Paul,

      Would a T-70 turbo be a good choice for a/c use?

      Mark S.

      It is getting hard to find info on the old T numbers.
      Garrett acts like they never existed and changed all the numbers
      with their new line of turbo's.

      The compressor looks fine.
      We need the A/R on the turbine. The flange is probably a T4
   "divided".

      You need to calculate the area of all three exhaust ports
      and compare that to the area of the area of the hole in the input
   flange
      of the turbo charger turbine. Each rotor housing port is about 2
      square inches.
      Six square inches total. Velocity out at full chat is 1100 fps as a
      first guess.

      That is the first basic info for evaluating the turbine. The
   pipes are
      probably larger than the area of the ports so the gas velocity will
      be reduced
      in the pipes and into the turbo charger hopefully. Then the A/R must
      be known. If it is "one" the gas velocity going into the blades
      will be the same as the velocity going through the flange.

      Looks like a T4 divided flange is on the small side for a 3 rotor.
      The old undivided TO4 flange hole area was 2 by 3 or perfect for a 3
      rotor
      at six square inches. Yes the exhaust pipes are larger in area
   and will
      slow the exhaust gas velocity but it will be speeded up again as
   it goes
      through the turbo charger flange hole.

      For an aircraft an A/R well over one is good. Hopefully the A/R
   will be
      much larger than one. You will probably need a large waste gate.

      Next is the diameter of the turbine. That will give an estimate of
      the max speed of the turbine blade and RPM with no load. Half of
      that RPM will
      be the max HP RPM of the turbine. You can then compare that RPM to
      the RPM
      and flow of the compressor.

      This is my best guess at my current level of research on this
   subject.


    -------------------------------------------------------------------------------------

      Mark, you are in an excellent position to broaden the info on this
      subject.
      If you can make a pito tube out of steel brake line and insert it
   into
      the center of your tail pipe we can get a handle on the exhaust gas
      speed.
      You will need a cheap zero to 15 psi pressure gage. If the
   pressure is
      10 psi the speed of the exhaust at full chat is about 750 MPH.
      The pito tube is expendable as all you need is a quick reading.

      Paul Lamar


      Paul,

      The turbo has been something I've thought about off and on.  I
      usually talk myself out of it before I go too far.  From the looks
      of things, I'm pretty close to VNE now without a turbo.  Last speed
      run I saw 214mph at 6500msl.  That was after installing a cowl flap
      (as you have suggested we all do).  The T70 turbo that I mentioned
      is for sale by a guy that's just 10 miles down the road from where I
      live.  is supposed to be new, still in the box.  It has an A/R of
      .84, (too low?).  The price is right at $150, including a new
      waste gate.  Could the A/R scroll be easily changed?  I may buy it
      just because...

      As for measuring the exhaust velocity, I have a spare ASI that I can
      use for measurements.  I'll rig it up and see what numbers I get.
      Any particular rpm you're interested in seeing?  7000 would be about
      the max that I ever reach.  Does it matter what diameter tube I use?

      Mark

   You might be able to port it out using an NC mill. You just need to
   machine
   the internal slot next to the blades.

   It might make a good turbo compound turbine as is if somebody comes up
   with a cheap high speed gear box.

   Will your ASI go to 750 MPH?  Is it out of a jet? :)
   The pito tube diameter does not matter. Take one quick reading
   at full power take off. If the pito tube survives that a reading at
   cruise would
   help. Do you see 7000 RPM at take off? Top speed? In low pitch I
   take it.
   Do you have wheel pants now?

   Here are some pictures of Mark's 3 rotor engine installation for the
   new people

   Paul Lamar


Paul,

Sorry, ASI doesn't go that high.  So, I guess I'll have to use a
pressure gauge.  I'll let you know the results of the exhaust velocity test.

At the start of my takeoff roll, I will usually see about 7200 rpm.  As
the prop adjusts to the change in engine rpm, it will usually settle in
at about 7000.  Once I get some altitude I gradually start dialing the
prop rpm down, just to be a little easier on the engine/psru.  The prop
is an M/T 76" 3-blade electric C/S.  I've found that it is not very
quick to respond to pitch/rpm changes.  So, what I suspect is happening
is that the prop has set itself to a finer pitch at low rpm, and when I
open the throttle, it takes it a while to catch up to the engine rpm.  I
usually set the prop controller to 2125 rpm, which would mean about 6000
for the engine, but it will go past that by about 1k until it can adjust
the pitch accordingly.  If it responded faster, I should be able to set
the prop rpm to 2450 and not go over 7K on the engine.

Mark S.