Rotating APU Inlet Door for Noise and Drag Reduction
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Solution Overview
Problem
Aircraft auxiliary power units face challenges in minimizing noise and drag during flight and ground operations, with existing inlet doors either increasing noise when fully open on the ground or compromising aerodynamics when closed in flight, and the use of inlet silencers to mitigate noise adds weight, cost, and complexity.
Innovation Solution
A rotatable inlet door assembly that transitions between closed, in-flight, and ground positions, using a lightweight and uncomplicated actuator system to minimize drag and noise, with a port design for smooth airflow and noise deflection, eliminating the need for a large inlet silencer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the inlet door is fully open on the ground, then airflow to the APU is improved, but noise propagation to the forward section increases
Solution Approach 1:
The inlet door is designed to be dynamically positionable between multiple configurations (fully open, partially open, closed) rather than being fixed. This allows the system to adapt the door position based on operational requirements, achieving optimal airflow during ground operations while redirecting noise away from the forward section when needed.
Solution Approach 2:
The inlet door incorporates a scoop configuration that creates localized airflow patterns and noise deflection zones. By shaping the door with specific geometric features (scoop shape, port positioning), the design achieves both adequate airflow intake and directional noise redirection to specific zones away from passenger areas.
2Productivity
If the inlet door projects into free stream airflow, then airflow intake is improved, but aerodynamic drag increases
Solution Approach 1:
The inlet door transitions from a static configuration to a dynamic one, allowing it to retract or adjust its projection into the free stream airflow based on flight conditions. During flight, the door can be positioned to minimize drag, while during ground operations, it can extend to maximize airflow intake.
Solution Approach 2:
The inlet door design incorporates segmented or modular features including ports and scoops that can be independently optimized. This segmentation allows different portions of the door to serve different functions - some areas optimized for airflow intake while others minimized to reduce drag projection.
3Object-generated harmful factors
If an inlet silencer is added to reduce noise, then noise attenuation is improved, but system weight and complexity increase
Solution Approach 1:
The noise attenuation function is merged with the existing inlet door structure rather than being implemented as a separate silencer component. The inlet door itself is designed with geometric features (scoop shape, port configuration, surface contours) that provide both airflow management and noise redirection/attenuation functions in a single integrated component.
Solution Approach 2:
The noise control function is extracted from the traditional silencer approach and integrated directly into the inlet door geometry. By taking out the need for a separate silencer and embedding noise management capabilities within the door structure itself, the system achieves noise attenuation without adding the weight and complexity of additional components.
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 solution reduces noise propagation and drag during flight, minimizes ice formation, and reduces the necessity for a large inlet silencer, thereby decreasing weight and complexity while ensuring efficient APU operation across flight and ground modes.
Implementation Method 1
Minimizing the extent to which the door projects into the free stream airflow improves the aerodynamics of the aircraft, reduces the amount of noise that is transmitted to the cabin
Implementation Method 2
The inlet noise typically travels from the compressor through the inlet duct and is deflected from the inlet door toward the forward section of the aircraft
Data Source
AI summary
An inlet door assembly includes an inlet door rotatable about an axis of rotation.