From: jthorn@aei.mpg-zebra.de.retro.com   
      
   bob_jenkins@burtleburtle.net wrote:   
   > How come the commercial airlines use jet fuel rather than LOX/H2?  I   
   > would have thought LOX/H2 would be lighter and would give the planes a   
   > longer range.  Is petroleum just cheaper?   
      
   In practice, the main reasons are probably historical (or "histerical"   
   as a friend of mine used to say).  But if you're thinking of "clean   
   sheet" designs...   
      
      
   On the pure-technical side:   
      
   H2 requires a *huge* volume of tankage, and pretty seriously insulated   
   too.  That's going to run up your frontal area and hence drag.  Not   
   nice for an aerodynamic vehicle.   
      
      
   Now to the reasons which are half-historical and half-technical:   
   Basically, nobody's done it before, so whoever tries to do it first   
   will have to spend all their own money to debug the technology.   
      
   For example, there's no existing airline-scale fueling infrastructure   
   for H2, so whoever tries to introduce this into service first will   
   have substantial up-front costs setting this up, and probably be   
   limited to a small number of airports at first.   
      
   Ditto there are no existing "off the shelf" H2/LOX jet engines and   
   other fuel-system components ready for Airbus or Boeing to incorporate.   
   Again, whoever goes first in designing for this will probably have to   
   spend a fair bit of money on R&D.   
      
   There's also the issue of persuading various governments' aircraft-   
   -licencing authorities that this is *really* safe:  The aviation   
   industry has *very* stringent safety standards.  In particular,   
   typical airline crashes-per-flight rates are below 1 per *million*   
   flights, and typical safety specs are at or below 1 safety-critical   
   failure per subsystem per *billion* flight hours.  Since these rates   
   are at least a factor of 10,000 better than the best achieved by   
   space-launch rockets, you can't just take "off the shelf" (space-   
   -launch) H2/LOX rocket hardware and drop it into an airliner, at   
   least not if you want to get it certified for revenue passenger   
   service.   
      
      
   None of these problems are impossible to solve, but all would take   
   nontrivial amounts of engineering effort, and hence money, to solve.   
   Even a "conventional" new airliner costs many billion dollars to   
   develop, and unlike the space-launch business, the government won't   
   bail you out if it's a flop.  So, you need a really solid cost   
   estimate before your bankers/stockbrokers will raise the money...   
   and it's hard to get a solid cost estimate in advance for "nontrivial   
   amounts of engineering effort".   
      
   ciao,   
      
   --   
   -- "Jonathan Thornburg -- remove -animal to reply"    
      Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),   
      Golm, Germany, "Old Europe"      http://www.aei.mpg.de/~jthorn/home.html   
      "Space travel is utter bilge" -- common misquote of UK Astronomer Royal   
                                       Richard Woolley's remarks of 1956   
      "All this writing about space travel is utter bilge.  To go to the   
       moon would cost as much as a major war." -- what he actually said   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)