THSA Upper Attachment With Dynamic Recess to Eliminate Backlash
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Solution Overview
Problem
Flight actuators with primary and secondary load paths face issues with backlash and flutter when the primary load path fails, leading to adverse aircraft performance and potential loss of control due to the secondary load path's inability to securely transfer loads without play.
Innovation Solution
An upper attachment system for a trimmable horizontal stabiliser actuator featuring a housing with a yoke and ballscrew, a nut, and a biasing mechanism that ensures the recess around the tie bar closes under axial load, preventing backlash and flutter by moving the ballscrew linearly to secure the tie bar, and optionally includes a no-back system and locking mechanism to prevent unintended actuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the secondary load path uses a tie bar with a spherical head mounted within a recess to carry load when the primary path fails, then the failsafe function is achieved, but backlash and flutter occur due to the small amount of play between the tie bar and recess during normal operation
Solution Approach 1:
The invention makes the recess dynamic by allowing it to change size. During normal operation, the recess is larger than the spherical head, allowing free movement without contact. When the primary load path fails and axial load is applied to the tie bar, the recess automatically closes around the spherical head, eliminating backlash and preventing flutter. This dynamic adaptation resolves the contradiction between maintaining failsafe capability and eliminating harmful play.
Solution Approach 2:
The invention changes the parameter of recess size based on operational conditions. The biasing mechanism applies a force that opens the recess during normal operation, creating clearance. When load is applied to the tie bar, this biasing force is overcome and the recess closes, changing its effective size parameter to eliminate play and prevent flutter while maintaining the failsafe function.
2Ease of operation
If the recess is kept larger than the tie bar upper part to allow free movement during normal operation, then ease of operation is improved, but the tie bar cannot securely transfer loads when the primary load path fails
Solution Approach 1:
The recess transitions from a static large opening to a dynamic closing structure. During normal operation, the larger recess size allows free movement of the spherical head. When the primary load path fails, the biasing mechanism is overcome and the recess dynamically closes around the spherical head, transforming from a loose fit to a secure load-bearing connection, thus achieving both ease of operation and strong load transfer capability.
Solution Approach 2:
The biasing mechanism applies a preliminary opening force to the recess during normal operation, maintaining clearance and preventing premature contact. This preliminary action ensures free movement during normal operation while being designed to be overcome only when necessary, i.e., when axial load is applied to the tie bar indicating primary path failure, at which point the recess closes to provide secure load transfer.
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 effectively cancels backlash and prevents flutter by securely holding the tie bar in place when the primary load path fails, ensuring stable aircraft performance and pilot control.
Implementation Method 1
a biasing mechanism arranged such that, in use, when no axial load is applied to the tie bar the yoke and the ballscrew are held by balanced forces from the biasing mechanism in a position with the recess being larger than the upper part of the tie bar
Data Source
AI summary
An upper attachment system for a trimmable horizontal stabiliser actuator (THSA) comprises: a housing, holding a yoke and a ballscrew; a nut coupled to the housing and cooperating with the ballscrew such that rotation of the ballscrew relative to the nut results in linear motion of the ballscrew; a recess formed between the yoke and the ballscrew and arranged to receive, in use, an upper part of a tie bar of the secondary load path of the actuator; and a biasing mechanism arranged such that, in use, when no axial load is applied to the tie bar, the yoke and the ballscrew are held by balanced forces from the biasing mechanism in a position within the recess.