2X Scale Moriya Hot Air Fan

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Stirling engines fascinate me, so when son Tad asked me to help with his Moriya,* I got the bug to make one for myself.

The Moriya's cold end is machined out of a chunk of aluminum. I didn't have the size needed, but I did have a piece of 3-inch thick aluminum plate that I'd gotten from Boeing Surplus in Seattle. That thickness was exactly twice the size needed for the Moriya, so, the obvious thing to do was to make the whole thing 2X size.

Here is a picture of the partially completed unit. I worked on it through the winter months and got this far by the time spring and yardwork stopped further progress.

To give you an idea of the size, the railing is 32-inches high. The fan blades sweep an 18-inch circle.

* The Moriya is a Stirling engine powered fan designed by Dr. James Senft, University of Wisconsin, River Falls.

The Stirling engine is a hot air engine designed by the Reverend Dr Robert Stirling in 1816.

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Dr. Senft's design doesn't call for counterweights, but with doubled dimensions, the reciprocating masses will weigh 8X the original. I used a balancing method found in the November 1989 issue of Live Steam magazine and it gave very good results.

Dr. Senft's design called for the power cylinder to be turned from a single piece of bronze. Scaled up, that would have been very costly, so I Loc-Tited the cylinder to a mild steel flange.

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It pays to hang on to scrap. I found a really scarred piece of brass plate at a salvage yard. It cleaned up, nicely, to make the fan's spider.

I couldn't find sheet brass wide enough to accomodate a double-wide blade, so the shape was a compromise. Hobby shop brass provided the raw material. I stuck four sheets together with double-sided Scotch tape and cut them out on my band saw. It took surprisingly little filing to clean them up.

The big job turned out to be getting them unstuck. Not wanting a disaster, I used too much tape. It took a long soaking in kerosene to soften the adhesive.

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The original design called for solid triangular plates for the crankshaft supports. At this size, they would have blocked too much air flow, so I took a cue from Jerry Howell and cut them out like he does.

About half of the materials came out of the scrap bin, even the graphite for the piston.

The engine started right off the first time I tried it; but, it seemed to require more heat than it should. Eventually, I found a crack in the weld at the end of the hot cap. After repairing it, the fan runs nicely from the heat of an alcohol lamp. If I really want to show off, I'll run it on the heat from a birthday candle.

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The Moriya languished, unfinished, in my cold and damp welding shop gathering dust, rust and corrosion for two years. Then, an event came up in which I needed something new to show. Right fast, I got busy and built the fan guard and burner assembly.

There's no incentive like saving face for gettin' the job done. ;-)

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Most of our shows are held outdoors, making it nearly impossible to run this style of engine without some kind of flame guard. A small Coleman "globe" seemed to be about the right size. The bottom of a seamless tuna fish can was an exact fit for the top cover. Another can with a bottom seam made a perfect bottom support.

The burner is an alcohol lamp bought at auction for $5.00. The stand and globe support is made out of the wire frame from a "vote for" political sign.

The font holds enough denatured alcohol to keep the fan spinning for 14-hours.

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Building the fan guard was the fun part of the job. The micrometer could stay in the drawer!

A jig made out of lengths of pipe and a board made sure all the wires looked the same. I didn't count on getting so much "spring-back" after bending, so they turned out a bit longer than planned. No problem. By making the center smaller, the overall size of the guard came out just right.

I brazed all the joints. Paint doesn't like to stick to bronze, so I roughed it up in the bead blast cabinet. Check back in a few years to see if the paint has flaked off.

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I owe a thank you to Dave Otto for construction details. I studied pictures of his Moriya's guard and copied a number of his features, such as how to attach the guard to the bearing support.

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Revised -- 1/18/07