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Alyn Robinson Hot Air Engine

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I am building the Alyn Foundry Robinsin hot air engine. Everything to this point has been done "by the book" if you will, but I do not like the heavy cast iron hot end (displacer cylinder). I am making one out of thin stainless tubing, with a copper bottom to put the heat into the cylinder and not up into the engine. Has anyone else replaced the cast iron hot end?  Brad Smith, Franklin, Wisconsin

Ian S C:
Brad, I would make the hot cap by making a stainless steel cup by TIG welding a stainless disc on the end of a bit o thin walled stainless tube, foreget about the copper base. The stainless hot cap can be run at red heat, and will last for years.
Ian S C

I seem to remember from the long thread about these engines that Graham reported that one of the best runners worked with a thin CI bottom and ran off a small tea light (candle) so can't see why copper would be needed. With his own engine being able to run all day at rallies there would not seem to be a problem with excess heat getting into the top half of the engine so don't know what you would gain by going for the less conductive stainless steel in place of the cast iron.

As you are new to the forum you may not have seen the thread started by Graham about his engines but worth a read.

Alyn Foundry:
Good morning Brad.

Welcome to MEM.

I'm intrigued, one of my kits in Wisconsin, wonderful. How did you get it?

The Robinson is as true a replica as we could make it. The original used a cast Iron " hot pot " as I call it and it works very well.

Thanks to Jason for posting a link to my thread you should be able to follow a couple of recent builds.

Sadly a lot of kits by other suppliers used Aluminium which, as you know is highly conductive. The heat is rapidly transferred to the " cold end " and they cease to function. Being of " all Iron " construction ours doesn't suffer the same fate. I used to demonstrate my kits at various Steam rallies here in the UK and the Robinson would run all day long. It would bring the cooling water up to the boil over a period of time and continue to run. I personally think your concerns are unwarranted.

There was one modification that I did on later engines. The drawing shows the " O " ring nearly fully embedded in the platform casting. On later builds we opted to reduce the depth of the groove in both the platform and hot pot castings. This physically separated the metal parts and the " O " ring became the thermal barrier.

I'm sure all the interested members would love to see some photos of your build, please feel free to post them in the thread, linked above.

Cheers Graham.

Thank you, guys. First, how do I post a pic????? Yes, I am new to posting on the forum and I think I have a lot to contribute. I specialize in building high efficiency Stirling engines. This will be my third Robinson engine. I love the Robinson design. Without the regenerator in the displacer piston, the engine won't run well, unless one extends the displacer cylinder to a ridiculous length, as was done with the Westbury Robinson years ago. More on that later.

I have recently acquired a 55kw Stirling generator (75hp engine) and hope to get it running. Last weekend, we were running a 5 watt experimental Stirling. But these are not models and this forum is about models.

I have used both the SS hot cap and the SS tube with the copper bottom. While both work very efficiently, the copper bottom exceeds the SS cap in efficiency. This time, I am going to inset the thin copper disc to trap the heat from the flame, as Robinson did.

For efficiency in the 1970's, in the US, I used a displacer made out of manmade pumice stone, which works well in combination with the copper bottom hot cap. However with a steel hot cap, much more heat has to be applied which causes the pumice stone to crumble. My Ericsson, Esses and Denny engines from that period are still running fine. You probably know the pumice stone as a grill cleaning stone. It weighs nothing and actually acts as a slight regenerator. Because of the heat factor, I no longer recommend the pumice stone. I used to sell Bremen engine kits and supplied the pumice stone block. We call it "stinky stone" from the smell given off during machining.

Graham, I have looked for this kit for years and found one on British eBay. A friend of mine in the state of Oregon had an unbuilt kit and I am not sure where he got it. There used to be someone in the state of Washington who sold your kits and has a "barn full" of them, but was unwilling to look for a Robinson hot air engine for me. 

Brad Smith Franklin, WI


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