Looking for plans for Cox radial model airplane engine

[MickeyDD]

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

 

[rlo1]

also interested in a .049 radial. Any luck finding plans?

 

[jkimberln]

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

I do not know the thread size but if you find out what it is, try Victornet.com for a tap and die source. They have been my go-to source for strange threads for years.

 

[Shopgeezer]

The Cox cylinder thread is 17/32-40. It is very hard to find. No supplier that I know of has any on hand. The only solution seems to be to have one made. Commercial suppliers will do it but very expensive for just one. It would help to get some model engineers together who want one and make up a dozen or so. The cost goes down the more you order.

 

[Ed T]

A million years ago I made a 90 degree V-twin from two COX .049's. I grafted two crankcases together to address the threading problem and modified the con rods to fit onto the crank pin. It ran on both cylinders, but I failed to take the crankcase compression issue into account so it didn't run very well. For a two cycle radial with a common crankcase, having crankcase compression becomes problematic since there probably won't be any; so some kind of supercharger becomes necessary. That is probably a bigger problem than the rest of the engine since superchargers don't scale very well. Somebody probably figured out how to do it, but it's a lot more involved than just the mechanicals of the crank, master rod and having the pistons go up and down.

 

[Mechanicboy]

The super charger can't work in the two stroke engine due the exhaustport and transferport is still open and mostly of the fuel mix is blown out of the exhaust port and then the transferport is closed before exhaust port, no filling the pressure in the cylinder and fuel mix is low in the cylinder. Tuned pipe works best in the two stroke engine. Enough about this supercharger in the two stroke engine (Two stroke with exhaust valve who are timed and works best with supercharger, mostly used in large ship engines) . Use reed valve in each crankcase in the common part who has the center of propeller shaft who has connection with each Cox engine via gear wheel.

 

[mu38&Bg#]

Supercharger, means a pump of some sort to provide scavenging, not necessarily as a means of boost pressure. There are countless examples of pump scavenged two stroke from Cox radials to ship diesels.

This video has been popular recently.



Jens, I read that electric cars outsold IC cars last year in Norway. And, they want to ban IC Cars by 2025?

 

[Tim Wescott]

On a two stroke it's probably more accurate to call that pump on the intake "forced scavenging". Basically, on a typical little two-stroke, there's a pump that uses the changing crankcase volume to generate primary compression and force crankcase air into the cylinder through the transfer ports. On big two-strokes, and on multi-cylinder models where the total crankcase volume doesn't change (because there's a piston going in any time another one is going out) then you have to use a positive-displacement blower.

I think a roots-style blower would work, but I don't know.

Does a Shurline lathe do threading? I'm not the world's best machinist, and I've made holes that Cox cylinders will thread into, using a Smithy lathe and single-point threading.

 

[SmithDoor]

The down side cox engines is they used odd thread sizes.

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

 

[Mechanicboy]

Supercharger, means a pump of some sort to provide scavenging, not necessarily as a means of boost pressure. There are countless examples of pump scavenged two stroke from Cox radials to ship diesels.

This video has been popular recently.



Happy new year, old mate!

Jens, I read that electric cars outsold IC cars last year in Norway. And, they want to ban IC Cars by 2025?

Yes, I saw at the engine in Youtube of this engine with centifugalpump to deliver the fuelmix to all cylinders due lack of the crank case pressure greated by the pistons.

In fact it's not so many electric cars when the diesel cars is most sold in Norway. 300.000 registered electric cars is sold. 1 295 134 dieselcars, 1 033 036 petrol cars in Norway

 

[Canyonman]

Dieselpilot
I am extremely interested in getting or purchasing plans of your project!!!
Ken

 

[olympic]

"Does a Shurline lathe do threading?"

The Sherline lathe does do threading with the right attachment, and I think it would work for this.

 

[Canyonman]

Hi All
I contacted Victor on the 17/32-40 tap. They responded promptly with a nice note. All in all a single tap will be approx $120. Less the more we get.
Ken

 

[mu38&Bg#]

Dieselpilot
I am extremely interested in getting or purchasing plans of your project!!!
Ken

I didn't mean to imply that was mine, it isn't. It's not the first Cox based radial and won't be the last. It is a bit odd that there isn't a plan for one. I certainly could design one and have enough cylinders to build several, but I have far too many other things going right now.

Don't let the tap stop you. Lathe threading isn't difficult, but does require that the lathe has the ability.

 

[Tim Wescott]

Learning how to thread on a lathe is a good way to build your skills. The apprentice way is to just cut and try until it finally fits -- I still haven't gotten to the point where I can just cut a thread, say "it's done!" and have it fit nicely without being sloppy. So I do a lot of itty bitty cuts until it fits -- but I'm getting better.

 

[rlo1]

I can thread mill any thread on my Tormach. Just learned! I am still looking for radial plans for the .049.

 

[SmithDoor]

Hi All
I contacted Victor on the 17/32-40 tap. They responded promptly with a nice note. All in all a single tap will be approx $120. Less the more we get.
Ken

That is why Cox engine used the odd tap. But using aluminum you can make a form tap for soft aluminum out of O1 or W1 tool steel or just make your own cylinder with a of shelf tap. That is very close to 9/16 UNEF thread tap. I have tap in my box.

Dave

 

[Canyonman]

MickeyDD, I keep coming across a n .049 radial called the "Tarantula" but I can't seem to nail it down.
Ken
PS...OK, the Tarantula was a 9 cyl radial built of Cox .049's covered up by dummy engine parts for a Wasp radial look. The engine was built from plans by John V Thompson in the 80's. Far as I got.
PSS... According to Model Engineering News (dot) org John's plans are no longer available. Also his design might be problematic. He designed a way to have all 9 cyls on the compression stroke at the same time..???
Onward ;-)
Google is not always your friend ;-)

 

[SmithDoor]

Hi All
I contacted Victor on the 17/32-40 tap. They responded promptly with a nice note. All in all a single tap will be approx $120. Less the more we get.
Ken

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.

Dave

 

[petertha]

The Tarantula was mentioned here
http://modelenginenews.org/cardfile/tarantula.html