# US 11,299,289 B1 · Angle-of-attack determination for aircraft stall protection

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- Number: US 11,299,289 B1
- Document ID: US11299289B1
- Status: Granted
- Kind: B1
- Application number: 16/431,375
- Filed: 2019-06-04
- Granted: 2022-04-12
- Earliest claimed: 2018-06-05
- Assignees: Textron Innovations Inc.
- Applicants: Textron Aviation Inc.
- Inventors: Brian Anthony Derstein; Steven G. Hagerott
- Web page: https://patentgrep.com/patent/US11299289B1

## CPC

- B64D 43/02: for indicating aircraft speed or stalling conditions
- G01P 13/025: {indicating air data, i.e. flight variables of an aircraft, e.g. angle of attack, side slip, shear, yaw}
- G05D 1/0607: {specially adapted for aircraft}
- G05D 1/0816: {to ensure stability}
- B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
- 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

## Abstract

A method for determining an aircraft angle-of-attack for aircraft stall protection includes providing an output signal from an angle-of-attack sensor and determining an initial angle-of-attack signal based on the output signal. The initial angle-of-attack signal is compensated to provide a pseudo angle-of-attack signal, and the pseudo angle-of-attack signal is mapped to a true angle-of-attack signal based on flight test data. The true angle-of-attack signal is compensated based on roll rate and sideslip or estimated sideslip to provide a compensated angle-of-attack. A complementary filter is applied that complements the compensated angle-of-attack signal with a higher frequency inertial angle-of-attack rate signal, calculated from aircraft inertial data, to provide an angle-of-attack complementary filter output. An angle-of-attack threshold for aircraft stall protection is determined based on one or more compensation parameters. Activation of aircraft stall protection is determined based on the angle-of-attack complementary filter output compared with the angle-of-attack threshold.

## Claims

### Claim 1

An aircraft angle-of-attack determining method, comprising:
providing an output signal from an angle-of-attack sensor to a controller;
providing a load factor component from the angle-of-attack sensor to the controller;
determining, via the controller, an initial angle-of-attack signal based on the output signal and the load factor component;
compensating, via the controller, the initial angle-of-attack signal to provide a pseudo angle-of-attack signal based on dynamic pressure;
mapping, via the controller, the pseudo angle-of-attack signal to a true angle-of-attack signal based on angle-of-attack flight test data,
wherein mapping the pseudo angle-of-attack signal is configured to remove nonlinear behavior of the pseudo angle-of-attack signal;
compensating, via the controller, the true angle-of-attack signal based on a measured aircraft roll rate and a measured aircraft sideslip to provide a compensated angle-of-attack; and
applying, via the controller, a complementary filter that passes the compensated angle-of-attack signal through a low-pass filter and complements it with higher frequency inertial angle-of-attack rate signal calculated from aircraft inertial data to provide an angle-of-attack complementary filter output.

### Claim 2 (depends on 1)

The method of claim 1, further comprising determining, via the controller, an angle-of-attack threshold for aircraft stall protection based on one or more compensation parameters.

### Claim 3 (depends on 2)

The method of claim 2, wherein the one or more compensation parameters include one or more of icing condition, flap position, landing gear position, Mach number, pressure altitude, inertial angle-of-attack rate, sideslip, engine shaft power/torque, thrust, pitch rate, axial deceleration, airspeed rate, filtered derivative of airspeed, and thrust coefficient, as well as any flight-test discovered dependencies or unexplained factors.

### Claim 4 (depends on 2)

The method of claim 2, further comprising determining when the aircraft stall protection should activate based on the angle-of-attack threshold compared with the angle-of-attack complementary filter output.

### Claim 5 (depends on 3)

The method of claim 3, wherein the step of determining the angle-of-attack threshold for aircraft stall protection includes determining a first angle-of-attack threshold for stick pusher activation based on adjustments for the one or more compensation parameters.

### Claim 6 (depends on 5)

The method of claim 5, wherein the step of determining the angle-of-attack threshold for aircraft stall protection includes determining a second angle-of-attack threshold for stall warning activation based on the first angle-of-attack threshold plus an adjustment for stall warning activation.

### Claim 7 (depends on 1)

The method of claim 1, wherein the angle-of-attack sensor is a lift transducer.

### Claim 8 (depends on 1)

The method of claim 1, further comprising adjusting the output signal from the angle-of-attack sensor based on a load-factor component associated with aircraft maneuvering for determining the initial angle-of-attack signal.

### Claim 9 (depends on 1)

The method of claim 1, wherein the step of compensating the initial angle-of-attack signal to provide a pseudo angle-of-attack signal is based on dynamic pressure.

### Claim 10 (depends on 1)

The method of claim 1, wherein the step of mapping the pseudo angle-of-attack signal to a true angle-of-attack signal is based on one or more of flap position, shaft power, shaft torque, thrust, and thrust coefficient.

### Claim 11 (depends on 1)

The method of claim 1, further comprising establishing a minimum airspeed cutoff to avoid singularities and angle-of-attack sensor inaccuracies caused by dividing by zero in data processing and scheduling implementation, such that when airspeed is below the minimum airspeed cutoff, stall warning and stick pusher activation is inactive.

### Claim 12

A method for determining an aircraft angle-of-attack for aircraft stall protection, comprising:
providing an output signal from an angle-of-attack sensor to a controller;
determining a load factor component for the aircraft;
determining, via the controller, an initial angle-of-attack signal based on the output signal and the load factor component;
compensating, via the controller, the initial angle-of-attack signal to provide a pseudo angle-of-attack signal based on dynamic pressure;
mapping, via the controller, the pseudo angle-of-attack signal to a true angle-of-attack signal based on flight test data, wherein the flight test data is acquired using a calibrated wing-tip-mounted angle-of-attack boom;
compensating, via the controller, the true angle-of-attack signal based on both roll rate and sideslip to provide a compensated angle-of-attack;
applying a complementary filter, via the controller, that passes the compensated angle-of-attack signal through a low-pass filter and complements it with higher frequency inertial angle-of-attack rate signal calculated from aircraft inertial data to provide an angle-of-attack complementary filter output signal;
determining, via the controller, an angle-of-attack threshold for aircraft stall protection based on one or more parameters; and
activating aircraft stall protection based on the complementary filter output signal compared with the angle-of-attack threshold.

### Claim 13 (depends on 12)

The aircraft angle-of-attack determining method of claim 12, wherein the step of applying the complementary filter further comprises removing higher frequency effects of wind gusts and turbulence that are naturally damped out by aircraft inertia without adding a time delay.

### Claim 14 (depends on 12)

The aircraft angle-of-attack determining method of claim 12, wherein the angle-of-attack threshold for aircraft stall protection may include an offset to compensate for the one or more parameters, the offset including a gain applied based on flight test data, including a nonlinear scheduling capability, by interpolating a lookup table.

### Claim 15 (depends on 12)

The aircraft angle-of-attack determining method of claim 12, wherein the one or more parameters include one or more of icing condition, flap position, landing gear position, Mach number, pressure altitude, inertial angle-of-attack rate, sideslip, engine shaft power/torque, thrust, thrust coefficient, flight-test discovered dependencies, pitch rate, axial deceleration, airspeed rate, filtered derivative of airspeed, and unexplained factors.

### Claim 16 (depends on 15)

The aircraft angle-of-attack determining method of claim 15, wherein the following parameters are a function of flap position: icing, landing gear position, angle-of-attack rate, pitch rate, engine shaft torque, shaft power, thrust, thrust coefficient, sideslip, and normalized angle-of-attack.

### Claim 17 (depends on 13)

The aircraft angle-of-attack determining method of claim 13, wherein the flight-test discovered dependencies may include a computed correction to compensate for unknown effects on angle-of-attack that may be encountered during flight test development.