From: bretcahill@aol.com   
      
   > >>>>>>>>> 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.   
      
   They already solved that issue!  Can they do anything about the dust?   
      
   > >> 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.   
      
   Higher bypass = faster climb.  That's not in dispute.   
      
   What's in dispute is keeping the engines on the wings.   
      
   >  Might maintain altitude.   
      
   If you don't have the numbers it's best to just stick to greater than and less   
   than logical decisions.   
      
   > At least it will   
   > descend at a lower rate enroute to the crash site.   
      
   What's surprising is how often a lot of people can survive crashes.   
      
   Best listen to the flight attendant.   
      
   > >> You'll want at least collective pitch control on your 100 fan   
   > >> blades.   
      
   > > Why?   
      
   > For instant response while taking off and touching down.   
      
   Faster, cheaper and more reliable to use control surfaces.   
      
   > 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.   
      
   Control surfaces are proven technology.  The Wright Bros used them.   
      
   > >> 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.   
      
   There's no duct so it just flings free of the rotor.  Even if it grazes a wing   
   it won't be a straight on collision.   
      
   > >> 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!   
      
   Why wouldn't the engine fail during the maximum rpm test conducted when the   
   plane is restrained in the launcher?   
      
   Again, there is more than enough thrust for take off at a lower safer fuel   
   efficient rpm.   
      
   > Near the ground, with no forward speed.   
      
   Exactly vertical may not be necessary or even desirable.   
      
   > Even if you could knock it over to horizontal in a split second... what now?   
      
   How's it any different than any other conventional aircraft flying horizontal?   
      
   > >> Won't glide either   
      
   > > Passenger airliners spend a lot of time gliding?   
      
   > When they have to.   
      
   Post some youtube videos of large passenger aircraft gliding.   
      
   > They have a pretty good range too.   
      
   Fuel is 80% of airline operating cost.  If you ever get much altitude gliding   
   a thermal, demand a partial refund of your ticket.   
      
   Just don't mention my name.   
      
   > But this craft, with huge drag rings encircling it, is doomed.   
      
   Why can't the fans be geared together like a tandem version of the Osprey?   
      
   If one engine goes down you still have an operational aircraft.   
      
   > >> 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.   
      
   They need even more monstrously yuge propulsion surfaces.  I'd look into   
   making the blades out of inflatable rubber.   
      
      
   Bret Cahill   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)