THSA Lower Attachment Bushing Assembly to Eliminate Flutter Backlash
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing lower attachment systems for trimmable horizontal stabiliser actuators experience undesirable 'flutter' and potential loss of control due to dynamic loading and clearance between failsafe plates and bushings in the secondary load path, leading to increased manufacturing costs and complexity.
Innovation Solution
A lower attachment system featuring a floating bushing with a flange portion and tightening ring, secured by contact screws, which eliminates clearance between the failsafe plate and bushing, and includes stiffness bars to maintain contact between failsafe plates and bushings, ensuring secure engagement and load transfer during primary load path failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If clearance is provided between failsafe plates and bushings in the secondary load path, then the bushing can float and accommodate misalignment, but this clearance causes dynamic loading and flutter during operation
Solution Approach 1:
The bushing is designed to transition from a static fixed position to a dynamic floating position. During normal operation, the bushing floats within the failsafe plate assembly, allowing dynamic adjustment and misalignment accommodation. The floating capability is controlled through the interaction between the bushing flange, failsafe plate, and stiffness bars, enabling the system to adapt to operational conditions while maintaining stability.
2Object-affected harmful factors
If stiffness bars are added to maintain contact between failsafe plates and bushings, then flutter is reduced, but device complexity increases
Solution Approach 1:
Stiffness bars are introduced as intermediary elements between the failsafe plates and the bushing assembly. These bars serve as mediators that maintain controlled contact and transmit loads while reducing flutter. The stiffness bars connect the failsafe plate assembly to the bushing flange, providing a compliant yet stable connection that eliminates harmful dynamics without requiring complete rigid fixation.
3Reliability
If a sheet plate is used to prevent motion in the secondary load path, then control stability is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The failsafe plate assembly is segmented into multiple functional components: failsafe plates, stiffness bars, and the bushing flange connection. This segmentation allows each component to perform its specific function - the failsafe plates provide structural support and load bearing, the stiffness bars control dynamics and reduce flutter, and the bushing flange maintains positional stability. This divided approach achieves the stability function of a sheet plate while reducing overall complexity and improving manufacturability.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
When the primary load path of a trimmable horizontal stabiliser actuator fails, the load may be transferred through a secondary load path. A functional backlash exists between these load paths, and can cause flutter of a flight surface when the secondary load path is loaded. The present invention therefore provides a connection for a lower attachment for a trimmable horizontal stabiliser actuator (THSA) for connecting the lower attachment to a flight control surface; comprising: a surface bracket (140) for coupling to a flight control surface, the surface bracket mounted about a gimbal (130) of the lower attachment by a bushing (110) disposed between the gimbal and the surface bracket; a failsafe plate (120) fittingly engaged on a first end of the bushing; and a tightening ring (170) mounted on a second end of the bushing opposite the first end and secured to the surface bracket by at least one contact screw (160), such that the contact screw is operable to urge the bushing against the failsafe plate.