# Presentation: 125596

## Flight Testing of the FAA OBIGGS On the NASA 747 SCA

- William CavageAAR-440 Fire Safety BranchWm. J. Hughes Technical CenterFederal Aviation Administration

- International Systems Fire Protection Working Group Place de Ville Tower C  Ottawa, Canada February 14-15, 2005

## Outline

- Background
- Goals and Objectives
- System Architecture
- OBIGGs Installation
- Instrumentation and Summary of Testing
- Results
- OBIGGS Performance
- Fuel Tank Inerting
- Summary

## Testing Goals and Objectives

- Study the FAA dual flow methodology as well as a variable flow system methodology and expand upon existing system performance data
- Develop/validate system sizing data
- Validate previous in flight inert gas distribution modeling done by FAA
- Additionally study CWT flammability in flight (not discussed in this presentation)

## OBIGGS - System Architecture

- Uses Air Separation Modules based on HFM technology
- Accepts hot air from aircraft bleed system
- Cools, filters, and conditions air using heat exchanger air from external scoop
- Air is separated by ASMs and NEA is plumbed to output valves to control flow
- OEA is dumped overboard with H/X cooling air through dedicated scoop under aircraft on pack bay panel
- System configured  to operate in a dual flow methodology for some tests and a variable flow methodology for others
- Prototype OBIGGS components wired to a system control box by a single cable

## OBIGGS - System Installation

- System installed in empty pack bay area by FAA as designed by Shaw Aero Devices with the System Interfacing
- Mounted with 6 brackets to the fairing super structure
- Gets bleed air from small T put in 8” main bleed duct
- NEA deposited in bay 6 of the compartmentalized (6 bays) CWT with no cross-venting in tank (vent system half blocked)
- Two exterior panels replaced with FAA test article panels which have the H/X scoops installed
- System controlled by box in cabin
- Manually controlled ASM air temperature

## FAA OBIGGS Installation Drawing in 747 Pack Bay

## Photos of FAA OBIGGS Installation on 747 SCA

## Instrumentation and DAS

- OBIGGS system pressures and temperatures same as in previous testing
- Eight sample locations within the CWT in six different bays

- FAA (OBOAS) utilized
- Aircraft altitude measured by pressure transducer
- Measured flammability of CWT and #2 wing tank
- Laboratory DAS utilized
- Simple out-of-the-box solution

## Instrumentation Racks Mounted in NASA 747 SCA 

- FAS Rack

- NDIR
- Analyzer

- OBOAS

- DAS Rack

- Existing Power
- Distribution Rack

## Flight Test Plan

- Operated system in dual flow configuration for first test and in variable flow configuration for remainder of testing
- Did a series of 7 flight tests ranging from 2 to 5 hours totaling approximately 30 hours of flight time
- Validated the two-flow mode methodology and studied maximizing system flow during top of descent
- Studied effect of CWT fuel on inerting and demonstrated the ability of a system to reduce the flammability exposure of an aircraft
- Examined the effects of long cruise times on system performance
- Examined existing fleet flammability with baseline flammability testing

## 747 SCA Results -  System Performance

- System performed as expected with predictable ASM dynamic characteristics

- Less bleed air pressure in cruise and greater deviations
- The data does not indicate deviations  decreases the system efficiency

## 747 SCA Results -  System Performance

- Correlation of pressure and flow for low flow mode as expected with test 1 data slope deviating from test 2 and 4 slope somewhat

- Probably an indication of system being operated (warmed up) before start of flight test
- As fiber gets warmer it becomes more permeable but more selective

## 747 SCA Results -  System Performance

- Correlation of pressure and flow for high flow difficult to see because of constantly varying ASM pressure
- Some data illustrates excellent correlation because of the stabilization of system temperature

- Other data illustrates wide range of results probably due to constantly changing ASM  conditions due to jockeying ASM pressure
- Delays in [O2] Instru-mentation make this even more difficult

## 747 SCA Results -  Fuel Tank Inerting

- Evolution of oxygen concentration from bay-to-bay typical of previous scale model and ground testing
- Oxygen concentration spike in bay 1 greater than in modeling exercises (spiked to 19.5%)

- Obtaining higher NEA flows with a wider orifice (variable flow valve) at the top of cruise more difficult than anticipated due to high back pressure on NEA output at times

## 747 SCA Results -  Fuel Tank Inerting

- Resulting ullage oxygen concentration about 11%
- Average spiked to 13.5% oxygen by volume
- Descent had a 10 minute hold

## 747 SCA Results -  Fuel Tank Inerting

- Comparison of average ullage oxygen concentration for 4 tests with different descent profiles that have similar features

- Main parameters that effect the average ullage oxygen concentration are descent time and change in altitude

## 747 SCA Results -  Fuel Tank Inerting

- Comparison of peak worst bay (bay 1) oxygen concentration for same 4 tests illustrates very similar relationships

- Average peaks correlate directly with worst bay peaks in oxygen concentration
- Worst bay peak tends to be sensitive to average peak oxygen concentration

## 747 SCA Results -  Fuel Tank Inerting

- Comparison of oxygen concentration distribution for same 3 tests with similar descent profiles illustrates pattern

- Have to extrapolate test 1 because does not have 42 min descent
- Greater flow tended to allow better distribution but had little if any effect on the resulting oxygen concentration

- 46 Min
-  Descent

- 42 Min
-  Descent

- 42 Min
-  Descent

## 747 SCA Results -  Fuel Tank Inerting

- Worst bay [O2] goes from 13% to 12% in one hour
- After 3 hours band of oxygen concentration is about 1%
- Increase in average ullage [O2] probably not real

- Increase in average
- ullage [O2]

## 747 SCA Results -  Fuel Tank Inerting

- Tank oxygen concentration change overnight illustrated expected results

- Overall average ullage oxygen concentration rose about 1%
- Bay oxygen concentrations completely equilibrated

- Line does not reflect
- Expected trend

## Summary

- Lower ASM pressures will give less NEA production from OBIGGS but wide varying system aircraft parameters had no noticeable adverse effect on the resulting system performance
- Increasing flow during the bottom of descent (variable flow valve) had little effect on the resulting oxygen concentration but did increase inert gas distribution in a compartmentalized tank

## Summary

- Dual flow methodology allows for relatively small OBIGGS, when sized correctly, to provided complete flight cycle protection for virtually all expected commercial transport airplane missions
- Inert gas distribution accomplished easily in single bay tank while differences in multiple-bay tank [O2] tend to equilibrate readily
- Fuel load effected ullage oxygen concentrations very little if at all
- Proper sizing of inerting system will tend to minimize peak worst bay oxygen concentrations in multi-bay CWTs
- Inert gas dispersion from CWT during long ground operations and overnight sits does not appear to be a problem