# Presentation: 897158

## Inerting a B-747 SP Center Wing Fuel Tank Scale Model with Nitrogen Enriched Air

**Inerting a B-747 SP Center Wing Fuel Tank Scale Model with Nitrogen Enriched Air**

## Outline

- Background
- Model
- Instrumentation
- NEA Distribution
- Equations
- Test Data
- Summary

## Background

- FAA is Seeking to Improve Upon Existing Fuel Tank Safety in Fleet in the Wake of TWA800 Air Disaster
- Inerting of Fuel Tanks Could Provide Significant Fuel Tank Protection.  Most Available Data on Fuel Tank Inerting for Rectangular Box
- Focus of the Testing is to Validate Existing Assumptions for Inerting Complex Geometric Spaces (Commercial Transport Fuel Tanks) as Compared to Simple Rectangular Boxes
- Also, Use Model to Determine the Most Efficient Deposit Configuration

## Description of Model

- Quarter-Scale Model of Boeing 747 SP CWT was Built from Three Quarter Inch Plywood By Scaling Drawings from Shepherd Report
- 24% length Scale (1.2% Volume)
- Spars and Spanwise Beams Simulated with Quarter Inch Plywood Installed in Slats with Scaled Penetration Holes
- Vent System Simulated with PVC Tubing Plumbed to an Aluminum Vent Channel Adhered to a Plywood Top
- Removable Lid to Allow for Model Maintenance and Modification

## Photo of Model

## Instrumentation

- Oxygen Sensor in Each Bay and in One Vent Channel
- Sample Returned to Each Bay to Have Minimal Effect on Inerting Process
- Sensors Plumbed in Unique Sample “Drafting”  Method
- Sensor Remote From Analyzer
- Thermocouple in Each Bay to Detect Temperature Changes During Testing
- NEA Generator Equipped with Oxygen Analyzer
- Calibrated and Checked before Each Test
- Used to Calibrate all Other Sensors

## B-747 SP Bay Diagram with Volume Data

- Dry

- 1

- 2

- 3

- 4

- 5

- 6

- Reported Volume   =  1775

- Percent Difference  = 4.47 %

## NEA Distribution System 

- “Variable Manifold” Allows for Depositing NEA in Any and All Bays of the Tank at Different Flow Rates
- Accepts Output of NEA Generator and is Plumbed to a Bank of Flow Meters
- Two Flow Meters in Parallel for Each Bay to Allow for Both Large and Small Deposit Quantities
- Measure Meter Back Pressure for Accurate Flow Reading
- Used Directing Nozzles on NEA Deposit Fittings for Some Uneven Deposit Cases

## NEA Distribution System Diagram

## Equations Used

- Volumetric Tank Exchange (VTE)

- Weighted Volumetric Average

- Inerting Solution (Perfect Mixing)

- Empirical Solution (FAA Ullage Washing Data)

## Cross-Vented Configuration Data 

- Inerted Tank Several Times with Different NEA Oxygen Concentrations with the Goal of Balancing the Flow into Each Bay to Obtain “Equal Inerting”
- Used the Volumetric Average Developed to Make Comparisons with Other Inerting Runs
- Results As Expected and Consistent with Previous Testing but New Numbers Point Toward a VTE of 1.6 for 95% NEA
- Depositing in and Uneven Manner Can Simplify Manifold and Have No Negative Impact on the Inerting Process

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## Blocked Vent Configuration Data 

- Inerted Tank Several Times with NEA 95% to Minimizing the NEA Volume Required to Inert the Tank with Left Half of Vent System Blocked (No Cross Venting)
- First did Balanced Run to Give Baseline;  Used the Volumetric Average Developed to Make Fair Comparisons with Other Methods
- Results Illustrated Modest Improvement with Simplest Deposit Scheme
- Deposit Scheme Has Poorer NEA Distribution But Data Indicates Oxygen Concentration From Bay to Bay Will Diffuse
- Method Does Not Appear to Be Sensitive to Flow Rate and NEA %
- Comparisons with Full-Scale Data Marginal, VTE Consistent

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## B-747 SP Scale Fuel Tank Inerting Data

## Summary

- This is Believed to be due to Better Measurement Techniques Developed
- Depositing in an Efficient Manner Can Greatly Simplify Manifold Design and Even Improve Inerting Efficiency
- Initial Full-Scale Test Article Data Highlight Potential Deficiencies with this Design Methodology.  More Testing Needed to Verify the Limitations of Scale-Model Inerting Evaluation