# Presentation: 518531

## Composite and Aluminum Wing Tank Flammability Comparison Testing

- Steve Summer	                               William Cavage                                     Federal Aviation AdministrationFire Safety Branch

- International Aircraft Systems Fire Protection Working GroupLondon, UK                                       April 2-3, 2008

## Outline

- Overview
- Test Apparatus
- Wing Tank Test Article
- Environmental Chamber Testing
- Previous Wind Tunnel Testing Results
- Wing Tank Test Article Planned Testing
- Preliminary Results
- Environmental Chamber Tests
- Planned Work

## Overview - Background

- Recent FAA rulemaking and regulation has focused on improving the safety of the fleet through more thorough systems analysis and ignition source reduction
- FAA proposes to make a rule requiring limits on flammability of some or all CWTs with an emphasis on inerting system technologies
- Next generation aircraft scheduled to enter service in the coming years have composite skin that could change baseline fleet wing tank flammability
- Logic assumes composite wings will be more flammable as they reject heat less effectively compared to aluminum
- Could also absorb more heat and/or transfer heat more readily to the ullage

## Overview:  Wing Tank Flammability Parameters

**Flammability Drivers on Ground**
- Top skin and ullage are heated from sun
- Hot ullage heats top layer of fuel, causing evaporation of liquid fuel
- Bulk fuel temperature however, remains relatively low

**Flammability Drivers In Flight**
- Decreasing pressure causes further evaporation of fuel
- Cold air flowing over the tank causes rapid cooling and condensation of fuel vapor in ullage

- These concepts were observed during previous testing and reported on recently (see rpt #DOT/FAA/AR-08/8)
- Now want to now compare flammability progression in a wing fuel tank test article with both aluminum skin and composite skin

## Test Apparatus - Wing Tank Test Article

- Had wing tank test article made from previous test article
- Has interchangeable aluminum and composite skin panels on top and bottom and an aerodynamic front shape

- Has vent and extensive array of thermocouples used for this testing as well as gas sample port for THC analysis

## Test Apparatus - Environmental Chamber Testing

- Used recently made wing fuel tank test article in altitude chamber to compare Al and Composite Flammability
- Did two identical tests, one with each skin, with 90 deg F ambient temperature, moderate top heat, and average F.P. fuel

- Measured skin, ullage and fuel temperature progressions over 5-hour period

## Previous Wind Tunnel Testing Results

- Previous testing of a 727 wing section mounted in the low speed section of the wind tunnel (along with other flight test data showed:
- that even low speed aerodynamics at ambient pressures will cause a rapid decrease in flammability
- that this cooling effect greatly overpowers any effect due to depressurization
- similar decreases in flammability whether heat was applied to top or bottom of the tank
- that fuel temperature in bottom heated tests decreased much more rapidly than in top heated tests
- little change in results seen when wing was pitched at 15° relative to the wind direction
- that cross-venting of tank resulted in a rapid decrease of tank flammability

## Wing Tank Test Article Planned Testing

- Tests in a similar manner to the 727 tests will be conducted with the tank that has been used in the altitude chamber
- Tank is currently being mounted in ***high-speed*** section of wind tunnel *(this will allow us to conduct tests at much more realistic wind speeds)*
- Testing will be conducted under varying fuel loads, fuel temperatures, and wind speeds to evaluate variation in cooling effects and its impact on tank flammability
- In addition, tank heating will be varied by applying heat both to the top and bottom of the tank
- Tests will be conducted with both aluminum and composite top skins to provide a comparison of composite vs aluminum tank flammability

## Preliminary Results - Scale Tank in Altitude Chamber

- Testing shows large increases in flammability with composite wing fuel tank skin not seen with aluminum skin when heated from top during ground conditions
- Used same heat source, fuel flashpoint, and ambient temperature on tank with both skin surfaces
- When bringing the fuel tank to altitude and dropping the temperature, spike in flammability occurred for both
- This is not representative of a wing fuel tank ullage because flight conditions not simulated
- Conditions not simulated with good fidelity (different conditions)
- Preliminary data suggests center-wing flammability would not be affected significantly

## Altitude Chamber Testing – Flammability Comparison

## Altitude Chamber Testing – Flammability Comparison

## Planned Work

- Fuel tank is currently being mounted in the wind tunnel
- Once installed and all instrumentation has been checked, testing will begin, starting with composite skin
- Testing should commence within the next 2-3 weeks and is expected to take 6-8 weeks to complete