Patent Publication Number: US-2021179278-A1

Title: Conformal thin film heaters for angle of attack sensors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Indian Patent Application number 201911051312 filed Dec. 11, 2019, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present invention generally relates to angle of attack sensors, and more specifically, to conformal thin film heaters for angle of attack sensors. 
     For aircraft technology, angle of attack specifies the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line (and also as the longitudinal axis). 
     BRIEF DESCRIPTION 
     Embodiments of the present invention are directed to an angle of attack sensor. A non-limiting example of the sensor includes a vane, a faceplate, an annular region under the surface of the faceplate, and a thin film heater assembly attached to a top most surface of the annual region. 
     Embodiments of the present invention are directed to a system. A non-limiting example of the system includes an angle of attack sensor including a vane, a faceplate, an annular region under the surface of the faceplate, a thin film heater assembly attached to a top most surface of the annular region, a temperature feedback sensor, and a controller communicatively coupled to the thin film heater assembly, wherein the controller is configured to receive temperature data from the temperature feedback sensor, and operate the thin film heater assembly based at least in part on the temperature data. 
     Additional technical features and benefits are realized through the techniques of the present invention. Embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed subject matter. For a better understanding, refer to the detailed description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The specifics of the exclusive rights described herein are particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the embodiments of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of an aircraft that may incorporate embodiments of the present disclosure; 
         FIG. 2 a    depicts a side view of an angle of attack sensor according to one or more embodiments; 
         FIG. 2 b    depicts a side view of an AoA sensor depicting the rotational mechanism for the AoA vane according to one or more embodiments; 
         FIG. 3 a    depicts a bottom view of an angle of attack sensor faceplate according to one or more embodiments; 
         FIG. 3 b    depicts a cutaway view of the angle of attack sensor faceplate according to one or more embodiments 
         FIG. 4  depicts the layers of the thin film heater apparatus according to one or more embodiments; and 
         FIG. 5  depicts a system for preventing ice accumulation in an angle of attack sensor according to one or more embodiments. 
     
    
    
     The diagrams depicted herein are illustrative. There can be many variations to the diagram or the operations described therein without departing from the spirit of the invention. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term “coupled” and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification. 
     DETAILED DESCRIPTION 
     For the sake of brevity, conventional techniques related to making and using aspects of the invention may or may not be described in detail herein. In particular, various aspects of computing systems and specific computer programs to implement the various technical features described herein are well known. Accordingly, in the interest of brevity, many conventional implementation details are only mentioned briefly herein or are omitted entirely without providing the well-known system and/or process details. 
     Referring now to the figures,  FIG. 1  depicts a perspective view of an aircraft  2  that may incorporate embodiments of the present disclosure. Aircraft  2  includes a fuselage  4  extending from a nose portion  6  to a tail portion  8  through a body portion  10 . Body portion  10  houses an aircraft cabin  14  that includes a crew compartment  15  and a passenger or cargo compartment  16 . Body portion  10  supports a first wing  17  and a second wing  18 . First wing  17  extends from a first root portion  20  to a first tip portion  21  through a first airfoil portion  23 . First airfoil portion  23  includes a leading edge  25  and a trailing edge  26 . Second wing  18  extends from a second root portion (not shown) to a second tip portion  31  through a second airfoil portion  33 . Second airfoil portion  33  includes a leading edge  35  and a trailing edge  36 . Tail portion  8  includes a stabilizer  38 . Aircraft  2  includes an engine  54  configured to provide propulsion to the aircraft  2 . The aircraft  2  also includes one or more angle of attack sensors  100 . 
     Turning now to an overview of technologies that are more specifically relevant to aspects of the disclosure, angle of attack (AoA) sensors are utilized to indicate the angle between the chord line of an aircraft wing and a relative motion vector between the aircraft and the airflow. This measurement will provide the amount of lift generated by the aircraft wing.  FIG. 2 a    depicts a side view of an angle of attack sensor according to one or more embodiments. The AoA sensor  200   a  includes a rotatable vane  202  and a stationary faceplate  204 . 
     The rotation of the AoA vane  202  included in the sensor is required for the angle of attack measurement of the AoA sensor  200   a . However, in icy conditions, the formation of ice in a cavity between the rotational surface  204  of the vane  202  and the stationary surface of a faceplate  204  can hinder the free rotation of the vane  202 . AoA sensors are, typically, mounted external to an aircraft and are equipped with appropriate heating mechanisms for ice prevention under extreme icing conditions.  FIG. 2 b    depicts a side view of an AoA sensor  200   b  depicting the rotational mechanism for the AoA vane  202  according to one or more embodiments. Critical areas include, but are not limited to, the stationary faceplate  204  exterior and the interior cavity regions  212  (shown as a dotted line) of the AoA sensor  200   b . Typical heating elements include positive temperature coefficient (PTC) properties which self-regulates the heater power at higher temperatures and prevents overheating. AoA sensors require the cavities to be at a minimum of 15 degrees Celsius under dry air conditions. In the current configuration, it is a challenge to adhere to the 15 degree Celsius requirement at extremely low ambient temperatures (e.g., −44 degrees Celsius). This is due to the heater elements not being placed near the critical areas  212  to be heated (i.e., longer heat flow paths) and there is potential for heat loss paths. 
     Aspects of the present disclosure address the shortcomings described above by providing systems for heating portions of the angle of attack sensors and portions of an aircraft surface using thin film heaters. Thin film heaters can be effected for electro-thermal wing ice protection since they provide benefits of quick, uniform, and reliable heating. The thin film heaters are made up of nano-composites of carbon allotropes in a polymer/silicon matrix. A few examples of thin film heaters include positive temperature coefficient (PTC) heaters based on carbon black/polymer composite and carbon nanotube (CNT)/silicone nano composite (CNT heater). The thin film heaters generate surface heating when electrically energized depending on the electric resistivity-temperature characteristics of the thin film heater composite material. PTC heaters are self-regulating heaters in which the heater surfaces are heated to a pre-defined set temperature, beyond which the electric resistance drastically increases reducing the circuit current. CNT heaters are not self-regulating by default but could be made self-regulating by providing temperature feedback control. 
     In one or more embodiments, aspects of the present disclosure provide for use of thin film heaters that are placed conformally to the critical areas  212  in an angle of attack faceplate  204  for efficient heating. Current AoA faceplate design can be modified to enable creation of a thin film heater assembly (shown in  FIG. 4 ) within an annular region or cavity (depicted in  FIGS. 3 a  and 3 b   ) below the surface of the AoA faceplate  204  thus providing the heater surfaces closer to the icing critical areas ( 212  from  FIG. 2 b   ). Also, the faceplate can be provided with enough material thickness to maintain the structural integrity of the faceplate to withstand external loads such as vibrational as well as hail strike impact loads. 
       FIG. 3 a    depicts a bottom view of an angle of attack sensor faceplate  301   a  according to one or more embodiments. The AoA sensor  300   a  includes a vane  302  and a face plate  304 . The bottom view of the faceplate  304 ? depicts an annular region  308  beneath the surface of the faceplate  304 . In one or more embodiments, a thin film heating assembly (shown in  FIG. 4 ) can be conformally applied to the top surface  310  of this annular region  308 .  FIG. 3 b    depicts a cutaway view of the angle of attack sensor faceplate  300   b  According to one or more embodiments. The cutaway view highlights the areas  324  than can be heated when a thin film heating assembly(shown in  FIG. 4 ) is conformally applied to the annular region  308  underneath the face plate  304 . The heat transfer areas  324  inside the faceplate can be thermally insulated and protected from corrosive agents or sediments. An inner protective and thermally insulating cover  322  (protective cover) can be utilized and bonded to the thin film heater assembly (shown in  FIG. 4 ). The protective cover  322  can be a thermal barrier coated metallic cover. 
       FIG. 4  depicts the layers of the thin film heater apparatus according to one or more embodiments. The thin film heater assembly  400  includes a number of layers as shown in  FIG. 4 . The assembly  400  can be attached to the surface  310  in the annular region  308  of the faceplate  202  depicted in  FIGS. 3 a  and 3 b   . The assembly  400  also includes an electric insulation and adhesive layer  404  that allows for insulation and adhesion of the subsequent layers to the surface  310  of the faceplate  202 . The next layer is the thin film heater layer  406  which can include PTC heaters or CNT heaters. The next layer is a second electric insulation and adhesive layer  408 . And the last layer is a protective cover and thermal insulation layer  410 . The electric insulation and adhesive layers  404 ,  408  prevent current leakage to prevent short circuits. The adhesive ensures enhanced contact between the thin film heater layer  406  and the surface  310  of the faceplate  202  (from  FIGS. 2, 3   a , and  3   b ) and the protective cover layer  410 . The combined thickness of the heater layer  406 , insulation layers and adhesives  404 ,  408  are on the order of 0.03 inches. The radius of curvature can be as low as 0.02 inches. 
     In one or more embodiments, the thin film heater assembly  400  can be created by laying out the thin film heater layer  406  with the adhesives and electrical insulation  404 ,  408  on the face plate surface  402  (within the annular region under the face plate) with the adhesive bonding all the layers to each other and to the faceplate surface  402 . The separate protective  410  cover can be fastened or bonded to the thin film heater assembly by curing. In one or more embodiments, the thin film heater assembly  400  can be bonded and cured to the protective cover  410  and then fastened to the face plate  402  for structural integrity and good contact with the surface of the face plate  402 . In one or more embodiments, the thin film heater assembly  400  can be attached to the face plate surface  402  by a fastener. 
     The power densities required for an AoA heating application are of the order of 60-300 kW/m 2  for quicker heating. The thin film heaters are capable for customized rapid and uniform heating with the required power density (max. ˜500 kW/m 2 ). Thin film heaters such as the CNT and PTC heaters are suited for quicker heating (e.g., in ground operations, reaching minimum 15 degrees Celsius in 3 minutes when heater is powered on). Both CNT and PTC heaters generate the required power density based on the electrical resistivity temperature characteristics. 
     In one or more embodiments, the AoA face plate critical surfaces are to be heated above freezing temperatures. Thin film heaters are made to heat surfaces to approximately 40 degrees Celsius which is more than sufficient to prevent/melt ice accumulation. The temperatures limit for the heater can be set at 40 degrees Celsius or below to meet the minimum temperature requirement by utilizing a standalone PTC heater or CNT heater with a temperature feedback sensor. During the ground operation, power consumption can be made minimal with thin film heaters operating above the minimum required temperature. In one or more embodiments, the PTC heaters are capable to provide variable heat densities to areas where more heating is required. For example, in an AoA under flight conditions, due to the increase airflow over the face plate surface in the upstream, there can be a higher heat transfer coefficients. That is to say, more power density has to be placed near the upstream region. In such cases, more localized power-density could be provided near the upstream and save power by reducing power density in other areas. Power densities depend on the concentration of carbon in the matrix. 
       FIG. 5  depicts a system for preventing ice accumulation in an angle of attack sensor according to one or more embodiments. The system  500  includes a controller  502  that is electrically and communicatively coupled to a thin film heater assembly  504 . The thin film heaters assembly  504  can be any type of configuration including the configuration described in  FIG. 4  or a CNT and PTC heater in other configurations. The thin film heater assembly  504  can be conformally applied to the bottom surface of an angle of attack faceplate  520  to provide heat to critical areas under the face plate  520 . The controller  502  is configured to provide power to operate the thin film heater assembly  504 . In addition, the controller  502  can be communicatively coupled to one or more external sensors  506  and/or the controller  502  can be communicatively coupled to one or more internal sensors within the thin film heater assembly  504 . As mentioned above, the internal sensors or external sensors  506  can collect temperature data associated with the AoA sensor environment to allow the controller  502  to determine that a minimum temperature is maintained in the AoA sensor. In addition, the internal sensors or external sensors  506  can be temperature feedback sensors to determine the temperature of the thin film heater assembly  504 . The feedback sensors can provide temperature data for the controller  502  to utilize to operate the thin film heater assembly  504 . For example, a maximum temperature can be determined to allow for sufficient heat to curb ice accumulation and also to allow for normal operation of the AoA sensor. The controller  502  can utilize the feedback data to control the heater assembly  504  to not go above the determined maximum temperature by either reducing the power supplied to the assembly  504  or turning the assembly off for a period of time. The feedback controller  502  is utilized for CNT heater assemblies. 
     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. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present 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. 
     Various embodiments of the invention are described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. 
     The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. 
     Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” may be understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms “a plurality” may be understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term “connection” may include both an indirect “connection” and a direct “connection.” 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.