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About a "Medium technology level" (not too high), feresenn with "today not too high level materials", Ive done a draft for a 5000 W engine.
I propose it to you.

- Alpha parallel architecture.
- One displacer, twoo motor pistons/cylinders.
Displacer dia 360 mm
Displacer stroke 260 mm
Displacement 26464 cm2
Motor piston dia 292,2 mm
Motor piston stroke 190 mm
The twoo motor pistons are considered necessary for better distribution of working fluid from refrigerator to cylinders, and also to allow adequate clearance downside the displacer to reduce the displacer pumping looses (being alpha, the downside of displacer is free of working gas, and have to be faced to outside.

Despite the compact architecture: the two cylinders are side by side, composed under the displacer, the engine (specifically sized for atmospheric, and for so very light) is higher than 1500 mm, wide 500 mm.
I'd like your comments, but please wait for answer, next week I'll be out home, this is however the scheme, (now I'm not able to post images):

D= Displacer
R= Regenerator
C= Cooler
M= Motor piston
A=Axis (three crankshafts)
- points are only for spacing...

.... DDD
.... DDD
...R....R
...R....R
...C....C
...C....C
MM....MM
AAAAAAAAAA

Ferraccio

Ferraccio, for an ALPHA motor with a 1:1 ratio between the hot and cold pistons, would you not be better with just a single cold cylinder. There would also be an advantage in reduced friction, and mechanical complexity. You can use a two crank crankshaft, or with a Ross Yoke, only a single crank is required. Or you could make a V shaped motor, again requiring only one crank. 5Kw is quite a big motor. Best wishes. Ian S C

Ian I do not agree,
the two cold pistons allow a perfect location, with almost reduced transfer ducts (dead spaces), which, in a large engine are really deadly (are feet of tubes!!!); with the frictions (already optimized) to have three rods is not detrimental, in fact is quite the contrary ... each motor cylinder bear 13000 cc !!!
I agree! It is a large engine! OK, If the linear dimensions are scaled 0.8 (multiply by 0.8), you get an engine power of approximately halved, ...if do it again you have halved again.
We aren't in a power-range that the friction of a bearing, if done properly, jeopardizing the operation: Instead so, loads on bearing are distributed, of course bearings have to be dimentioned....

Do you have considered how much are dead spaces in a V structure?
Using a single piston in a V structure (I think) become useless to do an alpha architecture, that is winner on Beta and Gamma for its quite inexistent dead spaces, (allowing pumping 1:1).

With all respect to Andy, that is genial, the Ross Joke is patented, and, in this case, with a single bearing, the loads are concentraded, with large dimensions (and light engine) the joke may be have to be balanced, and this is another patent I think...
Ciao,
Ferraccio

Ian,
In Ross Joke the motor piston stroke is smaller than the displacer one; with smaller stroke is necessary larger diameter of piston to conserve 1:1 rapport.
The geometry of displacer and and piston is fixed in consequence, and so they (displacer and piston), also if parallel, (very good!) are quite spaced, and need however a duct to connect the working gas from cooler to the power piston;... is not a "tube" as in a V architecture, but is however a duct, with relevant losses and dead spaces.
Fer.

Ferraccio, with the V type motor, the tube connecting the two cylinders could be utillised as a chamber for a regenerator. True with the Ross Yoke system you can have different strokes on the pistons by using an assymetric yoke, this method can be used on an ordenary GAMA motor. Ian S C

Ian
Negative: I know that the tube (between) are used (in part) as displacer, but with diameters of 360 mm (but also a lot smaller...), you have to connect the circonference of the hot heat to the (lateral) tube-regenerator and then the tube-regenerator to the piston, this involves other tubes and ducts.
Using alpha shape with Ross linkage, the different strokes are at all allowable, becouse to obtain 1:1 displacements you can increasse the diameter of the piston.
The geometry (distance between axis) of the Ross linkage is however obliged, and is necessary a "duct" to connect both displacer and piston, this is (for me) the main problem in the search of the maximum efficiency using Ross linkage.
One way is to reduce the cooler, and transform the duct in function of integrative cooler (so is not a dead space additive), but is not constructively simple, and losses in lamination of gas, and losses in turbolences are not avoidable.
I note only that we are speaking about an engine more large and complex than "wire and can".

Excuse for all but, from now till 24 of September I'll not allowable to give answers. Bye
Thanks
Ferraccio

I correct myself: between is used as regenerator; (not displacer..sorry
F

Ferraccio,

That's a hugh engine. How are you going to pump/remove heat into/from the engine? If your target is 5kw at 1 bar, you are going to need are very large contact area for the heat exchanger. Assuming you are using air as the working gas, the heat exchange area would almost be 1 sq meter (again assuming you are more than doubling the tempurature and have a lot of convection) on the side in the engine.

Please note that an ALPHA motor doe's not have a displacer, the hot piston may have aHeylandt crown, a light weight (stainless steel) cap on top of the piston to insulate the piston from the heat of the hot cylinder. Its construction is similar to a displacer, but is attached to a compressive piston.
Further thoughts on the motor above, perhaps the design would be better with two hot, and two cold cylinders, they could then all have equal bore and stroke. With two Ross Yokes it would be quite compact, arranged in a square.
If you get thing right 5Kw should be attainable, some authorities consider that one watt per CC is possible from an atmopheric motor, mind you, you'll need quite a good fire, you only get out what you put in, minus what you lose to inefficiency (quite a lot). Ian S C

ian:

When you say 'atmospheric engine' - what does that mean? Does that mean 'unpressurized'?

Thanks
sam

Ian:

To clarify my question.. Is that 1w/cc for an unpressurized engine?

Thanks again
sam

Pretty much. 1w per cc of displace running on 1 bar air.

skunkworks, sorry I'v been away for a couple of days, yes atmopheric = unpressurised. As the pressure goes up, the power goes with it, not a mathimatition, so i can't say the comparasin between the two. Ian S C

Yes atmospheric is unpressurized; the engine runs with compressions and decompressions done by heat, when the average of pressions is the atmospheric.
Excuse my incorrect translation of atmosferic = atmospheric)
This challenge comes from the fact that someone, in forum, wanted a "real" power with an engine not-pressurized, ...and this is the result.
My proposal is clearly provocative, the engine, properly designed, even if everything is stacked, is five feet high.

Not being pressurized, thicknesses are thin, and therefore the weight of the engine would not be excessive, even if is massive.
If you reduce the linear dimensions by half, would have a power of one-eighth of that shown, and this is more ...human.

Ian: Of course the "displacer" has a ring sealing at the base, (in cold area, in upper refrigeration zone), and being "alpha" on the underside of the displacer, to avoid dangerous and unnecessary pumping losses, must be vented to the atmosphere.
Ferraccio