Page 51 - MY STORY

compressing and warming it to human-compatible

conditions. The air compressor was spun by a turbine
wheel on the same shaft that took second stage bleed air
from the jet engine compressor. This pressurized bleed

air from the engine was around 600-700 degrees F. Every
pound of weight that could be eliminated in a commercial
aircraft was worth a lot of money and effort.

I believe for the DC-8 the value of one pound of weight
saved was approximately $72. This meant that saving

weight for the highly stressed cabin air compressor

turbine operating up to 700 degrees F was doubly
important.

Since the turbine spun at approximately 20,000 rpm it had
to be surrounded by armor shielding to prevent adjacent

structural or physical (people) damage in the event the
turbine failed. There were two of these systems on the

DC-8. Using a high-temperature titanium alloy in place of
stainless steel or nickel alloy saved 40% on weight just for
the turbine wheel. That weight saving was compounded

by the lowered weight of the required shielding by virtue
of the reduced kinetic energy (lower mass) of pieces being
ejected from a failed turbine.