The Stirling Hot Air Engine is unique in that it requires no fuel or water to run. Just a heat source like the Sun. Invented by The Rev. Robert Stirling in the 1800's to operate large coal crushing batteries this model achieves 1000 rpm at the flywheel. It was built from Raw metal Stock from plans drawn by Edwyn Jones using a 7" Myford 7 lathe and an SX2 vertical milling mahine. Interestingly, it has two pistons, one operating at right angles to the other! (2012) see video of the running engine.