Aircraft Actuator Secondary Load Path Engagement Detection
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Solution Overview
Problem
Aircraft flight control actuators face failures in primary load paths, leading to partial or complete loss of control of flight control surfaces, necessitating a redundant secondary load path to take over control.
Innovation Solution
A linear actuator design with primary and secondary load paths, where the secondary load path transitions to majority control upon primary path failure, and an engagement member moves to restrict relative movement between the paths, with sensors detecting these transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a secondary load path is added to protect against primary load path failure, then reliability is improved, but device complexity increases
Solution Approach 1:
The secondary load path is nested within the primary load path structure. The secondary ball nut assembly is positioned concentrically around the primary ball nut assembly, sharing the same screw axis and housing space. This nesting allows the redundant system to be integrated without proportionally increasing overall actuator volume or structural complexity.
Solution Approach 2:
The actuator is segmented into distinct primary and secondary load path systems, each with separate ball nuts, balls, and load-bearing components. This segmentation allows independent failure modes - the primary load path can fail while the secondary remains intact, enabling selective engagement of the backup system without requiring complete system redesign.
2Reliability
If an engagement member is added to restrict relative movement between load paths, then reliability is improved, but device complexity increases
Solution Approach 1:
The engagement member is biased by a spring into a default engaged position where it restricts relative axial movement between the primary and secondary ball nuts. When the primary load path fails and axial movement occurs, the engagement member passively disengages without requiring active control systems, sensors, or power sources. The system self-regulates based on the mechanical state of the load paths.
Solution Approach 2:
The engagement member acts as an intermediary mechanical element between the primary and secondary load paths. It mediates the interaction by allowing controlled relative movement during normal operation while preventing uncontrolled movement during failure conditions, thereby enabling smooth transition between load paths without direct electronic control.
3Measurement precision
If sensors are added to detect primary load path failure and secondary load path engagement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Sensors are positioned to detect the axial position of the engagement member, which directly reflects the state of the load paths. When the primary load path fails and the engagement member moves to restrict relative movement, the sensor detects this position change and provides feedback to the control system, enabling automatic response or alerting without complex diagnostic algorithms.
Solution Approach 2:
The patent replaces complex mechanical failure detection mechanisms with electronic sensors that directly monitor the engagement member position. This substitution provides precise digital measurement of the load path state, enabling accurate failure detection and secondary system engagement confirmation without requiring complex mechanical linkages or indirect measurement systems.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Ensures continued control of aircraft flight surfaces by transitioning the secondary load path to majority control upon primary path failure, maintaining stability and preventing catastrophic loss of control.
Implementation Method 1
A rotatable ball screw extends axially and usually vertically through the primary ball nut threaded member and the drive gimbal
Implementation Method 2
The primary ball nut includes a primary ball nut threaded member... As the ball screw is rotated, the primary drive gimbal and primary ball nut will be moved in translation
Implementation Method 3
A biasing member extends between the engagement member and the secondary ball nut and biases the engagement member toward the engaged position
Data Source
AI summary
A linear actuator, for controlling movement of a control surface of an aircraft, includes a screw, a primary load path and secondary nut engaged with the screw, and an engagement member. The engagement member moves from an ambush position, maintained by the primary load path or the secondary nut, to an engaged position, restricting relative movement between the primary load path and the secondary nut. The restricted relative movement may occur in response to free relative axial movement of the primary load path and the secondary nut caused by a failure of the primary load path of the linear actuator. A sensor of the linear actuator is configured to sense the failure of the primary load path and the free relative axial movement of the primary load path and the secondary nut.