Well, I am pleased to report that my turbo, stock housing with TO4
  wheel and 60-1 compressor with a fixed open waste gate has lasted
  over 230 hrs without a single problem.  The solution to good enough?
  Make it better.  I just finished my annual during which I upgraded
  my turbo to a similar TO4 big shaft wheel, but now it has a TO4E 50-
  trim compressor and the wastegate flapper and actuator are back in
  place.  Why the change?  Either I am a glutton for punishment or I
  am starting to pin down this turbo issue.  For those of you not
  familiar with my turbo history, here is a quick recap:

  First turbo - the stock second generation with waste gate flapper
  installed, ridden hard and put away wet...  it was run at full
  throttle at high altitudes, often at peak EGT.  It lasted 70 hrs
  before the turbine wheel fell apart and broke off.  The thought at
  the time was that the stock turbo was just too small for this heavy
  duty abuse and was overspeeding at altitude.

  Second turbo - small shaft TO4 wheel with 60-1 compressor and
  removed waste gate flapper.  It was also run mostly at peak EGT but
  the power produced was somewhat lower because of the bypassed
  exhaust.  It lasted about 140 hrs until it suffered the same fate as
  the first turbo while I was in a long full power decent (read extra
  high RPM and EGT's).  My thinking at this point is that the high
  EGT's are primarily the problem.

  Third Turbo - The one I just removed after 230 hrs.  Same
  configuration as the second but I kept the EGT's under 1600, mostly
  as lean as I could while keeping the engine running not too rough.
  It was also run at pretty low pressure ratios.  It could only make
  about 38" MAP on take off and about 40" at full bore down lot.  At
  16k altitude it was down to about 22".  My curiosity now is weather
  I can perhaps increase the boost and continue to have the turbo last,
  as long as I keep the EGT's under 1600.  I know, glutton for punishment...

  Other issues..

  Lean of Peak operation.  During the turbo change I discovered that
  my stock cast iron exhaust manifold had developed a number of
  serious cracks and some advanced erosion.  Much of the
  erosion/oxidation was near the mating surface with the turbo and it
  had started a small leak.  My concern is that all those hours of LOP
  operation allows too much oxygen into the exhaust to promote to
  oxidation and accelerates the problem.  The question is, should I
  start running rich of peak to prevent rusting away the exhaust
  system components?  ROP operations also allow me to keep even lower
  EGT's (for the turbo) and smoother engine running (for the wife).
  Turbos and exhaust components that I get from cars usually have the
  appearance of being run rich, rather than the dry orange color of
  the inside of my components.  The only obvious downside is the
  obvious much increased fuel usage.  I think that for the next couple
  hundred hours I have going to have to bite the bullet and fly ROP
  (while at higher power settings).  Thoughts?

  S.A.G. is really baffling.  Spark plugs only seem to be lasting 20-
  30 hrs before SAG starts kicking in.  Noted by a distinct and marked
  loss of power as I cross through about 1500' AGL after take off.
  The problem is usually intermittent and mildish at first becoming
  more consistent and remarkable as the hours accumulate on the spark
  plugs.  The problem is always solved by changing out the spark
  plugs.  I am switching to colder platinum plugs in order to try to
  get them to last longer.  Perhaps running ROP will help them last
  long too?

  Time for a new Prop?  On a test flight yesterday, the engine was
  running great.  No SAG.  At 7000' and 33"MAP I was at 6500 RPM,
  about 1/3 throttle and doing 175 KTAS [201 MPH].  It is a 64
  length x 77 pitch 3-blade Cato, but that is more like an
  effective pitch of closer to 71".  I seem to remember being able
  to get closer to 185 KTAS [213 MPH] at 6500 RPM in the past on
  the same prop but I did have a little taken off because of the
  low output of the previous turbo.  After some more experience I
  may discover that it is time for another new prop.  Might soon
  contact Paul Lipps, I liked his article in the last issue of
  Contact!  mag.  If that is my worst problem, I am going to be
  pretty happy.

  Doing some formation flying with the guys next week that may make
  its way into a movie...

  Keep building!
  --
  David Leonard

  Turbo Rotary RV-6 N4VY
  http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/ <
 http://n4vy.rotaryroster.net/ <
  http://n4vy.rotaryroster.net/
  http://RotaryRoster.net <http://rotaryroster.net/ <
 http://rotaryroster.net/ <
  http://rotaryroster.net/

  I really appreciate Dave's persistence on exploring
  turbo charged rotaries in aircraft use.

  The turbo life issue is not only the EGT it is the turbo RPM as well.
  If the RPM is high enough the blades will disintegrate regardless
  of the turbine inlet temp. The load on the blades is M times V
  squared divided by R. V is the the tangential velocity of the blade
  CG. M is the mass of the blade. R is the radius of the blade CG. All
  rotating device suffer from this problem. As the temp goes up the
  strength of the blade material is reduced. At 1600 F strength of
  exhaust valve steel is down to 5000 psi which is next to nothing.
  See the attached chart. Epoxy resin is 3000 psi :)

  Here is a chart from Caterpillar on the situation. The turbine
  MUST be kept within the limit lines of both temperature AND rpm.

  I have repeatably tried to get Dave to install a Garret turbine
  RPM kit. In fact I will buy it and send it to him. No luck
  so far. If you send me the compressor Dave I will install
  the RPM sensor for you and send it back as well. Perhaps Zack can
  convince him :) We need to know the turbine RPM!!!!!

  Somebody needs to try a Capacitor Discharge ignition system
  to further investigate the spark plug "sag" problem.

  Inconel is probably the only answer to high temp corrosion
  of ferrous materials. I have seen many cracked cast iron
  turbo exhaust manifolds.

  Paul Lamar


  Hi Dave,
  Auto OEM "wisdom" dictates running rich while boosted to prevent
  detonation.
  Also autos are regularly being accelerated off lights etc, which will give
  the
  black soot.
  How would ceramic coating the turbine housing work to keep heat out of the
  metal? You would have to compensate for the thickness of the ceramic at
  the
  mating surfaces or have them masked off so you do not coat those areas.

  Dale Davies


  Dave,

  What is your new turbo make, number and trim?  Same as the Cozy
  Girls but with a built in waste gate?  I have a similar cast
  iron manifold as yours and you are welcome to have it.  That
  will get you in air fast.  A better long term solution would be
  if I  donate a custom fabricated exhaust manifold  to your
  cause.  I can with your dimensional assistance design and
  manufacture a stainless 316L with altered pipe ells, It would
  have a tangential junction connecting both runners so that an
  external  wastegate could divert the exhaust flow BEFORE it hit
  the turbine.   It will be more robust and lighter than the Mazda
  cast iron manifold you are now using.  Paul can attest to the
  quality of the welds at the shop near me.  Most of their works
  is  fabricating exotic alloys  and they can guarantee fitting by
  using my 13B assembled engine.

  In return I as well as others need flight data.  If you can fly
  to at least 18k,  and cruise rpms  near or over 6K engine rpm
  then the data you collect will be invaluable for not only my
  project but scores of turbo rotary want- to-be's.  Paul will
  lend you a turbo tach and I believe a few of us could cobble up
  a ten channel flight recorder so you don't have to take notes.

  What do you say?

  Doug in Japan.

  Now that is an offer you should not refuse Dave.
  Doug's shop is second to none.
  3/16th inch thick 316 SS plate is ten times better than cast iron.
  Here is a simple design that will divert the exhaust
  gas before it reaches the turbine. The is the ultimate waste
  gate. Zero to 100%. This 3D could be dimensionally interchangeably with
  the stock cast iron 1990 manifold Dave is using now. Same
  dimensions.

  Paul Lamar



  HI Doug,
  Wow, that is quite an offer and I am inclined to take you up on it if you
  really want the data that badly, but I don't really need anything for the
  time being (and IMHO, turbo tach data will not be particularly useful to
  you
  either).  But first to answer your questions.

  I am using the stock series 5 housing and That is the ONLY thing that will
  fit.  Really, I have tried everything.  My clearances are very tight and
  changing one little thing cause a ripple effect that could keep me
 grounded
  for a year or more.  Simply nothing else will fit.  Not even Pauls
 manifold
  and wastegate above - the exhaust pipe from it would pass through my
  radiator...

  So given that I am stuck with the stock series 5 manifold and housing, it
  is
  ported larger to fit a big shaft turbine with and aggressive trim (not
 sure
  which one)  Compressor and housing can be changed out to almost any of the
  TO4 compressors.  I had some nice pictures showing my mods to the turbo,
  but
  just accidentally deleted them trying to move them to my computer.

  Anyway, the manifold cracks are not a big deal.  I had a couple of spare
  ones sitting around for just this occasion, and it could still probably be
  used for many more hours.  Though someday I may change it out for a SS
  manifold of the exact same dimensions.  In fact, if you think your shop
  could make me an essential copy of the stock series 5 turbo exhaust
  manifold
  (89-91) then I would be glad to install Pauls turbo tach and get you all
  the
  data you want.  But I think it needs to be smooth flow, not a box type.
  Box
  is likely to cause unacceptable back pressure.  Internal pipes would
  probably need to be supported by some sort of box, as the turbo has no
  other
  support.  No need for a wastegate, as there is no place for me to send the
  exhaust.  I am stuck using the stock (but ported) internal wastegate.

  That is a pretty big and difficult project (would cost me a pretty penny
  for
  such a custom manifold) and I don't think it is worth your while. Let me
  explain.  We have turbo maps that give us a very good approximation of the
  turbo speed for given conditions.  Paul argues that there are too many
  unknown factors in the mass flow so the maps are not that accurate.  Ok
  fine.  But suppose the map predicts that the turbo is turning 90k RPM and
  the tach shows it turning 100k. (the difference is unlikely to be
  particularly large)  What now? We don't really know where we should be
  drawing the line for continuous operation because it is a gray area trade
  off between performance and durability.  Maybe you could fine tune your
  compressor selection a little, but I am already running the biggest
  (slowest
  turning) compressor that matches the mass flow that I can find.  There are
  bigger compressors, but they require much higher mass flows.

  And if we do collect data, it really tells us more about the unknowns of
 my
  system (like volumectric efficiency and intercooler pressure drop. etc)
  than
  helping you design your system.  And those unknowns are going to change
  between particular installations.

  None the less, if you are still interested, I would love to have a nice
  custom SS manifold and as soon as it is done will fly up and "let" Paul
  help
  me install the turbo tach and come along to collect data if he wants. (or
 I
  can do it myself, it is not hard to collect data).  One thing, since I
 cant
  really run WOT with this turbo anywhere close to the ground (if at all)
 (it
  would over boost the engine), we really need to also measure the pressure
  upstream of the throttle body which will require the borrowing and
  installing of a manifold pressure sensor as well. (not a huge issue)

  --
  David Leonard

  Turbo Rotary RV-6 N4VY
  http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/ <
 http://n4vy.rotaryroster.net/ <
  http://n4vy.rotaryroster.net/
  http://RotaryRoster.net <http://rotaryroster.net/ <
 http://rotaryroster.net/ <
   http://rotaryroster.net/

  The turbo tach is NOT about turbo performance.
  The turbo tach is NOT about boost level.

  IT IS ABOUT STRESS ON THE BLADES.

  Stress = M X V squared over R.

  R is one M is one. 90K RPM squared is 8,100K.
  100K RPM squared is 10,000K RPM .

  10,000 divided by 8,100 is 24% more stress on the blades!!!!!!!

  Small increases in RPM makes a huge difference in stress!!!!!

  The stock 91 manifold has the turbo located in a asymmetric
  location and just about 4 inches from the face of the rotor
  housings. The diameter of the exhaust ports is 2 inches ID.

  Assume for the moment we used the tightest tubing bend
  we can find. That would be a 304 stainless railing casting
  From RB Wagner. The center line radius is 2 inches.
  As you can see from this to-scale-3D it is just not practical.
  What ever you build it will turn into a box like
  chamber and that is the reason Mazda did it that
  way. There is just no room for a streamlined turbo
  manifold that fits the stock turbo position.

  Perhaps it could be done with a SS casting but the pattern
  alone would cost thousands and the length of the runners
  would be drastically different.

  Perhaps it could be NC machined in two pieces of billet SS
  and welded together but that would also be rather expensive
  and the runner length would still differ.

  Paul Lamar

 I understand that it is about stress on the blades, but what will you do
 with the data we collect?  Will you use it to pick a different turbo (one
 that will be less stressed), or will you use it to set operational limits?
 In either case, what is the  RPM limit that we need to stay under.  Again,
 it is going to be a trade-off between durability and performance.

 I didn't expect Doug to be able/willing to make such a manifold.
  Definitely

 not worth it with the stock versions going for $10 on e-bay and lasting
 500hrs.  When that supply dries up I can consider a box of possibly
 re-doing
 my engine compartment altogether.

 David Leonard

 Turbo Rotary RV-6 N4VY
 http://N4VY.RotaryRoster.net <http://n4vy.rotaryroster.net/
 http://RotaryRoster.net <http://rotaryroster.net/

 I am learning along with you and others on this subject.
 The turbocharged rotary is a new animal in aircraft use.
 The EGT is anywhere from 200 to 300 F higher compared
 to a piston engine as far as TIT is concerned. GE started
 in the 1920's developing turbo's for aircraft piston engines
 so by the time WW II came a long they had a good feel for
 turbo RPM and turbine life design.

 This knowledge will add to our quantitative experience. We are
 a long way from setting a red line RPM.  We should have been doing
 this years ago. Perhaps by now we could have a RPM red line number.
 We need to start gathering data some time. The scientific method
 is to gather data first and then formulate a theory to
 predict what will happen when similar circumstances arrive.
 I know you know all that.

 Perhaps it would have saved you and others the expenses of
 replacing the turbo's. I am thinking of Mistral as well.
 To my knowledge Dave Garber, back in 1973, was the first
 to use a turbo charged rotary in an aircraft. Unfortunately he
 had no interest in cruising at high altitude so we learned
 little from that effort.

 I suspect we can get a longer life out of a larger turbine
 wheel running at lower RPM and then choosing a compressor
 to provide the desired boost. It takes X amount of HP
 to compress gas. That can be done with a larger turbine
 wheel as torque goes up while RPM goes down. HP can remain
 the same.  A larger, higher mass turbine, will run at a lower
 temperature with a given mass flow at a given temperature.
 We know that from disk brake experience.
 That is probably a linear relationship. The RPM however
 is a square law relationship so it is far more important
 for blade life.

 The down side is increased weight for the turbo but I think
 that is a small price to pay for the potential increased
 reliability.

 Paul Lamar


 I agree with every word you said and I would love to install a much larger
 turbo, as I am sure the best options lie there. But I am just one dude, with
 a toddler, working a 60hr/wk job and a wife who works full time, with no
 machine shop or welding skills.
 And all I really want is to be able to fly my plane.  If I kill this turbo,
 I can put the last one back on and fly aroud with my f.p.
 prop performing like an average 180h.p. c/s prop RV.  Not too shabby.
 --
 David Leonard

 Turbo Rotary RV-6 N4VY
 http://N4VY.RotaryRoster.net
 http://RotaryRoster.net



Dave,

OK without pictures I believe I 'got the picture' of your
situation.  I agree, making all of those changes for an unknown
result doesn't make sense.   Especially when the cast iron
manifolds are so cheap and it would be a better use of your time
to be flying.   I have been hanging on to my exhaust manifold
thinking that they are rare.  Seems I was wrong.  At this point
it would be wise to see how your turbo #4 performs.

One thing you could do is modify the wastegate and insert a
spacer plate  (Paul's idea) to make it open more and flow better
so you don't over boost down low.  I could help with that part
and make you up a new exhaust flange curved to your
specification.


Input these words "MAF sensors" into Google Images and you will
get hundreds of pictures.  E-bay and every used parts junkyard
all over the USA have these available.  Attached is t the Excel
chart describing electrical voltage verses airflow.  I bought
one used on a Nissan Infiniti which has a diameter of 80mm.
One of these before the compressor combined with  Map data and
inlet temp. should be able to tell
you the system losses.    All in all it seems you are zeroing in
on the turbo performance and doing good work.  Thanks



Cheers

Doug

OK Dave I'll come down this winter when you will be on duty
for awhile, remove the cowling and grab the compressor housing.
I'll take if over to Jeff's place in Escondito and install the tach sensor.
Jeff has a mill and an angle plate so it will be a precision
installation.  Then I'll take it back over to the air port and
install it and replace the cowling.  I'll build a bracket
to hold the dial instrument. If this is OK with Jeff.
This will save me a 3 or 4 hour drive back and fourth
to my hangar. I'll be busy through the end of September
with prior commitments.

Paul Lamar