Aircraft Stabilizer Nut Assembly With Cam-Actuated Secondary Locking
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Solution Overview
Problem
Existing mechanisms for engaging a secondary nut with a shaft in a trimmable horizontal stabiliser of an aircraft rely on friction torque dependent on aerodynamic loads and complex sensor systems, which are unreliable and prone to failure.
Innovation Solution
A mechanical locking mechanism using a nut assembly with a barrel and locking elements that engage based on torque applied by the actuator, independent of aerodynamic forces, ensuring reliable engagement and disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If friction torque between nut threads and shaft threads is used to engage the secondary nut (as in known arrangements), then the locking mechanism can be simple in structure, but it becomes unreliable when aerodynamic loads are minimal or when the actuator is not significantly loaded
Solution Approach 1:
The cam surface is pre-configured in the housing to guide the locking element's movement path. Before engagement occurs, the cam surface geometry is already in place to convert the actuator's rotational torque into the appropriate linear motion of the locking element, ensuring reliable engagement even when aerodynamic loads are minimal.
Solution Approach 2:
The cam surface employs a curved geometric profile that transforms rotational motion into linear displacement. This curvature allows the locking element to be reliably actuated by the actuator's torque through a mechanical advantage provided by the cam geometry, independent of aerodynamic loading conditions on the flight control surface.
2Reliability
If sensors and computer systems are used to detect primary load path failure and trigger secondary nut engagement, then engagement can be timely, but the system becomes complex and reliant on electronic systems that may fail
Solution Approach 1:
The secondary nut assembly is self-actuating through its mechanical design. When the actuator rotates the shaft, the cam surface automatically converts this rotation into linear motion that drives the locking element into engagement with the shaft. The system serves itself without requiring external sensors, controllers, or electronic systems to detect failure or trigger engagement.
Solution Approach 2:
The patent replaces electronic sensor and control systems with a purely mechanical engagement mechanism. The cam surface and locking element form a mechanical system that automatically responds to actuator operation, eliminating the need for electronic detection and control components while ensuring timely engagement.
3Device complexity
If the locking mechanism relies on aerodynamic forces applied to the flight control surface, then the mechanism can be simple, but it becomes unreliable when aerodynamic forces are minimal (e.g., during cruise)
Solution Approach 1:
The cam surface is pre-configured to provide the necessary mechanical advantage before engagement is needed. The geometry of the cam surface ensures that even small torques from the actuator during cruise conditions are sufficient to drive the locking element into firm engagement, making aerodynamic forces unnecessary for triggering the mechanism.
Solution Approach 2:
The curved cam surface provides a mechanical advantage that amplifies the actuator's torque. This geometric transformation allows the locking mechanism to engage reliably under all flight conditions, including low-load cruise flight, without depending on aerodynamic forces applied to the flight control surface.
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
The mechanical locking mechanism provides a secure and reliable secondary load path for the trimmable horizontal stabiliser, independent of aerodynamic forces and sensor systems, enhancing stability and reducing reliance on computer systems.
Implementation Method 1
the barrel is configured to rotate relative to the housing when the screw thread of the barrel is engaged and rotating with the screw thread of the shaft so as to move the locking element along the cam surface
Implementation Method 2
the housing comprises a radially inner cam surface adjacent to the locking element
Implementation Method 3
the locking element is wedged between the screw thread of the shaft and the housing thereby preventing relative rotation between the shaft and the housing
Implementation Method 4
a barrel located in the housing and comprising a screw thread for engaging with the screw thread of the shaft
Data Source
AI summary
An assembly for maintaining the pitch angle of a flight control surface for an aircraft. The assembly includes a shaft comprising a screw thread and defining a shaft axis, and a nut. The nut includes a housing, a barrel located in the housing and comprising a screw thread for engaging with the screw thread of the shaft, and at least one locking element located in the housing. The housing comprises a radially inner cam surface adjacent to the locking element. The barrel is configured to rotate relative to the housing when the screw thread of the barrel is engaged and rotating with the screw thread of the shaft so as to move the locking element along the cam surface from a disengaged position in which the locking element is spaced from the screw thread of the shaft, to an engaged position.