From: del@branta.demon.co.uk   
      
   On Tue, 13 Dec 2005, in sci.space.tech,   
   bob_jenkins@burtleburtle.net said:   
      
   >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?   
      
   Storing liquid oxygen would be a waste of effort, when there is so much   
   free air to be had right outside.   
      
   Kerosene is low energy, but it has one quality that makes it far   
   superior to hydrogen for commercial aircraft: high density. Since the   
   mass of fuel tanks depends on the volume of the fuel to be stored far   
   more than its mass, and the mass of pumps depends more on the volume to   
   be pumped than the mass, high density wins. The drag on the plane from   
   bulky hydrogen tanks would also be a factor.   
      
   This advantage is so strong that it is seriously suggested that   
   commercial jet air fuel should be used for earth-to-orbit rockets   
   instead of hydrogen, despite hydrogen's higher energy. The numbers make   
   the two options very comparable to one another. And historically, for   
   multistage liquid rockets like the Saturn 5, kerosene has been the fuel   
   of choice for lower stages, with hydrogen only used for the upper   
   stages.   
      
   --   
   Del Cotter   
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