Takeoff Trim Using Stabilizer-Elevator Pitch Moment Split
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Solution Overview
Problem
Existing airplane trim systems rely primarily on stabilizer orientation for takeoff trim, which can lead to excessive or insufficient tail pitching moments, causing uncontrollable pitch during takeoff due to variations in airplane weight and other parameters, limiting the stabilizer's travel range and increasing the risk of nonoperational conditions.
Innovation Solution
The integration of stabilizer and elevator orientations as takeoff trim settings, where the elevator's orientation is adjusted faster and independently to control the tail pitching moment, reducing the stabilizer's total travel range and enhancing control during takeoff.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the stabilizer total travel range is increased to accommodate variations in airplane weight, center of gravity, flap angles, and thrust settings, then the takeoff trim control range is improved, but the device complexity and risk of nonoperational conditions increase
Solution Approach 1:
The patent divides the trim control function into two independent segments: the stabilizer orientation mechanism and the elevator orientation mechanism. The stabilizer provides coarse trim adjustment while the elevator provides fine trim adjustment. This segmentation allows each component to operate within a limited, optimized range rather than requiring one component to cover the entire trim spectrum, thereby reducing complexity while maintaining adaptability.
Solution Approach 2:
The patent adds a new dimension to the trim control system by introducing elevator orientation as a secondary control variable alongside stabilizer orientation. This creates a two-dimensional trim control space where combinations of stabilizer and elevator settings can achieve the desired pitching moment without requiring extreme stabilizer positions, thus reducing the stabilizer's travel range requirements.
2Device complexity
If the stabilizer orientation is used as the primary trim setting, then the device complexity is reduced, but the reliability deteriorates due to uncontrollable pitch conditions
Solution Approach 1:
The patent implements a cushioning mechanism where the elevator orientation mechanism serves as a protective layer against pitch control instability. By providing fine trim adjustment capability, the elevator prevents the system from reaching extreme stabilizer positions that could lead to nonoperational conditions, thereby cushioning against potential failures and improving reliability.
Solution Approach 2:
The elevator acts as an intermediary between the pilot's trim demands and the stabilizer positioning. Instead of the stabilizer directly responding to all trim requirements, the elevator mediates by providing incremental adjustments, allowing the stabilizer to operate within a safer, more reliable range while still achieving the desired trim effect.
3Speed
If the elevator orientation is adjusted independently and faster than the stabilizer, then the control responsiveness is improved, but the device complexity increases
Solution Approach 1:
The patent applies different dynamic characteristics to the two orientation mechanisms. The stabilizer orientation mechanism is designed for slower, more stable positioning suitable for coarse adjustments, while the elevator orientation mechanism is designed for faster response to handle fine trim adjustments. This dynamic differentiation allows the system to achieve high overall responsiveness without requiring both components to be equally complex and fast.
Data Source
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AI summary
Provided are airplane trim systems and methods of controlling such systems. These systems utilize smaller portions of the stabilizer total travel range for takeoff trims, in comparison to other trim systems. A trim system described includes stabilizer and elevator, and these components are used together to achieved a takeoff total tail pitching moment. The elevator or, at least a portion of the elevator operating range, is available for flight control. As such, takeoff trim settings (520) include stabilizer and elevator orientation settings (523, 522). Addition of the elevator to control the takeoff tail pitching moment allows reducing the stabilizer total travel. The elevator orientation (555) can be changed much faster than that of the stabilizer providing pilot more control.