Hi Paul,
Honestly, the use of a radial engine is one of the things about Cyclone that turned me off. Radial engines came to prominence with their use in aircraft. The valuable feature was that all the cylinders stuck out and could be easily air-cooled because there were no other cylinders in front of them to block the airflow. Another reason that radial engines were easily air-cooled is that all those individual cylinders caused the engine to have a very high surface-to-volume ratio.
The problem with all this is that we DO NOT want to cool off steam engine cylinders. Quite the opposite, in fact, it is preferable if they are insulated. The temperatures inside a steam engine cylinder are far lower than in an internal combustion engine, every degree of temperature lost results in lower efficiency.
Of course, Cyclone mounted their engine so that the shaft is vertical....heaven only knows why. Outside of lawn mowers and outboard motors, we hardly ever see vertically mounted engines. Mounting a radial horizontallyis problematic, however. Crankcase lubrication drops down into the lower cylinders when the engine is idle and causes a number of problems.
There's also a balance issue with radial engines. Cyclone attempted to address this with their so-called spider bearing. Of course, this resulted in making the manufacture of connecting rods more difficult. Worse yet, it involved thousands of destructive impacts per minute. Since the motion was now unconstrained, the piston movements became unpredictable. And, ironically, they interrupted the sinusoidal motion of the pistons with a sharp discontinuity that generated many times greater unbalance forces than they were trying to fix. The correct solution is that adopted by US manufacturers during WW2 -- stay with the master rod and slighly differ strokes and rod lengths to for different pistons so as to minimize unbalance. This won't cancel all the unbalance but will reduce it greatly.
Then we get to manufacturing. Radial engines are more difficult and costly to make. For instance, a 7 cylinder radial block has to be indexed every 51.429 degrees to bore the recess for the cylinder and to face off the top of the block. By contrast, an inline engine needs no indexing whatsoever for the same operation -- merely move the block linearly from cylinder bore to cylinder bore. Likewise, we are going to see additional costs manufacturing a number of bolt on cylinders versus manufacturing the whole thing en bloc. Just the extra part handling and assembly will run up the bill.
Truthfully, the only advantage that I can see in building a radial is that you can get away with a crankshaft possessing just one crankpin. This certainly reduces cost and effort in that department. However, a V-4 engine only has two pins. It will take two indexings to work on the cylinders, so that's a bit of a hassle, but still much better than a radial.
