Looking for plans for Cox radial model airplane engine

[mu38&Bg#]

Here form tap it has no teeth just press in to the metal. It only for soft metals like aluminum Odds are this type tap Cox used.

If you examine a Cox engine you'll see they used cut taps.

The "odd" (non standard very fine pitch) sizes were used out of necessity. The joints needed to be compact.

 

[SmithDoor]

Cox used 17/32" 0.53125" [13.49375mm] that is real odd size.
Now they could used 0.5625 witch only 0.035" difference in size.
You look glow plug size they did the same way use a off the wall size.

Cox engine did good job of keeping the parts there own by using custom taps and dies.

This something that had work around most life. Machine Tool Manufacturers are well know for this pain, like using a 7/16" 10 acme when the standard is 1/2 10. This part not mush of problem if machining a new screw but big pain if just nut. Other time manufacturers making gear 51 tooth a standard deviding head does not work for making a new gear.

Dave

If you examine a Cox engine you'll see they used cut taps.

The "odd" (non standard very fine pitch) sizes were used out of necessity. The joints needed to be compact.

 

[mu38&Bg#]

The odd thread didn't prevent Cox from being successful. Has it prevented the creation of countless custom engines using Cox cylinders? I guess we'll never know....

 

[Tim Wescott]

I don't think it's such an odd thread, for that matter. If you're making both parts, and they're never meant to interchange with anything but stuff you make, why does it have to be "normal"?

 

[mu38&Bg#]

That's my point. They optimized the design. Availability of taps had nothing to do with the decisions.

 

[SmithDoor]

ENGINE MODEL	ENGINE SIZE	GLOW HEAD	CYLINDER NECK	BACK PLATE	VENTURI	FUEL TANK	PROP SCREW
OLYMPIC DRUM VALVE	.15​	¾-32​	¾-32​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
OLYMPIC	.15​	¾-32​	¾-32​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
SPORTSMAN	.15​	¾-32​	¾-32​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
QUEEN BEE .074	.074​	11/16-40​	11/16-40​	N/A​	N/A​	​	#5-40 X 1.0​
MEDALLION	.15​	¾-32​	13/16-32​	13/16-32​	N-A​	N/A​	#8-32 X 1.5​
MEDALLION	.09​	11/16-40​	11/16-40​	11/16-40​	N/A​	N/A​	#6-32 X 1.25​
MEDALLION	.049​	17/32-40​	17/32-40​	​	N/A​	N/A​	​
TD .09 R/C	.09​	11/16-40​	11/16-40​	11/16-40​	5/16-32​	N/A​	#6-32 X 1.25​
TD .09	.09​	11/16-40​	11/16-40​	11/16-40​	5/16-32​	N/A​	#6-32 X 1.25​
TD .050 R/C	.050​	​	​	​	1/4-32​	N/A​	#5-40 X 1.0​
SPECIAL MARK II	.15​	¾-32​	​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
TD SPECIAL MARK I	.15​	¾-32​	​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
TD .15	.15​	¾-32​	¾-32​	13/16-32​	3/8-32​	N/A​	#8-32 X 1.5​
TD .051	.051​	17/32-40​	​	​	1/4-32​	N/A​	#5-40 X 1.0​
TD .049	.049​	17/32-40​	17/32-40​	​	1/4-32​	N/A​	#5-40 X 1.0​
TD .020	.020​	25/64-48​	25/64-48​	#2-56 X 1/4​	​	#2-56 X 1/4​	#3-48 X 3/4​
TD .010	.010​	​	​	​	​	​	#2-56 X 5/8​
DRAGONFLY	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
RC BEE	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
VENOM	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40​
KILLER BEE	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40​
KILLER BEE	.051​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40​
RR 1	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
TEXACO JR	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
TEXACO	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
BLACK WIDOW	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
GOLDEN BEE	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40 X 1.0​
QRC	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40​
QZ	.049​	17/32-40​	17/32-40​	N/A​	N/A​	​	#5-40​
BABY BEE	.049​	17/32-40​	17/32-40​	N/A​	N/A​	#2-56 X 15/16​	#5-40 X 1/2​
PEE WEE	.020​	25/64-48​	25/64-48​	N/A​	N/A​	#2-56 X 1/2​	#3-48 X 1/2​
SPACE HOPPER	.049​	17/32-40​	17/32-40​	N/A​	​	N/A​	#5-40​
STRATO BUG	.049​	17/32-40​	​	N/A​	N/A​	​	#5-40​
THERMAL HOPPER	.049​	17/32-40​	17/32-40​	N/A​	​	​	#5-40​
SPACE BUG JR	.049​	17/32-40​	​	N/A​	N/A​	​	#5-40​
SPACE BUG	.049​	17/32-40​	​	N/A​	N/A​	​	#5-40​
SPACE BUG EARLY	.049​	​	​	N/A​	N/A​	​	#5-40​

 

[SmithDoor]

That's my point. They optimized the design. Availability of taps had nothing to do with the decisions.

Here his list of Cox thread sizes
On past post.

Dave

 

[ajoeiam]

Here form tap it has no teeth just press in to the metal. It only for soft metals like aluminum Odds are this type tap Cox used.

Form taps 'can' be used in other than soft metals.
The material ductility is very important (forget in cast iron!!).
Check with the form tap specifications - - - there should be plenty of information hidden in there.
If not enough information - - - time to talk to the supplier and/or the manufacturer!

 

[L98fiero]

Here form tap it has no teeth just press in to the metal. It only for soft metals like aluminum Odds are this type tap Cox used.

Form taps are for ductile metals, they won't work on cast iron but pretty much everything else a hobby machinist would use, there is a limit on how hard the tapped material is but one local shop is tapping duplex stainless 5/8 UNC, lots of torque on a horizontal machining center and exactly the right tapping compound or the coating comes off after one hole is tapped.
One of the attributes of those taps is that they produce no chips so they are really suitable for blind holes. It should be noted that the tap drill size is different and that the threads are generally stronger than cut threads.
Tap drill size for Inch taps is: OD - (0.0068x % of thread required)/TPI
and for Metric taps: OD - (% of thread x pitch)/147.06

 

[mu38&Bg#]

Here his list of Cox thread sizes

Yes, I'm quite familair with this list. Very few are doing anything with this information other than replacing screws.

 

[SmithDoor]

I do not think any would build a small engine out of cast iron.
Most use aluminum for crank case this where the form tap will very well. The form can made in most shops. It only 1 to 9 holes needing tap so it made without heat treatment. You buying the cylinder in this case.
If making everything from bar stock you pick your tap and die to use

Dave

Form taps are for ductile metals, they won't work on cast iron but pretty much everything else a hobby machinist would use, there is a limit on how hard the tapped material is but one local shop is tapping duplex stainless 5/8 UNC, lots of torque on a horizontal machining center and exactly the right tapping compound or the coating comes off after one hole is tapped.
One of the attributes of those taps is that they produce no chips so they are really suitable for blind holes. It should be noted that the tap drill size is different and that the threads are generally stronger than cut threads.
Tap drill size for Inch taps is: OD - (0.0068x % of thread required)/TPI
and for Metric taps: OD - (% of thread x pitch)/147.06

 

[stevehuckss396]

Very crude drawings. They were never meant to be released to the public. Use at your own risk. I built one but never tried to start it.

View attachment 121951

 

[SmithDoor]

Very crude drawings. They were never meant to be released to the public. Use at your own risk. I built one but never tried to start it.

View attachment 121951

It great
Good job on building

Dave

 

[SmithDoor]

See how your project is doing.
The tap they used custom but. The cylinder Cox probley a die like Landis that you buy dies for pitch and adjust the die head.
You can just make a form tap out of O1 or W1 tools steel with no heat treat as said in past posts.

Hear is Cox web site for new cylinder and pistons.

https://coxengines.ca/cox-.049-tee-dee-cylinder-and-piston.html
Have fun
Dave

Hi all,
As my next model airplane project I would like to build a small 3 or 5 cylinder radial model airplane engine utilizing Cox .049 or .051 cylinder/piston assemblies. I have built 5 small engines so far (3 diesels and 2 glow; both single cylinder and twin). I am using a manual Sherline lathe and mill (no CNC). I don’t want to gear complete engines together but would prefer to make a common crankcase and machine the internals. I know that there have been many home made Cox radial engines built but I have been unable to find a complete set of plans for one. Does anyone have plans for a Cox radial engine as well as where to purchase a thread tap that matches the Cox cylinder thread. I understand it is a very unique thread and a tap was once available but no longer.
Thank you,
Michael

 

[Canyonman]

stevehuckss396. Hi, I'm having trouble opening your file types. Any options? Thanks Ken

 

[KenC]

I have the write-up and drawings for a 9 cylinder radial looking like a Pratt and Whitney Wasp based upon Cox 049 engines. It uses complete engines so it is really just 9 engines geared to drive one shaft. Any interest please pm me for more details.

 

[stevehuckss396]

My apoligies. I meant to upload these. Those were the cad files. These are the same thing in PDF.

Sorry!

 

[SmithDoor]

Great job.
Just think of a two cycle full size engine

Dave

My apoligies. I meant to upload these. Those were the cad files. These are the same thing in PDF.

Sorry!

 

[Canyonman]

Great Steve!!! Much Thanks!!!!! Ken

 

[Tim Wescott]

@stevehuckss396 : those look like good drawings if you already know what's going on (you did say they were crude).

I think the only thing missing for most people is how the compressor works -- if anyone's wondering, take apart some air tools and look at how they're done.

Having maintained air tools in my youth, I'd probably make the vanes out of phenolic (the vanes are the rectangular things 1/32" thick, that fit into the compressor rotor, which is the round thing with the four matching slots). They should slide easily in the slots in the compressor rotor, without binding -- making sure that the interior of those slots is as smooth as possible, with just the barest (and smooth!) chamfer should extend the life of the compressor considerably.