Modeling In-Flight Inert Gas Distribution in a 747 Center Wing Fuel Tank

Abstract

Extensive development and analysis has illustrated that fuel tank inerting, using air separation modules, is a reasonably cost-effective approach to preventing fuel tank explosions. To support the development of the Federal Aviation Administration inerting system, analytical and scale replica models of a Boeing 747 center wing fuel tank were developed and used to gage the ability of these relatively simple modeling methods to predict the ullage oxygen concentration of a specific fuel tank, given a flight cycle and inerting system performance. The analytical and scale models resulting average ullage oxygen concentration of the multiple bay fuel tank agreed well with measured flight test data, given the measured system performance and flight profile. Oxygen concentration distribution, in terms of the difference in oxygen concentration between the different bays of the test aircraft during the descent portion of the flight test, correlated well with the results obtained from both models, while model peak values deviated significantly from some of the measured flight test peak values. The resulting bay oxygen concentrations predicted by both models agreed with the flight test results within 1 percent oxygen on average, but the critical bay 1 (highest oxygen concentration bay) model values deviated by as much as 2 percent oxygen when compared with two separate tests. The computational model of a single flight test event illustrated fair agreement with the flight test data.