Aircraft APU Variable Air Inlet Door Control
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Solution Overview
Problem
Conventional auxiliary power units (APUs) in aircraft are oversized to handle shock loads, leading to increased mass and reduced efficiency due to variations in ambient conditions such as altitude, air density, and electrical load demands, which affects power output and fuel efficiency.
Innovation Solution
An APU control system that adjusts the effective area of the air inlet by moving an air inlet door using an actuator, based on real-time ambient signals and power signals, to maintain a constant power output and improve efficiency by compensating for changes in air density, altitude, and electrical load demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the APU is oversized to accommodate shock loads, then the reliability is improved, but the weight increases
Solution Approach 1:
The patent applies dynamics by making the air inlet area variable through an adjustable inlet door that can change its opening position. This allows the APU to dynamically adapt its air intake according to actual operating conditions, enabling a smaller APU to achieve the required shock load capability only when needed, rather than being permanently oversized.
Solution Approach 2:
The patent changes the parameter of air inlet area from fixed to variable. By controlling the inlet door position, the system can adjust the effective air intake area to match varying operational demands, allowing the APU to maintain reliability under shock loads while minimizing weight for normal operations.
2Power
If the air inlet area is increased to maintain power output at high altitude, then the power output is maintained, but the device complexity increases
Solution Approach 1:
The patent changes the air inlet area parameter dynamically based on altitude and operating conditions. The inlet door position is adjusted to compensate for reduced air density at high altitudes, maintaining mass flow rate and power output without requiring a permanently larger APU or complex multi-component adjustment mechanisms.
Solution Approach 2:
The inlet door mechanism serves multiple functions: it controls air inlet area for power maintenance, and can be positioned in fully closed, partially opened, or fully opened positions for different operational modes. This single component handles various altitude and load conditions without requiring separate systems for each function.
3Power
If the air inlet door is kept fully open for maximum air flow, then the power output is maximized, but the fuel efficiency decreases
Solution Approach 1:
The patent applies dynamics by continuously adjusting the inlet door position based on actual power demands and ambient conditions. Rather than maintaining a fixed fully-open position, the system dynamically optimizes the air inlet area to match the required power output, reducing excess air intake and improving fuel efficiency during partial-load operations while maintaining maximum power capability 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 system allows for a smaller, lighter APU to maintain consistent power output across varying conditions, reducing fuel consumption and improving efficiency by dynamically adjusting the air inlet area to match changing operational parameters.
Implementation Method 1
an actuator configured to move the air inlet door into a set position
Implementation Method 2
the compressor draws in ambient air that is compressed and sent to the combustor
Implementation Method 3
The APU includes a compressor, a combustor, and a turbine
Data Source
AI summary
An auxiliary power unit (APU) control system for an aircraft is disclosed and includes an APU, an air inlet having an effective area, an air inlet door moveable to vary the effective area of the air inlet, an actuator configured to move the air inlet door into a set position, one or more processors, and a memory coupled to the one or more processors. The memory stores data comprising a database and program code that, when executed by the one or more processors, causes the APU control system to receive one or more ambient signals indicative of an air density value. The system also determines the effective area of the air inlet based on the air density value. The system is further caused to instruct the actuator to move the air inlet door into the set position.