It is just a slipping clutch, that allows the engine to come up through
starting RPM's, before it engages, then stays locked throughout the
operating range of RPM's. The starting RPM's produce a torsional
resonance that would shake the engine, gearbox and clutch, so badly that
it could likely destroy something in the drive train. Allowing the prop
to not be connected while the revs come up avoids the deadly resonance
range, so the drive system can run normally, when it is above the bad RPM
range.

After parking planes all weekend -- and staring right at the spinners at the
center of some really big Ginsu knives -- it's quite remarkable how much our
engines get tossed around during shutdown. Some of them appear to rather
violently move over 4 inches off-center while enduring the asymmetrical
loads during engine shut-down.

A clutch is one more thing to break -- but, wow, if it can eliminate that
violent twisting motion that our motor mounts and airframes must endure, it
might be a good thing?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"