Aircraft Secondary Nut Locking Assembly for Torque-Driven Engagement
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Solution Overview
Problem
Existing mechanisms for engaging a secondary nut with a shaft in aircraft trimmable horizontal stabilisers are unreliable and dependent on aerodynamic loads or complex sensor systems.
Innovation Solution
A nut assembly with a housing, a barrel, and at least one locking element, where the locking element moves from a disengaged to an engaged position as the barrel rotates with the shaft, wedging between the shaft and housing to prevent rotation and increase driving torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a friction-based locking mechanism is used that relies on aerodynamic loads, then the locking can be achieved, but the reliability deteriorates when the actuator is not significantly loaded (e.g., during cruise)
Solution Approach 1:
The cam surface is pre-configured with a specific profile that automatically converts rotational torque into radial locking force. The locking element is pre-positioned to engage with the cam surface, so that when torque is applied during any flight condition, the locking action occurs automatically without requiring minimum aerodynamic loads or external triggering mechanisms.
Solution Approach 2:
The cam surface acts as an intermediary mechanism between the barrel rotation and the locking element engagement. It transforms the rotational motion of the barrel (caused by actuator torque) into the radial motion required to wedge the locking element between the shaft and housing, providing a reliable mechanical advantage that works independently of aerodynamic loading conditions.
2Reliability
If sensors and computer systems are used to detect primary load path failure and trigger secondary nut engagement, then the locking can be triggered on demand, but the device complexity increases
Solution Approach 1:
The secondary nut assembly is designed to be self-activating through its mechanical structure. The cam surface and locking element are configured so that the actuator's own rotation during normal operation or failure conditions automatically drives the locking action. This eliminates the need for external sensors, control systems, or pilot intervention, making the system self-sufficient and fail-safe.
Solution Approach 2:
The patent replaces electronic sensor and control systems with a purely mechanical solution. The cam surface profile and locking element geometry are designed to automatically respond to torque application, substituting complex electronic failure detection and triggering systems with a simple, reliable mechanical mechanism that operates passively based on physical principles.
3Reliability
If a pliers mechanism or spring box is used to apply frictional force for locking, then the locking mechanism can engage, but the reliance on external components and aerodynamic loads increases
Solution Approach 1:
The invention extracts and eliminates the dependency on external components such as spring boxes and aerodynamic loads. The locking mechanism uses only the actuator's own rotational torque as the input energy source, with the cam surface converting this torque directly into locking force. This removes the need for additional external forcing mechanisms and makes the system self-contained.
Solution Approach 2:
The cam surface serves multiple functions: it guides the locking element, provides the mechanical advantage for engagement, and ensures reliable locking across all operating conditions. This single component performs what previously required multiple external components (springs, aerodynamic forces, sensors), making the system more versatile and independent.
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 solution provides a reliable locking mechanism that operates independently of aerodynamic forces, relying solely on the torque applied by the actuator, thus enhancing the structural link between the shaft and the trimmable horizontal stabiliser.
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 locking element is wedged between the screw thread of the shaft and the housing thereby preventing relative rotation between the shaft and the housing and optionally increasing the driving torque to a level sufficient to stall an actuator
Data Source
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AI summary
An assembly for maintaining the pitch angle of a flight control surface for an aircraft is disclosed. The assembly comprises a shaft comprising a screw thread and defining a shaft axis, and a nut. The nut comprises 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 in which 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.