Takeoff Stall Protection Control for Aircraft Pitch Over-Rotation
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Solution Overview
Problem
Conventional flight control systems during takeoff are prone to over-rotation, leading to a risk of aerodynamic stall, especially when using side-stick controllers with limited displacement, as they lack the range to prevent overshoot and do not effectively utilize in-air stall protection laws until lift-off, which can be inadequate due to ground aerodynamic effects.
Innovation Solution
A flight control system with a pitch rate command system and pitch angle target limiting function that applies a damping factor to the pitch angle command, transitioning to in-air control laws after lift-off, using a processor to adjust control surface settings and prevent over-rotation by limiting pitch attitude without relying on radar altitude information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a direct-gain pitch controller with small-displacement side-stick is used, then the aircraft responds quickly to pilot input, but the pilot tends to over-rotate the airplane during takeoff
Solution Approach 1:
The control system preemptively limits the pitch angle command to a pre-calculated saturation limit before over-rotation can occur. The processor compares the commanded pitch angle with the saturation limit and clips it if necessary, preventing the harmful over-rotation before it happens rather than reacting after detection.
Solution Approach 2:
The pitch angle saturation limit is not a fixed value but dynamically adjusted based on multiple flight parameters including airspeed, flight path angle, and normalized angle of attack. This dynamic adaptation allows the system to maintain optimal protection across varying takeoff conditions while preserving necessary control authority.
2Reliability
If control authority is decreased or inceptor control forces are increased to prevent over-rotation, then stall protection improves, but the ability to overcome stabilizer mis-trims or control surface jams is reduced
Solution Approach 1:
The pitch angle saturation limit acts as an intermediary constraint that selectively limits pitch commands only when necessary for stall protection. The system monitors flight conditions and applies limiting only when the commanded pitch angle exceeds the calculated saturation limit, otherwise full control authority is preserved for handling stabilizer mis-trims or control surface issues.
Solution Approach 2:
The control system changes the pitch angle saturation limit parameter dynamically based on flight conditions (airspeed, flight path angle, angle of attack). This allows the protection level to adapt to current aerodynamic conditions while maintaining full control authority when protection is not needed, resolving the contradiction between protection and versatility.
3Reliability
If pitch angle command is limited to prevent over-rotation, then stall protection improves, but takeoff field performance may be impacted
Solution Approach 1:
The pitch angle saturation limit is dynamically calculated and adjusted based on current flight conditions including airspeed, flight path angle, and normalized angle of attack. This dynamic adjustment ensures the limit is as permissive as safety allows under each specific condition, optimizing takeoff performance while maintaining protection.
Data Source
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AI summary
Flight control systems, method for controlling an aircraft, and aircraft are provided. A flight control system includes an input configured to receive a pitch rate command, a processor operative to receive the pitch angle command, to calculate a pitch angle saturation limit, to compare the sum of the pitch rate command, the scaled pitch rate, and the scaled pitch angle to the pitch angle saturation limit, to convert the pitch rate command system to the pitch angle command system in response to the sum exceeding the pitch angle saturation limit value to limit the pilot pitch-up pitch rate command , and to couple the pitch rate command to an aircraft control surface for the failure case of one of control surface, and the aircraft control surface configured to adjust an aircraft control surface setting in response to the pitch rate command and/or pitch angle command to protect an aircraft from being in stall condition.