Here's a link to all his paper models. His Sterling engine isn't very efficiet, but does work well, though I doubt it could do much but turn over. It's impressive how he hooks a balloon to the V-8 model and it acts as an air pump. There are many different motors in the link below. You actually get more efficient work from the air going through that motor by being metered than it just blowing out of the baloon! Good find. He's been doing this stuff for 5 years now, and they are getting better and better.