1. tadaaa

    tadaaa Active Member

    wasn't there a theory peddled around the Pentagon plane crash that used the (total misunderstanding of the) Bernoulli effect to argue that physics prevented the plane from flying that close to the ground


    the obvious retort was "well how to they land and indeed crash
     
  2. Svartbjørn

    Svartbjørn Senior Member

    I honestly have no idea. 9/11 isnt really my thing.. all that mattered to me at the time was the fact I had to look my Marines in the eye and tell them we were going to war as we were packing the 5 ton full of sandbags and turning it into a rolling fortress so we could get back to base.
     
  3. jaydeehess

    jaydeehess Senior Member

    That would be the "Ground Effect" you are thinking of. Truthers used it to declare that a plane flying close to the ground and relatively level could not fly low enough to hit the Pentagon's ground floor.
    Absolutely ridiculous but requires that one understand a bit about the effect. It has greater effect the higher the attack angle. Flight 77 was slightly nose down, not nose up. It has greater effect with flaps deployed, Flight 77 did not have flaps deployed. IIRC increased speed also lowers the effect, rather than increases it, due to the turbulence causing it being less attached to the aircraft.(a poor way of putting it. Perhaps a pilot could help out here)
    ,,,,,,,,and of course the planes that hit the WTC structures were 1000 above the ground so it would not apply to them, and Flight 93 was nose down and almost vertical when it plowed into the field near Shanksville.
     
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  4. Spectrar Ghost

    Spectrar Ghost Senior Member

    I think you're thinking of laminar flow seperation
     
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  5. jaydeehess

    jaydeehess Senior Member

    I looked a bit further and I was referring to the ratio between induced and parasitic drag.
     
  6. jaydeehess

    jaydeehess Senior Member

    Best explanation of ground effect.
    http://www.faatest.com/books/flt/chapter17/groundeffect.htm

    Of course Flight 77 was only in ground effect for a few seconds as it is not an issue at all until the aircraft is at a height equal to it's wingspan, and only becomes significant as the aircraft gets much closer than that. An increasing downstick pressure would easily counter this for the few seconds required. In fact, ground effect may have kept the aircraft from hitting the lawn in front.
     
  7. Mick West

    Mick West Administrator Staff Member

  8. Tumeni

    Tumeni New Member

    I recall crashing into the WTC many times (sometimes not even deliberately!), with all the available aircraft, on MS Flight Simulator in ... the late 1980s?

    It didn't seem too difficult.
     
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  9. Oystein

    Oystein Active Member

    Me too! I tried to land a Cessna on the roof, like a dove coming from below and using kinetic energy to just arrive at roof height and touch down. Never worked, of course. I assume that building surfaces were parametrised such that any touching with plane triggers "crash" :p


    Flying planes with precision is not really any more difficult at 450 mph than at landing speed - when you can control the big bird to within a few feet easily. Fighter planes in air shows sometimes fly by each other within a few yards at breakneck speeds - and they tend to be more difficult to control (as they react faster and more drastic to inputs).

    The main difficulty for the 9/11 hijackers I can think of is that UA175 and AA77 were speeding up considerably in the seconds before impact, and that also increased lift. This seems to have helped "save" both attacks, as it helped UA175 to pull the turn and AA77 to stay above ground.
     
  10. Whitebeard

    Whitebeard Senior Member

    you CAN do that with very high buildings in GTA San Andreas, takes some doing, but it is possible. However taking off again is a big problem
     
  11. Niz Loc

    Niz Loc New Member

    Sadly, I found this website too late. Some of the statements from 6 years ago I could go to town with. But now there is no point.

    I will say that in my limited experience (which spans fighters, down to biplanes and helicopters), yes, at 500 MPH I could crash into a skyscraper.
     
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