Description:

Some motors are difficult to build with just the technology available to a hobbyist. I therefore decided to acquire a completely assembled model of the Rupp engine (an open cycle hot air engine) from Hermann Schmidt. 
The initial reply was: "It's no longer in stock". After a while I received an e-mail notifying me that the Rupp engine was once again available. I was thrilled! 

The engine keeps running happily. I just love that deep plopping sound of the warm air being periodically released...