to the scheme. The relative position, types, shapes, and the number of individual parts of the aircraft are taken into account. For example, airplanes differ in the number of wings and their location, in the typhus of the fuselage, landing gear and engines, as well as in the location of the empennage. There are also mixed schemes, one of which is an amphibious boat. The location, type and number of engines greatly affects the scheme and is mainly determined by the purpose of the aircraft, which was described above.

· Equipping passenger seats with comfortable chairs, removable tables, individual lighting, ventilation and alarm;

· Good sound insulation of cabins;

· Performing flights at altitudes where "bumpiness" is less possible;

· Equipping passenger cabins with buffets, wardrobes, toilets and other utility rooms.

Special requirements apply to cargo aircraft. These requirements include:

· Large carrying capacity, increased dimensions of cargo compartments;

· Availability of means of securing (mooring) cargo;

· The presence of intra-aircraft means of mechanization of loading and unloading.

Many of the listed requirements are in conflict with each other: an improvement in some characteristics entails a deterioration in others. For example, an increase in the maximum flight speed causes an increase in the landing speed and a deterioration in its maneuverability; the fulfillment of the requirements for strength, rigidity and survivability is in conflict with the requirement to ensure the minimum mass of the structure; an increase in the flight range is achieved by reducing the weight of the transported cargo, etc. The impossibility of simultaneously fulfilling conflicting requirements makes it impossible to create a universal aircraft or helicopter. Each aircraft or helicopter is designed to perform specific tasks.

3.2. Classification of aircraft, helicopters and aircraft engines

3.2.1. Aircraft classification

The variety of aircraft types and their use in the national economy made it necessary to classify them according to various criteria.

Among the many criteria by which an aircraft can be classified, the most important is its purpose. This feature determines the choice of flight performance, the size and layout of the aircraft, the composition of the equipment on it, etc.

The main purpose of civil aircraft is to transport passengers, mail and cargo, to perform various national economic tasks. In accordance with this, according to the purpose, the aircraft are divided into: transport, special-purpose and training. In turn, transport aircraft are subdivided into passenger and cargo aircraft. According to the maximum take-off weight, the aircraft are divided into classes, tab. 3.1.

Table 3.1

Aircraft classes

		Aircraft type
	75 and more	Il-96, Il-86, Il-76T, Il-62, Tu-154, Tu-204
		An-12, Il-18, Il-114, Tu-134, Yak-42
		An-24, An-26, An-30, Il-14, Yak-40
		An-2, L-410, M-15

Training aircraft are used for the preparation and training of flight personnel in various educational institutions of civil aviation.

Special-purpose aircraft: agricultural, sanitary, to protect forests from fires and pests, for aerial photography, etc.

In terms of flight range, the aircraft are subdivided into long-haul long-haul (over 6,000 km), medium-haul (from 2500 to 6000 km), short-haul short-haul (from 1000 to 2500 km) and aircraft of local air lines (up to 1000 km).

Cargo planes, in contrast to passenger planes, have large internal volumes in the fuselage, allowing to accommodate various cargoes, a more durable floor, and are equipped with mechanization of loading and unloading operations.

The aircraft classification is shown in Fig. 3.1. Out of all the variety of design features, the main ones are highlighted: the number and location of the wings; fuselage type; type of engines, their number and location; chassis type; type and location of plumage.

Rice. 3.1. Aircraft classification

Consider the features of aircraft layouts, due to the number and location of the wings.

By the number of wings, airplanes are subdivided into monoplanes, that is, airplanes with one wing, and biplanes, an airplane with two wings located one above the other. The advantage of biplanes is better maneuverability compared to a monoplane, due to the fact that with an equal wing area, their wingspan is smaller for a biplane. However, due to the large frontal resistance due to the presence of inter-wing struts and braces, the flight speed of the biplane is low. At present, the civil aviation is operating an aircraft - the An-2 biplane.

Most modern aircraft are made according to the monoplane scheme.

By the location of the wing relative to the fuselage, low-wing, mid-wing and high-wing aircraft are distinguished. Each of these schemes has its own advantages and disadvantages.

Low-wing- an aircraft with a lower wing relative to the fuselage. It is this scheme that is most widely used for passenger aircraft, due to its following advantages:

· Low height of the landing gear, which reduces their weight, simplifies cleaning and reduces the volume of compartments for placing the chassis;

· Ease of maintenance of aircraft engines when placing them on the wing;

· During emergency landing on water, good buoyancy is provided;

· In case of an emergency landing with the landing gear not extended, the landing occurs on the wing, which creates less danger for passengers and crew.

The disadvantage of this scheme is that in the area of the junction of the wing and the fuselage, the smoothness of air cut-off is disturbed and additional resistance arises, called interference, and due to the mutual influence of the wing on the fuselage. In addition, on a low-wing aircraft, it is difficult to protect the engines located on the wing and under the wing from dust and dirt from the airfield runway.

Midplane- an aircraft with a wing located approximately in the middle of the fuselage height. The main advantage of such a scheme is the minimum aerodynamic drag.

The disadvantages of the scheme include the difficulty of placing passengers, cargo and equipment in the middle part of the fuselage due to the need to pass the longitudinal power elements of the wing here.

Vysokoplane- an aircraft with a wing attached to the top of the fuselage.

The main advantages of the vysokoplan:

· Low interference between the wing and the fuselage;

· Placement of engines high from the surface of the runway. That reduces the likelihood of their damage when taxiing on the ground;

· Good view of the lower hemisphere;

· The possibility of maximum use of the internal volumes of the fuselage, its equipment with means of mechanization of loading and unloading bulky cargo.

The disadvantages of the scheme include:

· Difficulty in retracting the landing gear into the wing;

· The complexity of servicing the engines located on the wing;

· The need to strengthen the structure of the lower part of the fuselage.

· According to the type of fuselage, the aircraft are divided into single-fuselage, double-boom with a nacelle and "flying wing".

· Most modern aircraft have a single fuselage to which the wing and tail are attached.

Depending on the type and location of the plumage, there are three main schemes:

· Rear arrangement of plumage;

· Forward arrangement of the tail (duck-type aircraft);

· Tailless aircraft of the "flying wing" type.

Most modern civil aircraft are tail-mounted. This scheme has the following variations:

· The central location of the vertical keel and the horizontal location of the stabilizer;

· Spaced vertical tail;

· V - shaped tail without vertical keel.

By the type of landing gear, aircraft are subdivided into land and seaplanes. The landing gear for land aircraft, as a rule, is wheeled, sometimes ski, and for seaplanes it is boat or float.

Aircraft are also distinguished by the type, number and location of engines. Piston (PD), turboprop (TVD) and turbojet (TRD) engines are used on modern aircraft.

The location of the engines on the aircraft depends on their type, number, dimensions and the purpose of the aircraft.

In multi-engine aircraft, propeller engines are installed in nacelles in front of the wing.

Turbojet engines are usually located on pylons under the wing or in the aft fuselage.

Advantages of the first method: direct placement of engines in the air flow, unloading of the wing from bending and torque moments, ease of maintenance of engines. However, the location of engines close to the ground is associated with the danger of foreign objects falling into them from the surface of the runway. On airplanes with such an arrangement of engines, difficulties are also created in piloting with one failed engine (flight with asymmetric thrust).

In the second method, the main advantages are as follows:

· The wing, which is free of superstructures, has better aerodynamic characteristics (there is more space for placing the means of wing mechanization);

· No difficulties arise when flying with unbalanced thrust;

· The level of noise in the cockpit is reduced;

· The wing protects the engines from dirt when the aircraft moves on the ground;

· Provides convenient maintenance of engines.

However, this arrangement of engines also has serious drawbacks:

· The horizontal tail must be moved upwards and the keel must be strengthened;

· The fuselage in the area where the engines are located must be reinforced;

· The centering of the aircraft moves backward as the fuel burns out, decreasing the stability of the aircraft.

3.2.2. Helicopter classification

Helicopters are classified according to various criteria, for example, according to the maximum take-off weight (Table 3.2), according to the type of main rotor drive, the number and location of the rotors, or the method of compensating for the reactive moment of these screws.

Table 3.2

Helicopter classes

	Maximum takeoff weight, t	Helicopter type
	10 and more	Mi-6, Mi-10K, Mi-26
		Mi-4, Mi-8, Ka-32

		Ka-15, Ka-18

In most modern helicopters, the main rotor is driven through a transmission from the engines. During rotation, the main rotor experiences the action of the reactive moment Mreakt, which is a reaction of air and is equal to Mcr - the torque on the rotor shaft. This moment tends to rotate the helicopter fuselage in the direction opposite to the rotation of the propeller. The way of balancing the reactive torque of the torque rotor mainly determines the helicopter design.

The single-rotor helicopter scheme is currently the most common. Helicopters of such a scheme have a tail rotor, which is carried out on a long tail boom beyond the plane of rotation of the main rotor. The thrust created by the tail rotor balances the reactive torque of the main rotor. By changing the value of the tail rotor thrust, it is possible to carry out directional control, that is, the rotation of the helicopter about the vertical axis.

Single-rotor helicopters are simpler to manufacture and operate than others, and therefore make it possible to obtain a relatively lower cost of a flight hour. Such helicopters are compact, have few parts protruding into the stream and allow them to achieve higher flight speeds than in other schemes. Sometimes a wing can be installed on these helicopters to increase speed. When approaching at a horizontal speed, a lift is created on the wing, as a result of which the main rotor is partially unloaded.

The power consumption (8 ... 10%) of the engine to drive the tail rotor, as well as the presence of a long tail boom and a large-diameter main rotor, increasing the dimensions of the helicopter, are the disadvantages of this scheme.

In helicopters of a twin-rotor scheme, the reactive torque balancing is achieved by imparting counter-rotating propellers. Twin-rotor helicopters can have different rotor positions.

With the coaxial scheme, the upper rotor shaft passes through the lower rotor hollow shaft. The planes of rotation of the propellers are removed from each other at such a distance that would exclude a collision between the blades of the upper and lower propellers in all flight modes.

Directional control of the coaxial helicopter is provided by installing the blades of the upper and lower propellers at different angles of attack. The resulting difference in torque on the rotors causes the helicopter to turn in the required direction. Sometimes, to improve directional control, such helicopters are equipped with rudders, the action of which is similar to the action of similar rudders on an aircraft. Longitudinal and lateral control is carried out by simultaneous inclination of the planes of rotation of both rotors.

Helicopters with coaxial propellers are the most compact and maneuverable, and have a high weight return. However, the complexity of the design increases the cost of their production and causes difficulties in operation, especially in the adjustment of the supporting system.

In the longitudinal configuration, the rotors are mounted at the ends of the fuselage. The propellers rotating in opposite directions are synchronized so that the blades of one propeller, when rotating, always pass between the blades of the other.

The advantage of this type of helicopter is a long, capacious fuselage, inside which bulky cargo can be transported. Otherwise, they are inferior to single-rotor helicopters.

Transverse helicopters have two rotors located in the same plane on the sides of the fuselage and rotating in opposite directions. From the aerodynamic point of view, such a layout of the rotors is the most expedient, but the wings, which take the loads from the rotors, significantly increase the weight of the helicopter structure.

3.2.3. Classification of aircraft engines

The power plant is designed to create thrust. It includes engines, propellers, engine nacelles, fuel and oil systems, engine and propeller control systems, etc.

Depending on the design and the nature of the work process, engines are classified into piston (PD) and gas turbine (GTE). In turn, gas turbine engines are subdivided into: turbojet (TRD), turboprop (TVD), double-circuit turbojet (DTRD) and turbo-fan, Fig. 3.2.

Rice. 3.2. Classification of aircraft engines

Turbojet engines are lightweight, compact and reliable, therefore they occupy a dominant position on long-haul aircraft.

Compared to turbojets, turbofan engines have a higher fuel efficiency, but their design is significantly heavier and more complicated by the propeller, which also causes additional noise and vibration. The theater is installed on the wing and in the nose of the fuselage. The presence of a propeller in the theater of operations restricts other options for their location on the aircraft.

The turbojet engine is installed on the wing, under the wing on pylons, inside the fuselage, along its sides in the tail section. Each layout has its own advantages and disadvantages and is selected taking into account the type and number of engines, aerodynamic, strength, mass and other features of aircraft, and their operating conditions.

The piston engines run on aviation gasoline of the B-70 and B-95/130 brands. The thermal energy of the fuel burned in the cylinders is converted into mechanical energy and transferred to the propeller, which creates the thrust necessary for flight. Gas turbine engines run on aviation kerosene grades T-1, TS-1, RT-1, etc.

Questions for self-control

1. What is "flight safety" and how is it ensured?

2. How is the "economy of operation" achieved?

3. In what areas is "passenger comfort" ensured?

4. On what grounds and criteria are airplanes classified? Disadvantages and advantages of various aircraft designs.

5. Classification of helicopters. What are the advantages and disadvantages of various helicopter designs?

6. Give the classification of aircraft engines.

CHAPTER 4

AERODYNAMIC CHARACTERISTICS

AIRCRAFT

Aerohydromechanics (fluid and gas mechanics) is a science that studies the laws of motion and equilibrium of liquids and gases and their force interaction with streamlined bodies and boundary surfaces. The mechanics of a fluid body is called hydromechanics, the mechanics of a gaseous body - aeromechanics.

The development of aeronautics, aviation and rocketry aroused particular interest in studies of the force interaction of air and other gaseous media with bodies moving in them (an airplane wing, fuselage, propeller, airship, rockets, etc.).

Design and calculation of aircraft (helicopters) are based on the results obtained in aerodynamic studies. Taking into account aerodynamics, it is possible to choose a rational external shape of the aircraft (taking into account the mutual influence of its parts) and establish the permissible deviations in external shape, dimensions, etc. during production.

For aerodynamic calculation of an aircraft, i.e., to determine the possible range of speeds, altitude and flight range, as well as to determine such characteristics as stability and controllability of the aircraft, it is necessary to know the forces and moments acting on the aircraft in flight. To calculate the strength, reliability and durability of an aircraft, it is necessary to know the magnitude and distribution of aerodynamic forces over the surface of the aircraft. The answer to these questions is given by aerodynamics.

It is very important to determine the aerodynamic characteristics of the aircraft and its parts during flight at supersonic speeds, since in this case an additional problem arises of determining the temperature on the surface of the streamlined body and heat transfer between the body and the medium.

Aerodynamics plays an important role not only in the design and calculation of an aircraft (helicopter), but also in its flight tests. With the help of aerodynamic data and flight tests, the values of deformations and velocities permissible for the aircraft are established, as well as flight modes in which vibrations, aircraft shaking, etc. take place.

According to the principle of mechanical interaction of several moving bodies, the forces acting on bodies depend on their relative motion. The essence of relative motion is as follows: if in a stationary air medium a body (for example, an airplane in the air) moves rectilinearly and uniformly at a speed V∞, then when the medium and the airplane simultaneously communicate the reverse speed V∞, the so-called "reversed" motion is obtained, i.e. That is, an air flow runs onto a stationary body (for example, an air flow in a wind tunnel on a stationary model of an aircraft), while the speed of the unperturbed flow is equal to V∞. In both cases, the equations describing the relative motion of the aircraft and air will be invariant. Thus, aerodynamic forces depend only on the relative motion of the body and air.

To determine the aerodynamic characteristics of bodies (for example, a wing, fuselage and other parts of an aircraft), streamlined by an air flow, a synthesis of theoretical and experimental methods is currently used: theoretical calculations with the introduction of experimental corrections or experimental studies taking into account theoretical corrections (on the effect variations of similarity criteria, boundary conditions, etc.). In both cases, electronic computers are widely used for calculations and processing of experimental data. After the creation of the aircraft, the final stage is flight tests - an experiment in full-scale conditions. It is difficult to directly measure aerodynamic forces (as, for example, in wind tunnels) during flight tests. The aerodynamic characteristics are determined by processing the parameters of the movement of the aircraft relative to the air measured during the tests. To obtain a sufficient amount of experimental data, the flights are carried out in different modes.

Aerodynamics is divided into two sections: low speed aerodynamics and high speed aerodynamics. The fundamental difference between these sections is as follows. When the gas flow velocities are small compared to the speed of sound propagation, the gas is considered practically incompressible in aerodynamic calculations and changes in the density and temperature of the gas inside the flow are not taken into account. At speeds commensurate with the speed of sound, the phenomenon of gas compressibility cannot be neglected.

The task of aerodynamics is to determine the aerodynamic forces on which the flight data of aircraft depend.

Aerodynamics as a science is developing in two directions: experimental and theoretical. Theoretical aerodynamics finds solutions by analyzing the basic laws of hydroaerodynamics. However, due to the complexity of the processes occurring when air flows around bodies, solutions are obtained approximate and require experimental verification. Experimental aerodynamic studies are carried out in wind tunnels or directly during flight tests of aircraft. Flight tests provide the most reliable results. As a rule, they are carried out after tests in wind tunnels have been carried out.

Wind tunnels are devices in which an air flow is artificially created that blows the studied bodies.

In fig. 4.1 shows a diagram of a wind tunnel. Fan - 2 is driven by electric motor - 1, which allows changing the fan speed and air flow rate. The air sucked in by the fan, passing through the return channel - 4, enters through a converging nozzle - 7 into the working part - 6, where the tested model is placed - 5. To lose air energy and prevent the appearance of vortices when turning the flow, the guide vanes are used - 9, and to create a uniform flow in the working area - a straightening grille - 8. The expanding diffuser - 3 reduces the speed and accordingly increases the pressure of the air flow, which reduces the energy required to rotate the fan.

Rice. 4.1. Wind tunnel diagram: 1 - electric motor; 2 - fan; 3 - diffuser; 4 - return channel; 5 - tested model; 6 - the working part of the wind tunnel; 7 - nozzle; 8 - straightening lattice; 9 - guide vanes

An aerodynamic balance is used to determine the aerodynamic forces acting on the test model. The pressure on different parts of the model surface is measured through special holes connected to the pressure gauges.

4.2. Characteristics of the air environment

Atmosphere called the gaseous envelope that surrounds the globe and rotates with it. The upper part of the atmosphere consists of ionized particles trapped in the Earth's magnetic field. The atmosphere flows smoothly into outer space and its exact height is difficult to establish. Conventionally, the altitude of the atmosphere is taken equal to 2500 km: at this altitude, the air density is close to the density of outer space. The study of the state of the atmosphere is of great interest for aviation, since the flight and technical characteristics of aircraft depend on the properties of the atmosphere. Meteorological conditions have a particularly great influence on the flight performance of aircraft.

Air pressure and density decrease with increasing altitude. The parameters of atmospheric air depend on the coordinates of the place and change over time within certain limits. Solar radiation has a significant effect on the state of the atmosphere. The atmosphere is in continuous interaction with space and earth.

The atmosphere consists of several layers: the troposphere, stratosphere, chymosphere, ionosphere, mesosphere and exosphere, each of which is characterized by different temperature changes depending on altitude.

In the troposphere, the temperature decreases with altitude by an average of 6.5 ° C every 1000 m. In the stratosphere, the temperature remains almost constant. In the chemosphere, a warm layer of air lies between two cold layers, therefore there are two temperature gradients: at the bottom, on average, + 4 ° C per 1000 m, and at the top - 4.5 ° C per 1000 m.In the ionosphere, the temperature increases with altitude by an average of 10 ° C every 1000 m. In the mesosphere, the temperature decreases by an average of 3oC every 1000 m.

All layers are separated from each other by zones 1 ... 2 km thick, called pauses: tropopause, stratopause, chymopause, ionopause, mesopause.

The lower layers of the atmosphere, in particular, the troposphere and stratosphere, are of greatest interest to aviation.

Long-term observations of the state of the atmosphere in various places of the globe have shown that the values of temperature, pressure and density of air change depending on time and coordinates over a very wide range, which does not allow accurately predicting the state of the atmosphere at the time of flight. For example, in Siberia, the air temperature in winter at ocean level sometimes reaches 2130 K, and in summer 3030 K, that is, it changes by 900K during the year. In middle latitudes, the temperature changes by about 700K. There are also significant fluctuations in temperature changes at different altitudes.

The range of pressure fluctuations is significant: at mid-latitudes at ocean level, it varies from 1.04 to 0.93 bar (1 bar = 105 N / m2). The air density changes accordingly (within ± 10%).

The lack of certainty in the state of the Earth's atmosphere and in the change in its state with increasing altitude creates serious difficulties in aerodynamic calculations of the flight characteristics of aircraft, which, as already noted, significantly depend on the state of the atmosphere. The need for unification of calculations related to aircraft when solving practical problems, for example, uniform calibration of various flight instruments (speed meters, tachometers, etc.), recalculation of aircraft flight characteristics obtained in specific atmospheric conditions, on others led to the creation of conditional characteristics of the atmosphere - standards. Such characteristics were introduced in the form of a conventional standard atmosphere (SA), which has the form of a table of numerical values of the physical parameters of the atmosphere for a number of heights.

4.3. General information about the laws of aerodynamics

Aerodynamics provides a qualitative explanation of the nature of the emergence of aerodynamic forces and, with the help of special equations, allows them to be quantified.

When studying the movement of gases, one proceeds from the assumption that these media are complex with a continuous distribution of matter in space. The flow of gas (hereinafter - air) in aerodynamics is usually represented in the form of separate elementary streams - closed circuits in the form of tubes, through the lateral surface of which air cannot flow, Fig. 4.2. If at any point in space the speed, pressure and other characteristic quantities are constant in time, then such a motion is called steady.

Let us apply the two most general laws of nature to the flow of air in a trickle: the law of conservation of mass and the law of conservation of energy.

For the case of steady motion, the law of conservation of mass is reduced to the fact that one and the same mass of air flows through each cross-section of the stream per unit time, that is:

ρ1f1V1 = ρ2f2V2 = const,

where: ρ is the mass density of air in the corresponding sections of the stream;

f is the cross-sectional area of the trickle;

V is the air speed.

This equation is called the jet continuity equation.

The product ρfV is the second mass flow rate of air passing through each cross section of the trickle.

For low flow rates (M< 0,3), когда сжимаемостью воздуха мож-но пренебречь, то есть когда ρ1 = ρ2 = const, уравнение неразрывности прини-мает вид:

f1V1 = f2V2 = const.

It is seen from this equation that at M< 0,3 скорость течения в струйке обратно пропорциональна площади ее поперечного сечения.

As the speed increases, it begins to more and more noticeably affect the change in density. For example, at velocities corresponding to M> 1, an increase in the velocity is possible only with an increase in the cross-sectional area of the stream.

https://pandia.ru/text/78/049/images/image012_75.gif "width =" 29 "height =" 38 src = ">, and the potential energy equal to the work of gravity relative to a certain conditional level is mgh1. In addition, the air above the first section performs work, moving the air mass in front.This work is defined as the product of the pressure force P1f1 and the path V1Δτ. Thus, the air energy transferred during the time Δτ through section II will be:

Thus, on the basis of the Bernoulli equation, we can conclude that with a steady motion, the sum of static pressure and dynamic pressure is a constant value.

The main components of the aircraft

Aircraft are heavier than air aircraft, they are characterized by the aerodynamic principle of flight. Aircraft have lift Y is created due to the energy of the air flow, washing the load-bearing surface, which is motionlessly fixed relative to the body, and the translational movement in a given direction is provided by the thrust of the aircraft power plant (SU).

Different types of aircraft have the same basic components (components): wing , vertical (IN) and horizontal (GO) plumage , fuselage , power plant (SU) and chassis (Figure 2.1).

Rice. 2.1. The main structural elements of the aircraft

Airplane wing1 creates lift and provides lateral stability to the aircraft during its flight.

often the wing is the power base for the landing gear, engines, and its internal volumes are used to accommodate fuel, equipment, various components and assemblies of functional systems.

For improvement takeoff and landing characteristics(VPH) of modern aircraft on the wing, mechanization means are installed along the leading and trailing edges. Place on the leading edge of the wing slats , and on the back - flaps10 , spoilers12 and spoiler ailerons .

In terms of power, the wing is a complex beam structure, the supports of which are the power frames of the fuselage.

Ailerons11 are transverse controls. They provide lateral control of the aircraft.

Depending on the scheme and flight speed, geometric parameters, structural materials and structural-power scheme, the wing mass can be up to 9 ... 14 % from the takeoff weight of the aircraft.

Fuselage13 unites the main components of the aircraft into a single whole, i.e. provides closure of the power circuit of the aircraft.

The internal volume of the fuselage is used to accommodate the crew, passengers, cargo, equipment, mail, baggage, rescue equipment in case of emergencies. In the fuselages of cargo aircraft, advanced loading and unloading systems, devices for fast and reliable mooring of cargo are provided.

The fuselage function of seaplanes is performed by a boat, which allows takeoff and landing on water.

the fuselage in terms of force is a thin-walled beam, the supports of which are the wing spars, with which it is connected through the nodes of the power frames.

the mass of the fuselage structure is 9 ... 15 % from the takeoff weight of the aircraft.

Vertical tail5 consists of a fixed part keel4 and rudder (NS) 7 .

Keel 4 provides the aircraft with directional stability in the plane X0Z, and RN - directional control about the axis 0y.

Trimmer NS 6 ensures the removal of prolonged loads from the pedals, for example, in case of engine failure.

Horizontal tail9 includes a fixed or partially movable part ( stabilizer2 ) and the movable part - elevator (PB) 3 .

Stabilizer 2 gives the aircraft longitudinal stability, and PB 3 - longitudinal controllability. RV can carry a trimmer 8 for unloading the steering column.

Weight, HE and AO structures usually does not exceed 1.3 ... 3 % from the takeoff weight of the aircraft.

Chassis aircraft 16 refers to the take-off and landing devices (TLU), which provide takeoff, takeoff, landing, run and maneuvering of an aircraft while moving on the ground.

The number of supports and their location relative center of mass (CM) of the aircraft depends on the landing gear schemes and the features of the aircraft operation.

The landing gear of the aircraft shown in Figure 2.1 has two main supports16 and one nasal support17 ... Each support includes a power rack18 and supporting elements - wheels15 ... Each support can have several legs and several wheels.

Most often, the landing gear of the aircraft is made retractable in flight, therefore, special compartments in the fuselage are provided for its placement. 13. It is possible to clean and place the main landing gear in special gondolas (or nacelles), fairings14 .

The landing gear absorbs the kinetic energy of the impact during landing and the energy of braking during the run, taxiing and when maneuvering the aircraft over the airfield.

amphibious aircraft can take off and land both from ground airfields and from the water surface.

Figure 2.2. Amphibious aircraft landing gear.

on the case seaplane a wheeled chassis is installed, and under the wing is placed floats1 ,2 (Figure 2.2).

The relative mass of the chassis is usually 4 ... 6 % from the takeoff weight of the aircraft.

Power point 19 (see Figure 2.1), provides the creation of the aircraft thrust. It consists of engines, as well as systems and devices that ensure their operation in the conditions of flight and ground operation of the aircraft.

In piston engines, the thrust force is created by the propeller, in turboprop - by the propeller and partially by the reaction of gases, in jet engines - by the reaction of gases.

The control system includes: engine mounts, nacelle, control system, engine input and output devices, fuel and oil systems, engine starting systems, fire and anti-icing systems.

The relative mass of the control system, depending on the type of engines and their arrangement on the aircraft, can reach 14 ... 18 % from the takeoff weight of the aircraft.

2.2. Technical-economic and flight-technical
aircraft characteristics

The technical and economic characteristics of the aircraft are:

Payload relative mass:

`m mon = m Mon /m 0

where m mon is the mass of the payload;

m 0 - takeoff weight of the aircraft;

Relative mass of maximum paid load:

`m knmax = m knmakh / m 0

where m кнmах mass of maximum payload;

Maximum hourly productivity:

NS h = m кнmах ∙ v flight

where v flight - aircraft cruising speed;

Fuel consumption per unit of performance q T

The main aircraft performance characteristics include:

Maximum cruising speed v cr.max;

Cruising economic speed V to p. eq;

Cruising altitude H to p;

Flight range with maximum payload L;

Average aerodynamic quality TO in flight;

Rate of climb;

Carrying capacity, which is determined by the mass of passengers, cargo, baggage transported on the plane for a given flight weight and fuel supply;

Takeoff and landing characteristics (VPH) of the aircraft.

The main parameters characterizing the VHF are the approach speed - V wp; landing speed - V NS; take-off speed - V omp; take-off run - l once; landing run - l np; the maximum value of the coefficient of lift in the landing configuration of the wing - WITH y max n; the maximum value of the coefficient of lift in the take-off configuration of the wing WITH at max hack

Aircraft classification

Aircraft are classified according to many criteria.

One of the main criteria for aircraft classification is appointment criterion ... this criterion predetermines flight performance, geometric parameters, layout and composition of aircraft functional systems.

According to their purpose, airplanes are subdivided into civil and military ... Both the first and the second aircraft are classified depending on the type of tasks performed.

Below is the classification of civil aircraft only.

Civil aircraft are intended for the transportation of passengers, mail, cargo, as well as for solving various economic problems.

Aircraft are subdivided into passenger , freight , experimental , training as well as on airplanes targeted national economic purpose .

Passenger airplanes, depending on the flight range and carrying capacity, are divided into:

- long-haul aircraft - range of flight L> 6000 km;

- medium-haul aircraft - 2500 < L < 6000 км;

- short-haul aircraft - 1000< L < 2500 км;

- aircraft for local airlines (MVL) - L <1000 км.

Long-haul aircraft(Fig. 2.3) with a flight range of more than 6000 km, usually equipped with a control system of four turbojet engine or propfan engines, which makes it possible to increase flight safety in the event of a failure of one or two engines.

Medium-haul aircraft(Fig. 2.4, Fig. 2 .5) have a control system of two or three engines.

Short-haul aircraft(Fig. 2.6) with a flight range of up to 2500 km, they have a control system of two or three engines.

Aircraft of local airlines (MVL) are operated on air routes less than 1000 km long, and their control system can consist of two, three or even four engines. The increase in the number of engines to four is due to the desire to ensure a high level of flight safety at the high intensity of takeoffs and landings typical of international aircrafts.

The MVL aircraft include administrative aircraft, which are designed to carry 4 ... 12 passengers.

Cargo aircraft provide transportation of goods. These aircraft, depending on the flight range and carrying capacity, can be subdivided similarly to passenger aircraft. transportation of goods can be carried out both inside the cargo compartment (Figure 2.7) and on the external suspension of the fuselage (Figure 2.8).

Trainer aircraft provide training and training of flight personnel in educational institutions and training centers for civil aviation (Figure 2.9) Such aircraft are often made in two-seater (instructor and trainee)

Experimental aircraft are created to solve specific scientific problems, conduct field research directly in flight, when it is necessary to test the hypotheses and design solutions put forward.

Aircraft for national economic purposes depending on the intended use, they are divided into agricultural, patrol, observation of oil and gas pipelines, forests, coastal areas, traffic, sanitary, ice reconnaissance, aerial photography, etc.

Along with specially designed airplanes for these purposes, low-capacity MVL aircrafts can be re-equipped for target tasks.

Rice. 2.7. Cargo airplane

Rice. 2.10

Rice. 2.9

Figure 2.8

Rice. 2.8. Transportation of goods on an external sling

Rice. 2.9. Trainer aircraft

Rice. 2.10. Aircraft for national economy

Aerodynamic layout an aircraft is characterized by the number, the external shape of the bearing surfaces and the relative position of the wing, empennage and fuselage.

The classification of aerodynamic configurations is based on two features:

- wing shape ;

- plumage location I am.

In accordance with the first feature, there are six types of aerodynamic configurations:

- with a straight and trapezoidal wing;

- with swept wing;

- with a delta wing;

- with a straight wing of low aspect ratio;

- with an annular wing;

- with a round wing.

For modern civil aircraft, the first two and partially the third type of aerodynamic configurations are practically used.

According to the second type of classification, the following three variants of the aerodynamic configurations of aircraft are distinguished:

Normal (classical) scheme;

Duck schemes;

Tailless scheme.

A variation of the tailless design is the flying wing design.

Aircraft normal scheme (see Figures 2.5, 2.6) have a HE located behind the wing. This scheme has become prevalent in civil aircraft.

The main advantages of a normal circuit are:

Possibility of effective use of wing mechanization;

Easy balancing of the aircraft with the flaps extended;

Reducing the length of the nose of the fuselage. This improves the pilot's view and reduces the AO area, since the shortened nose of the fuselage causes the appearance of less destabilizing travel moment;

Possibility of reducing the areas of VO and HE, since the shoulders of VO and VO are much larger than in other schemes.

disadvantages of a normal circuit:

GO creates a negative lift in almost all flight modes. This leads to a decrease in the lift of the aircraft. Especially on transient flight modes during takeoff and landing;

The HE is in a disturbed air flow behind the wing, which negatively affects its operation.

To remove the HE from the "aerodynamic shadow" of the wing or from the "wake" of the flaps in transient flight modes, it is shifted relative to the wing in height (Fig. 2.11, a), it is brought to the middle of the keel (Fig. 2.11; b) or to the top of the keel (Figure 2.11, c).

Rice. 2.12

Rice. 2.11

Rice. 2.11 Layout of the horizontal tail

a. VO., Offset relative to the wing in height;

b. AO is located in the middle of the keel (cruciform tail);

v. T-shaped plumage;

d. v - shaped plumage.

In the practice of aircraft construction, there are cases of using a combined, so-called v-shaped plumage (fig. 2.12). functions of GO and AO in this case are performed by two surfaces spaced at an angle relative to each other. The rudders located on these surfaces, with a synchronous deflection up and down, work as a RV, and when one rudder is deflected up and the other down, the aircraft is controlled in the directional relation.

Quite often, two-keel and even three-keel VO can be used on airplanes.

When the aerodynamic layout of the aircraft is duck pattern on GO is placed in front of the wing on the nose of the fuselage (Figure 2.13)

The advantages of the duck scheme are:

Placement of HE in undisturbed air flow;

The possibility of reducing the size of the wing, since the HE becomes load-bearing, i.e. participates in the creation of the lift of the aircraft;

Rather easy parrying of the emerging diving moment when the wing mechanization is deflected by the HE deviation;

Rice. 2.13 Airplane layout according to the "duck" scheme

An increase in the GO arm by more than 30% than in the normal scheme, which allows to reduce the wing area;

When large angles of attack are reached, the flow stall on the HE occurs earlier than on the wing, which practically eliminates the danger of the aircraft reaching supercritical angles of attack and stalling it into a tailspin.

In an airplane made according to the "duck" scheme, the focus position is shifted back when moving from M<1 к М>1 is less than that of airplanes of the normal scheme, therefore, an increase in the degree of longitudinal stability is observed to a lesser extent.

The disadvantages of this scheme are:

Decrease in wing bearing capacity by 10-15 % due to the bevel of the flow from the HE;

Relatively small AO shoulder, leading to an increase in the AO area, and sometimes to the installation of two keels to increase track stability. This compensates for the destabilizing moment created by the elongated nose of the fuselage.

Tailless scheme characterized by the absence of GO (see Fig. 1.13), while the functions of the GO are shifted to the wing. Aircraft made according to this scheme may not have a fuselage, in which case they are called "flying wing". These aircraft are characterized by minimal drag.

The tailless scheme has the following advantages:

Since triangular wings are used on such aircraft, with large side ribs, the relative thickness of the profile can be reduced, ensuring the rational use of the wing volume for fuel placement;

The absence of GO loads makes it possible to lighten the tail section of the fuselage;

The cost and weight of the airframe decreases, since there is no HE, for the same reason, the frictional resistance of the aircraft decreases due to a decrease in the area of the surface streamlined by the air flow;

Significant geometrical dimensions of the side rib make it possible to create the effect of an "air cushion" in the aircraft landing mode;

Since in the "tailless" scheme, double swept wings are used, in the takeoff mode there is a significant increase in the lift coefficient.

Among the disadvantages of this scheme, the most significant are:

Impossibility of full use of the wing bearing capacity on landing;

Decrease in the ceiling of the aircraft due to a decrease in aerodynamic quality, which is explained by holding the elevons in the upper deflected position to achieve the largest angle of attack of the wing;

The difficulty, and sometimes the impossibility of balancing the aircraft with the flaps extended;

The difficulty of ensuring the directional stability of the aircraft due to the small shoulder of the AO, therefore, sometimes three keels are installed (see Fig. 1.13).

In the practice of experimental aircraft construction, you can find options with a combination of basic schemes in one aircraft.

A variant is possible when two HEs are used on the plane - one in front of the wing and the second behind it. When implementing the "tandem" scheme, the aircraft has an almost commensurate wing and airfoil area. The "tandem" scheme can be considered as an intermediate between the normal scheme and the "duck" scheme, due to which the operational range of alignments is extended with relatively small losses of aerodynamic quality for balancing the aircraft.

The main design features by which aircraft are classified are:

The number and location of the wings;

Fuselage type;

Engine type, number and placement of them on the aircraft;

Landing gear scheme, characterized by the number of supports and their relative position relative to the aircraft CM.

Monoplanes and biplanes are distinguished depending on the number of wings.

Scheme monoplane dominates in aircraft construction, and most aircraft are performed precisely according to this scheme, which is due to the lower drag of the monoplane and the possibility of increasing the increase in flight speeds.

Aircraft schemes "biplane" (Figure 2.16) have a high
maneuverability, but they are slow-moving, so this scheme is implemented for special-purpose aircraft, for example, for agricultural ones.

Fig 2. 16 Airplane of the "biplane" scheme

According to the location of the wing relative to the fuselage, the aircraft can be performed according to the "low-wing" (Fig. 2.17, a), "mid-wing" (Fig. 2.17, b) and "high-wing" (Fig. 2.17, c) schemes.

Figure 2.17. Various wing layouts

Scheme "low-wing" the least advantageous in aerodynamic terms, since in the zone of conjugation of the wing with the fuselage, the smoothness of the flow is disturbed and additional resistance arises due to the interference of the "wing-fuselage" system. This disadvantage can be significantly reduced by setting fairings, ensuring the elimination of the diffuser effect.

Placing a gas turbine engine at the root of the wing allows you to use
ejector effect from the jet of the engine, which is called the active fairing.

The low-wing aircraft has a higher location of the lower fuselage contour above the ground. This is due to the need to exclude the touch of the wing tip to the runway surface during a roll landing, as well as to ensure the safe operation of the control system when the engines are placed on the wing. In this case, the process of unloading and loading cargo, baggage, as well as embarkation and disembarkation of passengers becomes more complicated. This disadvantage can be avoided by equipping the landing gear with a "squat" mechanism.

The "low-wing" scheme is most often used for passenger aircraft, as it provides greater safety compared to other options for emergency landings on the ground and water. In an emergency landing on the ground with the landing gear retracted, the wing absorbs the impact energy, protecting the passenger cabin. When landing on water, the aircraft submerges into the water along the wing, which gives the fuselage additional buoyancy and simplifies the organization of work related to the evacuation of passengers.

An important advantage of the "low-wing" scheme is the smallest mass of the structure, since the main landing gear supports are most often associated with the wing and their dimensions and weight are less than those of a high-wing aircraft. In comparison with a high-wing aircraft with a chassis on the fuselage, a low-wing aircraft has a lower mass, since no weighting of the fuselage is required due to the attachment of the main landing gear to it.

The low-wing aircraft with the main supports on the wing retains the basic rule: the supporting surface serves as the support for the aircraft. This rule is observed in all operating modes, both in flight and during takeoff and landing. In the latter case, the wing rests on the chassis during the run and take-off run. Thanks to this, it is possible to unify the power circuit, which determines the paths for transmitting maximum loads, and to reduce the weight of the aircraft structure as a whole. The considered advantages became the reason for the dominant position of the "low-wing" scheme on passenger aircraft.

Scheme "midplane" (Fig. 2. 17, b) for passenger and cargo aircraft is most often not used, since the wing box (its power section) cannot be placed in the passenger or cargo cabin.

With an increase in take-off masses and aircraft parameters, it becomes possible to bring the wing layout of wide-body aircraft closer to the mid-wing. In this case, the wing is raised to the level of the floor of the passenger compartment or cargo compartment, as is done on the A-300, Boeing-747, Il-96 and others. Thanks to this solution, it is possible to significantly improve the aerodynamic characteristics.

In its pure form, the "mid-wing" scheme can be implemented on double-deck aircraft, where the wing practically does not interfere with the use of fuselage volumes for accommodating passenger cabins, cargo spaces and equipment.

The "high-wing" scheme (Fig. 2.17, c) is widely used for cargo aircraft, and also finds application on MVL aircraft. In this case, it is possible to obtain the smallest distance from the lower bypass of the fuselage to the surface of the runway, since the high wing does not affect the choice of the height of the fuselage relative to the ground.

When using the scheme "high-wing" there is a possibility of free maneuvering of special vehicles during aircraft maintenance.

The transport efficiency of cargo aircraft is increased due to the lowest position of the cargo compartment floor, which makes it possible to ensure quick and easy loading and unloading of bulky cargo, self-propelled vehicles, various modules, etc.

The service life of the engines increases, since they are located at a considerable distance from the ground and the probability of particulate matter from the runway surface into the air intakes is sharply reduced.

The noted advantages of the vysokoplan explain the dominant position that this scheme took on transport aircraft in domestic (An-22, An-124, An-225), foreign (C-141, C-5A, C-17 (USA), etc. .) practice.

The "high-wing" scheme easily provides a standardized safe distance from the runway surface to the end of the propeller blade or the lower bypass of the GTE air intake. This explains the rather frequent use of this scheme on MVL passenger aircraft (An-28 (Ukraine), F-27 (Holland), Short-360 (England), ATR 42, ATR-72 (France-Italy)).

The undoubted advantage of the "high-wing" scheme is the higher value WITH at max due to the preservation of a completely or partially aerodynamically clean upper wing surface above the fuselage, greater efficiency of wing mechanization due to a decrease in the end effect on the flaps, since the side of the fuselage and the nacelle play the role of end "washers".

However, the large weight of the airframe structure, in comparison with other schemes, negatively affects either the payload or the fuel reserve and flight range. The weighting of the airframe structure is explained by:

The need to increase the VO area by 15-20 % due to falling of part of it into the shading zone from the wing;

An increase in the mass of the fuselage by 15-20 % due to an increase in the number of reinforced frames in the area of attachment of the main landing gear, strengthening of the structure of the lower bypass of the fuselage in the event of an emergency landing with an unreleased landing gear and due to the reinforcement of the pressurized cabin.

When attaching the main landing gear to the power base of the fuselage, difficulties arise in providing the required track.

The small track of the chassis increases the load on one concrete slab,
which may require a higher class of the aerodrome for the operation of the aircraft.

The desire to provide an acceptable track often forces an increase in the overall width of the reinforced frames in the area of the main supports, to form protruding landing gear nacelles and to increase the midsection of the aircraft, and hence its aerodynamic drag. As statistics show, in this case, the drag of the chassis nacelles can reach 10-15 % from the total resistance of the fuselage.

The lower safety of the vysokoplane during an emergency landing on water and land sometimes makes it impossible to use this scheme on aircraft with a large passenger capacity, since during an emergency landing on the ground, the wing, with its mass together with the engines, tends to crush the fuselage and the passenger cabin. When landing on water, the fuselage is submerged to the lower wing contours and the passenger compartment may be under water. In this case, the organization of work to rescue passengers is significantly complicated and the evacuation of people is possible only through emergency hatches in the upper part of the fuselage.

By fuselage type airplanes are subdivided into ordinary ones, i.e. made according to a single-fuselage scheme (Figure 2.18, a); according to the two-fuselage scheme and the "gondola" scheme (Fig. 2.18, b).

Rice. 2.18 Aircraft classification by fuselage type

The most widespread is the single-fuselage scheme, which makes it possible to obtain the most advantageous configuration of the shape of the fuselage from an aerodynamic point of view, since the drag in this case will be the lowest in comparison with other types.

When placing the aircraft tail not on the fuselage, but on two beams (Figure 2.18, b) or replacing the fuselage with a gondola, an increase in drag occurs. The "nacelle" scheme (Fig. 2.18, b) is characterized by poor streamlining of the nacelles, which can lead to instability of the aircraft at high angles of attack. Therefore, the two-girder "gondola" scheme is rarely implemented in aircraft construction, mainly on transport aircraft, where transport efficiency becomes paramount. An example of such a solution is the Hawker Sidley Argosi cargo plane.

Figure 2.19 Edgey Aircraft Airplane

By engine type distinguish between aircraft with PD, turbojet engine, TVLD, etc.

By the number of engines aircraft are subdivided into one-, two-, three-, four-, six-engine.

On passenger airplanes, in order to ensure flight safety, the number of engines should not be less than two. An increase in the number of engines over six turns out to be unjustified due to the difficulties associated with ensuring synchronization of the operation of individual control systems and an increase in the time and labor intensity of maintenance work.

By engine location Subsonic passenger aircraft can be classified into four main groups: engines - on the wing (Fig. 2.20, a), engines - in the wing root, engines - on the aft fuselage (b) and mixed version (c) of the engine layout.

When choosing a place for installing the engines, the peculiarities of the general layout of the aircraft, the operating conditions and ensuring the maximum resource of the engines are taken into account, they strive to obtain the lowest drag of the control system, and to minimize the loss of air in the air intakes.

So, on airplanes with three engines, it is advisable to use a mixed version of the layout (Fig. 2.20): two engines under the wing and the third - in the aft fuselage or on the keel.

Rice. 2.20 Aircraft engine installation diagrams

On airplanes with two engines, the SU is placed on the wing or on the aft fuselage.

With an increase in the degree of bypass of the engine, its diameter increases. Therefore, when arranging the engines under the wing, it is necessary to increase the chassis height to ensure the normalized distance from the nacelle bypass to the ground surface. This leads to an increase in the weight of the aircraft structure and creates a number of problems related to passengers, luggage and maintenance. First of all, this applies to MVL aircraft, which are often operated from airfields that do not have special equipment. At the same time, the effect of unloading the wing in flight due to the placement of engines on it is significantly reduced, since with an increase in the bypass ratio, the specific gravity of the turbojet engine decreases.

Figure 2.21 shows two aircraft, the design of which was created on the basis of the same requirements for payload, range, VHF, fuselage midsection, etc. Figure 2.21 shows the difference between the two aircraft in terms of wing and fuselage height relative to the ground.

Figure 2.21 Influence of bypass engines on the layout of the aircraft

By type of landing gear they are subdivided into wheeled, ski, float (for seaplanes), tracked and air cushion chassis.

The predominant distribution has received a wheeled chassis, and a float one is often used.

According to the chassis scheme aircraft are subdivided into tricycle and
two-bearing.

The three-bearing design is available in two versions: a three-bearing design with a bow support and a three-bearing design with a tail support. In most cases, aircraft use tricycle with bow support... The second variant of this scheme is found on light aircraft.

The two-bearing landing gear scheme is practically not used on civil aircraft.

On heavy, especially transport, aircraft, a multi-support landing gear scheme has become widespread. For example, a Boeing-747 aircraft uses a five-post chassis, an An-225 has a sixteen-post chassis, and a passenger Il-86 has a four-post chassis.

2.4. DESIGN REQUIREMENTS
AIRCRAFT

All requirements for the design of aircraft are subdivided into general mandatory for all airframe units, and special .

General requirements include aerodynamic, strength and stiffness, reliability and survivability of aircraft, operational, maintainability, manufacturability of aircraft production, economic and requirements, minimum weight of the airframe structure and functional systems.

Aerodynamic requirements are reduced to ensuring that the influence of the shape of the aircraft, its geometric and design parameters correspond to the specified flight data obtained at the lowest energy costs. The implementation of these requirements provides for the provision of the minimum resistance of the aircraft, the required characteristics of stability and controllability, high VPH, and indicators of the cruising flight mode.

Fulfillment of aerodynamic requirements is achieved by choosing the optimal values of the parameters of individual units (parts) of the aircraft, their rational mutual arrangement and a high level of specific parameters.

Strength and stiffness requirements are presented to the airframe frame and its skin, which must take all types of operational loads without destruction, while deformations should not lead to a change in the aerodynamic properties of the aircraft, dangerous vibrations should not occur, and significant residual deformations should not appear. The fulfillment of these requirements is ensured by the choice of a rational load-bearing circuit and cross-sectional areas of the load-bearing elements, as well as by the selection of materials.

Reliability and survivability requirements aircraft provide for the development and implementation of constructive measures aimed at ensuring flight safety.

Aircraft reliability represents the ability of a structure to perform its functions while maintaining performance indicators for a specified period of an inter-regulation period, resource or other unit of measurement of operating time. Reliability characteristics are flight hours per failure, the number of failures per flight hour, etc.

The reliability of the aircraft can be increased by the selection of reliable structural elements, their duplication (redundancy).

Aircraft survivability is determined by the ability of the structure to perform its functions in the presence of damage. To meet this requirement, constructive measures are necessary, for example, the use of statically indeterminate power circuits, effective fire prevention measures and, mainly, redundancy. These requirements are especially important to ensure the target level flight safety .

Operational Requirements provide for the creation of such
structures that allow you to provide technical
maintenance of aircraft with minimal material and technical costs.

The implementation of such requirements is possible by providing convenient access to units, standardization and unification of components, assemblies, aircraft parts and connectors, the use of built-in systems for automatic monitoring of the technical condition of aircraft systems and units, effective troubleshooting systems and their elimination, an increase in resource and inter-regulatory service life.

Maintainability requirements predetermine the possibility of quick and cheap restoration of failed (damaged) aircraft parts, operational maintenance of the aircraft engine fleet. The importance of these requirements is increasing due to the constant increase in the complexity of aircraft and equipment.