Application of Soft Porous Materials to a High-Speed Train Track

This paper explores the performance of an airborne jet-ski train that flies on a soft porous track within centimeters of the earth's surface at speeds approaching current commercial jet aircraft. The jet train employs a lift mechanism first described for red cells gliding on the endothelial glycocalyx and subsequently used to predict the lift forces generated in skiing and snowboarding by the transiently trapped air beneath their planing surfaces. Using an asymptotic analysis for large values of the permeability parameter H/root K-p, where H is the porous layer thickness and K-p the Darcy permeability, we first show that it is possible to support a 70 metric ton jet train carrying 200 passengers on a confined porous material if its K-p is approximately 5 x 10(-9) m(2). For this K-p one finds that the tilt of the planform is < 0.1 deg and the liftoff velocity is < 5 m/s. This value of K-p can be satisfied by a random fiber matrix with a fiber radius of 5 mu m and a void fraction of 0.995. Compression tests on a fiber-fill material with these properties show that the fibers contribute < 0.2% of the total lift at maximum compression, and hence, the friction force of the fiber phase is negligible. Using jet engines of 10,000 lbf thrust, about 1/5 that of a 200 passenger jet aircraft, one is able to obtain a cruising velocity approaching 700 km/hr. This would allow for huge fuel savings and greatly reduce greenhouse emission.