Aircraft Landing Gear Shock Absorber Strut With Non-Back-Driving Outstop
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Solution Overview
Problem
Aircraft landing gear shock absorber struts that are longer than standard require a mechanism to shorten for stowage without redesigning the landing gear bay, and existing mechanisms risk accidental extension due to spring force, potentially damaging the bay or inhibiting deployment.
Innovation Solution
Aircraft landing gear shock absorber strut with a non-back-driving screw thread mechanism that bi-directionally drives a mechanical outstop to compress the strut against spring force, using a rotatable member with a threaded surface and a screw helix angle less than 45 degrees to prevent accidental extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a standard shock absorber strut is used, then the landing gear can be retracted into the bay, but the ground clearance is insufficient
Solution Approach 1:
The patent applies preliminary anti-action by designing a non-back-driving screw thread mechanism that prevents the spring force from causing rotation of the rotatable member. The screw thread geometry (with helix angle less than 45 degrees) creates a mechanical lock that anticipates and counteracts the potential harmful back-driving action before it can occur, thereby preventing accidental extension of the shock absorber strut during stowage
Solution Approach 2:
The patent introduces a rotatable member with a screw thread as an intermediary between the spring force and the outstop. This intermediary mechanism converts the axial spring force into a rotational force that is then converted back into axial compression through the non-back-driving screw thread geometry, effectively mediating the force transmission while preventing direct back-driving that could cause accidental extension
2Volume of moving object
If a dedicated shortening mechanism is attached to the landing gear bay, then the landing gear can be shortened for stowage, but the device complexity increases
Solution Approach 1:
The patent merges the shortening function directly into the shock absorber strut assembly by integrating the rotatable member and screw thread mechanism within the existing strut structure. This combines the shock absorption function with the shortening function in a single integrated component, eliminating the need for separate dedicated shortening mechanisms attached to the landing gear bay, thereby reducing overall device complexity
Solution Approach 2:
The shock absorber strut is designed to perform multiple functions: it provides shock absorption during landing, enables retraction into the landing gear bay, and performs shortening for stowage. The rotatable member with screw thread mechanism serves as a multi-functional component that facilitates both the shortening action and prevents accidental extension, making the strut a universal component that handles multiple operational requirements
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 mechanism reduces the likelihood of accidental extension during stowage, ensuring safe retraction and deployment by preventing the spring force from rotating the rotatable member, thus avoiding damage to the landing gear bay.
Implementation Method 1
a rotatable member distinct from the inner cylinder and defining a threaded surface comprising a plurality of threads configured to drive the outstop axially as the rotatable member is rotated
Implementation Method 2
the inner cylinder being biased by a spring force to assume the second condition
Data Source
AI summary
An aircraft landing gear shock absorber strut including an outer cylinder having a bore defining an opening; an inner cylinder having a first end region movably coupled within the bore and a second end region which projects out of the opening. The inner cylinder being arranged to move along a longitudinal axis of the bore between a first condition and a second condition and is biased by a spring force to assume the second condition. A mechanical outstop is arranged to engage an abutment surface of the inner cylinder to limit extension of the shock absorber strut; and a rotatable member drives the out stop axially to move the inner cylinder from the second condition towards the first condition. The rotatable member is arranged such that the spring force cannot rotate the rotatable member to allow the shock absorber strut to extend.