Zimmerman Cirrus, Cirrii?
The late Merritt Zimmerman designed replicas of the DeHavilland Cirrus I in 1/4 and 1/6th scale. He built several for sale (I've heard the figure 25 bandied about), and presented the plans to Robert Washburn to help kick-start SIC Magazine. The 1/4 scale version was built and documented by Ron Colonna. Eric Whittle did likewise with the 1/6 scale version and later reduced it to 1/9 scale. His plans and the construction feature for the latter appeared in English magazine, Engineering in Miniture. The cylinders, pistons, 'rods, and head of this engine formed the basis for Eric's Aero V8 that was serialized in the Model Engineer. This makes for a very satisfying symmetry, as the full-size Cirrus I, designed by Major FB Halford, began as the (metric) cylinders, pistons, 'rods, and heads of a Renault V8!
The 1/4 scale version is more sophisticated than the smaller model, having spark ignition, a wet sump, and pressure fed lubrication. Eric Offen has had one of these underway for some time and recently found himself on a roll of energy for the project which is starting to come together nicely. The photos below show Eric's engine in early January. I especially like his timing adjustment innovation. Note the offset hole pattern he's used to secure the large timing gear to the carrier on the cam shaft. This allows very small adjustments to be made to the timing, while the gears are rigidly keyed to their respective shafts. Eric machined the cams using the Cam Calc page of this web site, using 3 degree increments. He says this made it so easy, he is making multiple shafts with different cam profiles to see which prduce the best results.
And to round off this item, a reference to an old friend: I just noticed that 5 Bears has posted construction pictures of the 1/6 scale Cirrus project. Lots of good pictures and words that describe not so much the build, as the re-build. The 1/6 scale model is a glow ignition version, so no oil pump is required. Just looking at this picture made me want to take my 1/6th scale Cirrus out from under the bench and fix the dog's breakfast I made of the timing gear carrier casting over five years ago. So I did, and that, as we'll see in the next item, resulted in a third Tech Tip for the month.
Tech Tip (3): The Putting-on Tool
There can't be an experienced model enginer reading this who has not unaccountably, accidentally, and surprisingly, turned some critical part disasteriously undersize. It's at times like these (after the blue smoke before one's eyes clears), that one could really use a tool that puts metal on, rather than taking if off. While such a magical device does not exist, we can in certain circumstances, achieve the same end. Our last tip this month is aimed mostly at those just starting in model engineering, and gives advice to store away for when (not if) this happens to you. So have a look at The Putting On Tool in the Model Engine Construction Techniques Section.