Aircraft Pitch Envelope Limiting with Predictive Elevator Commands
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Solution Overview
Problem
Existing aircraft flight control systems face challenges in seamlessly transitioning between envelope limiting control modes, leading to undesirable pitch responses and perceptible handling qualities when attempting to maintain the aircraft within a desired pitch axis envelope.
Innovation Solution
A method that determines aircraft state limits for multiple pitch axis variables, predicts future states, and translates errors into prioritized elevator commands to limit the primary pitch axis control law command, ensuring the aircraft operates within defined envelope limits without large pitch responses, using a non-transitory computer-readable medium to execute instructions for determining and comparing state limits and generating elevator commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If envelope limiting control laws are activated when aircraft exceeds or is about to exceed flight envelope parameters, then aircraft safety is improved, but large pitch responses and perceptible handling qualities occur during transitions
Solution Approach 1:
The system determines predicted future states of pitch axis variables by projecting current states and rates forward in time. This preliminary action allows the envelope limiting control law to engage before the aircraft actually exceeds envelope parameters, enabling smoother transitions and reducing perceptible handling qualities while maintaining safety.
Solution Approach 2:
The system dynamically adjusts the activation threshold for envelope limiting control law based on the rate of change of pitch axis variables. When rates are high, the system engages limiting control earlier, and when rates are low, it allows closer approach to limits. This dynamic adaptation reduces abrupt transitions and improves handling qualities while maintaining reliability.
2Reliability
If multiple pitch axis variables are limited simultaneously, then comprehensive envelope protection is improved, but complex interactions between limit commands occur
Solution Approach 1:
The system applies different limiting strategies to different pitch axis variables based on their individual characteristics and current states. Each variable (angle of attack, pitch rate, pitch attitude, airspeed) has its own predicted state calculation and limit determination, allowing tailored control actions that reduce complex interactions while maintaining comprehensive envelope protection.
3Reliability
If predicted future states are used to determine envelope limits, then proactive envelope protection is improved, but computational requirements increase
Solution Approach 1:
The system calculates predicted future states using simplified projection methods that use current states and rates with assumed constant or linearly varying conditions. This partial action approach provides sufficient proactive protection without requiring full-blown numerical integration or complex simulations, thereby reducing computational energy requirements while maintaining reliability.
Data Source
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AI summary
An example method of limiting an aircraft to a pitch axis envelope includes determining aircraft state limits associated with multiple pitch axis variables of an aircraft, determining predicted aircraft states, comparing the predicted aircraft states to the aircraft state limits to produce aircraft state errors, translating the aircraft state errors into a set of positive and negative limit elevator commands, selecting a highest priority positive limit elevator command, selecting a highest priority negative limit elevator command, limiting a primary pitch axis control law elevator command of the aircraft to a value that is less than or equal to the highest priority positive limit elevator command and greater than or equal to the highest priority negative limit elevator command, and controlling the aircraft according to the primary pitch axis control law elevator command limited to the value.