Combustion pressure was believed to be a major design issue.   Subsequent
design modifications and dyno and flight testing helped somewhat but
ultimately we concluded that even in improved, modified form,  housings of
aluminum alloy using materials available at that time was not the best
material for long term service life.   Our experience with the Mazda  factory
cast iron housings was very good in all respects except weight.  It  seemed
that the rigid cast iron housings, together with the steel insert in  the
throchoids, provided a very solid structure with none of the problems
involved with aluminum.  But due to the weight of the cast iron, to  attain
the best compromise of power-to-weight and longevity, it was  determined
thin-wall steel housings with nitrided wear surface would be best.  We
researched investment casting of these and found it was simply was too
costly.  That is when we turned to furnace brazing.

For doing the first set of these housings test housings, design  methodology
was very basic.  But Everett spent considerable time researching and
computing stress-deflection (compression) of  columns from combustion
pressure and  a stress analysis (elastic strain) of stress in the end
housing wall produced by combustion pressure of 1,000 psi.  Deflection rates
were calculated for a 1" square plate fixed on all edges and a  uniform load
over a small circular area at the center for steel .120 thick,  equivalent
cast iron .200 thick and aluminum .200.

After the prototype housings were furnace brazed they were machined  and
surface lapped, then shipped for nitriding.  After nitriding we  finished and
final lapped prior to assembly.

Weight of furnace brazed steel housings taken during assembly of the  power
section were:
Center housing--9.75 lb
End housings--10 lb each

By comparison, our cast aluminum housing weights--
Center housing--8.75 lb
End housings 7.5 lb.

Steve Beckham.

Thanks, Steve,  for the extremely interesting account.  All of this
information would be lost without your publication of it and it points
the way for us to go onward.  In particular it is amazing that
aluminum housings only  save 5 lbs total for the single. Thin steel
brazed inserts is the practical way to go as you have pointed out.   I
wonder if some of the machinists on this list could produce them.
All we need is two housings and an eccentric for the single cylinder
to be a viable reality.  That would be a nice package to find at the
door.     Jerry

Yes Steve, great work !! Thank you !

We should realize the aluminum housings save about 25 pounds over the
stock cast iron housing on a single rotor. So, these brazed steel at 20
pounds less than stock as so close :-)

http://www.racingbeat.com/FRmazda2.htm

One thing not clear to me, these brazed steel housings - they are simply
thinner versions of the cast stock, or is there an aluminum part as well
forming a sandwich end housing of a thin steel layer next to the
combustion chamber, and an aluminum section adding strength like the
foam in a Rutan plane ? If is it only a thinner steel end plate, the
e-shaft would need to be custom made shorter ?

-dave



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