From: henry@spsystems.net   
      
   In article <40FA69B7.A39EB843@nospam.com>,   
   Andrew Nowicki   wrote:   
   >> They tried peroxide rocket tips on helicopter blades too.   
   >   
   >This idea does not make sense because the thrust produced by the rotor   
   >is about the same as the thrust produced by the rockets.   
      
   No, wrong.  Please learn something about aerodynamics.  The rocket thrust   
   only has to counteract the drag of the rotor blades, while the rotor   
   thrust is produced by the blades' lift.  Asserting that rotor thrust is   
   about the same as rocket thrust is asserting that the rotor blades' L/D is   
   around 1.  But at subsonic speeds, the L/D of a good airfoil design is   
   more like 100... although issues like tip effects reduce that considerably   
   in a real design.   
      
   Moving large masses of air slowly produces much more thrust -- for the   
   same amount of energy -- than moving a small mass of exhaust jet quickly.   
   Various complications intervene if the air is already moving rapidly past   
   you, but at low speeds, using a rotor wins big over a rocket.  This is why   
   small, slow aircraft continue to use propellers, and the dominant engine   
   type for big subsonic aircraft is the turbofan, which uses a small turbine   
   core to spin a large fan -- essentially a high-speed ducted propeller.   
      
   The key question of a rocket-powered rotor is not whether it produces more   
   thrust at the start, but whether it gains you enough in total -- bearing   
   in mind that launchers want to accelerate very rapidly and that propeller   
   efficiency drops off badly as speeds rise -- to be worth its mass.  Gary   
   Hudson said that for the classical Roton design, the bottom line on rotor   
   lift was about neutral for ascent -- no big gain, no big loss -- with the   
   main benefits being its other roles:  drag device during reentry, lift   
   device for landing, and centrifugal pump for powered flight.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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