STUDY OF THE EFFECTS OF A PARTICULAR FUEL TANK FILLER IN CRASH ENVIRONMENT C. CAPRILE, G. JANSZEN, M. MORANDINI, A. FABBRI Dipartimento di Ingegneria Aerospaziale, Politecnico di Milano,Via La Masa 34, 20158 Milano ABSTRACT Data from a previous experimental work, carried out by the authors in the crash test laboratory of the Aerospace Department of the Politecnico di Milano, has been used to validate a numerical model of a fuel tank filled with water and with a particular aluminum filler. In that work several crash tests had been performed to analyse the behaviour of helicopter fuel tanks when filled with water and expanded aluminium foils. Accelerations and pressures had been measured to compare the behaviour of the tanks with and without this particular filler. Results of the previous work showed how the expanded aluminium foils (already known to be efficient passive explosion suppression media for aeroplanes fuel tanks) greatly reduce the leakage of the fluid in case of impact and subsequent failure of the tanks; a reduction of the pressure increment, caused by the movement of the fluid towards the impact area, has been noticed too. Besides these data, new experimental tests have been carried out to characterize the filler and its interaction with the fluid and the fuel tank. A porous model has been chosen to simulate this particular filler. Simulation of impact and leakage tests have been carried out showing the great capability of such a complete model to simulate different impact scenarios and to study the dynamics of both the fuel tanks and the filler when subjected to high decelerations or crashes. 1. INTRODUCTION Fuel tank explosion resulting from ignition of vapours by various means is a major cause of aircraft loss. Over the years, many concepts which seek to prevent or suppress such explosions have been explored. Among these a particular expanded aluminium foil has been investigated for several years by a performance and qualification test program to meet the Military Standard MIL-B-87162A (USAF). The purpose of the present research is to carry on the study of the effect of the filler on the fuel tank in case of a crash event started in a previous work (see ref. [1]). Failure of the tank or leakage of the fuel resulting in explosion of an aircraft would vanish the great efforts that have been made, in recent years, in the design of more crashworthy aircraft systems, with an eye to reduction of fatalities and serious injuries in survivable accidents. 2. EXPERIMENTAL RESULTS In the previous work tests were carried out using a deceleration sled facility of the Aerospace Department of the Politecnico di Milano. Several fuel tanks were driven against a rigid wall at the end of a test sled run. To perform the tests two wooden plates were mounted, one on the sled and one at the anvil impact area. Fuel tanks were put on the sled wooden plate, and left free to move forward during the sled braking phase (see figure 1). When the sled was at its final stop position the distance between the two plates was less than 1 cm, allowing a soft sliding of the tank from the first to the second plate. Two L shaped profiles were installed on both the plates to maintain the direction of the tank motion within a small angle. Acceleration and pressures were measured during the tests. Figures 2 and 3 show the comparison of the accelerations curves of the fuel tank and the pressures curves of the water measured during two of the several tests carried out with and without the filler. Comparison of accelerations as well as pressure time histories clearly shows how the presence of the filler help reducing peaks and loads on the structure. After the test residual deformations of tanks were measured by means of a laser distance transducer at different locations of the upper, lower and rear surface. Comparison of the deformed configuration (figs. 4, 5 and 6) shows that the tank with the filler has a lower final plastic deformation. 1