THSA Lower Attachment Locking Assembly for Flutter Elimination
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Solution Overview
Problem
The existence of clearance between components in a secondary load path of a trimmable horizontal stabiliser actuator leads to undesirable 'flutter' or backlash of the flight control surface, which is not effectively addressed by existing mechanisms.
Innovation Solution
A lower attachment for a trimmable horizontal stabiliser actuator featuring a nut assembly with a locking assembly that transitions to a loaded configuration, preventing relative movement between the nut and transfer plate by using a locking pin to bridge the clearance, thereby reducing or eliminating flutter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clearance is maintained between secondary load path components, then the secondary load path remains unloaded during normal operation, but this causes play and flutter when the secondary load path becomes loaded
Solution Approach 1:
The locking pin is designed to be movable rather than fixed, allowing it to transition between retracted and extended positions. A biasing member continuously urges the locking pin into engagement with the transfer plate, creating a dynamic system that automatically adapts to load conditions. When the secondary load path becomes loaded, the locking pin automatically engages to eliminate clearance, preventing flutter while maintaining reliability.
2Stability of the object's composition
If a locking mechanism is added to eliminate clearance, then flutter is reduced, but the device complexity increases
Solution Approach 1:
The locking assembly is designed to be self-actuating through the use of a biasing member that automatically urges the locking pin into engagement with the transfer plate. The system eliminates the need for external actuators, complex control systems, or manual intervention. The locking pin automatically engages when the secondary load path becomes loaded, and the biasing member ensures continuous engagement without requiring additional energy input or complex control logic.
3Stability of the object's composition
If the locking pin is continuously engaged, then clearance is eliminated, but the secondary load path cannot properly transition from unloaded to loaded state
Solution Approach 1:
The locking pin is pre-positioned and urged by the biasing member to engage with the transfer plate, but the engagement is designed to occur automatically when load conditions warrant it. The preliminary positioning of the locking pin allows it to quickly engage when needed, while the biasing member ensures that the pin is ready to engage but does not force engagement before the secondary load path is actually loaded, maintaining adaptability.
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 reduces or eliminates flutter by ensuring contact between components, maintaining stable control of the flight control surface even after primary load path failure, without requiring manual intervention.
Implementation Method 1
a biasing member arranged to bias the locking pin into the clearance
Data Source
AI summary
There is provided a lower attachment for a trimmable horizontal stabiliser actuator (THSA) for connecting the THSA to a flight control surface. The attachment includes: a nut assembly for providing a load path through the THSA to the flight control surface when the THSA is connected to the flight control surface. The nut assembly includes a nut for location on a screw shaft of the THSA, a failsafe plate for coupling to the flight control surface, and a transfer plate for transferring load between the failsafe plate and the nut. The nut assembly has a first unloaded configuration in which there is no contact between the nut and the transfer plate, and a second loaded configuration in which there is contact between a first pair of opposed surfaces of the nut and the transfer plate.