Tony Williams wrote:

The problems which have been experienced by the V-22 Osprey are a
reminder of one very successful alternative: the Fairey Rotodyne. See:
http://www.groenbros.com/tech/FaireyRotodyne.htm
This was a large, passenger gyrodyne which had a separate lift rotor
and two turboprops mounted on a short wing. For take-off and landing,
gas from the turboprops was diverted to jets at the tip of the lifting
rotor, providing the thrust to spin it. For level flight, the
turboprops drove conventional propellers with the autorotating rotor
providing about half the lift.

Disadvantages compared with the V-22? Separate systems for vertical
and level flight.

Advantages compared with the V-22? The lift rotor and propellers were
designed to be optimal for their tasks, instead of being a compromise.
The autorotating ability of the big lift rotor provided a safety
margin. And the whole thing was technically simple and trouble-free.
It WORKED - decades ago! Its only really problem was noise from the
tip-jets, but that would be far less of an issue for a military plane
and they were working on that anyway.

Noise is rather a large issue for the military, if you're trying to sneak
up on people to prevent them from shooting at you. The V-22 is much
quieter than a helo when in fixed-wing mode, which means the other side
doesn't hear you coming several minutes in advance (on the rare occasions
that a Huey flies around in the area, despite my lousy hearing I can
usually be dressed and outside my house before it comes over).

It was only cancelled due to
political/industrial reasons.

The company whose website contains the info listed above is proposing
developing new gyrodynes by converting ewxisting fixed-wing planes -
notably, the C-130 Hercules! This seems like a much lower-risk
approach than tilt-rotors.

It will be interesting to see if they can get development money,
especially for something like the modified C-130 prototype, what the loss
in payload is and what maneuver restrictions are imposed by the large
rotor (below 1g I could definitely foresee problems). What's clear is
that the military wants their next tactical transport to be either
superstol or V/STOL, combined with roughly C-130 capabilities, so that
they don't have to capture an airfield as was the case with FOB Rhino in
Afghanistan. Conventional helos just aren't going to cut it. Piasecki is
working on compounds again (UH-60 or AH-64 prototype, I forget which)
under a DARPA project, and then Boeing, Bell, Lockheed and everyone else
are looking at the next step beyond the C-130/CH-53E as well as a
potential XC-14/15 type a/c, even if the acronym seems to change monthly.

Guy