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In a message dated 9/17/2004 8:54:33 PM Central Daylight Time,
sladerj@bellsouth.net writes:
<< On my Cozy IV I have a '93 13B REW with high compression rotors
and an intercooled hi-flo (T04-V2) turbo. I blew the turbine wheels off two
stock single stage turbos by overspeeding them trying to find (and finding)
the limits.
What boost, oil temp, water temp limits would you recommend at sea level and
10,000 ft? Note: the RWS EC2 fires leading & trailing together and gradually
retards timing with boost.
Normal fuel is 93 octane, but I'm probably going to be forced to fuel it
with 87 octane mogas and/or 100LL on occasion. What boost limits would you
set under these circumstances?
Any other thoughts or comments on this setup?
Regards,
John Slade (currently single rotor turbo 6.5B)
>>
The weekend drifter kids are getting 700 HP at the rear wheels on their 95
RX-7s. In too many cases, engine life is counted in minutes. Detonation takes
out the apex seals, and /or shatters the corner seals. Debris wipes out the
rotor housings. Not on every pass, but one or two per event have to drop one into
the dumpster.
I know just enough about turbocharging that it scares me to death. You take a
bullet proof engine and make it as unreliable as a poorly designed piston
engine. Operating so close to the edge of the envelope seems to me to be in
opposition to what you want from an aircraft engine.
As you have read by now, installing a water cooled engine in aircraft is a
painful operation. There are just very few people that ever get into the air
without some difficulty in oil or water cooling, or both.
If I was forced to do it, I would go for just a few pounds of boost
maintained through maybe 12,000 feet. You can really be stepping along smartly at
better than sea level power and the thin low drag air at 12,000 feet.
I would contact an expert in turbocharging and have him select the pieces for
a turbo that will do just what I want it to and no more. If a turbo can
generate 30 pounds of boost for a second or so, if the waste gate hangs up just for
a second, plan on 30 pounds of boost. Eventually it will happen. Plan on a
setup that can maintain a few pounds only, perhaps even without a waste gate,
no matter what, and a few pounds is all that you will ever get.
I would work on a system that relies on physics and not talent to keep things
together. No matter how good your are with your brain or hand speed, if it
detonates, an apex seal will be out the exhaust port before you brain will know
anything is wrong. Even Tracy's seals will break.
There is a fellow on that other list running without a waste gate with good
success. I would design the system to be incapable of more than a specific
amount of boost, and then build in a popoff valve just above that value just in
case.
You should be able to get above 100 HP from a single rotor without much
drama, and without a turbo. Thus having the detonation proof safety factors as
described.
You could multiply the BSFC of maybe .666 (the devils own BSFC) times the HP
you need to have at cruise, and look up the BTUs per pound for the fuel you
will be running, and multiply that to find total BTUs then subtract 26% (the
actual amount lost to work) and what is left will have to be removed through
exhaust gas temperature water radiator and oil cooler.
You can get an amazing amount of power from a rotary without the turbo, so I
would get it all flying and reliable with lots of excess cooling capacity,
Perhaps with a big street port, and then add the turbo. Then you can be working
on just the one project and its problems and not an endless list of
interdependent items that change as you modify just the turbo installation.
Mount the turbo as high as you can. Make the oil return line very large and
have it return oil as close to a straight line straight down to a large
diameter tube that ends up below the sump oil level. Or if you are running a dry sump
oil system, you can mount it anywhere and run the return oil to one of the
scavenge sections of the oil pump. A scat tube to blow on the central (bearing
area) part of the turbo would be real good for long bearing life. I would have
a little cooler with a scat tube and little air manifold built over the
cooler. I would bleed cooled engine oil through the special cooler to feed the
turbo bearings. Wrap the hot section and down pipe to keep excess heat out of the
cowling.
Mount the aircraft engine in an old RX-7 and drive it around for a month. You
can see most of the problems coming up and just not put them into the
airplane. Lots of fun too. And if there is a real big problem, you're already on the
freeway instead of trying to find a freeway.
Water temp 180 at cruise hot day climb 200. Oil temp 160 (ideal) at cruise,
180 is OK, 210 hot day climb. Power goes down above 160 oil temp.
Over heated oil endangers the rotor bearings. They are cooled (and
lubricated) by the oil. Too much oil temp with the power up, and it melts a bearing.
Look for a freeway.
Time both L and T at 20 degrees or less for boosted engine. Split timing is a
bit better for low end torque and emissions.
The number one killer of rotaries is not getting all, of the air out of the
engine. The water pump is mounted at the top of the block (where the air ends
up) and that lets the pump cavitate and stop moving water. Then the engine
overheats. The very old engines had a temp sensor in a flat spot in the center
iron. You could loosen that to
let out much of the air.
Lynn E. Hanover
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