Landing Gear Hydraulic Actuator Modes to Limit Extension Loads
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Solution Overview
Problem
Existing aircraft hydraulic actuation systems for landing gear face challenges in managing forces during extension and retraction, leading to potential structural overloading and weight issues due to the need for strong actuators and attachment points, with prior art solutions like flow restrictors being prone to clogging and unreliable flow control.
Innovation Solution
The system employs a dual-mode hydraulic actuation system where the first chamber is supplied with pressurized fluid for retraction and disconnected for extension, allowing the piston to move under external forces like gravity, reducing the need for strong structures and minimizing pressurized fluid entry into the second chamber, thereby reducing structural loads and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If powerful actuators are used to retract the landing gear, then the retraction force is sufficient, but the actuator weight and structural weight increase
Solution Approach 1:
The system dynamically switches between two operational modes: a first mode where the actuator operates as a double-acting hydraulic actuator with both chambers connected to the hydraulic system for powerful retraction, and a second mode where the actuator operates as a single-acting actuator with only the first chamber connected to the hydraulic system during extension, allowing the landing gear to extend under its own weight without requiring equally powerful extension capability
Solution Approach 2:
The invention changes the operational parameters of the actuator by selectively connecting or disconnecting the second chamber from the hydraulic system. During retraction, both chambers are active with high pressure; during extension, the second chamber is disconnected and allows free movement under gravity, effectively changing the actuator's mechanical characteristics to match the operational requirements of each phase
2Force
If the second chamber is supplied with pressurized hydraulic fluid during extension, then the actuator can control extension, but large forces are transmitted to the structure at full extension
Solution Approach 1:
The invention extracts the second chamber from the pressurized hydraulic system during the extension phase by disconnecting it from the supply line. This allows the actuator to extend under the weight of the landing gear without generating large opposing forces that would require strengthened structural attachment points, while still maintaining the capability to control retraction when the second chamber is reconnected
3Ease of operation
If flow restrictors are used to control hydraulic fluid flow into the second chamber, then extension can be controlled, but the flow restrictor may clog and become unreliable
Solution Approach 1:
The invention introduces a selector valve as an intermediary component that controls the connection between the second chamber and the pressurized hydraulic supply. This valve provides reliable flow control by mechanically switching the hydraulic circuit configuration, avoiding the use of flow restrictors that are prone to clogging, while still enabling controlled extension when needed
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
This approach reduces the structural requirements and weight by minimizing the need for strong attachment points and actuators, while ensuring reliable operation by avoiding large forces at full extension, thus enhancing safety and efficiency in aircraft landing gear operations.
Implementation Method 1
the first chamber is supplied with pressurised hydraulic fluid from the supply line such that the piston is moved in a first direction so as to move a load
Implementation Method 2
the piston is able to be moved in a second direction, opposite to the first direction, under the influence of the load
Data Source
AI summary
An aircraft hydraulic actuation system for retracting an aircraft landing gear. The actuation system includes a supply line arranged to carry hydraulic fluid pressurised by a pump, a return line arranged to return hydraulic fluid to a reservoir, and a hydraulic actuator 128. In a first mode of operation, a first chamber 130 of the actuator 128 is supplied with pressurised hydraulic fluid from the supply line such that a piston 134 is moved in a first direction so as to move a load such as a landing gear. In a second mode of operation, the first chamber 130 is taken out of fluid communication with the supply line and a second chamber 132 is in fluid communication with the return line, such that the piston 134 is able to be moved under the influence of the load, for example when the landing gear extends under gravity.