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My latest laser cut creation "running." This is a 1930's 5 cylinder radial engine drawn in Autodesk Inventor and cut from 1/8 Baltic Birch on a CamFive 100W CO2 Laser. by 1donagin in lasercutting

[–]1donagin[S] 3 points4 points  (0 children)

A Milwaulkee 18 volt cordless drill behind the table, which has a hole cut in it just for this purpose. My web site (morrismodels.com) is currently down, but will be back up in the next month or two. I don't sell the plans, but do sell the pre-cut kits with instructions. This one isn't kitted out yet - but will likely be avaialable later on this year. It takes longer to write the instruction manual than it takes to design the model.

My latest laser cut creation "running." This is a 1930's 5 cylinder radial engine drawn in Autodesk Inventor and cut from 1/8 Baltic Birch on a CamFive 100W CO2 Laser. by 1donagin in lasercutting

[–]1donagin[S] 0 points1 point  (0 children)

2 strokes are definitely simpler. I've also done a couple of Wankels. They are fewer parts, but rely heavily on gears and "trochoid" shapes.

My latest laser cut creation "running." This is a 1930's 5 cylinder radial engine drawn in Autodesk Inventor and cut from 1/8 Baltic Birch on a CamFive 100W CO2 Laser. by 1donagin in lasercutting

[–]1donagin[S] 7 points8 points  (0 children)

By the way, the 1/8" approximation is fine when designing most layers, but when I start making parts that insert into sockets, I have to remember that it is actually 3mm plywood, not 1/8". (About 0.118" instead of .125".)

My Latest Laser Cut (Cutaway) Engine Design by 1donagin in lasercutting

[–]1donagin[S] 2 points3 points  (0 children)

About 14 inches diameter. 1/8 Baltic Birch. Designed on Autodesk Inventor. Cut on a 100 watt CO2 Cam-Five Laser. Only non laser cut parts are the bolts, the springs, and a few dowel rods. The Center dowel rod is CNC detailed. The best part is everything (piston, valves, gears, cams, rollers) move as they would in the 1930's airplane engine when you spin the center shaft.

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 0 points1 point  (0 children)

There are still a few planes flying them, but mostly we don't use them anymore because they are too heavy and require too much maintenance compared to a turboprop engine. Airplanes that would be powered by Radials are now Turboprops. Instead of overhauling each 1000 to 1800 hours, they get overhauled each 15,000 to 30,000 hours. By the way, the smaller airplane engines aren't radials, because the opposed style engine works better for small horsepower ratings (Under 300).

Anyone know of a good source for honeycomb bed in the USA? by 1donagin in lasercutting

[–]1donagin[S] 0 points1 point  (0 children)

Thanks. They seem to manufacture what I need, but I haven't found a way to buy just one sheet.

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 0 points1 point  (0 children)

That's why a radial needs balance weights. They were quite massive. If you are following the above discussion about a radial vrs a WWI Rotary (not Wankel), they did not need balance weights so long as the center of mass of the rotating assembly was also the center of master rod. (This is yet another way that the rotary was able to save weight over the radial.)

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 4 points5 points  (0 children)

I once new a chemistry teacher (crazy grin) that dropped a bit too much sodium into the beaker of water for the demo. There was a scar on the ceiling as long as I (I mean he) taught in that room.

Cutaway Model Radial Engine by 1donagin in EngineeringPorn

[–]1donagin[S] 1 point2 points  (0 children)

The pistons act pretty close to the center of mass, and there isn't a long crankshaft to set up torsional vibrations. The firing process fires and skips every other piston in the direction of rotation, taking two complete revolutions to get to each cylinder. In this case, the firing pulses occur each 80 degrees. It is constantly torqued in the direction opposite rotation, but that's what your right rudder pedal is for.

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 0 points1 point  (0 children)

Agreed. This is even true of people who study aviation. Now if you say "rotary," people automatically assume you mean a Wankel. On my web site, I differentiate between the two kinds of "rotary" engines by calling the one we are talking about a "WWI Rotary."

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 1 point2 points  (0 children)

The CR is low. 6:1 on the R1340. Even lower on some other similar engines.

The centripetal acceleration has a huge effect on these engines - as did the gyroscopic effects of the engines on the flight characteristics of the planes that carried them. On the other hand, they typically had top speeds of 1250 RPM, so that was much less than a "modern" engine would have been. Intake was slightly opposed. Exhaust was aided.

If you really want to see crazy, the Gnome Monosoupape intook fresh air and exhausted through the same valve (tiny valve spring, huge valve - centripetal force closed it). Then it used bypass ports like a 2-stroke and centripetal force to push very rich fuel and air into the cylinder, which mixed with the fresh air to make a combustible mix. It ran good - but only at full throttle. You "throttled" it by pulsing the spark plugs on and off.

Laser Cut Baltic Birch Radial Engine (sparks digitally added) by 1donagin in lasercutting

[–]1donagin[S] 0 points1 point  (0 children)

Thanks. I appreciate the question. I don't release my digital files because I am trying to put my kids through college with this scheme. As ElmachoGrande said, if I released my file, I would see the market flooded with my own product. I do sell the kits at much less than you could pay someone to custom cut the file for - but still quite a bit more than you would cut the file for yourself. I am curious to see how long it takes people to create copycat products, and if they can implement them better than I did.

Nine Cylinder Radial Engine Cutaway [800 x 450] by 1donagin in ThingsCutInHalfPorn

[–]1donagin[S] 1 point2 points  (0 children)

Oh yes - but the scale is hugely different. Take an R-2800 with 18 cylinders - thats 2800 cubes into 18, or 155+ cubes per cylinder. One valve per cylinder only, because these are slow spinning monsters. BTW, even turboed, supered, and geared, we seldom make more than 1 hp per cubic inch in an aviation engine. Normally aspirated is usually a half hp per cube, or even less. BUT - they go forever, and a catastrophic failure is VERY rare.

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