From: tunebonk@eleven.com   
      
   On 03/20/2019 09:05 PM, Bret Cahill wrote:   
   >   
   >>>>>>>>> 4.  Increased Safety.  If a fan blade snaps off it   
   >>>>>>>>> can't impale any passengers or critical structures.   
   >>>   
   >>>> 5. When the power fails in VTOL mode it won't autorotate, and   
   >>>> it won't glide.   
   >>>   
   >>> For a quick pre take off check the pilot first runs the engines   
   >>> at max locked in the launcher.  The plane is only released at a   
   >>> somewhat lower safer RPM still well above take off thrust.   
   >>> Maximum power is only used for this test and is not necessary or   
   >>> desirable for the rest of a fuel efficient flight.   
   >>>   
   >>> The props on an Osprey would hit the runway if they aren't   
   >>> tilted back a little.  The fans are fixed here so, if you don't   
   >>> want 1 story high landing gear, it's the same situation as an   
   >>> Osprey that somehow got rotors stuck in horizontal flight.   
   >>>   
   >>> Fans always need to be strong enough to chop up birds, but,   
   >>> without landing gear, they need to disintegrate like tempered   
   >>> glass when they first contact the runway in emergency landings so   
   >>> large shards don't impale passengers in the aft cabin.   
   >>   
   >> I read that Osprey blades disintegrate into broomstraws.   
   >   
   > Military hardware is supposed to be dangerous.  It's considered   
   > "romantic" when poor troops get needlessly killed.   
      
   The broomstrawed blades flail around, and remain attached.   
      
   >> You lose far more than half the performance if you lose one of your   
   >> two engines. The second engine just brings you to the crash site,   
   >> as they say.   
   >   
   > At least as safe the standard 2 conventional wing mounted ducted fans   
   > where a lot of rudder is required to fly on one engine.   
   >   
   > No rudder is necessary here.   
      
   No climb performance with one. Might maintain altitude. At least it will   
   descend at a lower rate enroute to the crash site.   
      
   >> You'll want at least collective pitch control on your 100 fan   
   >> blades.   
   >   
   > Why?   
      
   For instant response while taking off and touching down. The fans, and   
   these are big ones, aren't going to spin up or down quickly. But they'll   
   be good flywheels and hold RPM while changing blade pitch gives   
   precision control.   
      
   >> Probably cyclic control too. Lose a single blade, and you may lose   
   >> control of all the rest.   
   >   
   > Any imbalance forces from the loss of a blade are well over an order   
   > of magnitude less than a smaller low bypass fan like the GE 90.   
      
   The mess of pitch linkages between blades might not let one go cleanly   
   without jamming up the whole works.   
      
   >> A helicopter rotor disk is mostly empty space, and your fan disks   
   >> are mostly solid. This isn't going to autorotate.   
   >   
   > Why would there be much of a need to auto rotate?  It only spends a   
   > few seconds near vertical.   
      
   That's when the power fails! Near the ground, with no forward speed.   
   Even if you could knock it over to horizontal in a split second... what now?   
      
   >> Won't glide either   
   >   
   > Passenger airliners spend a lot of time gliding?   
      
   When they have to. They have a pretty good range too.   
   But this craft, with huge drag rings encircling it, is doomed.   
      
   >> unless you can stop the fans and feather all those blades.   
   >   
   >> But I don't want to discourage you.   
   >   
   > That's obvious as you haven't provided any argument on why this isn't   
   > at least as safe as conventional wing mounted ducted fans.   
      
   I want blimps to come back.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)