Hi, If you own a technical interest, take a look at this patent from 1951. [URL]http://www.guzzitech.dk/07/07-10/07-10_e.htm[/URL] You'll find drawings and an explanation to how it works – it's actually quite brilliant made, but there's probably a reason why it never was used widely. Regards Jens [URL="http://www.guzzitech.dk/english"]www.guzzitech.dk/english[/URL]