# US 11,029,706 B2 · Flight control system for determining a fault based on error between a measured and an estimated angle of attack

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- Number: US 11,029,706 B2
- Document ID: US11029706B2
- Status: Granted
- Kind: B2
- Application number: 16/213,423
- Filed: 2018-12-07
- Published: 2020-06-11
- Granted: 2021-06-08
- Earliest claimed: 2018-12-07
- Assignees: The Boeing Company
- Applicants: The Boeing Company
- Inventors: Sherwin Chunshek Li; Brian Whitehead; Brian Kenyon Rupnik; Kioumars Najmabadi
- Web page: https://patentgrep.com/patent/US11029706B2

## CPC

- G01P 21/025: {for measuring speed of fluids; for measuring speed of bodies relative to fluids (for measuring volume flow G01F25/10)}
- G05D 1/0808: {specially adapted for aircraft}
- B64F 5/60: Testing or inspecting aircraft components or systems
- G01P 5/16: using Pitot tubes {, e.g. Machmeter}
- G01P 13/025: {indicating air data, i.e. flight variables of an aircraft, e.g. angle of attack, side slip, shear, yaw}
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- B64F: GROUND OR AIRCRAFT-CARRIER-DECK INSTALLATIONS SPECIALLY ADAPTED FOR USE IN CONNECTION WITH AIRCRAFT; DESIGNING, MANUFACTURING, ASSEMBLING, CLEANING, MAINTAINING OR REPAIRING AIRCRAFT, NOT OTHERWISE PROVIDED FOR; HANDLING, TRANSPORTING, TESTING OR INSPECTING AIRCRAFT COMPONENTS, NOT OTHERWISE PROVIDED FOR

## Abstract

A flight control system for an aircraft is disclosed and includes one or more processors and a memory coupled to the processors. The memory stores data comprising a database and program code that, when executed by the one or more processors, causes the flight control system to receive as input a measured angle of attack that is based on a raw angle of attack and an estimated angle of attack based on a total pressure. The flight control system is further caused to compare the measured angle of attack with the estimated angle of attack to determine an error. In response to determining that the error between the measured angle of attack and the estimated angle of attack exceeds a threshold value, the flight control system determines the presence of a fault with an angle of attack value.

## Claims

### Claim 1

A flight control system for an aircraft including a plurality of displays, the flight control system comprising:
one or more processors; and
a memory coupled to the one or more processors, the memory storing data comprising a database and program code that, when executed by the one or more processors, causes the flight control system to:
receive a signal indicating a total pressure, wherein the total pressure is measured by a plurality of pitot tubes;
determine a measured angle of attack that is based on a raw angle of attack and a true airspeed of the aircraft;
receive as input an estimated angle of attack that is based on a total pressure;
compare the measured angle of attack with the estimated angle of attack to determine an error;
in response to determining that the error between the measured angle of attack and the estimated angle of attack exceeds a threshold value, determine the presence of a fault with an angle of attack value and provide the estimated angle of attack to the plurality of displays;
determine a measured dynamic pressure based on the total pressure and a static pressure;
determine an estimated dynamic pressure based on data collected from a plurality of control surfaces, inertial, and angle of attack sensors;
compare the measured dynamic pressure and the estimated dynamic pressure with one another to determine a difference;
in response to determining the difference between the measured dynamic pressure and the estimated dynamic pressure exceeds another threshold value for a threshold amount of time, determine the presence of a common mode fault of the measured dynamic pressure; and
in response to determining the presence of the common mode fault of the measured dynamic pressure, determine the measured angle of attack based on the estimated dynamic pressure.

### Claim 2 (depends on 1)

The flight control system of claim 1, further comprising a plurality of angle of attack sensors in communication with the one or more processors, wherein the plurality of angle of attack sensors are configured to measure the raw angle of attack.

### Claim 3 (depends on 2)

The flight control system of claim 2, wherein the measured angle of attack is determined based on a moment arm correction term, and an estimated Mach number in addition to the true air speed and the raw angle of attack.

### Claim 4 (depends on 2)

The flight control system of claim 2, wherein the plurality of angle of attack sensors each determine an angle of attack value, and wherein the one or more processors execute instructions to:
select one of a plurality of raw angle of attack values based on signal selection and failure detection (SSFD) logic.

### Claim 5 (depends on 1)

The flight control system of claim 1, wherein the one or more processors executes instructions to:
receive as input a measured longitudinal acceleration and a measured vertical acceleration;
determine an estimated longitudinal acceleration and an estimated vertical acceleration based on a drag coefficient and a lift coefficient, wherein the drag coefficient and a lift coefficient are based on a first plurality of operating parameters;
determine an acceleration error value for a first difference between the estimated longitudinal acceleration and the estimated vertical acceleration and a second difference between the measured longitudinal acceleration and the measured vertical acceleration; and
determine a residual Kalman value by multiplying the acceleration error value for the first difference and the second difference with a Kalman gain value.

### Claim 6 (depends on 5)

The flight control system of claim 5, wherein the one or more processors executes instructions to:
determine an estimated rate of change of the angle of attack based on an estimated normal acceleration component of the aircraft;
combine the residual Kalman value with the estimated rate of change of the angle of attack together into a sum; and
integrate the sum of the residual Kalman value and the estimated rate of change of the angle of attack to determine the estimated angle of attack.

### Claim 7 (depends on 1)

The flight control system of claim 1, wherein the one or more processors executes instructions to:
determine the estimated dynamic pressure based on both a drag coefficient and a lift coefficient, wherein the drag coefficient and the lift coefficient are based on a first plurality of operating parameters of the aircraft.

### Claim 8 (depends on 7)

The flight control system of claim 7, wherein the one or more processors executes instructions to:
determine the measured angle of attack based on a moment arm correction term and the raw angle of attack in addition to the estimated dynamic pressure.

### Claim 9

A flight control system for an aircraft including a plurality of displays, the flight control system comprising:
one or more processors;
a plurality of angle of attack sensors in communication with the one or more processors, wherein the plurality of angle of attack sensors are configured to measure a raw angle of attack; and
a plurality of pitot tubes in communication with the one or more processors, wherein the plurality of pitot tubes measure a total pressure;
a memory coupled to the one or more processors, the memory storing data comprising a database and program code that, when executed by the one or more processors, causes the flight control system to:
receive a signal indicating the total pressure;
determine a measured angle of attack that is based on the raw angle of attack and a true airspeed of the aircraft;
receive as input an estimated angle of attack that is based on the total pressure;
compare the measured angle of attack with estimated angle of attack to determine an error;
in response to determining that the error between the measured angle of attack and the estimated angle of attack exceeds a threshold value, determine the presence of a fault with a majority of the plurality of angle of attack sensors and provide the estimated angle of attack to the plurality of displays;
determine a measured dynamic pressure based on the total pressure and a static pressure;
determine an estimated dynamic pressure based on data collected from a plurality of control surfaces, inertial, and angle of attack sensors;
compare the measured dynamic pressure and the estimated dynamic pressure with one another to determine a difference;
in response to determining the difference between the measured dynamic pressure and the estimated dynamic pressure exceeds another threshold value for a threshold amount of time, determine the presence of a common mode fault of the measured dynamic pressure; and
in response to determining the presence of the common mode fault of the measured dynamic pressure, determine the measured angle of attack based on the estimated dynamic pressure.

### Claim 10 (depends on 9)

The flight control system of claim 9, wherein the measured angle of attack is determined based on a moment arm correction term, and an estimated Mach number in addition to the true air speed and the raw angle of attack.

### Claim 11 (depends on 9)

The flight control system of claim 9, wherein the one or more processors executes instructions to:
determine the estimated dynamic pressure based on both a drag coefficient and a lift coefficient, wherein the drag coefficient and the lift coefficient are based on a first plurality of operating parameters.

### Claim 12 (depends on 11)

The flight control system of claim 11, wherein the one or more processors executes instructions to:
determine the measured angle of attack based on a moment arm correction term the raw angle of attack in addition to the estimated dynamic pressure.

### Claim 13 (depends on 9)

The flight control system of claim 9, wherein the one or more processors executes instructions to:
receive as input a measured longitudinal acceleration and a measured vertical acceleration;
determine an estimated longitudinal acceleration and an estimated vertical acceleration based on a drag coefficient and a lift coefficient;
determine an acceleration error value for a first difference between the estimated longitudinal acceleration and the estimated vertical acceleration and a second difference between the measured longitudinal acceleration and the measured vertical acceleration; and
determine a residual Kalman value by multiplying the acceleration error value for the first difference and the second difference with a Kalman gain value.

### Claim 14 (depends on 13)

The flight control system of claim 13, wherein the one or more processors executes instructions to:
determine an estimated rate of change of the angle of attack is determined based on an estimated normal acceleration component of the aircraft;
combine the residual Kalman value with the estimated rate of change of the angle of attack together into a sum; and
integrate the sum of the residual Kalman value and the estimated rate of change of the angle of attack to determine the estimated angle of attack.

### Claim 15

A method for determining a fault with an angle of attack value for an aircraft, the method comprising:
receiving a signal indicating a total pressure, wherein the total pressure is measured by a plurality of pitot tubes;
determining, by a computer, a measured angle of attack that is based on a raw angle of attack and a true airspeed of the aircraft;
determining, by the computer, an estimated angle of attack that is determined based on the total pressure;
comparing, by the computer, the measured angle of attack with the estimated angle of attack to determine an error;
in response to determining the error between the measured angle of attack and the estimated angle of attack exceeds a threshold value, determining the presence of the fault with the angle of attack value, wherein the estimated angle of attack is provided to a plurality of displays;
determining a measured dynamic pressure based on the total pressure and a static pressure;
determining an estimated dynamic pressure based on data collected from a plurality of control surfaces, inertial, and angle of attack sensors;
comparing the measured dynamic pressure and the estimated dynamic pressure with one another to determine a difference;
in response to determining the difference between the measured dynamic pressure and the estimated dynamic pressure exceeds another threshold value for a threshold amount of time, determining the presence of a common mode fault of the measured dynamic pressure; and
in response to determining the presence of the common mode fault of the measured dynamic pressure, determining the measured angle of attack based on the estimated dynamic pressure.

### Claim 16 (depends on 15)

The method of claim 15, further comprising:
determining the measured angle of attack based on a moment arm correction term, and an estimated Mach number in addition to the true airspeed and the raw angle of attack.

### Claim 17 (depends on 15)

The method of claim 15, further comprising:
determine an estimated dynamic pressure based on both a drag coefficient and a lift coefficient, wherein the drag coefficient and the lift coefficient are based on a first plurality of operating parameters.

### Claim 18 (depends on 17)

The method of claim 17, further comprising:
determine the measured angle of attack based on a moment arm correction term, the raw angle of attack in addition to the estimated dynamic pressure.

### Claim 19 (depends on 15)

The method of claim 15, further comprising:
receive as input a measured longitudinal acceleration and a measured vertical acceleration;
determine an estimated longitudinal acceleration and an estimated vertical acceleration based on a drag coefficient and a lift coefficient;
determine an acceleration error value for a first difference between the estimated longitudinal acceleration and the estimated vertical acceleration and a second difference between the measured longitudinal acceleration and the measured vertical acceleration; and
determine a residual Kalman value by multiplying the acceleration error value for the first difference and the second difference with a Kalman gain value.

### Claim 20 (depends on 19)

The method of claim 19, further comprising:
determine an estimated rate of change of the angle of attack is determined based on an estimated normal acceleration component of the aircraft;
combine the residual Kalman value with the estimated rate of change of the angle of attack together into a sum; and
integrate the sum of the residual Kalman value and the estimated rate of change of the angle of attack to determine the estimated angle of attack.