APU Inlet Door Control for Stall Prevention
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Solution Overview
Problem
Existing systems for controlling auxiliary power unit (APU) inlet doors on aircraft are not optimal for high altitude load applications, as they either maintain a fully open position on the ground and partially open in flight, which can degrade APU performance and increase risk of stall due to ram effects.
Innovation Solution
A method and system that dynamically control the APU inlet door position based on aircraft status, commanding it to a partially open position during flight and transitioning to fully open when the APU reaches a predetermined speed threshold, ensuring optimal airflow and preventing degraded performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inlet door is commanded fully open when the aircraft is on ground and partially open when the aircraft is in flight, then the APU can provide basic airflow functionality, but the APU performance degrades and stall risk increases due to ram effects at high altitude
Solution Approach 1:
The inlet door position is made dynamic rather than static, transitioning between partially open and fully open positions based on real-time detection of aircraft airborne status and APU rotational speed. This dynamic adjustment allows the system to adapt to varying operational conditions, preventing stall by opening the door fully only when the APU reaches sufficient speed to handle ram effects.
Solution Approach 2:
The system changes the positional parameter of the inlet door based on detected operational parameters (airborne status and rotational speed). By monitoring these parameters and adjusting the door position accordingly, the system optimizes airflow characteristics to prevent stall while maintaining APU performance across different operating conditions.
2Power
If the inlet door is commanded partially open during flight, then ram effects are reduced, but power delivery is limited during start sequence
Solution Approach 1:
The system performs preliminary action by transitioning the inlet door to fully open position before the APU reaches its operational speed threshold. This anticipatory opening ensures that maximum airflow is available when the APU needs it most, preventing power delivery limitations while maintaining safety through the speed threshold requirement.
Solution Approach 2:
The system uses feedback from the rotational speed sensor to control the inlet door position. When the rotational speed reaches the predetermined threshold, the feedback signal triggers the transition to fully open position, ensuring that power delivery is maximized only when the APU is sufficiently stable to handle the increased airflow.
3Productivity
If the inlet door transitions to fully open position during start sequence, then airflow is maximized for power delivery, but stall risk increases due to ram effects
Solution Approach 1:
The system monitors the rotational speed parameter and uses it as a threshold for transitioning the inlet door position. By changing the door position parameter only when the rotational speed exceeds the threshold, the system ensures that maximum airflow is provided only when the APU is fast enough to prevent stall, thus balancing productivity with reliability.
Data Source
AI summary
There is provided a method and a system for controlling an inlet door of an auxiliary power unit provided on an aircraft. Input data indicative of whether the aircraft is on ground or airborne is received. If the aircraft is on ground, a first control signal comprising instructions to command the inlet door to a fully open position is output. If the aircraft is airborne, a second control signal comprising instructions to command the inlet door to a partially open position. When a current value of a rotational speed of the auxiliary power unit reaches a predetermined threshold indicative of an end of a start sequence of the auxiliary power unit, a third control signal comprising instructions to transition the inlet door from the partially open position to the fully open position is output.