Cesar Gomez

There is a need to clarify the wire flammability compliance requirements specified in the latest amendments of Title 14 Code of Federal Regulations and the Airworthiness Manual (CFR/AWM) for the detailed specification sheet MIL-W-22759/16. CFR requirements prescribe a 60 degree flammability test for the MIL-W-22759 specification sheet, while MIL-W-22759/16 calls for a vertical flammability test. Confusion lies as to which of the requirements should be followed. This technical note will show how the MIL-W-22759/16 specification sheet satisfies both flammability requirements.

John W. Reinhardt

This technical note presents the data from simulated aerosol can explosion tests while using bromotrifluoropropene (BTP) and pentafluoroethane (HFC-125) as fire suppression agents for aircraft cargo compartments. These explosion tests were conducted at below inert volumetric concentrations to determine the agent’s explosion attenuation performance. The tests were conducted inside a 402-ft3 pressure vessel. The collected data showed that BTP and HFC-125, at these below inert concentrations, enhanced the explosion (acted as fuel) instead of mitigating it.

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.