5 Cylinder Radial

[Brian]

The second jig will hold the cylinders for drilling and for final finishing of the bore. it will also hold the cylinder head for most of the work done on that component.
Both jigs are able to be fitted on the lathe or rotary table

   

   

Getting ready,  Brian

[TomG]

Brian,

It's nice to see someone who realizes the value of proper fixturing. A small investment in time will pay back with dividends on complex or multiple parts.

Tom

[Brian]

Well it had to happen, a member on another forum pointed out that I had not corrected the slave rod positions to give equal firing angles, and looking at my replies I ended up thinking that the real answer was laziness.
 So the drawings have been redrawn ( yet again ) to achieve equal angle and hopefully a smoother engine.
It was so easy to do that I cannot excuse myself in any way.
Brian
   

[Pete O]

Are you able to explain what the change is Brian? And perhaps what effect it has? It appears that the cylinders are now offset so that they do no radiate precisely from the centre of the crank, is that correct or is there something else I am missing?

[Brian]

Ok  Pete. I had better start at the beginning.
Radial engines have a problem in that only the number one cylinder is coupled directly to the crank by the master rod, all the other pistons have slave rods that connect to the master. If the pins in the rod are at equal angles around the big end
the secondary pistons do not arrive at TDC at the correct angle spacing of 72° for a 5 cylinder engine.
Now ( normal radial engines ) only have one cam and one ignition system so timing is never correct, my OHC allows me to correct these errors. I did not worry about the power pulses being not quite right on the basis that V twins and split vertical twins run quite  happily with power pulses Waaay out.
This problem is corrected by repositioning the pins in the rod ( if you look at the drawing you will see that the pins are radially positioned around the lower part of the rod. not at 72° spacing )  the pistons now arrive at TDC on time at 72°
Problem solved.
But we have  another problem with this system. only the master rod big end follows a perfect circle around the crank,
the pins follow an elliptical path caused by the master rod rocking as it turns,  this  causes the timing for number one cylinder to be slightly out compared with the others   Now on most engines this is simply ignored. but on some of the high powered ones the magnetos had the cams made to correct this, on my engine the ignition is independently set for each cylinder.  
Many model engine designs choose to totally ignore these problems and seem to run perfectly well, but as it was commented on I felt I must put things right.

I hope this answers your question if not feel free to ask.
Brian

[Pete O]

Thanks for the explanation Brian, that all makes sense although being somewhat of a tactile person I think I would have to have some time with a cutaway model or perhaps a good animation before I could make any claim to understanding the geometrical issues involved. I spent the first decade of my working life- and a whole lot of my leisure hours since then- working with engines but have never had anything to do with radials so they are still something of a mystery to me (as type this there is a photo behind my computer of me in a SNJ5B- navy variant of the T6- with a big P&W radial at the business end, only thing I've ever had to do with one!).

[Brian]

This may help Click to open.
Brian

   

[Pete O]

Yep that makes sense Brian, I did wonder what strong magic would be used to make the necessary calculations for the correction.

[Brian]

Well the time has come to order the first materials. I will be starting with the cylinders. mild steel EN1A the biggest problem will possibly be the fin's 2mm wide with 2mm gaps I intend cutting these on the mill using a slitting saw and rotary table. Looking forward to starting this project it's going to be a long one with lots of things to overcome, but that's the challenge isn't it.
Looking forward to your comments
Brian

[Brian]

Will have to wait awhile to get the leaded steel that want , so I am trying to Get a circuit to build a triggered strobe so I can dynamically balance the crank assembly when I get to that point in the build.
Another steep learning curve.
Brian.