A straight bar pitot tube

Abstract

The present application belongs to the field of aircraft technology, and particularly relates to a beam straight bar type air speed tube. The air speed tube comprises a probe main body and a connected mounting base, wherein the probe main body is an isometric body configuration, a gas collecting cavity is formed in the inside, an arc front surface is opposite to the air flow direction, and more than one total pressure hole is arranged on the arc front surface; more than two static pressure holes are arranged opposite to the air flow direction. The present application utilizes the aerodynamic basic principle that the air flow in the leeward area of an object is relatively stable, takes into account the total pressure hole design, and the redundancy backup design of the total pressure hole and the static pressure hole, and improves the reliability and safety of the air speed tube / probe.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft, and in particular relates to a cross-beam straight-rod type pitot tube. Background Art

[0002] An air data system (ADS) is an essential measurement device used by aircraft to perceive the flight environment in real time and measure speed, attitude, and altitude. It is crucial and essential for ensuring flight safety and improving flight quality. Pitot tubes and wind vanes are specific examples of ADS sensing equipment and design methods.

[0003] As we all know, the pitot tube (also known as the probe) in an aircraft measures the total pressure (P0) and static pressure (P∞) during flight, and then calculates the flight speed (V) and flight altitude (H) (the pressure altitude obtained based on the static pressure (P∞)). It can even calculate the flight attitude (angle of attack and sideslip angle). While measuring the total pressure (P0) on the pitot tube is relatively convenient, due to the single total pressure port, the total pressure value may be inaccurate or blocked due to blockage. The static pressure (P∞) data measured by the pitot tube is susceptible to errors or large fluctuations, which can lead to deviations in subsequent data processing results.

[0004] Most pitot tubes are installed on the left and right sides of the forward area of ​​the aircraft. The static pressure they measure is the result of disturbances caused by the aircraft's forward body, rather than the actual incoming static pressure, P∞. Furthermore, this disturbance causes significant fluctuations in the measured data, hindering subsequent data processing.

[0005] This phenomenon is Figure 1 , Figure 2 Even with the same pitot tube, the static pressure it senses will vary when installed on aircraft of different configurations or at different locations on the same aircraft. As the aircraft's flight attitude changes, the airflow pattern over the aircraft surface also changes, and the measured static pressure will inevitably vary. This characteristic is detrimental to the stable and accurate measurement of incoming static pressure information.

[0006] To address this issue, researchers have developed a pitot tube design method: the aerodynamically compensated pitot tube design approach. This approach involves repeatedly optimizing the pitot tube's shape for a specific aircraft configuration and its specific installation location (the actual location where the pitot tube is installed), ultimately ensuring that the static pressure measured by the pitot tube is equal to the static pressure of the incoming airflow. Figure 3 The appearance drawings of several pitot tubes after aerodynamic compensation design are given.

[0007] Depend on Figure 3It can be seen that the air speed tubes designed by the aerodynamic compensation method have different aerodynamic shapes. The more prominent contradiction is that the air speed tubes designed by the method can only be used for a specific aircraft and a specific installation position thereof, and cannot be conveniently and reliably transplanted to other aircraft or other positions of the same aircraft, and the technical transplantability and universality thereof are poor. This defect limits the development of the method. Currently, the design of the air speed tube by using the aerodynamic compensation method is not a technical mainstream.

[0008] How to design an air speed tube / probe with wide applicability, so that the measured static pressure can be basically stable in a relatively wide angle of attack range and the measured total pressure is accurate, is a problem to be solved. SUMMARY

[0009] The purpose of the present application is to overcome the defects of the prior art, and a beam straight rod type air speed tube is provided.

[0010] In order to achieve the above purpose, the present application provides a beam straight rod type air speed tube, comprising a probe body and a connected mounting base, wherein,

[0011] The probe body is an isometric body configuration, a gas collecting cavity is formed in the inside, an arc-shaped front surface is arranged opposite to the airflow direction, and more than one total pressure hole is arranged on the arc-shaped front surface; more than two static pressure holes are arranged opposite to the airflow direction.

[0012] Preferably, the gas collecting cavity comprises a total pressure pipe and a static pressure pipe, wherein the total pressure pipe is used for collecting pressure data of the plurality of total pressure holes and outputting an averaged total pressure data value; and the static pressure pipe is used for collecting pressure data of the plurality of static pressure holes and outputting an averaged static pressure data value.

[0013] Preferably, the arc-shaped front surface is designed by using a von Karman curve, and satisfies the following formula:

[0014]

[0015] ψ=arccos(1-2x / B)

[0016] wherein y is a curve longitudinal axis coordinate, x is a curve transverse axis coordinate, ψ is an intermediate variable, and A and B are both constants.

[0017] Preferably, a concave cavity is formed opposite to the airflow direction.

[0018] Preferably, the arrangement of the total pressure holes on the arc-shaped front surface is as follows: arranged at equal intervals along a cylindrical axis; or arranged at equal intervals along a perpendicular line of the cylindrical axis; or more than five total pressure holes are arranged in a cross shape, one side of the cross shape is parallel to the cylindrical axis, the other side is perpendicular to the cylindrical axis, and each total pressure hole is at equal intervals; or there are n*n total pressure holes, which are arranged at equal intervals in n rows and n columns, and n≥3.

[0019] Preferably, the static pressure holes on the back of the air flow direction are equidistantly arranged along the cylindrical axis to obtain stable static pressure data.

[0020] Preferably, the air speed tube is equipped with a motion mechanism on the mounting base to realize the expansion and contraction of the probe body.

[0021] In another aspect, the application provides an aircraft comprising the above-described beam straight rod air speed tube.

[0022] Compared with the prior art, the application has the following advantages:

[0023] The application provides a new beam air speed tube / probe design method and design object different from the traditional protruding type, which utilizes the aerodynamic principle that the air flow in the leeward area of an object is relatively stable, takes into account the total pressure hole design, and the redundancy backup design of the total and static pressure holes, and improves the reliability and safety of the air speed tube / probe. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of air flow over the surface of an object Figure 1 ;

[0025] Figure 2 is a schematic diagram of air flow over the surface of an object Figure 2 ;

[0026] Figure 3 is a schematic diagram of the shape of the air speed tube after aerodynamic compensation design

[0027] Figure 4 is a schematic diagram of the flow pattern at the bottom of the object

[0028] Figure 5 is a schematic diagram of the flow pattern at the bottom of the object and the inner cavity Figure 1 ;

[0029] Figure 6 is a schematic diagram of the flow pattern at the bottom of the object and the inner cavity Figure 2 ;

[0030] Fig. 7(a) is a schematic diagram of the windward surface of the beam straight rod air speed tube of the application

[0031] Fig. 7(b) is a schematic diagram of the leeward surface of the beam straight rod air speed tube of the application

[0032] Figure 8 is a schematic diagram of the "physical average" method of pressure measurement

[0033] Figure 9 is a schematic diagram of the von Karman curve of the front surface of the probe

[0034] Figure 10is another schematic diagram of total pressure hole arrangement;

[0035] Figure 11 is a third schematic diagram of total pressure hole arrangement;

[0036] Figure 12 is a fourth schematic diagram of total pressure hole arrangement;

[0037] Figure 13 is total pressure data comparison;

[0038] Figure 14 is the installation form and two states of the air speed tube obtained by the method;

[0039] Figure 15 is the static pressure data of the leeward area. DETAILED DESCRIPTION

[0040] Basic principle:

[0041] According to the basic theory of aerodynamics, when the airflow flows through the object with a turn, an expansion wave (Prandtl-Meyer flow theory) will appear, as shown in Figure 4 ; and a relatively stable "backflow area" or "dead water area" will be formed behind the turn; the airflow in this area is relatively stable, and the pressure is also relatively stable. Using this characteristic, a static pressure stable measurement air speed tube / probe is designed.

[0042] There is also similar experience from previous aerodynamic force tests. The flow in the object cavity often has a certain stability; the bottom pressure measurement data is relatively stable. As shown in Figure 5 、 Figure 6 .

[0043] The technical solutions of the present application will be described in detail below in combination with the drawings and examples.

[0044] Examples

[0045] The embodiment of the present application discloses a cross beam, straight rod type air speed tube, whose configuration is shown in Figures 7(a) and 7(b).

[0046] The specific form and technical idea are described as follows:

[0047] 1. The probe body is an arc-shaped front surface (facing the incoming flow design), an equal straight body configuration; the inside is hollow to form a gas collection chamber, which includes a total pressure tube and a static pressure tube.

[0048] 2、Probe arc surface directly faces the airflow, the arc surface design should make the airflow flow more stable on the surface, without flow separation and other conditions, to facilitate the stable measurement of total pressure. Three total pressure holes are designed on the arc surface (the number is not necessarily strictly limited to three, two or four can also be used; but not one), and finally output a total pressure data value through physical averaging method. The purpose of this is: ① "physical averaging" of pressure data, as shown in Figure 8 . Multiple pressure measurement holes data are collected into a total pressure pipe, and finally output a pressure data value. After data averaging, the accuracy of the data is ensured to some extent; the output total pressure value will not be invalid or distorted due to abnormal data of a certain hole; ② Redundancy backup design. Even if a hole is blocked or fails, there are still total pressure holes that can work normally to ensure that reliable data is obtained.

[0049] The probe arc surface is designed using von Karman curve, as shown in Figure 9 , and its equation is as follows:

[0050]

[0051] ψ = arccos (1-2x / B)

[0052] In the formula: A = constant 1, B = constant 2.

[0053] The von Karman curve has the advantage of better reducing air resistance and reducing aerodynamic load. This method uses von Karman curve to design the probe front surface.

[0054] A concave cavity is formed in the direction opposite to the airflow. It is inwardly recessed to form a certain dead water area, which is beneficial to the stability of airflow and accurate measurement.

[0055] As a derivative form of total pressure hole design method - longitudinal arrangement, it is different from the transverse arrangement shown in Figure 7, and also has its unique advantages. As shown in Figure 10 , the right side of the figure can be thought of as when the probe flies with the aircraft at a changing angle of attack, the middle hole is a conventional total pressure hole, and the upper and lower holes are not total pressure holes. But when the angle of attack increases (positive or negative) to a certain angle, the total pressure detection capability of the conventional total pressure hole will inevitably decrease, and at this time the upper hole (or lower hole) can take on the role of continuing to detect the total pressure. In this way, the angle of attack range of total pressure detection is expanded. This feature is very important for aircrafts that need to fly at large angles of attack. Further, in an embodiment, there are at least five total pressure holes arranged in a cross shape, and one side of the cross shape is parallel to the cylindrical axis, and the other side is perpendicular to the cylindrical axis, and each total pressure hole is equally spaced, as shown in Figure 11 . Such a design takes into account the horizontal axis of the cylinder (transverse arrangement of Figure 7) and Figure 10Furthermore, in one embodiment, the cross-shaped total pressure holes are expanded to 3 rows and 3 columns or more rows and more columns, that is, n rows and n columns, and the total pressure holes are equally spaced, such as Figure 12 shown.

[0056] Depend on Figure 13 It can be seen that compared with the measurement results of the traditional "single total pressure hole", the total pressure measurement data of this method has a larger angle of attack range of the "data platform", namely: -α2—α2; this "data platform" is the total pressure data available during flight.

[0057] 3. Five static pressure holes are designed on the back of the probe (the number is not limited to 5, but should be greater than 2). These 5 holes are equidistantly arranged along the axis of the cylinder. The pressure data collected by multiple static pressure holes are converged through the static pressure tube to output an averaged static pressure data value. The basis or purpose of this design is: ① As described in the third part "Basic Principles", the flow in the leeward area is relatively stable, which is conducive to obtaining stable pressure data; ② As described in the above 2, "physical averaging" and redundant design of pressure data are performed;

[0058] 4. This type of probe can also be further designed to be easy to expand and contract to adapt to more flight scenarios and environments. Figure 14 In one embodiment, a motion mechanism is added to the mounting base of the pitot tube to enable the probe body to be deployed and retracted, which can be applied in scenarios such as stealth requirements and hypersonic flight.

[0059] 5. From the test data, if Figure 15 As shown, the static pressure data Cp-α curve at the back (leeward) side of the model remains essentially unchanged with angle of attack. Furthermore, when Ma < 1.0, the data does not change dramatically with changes in Ma. This indicates that the pressure values ​​measured at the designed static pressure measurement points are insensitive to changes in flight attitude and speed. This characteristic is beneficial for stable static pressure measurement during flight and is the primary objective of the design.

[0060] 6. Explain the significance and role of accurately measuring static pressure during flight:

[0061] a. To calculate the flight airspeed V, static pressure data is required.

[0062] As the following formula shows, calculating airspeed requires both total pressure and static pressure. Only by accurately acquiring both pressures can we determine an accurate airspeed (hence the name "pitot").

[0063]

[0064] Where: V is airspeed; P0 is total pressure; P∞ is static pressure; ρ is air density;

[0065] b, solve the flight height (barometric height), need to use static pressure data

[0066] As can be seen from the following formula, the barometric height is a function of static pressure. Only accurate static pressure data can be obtained to obtain accurate barometric height.

[0067]

[0068] In the formula: H p The barometric height; P is the static pressure.

[0069] Summary:

[0070] 1, the present application gives a new, different from the traditional forward type, beam type airspeed tube / probe design method and design of physical;

[0071] 2, the core idea is: using the object leeward flow relatively stable aerodynamic principle, to carry out the design work;

[0072] 3, taking into account the total pressure hole design, as well as the total, static pressure hole redundancy design, improve the reliability, safety of the probe;

[0073] 4, can be derived design into telescopic structure;

[0074] 5, as a further optimization, can be designed as an arc-shaped leeward area. The core idea is still hope that this area of flow is relatively stable, reduce the volatility of pressure data, improve the data measurement accuracy, stability.

[0075] Finally, it should be noted that the above examples are used to illustrate the technical solutions of the present application rather than limiting. Although the present application is described in detail with reference to the embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalent, without departing from the spirit and scope of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A beam straight rod type pitot tube, characterized in that: include: The probe body and the attached mounting base, where: The probe body is of straight configuration, with a hollow interior forming a gas collecting cavity, an arc-shaped front facing the airflow direction, and more than one total pressure hole is provided on the arc-shaped front; more than two static pressure holes are provided facing away from the airflow direction; The curved front is designed using the von Karman curve, satisfying the following formula: in, y is the vertical axis coordinate of the curve, x is the horizontal axis coordinate of the curve, is an intermediate variable, A and B are both constants; The cavity is formed opposite to the airflow direction.

2. The beam straight rod type pitot tube according to claim 1, characterized in that: The gas collecting chamber includes a total pressure pipe and a static pressure pipe, wherein the total pressure pipe is used to gather the pressure data collected by multiple total pressure holes and output an averaged total pressure data value; the static pressure pipe is used to gather the pressure data collected by multiple static pressure holes and output an averaged static pressure data value.

3. The beam straight rod type pitot tube according to claim 1, characterized in that: The arrangement of the total pressure holes on the arc front is: arranged at equal intervals along the cylindrical axis; or arranged at equal intervals along the perpendicular line of the cylindrical axis; or the total pressure holes are arranged in a cross shape with no less than 5 holes, and one side of the cross is parallel to the cylindrical axis and the other side is perpendicular to the cylindrical axis, and the total pressure holes are equally spaced; or the total pressure holes are arranged in a cross shape with equal intervals between the holes. , arranged in n rows and n columns with equal spacing, .

4. The beam straight rod type pitot tube according to claim 1, characterized in that: The static pressure holes facing away from the airflow direction are arranged equidistantly along the cylinder axis to obtain stable static pressure data.

5. The beam straight rod type pitot tube according to claim 1, characterized in that: The pitot tube realizes the expansion and contraction state of the probe body by adding a motion mechanism to the mounting base.

6. An aircraft, characterized in that: It comprises the cross-beam straight rod type pitot tube as described in any one of claims 1-5.

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