Sunday, July 27, 2014

MODEL LEHMAN HOT AIR ENGINE

It was time for another model engine. This time I picked a Lehmann Hot air engine because it has such an interesting linkage motion.
The Lehmann engine was developed and patented in Germany, but the particular one I built the model of was manufactured in England by W H Bailey Co. under a license agreement around 1860.
Construction was carried out looking at an illustration that I copied out of a book. It is not and exact scale model, but a pretty close representation. At first glance it looks complicated, but is really a pretty simple engine.
To start I needed to find some tubing for the cylinder and displacer. I had a 5" long piece of tube from a Bimba air cylinder that could be used where the power piston operates, but it was not long enough for the hot tube, so I tried rolling up some sheet metal for that and also the displacer. When they turned out OK, I proceeded with the patterns for the castings.
I only needed to make patterns for the water jacket and stand it sits on. I was able to use a base pattern from previous models.
A graceful curved spoke flywheel like was used on the original German engines was poured, but I changed my mind and ended up using a straight spoke, round rim wheel like was used on the Bailey engines. Fabricating and machining proceeded a little bit each day until yesterday it became a complete and working engine.

video
 Except for the bolts and screws, it was built entirely from scraps, even melted down some old motorcycle parts for the castings. It turned out great and is one of my best running hot air engines. From what I've read about them, the original engines were some of the best. It has been a most satisfying project. Construction time approximately 5 weeks.



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