Paul,

   I've been thinking about the limp home
mode of the 13B.  I know
we try to design in redundancy, but say you end up with a
dead
rotor due to a fuel or ignition problem.  Do you have
any idea
how many hp would be absorbed in driving the dead rotar at
6k
rpm to overcome pumping/compression/friction losses? I'm trying
to figure how many hp would be left to drive the prop in
that
situation. And would peripheral vs side ports make a
significant
difference?

Dan Stanzione

I don't know but having the throttle wide open would help
I think. What gets compressed de compresses and feeds the
torque
back into the e-shaft. Friction is half of what a piston
engine is. BTW losing one rotor is like losing two
cylinders
of a four cylinder piston engine.

Paul Lamar

I did some extensive test on the matter while I was at
Mistral.  A Mistral
N/A engine produces approximately 170 hp per rotor,
gross.  Then you lose
~65hp to pumping losses, compression losses, friction
losses (from seals as
well as from the PSRU) and accessories losses for a net
power of ~105hp per
rotor.

If you lose ALL power on one rotor on a 2-rotor engine,
then you are down to
40hp on the prop, not enough to stay aloft unless you are
in a very light
aircraft or are benefitting from strong uplifts!  It
would just allow you to
stretch the glide, not to limp home.

On a 3-rotor engine, the arithmetics look better and, with
a fully failed
rotor,  you still have a good 140 hp on the prop, or
45 % of full power,
enough to stay aloft, at least at lower altitudes and
lowest drag airspeed.

The good news is that we NEVER lost the full power of one
rotor accidentally
(we made the missing-rotor tests by cutting ignition and/or
injection to
that rotor).  Detonation will damage your apex seals,
but actually, damage
steel seals don't leak too much as long as they stay
hot.  The worst power
loss we saw with steel seals after a major detonation event
(which always
happened on a single rotor, always the front one because of
less optimal
chamber wall cooling) was a loss of ~70hp, leaving 65%
power to the engine
and very little unusual vibrations.

We never damaged a single ceramic seal however (and we
tried hard, believe
me)!  Even if you were to crack one such seal, you
would keep perfect
compression on one chamber of the damaged rotor, and
probably some
compression on the two chambers separated by the damaged
seal.  The worst
case scenario is, however, a ceramic seal breaking away
from its slit and
pieces of it breaking the remaining seals.  Such
scenario would obviously
make you lose all power on the affected rotor.  But
believe me, it would
take an awfully violent detonation event to break those
ceramic seals;
possible only on a quite highly boosted turbo engine and
most improbable if
not impossible on a N/A engine.  By the way, Iannetti
makes 3mm thick seals
(instead of the normal 2mm ones) which he recommends for
high-power
applications.  We never felt the need to test those.

Of course, all I just said is mute if you don't have
reliable dual ignition
and injection like Mistral engines have.  Then, you
could lose 100% of a
rotor's engine because of a failed injector... and THAT
does happen!

Conclusion:  rotary engines are impressively robust
and forgiving, they
really are!  Some of Mistral's technicians, coming
from the piston engine
side of the industry, could initially not believe how much
abuse a rotary
engine could survive.

Best regards to all,

François Badoux

 Francois,  (sorry I don't have a c with the thing on the bottom)

   Thanks for that great info.  I guess that argues in favor of a
three rotar if your plane can handle it, or for at least very good
redundancy within each rotor for fuel and ignition.    Dan Stanzione
dan stanzione