Lehanover@aol.com wrote:

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 like to say that much of what you are typing makes sense, and from a practical standpoint, I am looking at a turbocharger not for heavy levels of boost over sea level ambient pressure, but rather to make a moderate to low level of boost (or none at all) at sea level and maintan that up to altitude. At 8000 feet, a normally aspirated engine at wide open throttle is only making 75% of its rated power, so without the benefit of turbo-charging or turbo-normalization, your true airspeeds really dont change too much at altitude.
 
I think its a pretty strong hint that Mazda felt 8.3 psi (approx 16" of boost) was a good limit with regards to boost over ambient sea level, and set that value into the design of the engine's control system (boost sensors and absolute altitude sensors).. I dont see a whole lot of reason to plan on MORE that that. Honestly, I feel that the design plan for the engine project I am involved in its more towards normalizing the deck pressure to sea level ambient.. or perhaps even just 4-5 psi.. I personally am not about making gobs of HP down low, but keeping the ability to make sea level HP up high..

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. 

 
There have been a few of us (non experts, however) kicking around a lot of numbers with regards to this trying to get the best turbo "fit" for aftermarket purposes. After looking at a LOT of different products, designs, etc... I am starting to think an external wastegate with an "E-Boost" brand absolute pressure controller isnt a bad way to go...Such a product could be set to be open completely (no boose/minimal turbo) in certain situations (starting, ground, and post-flight engine runs) and then also staged for flight boost settings. A pop-off valve on the deck side sounds like a must-have as well.

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. 

Those are sea-level numbers though, not at altitude (which is where we are all about).. Good point though, the no-wastegate setup removes a possible failure point at the cost of a lower critical altitude (if there is one, for that setup)..

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. 
  

One of my good friends recommended the same thing.. get the motor up and running, then add the turbo..

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.

Great idea, but probably not legal. A ported engine will have difficulty meeting emissions... Most of the emissions-specific items are removed in the aircraft engines, and many of us are using electronic control units that do not meet (or were never tested) to be street-legal from an emissions standpoint, so unless this month is "on the dyno" or "on the track" its probably not very practical

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. 

Good info, but low end torque and emissions arent applicable to an aviation mission.

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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Thanks... I know I am learning as I go here.. and every little bit of info does help.. so that I can take what is applicable to the project I am working on.
 
Dave