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The radial engine.

I’m within my comfort zone here with this one but it is 25 years since I flew one. The two I flew most were the Pratt and Whitney Wasp 1340 cubic inch which delivers 600hp and the Wasp junior, 985 cubic inch which delivers 450hp. I remember it all including every farmer asking me “how does this work?” I have been down several times in radials including when I had a master rod failure and the engine trashed itself. The master rod is at cylinder number 5, counting from the top in an anti-clockwise direction, viewed from the front. I was 8 foot off the ground and all ground around was contoured. I had nowhere to go and badly damaged the aeroplane.
All radial engines must be an odd number of cylinders, well each bank must be anyway. This allows each cylinder to complete each of it’s 4 cycles. Goes like this. I’ll make an example by using the power stroke. 1 3 5 7 9 2 4 6 8 1 3 5 7 9 2 4 etc etc. follow them around with your finger. You will notice the change in order of the cylinders the second time around.

The cam is a ring of about 12 inches in diameter. Both the R985 and R1340 has gear teeth on the inside of the ring and of course the lobs on the outer. The cylinder is steel and the head aluminium screwed on prior to the drilling of the cylinder stud holes. The cylinder in the picture has been unscrewed since manufacture. The stud holes in the cylinder base tell me that. There is only one crank journal. There is a supercharger in the picture. Piston engines have a centrifugal blower and jets have axial compressors. The PT6 have both. Note the collector oil sump (it’s a dry sump) is between cylinder numbers 5 and 6. You can see it. This oil is pumped back to the reservoir which is an airframe component. Notice the Pratt and Whitney badge on the sump. Engineers steal that on engine changes when removing it for overhaul. The push rod covers (the tubes) in the engine illustrated above are chromed. This massages the owners ego. Some times the rocker hats are too.
For those inquisitive people you will find plenty of information on Youtube. I couldn’t see any schematic diagrams. I would think there are some senior aeroplane engine mechanics in this forum who may like to add to this. Likewise current or former jet engine mechanics or pilots.
Hope you enjoyed reading that.
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