Abstract:
A device for maintaining and analyzing an aerodynamic probe of stagnation pressure type intended to be installed in an aircraft comprises a channel with a first end that is intended to penetrate into the probe, and an ejector fluidly coupled to the channel to create an air depression in said channel relative to the ambient pressure and a closed vessel recovering any particles sucked into the channel, the ejector and closed vessel being external to the probe when the channel is inserted into the probe. The ejector is coupled to a pressurized gas source and ejects gas in proximity to a second end of the channel opposite the first end to suction the air present in the channel and thereby create the air depression in said channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International patent application PCT/EP2012/054930, filed on Mar. 21, 2012, which claims priority to foreign French patent application No. FR 1100955, filed on Mar. 31, 2011, the disclosures of which are incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a device for maintaining and analyzing an aerodynamic probe. 
     BACKGROUND 
     The piloting of any aircraft requires the knowledge of its relative speed in relation to the air, that is to say to the relative wind. This speed is determined using sensors sensing the static pressure Ps, the total pressure Pt, the angle of attack α and the sideslip angle β. α and β give the direction of the speed vector in a reference system, or reference base, linked to the aircraft and Pt-Ps gives information linked to the modulus of this speed vector. In fact Pt-Ps gives so-called conventional airspeed information, critical for piloting, because it indicates whether or not the aircraft is present in a safe flight domain. The four aerodynamic parameters therefore make it possible to determine the speed vector of an airplane and, incidentally, of an aircraft with rotor, called helicopter, and with tilting rotor, called convertible. 
     The measurement of the total pressure Pt is usually done by measuring the stagnation pressure of the flow 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 the flow. 
     Inside the Pitot tube, close to the blocked end, there is an orifice connected to a means for measuring the air pressure prevailing therein. The thread of air penetrating into the tube through the open end of the tube is slowed down to zero speed in the tube. The slowing down of the speed of the air tends to increase the pressure of the air. This increased pressure forms the total pressure Pt of the air flow. 
     In practice, the air flow may convey liquids or solid particles likely to penetrate into the Pitot tube and to build up in the tube at the blocked end. To avoid having a build-up of liquid disrupt the pressure measurement, there is generally provided, at the blocked end, a drain hole through which any liquids can be evacuated. 
     In this hole both the solid particles and a portion of the air which has entered into the Pitot tube also circulate. Thus, the slowing down of the air in the tube is not complete and the measurement of total pressure Pt is corrupted. More specifically, the greater the effort to avoid the build-up of large particles or of a quantity of liquid, the more the total pressure measurement is corrupted by increasing the dimensions of the drain hole. Conversely, the greater the effort to improve the measurement of total pressure Pt by reducing the dimensions of the drain hole, the greater the risk of build-up of solid particles or of congestion by the liquid. With a Pitot tube, there therefore has to be a trade-off between quality of the measurement of total pressure Pt and risk of disruption of the measurement because of particles conveyed by the air flow where the measurement is performed. 
     The measurement of the static pressure Ps is usually done by means of cavities that open into the flow through an orifice situated substantially at right angles to the flow. In the cavity, there is an orifice connected to a means for measuring the air pressure prevailing therein. This pressure forms the static pressure Ps of the flow. Some Pitot tubes can be equipped with static pressure taps positioned on their sides. This type of aerodynamic probe is also called Pitot-static probe. 
     Currently, if the drain holes of the probes installed on aircraft are blocked, or if particles of sand or of volcanic ash are present in the tube itself, the probe is removed, then cleaned with soapy water. The change of probe entails checking the seal-tightness of the pneumatic subsystem, which renders the operation relatively lengthy, of the order of thirty to fifty minutes for an aircraft. 
     SUMMARY OF THE INVENTION 
     The invention proposes a maintenance device that makes it possible to clean aerodynamic probes directly on the aircraft without the removal thereof, and without risk of damage to the connected pressure sensors by overpressure. 
     To this end, the subject of the invention is a device for maintaining and analyzing an aerodynamic probe of stagnation pressure type intended to be installed in an aircraft, characterized in that it comprises a channel with a first end that is intended to penetrate into the probe, means for creating in the channel an air depression relative to the ambient pressure and means for recovering any particles sucked into the channel. 
    
    
     
       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 appended drawing in which: 
         FIG. 1  represents an exemplary aerodynamic probe for which the invention can be implemented; 
         FIG. 2  represents an exemplary maintenance device according to the invention; 
         FIGS. 3 a  and 3 b    represent, in more detail, a part of the maintenance device represented in  FIG. 2 . 
     
    
    
     In the interests of clarity, the same elements are given the same references in the different figures. 
     DETAILED DESCRIPTION 
       FIG. 1  represents a total pressure measurement probe  10  intended to be fixed through an opening produced in the skin  11  of an aircraft. The probe  10  comprises a part  12  external to the skin  11  and formed by a Pitot tube  13  borne by a mast  14 . The probe  10  also comprises an internal part  15  essentially comprising an electrical connector  16  and a pneumatic connector  17  enabling the Pitot tube  13  to be pneumatically coupled to a pressure sensor situated inside the skin  11  of the aircraft. The probe  10  is positioned on the skin  11  of the aircraft so that the Pitot tube  13  is oriented substantially along a longitudinal axis of the aircraft, excluding boundary layer, so that the direction of the flow, represented by an arrow  18 , substantially faces an inlet orifice  19  situated at a first end  20  of the Pitot tube  13 . 
     A second end  21  of the Pitot tube  13 , opposite the end  20 , is closed so as to form a stopping point in the stream of air taken from the flow and penetrating into the Pitot tube  13  through its orifice  19 . At the end  21  of the Pitot tube  13 , a pneumatic channel  22  opens into the Pitot tube  13  to form a pressure tap there at which the air pressure is to be measured. The pneumatic channel  22  is, for example, linked to a pressure sensor or to another pressure measurement device. The pressure sensor makes it possible to effectively measure the pressure of the air prevailing inside the Pitot tube  13  at its end  21 . The pressure sensor may belong to the probe  10  or even be sited elsewhere. In this case, the pressure sensor is coupled to the probe  10  by means of the pneumatic connector  17 . 
     At the end  21 , the Pitot tube  13  comprises one or more drain holes  23  making it possible to evacuate the liquid that is likely to penetrate into the Pitot tube  13 . Apart from the drain hole(s)  23 , the section of which is small compared to that of the Pitot tube  13 , the latter being closed at its end  21 , the pressure measured at this end therefore substantially represents the total pressure Pt of the air flow. 
     The electrical connector  16  makes it possible to electrically couple the probe  10  to the electrical network of the aircraft, notably to couple heating means for the probe  10  assembly. These heating means comprise, for example, a heating resistor, not represented in  FIG. 1 , and making it possible to heat up the mast  14  and the Pitot tube  13  over its entire length to avoid having any build-up of ice form on the probe. 
     In the example represented, the Pitot tube  13  is fixed relative to the skin  11  of the aircraft. It is obviously possible to mount the Pitot tube  13  on a movable mast such as a paddle that can be oriented in the axis of the flow, for example as described in the patent published under the number FR 2 665 539 and filed Aug. 3, 1990. Thus, when the local angle of attack of the flow in the vicinity of the probe  10  changes, the orientation of the Pitot tube  13  follows this angle of attack in order to be always facing the flow. The measurement of total pressure Pt is thereby enhanced in the event of variation of local angle of attack 
     It is also possible to complement the measurement of total pressure with a measurement of static pressure. To this end, it is possible to position one or more static pressure taps on an outer face of the Pitot tube  13  and to couple these pressure taps to pressure sensors by means of channels passing through the pneumatic connector  17 . 
     At the end  21 , the Pitot tube  13  generally comprises a water trap, not represented, that makes it possible to block the liquid likely to penetrate into the Pitot tube  13 , and evacuate it through the associated drain hole. This water trap makes it possible to avoid having the ingested liquid penetrate into the channel  22 . In the normal operation of the tube, the thus trapped water is evacuated from the Pitot tube  13  through the drain holes  23 . When the aircraft is flying, solid particles, such as sand or volcanic ash, can also penetrate into the Pitot tube  13 . These particles also build up at the bottom of the tube, at the end  21 , and notably in the water trap. These particles may not be able to be evacuated through the drain holes  23  and may block them or stagnate in the water trap. 
       FIG. 2  represents an example of a maintenance device  30  that makes it possible to clean the probe  10  of its particles without requiring it to be removed. 
     The maintenance device  30  comprises a channel  31  with a first end  32  that is intended to penetrate into the probe  10  to suck up any particles located therein. The end  32  is, for example, made of flexible material, such as, for example, a plastic material, so as not to damage the interior of the probe. 
     The maintenance device  30  is external to the probe  10 . It is implemented by maintenance personnel during aircraft stopovers. The maintenance device  30  is a tool which is not used in flight. More specifically, maintenance personnel, provided with the device  30 , go to a probe  10 , fits the first end  32  into the probe to perform a suction operation there, then remove the first end  32 . 
     The maintenance device  30  also comprises means  33  for creating in the channel  31  an air depression relative to the ambient pressure. It is important for this to be a depression, in order to avoid the overpressures that could damage the associated pressure sensor. This depression can be created by means of a pump actuated by an electric motor. Nevertheless, during aircraft stopovers, it is sometimes difficult to find an electrical power source in the vicinity of the aircraft parking points. It is easier to find a compressed air source made available to the ground teams for aircraft maintenance. This compressed air source, or more generally a pressurized inert gas source, is advantageously implemented to generate the air depression in the channel  31 . To this end, the means  33  comprise an ejector  34  intended to be coupled to a pressurized gas source and ejecting the gas in proximity to a second end  35  of the channel  31  in order to drive the air present in the channel  31 . The gas ejection speed at the output of the ejector  34  sucks the air contained in the channel  31 . 
     The ejector  34  is formed by a tube coupled at a first of its ends  36  to the pressurized gas source. To this end, the ejector  34  can be provided with a quick-release pneumatic connector  37 . The ejector  34  is open on the outside at its second end  38  thus creating a circulation of the gas in the ejector  34 . The direction of this circulation is shown by an arrow A. A valve  39  can be put in place in the ejector  34  downstream of the pneumatic connector  37  to allow an operator to control the circulation of the gas in the ejector  34  as required. The valve  39  can operate in on or off mode in order to allow or prevent the circulation of gas in the ejector  34  or even in proportional mode in order to control the speed of the gas in the ejector  34 . A pressure sensor  40  can be provided in the channel  31  in order to know the value of the depression in the channel  31 . More generally, the maintenance device  30  comprises means for measuring and displaying the depression prevailing in the channel  31 . An operator can regulate this depression by acting on the valve  39 . 
     The maintenance device  30  also comprises means for recovering any particles sucked into the channel  31 . These means advantageously comprise a closed vessel  41  positioned in the line of the channel  31  between these two ends  32  and  35 . More specifically, the channel  31  comprises a first end-fitting forming the end  32  and a second end-fitting  42  opening into the vessel  41 . The two end-fittings  32  and  42  are positioned upstream of the vessel  41  in the direction of circulation of the air sucked into the channel  31 . The end-fittings  32  and  42  can be coupled by means of a joint  43  that is more flexible than the two end-fittings  32  and  42  themselves. This makes it easier to handle the maintenance device  30  and notably the entry of the end-fitting  32  into the Pitot tube  13 . It is obviously possible to produce the two end-fittings  32  and  42  in a single tube. Furthermore, the channel  31  comprises a third end-fitting forming the end  35  and a fourth end-fitting  44  opening into the vessel  41 . The two end-fittings  35  and  44  are positioned downstream of the vessel  41 . As previously, the end-fittings  35  and  44  can be coupled by means of a joint  45 . The end fittings  42  and  45  open into the vessel  41  at a distance from one another so that the speed of the air in the vessel is very much lower than that of the air that is circulating in the channel  31 . This speed difference allows any particles circulating in the end-fittings  32  and  42  to be deposited in the bottom of the vessel  41  without continuing their way into the end-fittings  35  and  44  situated downstream of the vessel  41 . 
     Advantageously, the vessel  41  comprises at least one transparent wall  46  enabling the operator to view the particles present in the vessel  41 . 
     Advantageously, the vessel  41  comprises a removable wall  47  making it possible to remove the trapped particles from the vessel  41 . The recovered particles can be simply discarded or analyzed to determine their nature. The removable wall  47  may be formed by a cover that can be screwed onto a body of the vessel  41 , forming the wall  46 . The cover  47  and the end-fittings  42  and  44  are coupled to the vessel  41  in a sufficiently tight manner to be able to retain a substantially constant depression all along the channel  31 . 
       FIGS. 3 a  and 3 b    represent an exemplary embodiment of the means  33  for creating in the channel  31  an air depression and notably the relative positioning of the ejector  34  and of the end-fitting  35 . The ejector  34  is formed by a rectilinear tube of 6 mm internal diameter and 7 mm external diameter. The end-fitting  35  is formed by a rectilinear tube of 2 mm internal diameter and 3 mm external diameter. A block  50  makes it possible to fix the relative position of the end-fitting  35  relative to the ejector  34 . The block  50  is pierced with two through holes  51  and  52 , making it possible to each receive one of the two tubes respectively forming the ejector  34  and the end-fitting  35 . The two elements  43  and  35  are fitted into the block  50  and, for example, fixed by gluing, hard-soldering or welding in the corresponding holes  51  and  52 . 
       FIG. 3 a    is a front view of the means  33  for creating in the channel  31  an air depression and  FIG. 3 b    is a cross-sectional view in a plane at right angles to that of  FIG. 3 a   . The two holes  51  and  52  intersect and the respective axes extend in the plane of  FIG. 3 b   . In the example represented, the two axes form an angle of approximately 65° between them. Furthermore, the end of the end-fitting  35  is beveled to approximately 55° relative to the axis of the end-fitting  35  and opens into the ejector  34 . The gases expelled by the ejector  35  circulate by surrounding the opening of the end-fitting  35  and create a depression therein.