What the propeller of a light-engine aircraft is made of. How the propeller works. Airplane model description

The propeller is essential part of the power plant, and how much it matches the engine and aircraft depend on the flight performance of the latter.

In addition to the choice of the geometrical parameters of the propeller, attention should be paid to the question of coordinating the numbers of revolutions of the propeller and the engine, that is, the selection of the gearbox.

The principle of the propeller

The propeller blade performs a complex movement - translational and rotational. The speed of the blade element will be the sum of the peripheral speed and the translational (flight speed) - V

In any section of the blade, the velocity component V will be unchanged, and the peripheral speed will depend on the value of the radius at which the considered section is located.

Therefore, with decreasing radius, the angle of approach of the jet to the section increases, while the angle of attack of the section decreases and can become zero or negative. Meanwhile, it is known that the wing "works" most effectively at angles of attack close to the angles of maximum aerodynamic quality. Therefore, in order to force the blade to create the greatest thrust with the least energy consumption, the angle must be variable along the radius: smaller at the end of the blade and larger near the axis of rotation - the blade must be twisted.

The law of propagation of the thickness of the profile and twist along the radius of the screw, as well as the shape of the screw profile, is determined during the propeller design process and is refined later on the basis of blowing in wind tunnels. Similar studies are usually carried out in specialized design bureaus or institutes equipped with modern equipment and computer facilities. Experimental design bureaus, as well as amateur designers usually use already developed families of screws, geometric and aerodynamic characteristics which are represented in the form of dimensionless coefficients.

Main characteristics

Screw diameter - D called the diameter of the circle that the ends of its blades describe during rotation.

Blade width is the chord of the section at a given radius. The calculations usually use the relative blade width

Thick blade at any radius, the largest section thickness at this radius is called. The thickness varies along the radius of the blade, decreasing from the center of the propeller to its end. The relative thickness is understood as the ratio of the absolute thickness to the width of the blade at the same radius:.

The angle of installation of the section of the blade is the angle formed by the chord of the given section with the plane of rotation of the propeller.

Blade pitch H is the distance that this section will travel in the axial direction when the screw turns one revolution around its axis, screwing into the air as a solid.

The step and the angle of installation of the section are related by an obvious relationship:

Real propellers have a pitch that varies along the radius according to a certain law. As a characteristic angle of the blade, the angle of installation of the section located at 0.75R from the axis of rotation of the rotor is taken, as a rule, denoted as.

Spun blades called the change along the radius of the angles between the chord of the section at a given radius and the chord at a radius of 0.75R, that is

For ease of use, all the listed geometric characteristics are usually represented graphically as a function of the current screw radius

As an example, the following figure shows data describing the geometry of a two-blade fixed-pitch propeller:

If the screw, rotating with the number of revolutions, moves translationally at a speed V then in one revolution it will pass the way. This value is called the pitch of the screw, and its ratio to the diameter is called the relative pitch of the screw:

The aerodynamic properties of propellers are usually characterized by the dimensionless thrust coefficient:

Power factor

And the efficiency

Where R- air density, in calculations can be taken equal to 0.125 kgf s 2 / m 4

Angular speed of rotation of the screw, rev / s

D- screw diameter, m

P and N- respectively, thrust and power on the propeller shaft, kgf, l. with.

The theoretical limit of the propeller thrust

For the ALS designer, it is of interest to make approximate estimates of the thrust generated by power plant... This problem can be easily solved using the theory of an ideal propeller, according to which the propeller thrust is represented as a function of three parameters: engine power, propeller diameter and flight speed. Practice has shown that the thrust of rationally made real propellers is only 15 - 25% lower than the theoretical limit values.

The results of calculations according to the theory of an ideal propeller are shown in the following graph, which allows you to determine the ratio of thrust to power depending on the flight speed and the parameter N / D 2... It can be seen that at near-zero speeds, the thrust depends to a large extent on the diameter of the propeller; however, even at speeds of the order of 100 km / h, this dependence is less significant. In addition, the graph gives a visual representation of the inevitability of a decrease in the propeller thrust in terms of flight speed, which must be taken into account when evaluating the flight data of an ALS.

based on materials:
"Guide for designers of amateur-built aircraft", Volume 1, SibNIIA

Due to the lack of reasonable alternatives, almost all aircraft of the first half of the last century were equipped with piston engines and propellers. To improve the technical and flight characteristics of technology, new designs of propellers were proposed, which had certain features. In the mid-thirties, a completely new design was proposed that made it possible to get the desired capabilities. Its author was the Dutch designer A.Ya. Decker.

Adriaan Jan Decker started his work in the field of screw systems back in the twenties. Then he developed a new impeller design for windmills. To improve the main characteristics, the inventor proposed using planes that resemble an aircraft wing. In 1927, such an impeller was installed in one of the mills in the Netherlands and was soon tested. By the beginning of the next decade, three dozen such impellers were put into operation, and in 1935 they were already equipped with 75 mills.

Experimental aircraft with a propeller A.Ya. Decker. Photo Oldmachinepress.com

In the early thirties, after testing and introducing a new design in mills, A.Ya. Dekker suggested using similar units in aviation. According to his calculations, a special design impeller could be used as an aircraft propeller. Soon, this idea was framed in the form of the necessary documentation. In addition, the designer took care of obtaining a patent.

The use of a non-standard propeller design, as conceived by the inventor, should have given some advantages over existing systems... In particular, it became possible to reduce the speed of the propellers while obtaining sufficient thrust. In this regard, the invention of A.Ya. Decker is often referred to as "Low rotation speed propeller". This design was named in the same way in patents.

The first patent application was filed in 1934. At the end of July 1936 A.Ya. Decker received a British patent number 450990, confirming his priority in the creation of the original propeller propeller. Not long before the first patent was issued, another application appeared. The second patent was issued in December 1937. A few months earlier, the Dutch designer had sent the documents to the patent offices in France and the United States. The latter issued document US 2186064 at the beginning of 1940.

Screw design of the second version. Drawing from patent

British Patent No. 450990 described an unusual propeller design capable of providing sufficient performance with a certain reduction in negative factors. The designer suggested using a large ogival-shaped screw hub, smoothly turning into bow fuselage of the aircraft. Large blades were to be rigidly attached to it. unusual shape... It was the original contours of the blades, as A.Ya. Decker, could have led to the desired result.

The blades of the "low-speed" propeller had to have a low elongation with a large chord length. They had to be mounted at an angle to the longitudinal axis of the hub. The blade received an aerodynamic profile with a thickened nose. It was proposed to make the toe of the blade swept. The tip was located almost parallel to the axis of rotation of the screw, and it was proposed to make the trailing edge curved with a protruding end part.

Internal structure of the screw and gear. Drawing from patent

The first project of 1934 involved the use of four blades. A screw of this design had to be mounted on a shaft extending from the gearbox with the required characteristics. A significant area of the propeller blades in combination with the aerodynamic profile should have provided an increase in thrust. Thus, it became possible to obtain sufficient thrust at lower rpms in comparison with a traditional propeller design.

Already after filing an application for the first patent A.Ya. Dekker tested an experienced propeller and made certain conclusions. During the inspection, it was found that the proposed design has certain disadvantages. So, the air flow behind the propeller diverged to the sides, and only a small part of it passed along the fuselage. This led to a sharp deterioration in the efficiency of the tail rudders. Thus, in as it stands the Decker screw could not be used in practice.

Further development of the original propeller led to the emergence of an updated design with a number of important differences. It was she who became the subject of the second British and first American patents. Interestingly, the document from the United States, in contrast to the English one, described not only the screw, but also the design of its drives.

Airplane Fokker C.I - a similar machine became a flying laboratory for testing the ideas of A.Ya. Decker. Photo Airwar.ru

The updated product Low rotation speed propeller should have included two coaxial propellers of opposite rotation at once. The front propeller was still proposed to be built on the basis of a large streamlined hub. The rear rotor blades had to be attached to a cylindrical unit of comparable dimensions. As in the previous project, the front rotor spinner and the rear rotor ring could serve as the aircraft nose cone.

Both propellers were supposed to receive blades of a similar design, which was a development of the developments of the first project. Again, it was necessary to use significantly curved low aspect ratio blades with a developed aerodynamic profile. Despite the swept leading edge, the profile length increased in the direction from the root to the tip, forming a characteristic curvature of the trailing edge.

According to the description of the patent, the front rotor had to rotate counterclockwise (when viewed from the pilot's side), the rear rotor clockwise. The propeller blades had to be mounted appropriately. The number of blades depended on the required characteristics of the propeller. The patent showed a design with four blades on each propeller, while the later prototype got a larger number of planes.

The assembly process of the original screws, you can see the internal elements of the product. Photo Oldmachinepress.com

The American patent described the design of the original gearbox, which made it possible to transfer torque from one engine to two counter-rotating propellers. It was proposed to connect the motor shaft to the sun gear of the first (rear) planetary contour of the gearbox. With the help of a ring gear fixed in place, power was transmitted to the satellite gears. Their carrier was connected to the front rotor shaft. This shaft was also connected to the sun gear of the second planetary gear set. The rotating carrier of its satellites was connected to the hollow shaft of the rear rotor. This design of the gearbox made it possible to synchronously regulate the speed of rotation of the screws, as well as to ensure their rotation in opposite directions.

As conceived by the inventor, the main thrust was to be created by the blades of the front propeller. The rear, in turn, was responsible for the correct redirection of air flows and made it possible to get rid of the negative effects observed in the basic design. After two coaxial propellers, the air flow passed along the fuselage and should normally blow the tail unit with rudders. To obtain such results, the rear rotor could have a reduced rotational speed - about a third of the front rotor revolutions.

The original propeller propeller was created taking into account the possible introduction of aviation technology into new projects, and therefore it was required to carry out full-fledged tests. In early 1936, Adriaan Jan Dekker founded his own company, Syndicaat Dekker Octrooien, to test the original propeller and - if successful - to promote this invention in the aviation industry.

The finished propeller on the plane. Photo Oldmachinepress.com

At the end of March of the same year, the Dekker Syndicate acquired a Dutch-built Fokker C.I multipurpose biplane aircraft. This machine with a maximum take-off weight of only 1255 kg was equipped with a BMW IIIa gasoline engine with an output of 185 hp. With a standard two-blade wooden propeller, it could reach speeds of up to 175 km / h and rise to a height of 4 km. After some restructuring and installation of a new propeller, the biplane was supposed to become a flying laboratory. In April 1937, A.Ya. Dekker registered the upgraded aircraft; he received the number PH-APL.

During the restructuring, the prototype aircraft lost its regular bonnet and some other parts. Instead of them, an original gearbox and a pair of "low speed propellers" were placed in the nose of the fuselage. The front rotor received six blades, the rear one - seven. The basis of the new propeller is a pair of hubs, assembled from an aluminum frame with skin from the same material. The blades were of a similar design. In connection with the installation of the screws, the nose of the car changed its shape in the most noticeable way. In this case, the cylindrical fairing of the rear rotor did not protrude beyond the fuselage skin.

Tests of the flying laboratory with the original propeller started in the same year 1937. The site for them was the Ipenberg airfield. Already in the early stages of testing, it was found that coaxial propellers with low aspect ratio blades can actually create the required thrust. With their help, the car could perform taxiing and jogging. In addition, from a certain time, the testers tried to lift the car into the air. It is known that the experienced Fokker C.I was able to complete several flights, but there was no talk of a full-fledged takeoff.

Front view. Photo Oldmachinepress.com

Tests of the prototype aircraft made it possible to identify both the pros and cons of the original project. It has been found that a pair of counter-rotating propellers is indeed capable of producing the required thrust. At the same time, the assembled propeller group was distinguished by its relatively small size. Another design advantage was the reduced noise generated by low aspect ratio blades.

However, there were some problems. Propeller A.Ya. Decker and the gearbox he needed differed from existing samples in the unnecessary complexity of manufacturing and maintenance. In addition, the experimental propeller installed on the Fokker C.I showed insufficient thrust performance. He allowed the plane to move on the ground and develop enough high speed, but its thrust was insufficient for flights.

Apparently, the tests continued until the very beginning of the forties, but for several years they did not lead to real results. Further work was prevented by the war. In May 1940, Hitler's Germany attacked the Netherlands, and just a few days later a prototype aircraft with unusual propellers became a trophy of the aggressor. German experts expectedly showed interest in this development. Soon the flying laboratory was sent to one of the airfields near Berlin.

Starting the engine, the propellers began to rotate. Shot from newsreel

There is information about some tests carried out by German scientists, but these tests ended quickly enough. According to some reports, the very first attempt of the Germans to lift the plane into the air ended in an accident. They did not restore the car, and this was the end of the bold project. The only aircraft equipped with Low rotation speed propeller, could not show its best side, and therefore from original idea refused. In the future, only propellers of the traditional appearance were massively used.

According to the ideas behind the original design, the special "Low Speed Propeller" was to become a full-fledged alternative to traditional systems. Differing from them in some complexity, it could have advantages in the form of smaller dimensions, reduced revs and reduced noise. Nevertheless, the competition did not work out. Developed by A.Ya. Dekker was not even able to pass the entire test cycle.

Perhaps, with further development, the original propellers could show the desired characteristics and find application in certain projects of aviation technology. However, the continuation of work was slowed down due to various problems and circumstances, and in May 1940 the project was stopped due to the German attack. After that, the unusual idea was finally left without a future. Later in different countries promising propeller designs were again worked out, but direct analogs of the Adriaan Jan Decker system were not created.

Based on materials:
https://oldmachinepress.com/
http://anyskin.tumblr.com/
http://hdekker.info/
http://strangernn.livejournal.com/
https://google.com/patents/US2186064

G.V. Makhotkin

Propeller design

Air propeller has gained a reputation as an irreplaceable propulsion device for high-speed floating craft operating in shallow and overgrown waters, as well as for amphibious snowmobiles, which have to work on snow, ice and water. We have already accumulated considerable experience both in our country and abroad. propeller applications on high-speed small craft and amphibians... So, since 1964 in our country, amphibious snowmobiles (Fig. 1) KB im. A. N. Tupolev. In the United States, several tens of thousands of airboats, as the Americans call them, are operated in Florida.

The problem of creating a high-speed shallow-draft motor boat with a propeller continues to interest our amateur shipbuilders. The most accessible power for them is 20-30 liters. with. Therefore, we will consider the main issues of designing an air propulsion unit with the expectation of just such a power.

Careful determination of the geometrical dimensions of the propeller will allow full use of the engine power and obtain a thrust close to the maximum for the available power. In this case, the correct choice of the screw diameter will be of particular importance, on which not only the efficiency of the propeller depends in many respects, but also the noise level, which is directly caused by the magnitude of the peripheral speeds.

Studies of the dependence of thrust on travel speed have established that for the implementation of the capabilities of the propeller with a power of 25 liters. with. it must have a diameter of about 2 m. To ensure the lowest energy consumption, air must be thrown back by a jet with a larger cross-sectional area; in our particular case, the area swept by the screw will be about 3 m². Reducing the diameter of the propeller to 1 m to reduce the noise level will reduce the area swept by the propeller by 4 times, and this, despite the increase in speed in the jet, will cause a drop in thrust at mooring lines by 37%. Unfortunately, it is not possible to compensate for this decrease in thrust either by step, or by the number of blades, or by their width.

With an increase in the speed of movement, the loss in traction from a decrease in the diameter decreases; thus, increasing the speeds allows smaller propellers to be used. For propellers with a diameter of 1 and 2 m, providing maximum thrust at the mooring, at a speed of 90 km / h, the thrust values become equal. Increasing the diameter up to 2.5 m, increasing the traction at the mooring, gives only a slight increase in traction at speeds over 50 km / h. In general, each range of operating speeds (at a certain engine power) has its own optimal screw diameter. With an increase in power at a constant speed, the diameter optimal in terms of efficiency increases.

As follows from what is shown in Fig. 2 graphs, the thrust of the propeller with a diameter of 1 m is greater than the thrust of the water propeller (standard) of the Neptune-23 or Privet-22 outboard motor at speeds over 55 km / h, and the propeller with a diameter of 2 m - already at speeds over 30 -35 km / h. Calculations show that at a speed of 50 km / h, the kilometer fuel consumption of an engine with a propeller with a diameter of 2 m will be 20-25% less than the most economical outboard motor "Privet-22".

The sequence of selection of propeller elements according to the given graphs is as follows. The diameter of the propeller is determined depending on the required thrust at the mooring lines at given power on the screw shaft. If the motorboat is supposed to be operated in populated areas or areas where there are noise restrictions, the acceptable (for today) noise level will correspond to the peripheral speed - 160-180 m / s. Having determined, based on this conditional norm and the screw diameter, the maximum number of its revolutions, we will establish the gear ratio from the motor shaft to the screw shaft.

For a diameter of 2 m, the permissible noise level will be about 1500 rpm (for a diameter of 1 m - about 3000 rpm); thus, the gear ratio at an engine speed of 4500 rpm will be about 3 (for a diameter of 1 m - about 1.5).

Using the graph in Fig. 3, you will be able to determine the amount of thrust of the propeller if the propeller diameter and engine power have already been selected. For our example, the engine of the most available power is selected - 25 hp. with., and the diameter of the propeller - 2 m. For this particular case, the magnitude of the thrust is 110 kg.

The lack of reliable gearboxes is perhaps the biggest hurdle to overcome. As a rule, chain and belt drives made by amateurs in artisanal conditions are unreliable and have low efficiency. Forced installation directly on the motor shaft leads to the need to reduce the diameter and, consequently, reduce the efficiency of the propeller.

To determine the blade width and pitch, use the nomogram shown in Fig. 4. On the horizontal right scale from the point corresponding to the power on the screw shaft, draw a vertical line until it intersects with the curve corresponding to the previously found screw diameter. From the point of intersection, draw a horizontal line to the intersection with the vertical drawn from a point on the left scale of the number of revolutions. The resulting value determines the coverage of the propeller being designed (aircraft manufacturers call the ratio of the sum of the widths of the blades to the diameter).

For two-blade propellers, the coverage is equal to the ratio of the blade width to the propeller radius R. Above the coverage values, the values of the optimal propeller pitches are indicated. For our example, the following are obtained: coverage σ = 0.165 and relative pitch (ratio of pitch to diameter) h = 0.52. For a screw with a diameter of 1 m σ = 0.50 m and h = 0.65. A propeller with a diameter of 2 m should be 2-bladed with a blade width of 16.5% R, since the coverage is small; a propeller with a diameter of 1 m can be 6-bladed with a blade width of 50: 3 = 16.6% R or 4-bladed with a blade width of 50: 2 = 25% R. An increase in the number of blades will give an additional reduction in noise level.

With a sufficient degree of accuracy, it can be assumed that the propeller pitch does not depend on the number of blades. We give the geometric dimensions of a wooden blade with a width of 16.5% R. All dimensions in the drawing fig. 5 are given as a percentage of the radius. For example, section D is 16.4% R, located at 60% R. The chord of the section is divided into 10 equal parts, that is, 1.64% R each; the sock is broken through 0.82% R. The profile ordinates in millimeters are determined by multiplying the radius by the percentage value corresponding to each ordinate, that is, by 1.278; 1,690; 2.046 ... 0.548.

Converting the power (torque) of the engine into the thrust required for the forward motion of aircraft, snowmobiles, gliders, hovercraft. Propellers can be pulling - they are installed on the aircraft, etc. in front of the engine (in the direction of travel) and pushing - they are placed behind the engine. The screws can be single and double coaxial, when two screws are located one above the other, the shaft of the upper screw passes through the hollow shaft of the lower screw and they rotate in opposite directions. According to the method of attaching the blades to the sleeve, there are propellers: fixed pitch, the blades of which are made integral with the sleeve; variable pitch - the most common type, the blades of which in flight can be rotated in the sleeve around the axis by a certain angle, called the pitch of the propeller; reversible, in which in flight the blades can be set at a negative angle to create thrust directed in the direction opposite to the movement (such blades are used, for example, for effective braking and reducing the length of the aircraft's run during landing). A feature of the vane propeller is the ability to set the blades along the air flow in flight, so that when the engine stops in flight, it does not increase the drag of the aircraft from the propeller. The number of propeller blades is from 2 to 6 for single ones and up to 12 for coaxial ones.

The types of propellers are main rotor and tail rotor applied on helicopters, rotorcraft, autogyros.

Encyclopedia "Technics". - M .: Rosman. 2006 .

Vane propellers for converting engine torque into propeller thrust. Installed on airplanes, rotorcraft, snowmobiles, hovercraft, ekranoplans, etc.
V. in. subdivided; by the method of installing the blades - on the propellers of a constant, fixed and variable pitch (they can be vane or vane-reversible); according to the step change mechanism - with a mechanical, electrical or hydraulic drive; according to the scheme of work - direct or reverse scheme; by design - for single, coaxial, double-row, V. century. in the ring.
V. in. consists of blades ( cm. Propeller blade), bushings and may also include propeller pitch changes. V. in. differ in diameter D (0.5-6.2 m) and the number of blades k (2-12). The sleeve is used to attach the blades and transmit torque from the motor shaft. The pitch change mechanism provides a change in the angle of the blades in flight.
1) V. in. unchanged pitch, the blades do not rotate around their axes.
2) V. blades in. fixed pitch can be set at the desired angle before flight, but during operation they do not rotate.
3) V. in. variable pitch, you can change the angle of the blades using a manual control system or automatically using a speed controller. The regulator maintains a given engine speed by controlling the step by supplying oil through a system of channels to the corresponding cavities of the control mechanism V. c. with hydraulic drive.
4) At the weather vane V. the blades can be installed downstream to reduce aerodynamic drag when the engine is forced to stop in flight ( cm. Feathering of the screw).
5) Feather-reverse V.'s blades. can also be set in such a position where, when it rotates, negative thrust is created, which is used at landing to reduce the length of the run and maneuver on the ground ( cm. Screw reversal).
Mechanical and electrical mechanisms for changing the pitch have great inertia and therefore are practically not used. The most widespread V. in. with hydraulic drive.
1) V. in. with a hydraulic drive of a straight circuit, the blades are set at a small pitch using the forces created by the oil pressure, and at a large pitch by the centrifugal forces of the counterweights. Such V. in. are used with engine powers up to 2000 kW.
2) At powers above 2000 kW, the mass of counterweights significantly increases; therefore, V.V. are used. the reverse scheme, in which the blades are set at a large pitch using the forces created by the oil pressure, and at a small pitch - by the centrifugal forces of the blades themselves.
- A single propeller has one row of blades,
- coaxial V. century. consists of two single screws mounted on coaxial shafts and rotating in opposite directions ( cm. Coaxial screw),
- two-row V. century. consists of two single screws, one after the other and rotating in the same direction.
- v. v. it has a profiled ring in the ring, thanks to which additional traction will be created; effective at low speeds (up to 200 km / h).
To reduce aerodynamic drag and power losses at the inlet to the V. in. fairings (elliptical, conical, etc.) are installed, covering the bushing and near-butt parts of the blades. On the east century. anti-icing systems can be placed.
To V. in. new generation include V. in. reduced diameter with a large number of wide thin saber-shaped blades, which are unreasonably called propfans.
In the initial period of the development of aviation in the air force. were made mainly of wood, and in subsequent years others were used (steel, titanium, aluminum alloys, composite materials, etc.).
To assess the quality of V. in. and comparing them with each other, mainly dimensionless α and power
(β) = N / (ρ) n3D5
(N -, (ρ) - air density, n - rotor speed)
and the efficiency of the propeller
(η) = (αλ) / (β) ((λ) = V / nD - relative, V - flight speed). V. characteristics in. are determined in flight tests, from V.V.'s research. and their models in wind tunnels, as well as theoretically. When calculating, 2 cases are distinguished; determination of the shape, size, and number of blades according to the given values (α), (β), and (η) (direct problem) and determination of (α), (β), and (η) according to the well-known geometry of V. v. (inverse problem).
For the first time to consider V.'s blade. as suggested by the Russian engineer S. K. Dzhevetsky in 1892, he also put forward the hypothesis of flat sections in 1910 (each section of the blade is considered as). By decomposing the lifting force of the airfoil dY and its aerodynamic resistance dX, the thrust dP and the force dQ of resistance to rotation of the considered blade element are determined, and the total thrust of the blade and the force of resistance to its rotation (hence, the engine power required to rotate the airfoil) is obtained by integration along the blade. Basically, the forces acting on the blade element are determined by the relative velocity W of the incident flow and its geometric angle of attack
(α) r = (φ) -arctg (V / (ω) r),
(φ) - angle of installation of the blade element.
Ideally, the incident flow velocity is
W = (ω) Xr + V,
where (ω) is the angular velocity of the blade, r is the radius vector of the section under consideration, V is the flight speed vector. During its motion, the blade drags along, giving it an additional, inductive speed w. As a result, the true speed Wн ,. flow around the element and true ((α) n differ from ideal. Calculation of w and (α) n is the main problem of the theory of the screw.
In 1910-1911 G. Kh. Sabinin and B. N. Yuriev developed Dzhevetsky's theory, including in it, in particular, some provisions of the theory of the ideal propeller. V.'s calculations according to the formulas they obtained, they were in satisfactory agreement with the experimental results. In 1912, N. Ye. Proposed a vortex theory, which gives an accurate physical representation of the operation of a screw, and practically all calculations of a vortex. began to be carried out on the basis of this theory.
According to Zhukovsky's theory, the propeller is replaced by a system of attached and free vortices. In this case, the blades are replaced by attached vortices, which turn into one running along the axis of the propeller, and free vortices descend from the trailing edge of the blade, generally forming a helical vortex sheet. Under the assumption that (ω) is the connection (ω) with the circulation of velocity around the blade section. The hypothesis of flat sections with a continuous flow around the blade was confirmed experimentally by the coincidence of pressure distributions over the sections of the blade of a rotating vane. and wings with the same cross-sectional profiles. It turned out, however, that rotation affects the propagation of the flow stall over the blade surface and, in particular, the rarefaction in the separation region. The flow separation region beginning at the end of the blade is similar to a rotating pipe, the vacuum in it is controlled centrifugal force and on the inside of the blade is much larger than on the wing.
At (λ) 1, the difference between the true (ω) and the mean becomes noticeable, and the calculation of the V. v. with true (ω) becomes similar to the calculation of a wing of a finite span ( cm. Wing theory). When calculating heavily loaded V. in. (with a large ratio of power to the surface swept away by the screw) vortex deformation must be taken into account.
Due to the fact that the circumferential speed of V. in. translational is added, the influence of the compressibility of air affects first of all on the V. century. (leads to a decrease in the efficiency). At subsonic blade tip peripheral speed, aircraft translational speed and subsonic speed W, the effect of air compressibility on (ω) is weak and affects only the flow around the blade. In the case of subsonic flying and supersonic velocities W at the blade tip (when it is necessary to take into account the compressibility of the medium), the V.V. theory, based on the scheme of attached (carrying) vortices, becomes practically inapplicable, and a transition to the bearing surface scheme is required. Such a transition is also necessary at a subsonic speed of the blade tip, if its width is large enough. Obtained experimentally in the USSR by V. v. and corrections due to the compressibility of air were widely used in the choice of the diameters and number of blades of air conditioning. and together with the choice of the shape of the blades (especially the profiles of their cross-sections) made it possible to improve the flight characteristics of domestic aircraft, including those that participated in the Great Patriotic War.
During the first period of mastering high subsonic velocities, the main task of designing a high velocity considered the creation of large-diameter propellers (up to 6 m) with a high efficiency (Propeller 85%) at maximum flight speed. The characteristics of airfoils at high transonic speeds were first obtained experimentally on propellers with so-called drained blades, and one of the airfoils had the properties of a supercritical airfoil (1949). For the second period (from the 60s) an additional requirement is characteristic - an increased thrust of V. in. at takeoff. For this purpose, blades with increased curvature profiles have been developed. Further development V. in. associated with the development of screws with a large number of wide thin saber-shaped blades. With an increase in the number and width of the blades, the flow around their butt parts, where the effect of a lattice of profiles is significant, becomes of great importance. A means of reducing the wave impedance can be the choice of the shape of the coca. Calculations and experiments show that at flight speeds corresponding to the Mach flight number M. contributed by S. Sh. Bas-Dubov, B. P. Blyakhman, V. P. Vetchinkin, K. I. Zhdanov, G. M. Zaslavsky, V. V. Keldysh, A. N. Kishalov, G. I. Kuzmin , A. M. Lepilkin, G. I. Maykapar, I. V. Ostoslavsky, N. N. Polyakov, D. V. Khalezov.

Aviation: An Encyclopedia. - M .: Great Russian Encyclopedia. Chief editor G.P. Svishchev. 1994 .

air propeller Encyclopedia "Aviation"

air propeller- Rice. 1. Schemes of propellers. propeller - vane propeller for converting engine torque into propeller thrust. Installed on airplanes, rotorcraft, aerosleds, hovercraft, ekranoplans, etc. v … Encyclopedia "Aviation"

AIR PROPELLER- vane propeller, the working medium of which is air. The Propeller is a common aircraft propulsion system. Marine Propeller on the geometry of the blades and hydrodynamic characteristics are significantly different from aviation and ... ... Marine encyclopedic reference

A propeller, a propeller, in which radially located profiled blades, rotating, throw air and thereby create a thrust force. V. in. consists of a bushing located on the motor shaft, and blades with a span along the ... ... Great Soviet Encyclopedia

air propeller- orasraigtis statusas T sritis fizika atitikmenys: angl. impeller airscrew; propeller vok. Luftschraube, f; Propeller, m; Saugschraube, f rus. propeller, m; propeller, m pranc. aéro propulseur, m; hélice aérienne, f; hélice propulsive, f ... Fizikos terminų žodynas

Before jet engines were developed, all airplanes had propellers, that is, propellers driven by internal combustion engines like automobiles.

All propeller blades have a cross-sectional shape that resembles the cross-section of an aircraft wing. As the propeller rotates, air flows around the front surface of each blade faster than the back. And it turns out that the pressure in front of the propeller is less than behind it. This creates a forward thrust force. And the magnitude of this force is the greater, the higher the rotational speed of the propeller.

(In the image above) The air flow moves faster along the leading surface of the rotating propeller blade. This reduces the front air pressure and forces the aircraft to move forward.

A propeller-driven aircraft takes off into the air due to the thrust generated by the rotation of the propeller blades.

The ends of the rotating propeller blades describe a spiral in the air. The amount of air that a propeller drives through itself depends on the size of the blades and the speed of rotation. Additional blades and more powerful engines can increase the useful performance of the propeller.

Why are the propeller blades twisted?

If these blades were flat, air would be evenly distributed over their surface, causing only resistance to rotation of the propeller. But when the blades are curved, the air flow in contact with their surface acquires its direction at each point on the blade surface. This blade shape allows it to cut through the air more efficiently and maintain the most favorable ratio between thrust and air resistance.

Variable angle propellers. The angle at which the blade is mounted in the main rotor hub is called the pitch taper angle. On some aircraft, this angle can be changed and thus make the propeller work as useful as possible under various flight conditions, that is, during takeoff, climb or cruise flight.