Cowl Door Actuator Gap Design for Thermal Expansion Compensation
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Solution Overview
Problem
Conventional hydraulic actuators for aircraft cowl doors lack precise fluid displacement verification, leading to potential leakage and thermal expansion issues that can cause the cowl door to open during flight, due to complex internal sealing and thermal compensation mechanisms.
Innovation Solution
A hydraulic actuator design with a piston rod that moves axially to form a gap when the cowl door is closed, allowing thermal expansion without opening the door, and an external indicator for fluid displacement verification, eliminating the need for separate thermal compensation seals and reducing leakage risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal compensation mechanism with spring or mechanical device is used to push oil out of the actuator, then thermal expansion is compensated, but the structure becomes complex and leakage risk increases due to multiple seals
Solution Approach 1:
The patent removes the traditional thermal compensation mechanism (spring or mechanical device) from the actuator structure. Instead of using a separate thermal compensation component with its own seals, the invention uses the piston rod's axial movement capability to accommodate thermal expansion, thereby eliminating multiple seal locations and reducing leakage risk
Solution Approach 2:
The piston rod is given a dual function: it not only actuates the cowl door but also serves as the thermal compensation mechanism. By allowing the piston rod to move axially within the actuator body, it accommodates thermal expansion of the hydraulic fluid without requiring a separate dedicated thermal compensation device
2Reliability
If an accumulator is added as a thermal compensation mechanism, then thermal expansion is compensated, but the actuator structure becomes more complex with additional sealing locations
Solution Approach 1:
The patent extracts the accumulator from the actuator design. Instead of incorporating a separate accumulator component that would require additional seals and increase structural complexity, the invention uses the existing piston rod movement capability to provide thermal compensation
Solution Approach 2:
The piston rod serves multiple functions including actuation and thermal compensation. Its ability to move axially within the actuator body provides the necessary compliance for thermal expansion without requiring a dedicated accumulator component
3Reliability
If multiple seals are used in the actuator for piston rod and thermal compensation, then sealing is achieved, but leakage risk increases at multiple sealing locations
Solution Approach 1:
The patent removes the separate thermal compensation seals from the actuator. By using the piston rod's axial movement instead of a separate thermal compensation mechanism, the number of seal locations is reduced, thereby decreasing the probability of leakage
4Force
If the piston rod is always in contact with the rod end, then actuation force is transmitted, but thermal expansion of fluid cannot be accommodated
Solution Approach 1:
The patent introduces dynamic movement capability to the piston rod, allowing it to move axially within the actuator body. This dynamic adjustment enables the system to accommodate thermal expansion of the hydraulic fluid while maintaining proper actuation force transmission 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
The actuator ensures the cowl door remains closed during flight by accommodating thermal expansion within the actuator's gap, providing external verification of fluid displacement, thus preventing unwanted opening and reducing the complexity and leakage risks associated with multiple seals.
Implementation Method 1
the gap provided between the piston rod and the rod end enables an axial displacement of the piston rod that occurs due to thermal expansion of the remaining fluid
Data Source
AI summary
A cowl door actuator is arranged between a head end and a rod end connected to a cowl door in an aircraft. The cowl door has a closed position and an open position, and the cowl door actuator includes a piston rod that is axially moveable between the head end and the rod end. The piston rod has an extended position in which the piston rod contacts the rod end to move the cowl door to the open position, and a retracted position in which the piston rod is axially spaced from the rod end. When the cowl door is in the closed position, the gap between the piston rod and the rod end enables an axial displacement of the piston rod toward the extended position during thermal expansion of fluid remaining in the actuator, such that the cowl door is maintained in the closed position.