Patent Description:
The present application relates generally to the field of measurements for a rotary-wing aircraft and, more particularly, to a method and a system for determining an airspeed of a helicopter at low airspeeds.

Airspeed of rotary-wing aircraft is typically measured using airspeed probes, such as pitot probes. Pitot probes function by comparing the pressure in a tube facing the direction of travel of the aircraft to the static air pressure. Speaking generally, airspeed probe-type systems do not sense airspeed accurately at low airspeeds due to large rotor downwash, high angles of attack and slide slip, and poor signal to noise ratio in dimensionally low values of pressure measurement occurring at low airspeeds.

In an aircraft as described above, without information concerning low airspeed, control settings may not be readily adjusted to react to changes in airspeed efficiently. Consequently, an aircraft may be limited to operating at a single setpoint at speeds below a point at which air probe data alone is reliable. This may result in degraded handling qualities, performance, stability, and efficiency, for example.

<CIT> discloses systems and methods for airspeed estimation using actuation signals. In one embodiment, an on-board avionics airspeed estimation system is provided which comprises a wind estimator coupled to a plurality of aircraft sensors, wherein an actuator control output signal is further provided to the wind estimator. The wind estimator calculates a wind speed estimate by applying the actuator control output and the set of aircraft measurements to an onboard aircraft model. With an accurate wind speed estimate obtained, the airspeed of the aircraft may be derived. This airspeed estimate may then be used by various aircraft systems in lieu of airspeed data obtained from a pitot tube. In one embodiment, wind speed estimator includes selection logic as illustrated in <FIG>.

<CIT> discloses a rotorcraft which includes a flight control computer configured to receive a first sensor signal from a first aircraft sensor of the rotorcraft, receive a second sensor signal from a second aircraft sensor of the rotorcraft, combine the first sensor signal and the second sensor signal with a complementary filter to determine an estimated vertical speed of the rotorcraft, and adjust flight control devices of the rotorcraft according to the estimated vertical speed of the rotorcraft, thereby changing flight characteristics of the rotorcraft.

<CIT> discloses a method and device for estimating the airspeed of an aircraft which includes a first estimation unit configured to estimate the airspeed of the aircraft according to a first estimation method, a second estimation unit configured to estimate the airspeed of the aircraft according to a second estimation method, a weighting unit configured to weight the two airspeeds estimated by the first and second estimation methods and a computation unit configured to sum the weighted airspeeds so as to obtain an estimated airspeed of the aircraft.

The present disclosure describes methods, apparatuses, and non-transitory computer-readable media relating to measurement of airspeed, including low airspeed, for aircraft, according to the appended claims.

In an exemplary aspect, a method for controlling a rotary wing aircraft includes receiving information relating to a measured airspeed of the rotary wing aircraft and an estimated airspeed of the rotary wing aircraft, assigning a first fade value to the measured airspeed, the first fade value corresponding to a confidence level associated with the measured airspeed, and assigning a second fade value to the estimated airspeed, the second fade value corresponds to a confidence level associated with the estimated airspeed. The method further includes calculating a faded measured airspeed based on at least the measured airspeed and the first fade value, calculating a faded estimated airspeed based on at least the estimated airspeed and the second fade value, and calculating a blended airspeed based on both of the faded measured airspeed and the faded estimated airspeed.

According to an embodiment, controlling the rotary wing aircraft comprises sending an electrical signal instructing one or more actuators of the rotary wing aircraft to adjust a position thereof.

According to an embodiment, in the method as described above, the blended airspeed is closer to the measured airspeed than the estimated airspeed when the first fade value exceeds the second fade value; the blended airspeed is closer to the estimated airspeed than the measured airspeed when the second fade value exceeds the first fade value; and the blended airspeed is an average of the measured airspeed and the estimated airspeed when the first fade value is equal to the second fade value.

According to an embodiment, in the method as described above, the blended airspeed equals the estimated airspeed when the first fade value is zero; and the blended airspeed equals the measured airspeed when the second fade value is zero.

According to an embodiment, the method as described above further comprises providing the blended airspeed to a health usage and monitoring system of the rotary wing aircraft.

In yet a further aspect, a rotary wing aircraft is provided. The rotary wing aircraft includes a flight control computer, an actuator communicably coupled to the flight control computer, an airspeed probe communicably coupled to the flight control computer and configured to provide probe data to the flight control computer, and one or more cockpit controls. The flight control computer is configured to receive the probe data from the probe, receive control inputs from the one or more cockpit controls and determine commanded actuator positions, calculate a measured airspeed based on the probe data, calculate an estimated airspeed based on the commanded actuator positions, determine a first fade value based on the measured airspeed, determine a second fade value based on the estimated airspeed, determine a blended airspeed based on the measured airspeed, the estimated airspeed, the first fade value, and the second fade value, and control the rotary wing aircraft based at least in part on the blended airspeed.

In yet a further exemplary aspect, a flight control computer for controlling one or more components of a rotary wing aircraft is provided. The flight control computer includes one or more processors communicated with a one or more non-transitory computer-readable media configured to store fade value data, the one or more non-transitory computer-readable media storing instructions that, when executed by the one or more processors, cause the one or more processors to perform operations. The operations include determining a measured airspeed based on at least pitot probe data, determining an estimated airspeed based on at least swashplate position sensor data, determining a first fade value associated with the measured airspeed based at least in part on the fade value data stored in the one or more non-transitory computer-readable media, determining a second fade value associated with the estimated airspeed based at least in part on the fade value data stored in the one or more non-transitory computer-readable media, calculating a blended airspeed based on the measured airspeed, the first fade value, the estimated airspeed, and the second fade value, and controlling the rotary wing aircraft based on the blended airspeed.

According to an embodiment of the flight control computer, the instructions further cause the one or more processors to perform operations comprising providing the blended airspeed to a health and usage monitoring system of the rotary wing aircraft.

According to an embodiment of the flight control computer, controlling the rotary wing aircraft comprises adjusting at least one of a control schedule or a control mode.

According to an embodiment of the flight control computer, controlling the rotary wing aircraft comprises sending an electrical signal instructing one or more actuators of the rotary wing aircraft to adjust their positions.

According to an embodiment of the flight control computer, the first fade value is determined based on the estimated airspeed; and the second fade value is determined based on the measured airspeed.

The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying Figures, wherein like reference numerals refer to like elements unless otherwise indicated, in which:.

It will be recognized that the Figures are the schematic representations for purposes of illustration. The Figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the Figures will not be used to limit the scope of the meaning of the claims.

Following below are more detailed descriptions of various concepts related to, and implementations of, methods and apparatuses for providing airspeed data for rotary-wing aircraft at low airspeeds. The various concepts introduced above and discussed in greater detail below may be implemented in any of a number of ways, as the described concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

Referring to the figures generally, various embodiments disclosed herein relate to providing airspeed data for rotary-wing aircraft at low airspeeds. As explained in more detail herein, the methods include blending data from airspeed probe data with readily available aircraft state information to create a single airspeed data source. The airspeed data can be used to adjust the control settings of the aircraft to provide improved performance, stability, and efficiency. The airspeed data can further be used for health and usage monitoring of aircraft components. Prior methods of generating airspeed data at low airspeeds have included the use of aircraft state information (cyclic and collective control stick positions, pitch and roll attitudes, swashplate angle, rotor speed etc.) or additional sensors, such as optical or laser-based sensors. However, methods using only aircraft state information are not robust in a large range of speeds and configurations, and additional sensors add complexity and weight, have problems with reliability, and complicate control law voter algorithms. The methods described herein rely on existing airspeed probe data in addition to aircraft state data in a manner that reduces the number of additional sensors used. In particular, in some embodiments, airspeed is detected based on use of the airspeed probe data and aircraft state data without additional sensors.

<FIG> is perspective view of a rotary wing aircraft <NUM> in accordance with an exemplary embodiment. The rotary wing aircraft <NUM> includes a body <NUM>, a lower rotor <NUM> including a lower rotor hub <NUM> that drives four lower rotor blades <NUM>, an upper rotor <NUM> including an upper rotor hub <NUM> that drives four upper rotor blades <NUM>, a propulsor <NUM> including a propulsor hub <NUM> that drives a plurality of propulsor blades <NUM>, and at least one airspeed probe <NUM>. The airspeed probe <NUM> may be, for example, a pitot probe. In various embodiments, rotary wing aircraft <NUM> may have a different number of rotor hubs, rotor blades, propulsor hubs and propulsor blades. In various embodiments, the rotary wing aircraft <NUM> may have one or more tail rotors rather than a propulsor <NUM>. The aircraft <NUM> includes a plurality of actuators <NUM> that may be adjusted by one or more flight control computers (flight controllers) based on the flight regime, airspeed, and/or operator inputs.

In the rotary wing aircraft <NUM> shown in <FIG>, the upper and lower rotor hubs <NUM>, <NUM> rotate about a vertical axis (relative to the aircraft) to spin the rotor blades, <NUM>, <NUM> to generate lift. The rotor hubs may include swashplates or other control mechanisms configured to adjust the pitch angle of the blades <NUM>, <NUM> in response to an input from a pilot using a collective control, a cyclic stick, and/or yaw pedals. The pitch adjustments may change the amount of lift generated by the blades <NUM>, <NUM>, and may cause the blades <NUM>, <NUM> to generate thrust in a chosen direction. The propulsor hub <NUM> may rotate about a horizontal axis running from the nose to the tail of the rotary wing aircraft <NUM> to spin the propulsor blades <NUM> to generate moment or thrust. The propulsor hub <NUM> may include a swashplate or other control mechanism similar to the rotor hubs <NUM>, <NUM> to adjust the pitch of the propulsor blades <NUM>. The airspeed probe <NUM> may be positioned facing the front of the aircraft <NUM> and can measure the difference between the air pressure generated by air entering the tube during flight and the static air pressure.

Modern aircraft typically include fly-by-wire controls rather than manual cockpit controls alone. In a fly-by-wire system, movements of cockpit controls by an operator, such as the collective control, the cyclic stick, and the yaw pedals, are converted to electronic signals transmitted electronically to a flight control computer. The flight control computer determines how to adjust various actuators that control the swashplate or a control surface to provide a response to a command from the operator. Rather than directly converting the control inputs into actuator outputs, the fly-by-wire system uses control algorithms to adjust the actuator outputs based on various information, including flight speed. For example, in response to an identical collective control input, the control algorithms may adjust the actuators differently depending on whether the helicopter is traveling at <NUM> knots or <NUM> knots. These systems greatly reduce operator workload and enhance safety. The control systems rely on accurate airspeed measurements to control the actuators to produce the correct aircraft response. However, as discussed above, measuring airspeed at low airspeeds is difficult, and existing techniques may be inefficient or have other deficiencies. Because of the lack of airspeed data, the control algorithm cannot readily adjust to provide desired control. Instead, a single control algorithm is used at all airspeeds below a certain threshold. "Low airspeed" may be defined as an airspeed lower than a threshold airspeed, where airspeeds below the threshold airspeed are associated with unreliable air probe data. In some embodiments, "low airspeed" includes reverse flight (e.g., negative airspeed).

In some embodiments, for example, low airspeed may be an airspeed below approximately <NUM> knots, e.g., an airspeed that is (i) greater than <NUM> knots and (ii) less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, less than approximately <NUM> knots, or less than <NUM> knot. The foregoing are purely illustrative examples of low airspeeds and are not limiting. In some embodiments, a control algorithm may be used when there are one or more other indicia that the air probe data may be unreliable, including but not limited to an error rate exceeding a threshold error rate for sensing of a sensed parameter (e.g., rotor wash). In some embodiments, the control algorithm may be employed when a sensor resolution exceeds a predetermined resolution.

<FIG> illustrates a schematic block diagram of a flight control system <NUM> according to an exemplary embodiment. The system <NUM> includes a flight control computer <NUM> configured to calculate actuator outputs based on various control and sensor inputs. For example, the flight control computer <NUM> may receive inputs from the cockpit controls <NUM>, the sensor array <NUM>, and to the probe array <NUM>. The cockpit controls <NUM> may include a collective control <NUM>, a cyclic stick <NUM>, one or more yaw pedals <NUM>, and an engine control <NUM>. The cockpit controls <NUM> may send signals to the control module <NUM>, which determines the actuator positions necessary to execute the inputs from the cockpit controls <NUM> and commands the actuators to move to the determined positions. The actuator positions determined by the control module <NUM> may be referred to as commanded actuator positions.

The sensor array <NUM> may include one or more sensors <NUM>. The plurality of sensors may include, but are not limited to, rotor position sensors, swashplate position sensors, pitch rate sensors, roll rate sensors, yaw rate sensors, engine torque meters, and rotor speed tachometers, or any combination thereof. The probe array <NUM> may include one or more airspeed probes <NUM>, such as pitot probes. The flight control computer <NUM> may include one or more processors and one or more non-transitory computer-readable media configured to store instructions that, when executed by the one or more processors, cause the one or more processors to perform the calculations and methods described herein.

The flight control computer <NUM> is configured to include a blended airspeed calculation module (calculator or calculation circuitry) <NUM> configured to calculate the airspeed of the rotary wing aircraft <NUM> at low airspeeds and a control module <NUM> configured to control the flight of the aircraft <NUM>, including the swashplate actuators and other control surface actuators. In some embodiments, the blended airspeed calculation module <NUM> is configured to communicate with at least one of the sensor(s) <NUM> or the probe(s) <NUM>. In some embodiments, the commanded actuator positions sent from the control module <NUM> to the actuators are sent to the blended airspeed calculation module <NUM>. In some embodiments, measurements from the sensors <NUM> and the probes <NUM> are received by the blended airspeed calculation module <NUM>. The blended airspeed calculation module <NUM> may calculate the airspeed of the rotary wing aircraft <NUM> based on the sensor measurements, probe measurements, and/or commanded actuator positions. In some embodiments, the inputs from the flight controls <NUM> may also be used to calculate the airspeed. For example, the inputs from the flight controls <NUM> may provide an independent basis to infer airspeed. More particularly, in certain embodiments such as mechanical aircraft, the inputs from flight controls <NUM> may be used to calculate airspeed, such as mechanical control positions <NUM> being used to determine the position of the rotor cyclic to provide an independent basis to infer airspeed. For example, in some embodiments, swashplate position sensor measurements and other sensor measurements may be used to calculate the airspeed, while in other embodiments, the commanded swashplate actuator positions may be used to calculate airspeed directly without separately sensing the swashplate positions. In some embodiments, a combination of sensor measurements and commanded actuator positions may be used to calculate airspeed.

In some embodiments, the control module <NUM> receives the calculated airspeed from the blended airspeed calculation module <NUM> and the inputs from the cockpit controls <NUM>. The control module <NUM> applies a flight control algorithm using the calculated airspeed and the cockpit control inputs to calculate the control system outputs <NUM>. The control system outputs <NUM> may include instructions to adjust the position of one or more of the actuators <NUM>. For example, the flight control computer <NUM> may send electrical signals (e.g., control position signals) to the actuators <NUM> instructing and causing the actuators <NUM> to adjust their positions. In some embodiments, the control system outputs <NUM> may include instructions to adjust the rotational rotor speed, the rotational tail rotor or propulsor speed, the position of tail rotor or propulsor actuators, or any other feature of the aircraft <NUM> controllable by the flight control computer <NUM>.

In some embodiments, a measured airspeed may be determined based on the probe <NUM> measurements and an estimated airspeed may be determined based on sensor <NUM> measurements. For example, the estimated airspeed may be determined based on data from one or more swashplate position sensors <NUM>, and the measured airspeed may be determined based on data from one or more pitot probes <NUM>. In some embodiments, the measured airspeed may be determined based on the probe <NUM> measurements and the estimated airspeed may be based on commanded actuator positions from the control module <NUM>. The measured airspeed and the estimated airspeed may then be blended to determine a blended airspeed. Depending on the determined measured and estimated airspeeds, a different weight may be given to each of the measured airspeed and estimated airspeed in determining the blended airspeed. At low airspeeds, the blended airspeed may provide a more accurate calculation of airspeed than the measured airspeed or estimated airspeed alone.

<FIG> is a graph of experimental data illustrating the airspeeds predicted by the measured airspeed <NUM> and estimated airspeed <NUM> compared to the actual airspeed. On this graph, a theoretically perfect measurement of airspeed would appear as a straight line, with the x value equal to the y value, indicating that the measurement predicted is exactly equal to the actual airspeed. As can be seen in <FIG>, neither the measured airspeed <NUM> nor the estimated airspeed <NUM> perfectly predict the actual airspeed. However, the estimated airspeed <NUM> provides a relatively good prediction of actual airspeed from -<NUM> knots to about <NUM> knots, and then becomes less accurate as the airspeed increases. Conversely, the measured airspeed <NUM> provides a relatively poor prediction of actual airspeed in the negative direction (e.g., in a reverse air direction) and below about <NUM> knots, and becomes more accurate as the airspeed increases. According to some embodiments, the measured airspeed <NUM> and the estimated airspeed <NUM> may each be assigned a fade value to determine a faded measured airspeed and a faded estimated airspeed respectively. The faded airspeeds may then be blended to determine a blended airspeed that is more accurate (e.g., more closely predictive of the actual airspeed) than the measured airspeed <NUM> or the estimated airspeed <NUM>. For example, at low airspeeds, estimated airspeed <NUM> may be assigned a higher fade value than measured airspeed <NUM>. At higher airspeeds, measured airspeed <NUM> may be assigned a higher fade value than estimated airspeed <NUM>. When calculating the blended airspeed, the airspeed with the higher fade value may have a larger effect on the calculation of the blended airspeed than the airspeed with the lower fade value.

<FIG> is a graph representing the fade values assigned to the estimated airspeed and the measured airspeed, according to an embodiment. In this embodiment, the measured airspeed and the estimated airspeed are given different fade values depending on their values. A higher fade value indicates that the estimated or measured airspeed should be given more weight in calculating the blended airspeed. The fade values may vary from a minimum of zero to a maximum of one. In some embodiments, an estimated or measured airspeed with a fade value of zero is not used to calculate the blended airspeed. In some embodiments, when the measured airspeed and the estimated airspeed have the same fade values, the measured airspeed and estimated airspeed may be weighted equally when calculating the blended airspeed. It should be understood that the numerical values shown are for example purposes only. Alternative weighting curves and calculation methods are contemplated according to various embodiments within the scope of the present disclosure.

Fade values may correspond to the relative confidence in the accuracy of the estimated and measured airspeeds. A higher fade value indicates that the estimated or measured airspeed is relatively likely to be correct or nearly correct. For example, at a fade value of about <NUM> the measured or estimated airspeed is relatively highly likely to be accurate, within an acceptable tolerance. At a fade value of zero, the measured or estimated airspeed is not relatively likely to be correct or nearly correct. As shown in <FIG>, the measured airspeed is a relatively accurate measurement of the actual airspeed at higher airspeeds. Thus, the confidence in the accuracy of the measured airspeed is relatively high at higher airspeeds. Because the relative confidence in the accuracy of the measured airspeed is high at higher airspeeds, the measured airspeed fade value may increase as the measured airspeed increases, as shown in <FIG>. Conversely, as shown in <FIG>, the estimated airspeed is a relatively accurate measurement of the actual airspeed at lower airspeeds. Thus, the confidence in the accuracy of the estimated airspeed is relatively high at lower airspeeds. Because the relative confidence in the accuracy of the estimated airspeed is high at lower airspeeds, the estimated airspeed fade value may increase as the estimated airspeed decreases. Using the fade values, the blended airspeed calculation module <NUM> is configured to give more weight to the estimated airspeed than to the measured airspeed at lower airspeeds when calculating the blended airspeed because the relative confidence in the estimated airspeed is higher than the relative confidence in the measured airspeed. The blended airspeed calculation module <NUM> is also configured to give more weight to the measured airspeed than to the estimated airspeed at higher airspeeds when calculating the blended airspeed because the relative confidence in the measured airspeed is higher than the relative confidence in the estimated airspeed.

In some embodiments, the airspeeds may be defined using ranges. For example, the airspeeds may be defined as having an upper airspeed range and a lower airspeed range. The upper airspeed range may be the range at which the measured airspeed fade value is at a maximum (e.g., above <NUM> knots as shown in <FIG>). The lower airspeed range may be the range at which the estimated airspeed fade value is at a maximum (e.g., below <NUM> knots as shown in <FIG>). In these embodiments, the upper airspeed range and lower airspeed range may overlap (e.g., from <NUM> knots to <NUM> knots as shown in <FIG>). In some embodiments, the airspeeds may be described as having a middle airspeed range. For example, the middle airspeed range may be the range at which the measured airspeed fade value and the estimated airspeed fade value are both at a maximum (e.g., from <NUM> knots to <NUM> knots as shown in <FIG>). When the airspeed has a middle range, the upper airspeed range may include airspeeds above the middle range and the lower airspeed range may include airspeeds below the middle airspeed range. In various embodiments, the airspeed ranges may be referred to as first, second, and third airspeed ranges rather than lower, upper, or middle airspeed ranges. In some embodiments, the airspeed may have transition airspeed ranges. For example, the airspeed may be described as having a lower transition airspeed range (e.g., a first transition airspeed range), in which the measured airspeed fade value increases as airspeed increases. For example, the measured airspeed fade value may transition from a minimum to a maximum as airspeed increases in the first transition airspeed range (e.g., from <NUM> knots to <NUM> knots as shown in <FIG>). The airspeed may have an upper transition airspeed range (e.g., a second transition airspeed range), in which the estimated airspeed fade value decreases as airspeed increases. For example, the estimated airspeed fade value may transition from a maximum to a minimum as airspeed increases in the second transition airspeed range (e.g., from <NUM> knots to <NUM> knots).

<FIG> illustrates a process <NUM> (e.g., a method) for calculating blended airspeed and controlling one or more actuators based on the calculated blended airspeed. It should be appreciated that the process steps shown and described in connection with any depicted flow diagram are exemplary in nature. The order of steps may be varied from what is shown, and/or particular steps may be omitted, and/or additional steps may be added. As compared to what is depicted, various embodiments may include additional steps (e.g., prior to an initial depicted step, in between steps, or following a final depicted step). The method may be performed by flight control computer <NUM>.

In at least one embodiment, the process <NUM> begins at operation <NUM>. At operation <NUM>, the measured airspeed is determined based on probe data. The probe data may include, for example, measurements from one or more pitot probes.

At operation <NUM>, the estimated airspeed is determined based on commanded actuator positions from the control module <NUM>. For example, the control module may command the swashplate actuators and/or control surface actuators to extend or retract to a specific position based on the commands from the cockpit controls <NUM> to control the flight of the aircraft <NUM>. The airspeed of a rotary wing aircraft generally increases as the swashplate angle in the forward direction increases (e.g., as the forward tilt of the swashplate increases). When an operator pushes forward on the cyclic stick <NUM>, the control module <NUM> commands the swashplate actuators to tilt the swashplate forward to increase the forward speed of the aircraft <NUM>. The commanded actuator positions from the control module are sent to the blended airspeed calculation module <NUM>, which may determine that the estimated airspeed has increased based on the commanded actuator positions. Similarly, the blended airspeed calculation module <NUM> may determine that the estimated airspeed decreases (e.g., to zero) when the cyclic stick <NUM> is in a neutral position and the swashplate is commanded to be in a neutral position. When the cyclic stick is pulled black, the control module <NUM> commands the swashplate actuators to tilt the swashplate in the rearward direction, and the blended airspeed calculation module <NUM> may determine that the estimated airspeed is negative (e.g., the aircraft is being flown in a negative airspeed or reverse direction). In some embodiments, sensor data from various sensors <NUM> and/or inputs from the cockpit controls <NUM> may be used instead of or in addition to the commanded actuator positions to determine the estimated airspeed.

At operation <NUM>, the measured airspeed fade value (e.g., a first fade value) is determined based on the estimated airspeed. For example, the measured airspeed fade value may be determined by a fade value curve as shown in <FIG> or a fade value table that correlates each measured airspeed with a fade value. Using the fade value curve in <FIG>, the estimated air speed is correlated to a measured airspeed fade value. For example, if the estimated airspeed is <NUM>, the measured airspeed fade value is <NUM>. The measured fade value corresponds to a confidence level associated with the measured airspeed.

At operation <NUM>, the faded measured airspeed is calculated based on the measured airspeed fade value. In some embodiments, the faded measured airspeed also depends on the estimated airspeed. As a non-limiting example, the faded measured airspeed may be calculated according to the following equation: <MAT> where Airspeedfm is the faded measured airspeed, Airspeedm is the measured airspeed, Airspeede is the estimated airspeed, and Fadema is the measured airspeed fade.

At operation <NUM>, the estimated airspeed fade value (e.g., a second fade value) is determined based on the faded measured airspeed. For example, the estimated airspeed fade value may be determined by a fade value curve as shown in <FIG> or a fade value table that correlates each estimated airspeed with a fade value. Using the fade value curve in <FIG>, the faded measured airspeed is correlated to an estimated airspeed fade value. For example, if the faded measured airspeed is <NUM>, the estimated airspeed fade value is <NUM>. The estimated fade value corresponds to a confidence level associated with the estimated airspeed.

At operation <NUM>, the faded estimated airspeed is calculated based on the estimated airspeed fade value. In some embodiments, the faded estimated airspeed also depends on the faded measured airspeed. As a non-limiting example, the faded estimated airspeed may be calculated according to the following formula: <MAT> where Airspeedfe is the faded estimated airspeed, Airspeede is the estimated airspeed, Airspeedrn is the measured airspeed, and Fadeea is the estimated airspeed fade value.

At operation <NUM>, the blended airspeed is calculated based on the faded estimated airspeed and the faded measured airspeed. As a non-limiting example, the faded estimated airspeed may be calculated according to the following formula: <MAT> where Airspeedb is the blended airspeed, Airspeedfm is the faded measured airspeed, and Airspeedfe is the faded estimated airspeed.

At operation <NUM>, the aircraft <NUM> may be controlled based on the blended airspeed. The blended airspeed may be used as an input to schedule control gains or to adjust or change one or more control modes. The control may be adjusted based on at least one of a control schedule (or control schedules) and/or a control mode (or control modes). For example, the stability incidence angle can be controlled based in part on the blended airspeed. The blended airspeed may be used as an input to a lookup table that outputs a gain value and/or used in mixing equations to determine how the aircraft is controlled. Rotor controls change as a function of airspeed due to forces and moments changing with airspeed. Forces and moments have to be balanced to achieve a level flight trim. The blended airspeed may be used as an input to determine how actuators (e.g., swashplate actuators, control surface actuators, etc.) should be positioned. In some embodiments, certain control devices (e.g., yaw control devices) may be enabled or disabled based on the blended airspeed.

As a first example of process <NUM>, the measured airspeed may be determined at process <NUM> to be <NUM> knots and the estimated airspeed may be determined at operation <NUM> to be <NUM> knots. Referring in this example to the fade value graph of <FIG> it is determined at operation <NUM> that a first estimated airspeed (e.g., around <NUM> knots) corresponds to a measured airspeed fade value of about <NUM>. At operation <NUM>, the faded measured airspeed may be calculated using Equation <NUM>: <MAT>.

For example, Airspeedfm = [(<NUM> knots - <NUM> knots) * <NUM>] + <NUM> knots = <NUM> knots.

At operation <NUM>, it is determined the measured airspeed (e.g., <NUM> knots) corresponds to an estimated airspeed fade value of about <NUM>. In some embodiments, the discrete values in <FIG> may be populated into a look-up table, which is consulted by the blended airspeed calculation module <NUM> in implementing process <NUM>. At operation <NUM>, the faded estimated airspeed may be calculated using Equation <NUM> above: <MAT>.

Following the example above, Airspeedfe = [(<NUM> knots - <NUM> knots) * <NUM>] + <NUM> knots = <NUM> knots.

At operation <NUM>, the blended estimated airspeed may be calculated using Equation <NUM>: <MAT>.

For example, Airspeedb = (<NUM> knots + <NUM> knots) / <NUM> = <NUM> knots.

As a second example of operation <NUM>, the measured airspeed may be determined at process <NUM> to be <NUM> knots and the estimated airspeed may be determined at operation <NUM> to be <NUM> knots. Referring, in this example, to the fade value graph of <FIG>, it is determined at operation <NUM> that a <NUM> knot estimated airspeed corresponds to a measured airspeed fade value of <NUM>. At operation <NUM>, the faded measured airspeed may be calculated using Equation <NUM>: <MAT>.

At operation <NUM>, it is determined the measured airspeed (e.g., <NUM> knots) corresponds to an estimated airspeed fade value of <NUM>.

At operation <NUM>, the faded estimated airspeed may be calculated using Equation <NUM>: <MAT>.

As a third example of process <NUM>, the measured airspeed may be determined at process <NUM> to be <NUM> knots and the estimated airspeed may be determined at process <NUM> to be <NUM> knots. Referring, in this example, to the fade value graph of <FIG>, it is determined at operation <NUM> that a <NUM> knot estimated airspeed corresponds to a measured airspeed fade value of <NUM>. At operation <NUM>, the faded measured airspeed may be calculated using Equation <NUM>: <MAT>.

At operation <NUM>, it is determined the faded measured airspeed (e.g., <NUM> knots) corresponds to an estimated airspeed fade value of <NUM>.

As a fourth example of process <NUM>, the measured airspeed may be determined at process <NUM> to be <NUM> knots and the estimated airspeed may be determined at process <NUM> to be <NUM> knots. Referring, in this example, to the fade value graph of <FIG>, it is determined at operation <NUM> that a <NUM> knot estimated airspeed corresponds to a measured airspeed fade value of <NUM>. At operation <NUM>, the faded estimated airspeed may be calculated using Equation <NUM>: <MAT>.

At operation <NUM>, it is determined that the faded measured airspeed (e.g., <NUM> knots) corresponds to an estimated airspeed fade value of <NUM>.

At operation <NUM>, the faded estimated airspeed may be calculated using the formula above: <MAT>.

At operation <NUM>, the blended estimated airspeed may be calculated using the formula above: <MAT>.

As seen from these examples, using the exemplary Equations (<NUM>)-(<NUM>), when one of the measured or estimated airspeed has a fade value of <NUM> and the other has a fade value of <NUM> (e.g., in the first example), the resulting blended airspeed is equal to the airspeed with a fade value of <NUM>. The airspeed with a fade value of <NUM> does not affect the calculation of the blended airspeed. When the measured airspeed fade value is equal to the estimated airspeed fade value (e.g., in the second example), the resulting blended airspeed is an arithmetic average of the measured airspeed and the estimated airspeed. Here, the measured airspeed and estimated airspeed are weighted equally due to their equal fade values. As can be seen in the third and fourth examples, when one fade value is higher than the other, the blended airspeed will be closer to the airspeed with the higher fade value. When the estimated airspeed fade value is greater than the estimated airspeed fade value (e.g., in the third example), the resulting blended airspeed is closer to the estimated airspeed than to the measured airspeed. When the measured airspeed fade value is higher than the estimated airspeed fade value (e.g., in the fourth example), the resulting blended airspeed is closer to the measured airspeed than to the estimated airspeed. Thus, more weight is given to the airspeed with the higher fade value when calculating the blended airspeed.

<FIG> is a graph of experimental data, according to an exemplary embodiment, comparing the faded measured airspeed <NUM>, the faded estimated airspeed <NUM>, and the blended airspeed <NUM> to the actual airspeed based on the measured airspeed <NUM> and the estimated airspeed <NUM> shown in <FIG>. The faded measured airspeed <NUM>, the faded estimated airspeed <NUM>, and the blended airspeed <NUM> may be determined based on the methods described above. As explained above, in negative airspeeds and low positive airspeeds, the estimated airspeed <NUM> is more accurate than the measured airspeed <NUM>, and therefore receives a higher fade value. At these low airspeeds, the blended airspeed <NUM> may be similar to the estimated airspeed <NUM> as shown in <FIG> (e.g., within a predetermined threshold, which may be ± about <NUM>%, ± about <NUM>%, or ± about <NUM>%, for example). In some embodiments, at low airspeeds, the blended airspeed <NUM> may be the same as the estimated airspeed <NUM>, for example if the fade value of the measured airspeed <NUM> is zero.

As the airspeeds approach <NUM> knots, the fade value of the measured airspeed <NUM> may increase and the blended airspeed <NUM> may be increasingly affected by the measured airspeed <NUM>. From about <NUM> knots to about <NUM> knots, the measured airspeed <NUM> and the estimated airspeed <NUM> may be roughly equally accurate and may have substantially equal fade values. Thus, the blended airspeed <NUM> may be between the measured airspeed <NUM> and the estimated airspeed <NUM>. As can be seen in <FIG>, from about <NUM> knots to <NUM> knots, the faded measured airspeed <NUM> tends to underestimate the actual airspeed and faded estimated airspeed <NUM> tends to overestimate the actual airspeed. However, when the faded measured airspeed <NUM> and the faded estimated airspeed <NUM> are blended, the blended airspeed <NUM> is closer to the actual airspeed than the faded measured airspeed <NUM> and the faded estimated airspeed <NUM> alone. As the airspeed increases beyond <NUM> knots, the estimated airspeed <NUM> becomes less accurate and the measured airspeed <NUM> becomes more accurate. Accordingly, the fade value of the estimated airspeed <NUM> decreases and the blended airspeed <NUM> becomes increasingly similar to the measured airspeed. As shown in <FIG>, as the airspeed exceeds about <NUM> knots, the blended airspeed <NUM> is similar to the measured airspeed <NUM> shown in <FIG> (e.g., within a predetermined threshold as noted above), or may be the same as the measured airspeed <NUM>, for example if the fade value of the estimated airspeed <NUM> is zero. By blending the measured airspeed <NUM> and estimated airspeed <NUM> and using the fade values as described above, the blended airspeed <NUM> may provide a much closer estimation of actual airspeed.

According to one or more embodiments, the foregoing techniques including a determination of blended airspeed is utilized to carry out control of one or more components of a rotary wing aircraft, although the present techniques are not limited to this type of aircraft. Rotary wing aircraft are typically operated at the same control allocation, command model, gains and mixing throughout the low airspeed region. The embodiments described herein provide a more accurate airspeed estimation that allow the aircraft to adjust the control allocation, command model, gains and mixing within the low airspeed region. Not only can this provide operators with better control of the aircraft, it can provide improved health and usage monitoring for aircraft components. Rotary wing aircraft components are generally scheduled to be replaced based on the amount of time the aircraft spends in various flight regimes, subject to various maintenance and logistics considerations. For example, a given component may have an expected lifetime of about two years if an aircraft is primarily used at low airspeeds and hovering, while the same component may have an expected lifetime that is much shorter if the aircraft is often used at high speeds. With inaccurate low airspeed estimation, a Health and Usage Monitoring System (HUMS) may overestimate the wear on components as a safety factor. For example, if the aircraft is not able to distinguish between airspeeds in the range <NUM> knots to <NUM> knots, the HUMS may calculate the wear on various components based on the maximum wear in that range. This may result in the HUMS recommending early replacement of components that still have remaining useful life. Using the embodiments described herein, an aircraft provided with the flight control computer described above is configured to provide the HUMS with accurate airspeed data at low airspeeds, allowing the HUMS to adjust the calculation of the remaining life and replacement date of components accordingly.

While this specification contains specific implementation details, these should not be construed as limitations on the scope of what may be claimed but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

As utilized herein, the terms "substantially," "generally," "approximately," and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the appended claims.

Unless otherwise indicated, all numbers expressing quantities of properties, parameters, conditions, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations. Any numerical parameter should at least be construed in light of the number reported significant digits and by applying ordinary rounding techniques. The term "about" when used before a numerical designation, e.g., speed (velocity), indicates approximations which may vary by ( + ) or ( - ) <NUM>%, <NUM>% or <NUM>%.

The present disclosure contemplates methods, systems, and program products on any machine-readable media for accomplishing various operations, e.g., of the flight control computer. The embodiments of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. For example, the abovementioned description, steps, procedures and/or processes including suggested steps can be implemented using hardware, software, firmware (known as a combination of a hardware device and computer instructions and data that reside as read-only software on the hardware device), an optical printer, or a combination thereof. Examples of hardware can include analog, digital, and mixed circuits known as microcircuits, microchips, or silicon chips. Examples of the optical printer may include a system on chip (SoC), system in package (SiP), a computer on module (CoM), and an electrical system.

Claim 1:
A method for controlling a rotary wing aircraft (<NUM>), the method comprising:
receiving probe data from an airspeed probe (<NUM>);
receiving control inputs from one or more cockpit controls (<NUM>) and determine commanded actuator positions; the method being characterised by the following steps:
determining a measured airspeed of the rotary wing aircraft (<NUM>) based on the probe data;
determining an estimated airspeed of the rotary wing aircraft based on the commanded actuator positions;
determining a first fade value based on the measured airspeed;
determining a second fade value based on the estimated airspeed;
determining a blended airspeed based on the measured airspeed, the estimated airspeed, the first fade value, and the second fade value; and
controlling the rotary wing aircraft (<NUM>) based at least in part on the blended airspeed.