APU Cool Down Cycle for Composite Tail Cone Heat Management
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Solution Overview
Problem
Composite materials used in aircraft tail cones for auxiliary power units (APUs) cannot withstand the high temperatures generated during shutdown, as they are overwhelmed by the heat load from the APU, potentially leading to damage.
Innovation Solution
A control system that senses temperature challenges and initiates a reduced-load cool down cycle for the APU, directing all compressed air into the combustion chamber and reducing electricity generation to mitigate heat transfer to the tail cone, thereby preventing excessive heat damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If composite materials are used in tail cones, then weight is reduced and manufacturing ease is improved, but temperature resistance deteriorates
Solution Approach 1:
The APU performs a cool-down cycle before shutdown to pre-cool its components and reduce heat transfer to the tail cone. This preliminary cooling action allows composite tail cones to be used without compromising temperature resistance, as the heat is dissipated before it can damage the composite material.
Solution Approach 2:
The system changes operational parameters by reducing generator load and diverting air flow during the cool-down cycle. This parameter change reduces the thermal output of the APU, allowing composite materials to withstand the reduced temperature exposure while maintaining their weight and manufacturing advantages.
2Power
If APU operates at full load, then power output is maximized, but heat generation increases causing damage to tail cone
Solution Approach 1:
The APU operates in periodic cycles: full power mode during normal operation, followed by a cool-down cycle before shutdown. This periodic alternation between high power and cooling phases allows the system to maximize power output when needed while periodically dissipating accumulated heat to prevent tail cone damage.
Solution Approach 2:
The cool-down cycle maintains continuous useful action by keeping the APU running at reduced load rather than shutting down immediately. This continuous operation at lower power continuously removes heat from the system, preventing heat accumulation that would otherwise damage the tail cone structure.
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 the use of composite materials in tail cones without the need for additional thermal insulation, ensuring safe cooling and extending their temperature tolerance, thus preventing damage and maintaining operational safety.
Implementation Method 1
the APU continues to compress air, combust fuel and drive the turbine, and hence the compressor
Implementation Method 2
the APU continues to compress air, combust fuel and drive the turbine
Implementation Method 3
the APU continues to compress air, combust fuel and drive the turbine, and hence the compressor
Implementation Method 4
the control operates the APU with a reduced load in a cool down cycle to reduce the heat load from the APU on an associated tail cone
Data Source
AI summary
An APU has a control for controlling a load on the APU from an associated aircraft. The control further receives information with regard to a temperature challenge around the APU. If the temperature challenge exceeds a predetermined threshold, then the control operates the APU with a reduced load in a cool down cycle to reduce the heat load from the APU on an associated tail cone. A method is also disclosed.