Bob Chilcoat wrote:
Other interesting engines were the Napier Nomad (12 Cylinder horizontally
opposed turbo-compound diesel - target HP 6,000!) and the H 24 (two rows of
horizontally opposed 12's) Napier Sabre II, which developed 3,500 HP in
later versions. The Nomad was never produced, but is considered by many to
be the most complex aircraft engine ever attempted.

--
One of the engineers working for Lockheed designed a mulit-mode jet
engine back in 1947, that we would have trouble building even with all
the advanced technology we have today. It was a 47 stage tubojet that
used automatic controls to convert to a scramjet based on aircraft
speed and power needs. As the aircraft sped up and the dynamic
pressure in the inlet increased, the engine would decouple a stage of
compression and feather the tubine blades as well as the stator blades.
This would continue until all stages were feathered and only a single
stage in the hot section was turning, only to drive the accessory
gearboxes. By this point the aircraft would be well into the supersonic
regime of flight and the engine would be operating in the scramjet
mode. The data that I've seen suggested somewhere around 20,000 pounds
of thrust in an engine case of only about 20" in diameter.

Craig