John W. Reinhardt, Dung Do, and Jason Fayer

This report provides temperature data that could be used to establish the ultimate tensile strength (UTS) loss of candidate engine mount materials after been exposed to a standard flame for 5 and 15 minutes. The materials tested included 4130 steel (baseline),15-5 PH steel, titanium 6A1-4V, Inconel 718, and aluminum 7075. These materials were instrumented internally with thermocouples and exposed to the standard flame. MIL-Handbook-5H provides some data with regards to the UTS loss of these materials while heated, but additional strength tests must be conducted to account for the higher temperatures experienced by these materials while exposed to the standard fire.

Jill Suo-Anttila, Walt Gill, and Louis Gritzo

Federal regulations require that aircraft cargo compartment smoke detection systems be certified by testing their operation in flight. For safety reasons, simulated smoke sources are permitted in these certification tests. To provide insight into smoke detector certification in cargo compartments, this research investigates the morphology, transport, and optical properties of actual and simulated smoke sources.

Experimental data show the morphology of the particulate in smoke from flaming fires is considerably different than simulated smoke. The particulate for all three different flaming fires was solid with similar morphological properties. Simulated smoke was composed of relatively large liquid droplets, and considerably different size droplets can be produced from a single simulated smoke machine. Transport behavior modeling showed that both actual and simulated smoke particulate are sufficiently small to follow the overall gas flow. However, actual smoke transport will be buoyancy-driven due to the increased temperature, while the simulated smoke temperature is typically low and the release may be momentum-driven. The morphology of the actual and simulated smoke were then used to calculate their optical properties. In contrast to the actual smoke, which is dominate by absorption, all the extinction for the simulated smoke is due to scattering. This difference could have an impact on detection criteria and, hence, time for photoelectric smoke detectors, since they alarm based on the scattering properties of the smoke.

Jill Suo-Anttila, Walt Gill, Carlos Gallegos, and James Nelsen

Current regulations require that aircraft cargo compartment smoke detectors alarm within 1 minute of the start of a fire and at a time before the fire has substantially decreased the structural integrity of the airplane. Presently, in-flight tests, which can be costly and time consuming, are required to demonstrate compliance with the regulations. A physics-based Computational Fluid Dynamics (CFD) tool, which couples heat, mass, and momentum transfer, has been developed to decrease the time and cost of the certification process by reducing the total number of both in-flight and ground experiments. The tool provides information on smoke transport in cargo compartments under various conditions, therefore allowing optimal experiments to be designed. The CFD-based smoke transport model has the potential to enhance the certification process by determining worst-case locations for fires, optimum placement of fire detector sensors within the cargo compartment, and sensor alarm levels needed to achieve detection within the required certification time. The model is fast running, allowing for simulation of numerous fire scenarios in a short period of time. In addition, the model is user-friendly since it will potentially be used by airframers and airlines that are not expected to be experts in CFD. Following verification of this CFD code, full-scale experiments have been initiated to aid in the validation of the code and gauge the reliability of using such an approach to increase the efficiency of the aircraft fire detection system certification process. This document includes a description of the CFD model, the pre- and postprocessor, and the inital baseline validation results.

Steven M. Summer

This report discusses experiments to determine the reduction in oxygen concentration required to prevent a fuel tank explosion. A simulated aircraft fuel tank containing JP-8 fuel of an amount equivalent to a mass loading of approximately 4.5 kg/m3 was used to determine the limiting oxygen concentration (LOC) at pressures corresponding to altitudes ranging from 0 to 38 kft. In addition, the peak pressure rise was measured at various altitudes (pressures) due to ignition occurring at O2 levels approximately 1% to 1.5% above the LOC.

A wide range of ignition sources were used throughout the testing. An oil burner transformer connected to an analog timer provided a low power arc of both short (0.1 second) and long durations (1 second), a spark igniter taken from a J-57 engine provided a very short duration (175 µseconds) high powered spark, and a heated metal block was used as a hot surface ignition source. These varied capabilities allowed for an evaluation of the variation in the LOC due to a specific type of ignition source.

From these tests, it was determined that the LOC at sea level through 10 kft is approximately 12% O2, while exhibiting a linear increase from 12% at 10 kft to approximately 14.5% at 40 kft. Tests with various sparks/arcs as ignition sources at sea level showed little variation in results, with the LOC ranging from 12.0% to 12.8%. Also, a heated surface capable of igniting a fuel air mixture proved insufficient for ignition in a tank inerted to just 14%. Peak pressures resulting from ignition at oxygen concentrations 1% to 1.5% above LOC values decreased as the altitude was increased to 30 kft, while the duration to reach the peak pressure increased.

Michael Burns and William M. Cavage

The Federal Aviation Administration (FAA) is planning a series of ground and flight tests with Airbus to prove the concept of a simplified fuel tank inerting system, which has been developed by the FAA. The FAA has also developed an onboard oxygen analysis system to measure the oxygen concentration in the aircraft fuel tank during the testing. To help ensure smooth integration and the safety of the testing, the FAA has documented the system description, interfaces, operation, and has performed a failure mode effects criticality analysis. This analysis attempts to identify the failure modes of each system component and assess the effects of these failures on the component, system, and aircraft. The analysis also applies a hazard category to each hazard as well as some hazard probability when it was deemed necessary by the author. Hazard controls are also listed.

All relevant system information has been summarized to allow for the system to be properly integrated into the proposed flight test aircraft. The results of the analysis indicated that most failure modes had no effect on the aircraft or other secondary systems. The few hazards with potential aircraft effects have significant controls in place to reduce the likelihood of the hazard and mitigate any potential hazard exposure.