Compressed Air 3 cylinder radial engines

[cfellows]

I saw Nick Muller's 3 cylinder radial engine several weeks ago on another forum and asked him if he would be willing to sell me one of the castings.  He graciously agreed to and yesterday the casting arrived via US Mail.  There was no glaring evidence that the package had been opened by customs and, so far at least, no invoice from the Post Office or Customs Office for any fees or duties.

The casting was nicely done although it did require some cleanup with a file to remove flashing and smooth some of the edges.  Here is a photo of the casting mounted over the 3" 3-jaw chuck on my 7" minilathe. 



Not the best work-holding method, but by taking light cuts and slow feeds, I was able to face off and turn down the outer end.  I also drilled out the center hole for the crankshaft, starting with 1/8", followed by 5/32", and finishing up with 3/16". 

I plan to mostly follow Nick's plans but want to incorporate my slave exhaust valve in the head, so the top end will be quite different.  My head design won't be quite as nice looking as Nick's, but I can't use my slave valve with his design... bummer.

Chuck

[cfellows]

I made a prototype of the cylinder.  I also made the head as an integral just because I could and it simplifies things (if it works).









The piece was made from a 1 1/8" length of 3/4" diameter brass round.  The bore is 7/16".  The cuts for the fins are .060" deep and the diameter of the bottom which will slide into the casting is 9/16" diameter. The side with the small hole will face the front of the engine where the compressed air will be admitted with a tube, much like Nick's design.  The large hole, then, will face the rear.  The slave exhaust ball bearing and spring will be inserted from this end and will serve as the exhaust port.  This obviates the need for an exhaust port in the crankshaft, simplifying construction and reducing the air leakage (hopefully).

Chuck

[cfellows]

I completed the heads and began work on the body casting today.  My fixture isn't very fancy, but it's all I had and worked find.





I bored the opening for the cylinder with 1/4", then 3/8", then 1/2" end mills going very slowly.  I finished the bore diameter to 9/16 using a boring head.  Nick's castings are pretty accurate so no special fixtures were needed.  The cylinder clamping ring seems kind of fragile, so I was slow and cautious drilling, splitting, and tapping it.





I drilled the crankshaft bore out to 7/32" and Loctited in a 7/32" OD x 3/16" ID brass tube.  I figured that would make better bearing material for the crankshaft.

Next, I'll start the crankshaft...

Chuck

[cfellows]

Today I finished the connecting rods and the pistons.



I made the rods out of 1/4" x 3/16" aluminum, the milled the crankshaft ends to overlap each other.

Chuck

[Divided he ad]

Looks like you've got this one well under way Chuck 


Interesting to see your workholding set-ups. Logged for use someday in the future




Waiting for the next instalment 




Ralph. 

[cfellows]

Thanks, Ralph.

I think tomorrow will see this thing running. 







All I have left to do is mill the air valve flat on the crankshaft and make the air inlet tubes.  The cylinders are complete with the exhaust pipes, the slave ball valve, and springs installed.  The rods and pistons are also complete.  The engine turns over freely so if I can get the flat on the crankshaft in the right position, it should run.  Oh, yeah, I also have to make a mount for it.

Chuck

[Divided he ad]

Wow!

That's pretty rapid Chuck! 


It doesn't look like it'd be too hard to carve the main body from a solid Ali round.... I may have to investigate these radials?


I'm missing the bit on the valves.... I'm of no doubt you will have listed their build elsewhere. Any chance you can remember the thread name/location? I'll go and have a look 



Cheers,

Ralph.

[vtsteam]

I think this is it Ralph:

http://www.homemodelenginemachinist.com/f43/radial-3-cylinder-compressed-air-engine-20778/

[vtsteam]

I've kinda wondered if cylinder fins help a compressed air motor as opposed to lagging/insulation on a steam engine. At least where there is a warm ambient, seems like it might have the effect of limiting the temperature drop below ambient in expansion. Unless the compressed air supply was warmer than ambient. Pretty academic, I know. But seeing the fins just made me think about it.

[cfellows]

Here's the finished engine.  Runs great, scary fast!

Chuck

[cfellows]

Stuff deleted...

I'm missing the bit on the valves.... I'm of no doubt you will have listed their build elsewhere. Any chance you can remember the thread name/location? I'll go and have a look 

Cheers,
Ralph.

Ralph, here's a diagram of the Slave Exhaust Valve Setup...



Chuck

[vtsteam]

That is very cool. I would imagine it has resonance qualities -- possibly those could be taken advantage of as a governor.

If used in a steam engine, the temperatures would have to be prevented from reaching the point of annealing the spring, I imagine. But of course this is a compressed air engine.

Very interesting design. 


Just watched the video -- sounds great. Nice engine!

[Divided he ad]

Chuck... Great runner 

Gets up to some speed!    Think I'd have gone with a rubber prop.... I'd be bound to get my fingers in there somewhere! 



Thanks for the link to the original and the valve design pic'.  I get it now    






Ralph.

[cidrontmg]

cfellows:
"Here's the finished engine.  Runs great, scary fast!"

It sure runs (and sounds) great, excellent!
Just wondering, most propeller engines run counterclockwise, at least U.S. engines have always ccw direction. Big or small. But their engine runs clockwise  I also have seen a 4,1 ccm Sleeve Valve Engine, by Achim Steinke (http://www.metallmodellbau.de/), running "backwards". Why is your engine running the "wrong way"?   

[cfellows]

cfellows:
"Here's the finished engine.  Runs great, scary fast!"

It sure runs (and sounds) great, excellent!
Just wondering, most propeller engines run counterclockwise, at least U.S. engines have always ccw direction. Big or small. But their engine runs clockwise  I also have seen a 4,1 ccm Sleeve Valve Engine, by Achim Steinke (http://www.metallmodellbau.de/), running "backwards". Why is your engine running the "wrong way"?   

I was aware that aircraft engines typically turn anti-clockwise.  However, on my engine, the crank-pin, which holds the connecting rods,  screws into the crankshaft disk with a standard, right hand thread.  I made the engine to turn clockwise (counter clockwise from the back) so the crankpin would not loosen over time from the unwinding action of the connecting rods.

Chuck

[cidrontmg]

Fair enough answer. But the propeller and the spinner tends to getting loose and unwind, unless there's left-handed nuts with the crankshaft screwthreads       (Of course, Loctite helps).

[Henning]

Fair enough answer. But the propeller and the spinner tends to getting loose and unwind, unless there's left-handed nuts with the crankshaft screwthreads       (Of course, Loctite helps).

Or a locking pin?

Beautiful engine Mr. Fellows. I'm not much of an engine guy, but i will try and build something like this one day!