Originally Posted by
SansAnhedral
Hold onto your butt.
Remember that the S-97 pusher is wet clutched so it does not stop rotating. Defiant used a dry clutch to attempt to demonstrate the safety aspect of stopping it during ground ops. Unfortunately that clutch sh*t the bed and the Army knows all about it.
At a gas turbine company, I sometimes worked on design of high power aerospace clutches. The wet clutch is always superior to a dry clutch. It is possible to design the Raider wet clutch to be unclutched while idling on the ground, so it sounds like the Raider clutch design is a botch job. A brake would still be needed on the prop, and the clutch plates would need to have spring separators, to make sure the plates separated when the clamp force was removed. A dry clutch has a much much greater wear rate of the clutch plates. Therefore the plates have to be very thick. Then the clamp load has to be massively increased because there are fewer plates. So the dry clutch ends up just as large or larger than the wet clutch. Oil must continuously be supplied to the clutch bearings even with a "dry" clutch. Likely Sikorsky did not account for the very high wear rate of the dry clutch plates. Think of needing 1.5 inch thick plates instead of .125 inch thick clutch plates. The thermal management of the dry clutch requires shielding around the red hot dry clutch plates, to keep from coking the bearings oil, or even starting a fire. Cooling air is required, and the best source here is engine bleed air. Do everything right, and the dry clutch still has a much shorter clutch plate life than a wet clutch.
The Sikorsky X-wing clutch design, scaled to size, would work just fine.