From: hrubin@stat.purdue.edu   
      
   In article <44EC5ED3.B48E4A4C@nospam.com>,   
   Andrew Nowicki   wrote:   
   >Andrew Nowicki wrote:   
      
   >> The helicopter can fly much faster than the balloon.   
   >> If it flies vertically at the rate of 33 meters per second,   
   >> it will reach the altitude of 30 kilometers in 15 minutes.   
   >> Liquid oxygen and liquid methane will not evaporate   
   >> in 15 minutes.   
      
   >Herman Rubin wrote:   
      
   >> I question whether that rate can be maintained at   
   >> high altitudes.  Both an airplane and a helicopter   
   >> rely on air (or some other gas) for there to be   
   >> any power usable for lifting.   
      
   >The helicopter needs two sets of propellers/rorors:   
   >small propellers used at low altitude and big   
   >propellers used at high altitude.   
      
   >Another option is to use two helicopters having   
   >different size propellers: first stage helicopter   
   >and second stage helicopter. If we choose this   
   >option, there is no need to drop batteries on   
   >the parachutes.   
      
   >Andrew Nowicki wrote:   
      
   >> The airplane is superior to rocket as a means of transportation   
   >> through the troposphere because it is slower and much more   
   >> reusable. It is however not as slow as the helicopter, and   
   >> the separation of the rocket launcher and its cargo from the   
   >> airplane is tricky due to the aerodynamic drag.   
      
   >Herman Rubin wrote:   
      
   >> If it can reach 30 kilometers, the drag will be small.   
      
   >I disagree. The lift is constant regardless of altitude   
   >because the airplane mass is constant.   
      
   This would be the case if the air density was constant.   
   But it is not; the lift decreases with the density of   
   the surrounding medium, and becomes 0 when there is no   
   density outside.   
      
   		To keep the lift   
   >constant you have to fly it faster at high altitude.   
      
   This is because of decreased pressure.   
      
   Present military aircraft may reach somewhat more   
   than 10 km, maybe 15.  But at this altitude, air   
   pressure decreases rapidly relatively.  I doubt   
   that fuel-only aircraft can reach 30 km.   
      
   --   
   This address is for information only.  I do not claim that these views   
   are those of the Statistics Department or of Purdue University.   
   Herman Rubin, Department of Statistics, Purdue University   
   hrubin@stat.purdue.edu         Phone: (765)494-6054   FAX: (765)494-0558   
      
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