Auto-Trim Logic for Fly-by-Wire Aircraft Yaw Axis
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Solution Overview
Problem
Unique trim controllers in fly-by-wire rotary-wing aircraft complicate flight control during state sensor failures, particularly in direct rotor control mode, as the trim point varies with aircraft states like airspeed and gross weight, leading to increased workload during coordinated turns due to unnatural feel and the need for constant centering force.
Innovation Solution
The implementation of auto-trim logic in the flight control system, which provides a displacement feel and re-references the center of the controller displacement to match the control surface authority, allowing the aircrew to maintain control surface authority range without constant trim follow-up, especially in the yaw axis during direct mode operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If trim follow-up logic is implemented in unique trim controllers, then the controller returns to center position during trimmed flight, but the aircrew must slowly reduce yaw pedal input during coordinated turns increasing workload
Solution Approach 1:
The patent applies dynamics by making the trim follow-up logic axis-specific: pitch and roll axes have trim follow-up enabled while the yaw axis has it disabled. This dynamic configuration allows the system to adapt different control behaviors to different flight control axes, resolving the contradiction by eliminating the problematic trim follow-up effect in the yaw axis during coordinated turns while preserving it in other axes where it provides benefit.
Solution Approach 2:
The patent implements local quality by applying trim follow-up logic selectively to specific axes (pitch and roll) while excluding the yaw axis. This localized application of the trim follow-up feature allows each axis to have optimized control characteristics: pitch and roll benefit from automatic centering, while yaw maintains direct control without the artificial centering force that would interfere with coordinated turn execution.
2Extent of automation
If unique trim controllers are used in direct rotor control mode, then high level augmentation is provided, but the trim point varies with aircraft states requiring constant centering force
Solution Approach 1:
The patent applies dynamics by implementing mode-dependent trim follow-up logic that adapts to the flight control mode. In fully augmented mode, trim follow-up is enabled to provide automatic centering and simplify operation. In direct mode, trim follow-up is disabled to prevent the varying trim point from requiring constant centering force. This dynamic switching resolves the contradiction by providing the appropriate control characteristics for each operational mode.
Solution Approach 2:
The patent implements multi-functionality by designing the trim follow-up logic to serve different purposes in different modes: in fully augmented mode it provides automatic trim maintenance, while in direct mode it is suppressed to allow direct control without artificial centering forces. This universal trim follow-up mechanism adapts its behavior to serve the specific needs of each flight control mode.
Data Source
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AI summary
A flight control system (40) includes a controller (38) which defines a controller displacement and a control surface which defines a control surface authority. A module operable to provide a displacement feel to the controller (38) in response to a remaining portion of the controller displacement being greater than a remaining portion of the control surface authority and the module operable to re-reference a center of the controller displacement to equate the remaining portion of the controller displacement with the remaining portion of the control surface authority in response to the remaining portion of the controller displacement being less than the remaining portion of the control surface authority.