> Paul,
   >
   > I read that portion of the book too. Seems like they just rough mill
   > them then final grind and lap for accuracy. Then again this book was
   > written in 1969 when cnc equipment sucked so I bet it is much different
   > today. Also by there manufacturing methods back then lead to much
   > variance in the rotors as written about in the compression ration of the
   > rotors in that turbo 2 design paper you sent out. So two point
   > approximations and such are worthless these days.
   >
   > I think aluminum is the wrong direction to go. Talk of any of the exotic
   > alloys that it would take to make it work well will never happen and we
   > all know it in terms of cost,saftey,etc. With aluminums greater
   > expansion rate you would have to increase the clearances which means in
   > start up and part throttle the thing is going to blowby a bunch.
   > Aluminum does have a fatigue life and is just to damn soft to take any
   > kind of oops factor either from assembly or coughing seals. Titanium is
   > way to prohibitive after re-reading the nasa paper on it useage. Special
   > coatings on the seal grooves and needing chemical machining to take off
   > the out layers after heat treating is just unrealistic. Like I said
   > before Steve B. gave me an idea to do a furnace brazed sheetmetal rotor
   > after he mentioned they did it on the side housing with good results.
   > Welding is good but brazing is better since you would be able to get all
   > the fins/vanes/whathaveyou to join instead of just the outer edges where
   > the weld can go. A multi-piece steel rotor brazed I think is the
   > direction we should concentrate on. The only thing to beat steel in
   > strength to weight, modulus to weight,etc is carbon fibers and titaniums
   > which are not usable. If you went the extra mile and made the rotors out
   > of 4340 Hardened to RC 48-50 the yield is 180kpsi and ultimate is
   > 230kpsi. Not much is going to touch that. 1020 or 4130 is more realistic
   > but with steel you have a ton of choices.
   >
   > Rob Woods
   >
   > The problem is wall stiffness. To get it down to the weight of aluminum
   the walls would have to be one third as thick as cast iron. About the thinnest
   one can cast in iron is about 3/16 of an inch. That means most of the walls and
   webs would be 1/16 thick. I don't think that is going to be stiff enough for
   the rotor faces.
   >
   > What is the NASA paper you are referring to?. Can you upload a copy?
   >
   > If Ted wants to do Titanium let him try.
   >
   > BTW Rob please set your left margin to zero so it does not screw up the
   forwarding.
   >
   > Paul Lamar
   >
   > As far as the ringing is concerned I am not to familiar with the ins and
   > outs but the connection of the ringing would be pathed through the roll
   > pins of the gear, journal bearings,etc so I would assume that would take
   > care of it. I am unaware of any system in an engine that doesnt benefit
   > from stiffness.  I am against titanium for the reasons i listed in the
   > reply i just sent.
   >
   > Rob Woods
   >
   > It is local panel vibration due to the shock of combustion.
   > The roll pin loads would definitely be different due to the reduced
   > mass.
   >
   > Paul Lamar

     Rob,
    Can you upload that nasa paper you're reffering to?

    Thank You
    Ted

   Paul,

   Dont know what the zero margin thing is. I am just responding in the space
   yahoo gives me and I dont see any options for this. Please explain to me what I
   have to do.

   I dont follow you on your dimension conversion. If you were to cast the rotor
   out of aluminum to be equal in stiffness (since cast iron is only a little above
   aluminum) the aluminum would have to be about 2 times the thickness since the
   UTS and YS are about 1/2 to 1/3 the strength of nodular cast iron. If you were
   to go from cast iron to steel the E value is about 2.5 times greater. Not to
   mention you can get really high UTS and YS number out of it. But lets jst say we
   do it out  or 1020 then the UTS and YS are about the same but still a stiffer
   material. So you could go do half the thickness of the cast iron webbing which i
   think is more than enough. The centrifual loads wont effect anything but the
   base ring area so all you have to do it provide a 1000 psi load on the
   combustion chamber in FEA to see what the deformation is which I dont think
   would be that great. Point being with the increased stiffness and strength of
   steels over aluminums I dont think that it would be any kind of a problem to go
   thinner wall. If anything you could always go to a 15 pin for additional
   strutting if it is an issue. Until it gets modelled and worked out it is all
   conjecture. I just know which very strong alloys it wont be much of an issue.

   1000psi x 15in^2 = 15,000lbs load (but this is only peak) supported over the
   face thickness and the 4 webs. For comparison a AN-NAS 1/4 bolt can take about
   5000 lbs of load in double sheer. That area time three pales in comparison to
   the amount of metal on a rotor and sheer forces are the worst kind in terms of
   material strength(parallel vs perpendicular to grain axis).

   I sent that paper to you about 4 months ago or maybe it was the one that was
   too big for you to take. I will copy and paste the good and bad about the ti
   rotor they did. The negatives outweigh the positive since the amount of post
   work is prohibitively expensive for small scall operations.

   Do you have any scarpped rx-8 rotors handy anyone? I would like to get 2 to cut
   apart and disect for comparitive engineering purposes.

   Rob Woods.

   That explains it. Yahoo uses their own email program I think
   and I don't think you can set the margin.

   Aluminum density is .1 pounds per cubic inch and cast iron is around .3 pounds
   per cubic inch. Strength at room temp per se is probably not the problem as
   7075 T6 is 80 kips. Strength at 500 F is an issue and that is why you want to
   use Be/al allow not to mention the density is .076 pound per cubic inch.

   If the aluminum was 2 times the thickness of a cast iron  panel ignoring
   modulus of elasticity for the moment stiffness would be about 100 times stiffer
   as it is a fourth power function of the panel thickness. We are not talking
   tensile stiffness here. We are taking about panel stiffness. Roughly thickness
   to the fourth power. You cannot go to half the thickness of cast iron with steel
   and expect it to be as stiff.


   http://www.engineersedge.com/beam_bending/beam_bending1.htm
   This is a simplistic way of looking at it because I can't find
   simple steel panels uniform pressure loaded on the internet so far.

   Plus the panel support structure enters into the equation.
   Nothing less than a good FEA is going to help us out here.
   A simple FEA would be a 3 by 3 by 3 box with one side open.
   A constant pressure applied to the opposite panel would give
   good insight. What we are really interested in is the panel resonant
   frequency.


   Paul Lamar

Paul,

I can see what you are getting at but I would have to see the equations
to work things out. I dont see how you can separate MOI from E when
talking about stiffness so i'll leave that to you to produce those. Also
as you know the whole combustion area/tub is supported by 4 webs and two
pin bosses so again I dont see going thin a problem. Something to
investigate for sure.

Rob Woods