From: johnl@iecc.com   
      
   >>ObRail: for a truly bad idea, imagine a railcar designed by someone who's   
   >>previous effort has been on the composite body B787   
   >   
   >If composites come down in price, would they be a good idea for rail   
   >cars?   
      
   Interesting question, but I'd be surprised because the requirements   
   for planes and trains are so different.   
      
   For a plane, you need to minimize the weight since the engines are   
   keeping the plane in the sky, you need to maximize strength, but you   
   don't care much about rigidity.  It's OK if stuff deforms so long as   
   it recovers.  (There's an impressive youtube video of a B777 wing   
   strength test where it deforms to about 75 degrees above horizontal   
   before breaking.)   
      
   Safety concerns are primarily about keeping the plane flyable despite   
   multiple failures so the pilots can land it safely, and then evacuate   
   fast before leaking fuel catches fire.  It's vanishingly rare for a   
   plane to hit something, and not a coincidence that the most deadly   
   plane accident ever happened when two 747's collided on the ground in   
   the fog at an airport in Spain.   
      
   Trains are different.  The train's wheels hold it up, and since steel   
   on steel has such low friction, the main energy uses are accelerating   
   and decelerating, and the latter can often been recovered by dynamic   
   braking.  Trains bounce around like crazy, particularly if the track   
   is at all rough, and up to a point more weight makes a train ride more   
   smoothly.  There's certainly weight/performance tradeoffs, with TGVs'   
   being a good example, high power to weight so they can climb steeper   
   grades than conventional trains which allowed them more latitude in   
   picking new routes for them.  But it's still nothing like a plane.   
      
   Rigidity matters, since an insufficiently rigid train will derail or   
   sideswipe something.  Trains also tend to run in much more hostile   
   physical environments, such as the snow that Adam K.  mentioned, and   
   salt from deicing and nearby roads.   
      
   Train accidents generally involve derailing and/or hitting something   
   like another train, so the safety features require the cars to be   
   rigid enough to survive the accident without crushing the passengers,   
   and for something to absorb the train's energy slowly enough that   
   there isn't a sudden jolt that sends people flying through the   
   windows.  Collapsible engine noses are supposed to help.   
      
   So anyway, composites certainly don't rust, but I don't think they're   
   particularly rigid, and the light weight doesn't matter.  There are   
   buses with plastic trim panels that one can remove and replace if   
   they're damaged, so I can see uses like that, but it seems unlikely   
   for anything important.   
      
   --- SoupGate/W32 v1.03   
    * Origin: LiveWire BBS -=*=- UseNet FTN Gateway (1:2320/1)