About 1945/7 Avro of Manchester started to manufacture and build the Avro Shackleton Long rang Maritime aircraft, so good was this aeroplane that it only left service about 1989, what might you be asking has this got to do with the current disscusion regarding the contra prop Sikorsky X2 hybrid Helicopter, well my twopen'th is this. the Shackleton was powered by 4 Roll Royce Griffon 58 V12 piston engs mated to a very strong almost agricultural gearbox with a huge siamesed propshaft that drove Two Contra rotating props, originally with the early marques of the Griffon both props were equal in diameter, but as the engine was powered up through the years the design guys realise that the propellor tips were comming perilously close to each other at certian power settings and in fact had in some case acutually hit each other, the clever guys at a local factory to me here in Lancashire realised that the tips passing each other were causing supersonic shock waves this had the effect of bending the tip of both front and rear blades inwards towards each other, after much testing they decided that the rear prop would be longer than the front prop and the cord of the rear one would be altered to take out this possiblity of inward bending when under certain power conditions, it worked and from about the early 50's the props fitted to the Griffon 58 had a greater diameter at the rear.
Is/ or could this have any bearing on the two different diameter rotors on the Sikorsky X2 hybrid ?
Peter R-B
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