I have been reading a lot on PSRUs and it would seem that there is a lot
of
discussion about resonant frequencies and chatter. Tracy also mentions it
along the way in his books and online.

Question:
In helicopter applications either twin engines connected to a single
output
shaft, or a single engine application, they use an overrun clutch. This
lets the rotor continue to rotate in the event of engine failure.

The question is why couldn't we use such an item in the PSRU to control
the
idle condition where the firing pulses let the prop drive the engine, and
while in the air during descent when the prop drives the engine? The
drawback that first comes to mind is that without a prop speed control, it
would be possible to over-rev the prop itself, but aside from that what
would be the issues?

Also, has anyone thought of using helicopter technology to use 2 13B
engines connected to a single psru? If you use an overrun clutch on each
input shaft, you would have a twin engine plane. If one engine quit, the
overrun clutch would allow it to stop rotating, while the other engine
kept
on making power to get you back to a landing area.
Just a thought.

Kevin Alderman

There was a German plane with 4 engines driving a single 22' dia. prop
in 1918 that could fly on any 2 engines.  Lockheed built the Starliner in
1938 with Unitwin, twin pack Menascos. Twin packs do not have    completely
separate powerplants and are not considered true multi engine for
reliability purposes.  Convincing the FAA and insurance companies that the
Learfan was as reliable as a normal twin was one of the factors that sunk
the Learfan. A twin pack should be safer overall than a conventional twin
but might be more expensive.   It has been done so it is possible.   That
is what Experimental is for.

  Murry