As to trim, AR and so fourth I have no idea.
Chrissi, do we know what Greg is using?
Paul Lamar
Greg is using a TO-4e with P trim. We are going to go through
the
graphs
and charts in a couple of weeks and try to nail it down to something
more
optimal if it exists.
...Chrissi
Ernesto Sanchez wrote:
>From Paul Yaw site for his 250 hp aircraft turbo motor:(
http://personal.riverusers.com/~yawpower/ac13bt.html ) "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".
I'm not an expert but from my research the TO4E 50 compressor is the
best
all around (250-300 hp). At 10,000 feet, you'll hit its sweet spot.
Now
figuring out the exhaust AR is going to take some experimentation.
Too
small, too much boost at low rpm. Too big, the boost moves up too
high
on
the rpm band. Paul Yaw's number seems high but he's the expert. I
was
thinking of starting at .96 AR. Chrissi, what's Greg's exhaust AR?
Ernesto
Marc Wiese wrote:
Most aircraft turbos have an exhaust AR of over 1.
Marc Wiese
OK, I've been reading and watching, hoping my question would be answered. I'm sure Paul can shed some light on this for me. What do the terms Trim, and AR mean. I'm new to the whole Turbo talk.
Thanks Tom Webber
AR or A over R or A/R is the Area of the turbine scroll divided by the Radius
of the scroll. This is a constant as the scroll looks like a snail.
It can also be a constant as the turbo chargers get larger and larger.
If you are talking about a specific turbo charger say TO4 the A/R
can change. Mostly what changes is the area of the scroll. If the
area is made larger the turbine runs slower for a given volume
flow of exhaust gases. An A/R of 1 means the area of the nozzle and
the radius are the same number. If the number is 1.2 the area is larger
but the radius is the same and the turbine will slow down.
I think trim has more to do with the width of the blades.
Also larger diameter compressors can be used to generate higher
boost levels at a give turbo RPM. It is sometimes possible to mix
and match turbo charger parts. A TO4 compressor on a TO3 turbine
section for an example.
Turbo chargers for street cars are much more of a compromise as
the acceleration of the car is largely a function of how fast
the turbine can spin up. We don't have that problem in aircraft
engines.
I highly recommend "Turbochargers" by Hugh MacInnes and "Maximum Boost"
by Corky Bell.
Paul Lamar
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