Dynamic Angle of Attack Limiting for Zoom Climb Prevention
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Solution Overview
Problem
Fly-by-wire aircraft face challenges in preventing unfavorable flight conditions at high angles of attack, particularly rapid deceleration leading to excessive angle of attack, which can result in loss of control and other instability issues.
Innovation Solution
A method and system that set limits on control surface deflection based on the rate of change of angle of attack, using a control loop to prevent the control variable from exceeding a threshold, and switching between feedback loops to manage vehicle velocity and altitude, ensuring the angle of attack remains within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed control variable limit is used in the control loop, then the system is simple to operate, but the aircraft can still exceed safe angle of attack during rapid deceleration
Solution Approach 1:
The control variable limit is changed from a fixed value to a dynamic value that varies with flight conditions. The system calculates a desired angle of attack based on current velocity and rate of change of velocity, making the limit adaptive to prevent angle of attack excursions during rapid deceleration while maintaining simplicity in normal operation
Solution Approach 2:
The system incorporates feedback from velocity sensors and rate of change measurements to continuously adjust the control variable limit. This feedback mechanism ensures the limit adapts to current flight conditions, preventing unsafe angle of attack while maintaining ease of operation through automated adjustment
2Reliability
If excessive safety margins are built into the aircraft design, then unfavorable flight conditions are prevented, but landing speeds increase and runway length requirements increase
Solution Approach 1:
The system changes the parameter used for safety margins from fixed angular limits to dynamic velocity-based limits. By calculating the desired angle of attack as a function of current velocity and its rate of change, the system provides precise protection against unfavorable flight conditions without requiring excessive safety margins, enabling lower landing speeds and shorter runway requirements
3Productivity
If the control loop allows rapid response to pilot commands, then maneuverability is improved, but the angle of attack can quickly exceed safe limits during deceleration
Solution Approach 1:
The system performs preliminary calculation of the desired angle of attack based on current velocity and rate of change before the angle of attack can exceed safe limits. This predictive approach allows rapid response to pilot commands while preventing angle of attack excursions by establishing the safe limit in advance based on flight conditions
Data Source
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AI summary
A vehicle, such as an airplane sets a limit for a control variable used to deflect a control surface. The limit is set as a function of an unfavorable flight condition/target angle of attack and a rate of change of angle of attack so that a pilot control variable command is prevented from exceeding the limit to prevent the vehicle from reaching an unfavorable flight condition and/or exceeding a desired angle of attack limit.