Patent Publication Number: US-2015059465-A1

Title: Aerodynamic measurement probe for aircraft

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to foreign French patent application No. FR 1302016, filed on Aug. 30, 2013, the disclosure of which is incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to an aerodynamic measurement probe intended to equip an aircraft. 
     BACKGROUND 
     Piloting any aircraft entails knowing the modulus of its relative speed, more precisely of its conventional speed relative to the air, that is to say to the relative wind. This speed is determined using probes for measuring the static pressure Ps and the total pressure Pt. Pt−Ps gives the modulus of this conventional speed vector. This aerodynamic parameter makes it possible to determine the modulus of the speed of any aircraft, such as, for example, an aeroplane, a helicopter or an unmanned craft such as a drone. 
     The measurement of the total pressure Pt is usually done using a so-called Pitot tube. This is a tube that is open at one of its ends and blocked at the other. The open end of the tube substantially faces into the flow. 
     The stream of air situated upstream of the tube is progressively slowed down until it reaches an almost zero speed at the tube inlet. The slowing down of the speed of the air increases the air pressure. This increased pressure forms the total pressure Pt of the air flow: inside the Pitot tube, the air pressure prevailing therein is measured. 
     The duly determined speed can also be expressed as a Mach number M, that is to say its ratio to the speed of sound in the air surrounding the aircraft. This speed of sound is itself a function of the static temperature of the air. 
     On board a fast aircraft, the static temperature of the surrounding air is very difficult, even impossible, to measure. It would entail placing a temperature sensor at the bottom of a hole substantially at right angles to the outer surface of the aircraft in an area where the outer surface is substantially parallel to the flow of air with a local speed close to the upstream speed. This temperature sensor would notably be disturbed by the temperature of the outer surface which would risk corrupting the static temperature measurement. It is therefore preferable to measure the total temperature Tt of the flow of air by placing the temperature sensor in the flow of air by means of a tube similar to a Pitot tube. 
     The total temperature is a function of the static temperature and of the speed of the flow always expressed as a Mach number M. 
     The Pitot tubes and the total temperature measurement probes both have a tube facing into the flow. Based on the atmospheric conditions in which the aircraft can move, provision is made to trap the water likely to penetrate into the tube. Drain holes make it possible to discharge the duly trapped water. To be able to operate in icy conditions, the tube is electrically reheated. The reheating prevents the tube from being blocked by ice, during flights in icy conditions. The reheating also makes it possible to avoid the formation and the build-up of ice in the drain holes which would be detrimental to their role of discharging water penetrating into the tube in flight or on the ground. The dimensioning of the reheating is notably performed as a function of the atmospheric conditions that the probe may be required to encounter, as a function of the quantity of water that the probe is likely to ingest and as a function of the heat exchanges with the flow that the probe may be subjected to. 
     The electrical power needed for the reheating of such a probe can be as much as several hundreds of watts. 
     SUMMARY OF THE INVENTION 
     The invention aims to propose a novel aerodynamic measurement probe with reduced electrical consumption while retaining the same level of performance. The invention seeks to limit the penetration of particles of ice or of supercooled liquid water in the tube. Thus, it is possible to very significantly reduce the reheating. 
     To this end, the subject of the invention is an aerodynamic measurement probe intended to equip an aircraft, the probe comprising a tube intended to face substantially into a flow of air along the aircraft, the tube being open at a first of its ends, a transmitter for emitting an electromagnetic wave directed towards a free zone situated in the extension of the tube on the side of the open end, the electromagnetic wave making it possible to reheat the water likely to be located in the free zone. 
     The probe can comprise temperature measurement and/or pressure measurement means. 
     In an advantageous configuration of the invention, the electromagnetic wave is directed towards the free zone by the inside of the tube. This arrangement also makes it possible to reheat the walls of the tube and makes it possible to eliminate any particles of ice (or of supercooled water) that might have penetrated into the tube. The reheating of the walls of the tube makes it possible to dispense with any heating resistor incorporated in the walls of the tube, or at the very least to limit its use. The means for emitting the electromagnetic wave can be positioned inside the tube or outside while retaining a path of the electromagnetic wave via the inside of the tube upstream of the free zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, and other advantages will become apparent, on reading the detailed description of an embodiment given as an example, the description being illustrated by the attached drawing in which: 
         FIG. 1  represents an aerodynamic measurement probe comprising total pressure measurement means; 
         FIG. 2  represents an aerodynamic measurement probe comprising total temperature measurement means; 
         FIG. 3  represents an aerodynamic measurement probe comprising total pressure and total temperature measurement means; 
         FIG. 4  represents a mobile aerodynamic measurement probe; 
         FIG. 5  represents a variant aerodynamic measurement probe comprising total pressure measurement means. 
     
    
    
     In the interests of clarity, the same elements will bear the same references in the different figures. 
     DETAILED DESCRIPTION 
     The probe  10  represented in  FIG. 1  makes it possible to measure the total pressure of a flow of air circulating along the outer surface  11  of an aircraft. The probe  10  comprises a base  12  intended to be fixed onto the outer surface  11 , for example by means of screws  13 . The base  12  is essentially formed by a plate fixed in the extension of the outer surface  11 . The probe  10  essentially comprises a Pitot tube  14  secured to a strut  15  linking the Pitot tube  14  to the base  12 . Aerodynamic measurement probes are found positioned at different points of an aircraft, such as, for example, at the nose of the aircraft, fixed to its outer surface, often called skin of the aircraft. There are also probes in the air inlet of an engine of the aircraft. The invention can be implemented for any type of probe whatever its position on the outer surface of the aircraft. 
     The strut  15  for example has a wing profile having a plane of symmetry, situated in the plane of the figure. The profile of the wing at right angles to its leading edge  16  is, for example, a profile with low overspeed. In the example represented, the leading edge is substantially rectilinear. It is obvious that other strut shapes can be used to implement the invention. 
     The Pitot tube  14  comprises a tube  18  extending between two ends, one  20  open and the other  21  blocked, the tube extends substantially rectilinearly along an axis  22  between its two ends  20  and  21 . 
     The probe  10  is positioned on the outer surface  11  of the aircraft so as to face substantially into the flow of air circulating along the base  12  when the aircraft is in flight. In other words, the probe is configured to perform an aerodynamic measurement of a flow of air along the base  12 . A stream of air of the flow situated upstream of the tube is progressively slowed down until it reaches an almost zero speed at the inlet of the tube. The slowing down of the speed of the air increases the air pressure. This increased pressure forms the total pressure Pt of the flow of air. 
     The Pitot tube  14  comprises a pressure tap  24  positioned inside the tube  18  on the axis  22  between the two ends  20  and  21 . The pressure tap  24  measures the pressure prevailing inside the tube  18 . The pressure tap  24  is linked to a pressure sensor, not represented, which can be positioned inside the outer surface  11  of the aircraft. In this case, the pressure tap  24  is linked to the pressure sensor via an aeraulic channel  25  arranged in the strut  15  between the tube  18  and the base  12 . 
     The Pitot tube  14  can comprise a few drain holes  26  arranged crossing the tube  18  and making it possible to discharge any solid or liquid particles likely to penetrate inside the tube  18 . 
     According to the invention, the probe  10  comprises means for emitting an electromagnetic wave directed towards a free zone  28  situated in the extension of the tube  18  on the side of the open end  20 , the electromagnetic wave making it possible to reheat the water situated in the free zone. In other words the means for emitting are a transmitter, The water to be reheated can consist of liquid water droplets, in the supercooled state or not, or of ice crystals present in the atmosphere, in a cloud. The electromagnetic wave advantageously has a sufficient power to reheat these water droplets and transform the ice crystals into liquid water upstream of the end  20 . In severe cases of icy conditions, the flow may contain supercooled water droplets. The electromagnetic wave then reheats the supercooled water droplets, converting them into normal liquid water droplets which do not risk solidifying abruptly upon impact with a part of the probe. It is thus possible to reduce, in all cases, the power needed to reheat the probe. In the same atmospheric conditions, it has been found, that by implementing the invention, the sum of the powers needed to power the means for emitting an electromagnetic wave and for a residual reheating of the probe remains less than the power needed for a conventional reheating that is necessary in a probe with no means for emitting an electromagnetic wave. 
     Furthermore, inside a conventional Pitot tube, there is positioned a water trap making it possible to prevent the water penetrating into the tube from penetrating more deeply into the aeraulic channels. The water trap is linked to a drain hole passing through a wall of the tube and making it possible to drain the duly trapped water. By implementing the invention, because of the lesser penetration of water into the tube, it is possible to significantly reduce the dimensions of the water trap and of the drain hole. 
     Any electromagnetic wave transporting energy in sufficient quantity to reheat water can be implemented in the invention. The wavelength of the electromagnetic wave is advantageously chosen to excite mainly the molecules of water so as to enable them to vaporize. It is for example possible to use an electromagnetic wave in a frequency band used in the radar systems. The means for emitting an electromagnetic wave can be situated inside or outside the probe  10  in immediate proximity thereto. These means are dedicated to the reheating of the water likely to be located in the free zone  28 . 
     Tests carried out on the premises of the applicant have shown that an infrared light electromagnetic wave is particularly well suited. An incoherent wave can be implemented in the invention. Advantageously, the electromagnetic wave is a laser beam that can be easily collimated towards the free zone  28 . 
     Advantageously, the means for emitting an electromagnetic wave comprise a laser diode  30  emitting a laser beam and means for focusing the laser beam towards the zone  28 , in other words, a focuser. 
     In the variant represented in  FIG. 1 , the laser diode  30  and power supply means  31  for the diode  30  are positioned in the strut  15 . An electrical cable  32  connects the power supply means  31  to an electrical connector (not represented) of the probe  10  arranged at the level of the base  12  and enabling the aircraft to power the probe  10  electrically. The electrical connector can also power probe reheating means in addition to the means for emitting an electromagnetic wave. 
     In the example represented, the focusing means comprise a planar mirror  34  and a concave mirror  35  both arranged inside the tube  18 . The planar mirror  34  is for example fixed onto a support  33  of the pressure tap  24  and the concave mirror  35  is for example fixed at the blocked end  21  of the tube  18 . The beam emitted by the laser diode  30  is returned towards the concave mirror  35  by the planar mirror  34 . The concave mirror  35  directs the beam towards the free zone  28 . In  FIG. 1 , between the diode  30  and the planar mirror  34 , the beam is represented by a line  36 . Between the planar mirror  34  and the concave mirror  35 , the beam is represented by a line  37  and between the concave mirror  35  and the free zone  28 ; the beam is represented by a line  38 . 
     The line  38  runs along the internal walls of the tube  18 . In the example represented, the line  38  is parallel to the axis  22  of the tube  14 . It is also possible to offset the line  38 , for example to take into account the constraints of designing the probe  10 , constraints notably due to the presence of the pressure tap  24  and its aeraulic connection to the interior of the tube  18 . Over its entire path, the beam can contribute to reheating the internal walls of the tube  18 , notably between the concave mirror  35  and the free zone  28 . Conventionally, the reheating of the tube  18  is performed by means of a heating resistor wound on the internal walls of the tube. By implementing the invention, it is possible to dispense with this resistor by using only the beam to reheat the tube  18 . Alternatively, it is possible to provide a residual reheating of the tube  18  by winding a resistor along the internal walls of the tube  18 . This resistor will be of a power significantly lower than that of a conventional Pitot tube for two reasons: first of all, because of the possible lesser presence of water in the tube  18  and then because of the reheating of the tube  18  obtained by the means for emitting an electromagnetic wave. This resistor of lower power makes it possible to reduce its dimensions and consequently to reduce the section of the tube  18 . A tube of smaller section has a smaller outer surface, which makes it possible to reduce the heat exchange that it undergoes in the flow. The reduction of this heat exchange further contributes to reducing the electrical power consumed by the probe. 
       FIG. 2  represents a probe  40  making it possible to measure the total temperature of a flow of air circulating along the outer surface  11  of an aircraft. In the probe  40 , there are the base  12  fixed onto the outer surface  11 , by means of the screws  13 , the tube  18  and the strut  15  linking the tube  18  and the base  12 . As previously, the tube  18  can comprise a few drain holes  26  arranged across the tube  18  and making it possible to discharge any particles likely to penetrate inside the tube  18 . 
     The probe  40  comprises a temperature sensor  41  positioned inside the tube  18 , for example on the axis  22  between the two ends  20  and  21 . The temperature sensor  41  measures the temperature prevailing inside the tube  18 . The measured temperature is representative of the total temperature of the flow. The temperature sensor  41  delivers a measurement, for example in the form of an electrical signal, that it transmits to the aircraft via a cable  42  arranged in the strut  15 . 
     The probe  40  comprises, like the probe  20 , means for emitting an electromagnetic wave directed towards the free zone  28 . As for the probe  20 , the probe  40  can comprise a laser diode  30  positioned in the strut  15 . As an alternative, as represented in  FIG. 2 , the diode  30  can be positioned inside the tube  18 . The diode  30  can be positioned on the axis  22  or offset notably to facilitate its connection to the power supply means  31 . The positioning of the diode  30  inside the tube can also be implemented in the probe  10 . The diode  30  directs the beam that it emits towards the blocked end  21  of the tube  18  along the line  37 . The concave mirror  35  is once again fixed at the blocked end  21 . The mirror  35  receives the beam from the diode  30  and returns it towards the free zone  28  substantially parallel to the axis  22  of the tube  18  along the line  38 . The probe  40  also contains the power supply means  31  for the diode  30  positioned in the strut  15 . The signal from the temperature sensor  41  can pass through the power supply means  31 . The electrical energy necessary for the power supply means  31  can be carried by the cable  42 . 
       FIG. 3  represents a probe  50  making it possible to measure both the total temperature and the total pressure of a flow of air. 
     A tube  51  differs slightly from the tube  18 . Inside the tube  51 , there are the temperature sensor  41 , the pressure tap  24  and the diode  30 . The temperature sensor  41  is situated closer to the open end  20  than the pressure tap  24 . The diode  30  and the focusing means for the light beam from the diode  30  are advantageously positioned between the temperature sensor  41  and the pressure tap  24 . The focusing means comprise, for example, a lens  52  making it possible to direct the beam from the diode towards the free zone  28 . 
     Advantageously, the total pressure is measured at a fluid stopping point. The principle of such a measurement is described in the patent application FR 2 823 846 filed on 24 Apr. 2001 in the name of the applicant. The tube  51  comprises an open end  20  intended to face into the flow in which the probe  50  is situated. The tube  51  comprises another end  53  opposite the end  20  and having an opening  54  positioned along the axis  22  of the tube  51 . The opening  54  is smaller than the opening of the open end  20  but nevertheless allows for a circulation of air inside the tube  51 . 
     A number of streams of air circulate in the tube  51  annularly about a body centred on the axis  22  and here formed by the lens  52  and more generally by the focusing means for the laser beam. The different streams of air meet and are mutually slowed down in a zone  55  situated inside the tube  51  in the vicinity of the opening  54 . The mutual slowing down of the streams of air in the zone  55  forms a fluid stopping point at which it is possible to measure the total pressure of the flow or at the very least a pressure value representative of the total pressure. The pressure tap  24  is situated in the zone  55  for measuring this stopping pressure. 
     The end  53  is partially blocked. The internal shape of the tube  51  in the vicinity of the end  53  is defined in such a way as to bring the streams of air circulating about the lens  52  into contact. The different streams of air face substantially into the zone  55  so as to form the fluid stopping point. 
     The probes  10 ,  40  and  50  can be fixed relative to the outer surface of the aircraft. For this, the strut  15  is directly fixed to the base  12 . Alternatively, a probe according to the invention can be rotationally mobile so as to allow its alignment in the axis of the flow. There is thus obtained a better aerodynamic measurement by keeping the axis  22  in the axis of the flow even when the local incidence of the probe is great. 
       FIG. 4  represents a mobile probe comprising a pivot link  60  positioned between the strut  15  and the base  12 . The pivot link  60  enables the strut  15  to rotate freely about an axis  61  at right angles to the base  12 . The probe comprises a mobile part formed by the strut  15  and the tube  18  or  51  which is fixed thereto. 
     The orientation of the mobile part of the probe can be done naturally in the axis of the flow by virtue of the wing-shaped profile of the strut  15 . It is also possible to motorize the pivot link to obtain a better alignment notably at low speeds of the flow relative to the probe. 
       FIG. 5  represents an aerodynamic measurement probe  70  similar to that of  FIG. 1 . The probe  70  comprises a tube  18  equipped with its pressure tap  24 . The tube  18  is secured to the strut  15  linking the tube  18  to the base  12 . Unlike the probe  10 , the path of the electromagnetic radiation that makes it possible to reheat the water likely to be located in the free zone  28  does not pass inside the tube  18  but outside. This variant can of course be implemented for a probe equipped with a temperature sensor  41 . 
     The electromagnetic wave is directed towards the free zone  28  by the outside of the tube  18  by passing through a window  71  positioned on an outer surface  72  of the strut  15 . Alternatively, the window  71  can be positioned on an outer surface of the base  12 . 
     The means for emitting the electromagnetic wave can be situated directly behind the window  71  inside the strut  15 . This configuration is easy to implement for example when the means for emitting the electromagnetic wave comprise the diode  30 . Alternatively, it is possible to site the means for emitting the electromagnetic probe inside the outer surface  11  and guide the wave by means of a waveguide. This configuration can for example be used with a waveguide taking energy from a microwave source installed on board the aircraft. This source is for example that of an embedded radar.