Two-Stage Strut for Early Aircraft Touchdown Detection
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Solution Overview
Problem
Current aircraft landing gear systems struggle to detect touchdown at light loads due to high fully extended pressure requirements for supporting large static and ground loads, which complicates the indication of ground contact.
Innovation Solution
A landing detection system is integrated into the shock strut with a secondary chamber and a metering pin passage, allowing a smaller piston area to stroke initially at lower loads, enabling earlier indication of touchdown by using a sliding or pivoting moveable member, and adjusting damping through the metering pin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high fully extended pressure is maintained in the shock strut, then the strut can support large static loads and ground loads properly, but the touchdown detection becomes difficult at light loads
Solution Approach 1:
The shock strut is divided into two independent chambers: a first chamber with a first piston for supporting large static and ground loads, and a second chamber with a second piston for detecting touchdown at light loads. Each chamber operates independently with its own fluid volume and pressure characteristics, allowing the system to simultaneously handle both heavy load support and sensitive touchdown detection without interference between functions.
2Force
If a larger piston area is used in the shock strut, then the strut can generate sufficient force for supporting aircraft weight and ground loads, but the force required for touchdown indication becomes too high
Solution Approach 1:
The system uses two separate pistons with different area characteristics. The first piston has a larger area for generating high force during ground operations, while the second piston has a smaller area that requires only light touchdown loads to activate the indication system. This segmentation allows each piston to be optimized for its specific function without compromise.
Solution Approach 2:
Different regions of the shock strut system are given different properties: the first chamber is designed with characteristics suitable for heavy load support, while the second chamber is designed with characteristics optimized for sensitive touchdown detection. Each chamber can have different fluid volumes, piston areas, and damping characteristics tailored to its specific function.
3Device complexity
If the shock strut uses a single chamber design, then the structure is simpler, but it cannot simultaneously provide proper seal pressure and light load touchdown indication
Solution Approach 1:
The single chamber is divided into two separate chambers, each capable of performing specific functions. The first chamber handles seal pressure maintenance and heavy load support, while the second chamber handles touchdown detection. This segmentation enables the system to perform multiple functions that would be impossible in a single chamber design.
Solution Approach 2:
The shock strut system is designed to perform multiple functions simultaneously through its two-chamber architecture: it maintains seal pressure, supports static aircraft weight, absorbs ground loads, and detects touchdown events. Each chamber contributes to the overall multi-functionality of the system.
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 solution allows for earlier detection of touchdown events by stroking the axle independently of the main strut piston at lower loads, reducing the force required for detection and enhancing the system's ability to indicate ground contact.
Implementation Method 1
The fluid generally includes both a gas and a liquid, such as hydraulic fluid or oil. One type of shock strut generally utilizes an 'air-over-oil' arrangement wherein a trapped volume of gas is compressed as the shock strut is axially compressed, and a volume of oil is metered through an orifice. The gas acts as an energy storage device, similar to a spring, so that upon termination of a compressing force the shock strut returns to its original length.
Implementation Method 2
Shock struts also dissipate energy by passing the oil through the orifice so that as the shock absorber is compressed or extended, its rate of motion is limited by the damping action from the interaction of the orifice and the oil.
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A landing detection system (300) for a landing gear assembly of an aircraft may comprise a moveable member (309) mechanically coupled between an aircraft wheel and a strut piston (212), wherein the moveable member (309) is in communication with a strut chamber pressure of the landing gear assembly, wherein the moveable member (309) moves relative to the strut piston (212) in response to a first force applied to the aircraft wheel and the strut piston (212) strokes in response to a second force applied to the aircraft wheel.