To mention some alternative fuel projects, Tu-155 - a liquid hydrogen-powered version of Russian Tu-154 - was flight-tested as early as 1988. Mi-8TG, a Russian helicopter converted to LPG, was ready for mass production, but never made it for lack of orders. In Brazil, where alcohol has been used as car fuel for quite some time, they are testing it now as aircraft fuel. And of course, hemp or rape oil can be converted into diesel or turbine fuel; some testing has been done but there's a lot more to do...