Patent Description:
Ice can form on the surfaces of an aircraft in flight when water droplets impinge and freeze on the aircraft surfaces. The accretion of ice on certain aerodynamic surfaces can reduce the performance and handling characteristics of the aircraft. For example, ice accretion on the leading edges of the wings can alter the cross-sectional shape of the wings which can disrupt the flow of air over the wings, resulting in reduced lift capability of the wings, increased aerodynamic drag, added weight, and increased stall speed of the aircraft.

Current methods of addressing ice accretion on the leading edges of airfoils include the use of inflatable deicing boots mounted on leading edge surfaces. When ice has accumulated on a leading edge, the boots may be inflated with compressed air causing the ice to crack. Air flowing over the wings blows the ice off the wings, after which the boots are deflated to return the leading edge to its pre-inflated shape. Although generally effective, deicing boots add cost, complexity and weight to the aircraft.

Another method of addressing ice accretion on leading edges involves the use of a bleed air de-icing or anti-icing system in which hot air is bled from gas turbine engines of an aircraft. The bleed air is routed through spray tubes extending along the interior of the leading edges and is discharged in a manner to heat the wing surfaces. The bleed air may be periodically activated in a manner to maintain the surfaces of the leading edges above freezing to prevent the formation of ice, or to melt the ice to an extent that air flowing over the wings blows the ice off the wings. Although effective in addressing ice accretion, the extraction of bleed air from the engines reduces engine performance. In addition, the spray tubes and other hardware of a bleed air system add to the cost, complexity and weight of the aircraft.

In <CIT>, a system is described for detecting ice or supercooled large droplets within an area of interest having a detection system measuring radiance or reflectance of the area of interest when exposed to shortwave infrared radiation having a wavelength in the range of about <NUM> to about <NUM>. The detection system measures the radiance or reflectance in a first band having a wavelength in the range of about <NUM> to about <NUM> and outputting a first band signal, and further measures the radiance or reflectance in a second band having a wavelength in the range of about <NUM> to about <NUM> and outputting a second band signal. A processing unit determines a ratio of the first band signal and the second band signal and compares the ratio to a predetermined critical ratio and outputs a determination signal indicating presence of ice or supercooled water droplets.

In <CIT>, an aircrew automation system is described that provides a pilot with high-fidelity knowledge of the aircraft's physical state, and notifies that pilot of any deviations in expected state based on predictive models. The aircrew automation may be provided as a noninvasive ride-along aircrew automation system that perceives the state of the aircraft through visual techniques, derives the aircraft state vector and other aircraft information, and communicates any deviations from expected aircraft state to the pilot.

As can be seen, there exists a need in the art for a system and method for reducing ice accretion on an airfoil that reduces the need for ice protection hardware (e.g., deicing or anti-icing system hardware).

The above-noted needs associated with ice accretion on airfoils are specifically addressed and alleviated by the present disclosure which provides a system according to appended claim <NUM>.

Also disclosed is a method of modifying a location of a water impingement limit on a surface of an airfoil of an aircraft according to appended claim <NUM>.

A further example of the method includes sensing an air temperature and a droplet size of water droplets in an environment of a flight path of the aircraft, determining, based on the air temperature and the droplet size, an existence of icing conditions to which the aircraft is currently subjected or is predicted to be subjected, and upwardly deflecting, in response to determining the existence of icing conditions, at least one laterally symmetric pair of movable surfaces respectively coupled to the pair of wings. In addition, the method includes increasing a wing angle of attack of the wings in response to upwardly deflecting the laterally symmetric pair of movable surfaces to thereby cause a forward and downward shift of a water impingement upper limit on an upper surface of the wings and an aftward and downward shift of a water impingement lower limit on a lower surface of the wings.

The features, functions and advantages that have been discussed can be achieved independently in various examples of the present disclosure or may be combined in yet other examples, further details of which can be seen with reference to the following description and drawings below.

These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numbers refer to like parts throughout and wherein:.

Referring now to the drawings wherein the showings are for purposes of illustrating preferred and various examples of the disclosure, shown in <FIG> is a schematic diagram of a water impingement limit modification system <NUM> for modifying the location of the water impingement limits <NUM>, <NUM> (<FIG>) on at least one airfoil <NUM> (<FIG>) of an aircraft <NUM> (<FIG>). Modification of the location of the water impingement limits <NUM>, <NUM> on an airfoil <NUM> results in the modification of the location of ice accretion limits <NUM>, <NUM> (<FIG>) on the airfoil <NUM>. Modifying the location of the ice accretion limits <NUM>, <NUM> reduces the negative effects of ice accretion <NUM> on the aerodynamics of air flowing over the airfoil <NUM>. For example, modifying the location of the ice accretion limits <NUM>, <NUM> reduces the extent of flow separation (not shown) over the airfoil <NUM> that may occur as a result of the ice accretion <NUM>. In addition, modifying the location of the ice accretion limits <NUM>, <NUM> reduces the negative effect of ice accretion <NUM> on the maximum lift coefficient <NUM> (e.g., <FIG>), and reduces the amount of aerodynamic drag generated by the ice accretion <NUM>.

As described in greater detail below, the water impingement limits <NUM>, <NUM> on an airfoil <NUM> are the locations defined by the tangent trajectories <NUM> (<FIG>) of water droplets <NUM> (<FIG>), in the flow of air moving over the airfoil <NUM>. For example, referring to <FIG>, shown is a forward portion or wing leading edge <NUM> of a wing <NUM> which has a suction side <NUM> (i.e., a wing upper surface having a relatively high degree of curvature, the side of lower pressure side), and a pressure side <NUM> (i.e., a wing <NUM> lower surface having a relatively low degree of curvature, the side of higher pressure). The suction side <NUM> has a suction side water impingement limit <NUM> and the pressure side <NUM> has a pressure side water impingement limit <NUM> which are each measured along the airfoil <NUM> surface relative to the highlight <NUM> of the airfoil <NUM>. In the present disclosure, the highlight <NUM> of an airfoil <NUM> is the point furthest forward on the surface of the leading edge when the airfoil <NUM> is at an angle of attack of <NUM>°. For airfoils <NUM> having a symmetrical cross-section such as some horizontal tails (e.g., a horizontal stabilizer <NUM> and elevator <NUM> - <FIG>), the suction side <NUM> and the pressure side <NUM> may have the same degree of curvature. However, orienting the horizontal tail at an angle of attack in which the stabilizer leading edge <NUM> is oriented in a downward direction generates low pressure or suction on the stabilizer lower side such that the stabilizer lower side is the suction side <NUM> (i.e., the side of lower pressure side) and the stabilizer upper side is the pressure side <NUM> (i.e., the side of higher pressure side). Regardless of whether the suction side <NUM> of an airfoil <NUM> is on the upper side or the lower side of the airfoil <NUM>, the suction side water impingement limit <NUM> and the pressure side water impingement limit <NUM> of an airfoil <NUM> are each located at a respective tangent trajectory <NUM> (<FIG>) of a water droplet <NUM> (<FIG>) of a given size that starts out upstream of the airfoil <NUM> in the freestream flow <NUM> (e.g., <FIG>), as described in greater detail below.

When an aircraft <NUM> (<FIG>) is subjected to icing conditions, water droplets <NUM> (<FIG> and <FIG>) impinging on the airfoil <NUM> (e.g., between the suction side water impingement limit <NUM> and the pressure side water impingement limit <NUM> - <FIG>) will freeze, causing ice accretion <NUM> (<FIG>) on the airfoil <NUM>. Advantageously, in the presently-disclosed system <NUM> (<FIG>), the system <NUM> is configured to detect the existence of icing conditions such that when the aircraft <NUM> encounters or is predicted to encounter icing conditions, the system <NUM> is configured to increase the angle of attack (<FIG>) of at least one airfoil <NUM> of the aircraft <NUM> in a manner causing the location of the water impingement limits <NUM>, <NUM> (<FIG>) to proactively shift at least partially away from the suction side <NUM> (<FIG>), and shift more toward the pressure side <NUM> (<FIG>). In the example of the wing <NUM> of <FIG>, an increase in the wing angle of attack <NUM> causes a combination lowering and forward shifting of the suction side water impingement limit <NUM> relative to the highlight <NUM>, and a combination lowering and aftward shifting of the pressure side water impingement limit <NUM> relative to the highlight <NUM>. Correspondingly in <FIG>, the shifting of the water impingement limits <NUM>, <NUM> (<FIG>) has the effect of shifting the location of the ice accretion limits <NUM>, <NUM> (<FIG>) at least partially away from the suction side <NUM> (i.e., area of high curvature) of the wing <NUM>, which reduces the above-mentioned negative effects of ice accretion <NUM> on the aerodynamics of the wing <NUM>.

Referring again to <FIG>, the system <NUM> includes a flight control computer <NUM> configured to receive data representative of environmental parameters <NUM> sensed in an environment <NUM> (<FIG>) of a flight path <NUM> (<FIG>) of an aircraft <NUM> (<FIG>). The flight control computer <NUM> may include activation logic <NUM> configured to determine the existence of icing conditions based on the environmental parameters <NUM> and additionally, but optionally, based on aircraft state data <NUM>. In this regard, the flight control computer <NUM> determines the existence of icing conditions to which the aircraft <NUM> is currently subjected, or the existence of icing conditions to which the aircraft <NUM> is predicted to be subjected at some point along the flight path <NUM> of the aircraft <NUM>. Upon determining the existence of icing conditions, the flight control computer <NUM> may include angle of attack selection logic <NUM> for determining the amount by which the angle of attack of the airfoil <NUM> (<FIG>) is to be increased. The flight control computer <NUM> is configured to generate one or more command signals <NUM> at the appropriate time for actuating one or more movable surfaces <NUM> (e.g., spoilers <NUM>, ailerons <NUM>, horizontal stabilizer <NUM>, elevator <NUM>, etc. - <FIG> and <FIG>) of the aircraft <NUM>. For example, upon determining the current existence of icing conditions, the flight control computer <NUM> may immediately (e.g., within several seconds of detecting icing conditions) generate one or more command signals <NUM>. In contrast, upon determining the existence of icing conditions predicted to occur a later point along the flight path <NUM>, the flight control computer <NUM> may be configured to wait until the aircraft <NUM> nears the predicted location of the icing conditions, and then generate command signals <NUM> preferably prior (e.g., within several seconds) to the time when the aircraft <NUM> enters the icing conditions.

In <FIG>, the system <NUM> further includes one or more surface actuators <NUM> configured to receive command signals <NUM> from the flight control computer <NUM> and, in response to the command signals <NUM>, adjust one or more of the movable surfaces <NUM> in a manner causing an increase in the angle of attack of the airfoil <NUM> (<FIG>) to thereby modify the water impingement limits <NUM>, <NUM> (<FIG>) on the airfoil <NUM>. For example, in an example described in greater detail below, the flight control computer <NUM> may detect the existence of icing conditions, and may generate a command signal <NUM> causing existing spoiler actuators (not shown) to upwardly deflect the spoilers <NUM> (<FIG>) and/or existing aileron actuators (not shown) to upwardly deflect the ailerons <NUM> (<FIG>) in a manner causing the wing angle of attack <NUM> (<FIG>) to increase by a relatively small amount (e.g., <NUM> to <NUM>°), and resulting in a proactive shifting of the location of the water impingement limits <NUM>, <NUM> (<FIG>) at least partially away from the suction side <NUM> (e.g., <FIG>) of the wing <NUM> and at least partially toward the pressure side <NUM> (e.g., <FIG>), to thereby reduce the effects of ice accretion <NUM> (<FIG>) on the aerodynamics of the air flowing over the wing <NUM>.

Referring to <FIG>, shown is an aircraft <NUM> on a flight path <NUM> passing through a cloud <NUM> containing icing conditions. The aircraft <NUM> has one or more airfoils <NUM> (e.g., wings <NUM>, horizontal stabilizer <NUM> - <FIG>) that may be subjected to ice accretion <NUM> (<FIG>) when the aircraft <NUM> is in the icing conditions. The aircraft <NUM> additionally includes a plurality of movable surfaces <NUM> (e.g., spoilers <NUM>, ailerons <NUM>, etc. - <FIG>) for attitude and directional control of the aircraft <NUM>. In the present system <NUM> and method <NUM> (<FIG>), one or more of the movable surfaces <NUM> are temporarily actuated in a manner that increases the angle of attack of one or more of the airfoils <NUM> as a means for proactively shifting the location of the water impingement limits <NUM>, <NUM> (<FIG>) on the one or more airfoils <NUM> to thereby reduce the effects of ice accretion <NUM> (<FIG> on the one or more airfoils <NUM>. Although the present disclosure describes icing conditions as occurring within a cloud <NUM>, icing conditions may occur in non-cloud conditions. In this regard, icing conditions may occur at any time when water droplets <NUM> (e.g., liquid water - <FIG> and <FIG>) freeze upon impingement on an aircraft <NUM> surface, or freeze shortly after (e.g., within several seconds) impingement on an aircraft <NUM> surface.

Referring still to <FIG>, as mentioned above, the flight control computer <NUM> receives data representative of environmental parameters <NUM>, and determines the existence of icing conditions presently occurring and/or predicted to occur along the aircraft <NUM> flight path <NUM> (<FIG>). Such environmental parameters <NUM> include, but are not limited to, air temperatures <NUM> along the flight path <NUM> (<FIG>), droplet size <NUM> of water droplets <NUM> (<FIG>) in the atmosphere (e.g., in clouds <NUM> - <FIG>) along the flight path <NUM>, and liquid water content <NUM> of clouds <NUM> along the flight path <NUM>. Such environmental parameters <NUM> may be sensed by ground-based sensors and forward/or airborne sensors (e.g., onboard the aircraft <NUM>) prior to and/or during the flight of the aircraft <NUM>. The environmental parameters <NUM> may be periodically or continuously provided to the flight control computer <NUM>. For example, ground-based or airborne weather forecasting instrumentation may predict the occurrence of weather conducive to ice accretion <NUM> during the flight of the aircraft <NUM>, and may provide such environmental parameter data to the flight control computer <NUM> prior to and/or during the flight of the aircraft <NUM>. Information regarding the existence, location and/or severity of icing conditions encountered and reported by pilots of other aircraft <NUM> near the flight path <NUM> may also be manually or automatically entered into the flight control computer <NUM>.

Referring to <FIG>, in the present disclosure, air temperature <NUM> is the temperature of ambient air along the flight path <NUM> (<FIG>) and may be periodically or continuously measured and provided to the flight control computer <NUM> by ground-based or airborne temperature measurement instrumentation. Droplet size <NUM> may also be periodically or continuously measured and provided to the flight control computer <NUM> to facilitate a determination of the existence of icing conditions. For example, upon receiving data indicating an air temperature <NUM> of <NUM> or colder, and data indicating the presence of water droplets <NUM> (<FIG>), the flight control computer <NUM> may determine that icing conditions exist. For environmental conditions in which the air temperature <NUM> is slightly warmer than <NUM>, the flight control computer <NUM> may determine that icing conditions exist based on aircraft state data <NUM> including aircraft surface temperature <NUM> measurements lower than <NUM>, and which may occur if the aircraft <NUM> has been exposed to air temperatures <NUM> below <NUM>, and is later located in temperatures at or above <NUM> while the aircraft surface temperature <NUM> is still below freezing. Measurement of aircraft surface temperature <NUM> may be periodically or continuously provided to the flight control computer <NUM> by temperature sensors (not shown) for monitoring the temperature of the airfoil <NUM> surface. Such temperature sensors may be mounted on the wing leading edge <NUM> (<FIG>) of the wing <NUM> (<FIG>), stabilizer leading edge <NUM> (<FIG>) of the horizontal stabilizer <NUM> (<FIG>), and/or at other locations on the airframe.

At air temperatures <NUM> (<FIG>) between <NUM> and approximately -<NUM>, clouds <NUM> (<FIG>) may be comprised of supercooled water droplets which exist in liquid form at temperatures below <NUM>. Droplet size <NUM> (<FIG>) represents the size of water droplets <NUM> such as within a cloud <NUM>, and may be expressed in terms of median volume diameter (MVD). Given a droplet size <NUM> distribution within a cloud <NUM>, the MVD represents the droplet diameter (e.g., microns) for which half the total liquid water content <NUM> in the cloud <NUM> is contained in water droplets <NUM> that are larger than the median, and half the total liquid water content <NUM> is contained in water droplets <NUM> that are smaller than the median. Droplet size <NUM> may be measured and provided to the flight control computer <NUM> (<FIG>) by airborne light detection and ranging (LIDAR) instrumentation (not shown) or other optical instrumentation such as an optical spectrometer.

Liquid water content <NUM> may be described as the amount of water contained within a given volume of cloud <NUM> (<FIG>). Liquid water content <NUM> may be expressed in terms of total mass (e.g., grams) of water per unit volume (e.g., cubic meter) of cloud <NUM>. Liquid water content <NUM> may be indicated and provided to the flight control computer <NUM> by instrumentation such as a Rosemont Ice Detector (not shown) or by a heated-resistance wire (not shown) mounted outside of the aircraft <NUM> (<FIG>) which measures the reduction in temperature as water droplets <NUM> (<FIG>) hit the wire and evaporate. The reduction in wire temperature from water droplet evaporation may be correlated to the liquid water content <NUM> of a cloud <NUM>.

Air temperature <NUM> (<FIG>), droplet size <NUM> (<FIG>), liquid water content <NUM> (<FIG>) and other variables (e.g., altitude <NUM>, horizontal and vertical extent of clouds <NUM>, etc.) are used by aviation governing bodies such as the Federal Aviation Administration (FAA) and foreign equivalents for determining design envelopes for the design of aircraft <NUM> (<FIG>) to meet certification requirements for operation in icing conditions. For example, Federal Aviation Regulation (FAR) Part <NUM>, Appendix C, defines an icing envelope (identified as a continuous maximum atmospheric icing condition) in which the mean effective drop diameter (e.g., median volume diameter, MVD) is <NUM>-<NUM> microns. FAR Part <NUM>, Appendix O, defines an icing envelope of supercooled large drop (SLD) icing conditions in which the drop median volume diameter (MVD) is less than or greater than <NUM> microns, the maximum mean effective drop diameter (MED) of Appendix C continuous maximum (stratiform clouds) icing conditions. Such SLD icing conditions include freezing drizzle (e.g., conditions with spectra maximum drop diameters of from <NUM>-<NUM> microns) and freezing rain (e.g., conditions with spectra maximum drop diameters greater than <NUM> microns) occurring in and/or below stratiform clouds. In this regard, the icing conditions of Appendix O include droplet sizes <NUM> that are larger than the droplet sizes <NUM> included in the icing conditions of Appendix C. Due to their greater mass, the droplet sizes <NUM> under Appendix O will impinge further aft on an airfoil <NUM> (<FIG>) than the relatively smaller droplet sizes <NUM> under Appendix C, such that the icing conditions of Appendix O result in the suction side water impingement limit <NUM> (<FIG>) extending further aft on the suction side <NUM> (<FIG>), causing a correspondingly greater disruption of airflow over the airfoil <NUM> relative to the airflow disruption caused by icing conditions of Appendix C.

In general, the air temperature <NUM> (<FIG>) and/or the droplet size <NUM> (<FIG>), influence the severity of the icing condition. Additionally, the higher the liquid water content <NUM> (<FIG>), the more severe the icing condition. Similarly, the longer the duration over which the aircraft <NUM> (<FIG>) is exposed to relatively large water droplets <NUM> (<FIG>), the more severe the icing conditions. The horizontal extent (e.g., the horizontal distance) of clouds <NUM> (<FIG>) containing icing conditions and the airspeed <NUM> (<FIG>) of the aircraft <NUM> may be used by the flight control computer <NUM> (<FIG>) to determine the duration and therefore the severity of the icing conditions. The combination of airspeed <NUM> and liquid water content <NUM> may also be used by the flight control computer <NUM> to determine the severity of icing conditions, due to the fact that a higher airspeed <NUM> corresponds to a larger quantity of water droplets <NUM> impinging on the aircraft <NUM> per unit time. As described above, due to its relatively large droplet sizes <NUM>, FAR Part <NUM> Appendix O represents a higher level of severity of icing conditions than the icing conditions of FAR Part <NUM> Appendix C which includes relatively smaller droplet sizes <NUM>.

In any one of the system <NUM> (<FIG>) examples disclosed herein, the flight control computer <NUM> (<FIG>) may determine a severity of icing conditions based on at least one of air temperature <NUM> (<FIG>) and droplet size <NUM> (<FIG>) of water droplets <NUM> (<FIG>) in the environment <NUM> (<FIG>) of a flight path <NUM> (<FIG>). The flight control computer <NUM> may generate a command signal <NUM> (<FIG>) proportional to increasing severity of the icing conditions such that one or more surface actuators <NUM> (<FIG>), upon receiving the command signal <NUM>, adjusts one or more movable surfaces <NUM> by an amount proportional to the severity of the icing conditions. In addition to or as an alternative to determining icing condition severity based on air temperature <NUM> and/or droplet size <NUM>, the flight control computer <NUM> may determine icing condition severity based on the above-mentioned liquid water content <NUM> of clouds, airspeed <NUM> (<FIG>), duration of exposure, and other factors such as cloud type (e.g., vertically-developed cumulus-type clouds versus horizontally developed stratus-type clouds). The flight control computer <NUM> may determine the target angle of attack <NUM> (<FIG>) of an airfoil <NUM> (<FIG>) based on the severity of the icing conditions. In this regard, the flight control computer <NUM> may calculate a higher target angle of attack <NUM> (e.g., in an upward direction for a wing - <FIG>; in a downward direction for a horizontal stabilizer - <FIG>) for icing conditions that are more severe, and may calculate a lower target angle of attack <NUM> for icing conditions that are less severe. For example, the flight control computer <NUM> may calculate a relatively high (or higher) target angle of attack <NUM> (e.g., in the range of approximately <NUM>-<NUM>° higher than the current angle of attack) for icing conditions defined in FAR Part <NUM> Appendix O or foreign equivalents, and a relatively low (or lower) target angle of attack <NUM> (e.g., in the range of approximately <NUM>-<NUM>° higher than the current angle of attack) for icing conditions defined in FAR Part <NUM> Appendix C or foreign equivalents.

However, in other examples, the flight control computer <NUM> may generate a command signal <NUM> for actuating one or more movable surfaces <NUM> in a manner to increase the angle of attack of an airfoil <NUM> to an absolute value (e.g., the target angle of attack) regardless of the current angle of attack of the airfoil <NUM><NUM>. For example, upon determining the existence of icing conditions, the flight control computer <NUM> may generate a command signal <NUM> for achieving an absolute value of approximately <NUM>° for the wing angle of attack <NUM>, regardless of the current angle of attack of the wings <NUM>. In another example, the flight control computer <NUM> may generate a command signal <NUM> for achieving an absolute value for the target angle of attack regardless of the current angle of attack, but which is based on the severity of icing conditions. For example, the flight control computer <NUM> may calculate an absolute value for a target angle of attack <NUM> of approximately <NUM>° for icing conditions defined in FAR Part <NUM> Appendix O or foreign equivalents, and may calculate an absolute value for a target angle of attack <NUM> of approximately <NUM>° for icing conditions defined in FAR Part <NUM> Appendix C or foreign equivalents.

In <FIG>, the aircraft <NUM> is a tube-and-wing configuration having a fuselage <NUM> and a longitudinal axis <NUM> extending between the forward end and the aft end of the fuselage <NUM>. The aircraft <NUM> may include one or more propulsion units <NUM> and one or more airfoils <NUM>. For example, the aft end of the fuselage <NUM> may include a vertical tail <NUM> and a horizontal tail. The horizontal tail may include a pair of horizontal stabilizers <NUM> (<FIG>) symmetrically located on laterally opposite sides of an aircraft centerline <NUM> (<FIG>) which may be coincident with the longitudinal axis <NUM>. An elevator <NUM> may be pivotably coupled to each one of the horizontal stabilizers <NUM>.

Referring to <FIG>, the aircraft <NUM> may include a pair of wings <NUM>, each of which may have a plurality of movable surfaces <NUM> symmetrically located on laterally opposite sides of the aircraft centerline <NUM>. For example, the wings <NUM> may each include movable surfaces <NUM> such as spoilers <NUM> laterally symmetrically located on opposite sides of the aircraft centerline <NUM>. Each wing <NUM> may also include movable surfaces <NUM> such as flaps <NUM>, ailerons <NUM>, and/or flaperons <NUM> which may also be laterally symmetrically located on opposite sides of the aircraft centerline <NUM>. As described in greater detail below, the system <NUM> (<FIG>) and method <NUM> (<FIG>) is configured such that at least one laterally symmetric pair of movable surfaces <NUM> is deflected upon the generation of a command signal <NUM> (<FIG>) from the flight control computer <NUM> (<FIG>) in response to the flight control computer <NUM> determining the existence of icing conditions.

Although the presently-disclosed system <NUM> (<FIG>) and method <NUM> (<FIG>) is described in the context of a tube-and-wing airplane as shown in <FIG>, the system <NUM> and method <NUM> may be implemented in other airplane configurations including, but not limited to, a blended wing body configuration (not shown), a flying wing configuration (not shown), and any other one of a variety of aircraft configurations. In this regard, the movable surfaces <NUM> (<FIG>) for non-tube-and-wing airplane configurations may include elevons, canards, and/or other types of movable surfaces <NUM> laterally symmetrically located on opposite sides of the aircraft centerline <NUM>, and capable of increasing the angle of attack of an airfoil <NUM> (<FIG>) in response to a command signal <NUM> from a flight control computer <NUM> to temporarily increase the angle of attack of the airfoil <NUM> for purposes of shifting the water impingement limits <NUM>, <NUM> (<FIG>) of the airfoil <NUM>.

<FIG> is a section view of wing <NUM> and a horizontal stabilizer <NUM> and elevator <NUM> of the aircraft <NUM> of <FIG>. The wing <NUM> may include the above-mentioned movable surfaces <NUM> including flaps <NUM>, ailerons <NUM>, flaperons <NUM>, and/or spoilers <NUM>, each of which has a surface trailing edge <NUM>. The horizontal stabilizer <NUM> and the elevator <NUM> may also be referred to as movable surfaces <NUM>. The horizontal stabilizer <NUM> has a stabilizer leading edge <NUM>, and the elevator <NUM> has an elevator trailing edge <NUM>.

The wing <NUM> is oriented at a wing angle of attack <NUM> and the horizontal stabilizer <NUM> is oriented at a stabilizer angle of attack <NUM>. In present disclosure, the angle of attack of an airfoil <NUM> is the angle between the chord line <NUM> of the airfoil <NUM> and the direction of the freestream flow <NUM> located immediately upstream of the airfoil <NUM>. In the present disclosure, the chord line <NUM> of an airfoil <NUM> extends between the leading edge (e.g., wing leading edge <NUM>) and the trailing edge (e.g., surface trailing edge <NUM>) of the airfoil <NUM> when high-lift devices (e.g., flaps <NUM>, leading edge slats - not shown) are retracted. The chord line <NUM> for the horizontal stabilizer <NUM> extends between the stabilizer leading edge <NUM> and the elevator trailing edge <NUM> when the elevator <NUM> is non-deflected.

As mentioned above, an airfoil <NUM> has a suction side <NUM> and a pressure side <NUM>. The suction side <NUM> faces in the same direction as the direction of lift <NUM> generated by the airfoil <NUM>, and the pressure side <NUM> faces in a direction opposite the direction of lift <NUM>. For the case where the airfoil <NUM> is a wing <NUM>, the lift <NUM> is directed upwardly. In <FIG>, for the case where the airfoil <NUM> is a horizontal tail, the lift <NUM> may be directed downwardly to counteract a nose-down pitching moment caused by the upwardly directed lift <NUM> of the wings <NUM> acting aft of a center of gravity (not shown) of the aircraft <NUM>.

In the present disclosure, an increase in the angle of attack of an airfoil <NUM> causes the suction side <NUM> of the airfoil <NUM> to be angled more aftwardly or away from the direction of the oncoming freestream flow <NUM>, and the pressure side <NUM> of the airfoil <NUM> to be angled more forwardly or toward the direction of the oncoming freestream flow <NUM>. In <FIG>, an increase in the wing angle of attack <NUM> results in the wing leading edge <NUM> being increasingly oriented in an upward direction. An increase in the stabilizer angle of attack <NUM> results in the stabilizer leading edge <NUM> being increasingly oriented in a downward direction.

Referring to <FIG>, shown in <FIG> is a forward portion of a wing <NUM> oriented at a wing angle of attack <NUM> of <NUM>. As described above, the suction side <NUM> has a suction side water impingement limit <NUM> and the pressure side <NUM> has a pressure side water impingement limit <NUM> which are each defined by the tangent trajectories <NUM> of water droplets <NUM> in the freestream flow <NUM>. The suction side water impingement limit <NUM> and the pressure side water impingement limit <NUM> are each measured along the airfoil <NUM> surface relative to the highlight <NUM>. For example, the surface distance Ss is the distance between the highlight <NUM> and the suction side water impingement limit <NUM>. The surface distance Sp is the distance between the highlight <NUM> and the pressure side water impingement limit <NUM>.

<FIG> shows the forward portion of the wing <NUM> of <FIG> oriented at an increased wing angle of attack <NUM> relative to <FIG>. The increased wing angle of attack <NUM> in <FIG> results in the tangent trajectories <NUM> of the water droplets <NUM> impinging at different locations on the wing leading edge <NUM> relative to the impingement locations in <FIG>. In this regard, the increased wing angle of attack <NUM> results in a combination lowering and forward shifting of the suction side water impingement limit <NUM>, and a combination lowering and aftward shifting of the pressure side water impingement limit <NUM> relative to the location of the suction side water impingement limit <NUM> and pressure side water impingement limit <NUM> of <FIG>. Correspondingly, the surface distance Ss in <FIG> is shorter than in <FIG>, and the surface distance Sp in <FIG> is longer than in <FIG>.

<FIG> shows the forward portion of the wing <NUM> of <FIG> at a wing angle of attack <NUM> of <NUM>° and illustrating the shape and size of ice accretion <NUM> forming on the wing leading edge <NUM>. The ice accretion <NUM> forms between a suction side ice accretion limit <NUM> and a pressure side ice accretion limit <NUM>, which respectively correspond to the location of the suction side water impingement limit <NUM> and pressure side water impingement limit <NUM> of <FIG>. The ice accretion <NUM> has ice horns <NUM> that protrude into the freestream flow <NUM> and disrupt the air flowing over the airfoil <NUM>. For example, the ice accretion <NUM> with ice horns <NUM> in <FIG> may result in a flow separation bubble (not shown) on the suction side <NUM> downstream of the leading edge, which may lower the angle of attack at which the wing <NUM> stalls (i.e., the stall angle <NUM> - <FIG>) relative to the stall angle <NUM> (<FIG>) of the same wing <NUM> with no ice accretion. In addition, as mentioned above, the ice accretion <NUM> may reduce the maximum lift coefficient <NUM> (<FIG>) and generate aerodynamic drag.

<FIG> shows the wing <NUM> of <FIG> at an increased angle of attack (i.e., in the upward direction), resulting in a downward shifting of the location of ice accretion <NUM> on the wing leading edge <NUM> relative to the ice accretion <NUM> in <FIG>. The increased wing angle of attack <NUM> results in a combination lowering and forward shifting of the suction side ice accretion limit <NUM>, and a combination lowering and aftward shifting of the pressure side ice accretion limit <NUM> relative to the location of the suction side ice accretion limit <NUM> and pressure side ice accretion limit <NUM> of <FIG> Depending on the amount by which the angle of attack of the wing <NUM> is increased, the combination lowering and forward shifting of the suction side ice accretion limit <NUM> and the combination lowering and aftward shifting of the pressure side ice accretion limit <NUM> may result in ice accretion <NUM> being located in a more favorable part of the pressure gradient along the surface of the wing leading edge <NUM>, and/or may reduce the size of ice horns <NUM> or may avoid the formation of ice horns <NUM>, which may reduce the disruption of air flowing over the wing <NUM>. The pressure gradient occurs as a result of airflow over the curved surfaces of the wing <NUM>. A more favorable location of ice accretion <NUM> relative to the pressure gradient may be along or adjacent to the forwardmost portion of the wing leading edge <NUM>.

<FIG> is a graph <NUM> of coefficient of lift vs. angle of attack for the same airfoil <NUM> corresponding to three different states including: (<NUM>) a first state <NUM> in which the airfoil <NUM> is oriented at a relatively small angle of attack (e.g., <NUM>°) and having ice accretion <NUM> due to exposure to icing conditions, (<NUM>) a second state <NUM> in which the airfoil <NUM> is oriented at a relatively large angle of attack and also having ice accretion <NUM> due to exposure to the same icing conditions as in the first state <NUM>, and (<NUM>) a third state <NUM> in which the airfoil <NUM> is in a clean condition as a result of non-exposure to icing conditions. As can be seen, the maximum lift coefficient <NUM> for the airfoil <NUM> in the second state <NUM> is lower than the maximum lift coefficient <NUM> for the airfoil <NUM> in the third state <NUM> due to the ice accretion <NUM> on the leading edge in the second state <NUM>. In addition, the stall angle <NUM> for the airfoil <NUM> in the second state <NUM> is lower than the stall angle <NUM> of the airfoil <NUM> in the third state <NUM>. However, the maximum lift coefficient <NUM> and the stall angle <NUM> for the airfoil <NUM> in the second state <NUM> is higher than the maximum lift coefficient <NUM> and stall angle <NUM> for the airfoil <NUM> in the first state <NUM> as a result of a lower location of ice accretion <NUM> on the leading edge of the airfoil <NUM> in the second state <NUM> relative to a higher location of ice accretion <NUM> on the leading edge of the airfoil <NUM> in the first state <NUM>.

Advantageously, the shift in the location of ice accretion <NUM> (<FIG>) provided by the presently-disclosed system <NUM> (<FIG>) and method <NUM> (<FIG>) such as during cruise or holding of an aircraft (<FIG>) allows for increased lift and a higher stall angle <NUM> (<FIG>) at low airspeeds such as during approach. The relative increase in lift and stall angle <NUM> improves airplane performance by allowing for increased maximum landing weight for an equivalent approach speed or, conversely, a decreased approach speed for an equivalent maximum landing weight. In addition, the relative increase in lift and stall angle <NUM> allows for increased approach climb limit weights for an equivalent airspeed. The increased lift and stall angle <NUM> provided by the system <NUM> and method <NUM> also increases airplane safety by increasing the operating margin to stall. Furthermore, the system <NUM> and method <NUM> reduces the need for ice protection hardware such as by reducing anti-ice requirements for an equivalent approach speed. In addition, the system <NUM> and method <NUM> simplifies the icing conditions certification process for determining critical ice accretion <NUM> (<FIG>). In addition, the system <NUM> and method <NUM> increase airline service reliability by increasing the safety and efficiency to certify aircraft for operation in the most severe icing conditions such as the FAR Part <NUM>, Appendix O, SLD (and foreign equivalents) icing conditions discussed above.

<FIG> is a section view of a wing <NUM> and a horizontal stabilizer <NUM> and elevator <NUM> in a baseline configuration of an aircraft <NUM> (<FIG>). In <FIG>, the wing <NUM> is oriented at a current angle of attack <NUM> (i.e., a wing angle of attack <NUM>) of <NUM>° relative to the freestream flow <NUM> direction which, in <FIG> and <FIG>, is assumed to be parallel to the longitudinal axis <NUM> of the aircraft <NUM>. In addition, the horizontal stabilizer <NUM> is oriented at a current angle of attack <NUM> (i.e., a stabilizer angle of attack <NUM>) of <NUM>° relative to the freestream flow <NUM> direction. The wing <NUM> is assumed to generate lift <NUM> in an upward direction and the horizontal stabilizer <NUM> is assumed to generate lift <NUM> in a downward direction in a manner maintaining trimmed, level flight.

In any one of the examples disclosed herein, as described above with reference to <FIG>, the flight control computer <NUM> receives data representative of the environmental parameters <NUM> (e.g., air temperature <NUM>, droplet size <NUM>, liquid water content <NUM>) sensed in the environment <NUM> (<FIG>) of the flight path <NUM> (<FIG>) of an aircraft <NUM>. The flight control computer <NUM> may determine, based at least on the environmental parameters <NUM> and optionally using the activation logic <NUM>, the existence of icing conditions to which the aircraft <NUM> is currently subjected or is predicted to be subjected. The flight control computer <NUM> also generates, based on the determination of the existence of icing conditions, a command signal <NUM> for actuating at least one movable surface <NUM> of the aircraft <NUM> for increasing the angle of attack of an airfoil <NUM> (<FIG>) in a manner modifying the water impingement limits <NUM>, <NUM> (<FIG>) of the airfoil <NUM>.

Referring again to <FIG>, in addition to receiving data representative of environmental parameters <NUM> and determining the existence of icing conditions, in some examples, the flight control computer <NUM> is configured to receive data representative of a current angle of attack <NUM> of the airfoil <NUM> (<FIG>), calculate, using angle of attack selection logic <NUM> of the flight control computer <NUM>, a target angle of attack <NUM> (<FIG>) of the airfoil <NUM> based on the icing conditions, and determine an angle of attack differential between the current angle of attack <NUM> (<FIG>) and the target angle of attack <NUM> (<FIG>). Upon determining the angle of attack differential, the flight control computer <NUM> is configured to generate a command signal <NUM> representative of the angle of attack differential. One or more surface actuators <NUM> are configured to receive the command signal <NUM> from the flight control computer <NUM>, and adjust one or more movable surfaces <NUM> by an amount causing the angle of attack of the airfoil <NUM> to increase by an amount equal to the angle of attack differential to thereby bring the airfoil <NUM> into alignment with the target angle of attack <NUM> to thereby modify the water impingement limits <NUM>, <NUM> (<FIG>) on the airfoil <NUM>.

Furthermore, in some examples, the flight control computer <NUM> is configured to calculate, using the angle of attack selection logic <NUM>, the target angle of attack <NUM> based on the icing conditions and based on aircraft state data <NUM>. Aircraft state data <NUM> may include the current airplane configuration such as flap position <NUM>, speedbrake position <NUM>, gear position <NUM> and thrust setting <NUM>, and may also include airspeed <NUM>, altitude <NUM>, gross weight <NUM>, location of the center of gravity (not shown) relative to the center of lift (not shown), and other aircraft state data <NUM>. Flap position <NUM> data may include a flap setting such as on a flap control console (not shown) on a flight deck of an aircraft <NUM> (<FIG>). The flap position <NUM> may include an up position (e.g., flaps fully retracted for cruise flight), a hold position, a climb or approach position, a takeoff or go-around position, and a landing position (e.g., flaps fully extended). An increasingly extended flap position <NUM> may increase the nose-down pitching moment of the aircraft <NUM>, and may result in the flight control computer <NUM> compensating in the command signal <NUM> to cause increased deflection of the movable surfaces <NUM> to achieve the target angle of attack <NUM>.

Speedbrake position <NUM> refers to whether the spoilers <NUM> (e.g., flight spoilers - <FIG>) are retracted or deployed and, if deployed, the angle of deployment. Spoilers <NUM> that are partially deployed may increase the nose-down pitching moment and may result in the flight control computer <NUM> compensating in the command signal <NUM> to cause increased deflection of the movable surfaces <NUM> to achieve the target angle of attack <NUM>. Gear position <NUM> refers to whether the landing gear (not shown) is up or down. Landing gear in the down position generates increased aerodynamic drag and a nose-down pitching moment due to the location of the aerodynamic drag underneath the wings <NUM> (<FIG>), and may result in the flight control computer <NUM> compensating in the command signal <NUM> to cause increased deflection of the movable surfaces <NUM> to achieve the target angle of attack <NUM>. For propulsion units <NUM> (<FIG>) located underneath the wings <NUM>, an increased thrust setting <NUM> may generate a nose-up pitching moment causing the flight control computer <NUM> to generate a command signal <NUM> in a manner causing reduced deflection of the movable surfaces <NUM> to achieve the target angle of attack <NUM>. Increased airspeed <NUM> may increase the rate of ice accretion <NUM> (<FIG>) and may correspond to increased severity of icing conditions, resulting in the flight control computer <NUM> compensating in the command signal <NUM> by commanding increased deflection of the movable surfaces <NUM> to achieve a higher target angle of attack <NUM> than for less severe icing conditions. The flight control computer <NUM> may also factor in the altitude <NUM>, gross weight <NUM>, and/or location of the center of gravity (not shown) in determining the command signal <NUM> required for deflecting the movable surfaces <NUM> in a manner for achieving the target angle of attack <NUM>.

<FIG> illustrates an example in which the flight control computer <NUM> (<FIG>) generates one or more command signals <NUM> (<FIG>) causing one or more surface actuators <NUM> (<FIG>) to upwardly deflect the surface trailing edges <NUM> of at least one laterally symmetric pair of movable surfaces <NUM> respectively coupled to the pair of wings <NUM>. In some examples, the flight control computer <NUM> may generate command signals <NUM> causing the deflection of at least one laterally symmetric pair of flaps <NUM> (<FIG>), ailerons <NUM>, and/or spoilers <NUM>. However, one or more laterally symmetric pair of other types of movable surfaces <NUM> (e.g., flaperons <NUM> - <FIG>; canards - not shown) may be deflected to cause an increase in the angle of attack of an airfoil <NUM>. In this regard, the present disclosure contemplates deflecting any type of movable surface <NUM> mounted anywhere on the aircraft <NUM>, and is not limited to deflecting flaps <NUM>, spoilers <NUM>, and/or ailerons <NUM>.

<FIG> shows the upward deflection of at least one laterally symmetric pair (<FIG>) of spoilers <NUM> from an original position <NUM> (<FIG>) through a deflection angle <NUM> (<FIG>) to an adjusted position <NUM> (<FIG>). In the present disclosure, upward deflection of a movable surface <NUM> refers to the surface trailing edge <NUM> moving upwardly. Movable surfaces <NUM> may be deflected through relatively small deflection angles <NUM> such as from approximately <NUM>-<NUM>°, depending upon the severity of the icing conditions and the aircraft state. For icing conditions that are less severe, the flight control computer <NUM> may calculate deflection angles <NUM> that are less than <NUM>°, and/or the flight control computer <NUM> may generate command signals <NUM> for deflecting a single laterally symmetric pair of movable surfaces <NUM>. For icing conditions that are more severe, the flight control computer <NUM> may calculate deflection angles <NUM> that are larger than <NUM>°, and/or the flight control computer <NUM> may generate command signals <NUM> for deflecting multiple laterally symmetric pairs of movable surfaces <NUM>. In <FIG>, the deflection of the spoilers <NUM> causes an upward increase in the wing angle of attack <NUM> wherein the wing <NUM> moves from a current angle of attack <NUM> (<FIG>) to a target angle of attack <NUM> (<FIG>) calculated by the flight control computer <NUM>. The increase in the wing angle of attack <NUM> causes the above-described combination of lowering and forward shifting of the suction side water impingement limit <NUM> and corresponding combination of lowering and aftward shifting of the pressure side water impingement limit <NUM>, as illustrated in <FIG>.

<FIG> represents the upward deflection of at least one laterally symmetric pair of ailerons <NUM> from an original position <NUM> (<FIG>) through a deflection angle <NUM> to an adjusted position <NUM>. The upward deflection of the laterally symmetric pair of ailerons <NUM> causes the wing angle of attack <NUM> to increase from the current angle of attack <NUM> (<FIG>) to the target angle of attack <NUM>. In <FIG>, the increase in the wing angle of attack <NUM> increases the pitch angle (not shown) of the aircraft <NUM>. The horizontal stabilizer <NUM> and elevator <NUM> in <FIG> are at the same orientation relative to the longitudinal axis <NUM> as in <FIG>.

<FIG> illustrates an example in which the flight control computer <NUM> (<FIG>) is configured to generate one or more command signals <NUM> (<FIG>) causing one or more surface actuators <NUM> (<FIG>) to downwardly deflect the stabilizer leading edge <NUM> of the pair (<FIG>) of horizontal stabilizers <NUM>, and downwardly deflect the elevator trailing edge <NUM> of the elevator <NUM> (relative to the chord line <NUM> of the horizontal stabilizer <NUM>) pivotably coupled to each one of the horizontal stabilizers <NUM>. The downward deflection of the stabilizer leading edge <NUM> causes the stabilizer angle of attack <NUM> to increase (i.e., relative to the freestream flow <NUM> direction) in a downward direction from the current angle of attack <NUM> (<FIG>) to the target angle of attack <NUM> (<FIG>) as calculated by the flight control computer <NUM>. Similar to the above-described effect of increasing the wing angle of attack <NUM> in an upward direction, increasing the stabilizer angle of attack <NUM> in a downward direction causes a combination raising and forward shifting of a suction side water impingement limit <NUM> (not shown) on the suction side <NUM> (i.e., on the lower surface) of the horizontal stabilizer <NUM>, and a corresponding combination of lowering and aftward shifting of the pressure side water impingement limit <NUM> (not shown) on the pressure side <NUM> (i.e., on the upper surface) of the horizontal stabilizer <NUM>. The shifting of the suction side water impingement limit <NUM> and pressure side water impingement limit <NUM> on the stabilizer leading edge <NUM> shifts the location of ice accretion <NUM> (not shown) on the stabilizer leading edge <NUM>, which reduces aerodynamic drag and reduces the extent of disruption of airflow over the horizontal tail (i.e., the horizontal stabilizer <NUM> and elevator <NUM>) to thereby improve the ability of the horizontal tail to generate a downward force (e.g., lift <NUM> - <FIG>) for counteracting the nose-down pitching moment of the wings <NUM>.

In <FIG>, the elevator trailing edge <NUM> may be downwardly deflected in a manner resulting in a downward increase in the stabilizer angle of attack <NUM> without changing the wing angle of attack <NUM>. In this regard, the flight control computer <NUM> (<FIG>) may generate command signals <NUM> causing the elevator trailing edge <NUM> to be downwardly deflected from an original position <NUM> (<FIG>) through a deflection angle <NUM> to an adjusted position <NUM> that maintains the wing <NUM> at substantially (e.g., within <NUM> percent) the same wing angle of attack <NUM> as prior to the adjustment of the horizontal stabilizer <NUM> and elevator <NUM>. In addition, the flight control computer <NUM> may generate command signals and <NUM> to adjust the orientation of the horizontal stabilizer <NUM> and elevator <NUM> in a manner maintaining the altitude <NUM> (<FIG>) of the aircraft <NUM>. In any one of the examples disclosed herein, the flight control computer <NUM> may increase a thrust setting <NUM> (<FIG>) of one or more propulsion units <NUM> (<FIG>) of the aircraft <NUM> in a manner maintaining the aircraft <NUM> at an airspeed <NUM> (<FIG>) and/or an altitude <NUM> that is substantially equivalent (e.g., within <NUM> percent) to the airspeed <NUM> and altitude <NUM> of the aircraft <NUM> prior to adjusting one or more movable surfaces <NUM> (e.g., flaps <NUM>, ailerons <NUM>, flaperons <NUM>, spoilers <NUM>, horizontal stabilizers <NUM>, elevators <NUM>, etc.) and increasing the angle of attack of one or more airfoils <NUM> (e.g., wings <NUM>, horizontal stabilizers <NUM>) for purposes of modifying the water impingement limits <NUM>, <NUM>.

<FIG> illustrates an example in which the flight control computer <NUM> (<FIG>) generates one or more command signals <NUM> (<FIG>) causing one or more surface actuators <NUM> (<FIG>) to downwardly deflect the stabilizer leading edge <NUM> and downwardly deflect the elevator trailing edge <NUM> of the elevator <NUM> similar to that described above in <FIG>, while causing other surface actuators <NUM> (<FIG>) to upwardly deflect at least one laterally symmetric pair of movable surfaces <NUM> respectively coupled to the pair of wings <NUM> in a manner increasing the stabilizer angle of attack <NUM> in a downward direction (relative to the freestream flow <NUM> direction) and increasing the wing angle of attack <NUM> in an upward direction (relative to the freestream flow <NUM> direction).

<FIG> illustrates the downward deflection of the horizontal stabilizer <NUM> and the downward deflection of the elevator <NUM> with simultaneous upward deflection of the surface trailing edge <NUM> of a spoiler <NUM> from an original position <NUM> (<FIG>) through a deflection angle <NUM> to an adjusted position <NUM>, resulting in a downward increase in the stabilizer angle of attack <NUM> and an upward increase in the wing angle of attack <NUM>. The downward increase in the stabilizer angle of attack <NUM> and the upward increase in the wing angle of attack <NUM> each modifies the water impingement limits <NUM>, <NUM> (<FIG>) on the stabilizer leading edge <NUM> and wing leading edge <NUM> which advantageously reduces the effects of ice accretion <NUM> (e.g., <FIG>) on air flow over the horizontal stabilizers <NUM> and wings <NUM>.

<FIG> illustrates the downward deflection of the horizontal stabilizer <NUM> and the downward deflection of the elevator <NUM> with simultaneous upward deflection of the surface trailing edge <NUM> of an aileron <NUM> to achieve a downward increase in the stabilizer angle of attack <NUM> (relative to the freestream flow <NUM> direction) and an upward increase in the wing angle of attack <NUM> (relative to the freestream flow <NUM> direction). Similar to the above-described configuration of <FIG>, the downward increase in the stabilizer angle of attack <NUM> and the upward increase in the wing angle of attack <NUM> modifies the water impingement limits <NUM>, <NUM> (<FIG>) on the stabilizer leading edge <NUM> and wing leading edge <NUM>.

<FIG> illustrates an example in which the flight control computer <NUM> (<FIG>) generates one or more command signals <NUM> (<FIG>) causing one or more surface actuators <NUM> (<FIG>) to upwardly deflect the stabilizer leading edge <NUM> and upwardly deflect the elevator trailing edge <NUM> in a manner resulting in an upward increase in the stabilizer angle of attack <NUM>. The upward increase in the stabilizer angle of attack <NUM> biases the water impingement limits <NUM>, <NUM> (not shown) on the horizontal stabilizer <NUM> more toward the suction side <NUM>, and is therefore more adverse for the ice accretion limits <NUM>, <NUM> (not shown) on the horizontal stabilizer <NUM>. However, upwardly increasing the stabilizer angle of attack <NUM> may be advantageous for aircraft <NUM> (<FIG>) that have a reduced amount of elevator <NUM> authority in the nose-down direction in icing conditions. By adjusting the stabilizer angle of attack <NUM> to an upward direction (relative to the freestream flow <NUM> direction) and by correspondingly increasing the deflection angle of the elevator trailing edge <NUM>, the horizontal tail may maintain the aircraft <NUM> in trimmed flight while maintaining nose-down authority of the elevator <NUM> (e.g., to meet certification requirements).

<FIG> illustrates an example similar to <FIG> in which the flight control computer <NUM> (<FIG>) generates one or more command signals <NUM> (<FIG>) causing surface actuators <NUM> (<FIG>) to upwardly deflect the stabilizer leading edge <NUM> and upwardly deflect the elevator trailing edge <NUM> by an amount resulting in an upward increase in the wing angle of attack <NUM> in addition to the upward increase in the stabilizer angle of attack <NUM>. The upward increase in the wing angle of attack <NUM> improves the water impingement limits <NUM>, <NUM> (<FIG>) on the wing leading edge <NUM> in a manner as described above. As described above with regard to <FIG>, although an upward increase in the stabilizer angle of attack <NUM> is more adverse for the ice accretion limits <NUM>, <NUM> (not shown) on the horizontal stabilizer <NUM>, upwardly increasing the stabilizer angle of attack <NUM> may be advantageous in icing conditions in which the horizontal stabilizer <NUM> has reduced elevator <NUM> authority in the nose-down direction.

<FIG> shows an aircraft <NUM> on a flight path <NUM> through a cloud <NUM> containing icing conditions. <FIG> illustrates a temporary increase in the wing angle of attack <NUM> (shown exaggerated) as the aircraft <NUM> passes through the cloud <NUM> while maintaining the same altitude <NUM> (<FIG>) as prior to entering the cloud <NUM>. As described above, temporarily increasing the wing angle of attack <NUM> of the aircraft <NUM> modifies the water impingement limits <NUM>, <NUM> (<FIG>) on the wing leading edges <NUM> (<FIG>) which advantageously reduce the effects of ice accretion <NUM>, as shown in the graph of <FIG>. In some examples, the flight control computer <NUM> (<FIG>) may continuously monitor the environmental parameters <NUM> (<FIG>) to determine whether icing conditions continue to exist. Upon determining that icing conditions no longer exist, the flight control computer <NUM> may autonomously (i.e., without human intervention) command the movable surfaces <NUM> (<FIG>) from the adjusted position <NUM> (<FIG>) back to the original position <NUM> (<FIG>). Alternatively or additionally, the flight control computer <NUM> may at any time allow pilot input <NUM> (<FIG>) for commanding the movable surfaces <NUM> (<FIG>) to move from the adjusted position <NUM> back to the original position <NUM>.

Referring to <FIG>, shown is a flow chart of operations included in a method <NUM> of modifying the location of the water impingement limits <NUM>, <NUM> of an airfoil <NUM>. Step <NUM> of the method <NUM> includes sensing environmental parameters <NUM> in the environment <NUM> of the flight path <NUM> of an aircraft <NUM>. As described above, the environmental parameters <NUM> may include air temperature <NUM> and droplet size <NUM> of water dropped. In addition, the environmental parameters <NUM> may also liquid water content <NUM>, altitude <NUM>, horizontal extent and/or vertical extent of icing conditions, and other environmental parameters <NUM>. Step <NUM> may also include sensing the aircraft surface temperatures <NUM> to determine the existence of icing additions if aircraft surface temperatures <NUM> are below <NUM>, as described above.

Step <NUM> of the method <NUM> includes determining, based on the environmental parameters <NUM>, the existence of icing conditions. As mentioned above, the step of determining the existence of icing conditions may include determining the current existence of icing conditions, or determining the existence of icing conditions to which the aircraft <NUM> is predicted to be subjected at a later point along the flight path <NUM> of the aircraft <NUM>. The existence of icing conditions may be determined by ground-based or airborne weather measurement instrumentation. The determination of icing conditions may also be based on reports of icing conditions by pilots of other aircraft in areas near the flight path <NUM>.

Step <NUM> of the method <NUM> (<FIG>) includes adjusting, in response to determining the existence of icing conditions, at least one movable surface <NUM> of the aircraft <NUM>. The movable surface <NUM> may be moved from an original position <NUM> through a deflection angle <NUM> to an adjusted position <NUM>. In the present disclosure, the original position <NUM> of a movable surface <NUM> is the position immediately prior to changing the orientation of the movable surface <NUM> to achieve the target angle of attack <NUM> of an airfoil <NUM>.

Step <NUM> of the method <NUM> includes increasing the angle of attack of an airfoil <NUM> (e.g., the wings <NUM>, the horizontal stabilizers <NUM>) in response to adjusting the movable surface <NUM> to thereby cause a modification of the water impingement limit <NUM>, <NUM> on the airfoil <NUM>. As described above, an increase in the wing angle of attack <NUM> causes a combination lowering and forward shifting of a suction side water impingement limit <NUM> on the suction side <NUM> (i.e., the upper surface) of the wings <NUM> and a combination lowering and aftward shifting of the pressure side water impingement limit <NUM> on the pressure side <NUM> (i.e., the lower surface) of the wings <NUM>.

In some examples, the method <NUM> (<FIG>) may include determining a current angle of attack <NUM> of the airfoil <NUM>, calculating a target angle of attack <NUM> of the airfoil <NUM> based on the icing conditions, and determining an angle of attack differential between the current angle of attack <NUM> and the target angle of attack <NUM>. In such examples, step <NUM> may include adjusting at least one movable surface <NUM> by an amount causing the angle of attack of the airfoil <NUM> to increase by an amount equal to the angle of attack differential to thereby bring the airfoil <NUM> into alignment with the target angle of attack <NUM>, as described above.

The step of calculating the target angle of attack <NUM> may include calculating the target angle of attack <NUM> based on the icing conditions and based on aircraft state data <NUM> such as current flap position <NUM>, speedbrake position <NUM>, airspeed <NUM>, altitude <NUM>, thrust setting <NUM>, gear position <NUM>, and/or other aircraft state data <NUM>, as described above. In this regard, step <NUM> of determining the existence of icing conditions may include determining the severity of the icing conditions based at least on air temperature <NUM> and droplet size <NUM> of water droplets <NUM> in the environment <NUM> of the aircraft <NUM>. As mentioned above, the lower the air temperature <NUM> and/or the larger the droplet size <NUM>, the more severe the icing condition. In this regard, the longer that the aircraft <NUM> is exposed to water droplets <NUM> in liquid form existing in air temperatures <NUM> below <NUM>, the more severe the icing condition. Similarly, the higher the liquid water content <NUM> of the cloud <NUM>, the more severe the icing condition. The step of calculating the target angle of attack <NUM> may be based on the severity of icing conditions. For example, the more severe the icing addition, the larger the target angle of attack <NUM> of the airfoil <NUM>. In this regard, step <NUM> may comprise adjusting the movable surface <NUM> by an amount proportional to the severity of the icing conditions.

Referring briefly to <FIG>, in some examples, the step <NUM> of adjusting the movable surface <NUM> may comprise upwardly deflecting a surface trailing edge <NUM> of at least one laterally symmetric pair of movable surfaces <NUM> respectively coupled to a pair of wings <NUM> respectively located on laterally opposite sides of the aircraft centerline <NUM>. For example, upwardly deflecting a laterally symmetric pair of movable surfaces <NUM> may include upwardly deflecting a surface trailing edge <NUM> of a laterally symmetric pair of flaps <NUM>, spoilers <NUM>, and/or ailerons <NUM>. In such cases, step <NUM> of increasing the angle of attack of the airfoil <NUM> may comprise increasing the wing angle of attack <NUM> in response to upwardly deflecting the laterally symmetric pair of flaps <NUM>, spoilers <NUM>, and/or ailerons <NUM>.

Referring briefly to <FIG>, in some examples, the step <NUM> of adjusting the movable surface <NUM> may comprise downwardly deflecting a stabilizer leading edge <NUM> of a horizontal stabilizer <NUM> and downwardly deflecting an elevator trailing edge <NUM> of an elevator <NUM> such that the stabilizer leading edge <NUM> of the horizontal stabilizer <NUM> moves downwardly and the elevator trailing edge <NUM> of the elevator <NUM> moves downwardly as shown in <FIG>. In such cases, step <NUM> of increasing the angle of attack of the airfoil <NUM> comprises increasing the stabilizer angle of attack <NUM> in a downward direction in response to downwardly deflecting the stabilizer leading edge <NUM>. In some examples such as in <FIG>, the downward deflection of the stabilizer leading edge <NUM> and downward deflection of the elevator trailing edge <NUM> may be performed in a manner such that the wing angle of attack <NUM> remains unchanged. As mentioned above, increasing the stabilizer angle of attack <NUM> in the downward direction may cause a combination raising and forward shifting of a suction side water impingement limit <NUM> (not shown) on the suction side <NUM> (e.g., the lower surface) of the horizontal stabilizer <NUM> and correspondingly a combination lowering and aftward shifting of the pressure side water impingement limit <NUM> (not shown) on the pressure side <NUM> (e.g., the upper surface) of the horizontal stabilizer <NUM>.

Referring briefly to <FIG>, in some examples, the step <NUM> of adjusting the movable surface <NUM> may comprise downwardly deflecting the stabilizer leading edge <NUM> and downwardly deflecting the elevator trailing edge <NUM> while upwardly deflecting a surface trailing edge <NUM> of at least one laterally symmetric pair of movable surfaces <NUM> respectively coupled to a pair of wings <NUM> respectively located on laterally opposite sides of the aircraft <NUM>. For example, <FIG> illustrate the downward deflection of the stabilizer leading edge <NUM> and the downward deflection of the elevator trailing edge <NUM> with simultaneous upward deflection of at least one laterally symmetric pair of spoilers <NUM> (<FIG>) and/or ailerons <NUM> (<FIG>). In such cases, step <NUM> of increasing the angle of attack of the airfoil <NUM> comprises increasing the stabilizer angle of attack <NUM> in a downward direction and increasing the wing angle of attack <NUM> in an upward direction in response to downwardly deflecting the horizontal stabilizer <NUM> and downwardly deflecting the elevator <NUM> and upwardly deflecting at least one laterally symmetric pair of movable surfaces <NUM> (e.g., spoilers <NUM>, ailerons <NUM>, flaps <NUM>, flaperons <NUM>, etc.) of the wings <NUM>.

Referring briefly to <FIG>, in some examples, the step <NUM> of adjusting the movable surface <NUM> may comprise upwardly deflecting the stabilizer leading edge <NUM> of the horizontal stabilizer <NUM> and upwardly deflecting the elevator trailing edge of the elevator <NUM>. For example, <FIG> illustrates the upward deflection of the stabilizer leading edge <NUM> and the upward deflection of the elevator trailing edge <NUM>. In such cases, step <NUM> of increasing the angle of attack of the airfoil <NUM> comprises increasing the stabilizer angle of attack <NUM> in an upward direction in response to upwardly deflecting the stabilizer leading edge <NUM> to thereby maintain nose-down authority of the elevator <NUM> in icing conditions with ice accretion (not shown) on the horizontal stabilizer <NUM>, as described above. <FIG> illustrates an example similar to <FIG>, with the exception that the stabilizer leading edge <NUM> and the elevator trailing edge <NUM> in <FIG> are both deflected upwardly by an amount to increase the wing angle of attack <NUM> in an upward direction to thereby improve the water impingement limits <NUM>, <NUM> (<FIG>) on the wing leading edge <NUM>. Similar to the example of <FIG>, the horizontal stabilizer <NUM> and the elevator <NUM> in <FIG> may be deflected upwardly in a manner maintaining the aircraft <NUM> in trimmed flight while retaining nose-down authority of the elevator <NUM> in icing conditions.

In any of the examples disclosed herein, the method <NUM> (<FIG>) may further comprise increasing the thrust setting <NUM> of one or more propulsion units <NUM> (<FIG>) of the aircraft <NUM> in a manner maintaining the airspeed <NUM> and/or the altitude <NUM> of the aircraft <NUM> to be substantially (e.g., within <NUM> percent) equivalent to the airspeed <NUM> and the altitude <NUM> of the aircraft <NUM> prior to adjusting the one or more movable surfaces <NUM> for increasing the angle of attack of one or more airfoils <NUM>. In addition, the method <NUM> (<FIG>) may optionally include continuously monitoring the environmental parameters <NUM> to determine whether icing conditions continue to exist, and autonomously commanding the one or more movable surface <NUM> to move back to the original position <NUM> of the movable surfaces <NUM> when icing conditions cease to exist. For example, the autonomous commanding may be performed by a flight control computer <NUM> upon determining that icing conditions no longer exist.

<FIG> illustrates an example of an aircraft <NUM> on a flight path <NUM> that passes through a cloud <NUM> containing icing conditions. Prior to entering the cloud <NUM>, the wings <NUM> are oriented at a current angle of attack <NUM>. Prior to or immediately upon entering the cloud <NUM>, one or more movable surfaces <NUM> (<FIG>) may be autonomously or manually commanded to be deflected in a manner causing the wing angle of attack <NUM> to increase from the current angle of attack <NUM> to a target angle of attack <NUM>. Autonomous commanding of the movable surfaces <NUM> may be performed by the activation logic <NUM> (<FIG>) of a flight control computer <NUM> (<FIG>) upon determining the existence of icing conditions. Manual commanding of the movable surfaces <NUM> may be performed by pilot input <NUM> (<FIG>) in which a member of the flight crew initiates the activation logic <NUM> (<FIG>) of the flight control computer <NUM>. A pilot or other flight crew member may determine the existence of icing conditions by visually observing water drops on the aircraft surfaces, in combination with the pilot or flight crew member determining that the air temperature <NUM> (e.g., the outside air temperature) and/or the aircraft surface temperature <NUM> (e.g., of the wings <NUM>) are at or below <NUM>.

In the example of <FIG>, the wings <NUM> may be maintained at a target angle of attack <NUM> while the aircraft <NUM> is subjected to the icing additions (e.g., within the cloud <NUM>). Upon exiting the icing conditions, the movable surfaces <NUM> may be autonomously or manually commanded to return to their original position <NUM>, causing the wing <NUM> to be reoriented back to the same angle of attack as prior to entering the icing conditions. As the movable surfaces <NUM> are deflected and the angle of attack of the wings <NUM> is temporarily increased, the aircraft <NUM> is maintained at the same altitude <NUM> by temporarily adjusting (e.g., increasing) the thrust setting <NUM> (<FIG>) of the propulsion units <NUM> to compensate for the increased aerodynamic drag generated by the temporary deflection of the movable surfaces <NUM> (<FIG>) and/or by the increase in the angle of attack of the airfoils the wings <NUM> for the time period when the aircraft <NUM> is subjected to the icing conditions.

Claim 1:
A system (<NUM>) for modifying a location of a water impingement limit (<NUM>, <NUM>) on an airfoil (<NUM>) of an aircraft (<NUM>), the system (<NUM>) comprising:
a flight control computer (<NUM>) configured to:
receive data representative of environmental parameters (<NUM>) sensed in an environment (<NUM>) of a flight path (<NUM>) of an aircraft (<NUM>); and
determine, based on the environmental parameters (<NUM>), an existence of icing conditions to which the aircraft (<NUM>) is currently subjected or is predicted to be subjected; and
generate, based on the existence of icing conditions, a command signal (<NUM>) for actuating a movable surface (<NUM>) of the aircraft (<NUM>); and
a surface actuator (<NUM>) configured to receive the command signal (<NUM>) from the flight control computer (<NUM>) and adjust the movable surface (<NUM>) in a manner causing an increase in an angle of attack of the airfoil (<NUM>) to thereby modify a location of a water impingement limit (<NUM>, <NUM>) on the airfoil (<NUM>),
the flight control computer (<NUM>) further being configured to temporarily adjust a thrust setting (<NUM>) of a propulsion unit (<NUM>) of the aircraft (<NUM>) to maintain the aircraft (<NUM>) at the same altitude (<NUM>) for the time period when the aircraft (<NUM>) is subjected to the icing conditions.