451acd86   
   From: emoneyjoe@iglou.com   
      
   On Mon, 16 May 2011 16:50:48 -0700 (PDT), "miso@sushi.com"   
    wrote:   
      
   >On May 6, 11:46 pm, Gosh Darn  wrote:   
   >>          I thought it was well known that a helicopter cannot hover   
   >> or land in a courtyard, the walls cause the airflow to form a   
   >> doughnut shaped torus of air, instead of being accellerated   
   >> downward and outward.   
   >>   
   >>          This made the news 20 or 30 years a go when a woman   
   >> pilot was asked to hover in a church or school courtyard while   
   >> a man tossed out prizes of some sort.       
   >>          People were decapitated when the hekicopter lost   
   >> lift and fell.   
   >>   
   >>          As far as low radar cross section helicopters go, the   
   >> patent office included a 1977 study on the uh-60 in the   
   >> office response to the application I mailed on Dec. 22, 1978.   
   >>          It was stamped "Level 12", whatever that meant,   
   >> I had no clearance at any time, and that application was   
   >> never under secrecy order.   
   >   
   >This is the dreaded vortex ring. However they hover in choppers all   
   >the time, so I don't know why it is considered appropriate in some   
   >situations. Pilots given their druthers rather fly tight orbits than   
   >hover to avoid the vortex ring.   
      
            They don't hover in courtyards less than twice the diameter   
   of the rotors, it is not possible because the same air is moving   
   in the only directions it can, the doughnut vortex.   
      
             Maybe experiments should be done with walls made   
   of plastic film and supported by light duty twine that would   
   no break rotors of tail propellor, then data on courtyard   
   size compared to rotor diameter could be recorded.   
      
   >I was in a traffic helicopter that was doing tight orbits over a crash   
   >scene. I had a GPS with me and the horizontal velocity was about   
   >60mph. I think the pilot was trying to make me hurl.   
      
            An up and down roller coaster would do it. :-)   
      
   >I think you make a helicopter stealthy by flying it in the radar holes   
   >as much as possible. ACE has software to predict the dead spots.   
   >Of course there are civilian programs that can do the same thing, such   
   >as the open source version of GRASS, SPAT!, and radio mobile.   
      
             I think radar is easy to counter, noise is the big problem,   
   and too many shoulder missiles are heat seekers.   
      
             Detecting all possible wavelengths and types of radar   
   would be difficult, but what do I know, I have never seen a   
   radar set in operation. :-)   
      
   Ken   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)