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I spent quite some time over the last year on the phone with Turbonetics,
here is what I remember:
- Planes should have big exhaust turbines for slow spool up, especially if
there is a manual waste gate.
- big turbos have less back pressure, which in turn costs less performance
- back pressure means more exhaust gasses stay in the combustion chamber and
travel into the intake cycle where the gas heats up the incoming charge and
takes up room that should have been used by the incoming charge.
- a properly sized turbo for 160 HP turbo normalized needs a waste gate to
not bog down the exhaust flow at low altitude, there might be a need for a
muffler aft of the waste gate
- a turbo that needs no waste gate is the size of a semi truck turbo which
weighs way too much.
- a good airplane type waste gate costs about $1000 from Turbonetics, looks
like a butterfly valve for a straight through flow.
But a $400 one should do the trick, too, just a bit more backpressure since
the gases have to go around a corner.
- turbine housings get a little hotter on a rotary than a piston, besides an
inconel turbine wheel a stainless turbine housing might be appropriate (used
in Turbo Senecas and Mooneys and goes overhauled for $1500 plus core).
For a few stainless housings I got a datasheet, they are rated to 1750 F
another stainless one to 1650 continuous and 1750 max or cont 1700 to 1800
max. Since in an airplane that thing really gets heated up because of the
long duration with lots of boost the cast iron is likely to crack. In
addition the housing should be allowed to get some cooling air rather than a
heat blanked.
- water-cooled center sections are not needed for planes where the turbo has
lots of time to cool down during the descend and after landing during taxi.
- intercooling recovers energy by making the intake air more dense it
requires less compressor work to shove the same amount of O2 into the
engine, on the other hand this costs cooling drag. Some research was done in
the 40s but none with Mazda Rotaries and none with Long EZs or RVs, so some
intercooling might be a good idea.
- having flown with manual waste gates and turboprops - both of which can be
accidentally operated to run above their limits - I think a pop off valve is
a good idea, I think there are more instances where copilots or passengers
bump the throttle than most folks consider.
- forgot where this came from - someone found a broken off EGT probe left an
imprint in the turbine hot wheel.
Now everything should be clear as mud.
attached is a compressor map for the model TA0411 refurbished PN
466642-0002. This is the production turbocharger for the Piper Seneca V.
data points are for 6500 engine rpm or 3000 prop rpm which should be about a
65 inch prop diameter to keep it subsonic. As you can see there are data
points for 25,000 feet ;-)
I still haven't figured out how to get to 'corrected mass flow'
Marko
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On
Behalf Of Ernesto Sanchez
Sent: Friday, September 12, 2003 9:16 PM
To: Rotary motors in aircraft
Subject: [Fly Rotary] Turbo selection
Snip:
> That being said, has anyone
> come up with the real spec for the appropriate turbo, ie,
T-what? turbine
> trim? compressor trim? Lots of questions......
>
> <marv>
Please take everything I say with a grain of salt. I'm not an expert by
any means but here's Paul Yaw (who builds and dyno's 13b turbo motors)
describing a rotary aircraft 13b turbo motor he built:
"The turbo (From Turbonetics) is a Garrett TO4E, 50 trim
compressor, P trim
exhaust, with a modified 1.3 AR ratio housing. The turbine wheel
is made of
inconel. The center section is water cooled. The turbo feeds the engine
through a small intercooler made by Spearco.
Boost is 6.4 psi at 6500 rpm. (43" Hg. manifold pressure.) Boost is
controlled by a Turbonetics "Deltagate"
End of quote. Here is his web site:
http://personal.riverusers.com/~yawpower/ac13bt.html
Correct me if I'm wrong: As we climb the air gets thinner so to get the
same psi we have to make more boost (pressure ratio goes up).
The Garrett
TO4E, 50 trim compressor (see compressor map) appears to more efficient
(less heat and less likely to knock or ping) as you climb and
less likely to
over speed (explode). The exhaust A/R Paul Yaw is using 1.3
(very big) and
he is an expert. I think the 13b is different in that there is more
un-burned fuel in the exhaust and it's still burning (expanding)
so you use
a larger A/R. Also, I was told on this list that certified aircraft use
A/R's larger than 1. Again with a larger A/R you are less likely to over
speed at altitude. I'm not sure but I think I read an article in Contact
where Greg Rickter (sp) said his intake manifold (Turbo 13b Cozy) heat is
high and he is dumping allot of air. His turbo may be on the
small side but
again I'm not an expert.
Ernesto Sanchez
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
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