I have been watching Mistral quite closely, as my need is for a powerful
(400hp+) certificated engine, but I do not see where the Mistral engine
has achieved certification. At least, it doesn't show up in the FAA's
TCDS file - perhaps their legal name is something other than "Mistral"?

As a relative newcomer to this forum, I have been amazed at the amount
of information all y'all have. From your discussions I believe a 450 to
500 hp rotary is certainly achievable (2 or 3 rotor), with far better
sfc than the small turbines (Allison; Pratt; Walter).Flying certificated
aircraft, my needs are for a certificated engine, and I fully expect to
pay $60K+ per copy (perhaps $80 to $100K is more realistic - but I'd
hope for $60K!). If I have missed something, and a
+/-500 hp rotary exists, please clue me in.

If anyone is looking for a testbed aircraft, we operate several PA31P
aircraft - so we would have the capability to install a rotary on one
side for proving runs, while running a certificated (but no longer
factory supported) TIGO-541 on the other wing.

The Mistral G-360-TS installation will likely weigh in at 500 to 550 lbs
wet, with associated equipment (not including propeller), and is rated
at 360hp (320 max continuous).The TIGO-541 weighs in at roughly 750 to
800 lbs wet, with associated equipment (without propeller). While the
Mistral seems heavy compared to other rotary engines, it is
substantially lighter than the heavy (and touchy) TIGO-541.

Any thoughts / constructive comments / ideas from you would be
appreciated.

~ Nick Jilek
--------------------------------------------------

Mistral is working hard and highly focused on certification and it could
happen any day now. They have had a lot of FAA hoops to jump through as
the rotary is so different than a piston engine. One of the problems is
buying bearings with a paper trail as some rotary engine bearings are
quite different and bearing companies are reluctant to make aircraft
parts. They may wind up making their own. Also they are certifying a
FADEC at the same time. If you use existing aircraft carbs and magnetos
certification is much easier. I'll have more info when I get back from
Aero in Germany in a couple of weeks.

500 to 550 sounds heavy for a 3 rotor turbo as turbos can weigh as
little as
16 pounds. The bare block is only 260 pounds. This Mistral chart list
about 440 pounds for a G-360-TS. Less for a helicopter engine without
gear box.

Paul Lamar
--
Hi Nick,
You should contact Mistral and offer your plane as a test bed. At the
present time they are pursuing the certification of the TWO rotor
engine.
Next in line would probably be the two rotor turbo as 90% of the cert
work would already done from the N.A. engine. Their test bed plane is a
SINGLE ENGINE Piper something or other that can support the weight of
the two rotor engine because it is similar in weight to the Lycoming it
replaced. With the increased weight of the three rotor, it's likely they
will need to find a larger plane for testing. Keep in mind, this would
put your plane in the EXPERIMENTAL class and you could not use it for
commercial purposes until it was restored to the original configuration
and reinspected. They seem to do a lot of the test flying around their
facility near Daytona Beach, FL.

Dave M


No longer Dave. The Piper Turbo Arrow crashed. Non certified muffler
melted and plugged up. Several months after I went for a flight :) They
now have a Maule now I think. Nick may have missed an opportunity there.

http://www.youtube.com/watch?v=Lo1TqhQqOkg
http://www.youtube.com/watch?v=3JQVeMoKBT0
http://www.youtube.com/watch?v=aLY139b65a0

Nick, I have a question for you. When you overhaul those TIGO-541 what
parts must be replaced in the gear box? What is the TBO time anyway.

Paul Lamar

Paul - The recommended TBO on the TIGO-541 is 1200 hours.  The word on
the street is the engines seldom make that, but our experience
contraindicates that (professionally flown . . . and I don't mean by
pilots that fly for a living, but by pilots that are professionals and
treat their equipment as such . . . the engines will make TBO).  The
gearbox on this engine is integral to the engine case, and is primarily
a crankshaft extension with a helical gear driving a helical-geared
short prop shaft (no idler, no planetaries - result is a standard
rotation engine with a left-rotation prop).

I do not have adequate overhaul information to answer your question on
the longetivity of gearbox components - but will do some checking for
you.  Powerplant Solutions / Propellers Direct (they are affiliated but
I'm unclear how) purchased Lycoming's inventory when Lycoming dropped
factory support; I will check with them and with the folks at Firewall
Forward and advise.

~ Nick Jilek

Thanks Nick. I think the 1200 hour TGIO TBO says it all.
I had no idea there was a demand for these engines.
I guess a lot of people have bit the bullet and converted to PT6's or
some such. Where do they get the extra fuel capacity?

There for awhile people with PT6 powered King Airs were looking at
retrofitting Orenda V8's to lower the fuel burn but that fell through
partially due to the 1000 pound firewall forward excess weight of the V8
and 1200 hour TBO.

Can you get along on 360 HP?

TIGO-541-C1A
    Six cylinder, turbocharged, fuel injected, geared, 400 hp (298 kW)
engine, dry weight 703 lb (319 kg), AiResearch T-1879 turbosupercharger,
certified 19 November 1968. Has internal piston cooling oil jets, side
mounted accessory drives and a single oil supply from the propeller
governor. Provisions for a reverse pitch propeller control.

The Mistral 3 rotor turbo is an ideal replacement.

For the 450 HP higher power versions of the TIGO Mistral might have to
go up to four rotors or up the take off engine RPM to 7500.
The current takeoff  Mistral 360T engine red line is 6350 RPM which is
VERY VERY conservative indeed. There are several people out there with
Mazda's taking off at 7500 RPM. Some with hundreds of hours. My guess
is; with shorter intake manifolds the 360T power would be about 430 HP.
There are lots of NA three rotors racing up to 11,000 RPM for 24 hours
with that much HP. Four rotors are up to 690 HP at 9000 RPM for 24 hours
flat out.

BTW There is also some new tech on the horizon to cut the apex seal wear
by Teflon, DLC or other low friction coatings the apex seal itself and
or the apex seal slot in the rotor.
That would be the main thing limiting the TBO. It is also what the FAA
looks at when they assign a TBO. Coating with Teflon can be done in your
kitchen oven :) The rotor housing don't get the kind of wear you see in
cylinders.

The e-shaft NEVER fatigues or cracks. Same for the rotors.

Paul Lamar


Hello, Paul.  We are running the -E1A, which differs from the -C1A in
rated power (425 vs. 400) primarily via a different turbocharger and
higher manifold pressures. Converting to a PT6 can be done, but by the
time one is done they'd be better off simply purchasing a Cheyenne. I
looked hard at the Orenda / Trace engine, but the SFC wasn't where I
wanted it, although the performance appeared promising and the
installation also appeared promising (easier than the Aero Commander
installation Mr. RPM had accomplished). I've also considered the
direct-drive IO-720 as a replacement, but the engine was never turbo'd
by Piper and we need bleed air for the pressurized cabin. I'd also
really rather go with a rotary - I believe in the technology - and if
one is going to go through all the problems associated with swapping
powerplants it should be to something worth-while for the long run.

The Piper PA31P-350 (Mohave) was a re-engined PA31P, using the direct
drive TSIO-540 of 350 hp. The aircraft gross weight was restricted by
600 lbs, due to the reduced power.  Pure extrapolation would show if one
saved 500 lbs by replacing the 425 hp TIGO-541 engines with the Mistral
G-360-TS, the weight penalty would be 100 lbs off of useful load. That
being said, nobody ever wants less power :) unless there is a decent
tradeoff - lower operating costs, better SFC, etc. And, since we need to
take air off the compressor for cabin pressurization, I wouldn't want an
engine that was marginal at making rated power - at higher altitudes
where the engine needs the boost, the cabin also needs more bleed air.

I also believe the Mistral specs are extremely conservative, but this is
historically the way the certification game is played.  I believe if the
G-360-TS will honestly deliver 360 HP to altitude (FL280 / 28,000 ft)
while also delivering required cabin bleed air, the SFC is at least as
good as the TIGO-541-E1A, and an efficient propeller is developed for
this installation, this just may be the cat's meow - especially if we
can counter-rotate the engines (or at least the props). It is possible
installed weight could be low enough that useful load would not be
restricted, and that cooling drag could be minimized to allow a better
cruise speed.  However - Mistral has published a max continuous rating
of 320 HP, which is substantially less than the 425 HP the Lycoming is
certificated at (not that I know anybody that would run the Lycs at 3200
rpm and 47 inches at altitude - but they did get this certified).

Interested in your thoughts . . . especially when you get back from
Aero.

Thank you!

~ Nick Jilek