Aircraft Shock Strut Percolation Seals for Fluid Switching
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Solution Overview
Problem
Aircraft shock struts with mixed air/oil chambers face inefficiency and potential damage due to gas and oil leakage when retracted, leading to delayed fluid switching and increased landing loads, exacerbated by cold temperatures, which can result in suboptimal hydraulic damping characteristics.
Innovation Solution
Incorporation of first and second percolation seals within the shock strut cylinder and piston, respectively, which restrict fluid flow between chambers when inflated, and are controlled by a fluid source via a conduit to manage fluid distribution and prevent percolation, ensuring efficient fluid switching during retraction and extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the shock strut is retracted to an angle greater than ninety degrees, then the landing gear can be stowed within the landing gear bay, but gas and oil leak between chambers causing delayed fluid switching and reduced landing efficiency
Solution Approach 1:
A percolation seal is introduced as an intermediary component between the upper and lower chambers to prevent direct fluid leakage. The seal acts as a mediator that blocks the path of gas and oil during retraction while still allowing controlled flow when needed, thus maintaining chamber separation reliability without compromising retraction capability
Solution Approach 2:
The percolation seal is implemented as a flexible membrane or thin film structure that can deform to seal the interface between chambers during retraction. This flexible barrier effectively prevents gas and oil leakage while accommodating the geometric changes that occur during shock strut retraction to above-horizontal positions
2Device complexity
If the shock strut operates with insufficient flow area for fluid switching, then the structure can be simpler, but the landing gear cannot be ready to land within the prescribed time period
Solution Approach 1:
The flow area is made dynamic rather than fixed. The percolation seal can transition between sealed and open states, allowing the flow passage area to adapt based on operational requirements. This dynamic control enables rapid fluid switching when needed while maintaining structural simplicity
Solution Approach 2:
The percolation seal is positioned and configured in advance to optimize the flow path for rapid fluid switching. The seal geometry is designed beforehand to provide sufficient flow area when opened, ensuring that fluid can switch chambers quickly without requiring complex active flow control mechanisms
3Duration of action of stationary object
If the shock strut is maintained in retracted position for extended periods, then the landing gear can remain stowed, but gas and oil percolate between chambers reducing shock strut efficiency
Solution Approach 1:
The percolation seal serves as a persistent intermediary barrier that remains in place during extended stow periods, continuously preventing fluid percolation. This mediator maintains chamber integrity over long durations without requiring active control or monitoring systems
Solution Approach 2:
The flexible percolation seal membrane maintains its sealing function throughout extended stow periods, accommodating thermal expansion and contraction as well as minor structural movements without compromising fluid integrity. The material properties of the flexible film ensure long-term reliability
4Use of energy by moving object
If the shock strut uses cold temperature operation at cruising altitudes, then the aircraft can achieve efficient flight, but the viscosity changes exacerbate percolation and delay fluid switching
Solution Approach 1:
The percolation seal is constructed from flexible material that maintains its sealing properties across a wide temperature range, including cold cruising conditions. The material selection ensures that the seal remains effective despite viscosity changes in the hydraulic fluid, preventing percolation even when the fluid becomes more viscous at low temperatures
Solution Approach 2:
The percolation seal acts as a temperature-insensitive intermediary that provides consistent fluid barrier function regardless of thermal conditions. This mediator ensures reliable chamber separation and controlled fluid flow even when cold temperatures alter the rheological properties of the hydraulic fluid
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 restricts fluid flow between chambers, ensuring the shock strut operates efficiently by maintaining the optimal gas over oil column arrangement, reducing landing loads and preventing damage to the landing gear and aircraft structure.
Implementation Method 1
a first percolation seal configured to restrict a first flow of fluid between the shock strut cylinder and the rebound chamber, and a second percolation seal configured to restrict a second flow of fluid between the shock strut cylinder and the shock strut piston
Implementation Method 2
the first percolation seal restricting the first flow of fluid when inflated, and the second percolation seal restricting the second flow of fluid when inflated
Data Source
AI summary
A shock strut is disclosed herein. The shock strut includes a shock strut cylinder, a shock strut piston slidably disposed within the shock strut cylinder, a rebound chamber disposed within the shock strut cylinder and adjacent the shock strut piston, a first percolation seal configured to restrict a first flow of fluid between the shock strut cylinder and the rebound chamber, and a second percolation seal configured to restrict a second flow of fluid between the shock strut cylinder and the shock strut piston.