6 Cyl Radial Air Eng (GrabCad)

[Jmccrack]

So I have spent many hours building all the parts and pieces for this six-cylinder engine. I put it together and I seem to have a problem with it. When I rotate it by hand the center wheel that holds all the conrods seems to fall behind in rotation to the crank shaft. What happens is the conrod bind up against the cylinder edge. The center wheel is free running no binding and all the Pistons move easily in the cylinders. Am I missing something.

As you can see the Conrad is hitting the edge of the cylinder. Sometimes it runs well and it is not always the same cylinder. Any thoughts?

 

[Cogsy]

Are all the con-rods free to move on that 'center wheel'? Normally, radial engines have a 'master rod' which is fixed in relation to the 'center wheel' you mention and all the other rods are attached to it. This keeps everything in correct orientation and eliminated the binding you are experiencing, as well as ensuring correct piston timing and stroke as well. I don't think the engine will work without such a master-rod arrangement.

Something along the lines of this arrangement:

 

[Jmccrack]

Are all the con-rods free to move on that 'center wheel'? Normally, radial engines have a 'master rod' which is fixed in relation to the 'center wheel' you mention and all the other rods are attached to it. This keeps everything in correct orientation and eliminated the binding you are experiencing, as well as ensuring correct piston timing and stroke as well. I don't think the engine will work without such a master-rod arrangement.

Something along the lines of this arrangement:

View attachment 103801

 

[Jmccrack]

I had no idea. So you are saying in a radial one con rod is fixed? Thank you so much for that. I will try to fix one rod.

 

[Henry]

Been it an air motor I don't think that is a problem, I want to remember that is something with the timing, but radials I think, got always an odd number of cylinders.

 

[Jmccrack]

I am really confused now. Even when I turn it by hand the Conrad will sometimes bind up. Almost as if the center is not keeping up with the pistons. It can’t be timing because I am only turning it by hand.

 

[adolfgalland]

You can't have all the rods independent or it will bind up. You do need a master rod.

Gary

 

[stevehuckss396]

Gary is correct. Any radial no matter what kind, needs a master rod.

 

[Jmccrack]

Thank you so much for the guys. So now I’m gonna go out and try to figure out how to make one of these rods a master rod. Should be interesting because they’re all meant to move right now. Again thanks a lot I will keep you informed

 

[Jmccrack]

GOT IT! I will silver solder the master rod in place.

 

[Jmccrack]

So I now have a master rod

I silver solder and pin it

 

[stevehuckss396]

Should be all set now.

 

[Jmccrack]

You are right. Works like a charm now. Interesting I got this drawing from GrabCad. Nice plans and a great 3D exploded view. But no master rod on the drawing. If anyone uses these plans make that modification. Thanks again for the help.

 

[dennisa49]

Good day,
I am not familiar to the type of engine you have built. Aircraft radial engines use an odd number of cylinders in each row.
Single row use 7 or 9. Twin row 2 x 7 or 2 x 9 etc.
Your con rod arrangement may be out of whack. I will chase up a picture and post it.
50+ years since I completed my apprenticeship.
I hope this helps and I have not confused the whole thing.
Regards, Dennis

 

[dennisa49]

Good day again,
Here is a picture of a Pratt and Whitney twin row Wasp (2X 7) crank.
I hope this also helps.
Regards,
Dennis Thanks to Pratt and Whitney photo site.

 

[Brian Rupnow]

Don't trust any of the things you find on Grabcad. They are not vetted for accuracy or buildability. Any amateur can post something there, correct or not.---Brian

 

[nparmley]

All AC engines as you describe "with a master connecting rod" have odd numbers of cylinders. They have too, or they do not work for the same reason you have now. However, the Germans attached their connecting rods directing to the crank shaft, not in an outer orbital plane as yours, in some of their engines. By connecting directly they could achieve even numbers of pistons around each section of the connecting rod, and the engine could be made more compact, thus fitting in a smaller space. Do a search on "Fock Wolf 190", and see some of the cut-away pictures of the engine used to get an idea of the design.

 

[Jmccrack]

So here is some interesting drawings to look at. I have built all these parts and by changing one rod to a master rod it turns over by hand very easily. I posted the drawings because when I put air to it it does not rotate. I think it has something to do with the air Valve. As you can see the brass air valve sits on an eccentric shaft and as the crank turns moves over the port that injects air to the top of the cylinder. When I inject air into each port on its own it will drive the piston down no problem. I have not seen this type of valve arrangement before. It should work. Any thoughts? Again Brian this is from GrabCad. I may now have learned my lesson..

 

[Jmccrack]

This is May first radial. But I was wondering. Would the firing order (air in) be 123456. Or something different?

 

[adolfgalland]

Jmccrack, Where I.C. radials fire every other cylinder yours would be a 2 stroke and fire each cylinder as it rotates. I don't know how you number your cylinders or which direction it is suppose to run but each cylinder would fire (air in) as it rotates.

Gary