RU168938U1 - Aerodynamic sensor - Google Patents

Abstract

The utility model relates to measuring technique and can be used to measure aerodynamic parameters such as full and static air pressures, the local aerodynamic angle in the airborne signal systems of aircraft. The device comprises a housing with a weather vane placed on it, coupled to a full pressure receiver and mounted on a rotation shaft, wherein the weather vane is a streamlined body with holes for perceiving static pressure and having a vane sweep angle, static pressure pneumatic duct, full pressure pneumatic duct, vane angular position transducer, full pressure sensor, static pressure sensor, electric heating elements. The weather vane is made of two thin-walled elements mounted on the frame, which are a mirror image of each other with static pressure sensing holes located symmetrically from the beginning of the front edge of the weather vane at a distance of five diameters of its front edge, and the angle of the swept vane is inversely proportional to the speed of the incoming flow. The full pressure sensor and the static pressure sensor are located on the vane rotation shaft, the vane angular position transducer is connected to the rotation shaft, and the sensor contains integrated means for monitoring the operability of electric heating elements implemented by a cable with a positive temperature coefficient of resistance and / or ceramic resistors made in the form of small disks with a positive temperature coefficient of resistance and mounted directly on

Description

The utility model relates to measuring technique and can be used to measure aerodynamic parameters such as full and static air pressures, the local aerodynamic angle in the airborne signal systems of aircraft.

A known aerodynamic parameter sensor described in patent No. 4672846, US IPC: G01C 21/00, 1985, comprising a sensor body with a weather vane mounted on it with a rotation shaft. The weather vane itself is a streamlined body that is freely oriented along the incoming air flow. The weather vane is coupled to a full pressure receiver, and holes for absorbing static pressure are located on the side planes of the weather vane. First of all, such a combination increases the accuracy of measuring air pressures, since the known angular error in measuring air pressures by fixed air pressure receivers, which can reach 1% of the pressure head at flow angles of the order of 20-25 °, exceeds the permissible measurement errors in repeatedly. This sensor has two pneumatic outputs - full and static pressure, as well as an electrical output, the signal from which is proportional to the angle of rotation of the wind vane.

The error in the orientation of the wind vane in the flow (in fact, the error in measuring the aerodynamic angle) depends on the aerodynamic moment created by the incoming flow and the total frictional moment inherent in the moving parts of the wind vane (friction moments in potentiometers, axis bearings, etc.).

For well-known reasons, the transmission of pneumatic signals from the moving part of the sensor - weather vane to the fixed part is a difficult task. This transmission limits the range of angular movement of the wind vane.

In addition, uneven weathervane heating carried out by an electric heating cable leads to ice formation under icing conditions and, as a result, to the appearance of destabilizing aerodynamic moments, as well as to distortion of the perceived total and static pressures.

The essence of the utility model is as follows.

The problem to which the claimed utility model is directed is to reduce the measurement error of the aerodynamic angle, the total and static pressures, as well as to increase the efficiency of the electrical heating of the wind vane.

The technical result consists in reducing the measurement error of the aerodynamic angle, full and static pressures, as well as increasing the efficiency of electric heating of the wind vane.

The specified technical result is achieved by the fact that the aerodynamic parameter sensor comprises a housing with a weather vane mounted on it, paired with a full pressure receiver and mounted on a rotation shaft, the weather vane being a streamlined body having a vane sweep angle inversely proportional to the flow velocity, made of two thin-walled elements mounted on the frame, representing a mirror image of each other with holes for the perception of static pressure, are located and symmetrically from the beginning of the front edge of the weather vane at a distance of five diameters of its front edge, and the weather vane is equipped with electric heating elements made of a cable with a positive temperature coefficient of resistance mounted on the frame and / or ceramic posistors made in the form of small disks with a positive temperature coefficient of resistance and fixed directly to the walls of thin-walled elements by, for example, soldering, providing a uniform temperature field, pneum total pressure track associated with a sensor of the total pressure, static pressure pnevmotrassu associated with the static pressure sensor, which are installed on the rotational shaft, the angular position transducer wind vane connected to the rotation shaft, wherein the aerodynamic parameter sensor itself comprises a built-in control performance of the heating elements.

The essence of the proposed utility model is illustrated by the following drawings.

In FIG. 1 shows the aerodynamic parameter sensor, where

1 - housing

2 - weather vane,

3 - shaft rotation

4 - receiver full pressure

5-5 '- holes perception of static pressure,

6 - pneumatic system of full pressure,

7 - pneumatic duct static pressure,

8 - full pressure sensor,

9 - static pressure sensor,

10 - Converter angular position of the wind vane,

11-11 '- thin-walled elements,

12 - electric heating elements

- расстояние от оси симметрии вала вращения 3 до центра масс флюгера 2,

- the distance from the axis of symmetry of the shaft of rotation 3 to the center of mass of the vane 2,

a - the level of the holes perception of static pressure,

b is the center of mass of the vane 2,

χ - sweep angle of the weather vane 2.

In FIG. 2 shows graphs of the dependence of the dead zone Δα of the weather vane 2 on the speed of the incident flow V of the prototype (curve 1) and the proposed utility model (curve 2).

In FIG. 3 is a graph of the pressure coefficient p versus the relative length of the vane 2 in the cross section of the vane at the level of the static pressure sensing holes 8 "a".

In FIG. Figure 4 shows the zones along the surface of the weather vane 2 with conditional separation according to the magnitude of the convective heat transfer coefficient: I and IV - maximum heat transfer, II - minimum heat transfer, III - zone of moderate heat transfer.

The aerodynamic parameter sensor comprises a housing 1 with a weather vane 2 placed on it, coupled to a full pressure receiver 4 and mounted on a rotation shaft 3, wherein the weather vane 2 is a streamlined body having a vane sweep angle inversely proportional to the speed of the incoming flow made of two thin-walled elements 11-11 ', representing a mirror image of each other with holes for the perception of static pressure 5-5', located symmetrically from the front edge of the vane at a distance of five diame ditch of the leading edge, the weather vane is equipped with electric heating elements 12, implemented with a cable with a positive temperature coefficient of resistance, mounted on the frame 13 (not shown in Fig. 1), and / or ceramic posistors made in the form of small disks with a positive temperature coefficient of resistance and directly fixed on the walls of thin-walled elements by, for example, soldering, providing a uniform temperature field. The full pressure through the pneumatic pump of the full pressure 6 is transmitted to the sensor of the full pressure 8, and the static pressure through the pneumatic pump of the static pressure 7 is transmitted to the static pressure sensor 9 mounted on the rotation shaft 3 of the vane 2, the angular position transducer of the vane 10 connected to the rotation shaft 3.

The principle of operation of the proposed sensor aerodynamic parameters corresponds to the known weathervane sensors for aerodynamic angles described in the book "Measuring instruments of the aerodynamic parameters of aircraft" G.I. Klyuev, N.N. Makarov, V.M. Soldatkin, I.P. Efimov, Ulyanovsk, 2005, and air pressure receivers described in the book “Methods and Technique for Measuring the Gas Flow Parameters” A.N. Petunin M .: Engineering, 1972

The aerodynamic moment created by the incident air flow on the weather vane 2, which is a streamlined body with a sweep angle of the weather vane χ, is

- коэффициент подъемной силы флюгера 2,Where

- the coefficient of lift of the weather vane 2,

S is the area of the weather vane 2,

- расстояние от оси симметрии вала вращения 3 флюгера 2 до центра масс флюгера b,

- the distance from the axis of symmetry of the rotation shaft 3 of the vane 2 to the center of mass of the vane b,

q = 0.5⋅ρ⋅V ² - velocity head,

where ρ is the density of air,

V is the flow velocity;

Δϕ is the deviation of the weather vane 2 from the direction of the incoming flow;

. Коэффициент подъемной силы

изменяется в незначительных пределах и зависит в большей степени от профиля поперечного сечения флюгера 2.Thus, it is seen that the aerodynamic moment M can be increased by changing the area of the wind vane 2S and the distance

. Lift coefficient

varies insignificantly and depends more on the cross-sectional profile of the vane 2.

The useful moment is equal to the aerodynamic moment minus the moment of friction created on the shaft of rotation 3 of the wind vane 2 by mechanical elements (potentiometers, bearings, etc.).

. Оценочный расчет аэродинамических моментов прототипа и предлагаемой полезной модели показывает, что изменение геометрии флюгера 2 приводит к увеличению полезного момента приблизительно на 45%, что при прочих равных условиях уменьшает зону нечувствительности Δα, а, значит, и погрешность измерения аэродинамических углов.When moving most of the area of the weather vane 2 beyond the shaft of rotation 3, the aerodynamic moment increases due to the increase in distance

. An estimated calculation of the aerodynamic moments of the prototype and the proposed utility model shows that a change in the geometry of the weather vane 2 leads to an increase in the useful moment by approximately 45%, which, all other things being equal, reduces the deadband Δα, and, therefore, the error in measuring aerodynamic angles.

From the graphs of FIG. 2 obtained by mathematical modeling of the weathercocks of the prototype and the proposed model of approximately the same overall dimensions, it can be seen that the deadband Δα of the weather vane 2 of the proposed utility model is curve 2 at an incident flow velocity V of less than 300 km / h (the most vulnerable take-off and landing modes) by 45 % less dead zone Δα of the prototype - curve 1.

As mentioned earlier, in the prototype, the openings of the perception of static pressure 5-5 'are located on the front edge of the weather vane, and, as you know, (book "Methods and techniques for measuring gas flow parameters" A.N. Petunin M .: Engineering, 1972 ) for spherical and cylindrical bodies (the front edge of the vane is actually a cylindrical body), the flow breaks off in the region of 40-45 degrees, which leads to significant pressure fluctuations at the locations of the static pressure sensing holes 5-5 '. In addition, the separation itself occurs at certain Reynolds numbers, which makes it difficult to reliably determine the moment of separation of the air flow. The offset of the holes for the perception of static pressure 5-5 'about five diameters of the leading edge corresponds to the principles of choosing their location, which is proposed in the proposed utility model.

From the graph obtained by the results of mathematical modeling of the proposed weather vane, shown in FIG. 3, it is seen that in the initial region a strong gradient of the pressure coefficient is observed (up to about 10% of the total length of the vane 2 in the plane of the cross section at the level of the static pressure sampling holes “a”), then a small zone (from 10 to 20%) of the flow instability , and already with about 50% of the total length, stabilization of the flow occurs. Based on the above dependence, the preferred location of the holes for the perception of static pressure 5-5 'in the region of 60% of the total length of the weather vane 2, which stabilizes the static pressure perceived by the aerodynamic parameters sensor, which is proposed in the proposed utility model.

. Таким образом, для М=2…3 угол наклона μ меняется от 30 до 20 градусов.To reduce drag at transonic and supersonic speeds, the vane 2 is swept, and the vane sweep angle χ is selected based on the angle of inclination of the shock wave μ at supersonic speeds, which is described by the expression

. Thus, for M = 2 ... 3, the angle of inclination μ varies from 30 to 20 degrees.

Accordingly, the vane sweep angle χ is selected so that the shock wave from the nose of the vane is higher than the total pressure receiver 4 located in the upper part of the vane 2, which is proposed in the proposed utility model.

As mentioned earlier, the transmission of pneumatic signals from the moving part of the weather vane sensor 2 to the fixed part, carried out through the full pressure pneumatic duct 6 and through the static pressure pneumatic duct 7, is a difficult task that imposes restrictions on the permissible rotation angles of the weather vane 2, because in accordance with OST 100762-75 “Static and total pressure systems for supplying membrane-aneroid devices. Technical requirements ”are also required for the delay time of the pneumatic signal. In order to reduce the pneumatic flow of the total pressure 6 and the static pressure 7, and therefore the delay time of the pneumatic signals, it is advisable to install pressure sensors on the shaft of rotation 3 of the weather vane 2 - the full pressure sensor 8 and the static pressure sensor 9, for example, with a digital output.

To expand the range of measurement of aerodynamic angles, it is proposed to install on the shaft of rotation 3 of the weather vane 2 the angular position transducer of the weather vane 10, and the electrical signal is already transmitted using, for example, sliding contacts. This solution allows you to completely remove the restrictions on the angle of rotation of the wind vane 2.

One of the important problems in the reliability of the sensor is the uneven heating of the weather vane 2, carried out by the heating element 12, made mainly by an electric heating cable, which leads to ice formation under icing conditions and, as a result, to the appearance of destabilizing aerodynamic moments. However, electric heating elements are increasingly being used, which are a cable with a nichrome (nickel, etc.) wire.

It is known that to ensure effective electrical heating of the weather vane 2 and the full pressure receiver 4 and to prevent them from icing, approximately 3-5 W from each square centimeter of the surface is required (Tenishev PX, Stroganov V.A., Savin B.S., Kordinov V. K., Teslenko A.I., Leontiev V.N. De-icing systems of aircraft. - M.: Mechanical Engineering, 1967. - 320 p.).

This requirement is ensured with the same heat transfer along the entire length of the cable from the entire surface of the vane 2 and the full pressure receiver 4. The use of a cable with the so-called "Self-regulation", i.e. the core material has a positive temperature coefficient of resistance (TCR), i.e. as the temperature rises, the cable resistance increases, and the power output decreases, which meets the requirements of the efficiency of electrical heating. Thus, a limitation of the allocated power is obtained depending on the current temperature. The heating efficiency is much higher than in the case of constant power cables: the cable does not burn out due to the high temperatures to which it heats itself; reduced power consumption due to increased resistance.

In FIG. 4 shows that the surface of the weather vane 2 has four zones depending on the magnitude of the convective heat transfer coefficient. The greatest heat transfer is observed in zones I and IV, where the flow is inhibited and trapped in liquid particles of water. In zone II, on the contrary, the flow is established and the heat transfer is minimal, and the pressure coefficient is much smaller, sometimes two orders of magnitude.

The use of ceramic posistors in the form of small disks characterized by the fact that the resistance of the resistors increases according to the logarithmic law also helps to solve the problem of increasing the efficiency of electric heating.

Fixing posistors directly on thin-walled structural elements 11-11 ', weather vane 2 by soldering allows you to achieve the following results:

- the exclusion of heat loss, which reduces the power of the heating element, which in this case is determined by the number of posistors;

- the use of posistors in the form of small disks allows for a more uniform temperature field along the thin-walled elements of the weather vane due to the optimal placement of the resistors on the inner surface of the thin-walled elements in accordance with the icing conditions;

- a more uniform temperature field provides a reduction in mechanical stresses caused by the difference in the linear expansion coefficients of the materials used for thin-walled elements, current-carrying elements, which increases the number of temperature cycles for soldering.

However, there is a problem with the failure of the heating elements. Failure of the heating elements almost immediately leads to icing of the weather vane of the aerodynamic parameter sensor, which, in turn, leads to a distortion of the perceived air pressures by the full pressure receiver and holes for perceiving static pressure.

Due to the fact that the measured air pressures are practically the only sources for calculating altitude-speed parameters, the absence or unreliable value of which can lead to catastrophic consequences, it is advisable to exclude a sensor with a failed heating element from the calculation loop. For this purpose, it is proposed to introduce into the design of the sensor a monitoring of the operability of the heating elements, which consists in evaluating the electric power consumed by the heating elements by measuring the electric current and removing the signal of the heating service or issuing a heating malfunction signal in the absence of electric current.

Thus, it can be noted that the proposed utility model allows to reduce the measurement error of the aerodynamic angle, total and static pressures, as well as to increase the efficiency of electrical heating of the wind vane in terms of ensuring the functioning of the sensor under conditions of possible icing.

Claims (2)

1. The aerodynamic parameter sensor, comprising a housing with a weather vane mounted thereon, coupled to a full pressure receiver and mounted on a shaft of rotation, wherein the weather vane is a streamlined body with holes for sensing static pressure and having a sweep angle of the wind vane, pneumatic duct of static pressure, pneumatic duct of full pressure, vane angular position transducer, full pressure sensor, static pressure sensor, electric heating elements, characterized in that the vane is made and two thin-walled elements mounted on the frame, which are mirror images of each other with static pressure sensing holes located symmetrically from the beginning of the front edge of the vane at a distance of five diameters of its front edge, and the angle of the sweep of the vane is inversely proportional to the speed of the incoming flow, the full pressure sensor and the sensor static pressure are located on the shaft of rotation of the wind vane, the transducer of the angular position of the vane is connected to the shaft of rotation, the aerodynamic sensor ble parameters comprises built-in control efficiency of electric heating elements. 2. The aerodynamic parameters sensor according to claim 1, characterized in that the electric heating elements are implemented with a cable with a positive temperature coefficient of resistance and / or ceramic posistors made in the form of small disks with a positive temperature coefficient of resistance and mounted directly on the walls of thin-walled elements.

Images