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