Patent Description:
Modern aircraft often incorporate air data systems that calculate air data outputs based on measured parameters collected from various sensors positioned about the aircraft. For instance, many modern aircraft utilize angle of attack sensors having a rotatable vane that is used to determine the aircraft angle of attack (i.e., an angle between oncoming airflow or relative wind and a reference line of the aircraft, such as a chord of a wing of the aircraft). The angle of attack sensor is mounted to the aircraft such that the rotatable vane is exposed to oncoming airflow about the aircraft exterior. Aerodynamic forces acting on the rotatable vane cause the vane to align with the direction of the oncoming airflow (i.e., along a chord extending from a leading edge to a trailing edge of the vane). Rotational position of the vane is sensed and utilized to determine the aircraft angle of attack.

Hindrance of the free rotation of the angle of attack vane or interference with aerodynamic characteristics of the vane due to icing conditions can degrade the accuracy of angle of attack determinations derived from the rotational position of the vane. Accordingly, angle of attack sensors utilizing rotatable vanes typically include heating elements to prevent accretion of ice on the vane and faceplate. Such heating elements, however, may utilize a significant portion of an amount of electrical power allotted to the angle of attack sensor during operation of the aircraft (i.e., an electrical power budget of the angle of attack sensor). Accordingly, the amount of electrical power utilized by the heating elements during anti-icing and/or deicing operations is an important consideration in the design of such angle of attack sensors. <CIT> relates to an aircraft airflow sensor probe and a process of implanting an aircraft sensor probe. <CIT> relates to an air data probe with fluid intrusion sensor. <CIT> relates to a vane type airflow sensor.

An angle of attack sensor is provided as defined by claim <NUM>. The sensor includes a housing having an open end and a closed end, a faceplate positioned on the open end of the housing, the faceplate comprising a periphery at an outer edge of the faceplate, a central opening, and an exterior surface extending from the periphery to the central opening, and a vane assembly extending through the central opening of the faceplate. The exterior surface of the faceplate has a sloped profile from the periphery to the central opening.

An angle of attack sensor is provided as defined by claim <NUM>. The sensor includes a housing having an open end and a closed end, a faceplate positioned on the open end of the housing, the faceplate comprising a periphery at an outer edge of the faceplate, a central opening, and an exterior surface extending from the periphery to the central opening, and a vane assembly extending through the central opening of the faceplate. The exterior surface of the faceplate has a continuous incline from the periphery to the central opening.

An angle of attack sensor is provided as defined by claim <NUM>. The sensor includes a housing having an open end and a closed end, a faceplate positioned on the open end of the housing, the faceplate comprising a periphery at an outer edge of the faceplate, a central opening, and an exterior surface extending from the periphery to the central opening, and a vane assembly extending through the central opening of the faceplate. The exterior surface of the faceplate slopes downward and outward from the central opening to the periphery.

<FIG> is a partial side view of angle of attack sensor <NUM> with frustoconical faceplate <NUM>. <FIG> is a front view of angle of attack sensor <NUM>. <FIG> is an isometric view of angle of attack sensor <NUM>. <FIG>, <FIG>, and <FIG> will be discussed together. Angle of attack sensor <NUM> includes faceplate <NUM>, housing <NUM> (having first end 14A and second end 14B), vane assembly <NUM>, which includes vane hub <NUM> and vane <NUM> (including root <NUM> and tip <NUM>), vane shaft connectors <NUM>, and electronics interface connector <NUM>. Faceplate <NUM> includes interior surface <NUM>, exterior surface <NUM>, opening <NUM>, periphery <NUM>, mounting bores <NUM>, leading edge <NUM>, trailing edge <NUM>, upstream portion <NUM>, and downstream portion <NUM>.

Single-piece faceplate <NUM> of angle of attack sensor <NUM> is a heated faceplate. A heater provides heat to faceplate <NUM>, which is made of thermally conductive material. In this embodiment, faceplate <NUM> is metal, such as aluminum. In alternate embodiments, faceplate <NUM> may be any suitable thermally conductive material. Housing <NUM> is cylindrical with an annular sidewall between open first end 14A and closed second end 14B. Faceplate <NUM> is positioned on open first end 14A of housing <NUM>. Vane assembly <NUM> is adjacent faceplate <NUM>. Vane assembly <NUM> rotates about axis A. Vane assembly <NUM>, which includes vane hub <NUM> and vane <NUM>, has a portion that is positioned within faceplate <NUM> and extends through faceplate <NUM>. More specifically, vane hub <NUM> is positioned in faceplate <NUM>. Vane <NUM> has root <NUM> at a first end and tip <NUM> at a second end such that vane <NUM> extends from root <NUM> to tip <NUM>. Tip <NUM> is opposite root <NUM>. Root <NUM> of vane <NUM> is connected to vane hub <NUM>. Root <NUM> can be integrally formed with vane hub <NUM>, such that vane <NUM> is integral to vane hub <NUM> or otherwise attached to vane hub <NUM> (e.g., via welding, brazing, or other connection). Vane hub <NUM> receives vane shaft connectors <NUM>. Vane shaft connectors <NUM> extend through vane hub <NUM>. A first end of a rotatable vane shaft is connected to vane hub <NUM> via vane shaft connectors <NUM>.

Electronics interface connector <NUM> extends from housing <NUM> into an interior of the aircraft. Electronics interface connector <NUM> can be configured to connect with an aircraft communications data bus, such as a data bus configured to communicate via the Aeronautical Radio, Incorporated (ARINC) <NUM> communications protocol or other communications protocols. In other examples, electronics interface connector <NUM> carries electrical signals (e.g., analog alternating current voltages) from a rotational position sensor positioned within housing <NUM> and configured to sense rotation of a shaft connected to vane assembly <NUM>, as is further described below. In some examples, electronics interface connector <NUM> carries electrical power to angle of attack sensor <NUM> for use by heating elements included within vane <NUM> and/or faceplate <NUM> and/or electrical components included within housing <NUM>. In other examples, angle of attack sensor <NUM> includes additional connectors (i.e., separate from electronics interface connector <NUM>) configured to carry electrical power and/or additional electrical and/or communicative signals, though additional connectors need not be present in all examples.

Faceplate <NUM> has interior surface <NUM> facing toward housing <NUM>, or toward an interior of angle of attack sensor <NUM>. Exterior surface <NUM> of faceplate <NUM> is the surface opposite interior surface <NUM>, or the surface of faceplate <NUM> that faces external airflow. At its center, faceplate <NUM> has circular opening <NUM>, which extends from interior surface <NUM> to exterior surface <NUM>. Vane assembly <NUM> extends through opening <NUM> of faceplate <NUM>, or protrudes from faceplate <NUM> at opening <NUM>. More specifically, vane hub <NUM> is positioned in opening <NUM>. Opening <NUM> is concentric with periphery <NUM>. In alternate embodiments, opening <NUM> may be non-concentric with periphery <NUM>. Periphery <NUM> of faceplate <NUM> is the outermost part of faceplate <NUM>. As such, periphery is the circular outer edge, or circumference, of faceplate <NUM>. Faceplate <NUM> meets the aircraft skin at periphery <NUM>. Exterior surface <NUM> of faceplate <NUM> extends from periphery <NUM> to central opening <NUM>. Mounting bores <NUM> are located around periphery <NUM> of faceplate <NUM>. Mounting bores <NUM> extend through faceplate <NUM> from interior surface <NUM> to exterior surface <NUM>. In this embodiment, faceplate <NUM> has eight mounting bores <NUM>. In alternate embodiments, faceplate may have any number of mounting bores <NUM>. Leading edge <NUM> is a fore portion of periphery <NUM> of faceplate <NUM>, and trailing edge <NUM> is an aft portion of periphery <NUM> of faceplate <NUM>. Upstream portion <NUM> is a portion of faceplate <NUM> that is upstream with respect to oncoming airflow when angle of attack sensor <NUM> is installed on an aircraft. Upstream portion <NUM> is upstream of vane assembly <NUM>. Downstream portion <NUM> is a portion of faceplate <NUM> that is downstream from upstream portion <NUM> (and downstream with respect to oncoming airflow) when angle of attack sensor <NUM> is installed on an aircraft. Downstream portion <NUM> is adjacent upstream portion <NUM>. Downstream portion <NUM> is downstream of vane assembly <NUM>.

Exterior surface <NUM> of faceplate <NUM> continuously inclines, or has a sloped profile, from periphery <NUM> to opening <NUM> such that a height of faceplate <NUM> at opening <NUM> is greater than the height of faceplate <NUM> at periphery <NUM>. Faceplate <NUM> progressively increases in height from periphery <NUM> to opening <NUM>. As such, faceplate <NUM> surrounds vane hub <NUM> and exterior surface <NUM> of faceplate <NUM> slopes downward and outward from opening <NUM> to periphery <NUM>. Thus, an exterior surface of vane hub <NUM> and root <NUM> of vane <NUM> are above the skin of the aircraft. In this embodiment, the sloped profile, or continuous incline, of faceplate <NUM> is axisymmetric and has the same axis A as vane assembly <NUM>. In alternate embodiments, the sloped profile, or continuous incline, of faceplate <NUM> may be non-axisymmetric and/or have a different axis than axis A of vane assembly <NUM>. In this embodiment, faceplate <NUM> has a frustoconical exterior surface <NUM>. In alternate embodiments, faceplate <NUM> may have an exterior surface <NUM> that is ellipsoidal, hemispherical, trapezoidal, another convex shape, or any other suitable shape. In further alternate embodiments, exterior surface <NUM> of faceplate <NUM> may have exterior surface <NUM> with a continuous incline, or a sloped profile, only at upstream portion <NUM> such that faceplate <NUM> has sloped upstream portion <NUM> and flat downstream portion <NUM>.

Angle of attack sensors <NUM> are installed on the exterior of an aircraft and mounted to the aircraft via fasteners, such as screws or bolts, which interface with mounting bores <NUM> on faceplate <NUM>. As a result, periphery <NUM> of faceplate <NUM> is about flush with the skin of the aircraft, and housing <NUM> extends within an interior of the aircraft. Vane <NUM> extends outside an exterior of the aircraft and is exposed to oncoming airflow, causing vane <NUM> and vane hub <NUM> of vane assembly <NUM> to rotate with respect to faceplate <NUM> via a series of bearings within angle of attack sensor <NUM>. Vane assembly <NUM> rotates based on the angle the aircraft is flying at relative to the oncoming airflow. More specifically, vane <NUM> rotates to be parallel with, or align with, oncoming airflow. Vane <NUM> causes vane hub <NUM> to rotate. Rotation of vane hub <NUM> causes rotation of a vane shaft, which is within housing <NUM> and coupled to a rotational sensor that measures the local angle of attack or angle of the airflow relative to the fixed aircraft structure. The angle of attack measurement is communicated to an aircraft flight computer via electronics interface connector <NUM>.

When the aircraft is in flight, faceplate <NUM> is exposed to external airflow, which is cold and often contains water droplets or ice particles. Periphery <NUM> of faceplate <NUM> is also adjacent the aircraft skin, which is below freezing. Heated faceplate <NUM> conducts heat to the rotating components of angle of attack sensor <NUM>, such as vane assembly <NUM>. Ice particles from oncoming airflow directly impinge on heated exterior surface <NUM> of faceplate <NUM> and melt or bounce off faceplate <NUM>. Faceplate <NUM> eliminates icing that can result from both direct impingement and runback of the melted ice particles or liquid water.

A first failure mode avoided by angle of attack sensor <NUM> is runback icing, where liquid water or ice that has melted on a heated faceplate runs back to a colder surface of the faceplate, refreezes, and grows into a large ice horn that impacts angle of attack measurement. A second failure mode avoided by angle of attack sensor <NUM> is step icing, or ice growth at the interface between the faceplate and the aircraft skin.

The continuous incline of exterior surface <NUM> of faceplate <NUM> allows ice and water to shed from faceplate <NUM>, redirecting the melted ice particles or liquid water to eliminate runback.

The frustoconical shape of faceplate <NUM> also causes a static pressure bulge, or an increase in static pressure on leading edge <NUM> of faceplate <NUM>. As a result, incoming water droplets are diverted to the sides of faceplate <NUM> and vane <NUM>, creating a shadowing effect aft of vane <NUM> at trailing edge <NUM> of faceplate <NUM> where periphery <NUM> meets the aircraft skin. Ice is prevented from accumulating aft of vane <NUM> where any step, or height difference, between faceplate <NUM> and the aircraft skin would otherwise result in ice growth.

Additionally, the frustoconical shape of faceplate <NUM> causes flow separation at downstream portion <NUM> of faceplate <NUM>, or a trailing eddy. As such, any water droplets from downstream portion <NUM> are wicked away, preventing water droplets from freezing and accumulating into ice growths.

Further, the slope of exterior surface <NUM> of faceplate <NUM> causes faceplate <NUM> to project into the airstream, which shields downstream portion <NUM> of faceplate <NUM> from being directly hit by water droplets. Because an exterior surface of vane hub <NUM> is not flush with an entirety of exterior surface <NUM> of faceplate <NUM> and is above the skin of the aircraft, incoming water droplets are more likely to continue downstream than accrete on vane hub <NUM>, which is farther off the boundary layer, diminishing the impact of any ice build-up.

On heated faceplates having a flat outer surface, impinging water runback can refreeze and form ice growths on the colder downstream portion of the faceplate. The ice accumulation forms a shape behind the vane that becomes large enough to disrupt airflow and cause errors in measurements of the angle of attack sensor. Additionally, impinging water runback can freeze and accumulate at the interface between the faceplate and the aircraft skin, which is not heated. Such step icing affects the accuracy of the angle of attack sensor measurements. Faceplate <NUM> mitigates both (<NUM>) ice accumulation on downstream portion <NUM> of faceplate <NUM> aft of vane <NUM> and (<NUM>) ice accumulation at the interface of faceplate <NUM> and the aircraft skin.

<FIG> is a sectional view of faceplate <NUM> of angle of attack sensor <NUM>. <FIG> is a sectional view of angle of attack sensor <NUM> showing faceplate <NUM> having faceplate heater <NUM> and showing bearing support cage <NUM>. <FIG> is an isometric bottom view of faceplate <NUM>. <FIG>, <FIG>, and <FIG> will be discussed together. Angle of attack sensor <NUM> includes faceplate <NUM>, vane assembly <NUM> (shown in <FIG>), which includes vane hub <NUM> and vane <NUM>, vane shaft <NUM> (shown in <FIG>), rotating interface cavity <NUM>, rotational position sensor <NUM> (shown in <FIG>), outer bearing <NUM> (shown in <FIG>), inner bearing <NUM> (shown in <FIG>), and faceplate heater <NUM> (shown in <FIG>). Faceplate <NUM> includes interior surface <NUM>, exterior surface <NUM>, opening <NUM>, and bearing support cage <NUM>, which includes outer support <NUM>, inner support <NUM>, supporting leg <NUM>, supporting leg <NUM>, support cavity <NUM>, outer bearing bore <NUM>, and inner bearing bore <NUM>.

Angle of attack sensor <NUM> has the same structure and function as described with respect to <FIG>, <FIG>, and <FIG>. A first end of rotatable vane shaft <NUM> is connected to vane hub <NUM> via vane shaft connectors <NUM> (shown in <FIG>). More specifically, vane shaft connectors <NUM> extend through vane hub <NUM> to connect vane hub <NUM> to vane shaft <NUM>. Vane shaft <NUM> is rotatable about axis A (shown in <FIG>). Vane <NUM>, vane hub <NUM>, and vane shaft <NUM> are configured to rotate together. Vane hub <NUM> is positioned in rotating interface cavity <NUM>, which is a space within opening <NUM> of faceplate <NUM>. Rotating interface cavity <NUM> extends from exterior surface <NUM> of faceplate <NUM>. A first end of vane shaft <NUM> extends through rotating interface cavity <NUM>. A second end of vane shaft <NUM> extends into housing <NUM> (shown in <FIG>). Rotational position sensor <NUM> is connected to the second end of vane shaft <NUM> via a resolver shaft. In one embodiment, rotational position sensor <NUM> is a resolver that senses rotational position of vane shaft <NUM>. Rotational position sensor <NUM> is positioned within housing <NUM>. In alternate embodiments, rotational position sensor <NUM> may be an encoder, synchro, linear transformer, rotary variable differential transformer (RVDT), potentiometer, or any other suitable sensor that can sense relative (i.e., incremental) and/or absolute angular position of vane shaft <NUM>. Vane shaft <NUM> extends through outer bearing <NUM> and into inner bearing <NUM>. Outer bearing <NUM> is adjacent rotating interface cavity <NUM>. The second end of vane shaft <NUM> is within inner bearing <NUM>. Faceplate heater <NUM> is positioned on an inner surface of, or embedded in, faceplate <NUM>. Faceplate heater <NUM> may comprise a plurality of heater chips, heater rings, or any other suitable heating elements. Faceplate heater <NUM> extends around vane assembly <NUM>. Faceplate heater <NUM> is a self-regulating heater.

Bearing support cage <NUM> is an integral part of faceplate <NUM>. Bearing support cage <NUM> is an inner central portion of faceplate <NUM> that extends into housing <NUM>. Bearing support cage <NUM> has outer support <NUM> adjacent opening <NUM> and rotating interface cavity <NUM> and inner support <NUM> adjacent rotational position sensor <NUM>. Supporting leg <NUM> extends from outer support <NUM> to inner support <NUM>. Supporting leg <NUM> extends from outer support <NUM> to inner support <NUM> opposite supporting leg <NUM>. Support cavity <NUM> is a space between outer support <NUM> and inner support <NUM> and between supporting leg <NUM> and supporting leg <NUM>. Outer bearing bore <NUM> is an opening that extends through outer support <NUM> and is configured to accept outer bearing <NUM>. Inner bearing bore <NUM> is an opening that extends through inner support <NUM> and is configured to accept inner bearing <NUM>. Outer bearing bore <NUM> and inner bearing bore <NUM> are axially aligned. Outer bearing bore <NUM> and inner bearing bore <NUM> are machined from the same axis on the same machine without moving faceplate <NUM> so that misalignment of outer bearing bore <NUM> and inner bearing bore <NUM> is avoided. Outer bearing bore <NUM> and inner bearing bore <NUM> are cut in the same orientation from a single piece of metal, such as aluminum, via a CNC machining process. Rotating interface cavity <NUM> is also machined at the same time and along the same axis as outer bearing bore <NUM> and inner bearing bore <NUM>. A complex undercut geometry forms support cavity <NUM>.

Rotational position sensor <NUM> is connected to vane shaft <NUM> and measures angular rotation of vane shaft <NUM> and vane assembly <NUM> to determine the local angle of attack. Faceplate heater <NUM> provides heat to faceplate <NUM> near rotating vane assembly <NUM> and vane shaft <NUM>. Outer support <NUM> supports, or holds, outer bearing <NUM>, and inner support <NUM> supports, or holds, inner bearing <NUM>. Vane shaft <NUM> extends from rotating interface cavity <NUM>, through outer bearing bore <NUM>, through support cavity <NUM>, and into inner bearing bore <NUM>. Support cavity <NUM> provides space for a counterweight (not shown) connected to vane shaft <NUM> and heater wires (not shown) to freely rotate unobstructed between outer support <NUM> and inner support <NUM>.

Bearing support cage <NUM> has outer bearing bore <NUM> and inner bearing bore <NUM> that are machined from a single piece of metal, such as aluminum, on the same machine without repositioning faceplate <NUM> so that both boring procedures are performed on the same axis. As a result, precise alignment between outer bearing <NUM> and inner bearing <NUM> on single-piece monolithic faceplate <NUM> is achieved. As such, bearing support cage <NUM> ensures bearing alignment, which is critical because of the short length of vane shaft <NUM> and thus short distance between outer bearing <NUM> and inner bearing <NUM>.

Further, bearing support cage <NUM> provides a direct thermal conduction path from faceplate heater <NUM> to rotational position sensor <NUM>. Heat is routed from faceplate heater <NUM> to rotational position sensor <NUM> via direct conduction through bearing support cage <NUM>, with no other thermal interfaces. Heat conduction is tailored such that only the necessary amount of heat is bled from the faceplate heater <NUM> through bearing support cage <NUM> to rotational position sensor <NUM>, minimizing the amount of power used by faceplate heater <NUM>. Tailoring heat conduction results in less heat being lost to the cold oncoming airflow.

Traditionally, a series of parts stack up to create the structure to hold the outer bearing and the inner bearing. As angle of attack sensors are mounted in locations where aircraft interior compartments are relatively small, the overall length of the angle of attack sensor from the interior surface of the faceplate to the electrical interface connector must be kept to a minimum. Therefore, the vane shaft of the angle of attack sensor is short in length, requiring a stack up of multiple parts over a short distance. This stack up creates a series of tolerances that may compound to result in misalignment between the outer bearing and the inner bearing. Bearing misalignment can cause higher friction and spring-back that result in reduced overall performance (sensitivity and accuracy) of the angle of attack sensor. Misalignment is very difficult to correct and in some instances parts or complete assemblies are scrapped due to the inability to achieve stated performance.

Near perfect alignment (less than <NUM> inch, or <NUM> millimeters, center to center relative tolerance) between outer bearing <NUM> and inner bearing <NUM> is achieved via bearing support cage <NUM>, eliminating any risk of shaft bending due to misalignment and keeping friction to a minimum, which results in improved unit accuracy and sensitivity.

Further, traditional angle of attack sensors sometimes include specific heaters for heating the rotational position sensor. However, with modern icing requirements, the heaters have been redeployed as faceplate heaters, leaving the rotational position sensors less temperature controlled than in the past. Due to the complexity of heater architectures and the need to identify heater malfunction, simply adding another heater is less desirable. Additionally, angle of attack sensor <NUM> is cold prior to flight and must be fully operational typically within a short amount of time after power-on, resulting in a short warm up time for rotational position sensor <NUM>.

A direct conduction path from faceplate heater <NUM> to rotational position sensor <NUM> allows heating of rotational position sensor <NUM> within the required warm up time without requiring a tertiary heater, or an additional heater specifically for heating rotational position sensor <NUM>, which requires additional power, reduces overall reliability, and is less cost-effective. The single-piece design of faceplate <NUM> also reduces parasitic losses. As a result, more power from the limited overall power budget of angle of attack sensor <NUM> can be used to reduce icing and ensure performance of angle of attack sensor <NUM> in icing conditions.

As mechanical devices with varying coefficients of thermal expansion among components, angle of attack sensors are susceptible to operational temperature differences. As a result, it is difficult to achieve a common stated accuracy over the total temperature range of operation. Providing a direct thermal conduction path from faceplate heater <NUM> to rotational position sensor <NUM> allows angle of attack sensor <NUM> to utilize faceplate heater <NUM> positioned for anti-icing to reduce the operational temperature variation range of rotational position sensor <NUM> (for example, increasing the lower bound from -<NUM> degrees Celsius to <NUM> degrees Celsius), allowing rotational position sensor <NUM> to achieve a tighter accuracy over the entire operational environmental envelope. By utilizing self-regulating heaters instead of fixed resistance heaters, there is no increase to the upper temperature limit.

<FIG> is a top view of angle of attack sensor <NUM> showing collection efficiency pattern C of faceplate <NUM>. <FIG> is a top view of angle of attack sensor <NUM> showing temperature profile T of faceplate heater <NUM>. <FIG> and <FIG> will be discussed together. Angle of attack sensor <NUM> includes faceplate <NUM>, vane assembly <NUM>, which includes vane hub <NUM> and vane <NUM> (including root <NUM> and tip <NUM>). Faceplate <NUM> includes exterior surface <NUM>, opening <NUM>, periphery <NUM>, leading edge <NUM>, trailing edge <NUM>, upstream portion <NUM>, and downstream portion <NUM>. Collection efficiency pattern C includes first zone <NUM>, second zone <NUM>, third zone <NUM>, fourth zone <NUM>, fifth zone <NUM>, sixth zone <NUM>, and seventh zone <NUM>. Temperature profile T includes first temperature zone <NUM>, second temperature zone <NUM>, third temperature zone <NUM>, fourth temperature zone <NUM>, fifth temperature zone <NUM>, sixth temperature zone <NUM>, and seventh temperature zone <NUM>.

Angle of attack sensor <NUM> has the same structure and function as described with respect to <FIG>. As shown in <FIG>, frustoconical faceplate <NUM> has collection efficiency pattern C, which illustrates different zones that represent different areas of faceplate <NUM> with different collection efficiencies. A collection efficiency indicates the risk of ice growth on exterior surface <NUM> of faceplate <NUM> from ice crystals, water molecules, or other particles in the airflow traveling over faceplate <NUM>. The shape, or sloped profile, of faceplate <NUM> determines collection efficiency pattern C of faceplate <NUM>.

In this embodiment, collection efficiency pattern C of faceplate <NUM> has first zone <NUM>, second zone <NUM>, third zone <NUM>, fourth zone <NUM>, fifth zone <NUM>, sixth zone <NUM>, and seventh zone <NUM> that form a whale tail, or trapezoidal, shape on exterior surface <NUM> of faceplate <NUM>. First zone <NUM> is at upstream portion <NUM> of faceplate <NUM> near leading edge <NUM>. Second zone <NUM> surrounds first zone <NUM>. Third zone <NUM> is adjacent second zone <NUM>, having a strip on either side of second zone <NUM> that extends and expands from opening <NUM> to periphery <NUM>. As such, third zone <NUM> diverges toward leading edge <NUM> of faceplate <NUM>. Fourth zone <NUM> has two strips, each strip adjacent a strip of third zone <NUM> and extending and expanding from opening <NUM> to periphery <NUM>. As such, fourth zone <NUM> diverges toward leading edge <NUM> of faceplate <NUM>. Fifth zone <NUM> has two strips, each strip adjacent a strip of fourth zone <NUM> and extending and expanding from opening <NUM> to periphery <NUM>. As such, fifth zone <NUM> diverges toward leading edge <NUM> of faceplate <NUM>. Sixth zone <NUM> has two strips, each strip adjacent a strip of fifth zone <NUM> and extending and expanding from opening <NUM> to periphery <NUM>. As such, sixth zone <NUM> diverges toward leading edge <NUM> of faceplate <NUM>. First zone <NUM>, second zone <NUM>, third zone <NUM>, fourth zone <NUM>, fifth zone <NUM>, and sixth zone <NUM> are all located at upstream portion <NUM> of faceplate <NUM>, upstream of vane <NUM>. Seventh zone <NUM> is adjacent both strips of sixth zone <NUM> and is located at downstream portion <NUM> of faceplate <NUM>, including near trailing edge <NUM>. First zone <NUM> is most likely to accumulate ice. Seventh zone <NUM> has the lowest propensity for ice growth. The likelihood of ice accumulation on faceplate <NUM> decreases from first zone <NUM> to seventh zone <NUM>. In alternate embodiments, faceplate <NUM> may have a different shape, as indicated above with respect to <FIG>, and thus may have a different collection efficiency pattern C with different zones.

As shown in <FIG>, Temperature profile T illustrates the heating pattern generated by heating elements of faceplate heater <NUM> (shown in <FIG>) on an interior surface of, or embedded within, faceplate <NUM>, which is derived from collection efficiency pattern C of faceplate <NUM>. Temperature profile T of <FIG> illustrates the temperature profile of faceplate <NUM> within a few seconds of faceplate heater <NUM> being powered on. Faceplate heater <NUM> is comprised of multiple heating elements mounted on faceplate <NUM> and distributed asymmetrically around vane assembly <NUM> to address icing concerns. Faceplate heater <NUM> has heating elements arranged around vane hub <NUM> of vane assembly <NUM>. Additional heating elements of faceplate heater <NUM> are also positioned upstream of vane assembly <NUM>, toward upstream portion <NUM> and leading edge <NUM> of faceplate <NUM>. Heating elements of faceplate heater <NUM> are placed around vane assembly <NUM> to achieve the heat distribution of temperature profile T on faceplate <NUM>.

Temperature profile T has first temperature zone <NUM>, second temperature zone <NUM>, third temperature zone <NUM>, fourth temperature zone <NUM>, fifth temperature zone <NUM>, sixth temperature zone <NUM>, and seventh temperature zone <NUM> along exterior surface <NUM>. First temperature zone <NUM> is at upstream portion <NUM> of faceplate <NUM> near a leading edge of vane hub <NUM>. Second temperature zone <NUM> surrounds first temperature zone <NUM> at upstream portion <NUM>. Third temperature zone <NUM> is adjacent second temperature zone <NUM> and surrounds vane hub <NUM>. Fourth temperature zone <NUM> is adjacent and surrounds third temperature zone <NUM>. Fifth temperature zone <NUM> is adjacent and surrounds fourth temperature zone <NUM>. Sixth temperature zone <NUM> is adjacent and surrounds fifth temperature zone <NUM>. Seventh temperature zone <NUM> is adjacent and surrounds sixth temperature zone <NUM>. Seventh temperature zone <NUM> extends from sixth temperature zone <NUM> to periphery <NUM> of faceplate <NUM>. As such, third temperature zone <NUM>, fourth temperature zone <NUM>, fifth temperature zone <NUM>, sixth temperature zone <NUM>, and seventh temperature zone <NUM> all surround vane hub <NUM>.

First temperature zone <NUM> has the highest temperature among the zones. Temperature decreases from first temperature zone <NUM> to seventh temperature zone <NUM> or from opening <NUM> to periphery <NUM>. Some heat conduction still occurs within seventh temperature zone <NUM>. Temperatures within each of first temperature zone <NUM>, second temperature zone <NUM>, third temperature zone <NUM>, fourth temperature zone <NUM>, fifth temperature zone <NUM>, sixth temperature zone <NUM>, and seventh temperature zone <NUM> have some variation, with the amount of variation decreasing from first temperature zone <NUM> to seventh temperature zone <NUM>.

As seen in <FIG>, faceplate <NUM> has a higher collection efficiency at upstream portion <NUM> near leading edge <NUM> of faceplate <NUM>, indicating that ice or water particles are more likely to adhere to and form ice growths on leading edge <NUM> of conical exterior surface <NUM> of faceplate <NUM> than trailing edge <NUM> of faceplate <NUM>. Temperature profile T is designed to address the icing concerns associated with collection efficiency pattern C. Because downstream portion <NUM> of faceplate <NUM>, located in seventh zone <NUM>, has a very low collection efficiency, less heat is needed at downstream portion <NUM> of faceplate <NUM>, which is located in seventh temperature zone <NUM>. As such, more power for heat is focused on upstream portion <NUM> of faceplate <NUM> than downstream portion <NUM> of faceplate <NUM>, particularly near the leading edge of vane hub <NUM>. Variation in collection efficiencies throughout collection efficiency pattern C on faceplate <NUM> results in an asymmetric layout of heating elements of faceplate heater <NUM> to direct heat only where needed and thus use power efficiently. As seen in <FIG>, faceplate heater <NUM> maintains heat around an entire circumference of rotating vane assembly <NUM>, preventing water and ice particles from traveling beneath vane hub <NUM>, freezing, and locking vane assembly <NUM>. Faceplate heater <NUM> also has heating elements arranged to provide a higher concentration of heat to faceplate <NUM> upstream of vane assembly <NUM>.

Faceplate heater <NUM> creates temperature profile T of frustoconical faceplate <NUM> based on collection efficiency pattern C of faceplate <NUM> to provide efficient heating of faceplate <NUM>, and thus enable efficient use of power.

<FIG> are photographs showing the progression of temperature profiles illustrating the heating pattern generated by heating elements of faceplate heater <NUM> on faceplate <NUM> over time. <FIG> are a series of photographs taken from three seconds to twenty-five seconds after start-up showing the change in the heating pattern similar to that shown in <FIG>. <FIG> shows the temperature profile three seconds after start-up. <FIG> shows the temperature profile four seconds after start-up. <FIG> shows the temperature profile five seconds after start-up. <FIG> is shows the temperature profile twenty seconds after start-up. <FIG> shows the temperature profile twenty-five seconds after start-up. In <FIG>, the lighter the color, the higher the temperature. As illustrated in the photos of <FIG>, the heating pattern is growing and intensifying over a short amount of time after start-up, when power to the heating elements of faceplate heater <NUM> is turned on.

<FIG> is a partial side view of angle of attack sensor <NUM> showing vane <NUM> having vane heating elements 114A-114I. <FIG> is a sectional view of vane <NUM> showing a profile of vane <NUM>. <FIG> and <FIG> will be discussed together. Angle of attack sensor <NUM> includes faceplate <NUM>, vane assembly <NUM>, which includes vane hub <NUM> and vane <NUM> (including root <NUM>, tip <NUM>, leading edge <NUM>, trailing edge <NUM>, first lateral face <NUM>, second lateral face <NUM>, and chord <NUM>), and vane heating elements 114A-114I (shown in <FIG>). Faceplate <NUM> includes opening <NUM>.

Angle of attack sensor <NUM> has the same structure and function as described with respect to <FIG>. Vane <NUM> has leading edge <NUM> extending from root <NUM> to tip <NUM> at an upstream portion of vane <NUM> and trailing edge <NUM> extending from root <NUM> to tip <NUM> at a downstream portion of vane <NUM>, opposite leading edge <NUM>. First lateral face <NUM> and second lateral face <NUM> of vane <NUM> each extend from leading edge <NUM> to trailing edge <NUM>, second lateral face <NUM> being opposite first lateral face <NUM>. First lateral face <NUM> and second lateral face <NUM> are symmetric about chord <NUM> that defines a symmetrical center between first lateral face <NUM> and second lateral face <NUM>. Chord <NUM> of vane <NUM> extends in a direction from leading edge <NUM> to trailing edge <NUM> and bisects first lateral face <NUM> and second lateral face <NUM>.

The outer surface profile of each of first lateral face <NUM> and second lateral face <NUM> is both nonlinear and geometrically convex from leading edge <NUM> to transition point T. As such, vane <NUM> has a symmetric NACA (National Advisory Committee for Aeronautics) profile from leading edge <NUM> to transition point T. Transition point T is at the tangent to the widest point of the symmetric geometrically convex outer surface profile, or NACA profile, of first lateral face <NUM> and second lateral face <NUM>. Each of first lateral face <NUM> and second lateral face <NUM> extends or flares out from transition point T to trailing edge <NUM> so that vane has a diverging wedge shape from transition point T to trailing edge <NUM>. The diverging wedge shape has an angle of up to <NUM> degrees, and preferably up to <NUM> degrees. As such, vane <NUM> has a wedge profile extending from the NACA profile. Thus, first lateral face <NUM> and second lateral face <NUM> each have a forward section with an outer surface profile that is nonlinear and geometrically convex from leading edge <NUM> to an intermediate chord location (transition point T) and an aft section with an outer surface profile that extends out to form a diverging wedge shape that extends from the intermediate chord location (transition point T) to trailing edge <NUM>. First lateral face <NUM> and second lateral face <NUM> form a truncated symmetrical NACA profile and wedge-like profile. First lateral face <NUM> and second lateral face <NUM> of the wedge-like profile form an angle equal to or between <NUM> degrees (such that the wedge-like profile is parallel to the direction of airflow) and <NUM> degrees, and preferably between <NUM> degrees and <NUM> degrees. As shown in <FIG>, vane heating elements 114A-114I are disposed within vane <NUM> between first lateral face <NUM> and second lateral face <NUM> proximate leading edge <NUM> to provide heat to vane <NUM> for anti-icing and/or deicing operations. Vane heating elements 114A-<NUM> each have a forward end disposed at a distance from leading edge <NUM> of vane <NUM> that is less than ten percent of a length of chord <NUM> of vane <NUM>.

In this embodiment, vane <NUM> has nine separate heating elements (vane heating elements 114A-114I) extending from a location proximate root <NUM> to a location proximate tip <NUM>. In alternate embodiments, vane <NUM> may include any number of heating elements. For example, vane <NUM> may include a single vane heating element disposed within vane <NUM> from a location proximate root <NUM> to a location proximate tip <NUM> to provide heat to vane <NUM> during anti-icing and/or deicing operations. Vane heating elements 114A-114I can be self-regulating heating elements (e.g., self-regulating chip heaters) or heating elements that are controlled via continuous or pulsed electrical current. In some examples, vane heating elements 114A-114I can be thermostatically controlled to achieve and/or maintain a target temperature. Electrical power for vane heating elements 114A-114I is provided by a power supply (e.g., received via an external power source) and routed through, e.g., vane shaft <NUM> (shown in <FIG>) and between first lateral face <NUM> and second lateral face <NUM> to vane heating elements 114A-114I.

In operation, air flowing over vane <NUM> in a direction from leading edge <NUM> to trailing edge <NUM> acts on first lateral face <NUM> and second lateral face <NUM> to cause vane <NUM> to rotate such that pressures experienced by first lateral face <NUM> and second lateral face <NUM> equalize and chord <NUM> aligns with a direction of the oncoming airflow. Rotation of vane <NUM> causes corresponding rotation of vane hub <NUM> and vane shaft <NUM>. Rotational position sensor <NUM> measures the rotational position (e.g., relative and/or absolute rotational position) of vane shaft <NUM> and communicates the measured position signal to an external device, such as an air data computer, stall warning computer, data concentrator unit, aircraft display, or other external device via an electronic communication device within housing <NUM>. Vane heating elements 114A-114I provide heat to vane <NUM> during operation to prevent accretion of ice on vane <NUM>. An outer surface profile of each of first lateral face <NUM> and second lateral face <NUM> decreases an amount of heat dissipation from vane <NUM>, thereby decreasing an amount of electrical current required by vane heating elements 114A-114I to provide sufficient heat to vane <NUM> for the anti-icing and/or deicing operations.

Vane <NUM> has a NACA profile extending downstream from leading edge <NUM> to a wedge-like profile extending from the NACA profile the trailing edge <NUM>, the NACA and wedge profiles meeting at transition point T. The transition from the NACA profile to the wedge-like profile occurs at the point of maximum thickness of the symmetrical NACA profile of vane <NUM>. Leading edge <NUM> having a NACA profile allows vane heating elements 114A-114I to be closer to the surface of leading edge <NUM>, resulting in ice-free performance of vane <NUM>. The wedge-like profile makes vane <NUM> more stable and accurate at high Mach speeds. The overall length of vane <NUM> (from leading edge <NUM> to trailing edge <NUM>) is kept short, which results in less surface area to heat and thus ice-free performance.

Angle of attack sensors generally adopt a wedge profile that tapers to a sharper leading edge, which is inherently stable and offers high accuracy in flight conditions. However, that profile has proven difficult to certify to increasingly stringent icing conditions without also drawing excessive power as it is difficult to heat the leading edge of a traditional wedge design to keep it ice free across all icing conditions. A NACA vane profile has excellent icing performance, due to the NACA shape allowing vane heating elements to be installed in close proximity to the leading edge. However, it was discovered that this NACA profile can be unstable at High Mach numbers (<NUM>-<NUM>).

Vane <NUM> has a modified NACA profile to avoid flow separation and increase stability by adding material to form a wedge shape aft of the transition point T. As a result, vane <NUM> maintains an almost identical level of icing performance (ice-free) and is stable at High Mach numbers (<NUM>-<NUM>). Thus, this combination provides both optimal anti-icing performance and aerodynamic performance.

<FIG> is a side view of angle of attack sensor <NUM> showing a relationship of faceplate slope angle A, vane sweep angle S, and vane height H. Angle of attack sensor <NUM> includes faceplate <NUM>, vane assembly <NUM>, which includes vane hub <NUM> and vane <NUM> (including root <NUM> and tip <NUM>), and leading edge <NUM>. Faceplate <NUM> includes exterior surface <NUM>, opening <NUM>, periphery <NUM>, leading edge <NUM>, upstream portion <NUM>, and downstream portion <NUM>.

Angle of attack sensor <NUM> has the same structure and function as described with respect to <FIG>. Faceplate slope angle A is the slope of exterior surface <NUM> of faceplate <NUM> from periphery <NUM> to opening <NUM>. Faceplate slope angle A is equal to or between <NUM> degrees and <NUM> degrees, and is preferably equal to or between <NUM> degrees and <NUM> degrees. Faceplate slope angle A is great enough to have the ability to shed ice particles and/or water droplets and lower the risk of step icing at trailing edge <NUM> of faceplate <NUM> and low enough to not increase water droplet collection at leading edge <NUM> of faceplate <NUM>, which would require additional power to remain ice free. Vane sweep angle S is the angle between leading edge <NUM> of vane <NUM> and a line perpendicular to vane hub <NUM>. Vane sweep angle S is greater than zero. Vane <NUM> extends toward downstream portion <NUM> of faceplate <NUM> as a result of vane sweep angle S. Vane height H is the height of vane <NUM>, or the distance between the horizontal of root <NUM> and the horizontal of tip <NUM>. The greater the faceplate slope angle A, the shorter the vane height H. The shorter the vane height H, the greater the vane sweep angle S, in order to generate the required torque. In an example embodiment, faceplate slope angle A is <NUM> degrees, vane height H is <NUM>, and vane sweep angle S is <NUM> degrees. The distance from tip <NUM> of vane <NUM> to the skin of the aircraft is between <NUM> and <NUM> inches, and preferably <NUM> inches.

The effects of vane sweep angle S and vane height H, in addition to other aspects of vane shape, can be used to achieve interchangeability between vanes of different angle of attack sensors having various configurations. To ensure accuracy of angle of attack sensor <NUM>, vane height H or the distance from the aircraft is critical. Vane heights H that are too long or too short impact the accuracy of angle of attack sensor <NUM> as a function from the aircraft skin. Each of vane sweep angle S, vane height H, and faceplate slope angle A can be varied to produce a vane that is interchangeable with different vanes of various angle of attack sensors. For example, vane sweep angle S can be modified while vane height H may remain at a predetermined value in order to achieve required sensitivity.

As part of normal aircraft certification, the angle of attack vane output is calibrated for local flow effects across the flight envelope. Those calibration tables are typically located within the ADIRUs (Air Data Inertial Reference Unit) onboard the aircraft and any change to those devices is extremely expensive and complicated. Previously, interchangeability design levers were not completely understood. Angle of attack configuration to configuration interchangeable performance is achieved through modifying vane height H and/or vane sweep angle S.

While the invention has been described with reference to an exemplary embodiment(s), 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 invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof, which is defined by the appended claims.

Claim 1:
An angle of attack sensor comprising:
a housing (<NUM>) having an open end and a closed end;
a faceplate (<NUM>) positioned on the open end of the housing (<NUM>), the faceplate (<NUM>) comprising:
a periphery at an outer edge of the faceplate (<NUM>);
a central opening (<NUM>);
mounting bores extending through the faceplate around the periphery of the faceplate; and
an exterior surface extending from the periphery to the central opening (<NUM>); and
a vane assembly (<NUM>) extending through the central opening (<NUM>) of the faceplate (<NUM>), wherein the vane assembly includes a vane hub positioned in the central opening of the faceplate and a vane connected to the vane hub, wherein an exterior surface of the vane hub and the vane are configured to be positioned above a skin of an aircraft;
wherein the exterior surface of the faceplate (<NUM>) has a sloped profile from the periphery to the central opening (<NUM>); and
wherein the exterior surface of the faceplate has a slope equal to or between <NUM> degrees and <NUM> degrees and, when mounted on the aircraft, a distance from a tip of the vane to the skin of the aircraft is between <NUM> and <NUM>.