I think it was a centrifugal clutch, no linkages.  The assumption is
   that
   the resonant point is at low speed when the prop is not linked to the
   engine.  There might be a normal spring center in the clutch disk also.
   It is supposed to lock up at rpms where power is actually being used.

   Murry I. Rozansky

It matters not at all what engine is involved, or what drive system, or
what prop may have come apart, or what fuel injection computer my have
gone on break at a poor time.

It only matters that the pilot had less power than he thought was
prudent, and then instead of doing what his instructor had yelled at him
a thousand times, and landed straight ahead at the lowest possible
ground speed, he did what the instructor had yelled never to do and that
is make the dead mans turn with a dead engine.

Leave the low altitude low speed 180's to Bob Hoover.

Lynn E. Hanover