Aircraft Control Command Monitoring for In-Flight Stability Checks
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Solution Overview
Problem
Existing flight control systems for aircraft fail to robustly detect design and implementation errors in the presence of external disturbances or faults in other aircraft systems, leading to potential instability and transient issues during flight.
Innovation Solution
Implement a monitoring channel that independently checks the stability of control commands by comparing them against predefined criteria using a Lyapunov function, ensuring the aircraft converges to a stable state even with disturbances, and switches to a backup control if necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monitoring channel is implemented to detect design errors in flight control laws, then detection capability is improved, but false detection occurs under external disturbances or faults in other aircraft systems
Solution Approach 1:
The monitoring channel continuously monitors the Lyapunov function value and its rate of change, comparing them against expected ranges. This feedback mechanism allows the system to distinguish between normal transient behavior (where the Lyapunov function may temporarily increase) and actual design errors (where the Lyapunov function consistently fails to decrease), thereby improving detection accuracy while maintaining high reliability
Solution Approach 2:
The monitoring approach transitions from static threshold checking to dynamic evaluation by considering the rate of change of the Lyapunov function and its temporal evolution. This dynamic monitoring enables the system to adapt to changing flight conditions and external disturbances, reducing false detections while maintaining sensitivity to actual design errors
2Reliability
If dissimilar logic is implemented to check system outputs, then design error detection is improved, but system complexity increases significantly
Solution Approach 1:
The monitoring channel utilizes the Lyapunov function, which is inherently part of the control system's stability analysis, to perform self-monitoring. Instead of implementing completely separate dissimilar logic, the system uses its own stability metric (the Lyapunov function) to detect design errors, thereby achieving error detection without significantly increasing system complexity
Solution Approach 2:
The Lyapunov function serves multiple purposes: it is used for control law design, stability analysis, and error detection in the monitoring channel. This multi-functionality eliminates the need for separate dedicated error detection mechanisms, reducing overall system complexity while maintaining reliable error detection capability
3Reliability
If monitoring is performed during flight, then online detection is achieved, but external disturbances cause false alarms leading to channel isolation
Solution Approach 1:
The system pre-establishes expected behavior patterns for the Lyapunov function during normal flight operations, including acceptable ranges and rate of change limits. By having these criteria predetermined, the monitoring channel can distinguish between normal responses to external disturbances and actual design errors, reducing false alarms while maintaining online detection capability
Solution Approach 2:
The monitoring approach incorporates tolerance thresholds and temporal filtering that cushion against transient effects caused by external disturbances. By allowing temporary deviations within expected ranges and requiring sustained violations before triggering channel isolation, the system prevents false alarms while maintaining sensitivity to genuine design errors
Data Source
AI summary
A method for flight control of an aircraft with multiple actuators during flight is disclosed. For each actuator, a control command is computed according to at least one predetermined control law and based on pilot inputs and sensor measurements in relation to a physical state of the aircraft. The respective control commands are provided to the actuators. The control commands are independently monitored by estimating or measuring a current physical state of the aircraft and comparing it with the control commands. This comparison includes checking whether the control commands stabilize the aircraft in a stable state in the absence of both disturbances and pilot inputs according to at least one predefined criterion. If the monitoring indicates a lack of stability, transmission of the control commands is prevented and a backup control command is computed for each actuator.