Modeling of Single Bay Fuel Tank Inerting for FAA OBIGGS Research

1. Modeling of Single Bay Fuel Tank Inerting for FAA OBIGGS Research William CavageAAR-440 Fire Safety BranchWm. J. Hughes Technical CenterFederal Aviation Administration International Systems Fire Protection Working GroupPlace de Ville Tower C Ottawa, Canada February 14-15, 2005

2. Outline • Background • Goals and Objectives • Previous Work • Analytical (calculation) Models • Physical (scale) Models • Results of Modeling Methods • Analytical Model • Scale A320 Tank in Altitude Chamber • Summary AAR-440 Fire Safety R&D

3. Background • FAA has been developing and testing an OBIGGS for fuel tank inerting to illustrate the feasibility of light weight, simplified inerting systems to reduce flammability in commercial transport airplanes • Modeling inert gas effects and distribution in commercial transport fuel tanks could assist in the development process and allow for cost effective systems analysis and trade studies • Capitalize on previous FAA modeling work done in support of ground based inerting research (sea level inerting only) • Models have to be simple to be useful in a cost analysis study or rulemaking exercise • FAA has a relatively large amount of flight test data to validate any developed models AAR-440 Fire Safety R&D

4. Previous Work – Ullage [O2] Calculation Model • Uses perfect mixing assumption and calculates the volume of oxygen in and out of tank at every time step • Uses a basic spreadsheet iterating calculation and runs immediately given the volume of the tank, the flow rate and purity of the NEA • Constant inerting only AAR-440 Fire Safety R&D

5. Previous Work – Scale 747SP CWT • FAA built and performed tests in 24% scale 747SP (classic type) center-wing fuel tank • Made from plywood using NTSB Shepherd report drawings • Scaled all penetrations (holes) between bays and vent system • Variable NEA deposit capability to allow for inerting of tank with scaled flows in each bay • Oxygen concentration measured in each bay • Model data duplicated full-scale results very well for localized deposit method studied AAR-440 Fire Safety R&D

6. Scale Model Inerting Data Comparison AAR-440 Fire Safety R&D

7. Previous Work – Average [O2] Predictions • Regardless of methodology, all modeling methods predict bulk ullage oxygen concentration well AAR-440 Fire Safety R&D

8. Modeling Method – Altitude Analytical Model • An analytical model of average ullage oxygen concentration based on inert gas added and altitude change was developed based on existing model • Model changed from sea level model to calculate mass of oxygen added and removed at each time step, assuming perfect mixing, in a single bay tank given a tank volume and starting oxygen concentration • Must input system performance (NEA flow and purity) in terms of time and altitude • Calculates ullage gas removed from tank due to increase in altitude (decrease in pressure) to calculate mass of oxygen decrease in tank • Calculates air entering tank due to decrease in altitude (increase pressure) to calculate mass of oxygen increase • The model is a relatively simple time step spreadsheet that calculates instantaneously AAR-440 Fire Safety R&D

9. Altitude Inerting Calculation Model Data Comparison AAR-440 Fire Safety R&D

10. Modeling Method – Scale A320 CWT • FAA built and performed tests in 50% scale Airbus A320 center-wing fuel tank • Made from plywood using drawings given to us by Airbus in support of joint inerting flight test • Scaled all structural members of tank inside down to the smallest detail • Mass flow controller and NEA mixer used to inert the tank in altitude chamber • Altitude oxygen analyzer used to track ullage with additional basic instrumentation AAR-440 Fire Safety R&D

11. Block Diagram of Scale A320 CWT Experiment AAR-440 Fire Safety R&D

12. Results - Scale A320 CWT Model • Results indicate that duplication of the flight cycle with the system performance in the altitude chamber was accomplished with coordination of test personnel • Measured scale tank oxygen concentration data illustrated good agreement with flight test results considering the large differences in measurement systems sample lag • Localized oxygen concentration dynamics illustrated some fidelity when specific sample location data were compared with similar locations in the flight test aircraft AAR-440 Fire Safety R&D

13. Full-Scale Data Compared with Scale System Performance AAR-440 Fire Safety R&D

14. Full-Scale Data Compared with Scale Model [O2] Results AAR-440 Fire Safety R&D

15. Local Full-Scale Measurement Compared with Scale Data AAR-440 Fire Safety R&D

16. Results – Comparison of Analytical & Scale Models • Performed mock trade study of system sizing with both scale and analytical models • Studied effect of decreasing the size of the system by 25% and 50% • Used the previous discussed Airbus v1972 Test Descent • Data trends compared well as did the peak and resulting values with exception of peak 75% system performance (off by 1%) Modeling Data for System Size Comparison Ullage [O2] for Airbus v1972 Test Descent AAR-440 Fire Safety R&D

17. Summary • Simple calculation models of average ullage oxygen concentration have been developed and can duplicate single bay flight test data in a fairly accurate manner • Requires no unique engineering skills • Very easy to develop and modify for a wide variety of flight cycles, OBIGGS capabilities and ullage conditions • Scale models can be tested with an altitude facility in a relatively cost effective manner to give good agreement with flight test data • Some specialized instrumentation and facilities needed • Provides some ability to analyze internal flow dynamics AAR-440 Fire Safety R&D