Technical Field

The present invention relates to a pitot tube that provides high accuracy of speed and altitude information designed for air vehicle.

Prior Art

In air vehicles used in military and civil aviation, pitot static tubes, which are placed on the vehicle and are also called Prandtl tubes, are used to obtain speed and altitude (height) information. In the system based on the basis of Bernoulli equation, the total pressure from the space of the tube at the nose and the air taken to form the static pressure data from the holes in the body at the lateral surface are transferred to the pressure sensors via pneumatic channels. The flight velocity is calculated by reaching the dynamic pressure information in the direction of the received signal. Altitude can be calculated directly from static pressure information through empirical correlations.

At speeds close to the sound velocity (Mach>~0.65) (transonic), especially the error of the static pressure measurements increases at a considerable rate as the speed increases due to the effect of pressure shock/ shocks on the nose of the conventional pitot tube geometry. Pressure shocks disrupt the laminar flow-viscous sublayer of the flow along the boundary layer, and this deterioration affects the pressure information from the openings in the middle of the lateral surface of the tube in general from which static pressure measurement is taken. To solve this problem today, especially static pressure measurements in civil aviation are carried out in static ports which have holes for measuring static pressure at one or more points on a suitable surface of air vehicles such as civil aircraft, jets and helicopters. For example, in air vehicles such as military jets traveling at speeds above 0.7 Mach and even at supersonic speed, tubes that are much longer than the conventional pitot tubes attached to the nose of the air vehicles usually have at least two different diameters are used. The small diameter section of the long tube is located on the front side and the total pressure measurement is carried out by air taken from the opening in the nose of this section. At high speeds, pressure shock / shocks occur in the nose region of the small diameter part. The holes for static pressure measurement are located on the larger diameter section and are located at a certain distance from the nose section so that they are not affected by shock waves. In some special pitot tube geometries, the presence of a large (curved) section at a short distance in the approximately middle part of the tube improves the static pressure measurements by distributing the pressure shocks generated in the nose portion, preventing it from reaching the static pressure openings behind the tube. Because of pressure shock and boundary layer interactions, static and total pressure errors due to geometry and flow can be reduced to acceptable levels in use through correction factor / factors obtained as a result of calibration for long tubes with two different diameters used for both conventional pitot tubes and high speeds.

In the United States patent document no US5099686, a sensor and a method for measuring the relative speed of the incoming environment has been mentioned. In the invention mentioned in the document, the air data for the total pressure measurement in the pitot static probe having a conical geometry similar to the invention of the present patent application is again provided from the opening at the end of the nose geometry, but the static pressure measurement is provided through the holes facing to the back part of the conical nose geometry not upright to flow. There is a significant diameter narrowing in passing to the probe body from the nose described in the document. This will also cause large errors in the measurement of the static pressure, which is the vortex effect of the parts where static holes are present.

Brief Description of the Invention

The aim of the present invention is to realize a pitot tube designed for air vehicles which ensures that the speed and altitude information with high accuracy.

Another aim of the present invention is to realize a pitot tube which allows high speed and altitude information to be acquired with high accuracy without having to calibrate the static pressure and total pressure measurements for the transonic (near sonic) speed range.

Detailed Description of the Invention

"A Pitot Tube That Provides Speed and Altitude Information for Air Vehicles" to achieve the purpose of this invention is shown in the attached figures, from these figures;

Figure 1 Schematic perspective view of an application of the pitot tube subject of the invention;

Figure 2 Schematic perspective view of another application of the pitot tube subject of the invention;

Figure 3 Schematic perspective view from above of the pitot tube subject of the invention;

Figure 4 Schematic front view of an appointment of the pitot tube subject of invention,

Figure 5 The graph showing the variation of the error values obtained from the transonic wind tunnel tests (symbols) and the CFD (Computational Fluid Dynamics) simulations / analyzes (lines) using the pitot tube subject of the invention for air pressure measurements for static pressure measurements; Figure 6 The graph showing the changes at the error values obtained from the transonic wind tunnel tests (symbols) and the CFD simulations / analyzes (lines) to the air speed by using the pitot tube subject of the invention for the total pressure measurements.

The parts in the figures are numbered individually and the correspondences of these numbers are given below.

1. Pitot tube

2. Cylindrical body

3. Cylindrical opening

4. Measurement of total pressure opening

5. Flat surface intersecting perpendicular to the flow

6. Smooth passing formed surface

7. Static pressure measurement opening

8. Total pressure measurement air duct

9. Static pressure measurement air duct

10. Mounting item

D: cylindrical body diameter

d: cylindrical opening diameter

t: flat section width

r: curvature radius of the smooth -pas sing formed surface

L: the distance between the static pressure measurement opening and the flat surface perpendicular to the flow on which the cylindrical body extends in longitudinal direction

a: the conical angle between the inclined surface of the conical region and the cylindrical body

A pitot tube (1) for obtaining information on speed and altitude for air vehicles includes following; a cylindrical body (2) having a region having a specific diameter (D) and having a conical nose extending narrowly at a certain angle (a) from the end of the region and having said specific diameter (D) and extending along a longitudinal axis, a cylindrical opening (3) which is opened on the nose of the cylindrical body (2) in narrowing diameter, and extending over the same longitudinal axis as the cylindrical body (2) concentrically with the cylindrical body (2) in a form not exceeding the nose and having a specific diameter (d), for the total pressure measurement, through which air flow can enter,

at least one total pressure measurement opening (4) which is located on the wall perpendicularly to the longitudinal axis extent of the cylindrical opening (3) opened for measuring the total pressure on the nose of the cylindrical body (2), and which provides for the intake of the air necessary to carry out the total pressure measurement,

a flat surface (5) having a certain width (t) completely surrounding the end portion of the cylindrical opening (3) located on the nose opposite to the body (2) and perpendicularly intersecting the incoming flow to the nose,

smooth passing formed surface (6) which is made by forming a total pressure opening (3) on the nose and a flat surface (5) perpendicular to the flow and a certain radius (r) in the combination of the body (2),

at least one static pressure measuring opening (7) which is located at a certain distance (L) along the axis of the cylindrical body (2) extending from the end of the flat surface (5) over the region of the cylindrical body (2) having a certain diameter (D) of the cylindrical body (2) and which provides taking the incoming air flow necessary for the static pressure measurement,

at least one total pressure measurement air duct (8) extending in the cylindrical body (2), connected to total pressure measurement opening (4) from one end and to a total pressure sensor (not shown in Figures) from the other end, and carrying air taken from total pressure measurement opening (4) to the total pressure sensor in order to obtain velocity and altitude information and

at least one static pressure measurement air duct (9) extending in the cylindrical body (2), connected to static pressure measurement opening (7) from one end and to a static pressure sensor (not shown in Figures) from the other end, and carrying air taken from static pressure measurement opening (7) to the static pressure sensor in order to obtain velocity and altitude information (Figure 1). In the pitot tube (1) subject of invention; the ratio of the diameter (d) of the cylindrical opening (3) to the diameter (D) of the region of the cylindrical body (2) having a specific diameter (D), (d/D) is between 0.35 and 0.45.

In the pitot tube (1) subject of invention; the ratio of the sum of two folds (t) of the width (t) of the flat surface (5) forming the nose perpendicular to the flow from the cylindrical opening (3) and diameter (d) of the cylindrical opening (3) to the diameter (D) of the region having a specific diameter to the cylindrical body (2), ((d+2t) /D) is between 0.62 and 0.7. In the pitot tube (1) subject of invention; the ratio of the radius (r) of the smooth passing formed surface (6) on the nose to the diameter (D) of a region having a specific diameter of the cylindrical body (2), (r/D) is between 0.1 and 0.14.

In the pitot tube (1) subject of invention; the specific conical angle (a) of the inclined surface corresponding to the diameter (D) of the region having a specific diameter of the cylindrical body (2) with conical passing of the nose having relative narrow diameter (D) nose is maximum 8° and minimum 3°.

In the pitot tube (1) subject of invention; the ratio of the distance (L) between the flat surface (5) on the nose of the cylindrical body (2) and the static pressure measurement opening (7) to the diameter (D) of the region of the cylindrical body (2) having a certain diameter (D), (L/D) is maximum 6.

By virtue of the above-mentioned geometrical properties of the pitot tube (1) subject of the invention, the effect of pressure shocks around the conical passing region of the flat surface (5) and the cylindrical body (2) is considerably reduced. Thus, measurement is made with the incoming air taken from the total pressure measurement openings (4), so that speed and altitude information are obtained at high accuracy, especially at the transonic speed range, without need of any calibration.

In the preferred application of the invention, the diameter (D) of the region of the cylindrical body (2) having a certain diameter (D) is between 5mm and 15mm.

In the preferred application of the invention, the pitot tube (1) comprises at least four, at most eight total pressure measurement openings (4).

In the preferred application of the invention, the axis of the total pressure measuring opening (4) is parallel to the axis which extends longitudinally through cylindrical body (2).

In another application of the invention, the axis of the total pressure measuring opening (4) is at most 75° with the axis extending longitudinally of the cylindrical body (2). The pitot tube (1) subject of invention further comprises at least one heater (not shown in Figures) configured to prevent the icing of the total pressure measurement opening (4) and the static pressure measurement opening (7) contained in the cylindrical body (2). The pitot tube (1) subject of invention further comprises at least one mounting item (10) fixed to the cylindrical body (2) from one end and secured to a suitable location of the air vehicle from the other end in order to provide connection on air vehicle (Figure 2). In the preferred application of the invention, the mounting item (10) connects the pitot tube (1) in such a way that its axis extending longitudinally from the cylindrical body (2) is parallel to the axis of the air vehicle. The graphs in Figures 5 and 6 show static and total pressure errors, respectively, obtained from CFD (Computational Fluid Dynamics) analyzes and high speed wind tunnel tests, respectively, of a pitot tube (1) according to the invention in the direction of the geometric ratios described above. The values expressed by the line represent the values obtained from the CFD solutions and the symbols represent the experimental data. In the graphs, wind tunnel tests are available for Mach values between 0.5 and 0.8, while CFD analysis results are available for Mach values between 0.5 and 0.95. As can be seen from the described graphs, the total and static pressure measurement error carried out with a pitot tube subject of the invention according to the test results is approximately ±0.1 % (Figure 5 and 6).

Around this basic concepts, it is possible to develop a wide variety of applications relating to the invention "A Pitot Tube Providing Speed and Altitude Information for Air Vehicles" and the invention cannot be limited to the examples mentioned herein, it is essentially as indicated in the claims.