I'm pleased to say that this project is now registered (Over 20Kg category), and, is finally underway. No quarter-scale documentation has been found so far, so, I expect that everything will have to be adapted from other scales. This may mean that I'll have to teach myself CAD ! (Normally, I'm more at home on the drawing board). One advantage of CAD is the ease of re-sizing things plus you can give a "DXF" file to the laser cutting boys once you have worked out all the wood sizes etc.
The spec' for the model is very ambitious and includes working variable pitch contra-props, double wing-fold, sliding canopy and actuating deck hook as per full-size. To date, I have been working on the design of the contra gearbox with some initial ideas on how I'll integrate this with the variable pitch mechanism.
On the workbench now is a 20% mock-up of the two co-axial props together with 'Mk 1' of the planetary gearset. This will be used to drive the front prop, reverse the rear prop and accept the input from the turbine's reduction gear. So far, the props have been run up to 2400 rpm without problems. Blade pitch is fixed at present as the rear prop has been adapted from a right-hand tractor but still gives a 'healthy draught' when reversed against the front prop. The planet gears have suffered a few broken teeth. They are only in wood at present so no surprises there ! However, the exercise has taught me the correct number of teeth, pitch, profile and gear ratios. It is helpful to sort all this out now before going into metal...
I'm really enjoying the project so far. There will be many other engineering challenges along the way but, I hope that working out the driveline and prop control issues, up-front, will pay dividends in the long run. My wife is the photography expert, so, as soon as I have the bugs out of the contra gearbox, I'll post some pic's of it in operation.
