RU2818823C1 - Method of preventing rotorcraft from entering vortex ring state zone at pre-landing maneuvers in hovering mode - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: invention relates to aircraft engineering, namely to rotorcraft rotor aerodynamics, in particular, to a method of preventing rotorcraft, including helicopters, from entering into a zone of the vortex ring state during pre-landing manoeuvres in hovering mode. Result is achieved due to automatic maintenance of true longitudinal and vertical air speeds within the limits at which the rotorcraft cannot get into the zone of the vortex ring state. To perform said automatic maintenance, measuring the longitudinal and vertical true air speeds of the aircraft, the current weight of the aircraft, current overload on vertical axis, static pressure at flight altitude, ambient air temperature at flight altitude. Measured parameters are used to generate signals, which by means of automatic control system of helicopter limit its true air speeds to values excluding entering of rotorcraft into zone of vortex ring state.

EFFECT: increasing the flight safety of rotorcraft by preventing them from entering into the zone of vortex ring state.

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Description

Field of technology to which the invention relates

The invention relates to aviation, namely to the aerodynamics of the main rotor of a rotary-wing aircraft, in particular to a method for preventing a helicopter from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode.

The “vortex ring” mode is a special mode of operation of both single and coaxial rotors of helicopters and rotary-wing aircraft. The main feature of this mode is the global violation of the laws of jet flow of air flow in the area of the rotors. It occurs at low horizontal speed of the helicopter during descent. In this mode, the rotors do not create sufficient thrust, resulting in poor controllability of the aircraft and spontaneous and unpredictable accelerated descent of the aircraft.

State of the art

It is known that during pre-landing maneuvers of a helicopter, the helicopter enters the “vortex ring” mode with an unexpected and sharp loss of flight altitude, which leads to accidents and disasters of helicopter equipment due to inevitable rough landings (publication “Helicopter Theory” / Johnson W. - World, 1989, 108 pp.).

There is a known method of preventing a rotorcraft from entering a stable “vortex ring” mode (CN 1784338A, B64C27/28, B64C27/57, published 06/07/2006), which is carried out by measuring the lifting force of the helicopter rotor and creating a lateral cyclic disturbance on it when entering “vortex ring” mode.

However, this method does not prevent the rotorcraft from entering the vortex ring zone. It reduces the dangerous situation when entering the “vortex ring” mode, but does not prevent the situation itself.

There is a known method for detecting and signaling the approach to the “vortex ring” mode of a rotorcraft, which includes measuring the tangential and normal components of the air velocity near the main rotor during preliminary flight tests (CN 101808897A, B64C27/00, published 08/18/2010). Based on the measured values, the boundaries of the occurrence of the “vortex ring” mode are formed and the helicopter air speed and the associated vertical speed are compared with the boundary parameters of the “vortex ring” mode. If the parameters correspond to the “vortex ring” mode, a warning signal is generated. In this case, the air pressure receivers are installed on two arms of a rotating lever mounted on a rod above the main rotor of the rotorcraft.

However, in the known method, the tangential and normal (axial) velocities of the oncoming air flow near the rotor are determined without taking into account their dependence on the angle of attack of the rotor, which significantly reduces the accuracy of determining the “vortex ring” mode and the moment when alarms are triggered, increasing the likelihood of flight accidents. In addition, increasing the complexity of the rotor design reduces reliability and affects the flight path during pre-landing maneuvers.

The closest to the proposed invention is a method for determining and signaling the approach of the main rotor of a single-rotor helicopter to the “vortex ring” mode during pre-landing maneuvers (RU 2486596 C1, G08B21/00, B64C 27/00, published 06.27.2013), according to which it is measured at During preliminary flight tests using a measuring system, the tangential and normal components of air speed near the main rotor and, based on these paired values, form the boundaries of the occurrence of the “vortex ring” mode of the rotorcraft. At the same time, the accuracy of the formation of the boundaries of the occurrence of the “vortex ring” mode is increased by taking into account the angle of attack of the main rotor. Then, during the flight, the helicopter’s air speed and the associated vertical speed are compared with the boundary parameters of the “vortex ring” mode and, if the parameters match, a warning signal is generated.

However, this method does not prevent the helicopter from entering the “vortex ring” zone.

The boundary conditions for the emergence of the “vortex ring” mode are known (publication “Helicopter dynamics. Limit flight modes” / Braverman A.S., Vaintrub A.P. - M.: Mashinostroenie, 1988, 278 pp.). This work on page 193 provides formulas (1) and (4) for calculating true air speeds at which, during pre-landing maneuvers in hover mode, single-rotor helicopters are excluded from entering the “vortex ring” mode zone:

Where - true longitudinal airspeed of the rotary-wing aircraft, km/h;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

where R _n - static air pressure at flight altitude, mm Hg;

_Tn - outside air temperature, degrees Kelvin;

where t is the outside air temperature at flight altitude, °C;

F is the area swept by the propellers of a rotary-wing aircraft, ^m2 .

Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

F is the area swept by the propellers of a rotary-wing aircraft, ^m2 .

The quantities Δ and n _y are dimensionless.

The results of experimental studies of “vortex ring” zones for single-rotor and coaxial helicopters are known (publication “Aerodynamics of a coaxial helicopter” / Petrosyan E.A. - Kazan: Polygon-Press, 2004, 816 pp.) which are reflected in Fig. 12.

In the said publication by Petrosyan E.A. in Fig. 8.2.6, p. 699 shows graphs of the “vortex ring” zones for coaxial and single propellers (Fig. 1). The solid and dotted lines in the graphs show the boundaries of the “vortex ring” zones for coaxial and single propellers, respectively. Velocities are presented in dimensionless units , where Vy is the component of the velocity vector along the axis of rotation of the propeller, Vxz is the projection of the velocity vector onto the design plane of rotation of the propeller.

The “vortex ring” zones are limited by the axis and constructed graphs, which were obtained based on processing the results of experimental studies of coaxial and single propeller models in a wind tunnel. In these areas between the axis and the constructed graphs, a “failure” of the propeller thrust coefficients occurs, and a spontaneous and unpredictable accelerated descent of the helicopter occurs.

In the absence of a helicopter's sideslip angle, the speed Vxz is equal to the true longitudinal airspeed , a Vy is equal to the true vertical airspeed .

During pre-landing maneuvers in hover mode, the helicopter can enter the upper boundaries of these zones, which are almost the same for both single-rotor helicopters and coaxial helicopters (Fig. 1). This means that formulas (1) and (2) are true for both single-rotor helicopters and helicopters with coaxial rotors.

In the said publication by Petrosyan E.A. in Fig. 8.3.4, p. 705 shows the boundary of the “vortex ring” of the Ka-32 helicopter, obtained as a result of flight tests (Fig. 2).

Disclosure of the invention

A technical problem not solved in known devices, the solution of which is provided by the claimed invention, is to create a method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone, which eliminates the occurrence of vibrations, poor controllability of the aircraft, and spontaneous and unpredictable accelerated descent of the aircraft.

This is an urgent task, especially taking into account the trends in creating optionally piloted helicopters and ensuring their safe piloting, both in manual and automatic modes.

The technical result consists in increasing the flight safety of rotary-wing aircraft during pre-landing maneuvers.

To achieve a technical result, a method is proposed to prevent a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode, including measuring the longitudinal and vertical true air speeds of the rotary-wing aircraft, the current weight of the aircraft, the current overload along the vertical axis, static pressure at flight altitude, the temperature of the outside air at flight altitude, characterized in that the measured parameters are supplied to the flight computer and signals are generated in it, which, using an automatic control system, limit the true air speeds of the rotorcraft in accordance with inequalities (5), (6) :

Where - true longitudinal airspeed of the rotary-wing aircraft, km/h;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

where R _n - static air pressure at flight altitude, mm Hg;

_Tn - outside air temperature, degrees Kelvin;

T _n =273+t,

where t is the outside air temperature at flight altitude, °C;

F is the area swept by the propellers of a rotary-wing aircraft, m ² ;

Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

F is the area swept by the propellers of a rotary-wing aircraft, ^m2 .

In addition, according to the method of preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode for medium and heavy rotary-wing aircraft with a mass of more than 3100 kg, a signal proportional to the acceleration of the true vertical air speed is introduced into the helicopter control via the vertical channel with the lead value t _control , depending on the mass of the rotary-wing aircraft, according to inequality (7):

Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

F is the area swept by the propellers of a rotary-wing aircraft, m ² ;

t _control - lead time, depending on the mass of the rotary-wing aircraft, sec;

- acceleration of true vertical air speed, m/s ² .

In addition, according to the method of preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode, when the true altitude of the rotary-wing aircraft increases during the pre-landing maneuver, the flight route of the rotary-wing aircraft is changed by a signal from the radio altimeter for landing at an alternate airfield .

In addition, a method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers is used on helicopters.

Thus, a technical result is achieved.

An increase in the flight safety of rotary-wing aircraft, including helicopters, during pre-landing maneuvers is achieved due to the fact that, in accordance with the proposed method of preventing a rotary-wing aircraft from entering the “vortex ring” mode zone, longitudinal and vertical true values are measured during pre-landing maneuvers in hover mode air speeds of a rotary-wing aircraft, current weight of the aircraft, current overload along the vertical axis, static pressure at flight altitude, outside air temperature at flight altitude. These parameters are fed to the flight computer to generate signals that, using an automatic control system, limit the true air speeds of the rotorcraft to values that prevent it from entering the “vortex ring” mode zone. When the true altitude of a rotary-wing aircraft increases during a pre-landing maneuver, a signal from the radio altimeter changes the flight route of the rotary-wing aircraft to land at an alternate airfield.

Brief description of drawings

The essence of the invention is illustrated by drawings:

In fig. Figure 1 shows the “vortex ring” zones obtained by processing the results of experimental studies of coaxial and single propeller models in a wind tunnel.

In fig. Figure 2 shows the boundaries of the “vortex ring” zone of the Ka-32 coaxial helicopter, obtained as a result of flight tests.

Carrying out the invention

In accordance with the proposed method of preventing a rotary-wing aircraft from entering the “vortex ring” mode zone, during pre-landing maneuvers in hover mode, the longitudinal and vertical true air speeds of the aircraft, the current mass of the aircraft, the current overload along the vertical axis, static pressure at flight altitude are measured, outside air temperature at flight altitude included in formulas (1) and (4). These parameters are fed to the flight computer. Then it generates signals in it that, using an automatic control system, limit the true airspeeds of the rotary-wing aircraft during the pre-landing maneuver in accordance with inequalities (5), (6):

Where - true longitudinal airspeed of the rotary-wing aircraft, km/h;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

where R _n - static air pressure at flight altitude, mm Hg;

_Tn - outside air temperature, degrees Kelvin;

T _n =273+t,

where t is the outside air temperature at flight altitude, °C;

F is the area swept by the propellers of a rotary-wing aircraft, ^m2 .

Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

F is the area swept by the propellers of a rotary-wing aircraft, ^m2 .

In fig. Figure 1 shows the “vortex ring” zones obtained by processing the results of experimental studies of coaxial and single propeller models in a wind tunnel. During pre-landing maneuvers in hover mode, the helicopter can fall into the upper boundaries of these zones, which are almost the same for both single-rotor helicopters and coaxial helicopters.

This indicates that the fulfillment of inequalities (5) and (6) excludes both single-rotor helicopters with a single main rotor and coaxial helicopters from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode.

In order to improve the flight safety of medium and heavy rotary-wing aircraft with a mass of more than 3100 kg, which have high inertia, an additional lead signal is introduced into the control of the rotary-wing aircraft via the vertical channel, proportional to the acceleration of the true vertical air speed, with the lead value t _control depending on the mass rotary-wing aircraft. In this case, inequality (6) is transformed into inequality (7):

Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s;

m is the current mass of the aircraft, kg;

g - gravity acceleration, m/s ² ;

n _y - current overload along the vertical axis;

Δ - relative air density;

F is the area swept by the propellers of a rotary-wing aircraft, m ² ;

t _control - lead time, depending on the mass of the rotary-wing aircraft, sec;

- acceleration of true vertical air speed, m/s ² .

True vertical airspeed of descent of a rotorcraft is the sum of the speeds: the speed of descent of the rotorcraft relative to the Earth and the speed of the air flow directed upward. When the speed of the air flow directed upward is greater than the permissible rate of descent of the rotorcraft indicated in inequality (6), the automatic control system of the helicopter during the pre-landing maneuver will begin to increase the true altitude of the rotorcraft. In order to prevent the rotary-wing aircraft from entering the “vortex ring” mode, in this case, when the true altitude of the rotary-wing aircraft increases during the pre-landing maneuver, the navigation computer, based on a signal from the radio altimeter, changes the flight route to land the rotary-wing aircraft at an alternate airfield.

The proposed method of preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers is used, including on helicopters.

Thus, the technical result, which consists in increasing the flight safety of rotary-wing aircraft, including helicopters, during pre-landing maneuvers, is achieved by limiting the vertical true air speeds depending on the longitudinal true air speeds to values that prevent the rotary-wing aircraft from entering the zone "vortex ring" mode.

An example of the implementation of the invention will be given on a helicopter of the Ka-32 type (Ka-32A11 VS). Let us evaluate the permissible vertical rate of descent of the Ka-32 helicopter (Ka-32A11 BC) during pre-landing maneuvers in hover mode, which prevents them from entering the “vortex ring” mode zone using the proposed method.

Calculation of permissible vertical rate of descent We will conduct at an overload of 1.0, standard atmosphere (pressure 760 mm Hg, temperature +15°C).

With these parameters, the relative density of air is:

The parameters of the Ka-32 helicopter (Ka-32A11 BC) required for calculations are as follows: the current mass of the aircraft is 11000 kg; The radius of the main rotor is 7.95 m.

Permissible vertical rate of descent while hovering for a Ka-32 helicopter using the proposed method:

In fig. Figure 2 shows the boundary of the “vortex ring” zone obtained as a result of flight tests of the Ka-32 helicopter. They show that while hovering with the specified parameters, the Ka-32 helicopter enters the “vortex ring” zone at a descent speed of 6 m/s. Thus, with an allowable vertical rate of descent equal to minus 1.5 m/s, there is a significant speed reserve that ensures that a Ka-32 helicopter does not fall into the “vortex ring” mode zone. This indicates that the proposed method ensures that during pre-landing maneuvers in hovering mode the landing speed of rotorcraft, including helicopters, is significantly less than the speed of aircraft entering the “vortex ring”.

Claims (32)

1. A method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode, including measuring the longitudinal and vertical true air speeds of the rotary-wing aircraft, the current weight of the aircraft, the current overload along the vertical axis, static pressure at flight altitude , the temperature of the outside air at flight altitude, characterized in that the measured parameters are supplied to the flight computer and signals are generated in it, which, using an automatic control system, limit the true air speeds of the rotorcraft in accordance with inequalities (5), (6): Where - true longitudinal airspeed of the rotary-wing aircraft, km/h; m is the current mass of the aircraft, kg; g - gravity acceleration, m/s ² ; n _y - current overload along the vertical axis; Δ - relative air density; where R _n - static air pressure at flight altitude, mm Hg; _Tn - outside air temperature, degrees Kelvin; T _n =273+t, where t is the outside air temperature at flight altitude, °C; F is the area swept by the propellers of a rotary-wing aircraft, ^m2 . Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s; m is the current mass of the aircraft, kg; g - gravity acceleration, m/s ² ; n _y - current overload along the vertical axis; Δ - relative air density; F is the area swept by the propellers of a rotary-wing aircraft, ^m2 . 2. A method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode according to claim 1, characterized in that for medium and heavy rotary-wing aircraft with a mass of more than 3100 kg, a signal is introduced into the helicopter control via the vertical channel, proportional to the acceleration of the true vertical air speed with the lead value t _control , depending on the mass of the rotary-wing aircraft, according to inequality (7): Where - true vertical airspeed of descent of the rotary-wing aircraft, m/s; m is the current mass of the aircraft, kg; g - gravity acceleration, m/s ² ; n _y - current overload along the vertical axis; Δ - relative air density; F is the area swept by the propellers of a rotary-wing aircraft, m ² ; t _control - lead time, depending on the mass of the rotary-wing aircraft, sec; - acceleration of true vertical air speed, m/s ² . 3. A method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode according to any one of paragraphs. 1 or 2, characterized in that when the true altitude of the rotary-wing aircraft increases during a pre-landing maneuver, the flight route of the rotary-wing aircraft is changed upon a signal from the radio altimeter for landing at an alternate airfield. 4. A method for preventing a rotary-wing aircraft from entering the “vortex ring” mode zone during pre-landing maneuvers in hover mode according to any one of claims. 1-3, characterized in that the method is used on helicopters.