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6 Cylinder Radial Air Engine

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Canuck75

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Have not made a model engine before so looked at compressed air engines an the Net and thought I would start with a simple single cylinder oscillating model. Soon had grander ideas and settled on a 6 cylinder double acting radial. Bore and stroke is 3/4" by 1" with 1/4" dia rods. Flywheel is 6" by 1" with 1/2" spokes and bored for a 1/2" shaft. Crankshaft is 1/2" CRS running on 2 sealed ball bearings with the connecting rod throw and counterweight made from 2-1/2" CRS with the 1/4" pin at max offset. This left a large enough area for a counterweight to roughly match the collective weight of the connecting rod bottom ends. Cylinders are all on the same plane so made 6 rod bottom ends .600" wide and then milled each to leave a .090" tang stepping across so all the rod ends mounted on the same throw with a little slack between but kept the same centreline plane. There is no "master rod" and are thus just mounted on the crank pin in clockwise order. Then made 2 plates which are sandwiched together with a sturdy gasket between. Milled an intake manifold in the rear of the front plate with runners to the intake ports. likewise, an exhaust manifold was milled into the back plate with runners to the exhaust ports with the gasket breached at the appropriate places to get to the exhaust ports on the cylinders.
Was a lot of fun making it and it starts easily, With 6 double acting cylinders at 60 degrees there is lots of oomph to get the crank turning. It runs well and I get about 1750 RPM with the air volume available from my little compressor. Runs smooth at full RPM so my guess at the counterweight size was okay. One interesting side result is that if the air supply is cut off suddenly there is a "Jake Brake" effect which rapidly stops the engine. Here are some pics and a short video.

Have now started a V8 compressed air engine.

Cheers

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Dabbler

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did you use someone else's plans or did you design it yourself?
 

Cooter Brown

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WOW! This is impressive work.... You did an amazing job on that engine.... Runs great!
 

Canuck75

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The radial design is mine and was influenced by the materials available. Didn't want to use a master rod idea so the only problem was figuring out the shape of the rod bottom ends. They needed to fit on one pin and not interfere with each other, that was a bit of trial and error, otherwise it is just an oscillating cylinder engine x 6. Interestingly the flywheel is hub, spokes, and rim, and when pressed together self centered to .004". I batted it about a bit and got .002" and then just skimmed it to run true and then did the centre bore, that was a relief. Anyways, glad you enjoyed it and thanks for your comments.

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