Paul:
On the discussion forum with CompAir, I posed an idea about using
a rotary to replace their Garrett turbine. I had an interesting
response. Please, can you check my post at this link:
http://www.compairaviation.com/forum/index.php?topic=72.0
to establish if my claims are legit or have I overstated
the rotary engine potential. They would like
to know dimension, spec sheet, drawings.
Their offer to work with us in development might open some doors.
Thanks in advance
Greg Fleming
I'll reproduce what you said here for the purposes of discussion.
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I'm a commercial pilot interested in the CA11. I have flown aircraft for
over 30 years, mostly twin engine, in the 1000 -1500 shp range. I'm so
glad I don't have to pay for the fuel. In fact, the cheapest hourly cost
on our aircraft is the crew. How did aviation get so expensive??
Anyway, I'm so interested in the -11 that I'm researching an alternate
engine. It may never amount to anything more than a passing idea but
let's try this on for size. A 4-rotor Mazda rotary turbocharged,
turbocompound capable of 1,000 hp takeoff (5 min) and 750 hp max continuous
at FL 250. This engine will provide sea level power up to 25,000 and
give a 6.5 psi cabin. It will burn car gas as well as Avgas. Instead
of 75 gph cruise in the TPE-331-14 (or even the -10) the rotary will
burn 35 gph cruise. Instead of paying for Jet-A at the airport FBO,
you can either buy 100 LL at the FBO or buy Premium Octane at your
local gas bar. (You tell me the price difference, I don't know anymore)
Instead of carrying 400 gallons of Jet A (at 2,800 lbs) it will carry 200
gallons of Avgas (at 1,200 lbs). Max gross weight of the -11 is currently
projected at 7,500 lbs. With the rotary engine, the max gross might have
to be reduced by 1,500 lbs and you'd still be ahead by 100 lbs useful.
Instead of a turbine purchase price of $250k (0 time rebuilt) it will
cost $60k (0 time new). Instead of a $180k overhaul at 5,000 TBO it will
have a $15k overhaul at 1,000 TBO. This engine will be the same weight as
the turbine thanks to the all-aluminum block (and that's including the
accessories and coolant system). It will have the same power available on
takeoff as the -10 and much more power available at altitude (thanks to
the turbo critical altitude of 25,000'). Ample torsional dampening will
allow for the same 98" McCauley propeller with Beta as found on the -9.
Engine coolant will provide cabin heat as opposed to robbing precious
compressor bleed air. The profile drag for both engines will be the
same, except the coolant radiator will be designed to accelerate the
heated air out the bottom thru a divergent nozzle (cowl flap), utilizing
the 'Meredith Effect' as found on the P-51 Mustang. The P-51 radiator
generated enough thrust at altitude to compensate for the cooling drag.
Zero increase in drag at speeds over 300 mph. I don't know offhand
the drag profile of the TPE-331 air inlet so let's say it's zero, as well.
So, that's my initial idea. The turbine has a high initial purchase cost
followed by a high overhaul cost (granted, a 5000 hr TBO is really good),
a high fuel burn (BSFC of around 0.55), high cost of Jet A fuel, and
performance loss at altitude (true with all turbines). The rotary,
if built, approved and designed for alternate powerplant install
would cost less....a lot less. I don't know. I think it would
sell itself just on the numbers above. And what a great airframe
to attach it to. More affordable than anything else in its class.
Anyone care to comment, agree, disagree, question my math,
question my sanity.........anyone?
Greg Fleming
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It is pretty accurate for the most part but one might be pushing a turbo
4 rotor a bit at 1000 HP take off. Nobody has flown a four rotor yet to
my knowledge.
750 HP cruise would be about 350 pounds per hour if the BSFC equals .47 or about
56 GPH assuming gasoline is 6.25 pounds per gallon. If the turbo compound gets
it down to .4 then it would be 300 pounds per hour or 48 GPH.
So far other than Mazda nobody has built an all aluminum 4 rotor.
Quite possible however. All it takes is a lot of money to develop
these things. It might be easier to achieve with a 16B base instead
of a 13B base.
Paul Lamar
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