Aircraft Fuel System Flammability Control via Reserve Level Management
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Solution Overview
Problem
Aircraft fuel tanks located within the fuselage or partially within it face challenges in meeting flammability exposure criteria, particularly during warm day operations, and require a method to manage fuel consumption and center of gravity while maintaining fuel reserves, reducing flammability risks, and optimizing structural weight.
Innovation Solution
A fuel system configuration where the main tank adjacent to the fuselage is prioritized for fuel consumption, maintaining a reserve level to reduce ullage and flammability exposure, with a collector bay connected to outboard wing tanks, ensuring continuous fuel supply to engines and compliance with federal regulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fuel tanks are located within the fuselage contour to meet flammability exposure criteria, then flammability compliance is improved, but fuel consumption management and center of gravity control become more complex
Solution Approach 1:
The fuel system is divided into multiple tanks (inboard main tanks and outboard auxiliary tanks) with distinct functions. The inboard tanks are designated as main tanks for flammability compliance, while outboard tanks serve as auxiliary storage, allowing the system to meet regulatory requirements while managing fuel consumption complexity through functional segmentation
Solution Approach 2:
Fuel transfer pumps and control systems act as intermediaries between the outboard auxiliary tanks and the inboard main tanks. These intermediaries enable automated fuel management by transferring fuel from auxiliary to main tanks based on flight phase and consumption patterns, reducing the complexity of direct manual management
2Reliability
If main tanks continuously hold fuel reserves to meet flammability criteria, then flammability exposure is reduced, but aircraft longitudinal center of gravity stability deteriorates
Solution Approach 1:
The fuel reserve management system dynamically adjusts fuel distribution between inboard and outboard tanks based on flight phase, consumption rate, and center of gravity position. This dynamic management allows the system to maintain required flammability compliance while compensating for center of gravity shifts through controlled fuel transfer operations
Solution Approach 2:
The system changes operational parameters by designating specific tanks as main tanks with reserve requirements only during certain flight phases. By adjusting which tanks maintain reserves and at what levels based on flight conditions, the system maintains flammability compliance while optimizing center of gravity stability
3Weight of moving object
If outboard wing tanks are used for fuel storage to optimize structure, then structural weight is reduced, but fuel vapor ignition risk increases
Solution Approach 1:
The harmful function of fuel storage in outboard tanks is extracted and separated from the main fuel consumption system. Outboard tanks serve only as auxiliary storage with automated transfer to inboard main tanks, removing the ignition risk associated with outboard tank consumption while preserving the structural weight benefits of utilizing outboard storage capacity
4Productivity
If fuel consumption sequence is optimized for range, then operating range is maximized, but flammability exposure criteria compliance becomes more difficult
Solution Approach 1:
The system performs preliminary actions by pre-designating inboard tanks as main tanks with reserve fuel requirements before flight. This preliminary configuration ensures flammability compliance is established from the outset, while the automated fuel management system subsequently optimizes consumption patterns to maintain both range efficiency and compliance throughout the flight
Data Source
AI summary
Disclosed is a method for controlling the flammability of fuel vapors in an aircraft main fuel tank that is located in whole or in part in the fuselage contour. The method comprises a fuel system architecture and fuel consumption sequencing maintaining liquid fuel in said main tanks during all normal operations. Ceasing the withdrawal of fuel from the main tank when the fuel reaches a predetermined level thereby limiting the volume and flammability exposure time of the fuel vapor ullage. Once the predetermined level is met the fuel is supplied from wing tanks throughout the remainder of the mission. The predetermined main tank fuel level at which wing tank fuel begins to be consumed is determined by the aircraft flight reserves fuel volume stored in the main tank as well as the amount necessary to continuously submerge the main tank fuel pumps during the entire mission.