Compressed Air Radial Engine

[cfellows]

I started posting this build over on HMEM and decided to copy it over and continue posting progress on this board as well.  It'll be compressed air using my ball slave valve arrangement.  Operation will be 4-stroke using a 2 lobe, coaxial cam turning at 1:4 ratio to the crankshaft.  Here's the beginnings of a concept picture:



I started out rough cutting a hexagon out of 1.25" thick aluminum tool plate with my 4 x 6 band saw.   Then used a 1" arbor to chuck it up in my 5C hexagonal block.  I used a 2" indexable carbide mill to face off each of the 6 faces.







Wound up with what seems like a respectable hexagon 1.25" thick and minor diameter of 2.443" (Yeah, I over shot the target diameter of 2.500"  :-[)



Chuck

[cfellows]

I finished a prototype of one of the cylinders today.  As you can see in the drawing, I've made a change in the design.  Instead of using 2 long studs on either side of the cylinder to hold the cylinder and head in place, I decided to make the cylinder and the head one integral piece and use 4 SHCS's to faster the cylinders to the crankcase through a square flange in the base of the cylinder.  I don't like the look quite as much, but it will be easier to build.







I still have a little work to do to the cylinder before I'm finished with it.

Chuck

[cfellows]

I made a few more chips today.  I'm proceeding cautiously since I'm still designing as I go along.  The first thing I did was radius the edges of the fins and the head on the cylinder.  I was trying to make a radius form tool but decided in the end I was overthinking the problem.  I ended up just using a small file and sandpaper to make the radiused edges.  I also started doing some milling on the crankcase.  I may leave the outside profile this way or I may go ahead and finish radiusing the parts of the crankcase between the cylinders like the drawing.  Finally, I started work on the master connecting rod spool.  It was my first foray into machining 12L14 steel (a piece I inherited from Shred, I might add).  Lovely stuff to work with.







Chuck

[cfellows]

Managed to squeeze in a little more time on the radial.  I'm designing and making different components to see a)if I can, and b)whether they'll fit together as planned.

In these pictures, I'm making up the components of the connecting rod assembly.  There is still a lot of finish work to do on the pieces, but there's some tips here I thought worth sharing.

First picture is an overall shot of what I'm trying to get to.  You can see the master rod in the upper left.  The 5/16" curve at the bottom fits snugly against the center hub of the spool. 



The three little pins are 1/8" diameter and are shouldered down on the end to accommodate a 2-56 thread.  The pins slide through a 1/8" hole in the top of the spool and thread into 2-56 holes in the bottom of the spool.  The pins will be cut off flush with spool and a screwdriver slot cut on the top end.  This was the method Rudy Kouhoupt used on his 5 cylinder radial air engine.



So the first problem is to shoulder down the end of each pin to .085" for a length of 1/8"  I wanted to use my minilathe for accuracy and to take advantage of the freshly sharpened tangential tool bit.



Since I don't (yet) have a carriage stop, I engaged the lead screw and used my leadscrew crank on the left end of the lathe to control the length of the cut.  Since the leadscrew is 16 TPI, 2 full turns advanced the tool bit 1/8".



The next trick was to cut a 2-56 thread (squarely) on the shouldered end of the 1/2" long pins.  So, I mounted the pin in the chuck of my tapping guide and laid the die, mounted in a die holder, on the table.  This worked very well to cut the threads squarely.





Chuck

[cfellows]

I'm pretty pleased with way the crank assembly is turning out, especially the 3 shouldered screws that hold the connecting rods in.  This fiddly little pieces tend to give me problems, but I took my time and they turned pretty good. 





I plan to do some additional milling on the center spool to remove some weight.  I may also do some light shaping of the connecting rods so they look less clunky.

Chuck

[cfellows]

Today I shaped the Connecting Rod Master Spool (is there a proper name for this piece???)  I used a 1.25" end mill to cut the curved part.  As you can see, I used the crankcase as a fixture to hold and position the spool for cutting.





I'm going to leave the connecting rods alone for now.  Next I'll be working on the crankshaft.

Chuck

[cfellows]

I hogged out the crankcase today and mostly finished the other two cylinders yesterday.  Still have to round off the edges and fins on the cylinders and crop the base flanges down to size.  If you like exercises, try centering a six sided piece on 3 opposing sides in a 4 jaw chuck.  Had me scratching my head a few times.



You can begin to get an idea of what it's going to look like:



Chuck

[cfellows]

I hogged out the crankcase today and mostly finished the other two cylinders yesterday.  Still have to round off the edges and fins on the cylinders and crop the base flanges down to size.  If you like exercises, try centering a six sided piece on 3 opposing sides in a 4 jaw chuck.  Had me scratching my head a few times.



You can begin to get an idea of what it's going to look like:



Chuck

[cfellows]

Did a little softening and finishing work today.  This first series of pictures shows the radial set of holes being drilled which will hold the front crankcase cover to the main crankcase.  I thought the group might like to see the indexing fixture I have built into my drill press.  I picked up this round table at a scrap yard a number of years ago.  It already had the 24 holes in the sides (well, two holes on opposite sides are missing, but I work around those).  I had to turn the spigot down to fit my drill press.  Then I bored out the center to fit a 5C collet.  Finally, I made an indexing pin and lever from some strap I had on hand.







And here are some pictures of the engine in its current state:

[cfellows]

I spent most of today doing remedial work.  Paying the price for getting in a hurry earlier on.  I discovered the cylinder openings in the crankcase were .010" closer to one edge than the other.  And, they varied in size by + / - .005".  So I set the crankcase up again and enlarged all the openings so they were centered and equal in diameter.  Of course, that meant that the spigot at the bottom of the cylinders was now too small, so I had to build them up by soldering short lengths of brass pipe on them and re-turning them to fit the new openings.  Now they are all consistent and fit nicely.  I feel much better now!  8)

So, finally some pictures with the engine in an upright position.  They always look better when you get some fasteners in place. 

Yeah, I know, including the picture of the B-17 which adorns my shop wall is a bit over the top!





The overall diameter of the engine is a tad over 6".  Here's a picture with a soda can for size reference:



Chuck

[cfellows]

Took a break from the small rotary table to get some work done on the crankshaft for my radial.  Here it is, clampted into a v-block while the loctite cures (Thanks for the v-block idea, MB).  Tomorrow I'll drill it out and insert a roll pin.  A taper pin would be better, but I ain't got none of those nor do I have the needed reamer so a roll pin will have to suffice.



Chuck

[cfellows]

I've decided to go ahead with the overhead valve arrangement on this engine.  It will be 4 stroke in operation and will use a combination of my slave exhaust valve and a ball inlet valve similar in operation to the Liney Halo radial.  High pressure air will be presented to the top of the cylinder where it will be stopped by a ball bearing check valve.  To "fire", a valve stem which is an interference fit with the ball valve will open the valve by pushing it to the side when the stem is depressed.  This will admit air into the head where it will push a second ball bearing to the side, exposing a hole which leads into the cylinder.  This will push the piston in a manner similar to my other slave valve engines.

So here is the first series of pictures on work done the past couple of days.  Here is one of the cylinders with the valve stem hole drilled down through the top into the and a 1/8" hole drilled radially all the way through.





Here I've milled a flat on both the intake and the exhaust sides to receive the input and exhaust pipe flanges.  I've also enlarged the hole to several different sized.  The intake side is 7/32" so the 3/16" ball bearing is a very loose fit.  This allows air to flow around the ball bearing when it is unseated by the valve stem.  Then the hole is stepped down to 5/32" where it passes around the valve stem.  Finally, on the other side of the valve stem, it opens up to 3/16" so the slave ball bearing is a close sliding fit.



Inlet side, showing the step down to 5/32" around the valve stem hole.



This shows the inlet side on the left and the exhaust side on the right.



I will be attempting to emulate the layout of the Anzani radial engine as close as I can, perhaps without as much detail.  Here, you can see that on the rear side of the cylinders, there is a tube going up the back into an elbow at the top which leads into the cylinder head.  This is the air/fuel inlet manifold.



On my engine, the high pressure air supply will go up a tube on the rear of the cylinder and into an elbow, similar (or at least as close as I can get it!) to the Anzani.  So, in the next series of pictures, I am making my version of the elbow.

I'm milling all three manifolds in one piece of brass and will cut them apart later.  Here I'm using a 1/4" end mill with radiused corners to cut out the sides.



Next I use corner rounding bitto round off the top edges.



And, the finished manifold before cutting in to three separate pieces.



Here they are cut apart and the holes for the tube have been drilled.  There is also a hole on the bottom which will lead into the cylinder head.



And, here they are with tube soldered on, mounting holes drilled and pretty much ready to mount, well, after I pickle them and get them polished up!



I'm still figuring this thing out as I go along, so progress is a little slow.

Chuck

[cfellows]

Thanks for the comments, Stew, Dave, Deanofid.  After a lot of noodling and mind changing, I think I've worked out the details for the back end of the engine.  The cam will have two lobes, 180 degrees apart and will turn at 1/4 the speed of the crankshaft.  The cam will be coaxial to the crankshaft with double reduction gears 12/24, 12/24 to arrive at the 1:4 reduction.  So here are a couple of pictures of the back crankcase cover.  Here I'm machingin the back side and the timing gears will be inside the hollowed out part.  The valve lifters will be set into the ring that has been formed.  Further maching will be done on the ring and, in the end, it won't be a ring.  Hard to explain what I have in mind, guess you'll just have to wait and see it.  ;)





The ring part, btw, is 1 7/8" OD x 1 3/8" ID.

Chuck

[Bogstandard]

Hi Chuck,

I'm glad you have decided to show us over here what you get up to.

As you know, I have followed your designs for a while now, and it always amazes me how well your little engines sound and run, and as yet, I have still only got one engine with your design of poppet valve made. Maybe a little further into the future, I will be able to make another one.


But please remember, on here, we would like to see your other projects as well. Anything goes.


John

[sbwhart]

Hi Chuck

Thanks for showing your engine build I have a weekness for radials, the poppet valve looks interesting, just finished reading an engine book that has a design for a single cylinder poppet valve engine. hmmmmmmm 

 

Stew

[cfellows]

Got some work done since the last post.  Here are some pics of the timing gears.  The two larger ones are 40DP, 24 teeth, 1/8" thick and about 6.5" OD.  The smaller gears are on the 3/8" rod and haven't been parted off yet.  They will be 12 teeth and are .35" OD. 



One of the 12 tooth gears will be loctited onto the crankshaft and drive a 24 tooth gear below it.  The 24 tooth gear will be ganged to a 12 tooth gear, which will, in turn, drive the other 24 tooth gear which turns freely on the crankshaft.  The double lobed cam will be attached to the second 24 tooth gear on the crank and will turn at 1/4 the RPM of the crankshaft.

Chuck

[Brass_Machine]

Stunning ofc Chuck 

I have an idea for an engine... Might work well with your valve design... Hmmm...

Eric

[saw]

Nice, good work. 

[cfellows]

Stunning ofc Chuck 

I have an idea for an engine... Might work well with your valve design... Hmmm...

Eric

Come on, Eric, you gotta share...

[CallMeAl]

Hey Chuck,

Just found this build, beautiful and intriguing work.  I aspire to make something as nice as engines someday.

AL

[cfellows]

Got all the timing gears done.  I decided to make the primary gear and shaft one integral unit rather than trying to loctite or solder the gear to a shaft.  The second and third gears are ganged and soldered together.  Then, the fourth gear rides on the crankshaft at 1/4th the speed of the crankshaft.  The cam will be attached to the fourth gear, probably with a mechanism which allows for timing adjustments.









Chuck

[greener121]

Very nice.  Show the cutter for the gears, I'm assuming a Sir John cutter?

Brian

[cfellows]

Just used commercial involute gear cutters.  I have a complete set of 40 DP cutters as well as an assortment of 24 DP, 32 DP and 16 DP.  I want to try making my own hobb one of these days.

Chuck

[cfellows]

I think I've wrestled all the remaining design questions to the ground so the worst part is over.  Today I made the back timing gear cover or back cover for the back crankcase cover which is confusing, I know.  I've also drilled and tapped the holes.







Next, I'll be cutting away a significant part of the back cover and the sides of the ring to look something like this:



Chuck

[saw]

Nice 

[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

[Bogstandard]

Like all your models Chuck, absolutely wonderful.

They are the nearest to sounding and looking like an ic engine without being so that you will ever get, remarkable.


John

[sbwhart]

Fantastic Chuck just fantastic
 



Stew

[saw]

Good work 

[joshagrady]

Absolutely beautiful.  Thanks for sharing.

[Brass_Machine]

Wow! 


What a stunning engine...

[earnie]

this thing is a true work of art thanks

[cfellows]

Hey chuck, I've got a follow on question.  Do you think it would vibrate less if it had a 3-bladed propeller on it?  I agree with your choice to use the 2-bladed propeller as a 3-bladed propeller would be period incorrect, more, I'm just asking because I'm curious.  BTW, I had to come back and watch the video a 2'nd time.  I'm really liking this! 

Thanks for the kind words!  The type of propeller shouldn't make any difference.  Radials are notorious for vibration problems because of the mass of the connecting rod assembly.  I tried to offset that a little bit by machining a counterweight in the crank and frankly, I'm a bit surprised that the engine doesn't vibrate more than it does.

Chuck

[CallMeAl]

Let me join the rest: Fantastic work! and Beautiful engine!

Al

[dickda1]

It even sounds like a real radial engine - truly a work of art!  By the way, did you grind and polish the primary mirror on your telescope?

-Dick

[NickG]

Brilliant! 

[cfellows]

It even sounds like a real radial engine - truly a work of art!  By the way, did you grind and polish the primary mirror on your telescope?

-Dick

Thanks Dick.  No, the mirror was ground and polished by Nova Optical.  It is a very good mirror.  Been looking at Saturn through it the past couple of nights.  Nice sharp images.

Chuck