An unconventional approach to aircraft safety that incorporates fluids that thicken under impact is being tested
An international team of scientists has incorporated a shear thickening fluid (STF) into a bag to protect planes from bombs in passenger luggage.
The bag, named the Fly-Bag, is designed to be filled with passenger luggage and then placed in the hold. Then, if there were a bomb in the luggage somewhere - and it exploded during the flight - the resulting blast would be absorbed by the bag, preventing damage to the plane.
STFs are unusual in that they increase in viscosity in response to impact. It is possible to make a simple STF from cornflour in water: if you get the quantities right, you can roll it up into a ball that will bounce on hard surfaces but return to a fluid as soon as it is left alone. In general, STFs are colloidal systems that are dispersions of hard particles in a liquid. Under normal circumstances, the particles repel each other slightly. But under sudden impact, the extra energy in the system overwhelms these repulsive forces, causing the particles to clump together in structures called hydroclusters, which bump into each other thereby thickening the fluid.
There is significant commercial interest in the non-Newtonian behaviour of STFs, which have been used to improve items of body armour designed to protect the wearer from bullets, knives and other weapons.
For the Fly-Bag, the STF is coated onto the yarn of the fabric, explains team member Jim Warren from the University of Sheffield in the UK. As the fabric comes under strain, shearing forces between the yarns cause the STF to thicken, temporarily increasing the stiffness of the fabric. He adds that the precise composition of the STF is a trade secret.
Bombs hidden in passenger luggage are not a new threat. Hardened luggage containers (HULD) have been developed, but they are heavier and more costly than conventional equivalents and only suitable for wide body aircraft.
Warren says the team expects certification of the Fly-Bag to take one to two years. Cost would depend on a range of variables, including the structure of the plane, he adds.
The Fly-Bag project was funded with €2.2 million (?2 million) of EU money.