Xref: utzoo rec.aviation:12845 sci.space.shuttle:2520
Path: utzoo!attcan!uunet!mitel!sce!cognos!roberts
From: roberts@cognos.uucp (Robert Stanley)
Newsgroups: rec.aviation,sci.space.shuttle
Subject: Re: SR71 to be retired October 1st.
Keywords: titanium, SST, Boeing, Concorde
Message-ID: <5527@cognos.UUCP>
Date: 10 Mar 89 21:01:50 GMT
References: <1659@trantor.harris-atd.com>
Reply-To: roberts@cognos.UUCP (Robert Stanley)
Organization: Cognos Inc., Ottawa, Canada
Lines: 52

In article <1659@trantor.harris-atd.com> mjt@super.UUCP (Michael J. Tighe) writes:

> ...  To make matters worse, the US was planning to build
> a mach 3 SST whereas the rest of the world was planning mach 2.5 SSTs.
> It was "common knowledge" that mach 3 put the US at a schedule
> disadvantage since such speeds required stainless steel or titanium
> aircraft and there had never been a titanium aircraft built before.
> Basic titanium metallurgy techniques were a mystery.

This doesn't ring altogether true.  I agree that the limiting mach on
Concorde was dictated by the choice of alloys, which were chosen on the
grounds of practicality; there were already a great many unknowns.
However, one of the reasons that Boeing put forward their SST proposal was
surely because they had exactly the experience that was needed.  The XB-70
(Valkyrie) was the pioneer in this respect, and didn't it make extensive
use of epoxy-bonded, honey-comb titanium sandwich?

In the same time-frame, Lockheed built the A11 (where this thread
started!) with Titanium as the primary skin material.  Several interviews
with Kelly have described at length the problems they went through, ranging
from discovering that cadmium plating on tools was a disaster, through to
developing a formal recording process for every sheet rolled that included
such information as the grain direction!  Part of developing the necessary
titanium-production infrastructure included building the (then) largest
cold forging press in the country (250,000 tons pressure, from memory).

The design process for the A11 began in the '50s, although I forget exactly
the date that manufacturing started.  However, experiments had already been
conducted to prove that titanium technology was workable before Lockheed
committed to building the aircraft.  As an aside, I believe that stainless
steel has always suffered from being too dense, and that is what has
excluded it from consideration, rather than the difficulty of working the
material.

There was in fact an absolute wealth of knowledge on the subject in the
early '60s, although there is a real chance that much of this came under
various levels of classification.  What was lacking was any way to reduce
the cost of working with such a difficult material as titanium, and I
believe that still to be the case.  The very properties that make it so
interesting as a structural material in high-speed aircraft (low creep,
high tensile strength, low thermal conductivity) are the same properties
that make it fiendishly difficult to work.

Caveat: I was an aero-engineering student in the '60s, but I have never
	worked in the aircraft manufacturing industry.  Memory is fallible.

Robert_S
-- 
Robert Stanley - Cognos Incorporated: 3755 Riverside Drive, P.O. Box 9707, 
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