Hehehe, the problem here is the cost-mass-performance triangle, Nick. If I had my way our customers would be hovering that payload direct from mine to mill!
I had wondered about the use in the intermediate gearbox, if only as a means of saving weight. The link below suggests the Thompson Coupling could handle 20 degrees, but unlikely at high torque (Dana would certainly not approve a UJ for 15 degrees). Since I imagine the tail boom / fin corner is positioned to allow main rotor clearance then that angle is not enough. However, the standard joint is designed for grease lubrication inside rubber bellows – if the joint was oil immersed it would handle higher angles without heat build up. Since the joints are constantly in mesh then you would not be carrying around unmeshed teeth on gears, and the fixed angle removes the need for the complicated mechanism.
http://cvcoupling.com/index.php?opti...d=12&Itemid=44
For helicopter applications Thompson would need to do a dedicated design study for an oil housed assembly with several couplings in series for say 45 degrees. This might result in half the mass and cost, over a gearbox, since there is less machining and heat treatment. Certainly there would be increased damage tolerance, from secondary particulate contamination such as tooth spalling & failure from say a bearing breakup. I would be happy to make some enquiries on Sikorsky’s behalf…
Dave, for the purposes of driveshaft mass guestimation:
3000HP (2237kW) / 18966rpm (1986.1 rad/sec) = 1126 Nm
4.506 g/cm^3 (Ti) / 1000 x 2 PI x ~7”/ 4 (50mm) x 0.050” (1.27 mm) = ~1.8 kg/m
Mass per torque per length = 1.6 kg/m per 1000 Nm input torque.
I’ve taken some liberties here for a first estimate, but maybe i'm wrong to criticise some of your designs...