A novel rotary engine design.

[Peter Twissell]

Induction from the carburettor passes through the hollow crankshaft, which has a port cut into one side.
As the engine rotates around the shaft, the port in the crankshaft aligns with the ports leading to each cylinders pump chamber, below the piston.
In this respect, induction timing is similar to that used on conventional model aircraft 2 strokes.

 

[The Ignoble Troll]

Oh! Thank you, that makes sense. Very clever.

 

[Peter Twissell]

Started on the single cylinder test engine:

This is the cylinder. I have roughed out the outside, milled the profile for the induction port (rectangular lump on the side), milled the transfer ports and machined the bore. The thread in the end is M20 x 0.5mm.

The cylinder is from EN16T. The piston will be aluminium with an Iron ring.

I am machining this on my recently acquired Cowells 90ME lathe. It's an early model with M14 x 1.5 spindle nose and no variable speed control, but it's in remarkably good condition.
I bought a cheap (£40) 4 jaw chuck for 'occasional' use, but it turns that it holds the part much more rigidly than the 3 jaw 'slimline' chuck that came with the lathe. I suspect the 4 jaw may see more action than the 3 jaw!
I am surprised how capable this little lathe is. With a CCGT tipped 6mm boring bar at 880 rpm, it produces a parallel bore (as near as I can measure withe telescopic gauge and micrometer) with a near mirror finish. It looks good enough that I'm going to try it without honing.

 

[a41capt]

I love the experimentation approach Pete! Takes me back to my early motorcycle racing days before there were “bolt on” accessories, especially for 2 strokes.

John W

 

[Peter Twissell]

The cylinder is finished all but some final deburring.

I tried to cut all the fins using a slitting saw. This was necessary for fins at the top and bottom, as they are not a full circle, but since I had the cylinder set up on the rotary table, I thought I'd do all of them.
I used a 20mm diameter saw mounted on a 12mm arbor. To cut the fins all the way down the cylinder, I had the arbour hanging out of the collet by about an inch.
This was enough that the arbour started to work its way out of the collet, leading to a couple of helical fins.
I'm not worried for this test cylinder, but I won't be trying that operation again.
Next will be the rocker support, which will be held in place by the valve cage which screws into the M10 x 0.5 thread in the top of the cylinder.

 

[a41capt]

The cylinder is finished all but some final deburring.View attachment 159227
View attachment 159228
I tried to cut all the fins using a slitting saw. This was necessary for fins at the top and bottom, as they are not a full circle, but since I had the cylinder set up on the rotary table, I thought I'd do all of them.
I used a 20mm diameter saw mounted on a 12mm arbor. To cut the fins all the way down the cylinder, I had the arbour hanging out of the collet by about an inch.
This was enough that the arbour started to work its way out of the collet, leading to a couple of helical fins.
I'm not worried for this test cylinder, but I won't be trying that operation again.
Next will be the rocker support, which will be held in place by the valve cage which screws into the M10 x 0.5 thread in the top of the cylinder.

Loose collet or not, that’s a mighty good looking test piece!!!

Nice work,

John W

 

[Steamchick]

I'm impressed! A big "Wow"!
On miniature spark plugs. Comment # 8:
A late friend (Watch/clock maker/repairer) who made a 9-cylinder radial engine, and various other models that all ran... used home made spark plugs the same size as those glow plugs. He used domestic plug fuse body ceramics, (Some difficult to machine, or others easier, depending on brand of fuse and ceramic material! The fuse body is a few mm diameter, with a hole in the middle - for the central electrode, sealed with epoxy resin. He later managed to buy some 1/8in stock machinable ceramic so he could make better ceramics for the miniature spark plugs with 3/16" x 40 thread! He used lighter fuel petrol of lighter fuel butane to run his engines (Mostly around 1/2in bore and stroke.) for demonstration.
But I like the glow-plug arrangement for simplicity and reliability in an aircraft!
K2

 

[Steamchick]

Incidentally, I like the idea of the spiral fins! But wonder how that could interfere with air-flow past the prop and engine? A lot of turbulence perhaps?
K2

 

[Peter Twissell]

I don't see why helical fins would make any difference to the air flow, especially on a rotary.
It might be nice if my bike engines had helical fins - it would be easier to clean between them.

 

[Steamchick]

Straight, parallel gaps on both sides of the cylinder - in the airflow, develops laminar , or less turbulent flow. A helix of cooling fins could develop an up draught one side and down draught on the other, which multiplied by the number of cylinders in this radial could counter the helix of draught from the prop...?
A guess?
K2

 

[Peter Twissell]

But this is a rotary. The cylinders are spinning in the same direction as the prop.
Airflow on the lee side of each cylinder will be turbulent and the small helix angle would be insignificant by comparison to the centrifugal "fan" effect.

 

[Steamchick]

Thanks Peter. I didn't know, but now I do.

K2