Abstract:
A method of forming a pitot tube includes forming a substantially cylindrical body portion including an outer surface, a tip portion having an inlet opening and an interior defining a flow passage, radially tapering the outer surface from the body portion toward the inlet opening, and disposing at least one electrical coil including one or more coil wraps along the flow passage of the pitot tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/065,878 filed Oct. 29, 2013, which claims priority to U.S. Provisional Application Ser. No. 61/720,643 filed Oct. 31, 2012, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The subject matter disclosed herein generally relates to pitot tubes. More specifically, the present disclosure relates to ice prevention and removal from pitot tubes. 
         [0003]    A pitot tube is widely used to determine airspeed of an aircraft or other vehicle, or to measure air or gas velocities in industrial applications. In particular, by measuring stagnation pressure of a fluid driven into the pitot tube, together with a measured static pressure, the airspeed of the aircraft can be determined. In certain flight conditions, the pitot tube may be subject to ice accumulation from moisture in the air. For this reason, pitot tubes are equipped with heating elements to prevent such ice accumulation. Further, in other conditions, the pitot tube may ingest ice crystals which then accumulate inside of the pitot tube and cause failure in its operation. A typical pitot tube is substantially cylindrical with an internal diameter containing the heating elements, or coils. Forward of the heating elements is a tip portion that extends radially from a throat diameter, typically smaller than the internal diameter, to an outer diameter of the pitot tube. The tip portion extends axially from the throat to a pitot tube inlet. The pitot tube inlet has a diameter greater than the throat. An exterior of the typical tube is cylindrical along its length to the inlet. Such a tube has a large surface area of material in the tip portion forward of the heater, and is difficult to heat and therefore to prevent ice accumulation thereon. Further, a large inlet diameter allows for proportionally more ice crystals to be ingested by the pitot tube. Such ingested ice crystals must be melted by the heating elements and drained from the pitot tube. 
       BRIEF DESCRIPTION 
       [0004]    According to one aspect of an exemplary embodiment, a method of forming a pitot tube includes forming a substantially cylindrical body portion including an outer surface, a tip portion having an inlet opening and an interior defining a flow passage, radially tapering the outer surface from the body portion toward the inlet opening, and disposing at least one electrical coil including one or more coil wraps along the flow passage of the pitot tube. These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0006]      FIG. 1  is an illustration of an embodiment of a pitot tube; 
           [0007]      FIG. 2  is a cross-sectional view of an embodiment of a pitot tube; 
           [0008]      FIG. 3  is a comparison of an embodiment of a pitot tube with a previous pitot tube; and 
           [0009]      FIG. 4  is a cross-sectional view of another embodiment of a pitot tube. 
       
    
    
       [0010]    The detailed description explains embodiments of the disclosure, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION 
       [0011]    Shown in  FIG. 1  is a view of an embodiment of a pitot tube  10 . The pitot tube  10  includes a cylindrical body portion  12  and a tip portion  14  extending along a tube axis  16  from the body portion  12  toward a tube inlet  18 . In the embodiment of  FIG. 1 , the tip portion  14  includes an inlet opening  20  having an inlet diameter  22  smaller than a body diameter  24  of the body portion  12 . The tip portion  14 , between the body portion  12  and the inlet opening  20 , tapers in diameter along a concave curve  26 . In some embodiments, the concave curve  26  does not extend entirely to the inlet opening  20  as the inlet diameter  22  extends axially from the inlet opening  20  to the concave curve  26 . 
         [0012]    Referring now to the cross-sectional view of  FIG. 2 , the pitot tube  10  has an interior  30  having an interior diameter  32 . A heating element, or coil  34 , is located in the interior  30 . When an electrical current is applied to the coil  34 , the pitot tube  10  is heated, thus melting accumulated ice, or preventing ice accumulation at an exterior  36 , interior  38  of the tip portion  14 , and interior  30 . The tip portion  14  is separated from the interior  30  by a tube throat  40  having a throat diameter  42 . The inlet diameter  22  and the throat diameter  42  are reduced, compared to prior art pitot tubes, to limit or reduce the particle size and/or number of particles, including ice crystals, ingested into the pitot tube  10  thereby reducing ice accumulation in the interior  30  of the pitot tube  10 . In some embodiments, the inlet diameter  22  is between about 0.200 inches (0.508 centimeters) and about 0.300 inches (0.762 centimeters), while the throat diameter  42  is between about 0.100 inches (0.254 centimeters) and 0.200 inches (0.508 centimeters). The configuration of  FIG. 2  increases the effectiveness of the coil  34  in heating the tip portion  14  by reducing a distance  44  between the coil  34  and the inlet opening  20 , thereby reducing a temperature difference between the coil  34  and the inlet opening  20 , an area of high convective activity. This, in turn, reduces demands on the coil allowing a coil size, or number of windings in the coil  34  to be reduced. Further, the concave curve  26  reduces a cross-sectional area of material in the tip portion  14 . This, in turn, reduces demand on the coil  34 , especially a forward-most one of the plurality of wraps  46  of the coil  34  through which heat is conducted into the tip portion  14 . 
         [0013]    Referring now to  FIG. 3 , when particles  48 , for example, liquid water or ice, impinge the pitot tube  10 , they do so nearer to the coil  34  than in previous pitot tubes. As shown, particles  48  travelling substantially along the tube axis  16  travel further along the tube axis  16  past the inlet opening  20 , when compared to a prior art tapered tube  50 , before impinging on the pitot tube  10  due to the concave curve  26  of the tip portion  14 . Particles  48  traveling at an angle  52  relative to the tube axis  16  impinge the tip portion  14  at a location radially inboard, when compared to a prior art tapered tube  50 , due again to the concave curve  26  of the tip portion  14  Impingement of particles  48  closer to the coil  34  results in more effective prevention of ice build-up by the coil  34 . 
         [0014]    Referring now to  FIG. 4 , the coil  34  includes a plurality of wraps  46  arranged along the tube axis  16 . The wraps  46  generally decrease in watt density, and heating performance with distance from the inlet opening  20 , with the forward-most wrap  46 A having the greatest watt density, and successive wraps  46 B and  46 C having decreased watt density. One or more bulkheads  56  are located in the interior  30  to block, or partially block, pathways for ingested particles  48 , such as ice crystals, to travel down the pitot tube  10 . In a typical pitot tube  10 , the bulkheads  56  are located far down the pitot tube  10 , for example, between wraps  46 B and  46 C. In the embodiment of  FIG. 4 , however, the bulkheads  56  are located as close to the inlet opening  20  as possible, between wraps  46 A and  46 B. This prevents ice crystals from traveling down the pitot tube  10  to portions of the pitot tube  10  where the watt density of the wraps  46  is decreased from optimal. The embodiment of  FIG. 4  takes advantage of the relatively high watt density of the forward-most wrap  46 A to quickly melt any ingested ice crystals. Thus performance of the coil  34  in preventing ice crystal accumulation is improved while not increasing an amount of electrical power directed to the coil  34 . 
         [0015]    Once melted, the resulting water from the ice crystals is drained from the pitot tube  10  via one or more drain openings  58 . In some embodiments, the drain openings  58  are located forward of at least one bulkhead  56  of the plurality of bulkheads  56 . As shown in  FIG. 4 , in some embodiments, the drain opening  58  location is between wraps  46 A and  46 B. By melting ice crystals and draining the resulting water from the pitot tube  10  at locations forward of wrap  46 B, watt density of wraps  46 B and  46 C, and further successive wraps, can be reduced, and the amount of electrical power supplied to the coil  34  can be reduced. In some embodiments, the successive wraps  46 B or  46 C downstream of the bulkheads  56  may be eliminated entirely. 
         [0016]    The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of ± 8 % or 5%, or 2% of a given value. 
         [0017]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof 
         [0018]    While the disclosure is provided in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that the exemplary embodiment(s) may include only some of the described exemplary aspects. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.