Compressed Air Radial Engine

[cfellows]

Today I got started opening up the timing gear cover.  Milling, filing and sanding are not my favorite operations, but it did turn out OK.

Here you can where I've got the back part of the crankcase in a 4 jaw chuck on a rotary table.  I'm using a 1/4", 2 flute end mill to do the hogging, taking .050" per pass.



Here you can see the whole lash-up.



For the last pass of the cut, I've switched to a ball end mill to give me a radius at the bottom.



Here I've moved over and am cutting out the waste on the other side.



I've finished up all the work with the end mill.



Several operations later, I've removed the rest of the waste, and filed and sanded to get it prettied up.



The next series of pictures shows the part on the engine in various positions so you can kind of see what it's going to look like.









Still have a little refining and tuning to do, then I'll get on with cam...

Chuck

[Bogstandard]

That is coming along just great Chuck, it sure is a long way from the original poppet valve concept.

You have really brought it along over the years. What next, a V-8.


John

[cfellows]

That is coming along just great Chuck, it sure is a long way from the original poppet valve concept.

You have really brought it along over the years. What next, a V-8.


John

Thanks, John...  Funny you should mention a V-8, I've been thinking about it, or maybe a V-6 just to be different.  I've also been thinking about about an inline 6 and a straight 8.  I think either of those would also be a pretty interesting engine.

In my earlier years of model building, all the emphasis was on getting the engine to run and looks were secondary.  But these engines spend a lot of time in the display case not running but I still look at them every day.  So, I've kind of learned that it's important to make them look interesting and "pretty" when they are just sitting there.  So now I spend a lot more time trying to make them look like the real thing, just smaller.

Chuck

[cfellows]

Tonight I made the cam for my radial.  I was able to use my new rotary mounted chuck and it worked great.  The cam is made from a 1.125" diameter brass disk about 5/32" thick.  The lobes of the cam extend 1/16" so the disk diameter that is left is 1" diameter.  In this first picture I have started cutting the disk.  I advanced the disk .030" into the cutter, then turned the chuck with 28 turns of the crank.  This rotated the cam 140 degrees.  Then I raised the cutter above the work and turned the crank another 8 turns, rotating the the disk 40 degrees before lowering the cutter back into the disk.   Then I repeated the procedure to cut the other half of the cam.  I made two more passes advancing the part .020" then another .015" for the final pass.



Here is a picture of the whole setup:



Here is a picture of the arbor setup I used to hold the disk for milling:



Here is the timing gear and cam setup as it will sit in the engine:





I still have to round off the cam lobe tips and fasten the cam to the final gear in the gear train.  I will probably cut a radiused slot in the cam disk so I will have some timing adjustment available to me.

Chuck

[cfellows]

After a week of being sick and a couple of weeks working on projects deemed higher priority by the chief financial officer, I finally got some work done on this engine.  I completed the profile on the cam disk, attached it to the final timing gear and made and fitted the valve lifters.  Running the assembly with my drill proved it to be a smooth working assembly.  I think this part is going to be particularly interesting to watch when the engine is running slow.





Chuck

[cfellows]

Chuck this work and the pictures you are posting have me wanting to start another project in the middle of my current one.  Nice!

Thanks!  Considering the amount of time before you get your current project completed, you probably need another project.  A little instant gratification never hurt anyone.

Chuck

[Bogstandard]

It's looking really well Chuck, and as usual, well planned and thought out first.

This is making me look at rebooting my Halo project very seriously.


John

[sorveltaja]

Nice work, especially on the gears and the slave valve system, Chuck  .

I have tried that slave valve system with piece of brass tube, suitable size bearing ball, and spring.

My humble compressor gives only max 3.2 bar(~46 psi), and can't even move the valve/ball. Reason being mostly too stiff spring. I made a new spring, using 0.010" guitar string, but still too stiff. I'm still looking a way to make a lighter spring. Copper or brass maybe?

But (finally) to the point. What is the air pressure, that you use to run your engines? Also, what size are the spring(s)(to be more precise, thickness of the spring wire) on your engines?

Just a wild guess, that there is some relation between air pressure and spring tension? And of course size of tubes(volumes), that the compressed air goes through .

[lordedmond]

not to try and tell you how to suck eggs , but have you tried the springs found in the cheap retractable ball point pens they are a nice size for our use





Stuart

[sorveltaja]

Stuart, I took apart one(all) of my pens, and found out, that they all have ~0.015" springs. Bit thicker than the 0.010" guitar string, that I've already tested.

But thanks for suggestion anyway .

[cfellows]

The springs I use look like they are out of a ballpoint pen and have a wire size of about .013".  They are also about 3/4" long and are virtually uncompressed when placed in the head.  My air compressor runs up to 120PSI and I don't use a pressure regulator.  Rather, I just use an inline ball valve to meter the amount of air.  However, it seems I recall measuring the pressure one time and coming up with about 40 PSI.

Chuck 

[cfellows]

The work I finished yesterday and today doesn't look like much, but I am happy to report that all the engine internals inside the crankcase are completed.  Also completed is all the timing gear and cam assembly including the valve lifters.  All that remains are the pistons, the the rocker arm assemblies, push rods, air supply hookups, and exhaust pipes.  Fit and finish to this point all seem as good as I've ever done and the engine turns over smoothly with a drill, albeit, still a little tight.

Here you can kind of see the master connecting rod and a bit of the crank assembly.



Here's another shot of the cam gears and cam, lots of oil on everything.



The front of the engine, showing the beefy, 5/16 crankshaft.



And and overall side shot, again showing the cam and cam gears.



Later, I'll post some pictures of the engine disassembled to better show off the internals.

Chuck

[saw]

It looking realy good 

[cfellows]

After a bit of a hiatus while I worked on another project, finishing my latest telescope in time to view Saturn which is now appearing in the late evening sky, I've gotten back to work on the radial.  Here are some pictures of work being done on the push rod assemblies.  The push rods are 3/32" drill rod, but I didn't have a 3-48 die, so I turned the ends of the push rods down to .081" so I could thread the ends 2-56.  Here is the beginning of the 3 clevises which will attach the push rods to the outboard end of the rocker arm.  These are made from 3/16" square steel and I used a 3/32" slotting saw to cut the slot in the end.



And here are the (almost) finished clevises threaded on to the end of the push rods with the 2-56 lock nuts in place:



Still have to drill the holes in the ends of the clevises to accept the clevis pin.

I'm getting pretty close to having this engine running.  I still have to complete the pistons, exhaust manifolds, and the rest of the valve assemblies.  Also gotta figure out what I'm going to do for a prop.  I would like to make another steel prop for it's flywheel attributes.  Still noodling around what I want to do.

Chuck

[cfellows]

Here's a picture of the roughed out flywheel.  Looks suspiciously like a propeller, huh?  It's made from 3/16" thick steel and is about 10" long.  I wanted the look of the old wooden propellers, but also needed the weight of the steel.  Still got some shaping to do, but don't want to remove too much of the weight.  Also want to keep it nice and rounded on the ends and edges so if a finger gets in the way, it won't remove said digit.



I'm getting close now.  Got the pistons and the exhaust manifolds done.  As soon as I can sort out the air inlet manifold assembly, I'll be ready for a test run.

Chuck

[j45on]

Cant wait to see this running 

After a bit of a hiatus while I worked on another project, finishing my latest telescope in time to view Saturn which is now appearing in the late evening skyChuck

Also I am interested in your telescope can we see some pics ?

[cfellows]

Thanks all.  Here are a couple of pictures of the my latest and probably last telescope build.





You can see many of the other telescopes I've built on my website at

http://www.cfellows.com

Chuck

[saw]

Nice good work 

[j45on]

Thanks Chuck your telescope is a work of art 

[dsquire]

Chuck

Thanks for the link. I went and had a look around and liked what I saw. There are a lot of very nice items that you have built. I can see that you are a man of many talents and your work shows that in its beauty. Thanks for showing us Chuck. 

Cheers 

Don

[cfellows]

Thanks, all, for the the kind words.  I like building things... keeps me out of the bars (most of the time!) 

Here's a few pictures of the engine assembled.  Still noodling around with the air supply manifold.  I did finish up shaping and smoothing the propeller.  Everything else is operational at this point.  Soon as I get the air supply figured out and built, she'll be ready to run.  Then I have to figure out a stand and add a few finishing touches.









Chuck

[saw]

This is nice good work 

[Bernd]

Looking mighty fine Chuck.   

Bernd

[NickG]

Absolutely great looking engine Chuck 

[cfellows]

It's done!

I'm considering this engine finished, although, like most of my engines, I will most likely always be tweaking and changing things a bit.  For those of you who might think my engine mount resembles the lid of a crypt with a tombstone, my wife already pointed that out to me.  Wasn't my intent, just turned out that way.

The curved bottom of the base was inspired by some of the excellent models made by Tom Hall.  It is made from a 1.75 inch diameter steel pipe, split lengthwise into quarters.  The ends were then mitred and all pieces welded together.  Lots and lots of grinding and sanding got it to resemble a casting rather than being built up by welding.  The top of the base is made from 1/4" cold finished steel, rounded on all edges and welded to the mitred frame.  The upright is made from 3/8" thick aluminum angle.  The base took me 3 full days to complete.  Usually I just throw something together, but since my models spend a lot of static time being admired on the shelves of my study, I decided to make it "pretty".

One bit of serendipity is that this engine idles and runs kind of rough, missing a lick now and then and generally sounding like it needs a tuneup.  I find this to be amazingly like many of the videos of old radial engines running on youtube.  Almost sounds like it has a 3/4 cam in it.  It's also kind of hard to start sometimes, kicking back and endangering my prop spinning finger.  Not sure how I managed this bit of realism, but I'll take it!

In retrospect, the cam assembly, lifters, pushrods,  rocker arms and valve assemblies added a huge amount of complexity to the build compared to the much simpler valving mechanism of my opposed 4.  But, perhaps the visuals and the irregular running make it all worth it.  Now if I could just get it to backfire occasionally...























This is my first video.  I noticed later, after I had uploaded the video, that one of the pushrods was dislodged from the lifter, so the engine is only running on 2 cylinders.

http://www.youtube.com/watch?v=VbuiCROHeVY

This is the second video, taken with a different camera and with the engine running on all three cylinders.

http://www.youtube.com/watch?v=bIYcx4-uyYE

As a recap, the engine has a bore and stroke of 5/8" x 5/8".  It is 4 stroke in operation with each cylinder "firing" on every other revolution.  The cam has 2 lobes 180 degrees apart and turns at 1/4 the RPM of crankshaft.  Two sets of gears, each reducing the speed by 1/2, are positioned so that the cam sits on and is concentric to the crankshaft.  The propeller is made of from a steel bar, 1" x 1/4" x about 10" long. 

Chuck