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 downto
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 youto
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