I just found the reference to the lowest recorded SFC in an aviation
engine.  The 1950 Napier Nomad with a 0.36 SFC turbo-compound,
supercharged 12 cylider diesel 3,000 hp.
http://en.wikipedia.org/wiki/Napier_Nomad  Now, that's a
worthy challenge to beat with a 16X rotary engine. (not the hp, the SFC)

Greg


They have one in the Ottawa museum as well as the Smithsonian.
Here are some pictures I took at the Smithsonian.

Paul Lamar

Paul,

In case you or others missed it, two rotaries sandwiched together plugs
up would imply one of them is rotating the opposite direction.  A shaft
within a shaft solves this and propellers are thus contra rotating.

I just found the answer to the merits of contra rotating propellers, or
those that are co-axial.

"When airspeed is low the mass of the air flowing through the propeller
disk (thrust) causes a significant amount of tangential or rotational
air flow to be created by the spinning blades. The energy of this
tangential air flow is wasted in a single propeller design. To use this
wasted effort the placement of a second propeller behind the first takes
advantage of the disturbed airflow.

If it is well designed, a contra-rotating propeller will have no
rotational air flow, pushing a maximum amount of air uniformly through
the propeller disk, resulting in high performance and low induced energy
loss. It also serves to counter the asymmetrical torque effect of a
conventional propeller. Some contra-rotating systems were designed to be
used at take off for maximum power and efficiency, and allowing one of
the propellers to be disabled during cruise to extend flight time......"


Hmmm...... shut one engine down and keep the other operating at a high
duty cycle thus maximizing turbo compound merits.


Doug in Japan

Or drive one prop with a large exhaust  turbine and the other with the ICE.

Paul Lamar

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