> Dear AREN Gang:
 >
 > Rotary v. Gas Turbine
 >
 > So now, they are going to put a gas turbine engine into that most
 > bread-and-butter of airplanes, the Cessna 206.
 >
 > I have posted some information about this, as well as links, below.
 >
 > Of course, you know me: I go with the rotary, But! how do you members of
 > the board compare and contrast this gas-turbine installation with the
 > rotary? The good and the bad?
 >
 > Curiously yours,
 >
 > Les Nordman :-)
 >
 > AVWeb has published this:
 >
 > Soloy Receives FAA Certification For Turbine Cessna 206
 > http://www.avweb.com/eletter/archives/bizav/1245-full.html#199126
 >
 > Soloy Aviation Solutions, of Olympia, Wash., received FAA certification
 > on Oct. 28 for its Soloy 206 Turbine Mk II, a turbine version of the
 > piston-powered Cessna 206H. Powered by the Rolls Royce 250-B17F/2
 > turbine engine, the Mk II provides an increase of 110 hp over the
 > standard Cessna 206H, Soloy said this week. With the turbine conversion
 > paired with a Hartzell three-bladed prop, the airplane can carry more
 > weight, fly faster and operate in high and hot conditions. The
 > performance also improves the airplane's STOL performance, especially in
 > its amphibious configuration, Soloy said. "The Mk II is the perfect
 > platform for vast number of applications, from law enforcement to
 > adventurous backcountry operations," said Dave Stauffer, president of
 > Soloy Aviation Solutions. "The lighter turbine engine increases the
 > power while reducing the basic empty weight by approximately 150 pounds."
 >
 > The aircraft can climb at 2,460 fpm at sea level, cruise at 20,000 feet
 > at 213 ktas, carry 775 pounds with full fuel, and has a range of about
 > 550 nm, the company said. The Mk II is initially offered in four
 > configurations, for law enforcement, skydiving, amphibious flight and
 > commercial/private operations. Soloy has started accepting orders and
 > plans to deliver the first aircraft later this month. The aircraft will
 > be on display this week at the AOPA Expo in San Jose, Calif.
 >
 > Rolls-Royce publishes a description of the engine here:
 >
http://www.rolls-royce.com/defence_aerospace/products/tactical/model250/desc.jsp
 >
 > Description
 >
 > "The Model 250 Series II turboprop engines are of two-shaft modular
 > design featuring four to six-stage axial and single-stage centrifugal
 > compressors, a two-stage LP turbine, two-stage HP turbine with a
 > hydromechanical fuel control system, and a gearbox with 2,800rpm output.
 > Compressed air is routed to the aft end of the engine for combustion,
 > with exhaust gases exiting upward from the middle of the engine.
 >
 > "Developed from the famous Model 250 turboshaft, the first 317shp Model
 > 250-B15 turboprop has spawned a family of highly successful derivatives,
 > culminating in today's 450shp Model 250-B17F.
 >
 > "The Model 250 turboprop has found popularity due to its small size and
 > high power-to-weight ratio, which make it ideal for turbine conversions
 > of existing piston-engined designs."
 >
 > Technical data
 >
http://www.rolls-royce.com/defence_aerospace/downloads/tactical/model250_turboprop.pdf
 >
 > Engine Model 250-B17F
 > Power (shp) 450
 > Bypass ratio N/A
 > Pressure ratio 7.9
 > Length (in) 45
 > Diameter (in) 19.4
 > Basic weight (lb) 205
 > Compressor 4 (Axial) 1 (Centrifugal)
 > Turbine 2HP, 2
 >
 > © Rolls-Royce plc 2004
 >
 > Small turbines are gas hogs. The BSFC is .65 or above.
 > A rotary is about .47.
 > A turbo compound rotary may be as low as .4 or below.
 > A p-port four rotor would easily put out 450 HP NA.
 >
 > Paul Lamar

No, no dead horses are being beaten here.  In the latest AVWeb video
interview, the Rolls-Royce Engines rep says that they are talking with
OEM's and are performing "proof of concept" work with Mooney.  So this
is another factor we face.  Also, the numbers differ from the numbers
earlier quoted.

I transcribed part of the interview.  The transcription and the link to
the video interview I have attached below.

http://www.youtube.com/watch?v=j2nD7Nqh7B4
Paul Bertorelli interview of David Newbill of Rolls-Royce Engines

The new RR 500 turboprop engine for the general aviation market.

"Bertorelli:  Let's talk about some numbers here: weight, power output
and fuel specifics.

"Newbill:  Let's start with weight.  The total engine, (from) flange to
flange, is going to be 225 pounds, that includes the starter/generator
and some of the accessories--all of the accessories are gear-driven
accessories, and of course, it depends on what (accessories) you put on
that determines the final installed weight.  That's about half of what a
typical, equivalent, 500-series piston engine is today.

"So in terms of power, You're going to see this engine flat-rated, which
means it has that horsepower from takeoff to a certain altitude.  Right
now that's up to between 12 to 14 thousand feet at 320-325 horsepower.

"It is essentially a mid-300 horsepowers engine at mid-tweens for most
pilots.  We look at this engine as flying at about 15,000 feet, plus or
minus 1,000 (feet) for most operations, but we will certify it to flight
level 250.

"Bertorelli:  And how about the fuel specifics?

"Newbill:  Fuel specifics on this, on a turbine, we use an SST term in
the .6-something numbers.  If you want to change it into
gallons-per-hour for most people, they tend to think of it as a 21-24
gallons per hour at full power.  You fly turbines at full throttle, you
want them all the way forward to get the maximum efficiency out of the
turbine,  Of course that means you are going to go to point a to point b
very quickly.  So you are spending less time in the air even though you
may be burning more fuel per hour, you spend less hours (in the plane?
going somewhere? -Les), In summation, we like to talk about "nautical
miles per gallon." And in that case, When as compared to a
twin-turbocharged, 500-series engine, it comes out very, very close on a
flight.

"Bertorelli: Now typically in the past, the larger turboshaft engines
have run in the high .6's for SST's, but this one is the low .6's?

"Newbill:  This going to run right about in the middle of the
.6's--it'll be in the .6 something.  At the moment, because we're just
now running this compressor--it's a new design compressor--as soon as we
can get it coupled up with whatever loads to the turbine, we'll have a
better feel for what that number is."

------------------------------------
 >From the video, it seems like "flange to flange means from the front
of the PSRU to the back of the turbine engine.  225 pounds!

I'm sorry, either I am going deaf or they were using terminology with
which I am not familiar: I do not know what they are talking about when
they say "an SST term.

And does that "nautical mile per gallon" measurement that Mr. Newbill
used make sense?

Les Nordman

I'll bet the price is well over $100,000 for the engine.

One of the drawbacks to a small turbo prop is its limited altitude performance.
HP starts to fall off rapidly. This is why RR is talking up 15,000 feet.

A good flat rated turbo charged piston engine far out does it at 25,000 feet. So too a turbo charged rotary. WW II turbo charged and super charged piston engine fighters were going well above 40,000 feet. If you are going to spend that much money and burn that much fuel you probably want to go high IFR above 20,000 feet and a lot more of the weather. A good Lancair IV P will out do it at 25,000.

Sounds like BSFC for the SST's which is about right at .65 pounds of fuel
per horsepower per hour. A good rotary, properly leaned at cruise power, should be about .47. A good piston engine less than that at about .44 or so.


http://www.answers.com/topic/specific-fuel-consumption

"The ratio of the fuel mass flow of an aircraft engine to its output power, in specified units. Specific fuel consumption (abbreviated sfc or SFC) is a widely used measure of atmospheric engine performance. For reciprocating engines it is usually given in U.S. Customary units of pound-mass per hour per horsepower [(lbm/h)/hp or lbm/(hp·h)], and International System (SI) units of kilograms per hour per kilowatt [(kg/h)/kW]."


"For the gas turbine family of atmospheric aircraft engines, and for ramjets, performance is usually given in terms of thrust specific fuel consumption (abbreviated tsfc or TSFC) expressed as fuel mass flow per unit thrust output with Customary units of pound-mass per hour per pound-force [(lbm/h)/lbf] or SI units of kilograms per hour per newton [(kg/h)/N; 1 N equals approximately 0.225 lbf]."

Paul Lamar

Turbine dealers will go to great length to confuse the reader, specially
potential buyers.
Is it that hard to measure fuel burn from the actual fuel burned to make one
trip -- from one fuel pump at the start of the trip to the fuel pump at the
end of the trip.   Same plane, same weight, same weather condition,  same
speed or  how much time is saved.  Miles per US Gallon is a measure I can
understand -- BSFC also.

Rino Lacombe
Renesis powered Glass Goose