Gallery, Projects and General > Project Logs
The Return of No. 83, a Hot Air Engine
vtsteam:
Eighteen years ago for my father's 83rd birthday, I built a hot air engine using my own aluminum castings, skate ball bearings, a graphite piston, and many borrowings from my scrap pile. It was a very rushed 2 week project, since I had little idea of the complexities I was getting myself into. I worked long into the nights. Nevertheless I finished the little engine the night before leaving to see him, and got the bare engine to run, rather impressively, by heating the displacer cylinder over the kitchen stove. I quickly added a channel Iron base, a firebox out of square tube, and a smokestack out of a brass sink drainpipe. The firebox even had a door.
When visiting him a few states away, I brought a small can of Sterno as a heat source, and this fit into the firebox, and luckily was enough to power the engine as well, running steadily. All was well!
Because we had to return home the next day, I took some pictures of the engine on a rather fancy table. The engine was named "No. 83" in honor of my father's birthday. Those photos were all I had of the engine for many years, and I really regretted I didn't have more time to run it, improve it, and try out the many ideas I had as experiments. In fact the original intention was to run it with wood as a fuel, and the firebox and stack were built with that in mind. But that never happened.
Not to go into too many personal details but my father later had a bad fall, was hospitalized and sedated for a week, lapsed into partial dementia, and my brother, an heroin addict and ex-con, took over his life. My father passed away, and my brother took everything, including the little engine. That was the end of it, so I thought.
My nephew, a kind person, recently returned the engine to me after his father, my brother, had also passed. It had been 18 years. My brother had pronounced my engine non-workable after trying and failing to run it once for my father. He had no concept of what a hot air engine really is or how it works. After my father died, my brother had left No. 83 in the corner of a garage on the bare concrete to rust.
The .008" walled displacer cylinder had been overheated and ruptured. The fire door was missing. No. 83 was in sad shape.
vtsteam:
Of course, we're not going to leave it that way......
tom osselton:
Great story it will be nice to see it going again.
vtsteam:
Hi Tom! :wave: Done any casting lately?
I haven't, a lot my stuff is under tons of snow here which came off the open sided casting shed roof on top of the two feet we already had. A lot of it had drifted underneath. I just shoveled a lot of it out today. Hoping to cast something when this last bunch of ice and snow clears up more.
re. No 83: Well as a start, I cleaned the outer engine with mostly just soap and hot water and a 3M Scotchbrite pad. That felt a lot better!
Then I took apart the linkages, cleaned them and put them back together. No telling whether it will run again without replacing some of those parts. But for the moment I think I'll try with what I have.
vtsteam:
I had a piece of stainless steel tubing a friend had given me long ago -- I think it was from a sailboat stanchion. Anyway it measured on the OD the same as the ruined displacer cylinder. Probably the same piece of material I used for that one. I just don't remember. So it will be a natural fit into the engine -- I have about a foot and a half of that stuff left. So I cut off a piece the right length, and cleaned up the ends in the lathe, and then silver soldered another thin piece of stainless steel sheet to the outer end. Then I chucked it back in the lathe and bored it out to what the old displacer cylinder had been.
This is quite a bit thicker walled than the old one was. It's .047" while the older cylinder had a wall thickness of only .008" at the hot end! (The cold end was full thickness, also ~.047", so the mount in the massive bulkhead/heat sink will be the same).
Turning the hot end down that thin was very tedious. Eighteen years ago I had turned it between centers using tiny cuts. The cylinder had been jam-mounted onto a carefully turned oak dowel arbor, to give it support.
I'm anxious to see if the engine works, so I'm just going to try it as-is. I can always turn it down in thickness in future. I hope it will at least run okay without the thinning, just not at maximum efficiency. Or maybe it won't run at all, for this or other reasons. We'll see.....
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