RT wrote:

From my experience with the Twin Comanche, the feathered position is a
you-beaut, fair-dinkum FEATHERED position and no way known to man would
diving the a/c to Mach 4 to Mach 6 have any effect on the prop/engine.
BUT, because the feathered position did/does require a lot of travel and
wasn't often used, the effect of sludge in the prop cylinder was very
marked....

Thanks, RT, I was wondering if someone might bring this topic up. In the
Comanche owner's forum I was surprised when a very senior and respected flight
instructor made a comment which I had never considered before. The subject of
discussion was air-restarts and the effect, either beneficial or detrimental,
that an increased airspeed would have on the restart process. In his opinion,
additional airspeed would actually inhibit the restart process (during that
period before the engine had started and the prop started coming out of feather)
because "the prop would have to 'displace' a greater amount of air" or words to
that effect, which was opposite of what I would have thought. My initial
opinion was that since no prop is truly completely feathered - i.e. 82 degrees
is a typical 'feathered' position, and some surface of the propeller airfoil
will always be presented at some angle to the relative wind, more wind would be
better to restart the prop. After all, props want to windmill.

The conversation continued and it was specified that we were talking quite
specifically about the portion of the restart process in which the prop was
feathered, NOT as it started coming out of feather. It was agreed upon by all
that increased airspeed would assist in bringing up the RPM as the prop came out
of feather, but not before (i.e. the initial cranking period prior to engine
start.) This distinction was important in understanding this person's point.

The conversation meandered from that point but I've always wondered since if
diving to increase airspeed would in any way assist in getting the engine
started, assuming of course the prop was fully feathered.

-Ryan
CFII-A/MEI/CFI-H