>     Hi,
    >      Finally, got the rotor in the mail. Thanks to Paul. (Is  it RX8
    rotor? I
    >     remember that You mentioned that pocket and faces are  machined.  On
    this one
    >     pockets a left as cast.)
    >     I agree totally with what Paul and Rob are suggesting.
    >     Next steps:
    >     1) Disassemble it.
    >     2) Cut in two halves.
    >     3) Scan it.
    >     4) Create a valid 3D model of standard Mazda rotor.


    >     Here I will need help from Rob.
    >     Rob, as I understand You've got
    >      all the math to model the rotor faces. If I
    >     remember correctly You're working with Pro/E. Is it  possible  that
    You model
    >     outer geometry (faces) and send me the file
     (native Pro/E or  any
    common -
    >     Parasolid, Step or IGES). Modeling the faces out of scan  data  is not
    the best
    >     idea IMHO.

    >
    >     5) As Rob mentioned "Cast Ti has anywhere
    >     from a 1/2 to a 1/3 less thermal conductivity versus  cast  irons. 40
    >     percent less density, half the expansion rate, double to  triple  the
    >     tensile strength but anywhere from equal to half the  modulus of
    >     elasticity. If i were just looking at it, without  changing any
    >     dimension(based on modulus vs. tensile) it would be about  40  percent
    of
    >     the weight of the rotor."
    >
    >     If I remember it right Mazda rotor is made out of ductile  iron.  Its
    properties:
    >     Elastic Modulus    120000    N/mm^2
    >     Poissons Ratio    0.31   
    >     Shear Modulus    77000    N/mm^2
    >     Thermal Expansion
    >      Coefficient    1.1e-005   
    >     Density    0.0071
        g/mm^3
    >     Thermal Conductivity    75    W/m K
    >     Specific Heat    450    J/kg K
    >     Tensile Strength    861.695    N/mm^2
    >     Yield Strength    551.485    N/mm^2

    >
    >
    >     Now for the Ti cast rotor I'm planning to use VT20L which  was
    designed for
    >     extended work at 500C.
    >        Fe     C      Si       Mo    V    N       Al     Zr        O
    H
    >     <0.3   <0.1  <0.15    2     2.5 <0.05    6     2
    <0.15
    >     <0.012
    >
    >     Elastic modulus    123000    N/mm^2
    >     Poisson's ratio    0.33   
    >     Shear modulus    46000    N/mm^2
    >     Thermal expansion coefficient    9e-006   
    >     Mass density    0.00465    g/mm^3
    >     Thermal conductivity    7.8    W/m K
    >     Specific heat    500    J/kg K
    >     Tensile strength    1160    N/mm^2
    >     Compressive strength    1170    N/mm^2
    >     Yield strength    1070    N/mm^2
    >     Hardening factor
     (0.0-1.0; 0.0=isotropic; 1.0=kinematic)   
    8.5e-007    N/mm^2
    >
    >     Advantages that we may have:
    >     Strength =   134.6%
    >     E modulus = ~ 100%
    >     Density =  65.5%
    >     Thermal
    >      conductivity =  10.4%
    >     Thermal expansion =  82%
    >
    >     More than that at high temperatures  mech. prop.  advantages  will be
    higher.
    >
    >     Anyway as Bob mentioned we can  safely assume 30% weight   reduction of
    rotor
    >     assembly. I agree with Rob that revving the engine  20000RPM may  cause
    all sorts
    >     of problems. But revving the  3 rotor engine to 12 -  13,000 RPM
    sounds realistic
    >     to me.
    >
    >     Now, what's the current thinking about feasible price for  a 7 -
    6.5lb
    >     Titanium rotor? We're not talking about mass production  but  high
    power
    >     applications.
    >
    >     Thank You
    >
     Ted
    >
    > Ted,
    >
    > I don't like scanning either. What is inherently wrong with  it is that
    > it only lets you copy something without having the ability  to  modify it.
    > Point clouds to surfaces is a useless tool unless you are  trying to
    > knock something off. Part of all or our endeavors should be to
    > understand what we are doing so when we want to make a  logical changes
    > they can be done easily and effectively. I think a particular  good
    > product would be a lower compression ratio rotor for the RX-8  for
    > instance which has almost nothing to do with copying the  current  rotor.

    >
    > I think a very good idea would to send a rotor to a material  science
    > center, maybe the one we had at University at Buffalo, to  determine
    > exactly what type of cast iron that Mazda uses in the RX-8  rotors.
    > Especially to find out what the hardness levels are at the apex
     seal
    > slots. Cast iron is such a variety metal that speculating as  to  what it
    > is pointless. Just test it. This should be on the hot list to  do.  Other
    > rotors don't really matter so much since the RX-8 rotors are  of the
    > highest apparent quality/engineering. If we don't have real  data on
    what
    > we are trying to improve then it will make it harder to make the
    > replacement as good as it could be.
    >
    > I couldn't tell you what the cost would be for a Ti rotor. I am
    looking
    > into it and will let you guys know when I find out. Read up  on the  post
    > up to this point.
    >
    > I don't use pro-e but that is the program it looks like we  will  need
    to
    > use in order to accurately model the rotor and housing. Once  done in
    > pro-e it can be imported into solidworks.
    > That os fine with me for now
    > since the primary function is to replicate what Mazda has
     done but  in the
    > long run I want to try different configurations so a better  solution
    > will have to be found. I hope to find a way to make a macro  that will
    > have this functionality.
    >
    > Example:
    >
    > http://www.profilesmagazine.com/p33/marsalek.html
    >
    > Rob Woods

    Trying to get my hands around this topic, and guess I will do some
    cut and paste comments and see how it goes. (Don't do that  Scott. Makes
    a mess down the road.PL)

     "4) Create a valid 3D model of standard Mazda rotor."

    by this I assume you were wanting to get the rotor drawn out as  much
    or as accurate as possible?  There are CMM machines or digital  laser
    measure devices that will do a far far better job.  You do not  have
    to own one of these for this as there are many folks that  measure and
    draw out parts. or measure and give full dimensions.  More on this
    below:

    "Modeling the faces out
     of scan data is not the best idea IMHO."

    With all the work done in 3D drawings for this motor, is this  to say
    that the drawings for the rotors have not been done before? or is
    this a special rotor?  I must be missing something here.

    "Yield Strength    551.485    N/mm^2"
    I wish I could remember things that good.   ;-)

    "But revving the  3 rotor engine to 12 - 13,000 RPM sounds
    realistic to me."

    I think this must now be taking this motor out of the aviation
    catagory and into racing?  but still weight savings is king in the
    aviation world, thus my interest.

    "I think a particular good product would be a lower compression  ratio
    rotor for the RX-8 for instance which has almost nothing to do  with copying the
    current
    rotor."

    So was the first rotor mentioned above, a new and improved one, or
    different type?  just asking.

    "Once done in pro-e it can be imported into solidworks."

    I am
     not sure of what function that Pro E has that 2009 Solidworks
    can not do and do faster, easier and so on. Thus less money  involved
    for final end product.

    Well just some thoughts tossed out.

    cheers

    Scott- Iron Design L.L.C.
    Scott Weinberg

    Not to worry for aircraft Scott. We have to be cognizant of  racing car needs as
    racing is partially responsible for keeping the RX8 alive. No  RX8... no rotary.

    I am happy to see we will have five or six normally aspirated  RX8's in the
    Jan 2009 Daytona 24 hour race. Stupidly... with a mandatory red  line 500 RPM
    under the street RX8 car red line and ballast to make it fair  to Rube Goldberg
    piston engines. Mostly Porsche's.

    http://www.youtube.com/watch?v=zMW09hKJQIQ
    http://www.youtube.com/watch?v=d5-5Autjr0w
    http://www.youtube.com/watch?v=Xk7hcjX8fVU

    Paul Lamar


Scott,

The point is that any measurement method used, wether it is a laser
scanner, cmm, etc will give you a best fit spline to a a series of
points it/you decide to have. This will not give you the true  surface of
the rotor. Only a best approximation. A much more accurate way to do
this is to use CAD to make a bunch of points in a sketch using the
equations that are provided in Kenichi's book, and fit a sline to the
points. This will be more accurate than any measurement system but  still
lacking in accuracy due to curvature comb issues and such. Would it be
accurate enough to make a part from? Yeah but as soon as you invite
"good enoughs" into your design process then you end up with something
in the end that isnt as good as it could be. I myself wont be party to
that as I am intersted in the "right" answers and also a setup that  will
allow me to design bigger rotary engines int he future.

Everything I have seen that people have modeled before is just simply
wrong.

The RX-8 rotor is is better casting with differnent internal webbing
thicknesses and such along with a different side and apex seal design.

I am a Solidworks lover myself but I am not scared to admit that Pro-e
is a much superior program to Solidworks. The equation based editor in
Solidwork 2009 cant do what I need it to do and it isn't anywhere  close
to what pro-e can do. Its a shame that Solidworks sucks for equation
based line structures since people have been complaining about it for
years. If they did have it they could actually model a true involute
profile, wankel geometry, etc.

Rob Woods

Rob, your explanations tell me a lot more about the project... and I
understand fully that exact precise nature of what your trying to
create now. Perhaps this difference is mostly by my striving for a
low cost mid range HP 2 rotor unit with the lightest weights, and
your striving for the ultimate power 3 rotor unit that has some scale
factors.  What works in the future for  you will also help me in the
end.  I wish you all the best.

Scott- Iron Design L.L.C.
Scott Weinberg