Nested Piston Hydraulic Actuator for Semi-Levered Landing Gear
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Solution Overview
Problem
Current semi-levered landing gear systems are complex, heavy, and costly, with mechanical linkages and hydraulic struts increasing complexity and weight, and often lack sufficient space for efficient operation, particularly in aircraft with limited clearance between the shock absorber and bogie beam.
Innovation Solution
A telescopic hydraulic actuator assembly comprising a housing with nested pistons, where a first piston is positioned between outer and inner cylindrical structures, forming an outer chamber for a first fluid and an inner chamber for a gas, allowing the pistons to move parallel to the axis, providing a compact, lightweight, and cost-effective solution for positioning the bogie beam during takeoff and landing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional locking hydraulic strut is used to lock the bogie beam in a semi-levered position, then the bogie beam can be locked in the desired orientation for takeoff, but the hydraulic strut requires significant space and cannot be efficiently positioned in aircraft with limited clearance between the shock absorber and bogie beam
Solution Approach 1:
The patent employs a nested telescopic piston structure where multiple pistons are arranged concentrically within each other. The first piston is nested within the second piston, allowing the hydraulic actuator to achieve the required stroke length and locking capability while occupying minimal space between the shock absorber and bogie beam, thus resolving the space constraint issue.
Solution Approach 2:
The telescopic piston structure allows the hydraulic actuator to dynamically adjust its effective length through extension and retraction. This dynamic capability enables the actuator to provide sufficient force for locking the bogie beam while maintaining a compact retracted profile that fits within the limited clearance space during different operational phases.
2Ease of operation
If mechanical linkages and shrink-links are used to reposition the shock absorber for retraction, then the landing gear can be repositioned for stowing, but the mechanical complexity, expense and weight of the system increase more than desired
Solution Approach 1:
The patent integrates multiple functions into the single telescopic hydraulic actuator. The same actuator that locks the bogie beam in the semi-levered position also provides the force for repositioning the landing gear for stowing. This merging of functions eliminates the need for separate mechanical linkages and shrink-links, thereby reducing mechanical complexity, weight, and cost.
Solution Approach 2:
The telescopic hydraulic actuator serves multiple purposes: it locks the bogie beam in the takeoff position, provides pitch damping during landing, and enables repositioning of the landing gear for wheel well stowing. This multi-functionality replaces what would traditionally require multiple separate mechanical systems, reducing overall device complexity.
3Reliability
If a locking hydraulic strut with additional chambers and internal floating piston is used, then the bogie beam can be locked in the desired orientation, but the landing gear may not have sufficient clearance or room for the hydraulic strut to be positioned between the shock absorber and bogie beam
Solution Approach 1:
The patent uses a nested telescopic piston design where the first piston is positioned within the second piston, and both are contained within a compact cylindrical housing. This nested arrangement achieves the required locking force and stroke length while minimizing the cross-sectional area and overall volume, allowing the actuator to fit within the limited clearance between the shock absorber and bogie beam.
Solution Approach 2:
The patent employs hydraulic pressure acting on the nested pistons to generate the locking force. The hydraulic system provides a compact force multiplication mechanism that eliminates the need for larger mechanical leverage systems, enabling the actuator to deliver sufficient locking force within the constrained space available.
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 enhances aircraft operation by increasing ground clearance for takeoff, providing additional pitch damping during landing, and reducing mechanical complexity, weight, and cost, while maintaining efficient operation in aircraft with limited space constraints.
Implementation Method 1
The second piston and the first piston are retracted in response to a load being applied to the second piston when the landing gear assembly contacts a ground on which the aircraft is landing. The gas in the inner chamber compresses when the second piston retracts.
Data Source
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AI summary
A hydraulic strut assembly, for use in a semi-levered landing gear in an aircraft, comprising an actuator and a manifold associated with the actuator. The actuator comprises a housing, a first piston (116), a second piston (118), and a third piston (130). The first piston (116) is positioned between outer and inner cylindrical structures of the housing. The outer and inner cylindrical structures and first piston (116) form an outer chamber that receives a first fluid. The inner cylindrical structure, the first piston (116), and the second piston (118), which is nested within the first piston, form an inner chamber, which holds a second fluid comprising a gas. A volume of the inner chamber changes when at least one of the first and second pistons (116,118) moves. The third piston (130) is positioned between the outer cylindrical structure and the first piston (116). The first, second, and third pistons move in a direction parallel to an axis through the housing.