RU2538497C1 - Helicopter enclosed antitorque propeller - Google Patents

Abstract

FIELD: aircraft engineering.

SUBSTANCE: this antitorque rotor has shaped leading part, cylindrical part and trailing part. It consists of stator accommodating reduction gear with input and output shafts whereat the hub with vanes secured thereto is mounted. Fixed directing vanes are fitted inclined to the surface of encasement and are secured by one end to encasement cylindrical part and by other end at stator. Antitorque rotor comprises twelve blades arranged in two lines. Second line of blades is located in encasement cylindrical part. Spacing between said lines makes 0.08-0.20 of rotor radius. Note here that angular distances between two adjacent blades in common sequence for two lines of blades in each of three consecutive pairs of blades are related as 3:5:7. Note also that the number of blades in every line is even and that said blades are located diametrically opposite. Supports of directing vanes at encasement cylindrical surface are arranged in symmetry relative to input shaft axis. Attachment of every blade to stator is shifted relative to this blade to encasement surface in clockwise direction on the side of shaped inlet part of said encasement.

EFFECT: decreased acoustic radiation of rotor at minimum vibration, better aerodynamics.

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Description

The invention relates to aircraft, in particular to the design of the tail rotors of helicopters, used to compensate for the reactive moment of the rotor, as well as for directional control of the helicopter.

A known tail rotor in a tunnel is described in US Pat. No. 8,286,908 B2 (B64C 27/82).

The tail rotor creates the traction force necessary to compensate for the rotor torque and the directional control of the helicopter. The steering screw is mounted in a transverse tunnel, which has a profiled inlet, cylindrical and outlet parts. The transverse tunnel is located in the rear of the helicopter. To the walls of the tunnel fixed blades of the rectifier apparatus are attached at one end, and the stator is held at the other end of the blade, inside of which the gearbox is fixed. The blades of the rectifier are tilted in two planes relative to the stator and the tunnel. A rotating sleeve with blades creating traction force is fixed on the output shaft of the gearbox. The blades are fixed in the same plane of rotation with an uneven azimuthal pitch. The values of the uneven azimuthal pitch between adjacent rotating blades are calculated by known theoretical formulas.

Placing all the rotor blades in one plane limits the number of blades on the sleeve, due to the lack of space for assembling their butt parts and mechanisms for controlling the pitch of the blades. The chord values of the tail rotor blades are limited from the condition of permissible loads on the pitch control wiring of the blades.

Since both the number of blades and the chord of the blades are limited, the maximum propeller thrust is limited, which is a critical parameter for the directional control of the helicopter. The uneven step calculated in accordance with theoretical formulas in azimuth between successive blades does not provide a diametrically opposite arrangement of the blades.

With this arrangement of the prototype propeller blades, the centrifugal forces of the rotating blades are not balanced, the total, rotating together with the blades, unbalanced centrifugal force is transmitted to the tail of the helicopter, causing vibration. The main disadvantage of single row arrangement of the blades on the sleeve is the structural and layout spatial restrictions that do not allow placing pairs of adjacent blades with the smallest angular distances in azimuth, when this is required according to theoretical formulas from the condition of reducing acoustic radiation. The aerodynamic quality of the screw with a single row arrangement of the blades is limited and can be increased compared to the prototype.

The technical problem of the proposed technical solution of the tail rotor in the tunnel is to provide the smallest acoustic radiation of the propeller with the lowest possible level of vibration due to mutually balanced centrifugal forces while increasing aerodynamic quality.

The solution of the technical problem is provided by the fact that the tail rotor of the helicopter installed in the tunnel, which has a profiled input, cylindrical and output parts, consisting of a stator, inside of which is mounted a gearbox with an input shaft and an output shaft, on which a sleeve is mounted with it fixed blades, fixed blades of the rectifier, mounted obliquely to the surface of the tunnel and fixed at one end on the surface of the cylindrical part of the tunnel, and the other on the stator housing the screw contains twelve blades, and the sleeve is provided with a second row of blades located in the cylindrical part of the tunnel with a distance between the rows of 0.08-0.20 radius of the tail rotor, while the angular distances between the nearest blades in a common for two rows of the sequence of blades in each of consecutive in rotation of three pairs are correlated as 3: 5: 7, while the number of blades in each row is even and they are diametrically opposed, the supports of the blades of the rectifier on the cylindrical surface of the tunnel are laid symmetrically relative to the input shaft and the even number of blades, and mounting each of the stator blades is biased against the blade mounting same to the surface of the tunnel, in the clockwise direction by the shaped part of the tunnel entrance.

The invention is illustrated by drawings, where:

figure 1 shows a General view of the tail rotor installed in the tunnel;

figure 2 shows the tail rotor bush with blades mounted in two rows;

figure 3 shows a view in plan of the sleeve of the tail rotor;

figure 4 shows the location of the fixed blades of the straightening apparatus of the tail rotor, a plan view from the side of the profiled entrance of the tunnel.

The helicopter tail rotor is installed in the transverse tunnel 1 and contains a sleeve 2 to which the blades 3 of the first row and the blades 4 of the second row are attached. The tail rotor contains twelve blades 3, 4, and the number of blades 3 in the first row and the number of blades 4 in the second row is even and they are diametrically opposed in each row. The distance between the rows of blades 3, 4 is 0.08-0.20 of the radius of the tail rotor, and the angular distances between the nearest blades 3, 4 in the sequence of blades common to two rows in each of the rotational pairs of the three pairs of blades are correlated as 3: 5: 7.

Between three consecutive pairs of blades, a ratio of angular distances of 3: 5: 7 is ensured as follows.

For the first pair, two blades 4, 3 are taken, the distance between which is 18 degrees, between the next pair of blades 3.3-30 degrees, and then the third pair of blades 3.4-42 degrees.

For twelve rotor blades, this ratio is performed periodically - four times, i.e.: (18 ° + 30 ° + 42 °) · 4 = 360 °.

The gearbox 5 has an output shaft (not shown), on which the sleeve 2 is fixed and rotates, and an input shaft 6, to which torque is transmitted from the engines (not shown). The tunnel 1 has a profiled inlet part 7, a cylindrical part 8 and an outlet part 9. Both rows of blades 3, 4 are located in the cylindrical part 8 of the tunnel. The fixed blades 10 of the rectifier are mounted obliquely to the surface of the cylindrical part 8 of the tunnel and fixed at one end on the surface of the cylindrical part 8 of the tunnel, and the other end on the stator 11, inside of which the gearbox 5 is fixed. The supports of the blades 10 on the cylindrical part 8 of the tunnel are symmetrical with respect to the input shaft 6 of the gearbox 5. The number of blades 10 is even, while the fastening of each of the blades 10 to the stator 11 is offset in relation to the fastening of the same blades 10 to the surface of the cylindrical part 8 of the tunnel 1 in the direction SRI clockwise from the inlet portion of the tunnel.

The operation of the tail rotor of a helicopter installed in the tunnel is as follows.

Part of the engine power is transmitted in the form of torque to the input shaft 6 of the gearbox 5 and then rotates the sleeve 2 through the output shaft together with the blades 3, 4, which suck in the air at the entrance to the tunnel 1.

On the rotating blades 3, 4, a vacuum is created and as a result a thrust of the blades is formed. Air accelerates into tunnel 1 and is thrown out of the tunnel. Air moving toward the exit of the tunnel meets the vanes 10 of the straightening appart.

The blades of the rectifier reduce the swirling of the air flow, which increases the thrust of the screw, i.e. increases aerodynamic quality.

The blades 3, 4 rotate and thus move relative to the motionless blades 10, on which a vacuum is also formed, therefore, air forces.

Since the location of the blades 3, 4 and blades 10 periodically varies in time, both air velocities and forces are variable, and the interaction of forces, air flows and pressure fields forms acoustic radiation, i.e. noise of time-varying airflow.

The fixed blades 10 are tilted relative to the body of the tunnel 1 and the rotating blades 3, 4. Due to this slope, the average distance between the blades and the blades is structurally increased and the variable interaction forces are reduced, which leads to a decrease in acoustic radiation.

The frequencies of alternating air forces are equal to the frequencies of acoustic radiation, i.e. noise frequencies.

The blades 3, 4 located in two planes, which rotate in one direction, are essentially a coaxial screw in the tunnel 1, and the coaxial effect further increases the thrust of the blades 3, 4 and the aerodynamic quality of the screw.

In this way, an increase in aerodynamic quality is achieved.

The proposed ratio of the angular distances between the nearest blades 3, 4 in a common for two rows of a sequence of blades in each of three consecutive rotation pairs of 3: 5: 7 provides a solution to the technical problem, namely a wide range of acoustic radiation from the interaction of the pressure fields of the rotating blades 3, 4 with fixed blades 10.

The air pressure fields on the blades 3, 4 and on the blades 10, fastening the stator 11 to the wall of the tunnel 1, interact with each other at the time of passage of the blades 3, 4 and blades 10 at a minimum distance. In other words, the frequencies of acoustic radiation are equal to the frequencies of the “meetings” of the rotating blades 3, 4 and the fixed blades 10.

We calculate the frequency of acoustic radiation according to the well-known formula:

$$F=f\cdot \frac{{360}^{\circ }}{\Delta \psi }\cdot n$$

Where:

f is the rotational speed of the tail rotor [Hz],

Δψ is the pitch between the blades [deg],

n is the number of blades of the rectifier,

F is the frequency of acoustic radiation at a step between the blades ΔΨ ₁ .

Let us calculate, for example, the frequency of “encounters” for a screw with twelve blades with a uniform pitch between the blades (360 ° / 12 = 30 °) at a rotational speed of the sleeve (blades) of 50 Hz and six blades securing the stator.

The frequency of "meetings" (sound frequency) = 50 × 12 × 6 = 3600 Hz

Almost all the energy of acoustic radiation is concentrated near a frequency of 3600 Hz

With an uneven step of 3: 5: 7 between pairs of blades, which for a 12-blade screw corresponds to a step of 18 degrees, 30 degrees, 42 degrees, the frequencies of acoustic radiation are calculated by the formula:

The frequency of “meetings” = 50-6- (360 ° / 18 °, 360 ° / 30 °, 360 ° / 42 °) =

= 300 · (20, 12, 8.75) =

= 6000 Hz; 3600 Hz; 2570 Hz

From the formula it is obvious that there are three base frequencies of 6000 Hz, 3600 Hz, 2570 Hz and acoustic energy is emitted at three frequencies, i.e. in the range of 2570 ÷ 6000 Hz. Compared to radiation at one frequency, the distribution of acoustic radiation energy in three ranges results in a decrease in the maximum level and, accordingly, a decrease in the acoustic impact on the environment and the acoustic visibility of the aircraft.

The diametrically opposite arrangement of the blades 3, 4 provides perfect balancing of the screw by the centrifugal force of the blades, the resulting vector value of which is zero.

The above-described set of design features of the tail rotor of a helicopter installed in the tunnel made it possible to solve the technical problem while preserving all the positive properties and qualities of the prototype, namely, providing the smallest acoustic radiation of the propeller with the lowest possible level of vibration due to mutually balanced centrifugal forces while improving the aerodynamic quality of the steering screw.

Claims (1)

The helicopter tail rotor installed in the tunnel, which has a profiled input, cylindrical and output parts, consisting of a stator, inside of which a gearbox with an input shaft and an output shaft is fixed, on which a sleeve is mounted with blades fixed to it, fixed blades of the straightening apparatus mounted obliquely to the surface of the tunnel and fixed at one end on the surface of the cylindrical part of the tunnel, and the other on the stator, characterized in that the tail rotor contains twelve blades, and the sleep sleeve the second row of blades located in the cylindrical part of the tunnel with the distance between the rows of 0.08-0.20 radius of the tail rotor, while the angular distances between the nearest blades in the common for two rows of the sequence of blades in each of the rotational three pairs of blades are correlated as 3: 5: 7, and the number of blades in each row is even and they are diametrically opposed, the blade supports on the cylindrical surface of the tunnel are symmetrical about the axis of the input shaft and the number of blades is even, and the fastening of each of the blades to the stator is shifted, respectively, with respect to the fastening of the same blades to the surface of the tunnel, in a clockwise direction from the side of the profiled entrance of the tunnel.

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