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 rotor if your plane can handle it, or for at least very good
redundancy within each rotor for fuel and ignition.

Dan Stanzione


-
Paul,

Now I know you haven't forgotten the old cut-and-paste routine!  François

George


Parlez vous francais George? :)

Paul Lamar