9/11: How hard is it to hit a building at 500mph?

[tadaaa]

I wouldnt say its a bad comparison though Mick... If I recall, "Landings are just controlled crashes." If you can aim your aircraft at something and keep it lined up, youll hit it one way or another. I think the issue is that people confuse flying an aircraft with taking the controls and making it go boom... any idiot can crash a plane, but it takes skill to "fly" one.. IE straight and level, follow all the rules, do things so that they're comfortable for your passengers etc. If you're not concerned with any of that, then its a matter of controlling physics.

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

 

[Svartbjørn]

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

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.

 

[jaydeehess]

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

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.

 

[Spectrar Ghost]

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)

I think you're thinking of laminar flow seperation

 

[jaydeehess]

I think you're thinking of laminar flow seperation

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

 

[jaydeehess]

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.

 

[Mick West]

I finally got a working flight simulator and did a recreation of the turn and impact:
https://www.metabunk.org/inexperien...-77s-descending-turn-into-the-pentagon.t9438/

 

[Tumeni]

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.

 

[Oystein]

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.

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"


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.

 

[Whitebeard]

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

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

 

[Niz Loc]

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.