Aircraft Angle-of-Attack Filtering for Stall Protection Thresholds
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Solution Overview
Problem
Existing aircraft systems face challenges in accurately determining angle-of-attack, particularly at low speeds and during stall conditions, leading to potential performance penalties and inadequate stall protection.
Innovation Solution
A method involving an angle-of-attack sensor output signal processed by a controller to provide an initial signal, which is compensated and mapped using flight test data, then filtered to produce a complementary output, allowing for accurate stall protection thresholds and activation of stall warning and stick pusher functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional angle-of-attack sensors are used, then the system is simple, but the measurement precision deteriorates at low speeds and during stall conditions
Solution Approach 1:
The system performs preliminary compensation for dynamic pressure effects and roll rate deviations before final angle-of-attack determination. By pre-correcting these known error sources through calculated compensation values, the system improves measurement accuracy without requiring complex real-time processing during critical stall conditions.
Solution Approach 2:
The system introduces an intermediary mapping process that transforms raw sensor signals through multiple compensation stages. This intermediary processing layer, including dynamic pressure compensation and roll rate correction, acts as a mediator between the simple sensor input and the accurate angle-of-attack output, resolving the contradiction between simplicity and precision.
2Measurement precision
If compensation for roll rate and sideslip is applied, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The compensation system is segmented into distinct functional modules: dynamic pressure compensation, roll rate compensation, sideslip compensation, and complementary filtering. Each module handles a specific aspect of error correction independently, making the overall complex system manageable and allowing each segment to be optimized for its specific function without increasing overall complexity unnecessarily.
Solution Approach 2:
The system changes parameters dynamically based on flight conditions by adjusting compensation values according to measured dynamic pressure, roll rate, and sideslip angles. This parameter-based approach allows the system to maintain high precision across varying flight regimes without requiring a fundamentally different complex system structure for each condition.
3Reliability
If multiple compensation steps are applied, then the reliability of stall protection improves, but the loss of time in processing increases
Solution Approach 1:
The complementary filter applies periodic smoothing to the compensated angle-of-attack signal, allowing the system to maintain reliability through consistent filtering while managing processing time through regular, predictable filter operations. This periodic action ensures stable stall protection decisions without requiring continuous complex computations.
Solution Approach 2:
The system applies partial compensation for certain effects based on their relative importance. By focusing compensation efforts on the most critical error sources (dynamic pressure and roll rate) while using simpler handling for less significant factors, the system achieves sufficient reliability for stall protection without the excessive processing time that would result from equally complex treatment of all possible error sources.
Data Source
AI summary
A method for determining an aircraft angle-of-attack for aircraft stall protection includes providing an output signal from an angle-of-attack sensor and determining an initial angle-of-attack signal based on the output signal. The initial angle-of-attack signal is compensated to provide a pseudo angle-of-attack signal, and the pseudo angle-of-attack signal is mapped to a true angle-of-attack signal based on flight test data. The true angle-of-attack signal is compensated based on roll rate and sideslip or estimated sideslip to provide a compensated angle-of-attack. A complementary filter is applied that complements the compensated angle-of-attack signal with a higher frequency inertial angle-of-attack rate signal, calculated from aircraft inertial data, to provide an angle-of-attack complementary filter output. An angle-of-attack threshold for aircraft stall protection is determined based on one or more compensation parameters. Activation of aircraft stall protection is determined based on the angle-of-attack complementary filter output compared with the angle-of-attack threshold.