Hot air was used as a power source for many years beginning in the early 1800s, Dave says.
"These engines were run by heating the air that's trapped inside the engine. The displacer in there moves the air from the hot side to the cold side, so when the hot air expands, it pushes the piston out," he explains. "Then, when the displacer moves the air to the cool side, the air cools and creates a vacuum, which pulls the piston back in. The big ones work the same way, only in bigger scale."
Another model engine Dave is making is of a Lake Breeze fan powered by hot air.
How To Do It
"When you're going to build models," Dave says, "they suggest starting out by making larger-size models before the smaller ones, so you get an idea of how to do it, I suppose. But I didn't have any problems making that small Associated, probably because I've worked in a machine shop for over 30 years already, so things that would have been difficult for others probably weren't for me, because I've already done them. The biggest hurdle for a lot of people would be getting parts machined or machining them themselves. You've got to know the machining tools and how to use them."
If not, things can go wrong. Even with Dave's experience, he still makes mistakes.
"I have my 'oops' pile. Fortunately, all the casting models that I've gotten so far I haven't had to go out and purchase another casting because I made an 'oops' on it, because my 'oopses' hap- pened to be fixable," he says. "So I'm kind of lucky. But I've had other parts I've made for them, made from steel or brass or whatever material I was using, and I made a little 'oops' on them, and threw it into the dump and started on another one."
In order to make a model, Dave says you either have to make the castings for the engine yourself, or purchase raw, unmachined castings. "Then you proceed to machine them, making spaces for where the crankshaft goes, and where the cylinder goes, depending on what kind of casting it is, and how many pieces of casting there are."
Castings for one model won't work for another model, he says, because each model calls for something very different. He did try making his own castings in aluminum once, he says, but not with great success, so now he leaves that to others. Most castings for the engines are made of cast iron, or brass or aluminum, he says.
"I don't see much of the cast steel, as far as the models go." After the castings, "You have to drill the taps for the bolts, make the piston - on the 'Little Brother', the guy who made the castings sent me a chunk of aluminum for the piston, with high silicone content so it would wear a lot longer. But with some of the engines, you get just the castings, and whatever other pieces you need - like the gears - you either make them out of pieces of aluminum or steel or brass or whatever material you need, or else you buy them."