Angle-of-Attack Fault Detection Using Estimated Pressure Signals
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Solution Overview
Problem
Current flight control systems face challenges in accurately detecting faults, particularly when a majority of pitot tubes are blocked, leading to inaccurate airspeed and altitude measurements, which can result in unnecessary mode switches and reduced aircraft performance.
Innovation Solution
The system employs an extended Kalman filter to estimate dynamic pressure and angle of attack independently of pitot tube measurements, using operating parameters and sensor data to determine a fault by comparing measured and estimated values, and switches to an estimated value when the error exceeds a threshold, thereby maintaining normal operation and reducing false alarms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system uses measured angle of attack from sensors, then the measurement is direct and simple, but the fault detection capability is reduced when sensors are blocked or malfunctioning
Solution Approach 1:
The patent introduces an intermediary estimated angle of attack value derived from flight dynamics models and sensor fusion (using accelerometer, gyroscope, and other sensor data) to mediate between the direct sensor measurement and the final control decision. This intermediary value serves as a cross-check that can detect when the primary angle of attack sensor is faulty, resolving the contradiction by providing both direct measurement capability and fault detection capability simultaneously
Solution Approach 2:
The system implements feedback by continuously comparing the measured angle of attack with the estimated angle of attack and using this comparison to detect faults. When the difference between measured and estimated values exceeds a threshold, the system identifies a sensor fault and switches to using the estimated value, thereby maintaining reliability while preserving the simplicity of direct measurement during normal operation
2Reliability
If the system implements comprehensive fault detection comparing measured and estimated values, then the fault detection accuracy is improved, but the system complexity increases
Solution Approach 1:
The flight dynamics model and sensor fusion algorithm serve multiple functions: they provide the estimated angle of attack for fault detection, enables cross-validation of sensor readings, and can serve as a backup source of angle of attack information when sensors fail. This multi-functionality reduces the need for separate dedicated fault detection hardware, thereby improving reliability while limiting the increase in system complexity
Solution Approach 2:
The system uses its own existing sensors (accelerometers, gyroscopes, air data sensors) and flight control computer to generate the estimated angle of attack for fault detection purposes, rather than requiring external or dedicated fault detection equipment. The flight control system essentially services its own fault detection needs, improving reliability without proportionally increasing complexity
3Reliability
If the system switches to estimated values when faults are detected, then the operational reliability is maintained, but the response time for mode switching increases
Solution Approach 1:
The estimated angle of attack value is continuously calculated and prepared in advance using flight dynamics models and sensor fusion, even before a fault occurs. This preliminary computation ensures that when a fault is detected through comparison, the system can immediately switch to the pre-computed estimated value without delay, maintaining both reliability and fast response time during the mode transition
Data Source
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AI summary
A flight control system (18) for an aircraft (10) is disclosed and includes one or more processors (1032) and a memory (1034) coupled to the processors (1032). The memory (1034) stores data comprising a database and program code that, when executed by the one or more processors (1032), causes the flight control system (18) to receive as input 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 (18) 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 (18) determines the presence of a fault with an angle of attack value.