FLIGHT VIBRATION AND ENVIRONMENTAL EFFECTS ON FORMATION OF COMBUSTIBLE MIXTURES WITHIN AIRCRAFT FUEL TANKS
Final rept. 23 Jun 1969-31 Mar 1970
DYNAMIC SCIENCE IRVINE CA
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The objective of the study was to determine fuel tank vapor space characteristics for a simulated helicopter fuel tank and to evaluate the potential hazard which exists. Fuelair ratios were measured as a function of time and position within the ullage of the fuel tank for specified flight profiles. These results were compared to published flammability limits as a basis for assessing flight hazard potential. The flight profiles were simulated by withdrawing fuel at rated engine usage from a vibrating tank held at constant pressure and temperature. Parametric variations were made in fuel temperature 40 to 100F, flight altitude 0 to 15,000 feet, vibration environment, and fuel properties liquid JP-4 versus JP-4 emulsion EF4-104H. Another important variable not considered initially but which was uncovered during the course of this investigation was the effect that the rubberized tank liner could have on the measured fuelair ratios. The extent of this effect was found to be related to fuel temperature and exposure time of the liner to the fuel. The experimental results showed those ranges of the test variables which had a significant effect on the measured fuelair ratios. They also demonstrated that fuelair mixture gradients do exist in fuel tanks under flight conditions. It was found that tanks which would be considered safe as determined by calculations for equilibrium conditions actually contain flammable regions, even for level flight. An analytical model for the ullage space was written which included transient fuel vapor diffusion and convection which was brought about by venting of the ullage.
- Military Aircraft Operations