Paul asked for my experiences with the Subaru. It is a 2.7L, six from a
small wedge shaped coupe called an XT-6. It is a single overhead cam, two
valve, low tech expansion of the familiar 1.8L. Designed to produce 145HP, I
was hoping for more with straight pipes. Art did a ton of machine work
cutting down the intake manifold four inches, mating the gear reduction, and
doing the dynafocal mount. Then he added the starter and alternator, all
under the RV-6 cowling. I had a too big radiator, and great oil cooling.
The problems were just too damn much. Getting the computer to work was a
nightmare. The problem was the TPS is not just a pot but a switch too and
the adjustment is critical. We started with a sidedraft Weber which was fine
untill 8000 feet when the mixture was too rich and nothing could be done
except get ready for plug fouling in the pattern. We changed to factory fuel
injection which helped some. Had a terrible time holding coolant. Was slow to
recognize leaky water pump. Battleing prostate cancer did not help thinking.
Stay on top of your PSA's. Being a friend of Laura and Tracy for years, I
felt the 13B was mandatory for now. I had no problem with insurance. The
Subaru four cylinder would be a better choice. I have a six for sale cheap
with alot of machine work.
I wanted to save the dynafocal mount for the future. I personally think
someday, the diesels will replace everything. The efficiency isn't just
economy. It's potentially our biggest weight reduction. A 20% reduction of
40 gal of fuel is 48 #. Try reducing our metal 48#. TBO's will be
extended. The Ford Vans used in Tampa for airport limo's go 600K miles and
the engines are still strong. The 2001 Trinidad will have a Morane-Renault
diesel.
Comments?
Bill
To summarize my thoughts on the rotary verses the world based on
what I have learned from running the news letter for two years:
I feel the 13B has potential in AC use for at least 250 HP.
I know Tracy does not agree with that and he thinks 200 HP
should be the limit because of cooling limitations. If 250 HP is assumed
the power to weight ratio of the 13B becomes superior compared
to an air cooled AC engines. 250 HP can be achieved by running the engine
at slightly higher RPM and better porting or by using a turbo.
I think a diesel will have a tough time matching that. The high compression
ratio that allows the diesel to achieve good efficiency adds greatly to
the weight through the necessity to resist the higher structural loads.
I also think 20% less fuel burn for the diesel is optimistic at the high
power levels found in aircraft use. I have no doubt, at part throttle in
around town operation, 20% less fuel burn for a diesel is common.
I base my thinking about the cooling issue on the discovery of
the lack of oil coking on the rotor housing when using two cycle oil
instead of common engine oil to lube the apex seals. Everything Mazda did
in regards to housing cooling was in deference to the coking problem.
Many SAE papers Mazda published mentioned this. This means the rotor
housing wall can run hotter when using two cycle oil to lube
the apex seals with out coking occurring. Further improvements can
be made by grooving the water jackets internally and using ceramic
apex seals.
There is one other problem I can see in this regard and it has to do
with the constraint of the tension bolts. The bolts are steel and the
rotor housings are aluminum. That means the bolts expand less than the aluminum
with the possibility of yielding the aluminum housing in compression if
the engine is allowed to over heat. I feel improvements can be made by going
back to the old, less stiff, necked down tension bolts.
For gas piston engines that run high exhaust valve temperatures at high power
levels there is no contest what so ever as the rotary has no exhaust valves
to burn! This is the achilles heel of the aircraft piston engine.
The piston diesel is not affected by this so much as the exhaust runs cooler
in a diesel.
Admittedly the rotary as it stands is still not as fuel efficient as it could be.
There are recent breakthroughs in mass produced high pressure direct fuel
injection. These devices could be applied to the rotary in the stratified charge
mode to improve the fuel consumption.
Finally there is the noise and vibration issue. The rotary is head and shoulders
above any piston engine and particularly the diesels. This issue alone
could change the entire perception of light plane travel and expand general
aviation greatly IMHO.
Paul Lamar
The Aircraft Rotary Engine Newsletter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org