Originally Posted by M2Dude
Clive, you really surprise me when you say you don't think that composites would be used from a future SST, is there a material reason for this?
Now you didn't really mean that pun did you?
My reticence on using composites springs from the fact that, although it is little known, there are doubts about the life of the resins that bind the carbon fibres together when the material is exposed to a combination of high temperature and low atmospheric pressure over a long period. I know the Americans were worried about it for their 'supercruise' fighter designs and were experimenting with various exotic, expensive and obnoxious materials. Since all this was over 20 years ago and they now have their supercruise I expect they have a solution by now, but it is probably secret (I don't know that for sure however, it may well be in the public domain, I just haven't been following it). But even if they have a solution for military aircraft there is a world of difference between something that is OK for military designs with a supersonic 'life' of say 5000 hrs with a safety factor of what? 1.5? and a commercial transport with a life requirement of 50,000 hrs with a factor of 3.
BTW, if you thought the underfloor mixing unit was complex, you should have seen it in the original BAC project that didn't have electric signalling so the mechanical mixing was non-linear to try to account for varying flight condition demands
CL