Dual-Nut Actuator Load Path Switching Without Secondary Loading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing trimmable horizontal stabiliser actuators for aircraft face challenges in avoiding undesired loading of the secondary load path during normal operation, which can lead to inefficiencies and potential failures under aerodynamic loads such as flutter.
Innovation Solution
The actuator design incorporates a secondary nut with axially movable portions and a resilient member, along with fuse pins and movable abutments, to ensure that the secondary load path remains unloaded during normal operation and efficiently transitions to load transfer upon primary path failure, utilizing screw threads and clearances to manage load distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a secondary load path is provided in the actuator, then reliability is improved by having a backup load transmission path, but the secondary load path may be undesirably loaded during normal operation
Solution Approach 1:
The actuator is segmented into distinct primary and secondary load paths that are physically separated and functionally independent. The secondary nut and its associated components form a separate load transmission system that only engages when the primary load path fails, preventing interference between the two paths during normal operation.
Solution Approach 2:
The fuse pins are pre-installed in a loaded state during manufacturing, creating a mechanical constraint that prevents the secondary nut from engaging the screw shaft during normal operation. This preliminary constraint ensures the secondary load path remains unloaded until the fuse pins fail under excessive load conditions.
2Adaptability or versatility
If clearances are provided between components to account for excessive loading, then adaptability is improved, but backlash increases
Solution Approach 1:
The actuator employs dynamic engagement characteristics where the secondary load path transitions from a disengaged state to an engaged state based on load conditions. The fuse pins act as a dynamic constraint that fails at a predetermined load threshold, automatically transitioning the system from primary to secondary load path without requiring fixed clearances that would create backlash.
3Device complexity
If the secondary nut remains stationary during normal operation, then device complexity is reduced, but the mechanism cannot efficiently transition to the secondary load path upon failure
Solution Approach 1:
The secondary nut is designed with periodic engagement characteristics through the fuse pin mechanism. During normal operation, the fuse pins constrain the secondary nut in a stationary position. Upon failure of the primary load path, the constrained secondary nut can move axially to engage the screw shaft, creating a periodic transition from stationary to active load-bearing state.
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
This design effectively prevents undesired loading of the secondary path during normal operation and ensures reliable transition to the secondary load path upon primary path failure, meeting certification requirements for backlash and enhancing the actuator's reliability under aerodynamic stresses.
Implementation Method 1
a resilient member biased between the first portion and the second portion and configured to cause said relative movement of the first and second portions to engage/contact the screw shaft
Implementation Method 2
The actuator comprises a screw shaft and a nut assembly. The nut assembly includes a secondary nut having first and second screw threads configured to engage with the screw shaft
Implementation Method 3
one or more fuse pins configured to prevent said relative movement of the first and second portions to engage the screw shaft whilst load is transmitted through the actuator along the primary load path. These pins can help to prevent inadvertent movement of the first and second portions prior to a predetermined shear force on the pins
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
There is provided an actuator (10) comprising screw shaft (32) and a nut assembly (25). The nut assembly (25) comprises a primary nut (50) for transmitting load through the actuator (10) along a primary load path, and a secondary nut (60) for transmitting load through the actuator (10) along a secondary load path. The secondary nut (60) comprises first and second portions (100, 102) movable relative to one another. As load is transmitted through the actuator (10) along the primary load path the secondary nut (60) does not transmit load through the actuator (10), wherein upon failure of the primary load path the first and second portions (100, 102) move relative to each other, such relative movement causing the first and second portions (100, 102) to engage the screw shaft (32) and enable transmittal of load through the secondary nut (60) of the actuator (10) along the secondary load path.