A couple of things I picked up here and there:
- The Fairey Gannet had two engines with their own props, so all you needed was some sort of 'mixing unit' to get the power to the co-axial shafts. A similar system must have been used on the Macchi MC72 (the italian racer), this airplane had two V12s bolted end to end with seperate twin bladed props. I'm guessing they had seperate shafts as they probably weren't up to keeping a V24 engine running smoothly in those days.
- On an airplane like the Shack or a contra-prop Spitfire (one of which is flying again in the US!) you've got one engine, the output of which is split into two co-axial shafts in the gearbox, each with their own prop. You also need something called a 'translational bearing' (if my memory is correct) to transfer the prop pitch setting from one prop to the other. There have been instances of this piece of kit failing and the whole unit (all six blades) going to flat pitch. No matter what amount of power you can get from your engine in such a situation, you'll be going down fast! After 'Red Baron' another Mustang was fitted with a contra-prop Griffon: 'Precious Metal', this one was once belly-landed after such an incident. The aircraft was repaired though and is once again active at Reno.
Indeed the TU-95 'Bear' has contra-props too. Also the Bristol Brabazon, the Saunders-Roe Princess, MB-5 and Koolhoven FK56 (can someone find a photo on the net of that one, just to check if I got it right!
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