Dynamic 049
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This is an example of the highly rare and sought-after Dynamic 049 twin ball-race, rear drum induction diesel designed by Gordon Cornell in the 1961. The engine was intended for competition free-flight events and was designed for light-weight and high performance. However the die makers ran into trouble, so Gordon produced interim dies for the crankcase as seen in the photo and recalls completing, testing, and boxing twenty production models of this type. Sadly, the project collapsed due to insufficient seed funding and none of the intended light-weight, gravity die-cast models were produced. Later, some further examples were completed from spares obtained from Gordon by Mike Clanford. These do not have the red anodized head of the "factory" models and although built by a respected engine builder, they may fall short of the performance of the the Cornell built ones which were guaranteed to exceed 17,000 rpm on a Kiel Kraft 6x3 nylon prop. The Dynamic 049 had a bore of 0.406" and a stroke of 0.386" for a displacement of 0.049 cuin (0.823cc).
The engine was advertised twice only in the Aeromodeller in March and April of 1961 by a company called "Dydesyne Ltd" (pronounce it like die-design, not died-sign), presumably after the company head, Alan Dye, and made prominent use of Gordon's reputation in the advertising. No advertising appeared in Model Aircraft, but the October 1961 issue carried a mini-review by Peter Chinn of the Dynamic and the other Cornell designed, Dydesyne produced 049 which was named the Tutor. This engine was to utilize the same cylinder/piston assembly as the competition engine, but was to feature a plain bearing, front rotary induction, with bulkhead only mounting for sport use. Like the ball-race engine, very few exist today, victims of a fine effort in a difficult market requiring deeper pockets.
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Update
Tests conducted on the example pictured here suggested that this one was just not coming up to scratch, so the owner contacted Gordon for advice regarding props, fuel, and possible faults. The first step was a complete pull-down for inspection and thorough cleaning. This revealed that the ball races were worn, and not of the correct type according to Gordon, who would know if anyone should! The tear-down also revealed to case to cylinder gaskets, one of which appeared distinctly agricultural in comparison with the rest of the engine. More on that later.
Despite what otherwise good references like Dave Gierke's Two-Stroke Manual say, pushing ball races into their cavities by hand is really not going to obtain the best from them; they need to be aligned with each other and you really should not expect the shaft to do this job when you shove it in. This picture shows the press tools made to the instructions described by Gordon in Part 6 of his Model Engine Design Series. Using them, the reassembled shaft spun very freely in new races of the correct type as supplied by Gordon for the job. Despite this, the engine was still not delivering the performance all Dynamic 049's were capable of.
Suspecting the pig's ear gasket was a modification by a previous owner, it was removed and the engine retested. Success! The little Dynamic 049 was now turning an APC 6x2 at 18,500 rpm, somewhat up on the 12,500 previously produced. Obviously, lowering the cylinder a little had opened up the exhaust and transfer duration to where they should be. The reason for the shim remains a mystery. Perhaps the earlier owner was after better break specific consumption or something. Whatever, this most worthwhile exercise shows that the Dynamic was capable of performance competitive with the TeeDee 049 glow on FAI fuel.