School Project questions

[jjohnson1]

so i am new to stirling engines, and had a few questions for the experts.

i am building a 3 inch diameter LTD engine, found some plans on youtube and modified them for the materials i have available to me.

• i am working with brass sheet stock for my engine case, will two sheets of 16 gauge sheet, soldered together work? or will heat retention be an issue?
• the displacer, i understand that a roughly 2/3 of the volume of the cylinder is ideal, but on a 3 inch outer diameter (so probably 2.75 inch inner diameter) does my secondary piston...the "power" piston according to my plans, need to occupy the same volume as the air inside the chamber?
• is there a easier alternative to point bearings for someone without a machine shop? i can try to build them by hand but i thought some one might know a better solution than hand sanding them.

thanks, for any help you can render, i hope this turns out well.

[Ian S C]

jjohnson,would I be right in thinking that your motor will be of the conventional LTD pattern ie., displacer of reasonably large diameter, and short (a disc), if so the top and bottom plates should be separated with an insulated section, make the cylinder wall from a bit of plastic tube (water pipe or something), transparent is good, perspex or similar. This reduces heat transfer from hot side to cool.
If you need to make points on the end of a shaft, do you have a drill press? If so you have a lathe, all you need is a fine file. If all you have is a hand drill, can you clamp it in a vise, then using a file you can point a small shaft. You could make the bearings from old brushes from an electric motor( an electric drill / angle grinder, or similar motor), they often come with a spare set, change them , and use the the old onesis how I would go.
My LTD is bigger, 6" dia, and I use ball bearings from a VHS recorder, but the carbon blocks would have much less friction. Ian S C

[jjohnson1]

yes its a traditional vertical cylinder design, large displacer and such. sorry if i wasn't that clear about that. i ran into another question last night while thinking about the power piston. is it important to have an air tight seal on the displacer cylinder? and can the power piston be made out of say aluminum? or is weight an issue with that piston? if so can it be offset by adding more counter weight on the fly wheel?

[Ian S C]

Some say aluminium is OK, but most aluminium alloys have a fairly high coefficient of friction, and unless treated do not make a good bearing surface. There is a teflon surface coating system that works well, another way is hard anodising. My LTD motor has a cast iron piston, made as light as possible (it's hollowed out), the skirt of the piston is just about 1 mm thick, and the crown 2 mm thick. The piston is 24 mm dia by 12 mm high. Ian S C