The present invention relates to a pressure altering surface for a dynamic pressure sensing apparatus for use in determining the airspeed of a vehicle, such as but not limited to an aircraft.

Background to the Invention

Pitot-static systems for determining the airspeed of aircraft are well known, whereby air pressure measurements are obtained from a pitot tube and a static port, or a pitot-static tube, for conversion into an airspeed measurement that is displayed on an airspeed indicator. The pressure measured by the static port is static pressure. The pressure measured in the pitot tube is referred to as pitot pressure, and is a measure of ram air pressure into the tube. In an analogue airspeed indictor, the instrument is connected to both the pitot and static pressure sources, whereby the ram air from the pitot tube enters a pressure diaphragm of the instrument, and the static pressure in the airtight casing surrounding the diaphragm is vented to the static port. As the airspeed increases, the ram air pressure increases. The difference between the pitot pressure and the static pressure, i.e. the dynamic pressure, correlates to the airspeed and is conveyed to the needle of the airspeed indicator from the diaphragm via a mechanical linkage. In a digital system, an Air Data Computer (ADC) is connected to the pitot and static pressure sources and performs the calculation of airspeed for display on a digital instrument.

Pitot-static systems have a number of drawbacks. Pitot tubes project from the front section of aircraft and face forward in a fixed orientation. If the tube becomes blocked, for example by ice, water, insects or other obstructions, this will cause the airspeed indicator to register an increase in airspeed when the aircraft climbs as the pressure in the pitot pressure will remain constant while the static pressure decreases. When descending the reverse occurs, whereby airspeed indicator will show a decrease in airspeed. Summary of the Invention

In accordance with an aspect of the invention there is provided a pressure altering surface for use in an airspeed measurement system of an aircraft, the pressure altering surface comprising a fluid engaging exterior surface, the fluid engaging outer surface having a portion that is substantially domed in profile and configured to induce a pressure drop in the vicinity of the apex of the dome.

Optionally, the domed portion has circular symmetry.

Optionally the domed portion is a spherical dome.

Optionally the domed portion is an oblate spheroidal dome.

It will be understood that within this description, the terms “the dome” and “the domed portion” are synonymous and interchangeable.

Optionally, the pressure altering surface is the outer surface or airstream engaging surface of a pressure sensing apparatus.

Advantageously, in use, airflow passing over the vicinity of the apex of the dome is substantially transverse the dome. In other words, the dome projects substantially orthogonally relative to the incident airflow such that the velocity of the airflow is increased as it passes over the dome, the maximum velocity being reached at or proximate the apex of the dome.

Optionally, the pressure altering surface comprises a pressure sensing means associated with the domed portion.

Advantageously, the pressure sensing means is configured to measure the total pressure (po) in the vicinity of the domed portion.

Optionally, the pressure sensing means associated with the domed portion is a surface mounted pressure sensor. Optionally, the surface mounted pressure sensor is located substantially at the apex of the domed portion

Optionally, the pressure sensing means associated with the domed portion is a pressure sensor in fluid communication with an aperture provided in the dome.

Optionally, the aperture provided in the dome is located substantially at the apex of the dome.

Optionally, the pressure sensor is in fluid communication with the aperture in the dome via a conduit extending between the pressure sensor and the aperture.

Advantageously, the pressure sensor in fluid communication with the aperture is configured to measure the total pressure (po) at the dome in the vicinity of its apex. Optionally, the pressure sensor in fluid communication with the aperture in the dome is offset with respect to a longitudinal central axis of the aperture so that the conduit extending between the pressure sensor and the aperture slopes downwardly from the pressure sensor to the aperture in use.

Optionally, the fluid engaging exterior surface of the pressure altering surface is substantially in the form of a flush fitting mounting plate contoured to fit flush with a surrounding aircraft surface at the perimeter of the pressure altering surface.

Optionally, the mounting plate defines a portion of a surface of an aircraft fuselage.

Advantageously, the domed portion projects outwardly from the fluid engaging outer surface to project proud of a surrounding aircraft surface in use.

Optionally, the domed portion is formed in the mounting plate so that its perimeter is fillet formed or blended with said mounting plate.

The mounting plate may have any suitably shaped outline.

Optionally, the mounting plate has a substantially quadrilateral outline. Optionally, the mounting plate has a substantially circular outline.

Optionally, the air flow conduit and associated pressure sensor are enclosed within a housing.

Optionally, the housing is demountably secured to the underside of the mounting plate.

Conveniently, the pressure sensing means is configured to generate signals that are representative of the total pressure (po) measured.

Optionally, the pressure altering surface further comprises a static port, the static port being spaced apart from the domed portion.

Optionally, the static port is in communication with a static pressure sensor for the measurement of static pressure (p).

Conveniently, the static pressure sensor is configured to generate signals that are representative of the static pressure (p) measured.

Optionally, the signals representative of total pressure (po) and/or of static pressure (p) are transmittable to a data processor, for example an Air Data Computer (ADC) of an aircraft.

Optionally, the pressure sensing means is in communication with signal conditioning and/or processing components to receive and condition/process the signal representative of total pressure (po) and/or of static pressure (p) prior to communication to the data processor or ADC.

In accordance with a further aspect of the invention there is provided an airspeed measurement system for an aircraft comprising: an air data processor; and one or more pressure altering surfaces, wherein the or each pressure altering surface comprises a fluid engaging exterior surface, the fluid engaging outer surface having a portion that is substantially domed in profile and configured to induce a pressure drop in the vicinity of the apex of the dome.

Optionally, the domed portion has circular symmetry.

Optionally, the domed portion is a spherical dome.

Optionally, the domed portion is an oblate spheroidal dome.

Advantageously, the airflow in the vicinity of the apex of the dome is substantially transverse the dome.

Advantageously, the domed portion is configured to induce a pressure drop in the airflow over the sensing apparatus in use.

Optionally, the dome may be provided with a heating means to prevent or mitigate the formation of ice.

Optionally, the heating means is an electrical resistance heating element.

Optionally, the pressure altering surface comprises a pressure sensing means associated with the domed portion.

Advantageously, the pressure sensing means is configured to measure the total pressure (po) in the vicinity of the domed portion.

Optionally, the pressure sensing means associated with the domed portion is a surface mounted pressure sensor.

Optionally, the surface mounted pressure sensor is located substantially at the apex of the domed portion

Advantageously, the surface mounted pressure sensor is configured to measure the total pressure (po) at the dome in the vicinity of its apex. Optionally, the pressure sensing means associated with the domed portion is a pressure sensor in fluid communication with an aperture provided in the dome.

Optionally, the aperture provided in the dome is located substantially at the apex of the dome.

Optionally, the pressure sensor is in fluid communication with the aperture in the dome via a conduit extending between the pressure sensor and the aperture.

Advantageously, the pressure sensor in fluid communication with the aperture is configured to measure the total pressure (po) at the dome in the vicinity of its apex.

Optionally, the pressure sensor in fluid communication with the aperture in the dome is offset with respect to a longitudinal central axis of the aperture so that the conduit extending between the pressure sensor and the aperture slopes downwardly from the pressure sensor to the aperture in use.

Optionally, the fluid engaging exterior surface of the pressure altering surface is substantially in the form of a flush fitting mounting plate contoured to fit flush with a surrounding aircraft surface at the perimeter of the pressure altering surface.

Optionally, the mounting plate defines a portion of a surface of an aircraft fuselage.

Advantageously, the domed portion projects outwardly from the fluid engaging outer surface to project proud of a surrounding aircraft surface in use.

Optionally, the domed portion is formed in the mounting plate so that its perimeter is fillet formed or blended with said mounting plate.

The mounting plate may have any suitably shaped outline.

Optionally, the mounting plate has a substantially quadrilateral outline.

Optionally, the mounting plate has a substantially circular outline. Optionally, the air flow conduit and associated pressure sensor are enclosed within a housing.

Optionally, the housing is demountably secured to the underside of the mounting plate.

Conveniently, the pressure sensing means is configured to generate signals that are representative of the total pressure (po) measured.

Optionally, the pressure altering surface further comprises a static port, the static port being spaced apart from the domed portion.

Optionally, the static port is in communication with a static pressure sensor for the measurement of static pressure (p).

Conveniently, the static pressure sensor is configured to generate signals that are representative of the static pressure (p) measured.

Optionally, the signals representative of total pressure (po) and/or of static pressure (p) are transmittable to the air data processor.

Optionally, the pressure sensing means is configured to generate signals that are representative of the total pressure (po) measured and is configured to transmit the signals representative of total pressure (po) to said data processor for use in calculation of airspeed.

Optionally, the pressure sensing means communicates with signal conditioning and/or processing components to receive and condition/process the signal representative of total pressure (po) and/or of static pressure (p) prior to communication to the data processor or ADC.

In accordance with an aspect of the invention there is provided a dynamic pressure measurement apparatus comprising a pressure altering surface in accordance with the aforementioned aspects of the invention. In accordance with a further aspect of the invention there is provided a method for determining the airspeed of an aircraft comprising the steps of: measuring total pressure (po) at a substantially domed surface of a pressure altering surface provided on a surface of an aircraft, wherein the domed surface projects outwardly from the surface of said aircraft; generating a signal representative of the total pressure (po) measured at the substantially domed surface of the pressure altering surface; generating a signal representative of the static pressure (p) measured at a static port; collecting at a location remote from the substantially domed surface and the static port the signals representative of the total pressure (po) and the static pressure (p); calculating at the remote location the dynamic pressure ( q ) at the substantially domed surface; and calculating the airspeed of the aircraft.

Optionally, for example to compensate for the effect of aircraft yaw angle, the method for determining the airspeed of an aircraft may comprise the further step of measuring total pressure (po) at a domed surface of a second pressure altering surface provided at a corresponding location on an opposing side of an aircraft from the first pressure altering surface, wherein the domed surface of the second pressure altering surface projects outwardly from the surface of said aircraft; generating a signal representative of the total pressure (po) measured at the substantially domed surface of the second pressure altering surface; generating a signal representative of the static pressure (p) measured at a static port; collecting at a location remote from the substantially domed surface of the second pressure altering surface and the static port the signals representative of the total pressure (po) and the static pressure (p); calculating at the remote location the dynamic pressure (q) at the substantially domed surface of the second dynamic pressure sensing apparatus; and calculating the airspeed of the aircraft based on the measurements for dynamic pressure (q) obtained via the first and second domed surfaces. Optionally, the step of calculating the airspeed of the aircraft based on the measurements for dynamic pressure ( q ) obtained via the first and second domed surfaces comprises blending the measurements.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination.

Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word “comprise” or variations thereof such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of”, "consisting", "selected from the group of consisting of”, “including”, or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non- essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

Any references to directional and positional descriptions such as, upper, lower, proximal, distal, inside, outside, rear, and directions e.g. “vertical”, and “horizontal” etc. are to be interpreted by a skilled reader in the context of the examples described to refer to the orientation of features shown in the drawings, and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee.

Brief description of the drawings

In the drawings:- Figure 1 is a schematic side elevation of an exemplary aircraft forward fuselage incorporating a pressure altering surface of a dynamic pressure sensing apparatus for use with in the airspeed measurement system of an aircraft;

Figure 2 is a schematic plan view of the exemplary aircraft forward fuselage of Figure 1;

Figures 3a, 3b and 3c are schematic perspective views of examples of a pressure altering surface in accordance with the invention;

Figures 4 and 5 are schematic cross-section views of exemplary dynamic pressure measuring apparatuses comprising pressure altering surfaces in accordance with the invention; and

Figure 6 is a schematic perspective view of a pressure altering surface including a static pressure port.

Detailed description

With reference to Figures 1 and 2, there is shown a forward fuselage section of an exemplary aircraft 1 incorporating a pressure altering surface 10. The pressure altering surface 10 is located at a position on the fuselage which will vary depending on aircraft model. The pressure altering surface 10 may be the airstream-engaging surface of a dynamic pressure sensing apparatus.

The pressure altering surface 10 comprises a mounting plate 11 having a fluid engaging exterior surface 12. The mounting plate is a flush fitting mounting plate, contoured to fit flush with the surrounding aircraft surface 2. The fluid engaging outer surface 12 has a substantially domed portion 13, the substantially domed portion projecting outwardly from the surface 12 so that it projects proud of the surrounding aircraft surface 2 in use.

In the exemplary Figures 1 3a and 3c, mounting plate 11 is shown having a substantially quadrilateral outline however it should be understood that the mounting plate is not limited to having a substantially quadrilateral outline but may have other suitably shaped outline, for example a substantially circular outline as shown in Figure 3b.

As shown by way of example in Figure 3a, mounting plate 11 may also comprise a plurality of suitably arranged mounting holes 20 to enable fastening of the dynamic pressure sensing apparatus to the structure of an aircraft. Preferably, mounting holes 20 are countersunk.

The domed portion 13 is formed in the mounting plate 11 so that its perimeter 14 is aerodynamically blended with said mounting plate 11. The aerodynamic blend helps mitigate stagnation of incident airflow at the transition between the domed portion and the surrounding mounting plate. The aerodynamic blend also ensures that the incident airflow moves smoothly over the domed portion.

In use, incident airflow is substantially transverse across the pressure altering surface as shown in Figure 2.

The height of the dome 13 is such that it extends outwardly from the surface 2 of an aircraft 1.

The domed portion 13 induces a pressure drop in the airflow in the vicinity of its apex in use. This is achieved by the dome causing the incident airflow to increase in velocity as it passes over the dome, the maximum velocity being reached at or proximate the apex of the dome.

Preferably the domed portion 13 has circular symmetry. This assists in maintaining consistent flow characteristics of incident airflow over the dome 13 regardless of the angle of attack of the aircraft.

Optionally the domed portion 13 is a spherical dome.

Optionally the domed portion 13 is an oblate spheroidal dome.

The domed portion is dimensioned dependent upon the aircraft type with which the pressure altering surface is to be used, with the radius of and/or height of the dome being tailored to enable accurate dynamic pressure measurement within the anticipated operating airspeed range of the aircraft.

Optionally the trailing edge of the dome may be a faired, i.e. include a fairing, or may include a suitable aerodynamic feature to reduce the drag created by the dome.

The dome 13 may be formed in the mounting plate by press forming, for example when the mounting plate 11 is made from aluminium or other metal or metal alloy. Alternatively, the domed portion 13 may be formed in the mounting plate by vacuum or other suitable forming means, for example where the mounting plate is made from composite or polymeric material.

As shown in Figure 4, the dome may be provided with a heating means 21 to prevent or mitigate the formation of ice. The heating means may be any suitable heating means, for example, but not limited to, an electrical resistance heating element.

As shown by way of example in Figures 3a - 3c, the pressure altering surface apparatus comprises a pressure sensing means associated with the domed 13 portion.

The pressure sensing means is configured to measure the total pressure (po) in the vicinity of the domed portion. Together, the pressure altering surface and the pressure sensing means provide a pressure sensing apparatus.

In one example as shown schematically in Figure 3c, the pressure sensing means associated with the domed portion may be a surface mounted pressure sensor 15b.

Surface mounted pressure sensor 15b may include any suitable surface mounted pressure sensing device as will be understood by those of skill in the art.

The surface mounted pressure sensor 15b may be located substantially at, near or overlapping the apex of the domed portion 13. Surface mounted pressure sensor 15b is configured to measure the total pressure (po) at the dome 13. In the example shown in Figures 3a, 3b and 4a, the pressure sensing means associated with the domed portion 13 is a pressure sensor 17 (shown in Figure 4) in fluid communication with an aperture 15a provided in the dome. Aperture 15a may be located substantially at, near or overlapping the apex of the domed portion 13.

With reference to Figure 4, aperture 15a is in fluid communication with a conduit 16, the conduit 16 extending from aperture 15a to pressure sensor 17. The conduit 16 and pressure sensor 17 are enclosed within a housing 18. Housing 18 may be demountably secured to the underside of the mounting plate 11. Housing 18 locates within the aircraft fuselage in use.

Optionally, conduit 16 slopes downwardly towards the aperture 15a when the apparatus is positioned at an in use orientation as shown in Figure 5. For example, the pressure sensor 17 may be located or offset with respect to a longitudinal central axis 19 of the aperture 15a so that the conduit 16 slopes downwardly from the pressure sensor 17 to the aperture 15a when the apparatus is positioned at an in use orientation. The slope of the conduit 16 permits debris or water or other liquid contaminants to flow from the conduit 16 and out of the dome thus mitigating blockage of the conduit.

Pressure sensor 17 is configured to measure the total pressure (po) at the dome 13.

Pressure sensor 17 may include any suitable pressure sensing device as will be understood by those of skill in the art.

The pressure sensor 17 or surface mounted pressure sensor 15b generates a signal that is representative of the total pressure (po) measured. This signal representative of total pressure is sent to a data processor, for example an Air Data Computer (ADC) 30 of an aircraft. The signal may be analogue or digital, or may be converted from analogue to digital by analogue to digital converter either before, or by, the data processor or ADC 30. Suitable signal conditioning and/or processing components may be provided to receive and condition/process the signals prior to communication to the data processor or ADC 30. It will be understood the art that the pressure altering surface 10 in accordance with the invention as described above may be the airstream engaging surface of a dynamic pressure sensing apparatus 50 in accordance with a further aspect of the invention, for example as indicated generally in Figures 4 and 5.

With reference to Figure 2, the total pressure (po) measured at the dome 13 is the sum of the static pressure (p) acting upon the dome, and the dynamic pressure ( q ) as a result of the airflow across the dome. This is expressed by Bernoulli's principle and simplified as po = p + q

While the static pressure will be a positive value, the dynamic pressure will be a negative value as the airflow across the dome induces a pressure drop in conduit 16 or at the surface mounted pressure sensor 15b, where applicable.

A static port 40 and associated static pressure sensor 41 spaced apart from the dome 13 as shown by way of example in Figures 1 and 4 provides a reference value corresponding to the static pressure (p), and a signal representative of the measured static pressure is also sent to the data processor ADC 30.

Such a static port 40 and associated static pressure sensor 41 may be provided integrally with the pressure altering surface as shown by way of example in Figure 6, in which the static port 40 is formed in the mounting plate 11 at a position spaced apart from the domed portion 13.

By subtracting the reference value corresponding to the static pressure (p) from the total pressure (po) measured by pressure sensor 17 or surface mounted pressure sensor 15b, the data processor or ADC can calculate the dynamic pressure (q).

As will be understood by persons skilled in the art, there are a number of possible equations which can used by an ADC for calculating air speed velocity on the basis of a dynamic pressure measurement in a known manner.

A second pressure altering surface 10 may also be provided at a corresponding location B (Figure 2) on the opposing side of an aircraft from the first pressure altering surface. Thus readings for dynamic pressure can be obtained from both sides of an aircraft, which may differ due to the effect of an aircraft’s yaw angle, and the difference between the values measured or obtained from the first and second pressure altering surfaces 10 can be used to calculate the airspeed, or a yaw-angle compensated airspeed.

As will be understood by persons skilled in the art, alternative equations, for example refined to take into account the compressibility of airflow, can also be used, as can empirically derived values of dynamic pressure ( q ) at the dome at various airspeeds. In any event, the computed airspeed value can be conveyed to the cockpit for display on the cockpit instrumentation.