From: henry@spsystems.net   
      
   In article <1pvgb2xta9.ln2@homer.edgehp.invalid>,   
     wrote:   
   >> It would not have made any great difference to Columbia.  Titanium is not   
   >> *that* much better; the conditions in Columbia's wing were far beyond the   
   >> working limits of *any* reasonable structural metal.   
   >   
   >I was wondering about using titanium for just the leading structural   
   >member. Comparing Al to Ti the melting points are 669C vs 1660C,   
   >quite a bit different. I guess that says nothing of how much strength   
   >either loses as they approach the melting point.   
      
   Exactly.  The maximum *working* temperatures -- temperatures at which they   
   still dependably retain most of their strength -- are much, much lower,   
   and if I recall correctly, only a couple of hundred degrees apart.  This   
   is significant for aircraft but a very minor advantage for space reentry.   
      
   If memory serves, the strength loss in aluminum is fast enough that   
   there's little advantage in just making it thicker to reduce the working   
   stresses.  With titanium you can go a bit higher by doing that, but there   
   is of course a mass penalty.   
      
   >How hot do they estimate it was inside the leading edge?   
      
   Don't remember the accident-report numbers, but RCC panels are used only   
   where temperatures exceed about 1250degC, and the stagnation points -- the   
   worst case -- on nose and leading edge are at about 1650degC.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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