Aircraft SCAS Piston Layout for Fault-Tolerant Control Authority
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Solution Overview
Problem
Current Stability and Command Augmentation Systems (SCAS) for aircraft are prone to failures, require complex configurations with many levers and cables, leading to production and maintenance difficulties, and are susceptible to signal interference, with limited adjustability in actuator travel ranges.
Innovation Solution
A revised SCAS with a pair of pistons and control valves arranged in series, allowing independent force control and adjustable travel limits, reducing the number of levers and cables, and enhancing fault tolerance by maintaining full authority actuator control without increasing piston travel in case of failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a known SCAS configuration with multiple levers and cables is used, then the aircraft can be stabilized against external disturbances, but the system becomes complex and difficult to manufacture and maintain
Solution Approach 1:
The patent combines multiple levers and cables into a single integrated connection chain that directly links the flight control to the actuator. This merging eliminates the need for separate SCAS levers and cables while maintaining the stability augmentation function, thereby reducing device complexity without sacrificing reliability
Solution Approach 2:
The patent extracts and removes the intermediate SCAS levers and cables from the connection chain, leaving only the essential direct mechanical link between flight control and actuator. This extraction simplifies the system by eliminating unnecessary components that contributed to complexity and potential failure points
2Reliability
If the second and third actuators are controlled by mutually independent valves in parallel configuration, then the system can provide full authority control, but the piston travel must increase in case of failure which may lose actuator authority
Solution Approach 1:
The patent incorporates a buffer element in the connection chain that provides mechanical cushioning and absorbs unexpected movements. This buffer prevents excessive piston travel in case of failures or hardovers, maintaining actuator authority without requiring increased piston travel range, thereby protecting the full authority control capability
3Reliability
If multiple levers and cables are used in the SCAS, then the system can provide stability control, but production and maintenance difficulties increase
Solution Approach 1:
The patent merges the complex multi-lever and multi-cable SCAS system into a single integrated connection chain with direct mechanical linkage. This consolidation dramatically simplifies manufacturing by reducing the number of parts that need to be assembled and calibrated, while also simplifying maintenance by eliminating multiple potential failure points and reducing the skill level required for troubleshooting
4Ease of operation
If the flight control system is positioned remotely from the SCAS, then the pilot has better control, but signal interference increases and control precision decreases
Solution Approach 1:
The patent introduces a buffer element as an intermediary component in the connection chain between the flight control and actuator. This buffer acts as a mechanical mediator that isolates and filters out vibrations and signal interference, ensuring accurate control signal transmission while allowing the flight control to remain positioned for optimal pilot accessibility
Data Source
AI summary
A stability and command augmentation system for controlling an aircraft, comprising: a first member moveable by a pilot input device to a first position defining a first input; a second member moveable to a second position associated with a second input; and an adder device configured to add the first and second inputs and supply an output signal defining a command for an element to be controlled of the aircraft; the stability and command augmentation system comprises: a casing, a first and a second piston integrally movable with one another inside the casing and operatively connected to the second member; and control means configured to exert a first force on the first piston and a second force on the second piston; the second force is independent of the first force.