Wet versus Dry
Another large benefit of a wet clutch over a dry clutch is more predictable coefficient of friction. The highest risk of damage in this clutch application is during engagement with the main rotors spinning and the propeller stopped. This must be achieved smoothly to prevent damage to the drive system.
With a dry clutch, the coefficient of friction is higher than on a wet clutch, and dry friction can change significantly with wear and temperature. This makes safety engaging a dry clutch in this application much more problematic.