Foam-Stiffened CFC Sandwich Panel Thermal Insulation
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Solution Overview
Problem
Aircraft skin constructions with Carbon Fibre Composite (CFC) sandwich panels face challenges in thermal insulation, as the CFC material and fasteners conduct external heat into the aircraft interior, increasing the load on the Environmental Control System (ECS) and affecting performance characteristics such as weight, range, and payload, especially in extreme temperature conditions.
Innovation Solution
The use of foam-stiffened CFC sandwich panels with a continuous foam layer across the panel, where the foam material extends between two outer CFC layers, reduces heat conduction and transfer into the aircraft interior by utilizing the thermally insulating properties of the foam, eliminating the need for monolithic CFC landings and allowing for shorter fasteners and a smoother aerodynamic surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If monolithic CFC landings are used for fastening panels to the structure, then mechanical strength and fastening capability are improved, but thermal insulation deteriorates due to heat conduction through the CFC material and fasteners
Solution Approach 1:
A thermally insulating shim is introduced as an intermediary element between the CFC landing and the metallic structure. This shim acts as a thermal barrier that interrupts the heat conduction path while still allowing the fastener to mechanically connect the panel to the structure, thus resolving the contradiction between mechanical strength and thermal insulation.
Solution Approach 2:
The solution employs a composite construction combining CFC material, foam insulation, and a thermally insulating shim. This multi-material approach allows each layer to perform its specialized function: CFC provides structural strength, foam provides thermal insulation, and the shim provides additional thermal barrier at the critical fastening interface.
2Strength
If foam material is completely removed from areas where panels overlie the structure, then mechanical strength is improved, but thermal insulation deteriorates
Solution Approach 1:
The thermally insulating shim serves as a mediator that allows the foam to be removed from the fastening area while still maintaining thermal insulation. The shim compensates for the removed foam's insulating function by providing a dedicated thermal barrier at the structure interface.
Solution Approach 2:
The solution applies different material properties to different locations: foam insulation is retained in areas where thermal insulation is critical, while the thermally insulating shim is specifically applied at the fastening interface where mechanical strength is required. This localized application of different insulating solutions optimizes both strength and thermal performance.
3Reliability
If the ECS is made more powerful to handle increased heat load, then thermal control effectiveness is improved, but power consumption and aircraft weight increase
Solution Approach 1:
The patent converts the harmful effect of heat conduction through the CFC landing into a benefit by introducing the thermally insulating shim. This shim transforms the thermal conduction path into a thermal barrier, reducing the heat load on the ECS and thereby reducing the power and weight requirements of the thermal management 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 effectively limits external heat transfer, reducing the ECS's workload and maintaining consistent thermal insulation across the aircraft's outer surface, enhancing performance by minimizing weight increase and maintaining aerodynamic smoothness, while being applicable in both hot and cold climates.
Implementation Method 1
the foam material extends between two outer CFC layers... reduces heat conduction and transfer into the aircraft interior by utilizing the thermally insulating properties of the foam
Data Source
AI summary
The invention provides an arrangement and methods for thermally insulating aircraft, particularly but not exclusively for when the aircraft is operating in extremely hot or cold conditions, and describes an aircraft skin construction including a foam-stiffened CFC sandwich panel forming part of the aircraft outer skin mounted to an underlying load bearing aircraft structure, wherein the panel at the mounting to the structure includes two outer layers of CFC material with an inner layer of foam material sandwiched therebetween.