Hi. I'm not a pilot but find myself in a discussion with one who ...

1) insists that ground effect would have made it impossible for flight 77 to hit the first floor of the Pentagon on 9/11

and

2) that the top speed of a 757 at ground level would be far less than the 460 kts recorded by the FDR.

I would appreciate an objective opinion on these issues and also what would the top speed of a 757 be given the flight path it took that day.

I know there are a lot of variables that factor into this but I'm just looking for a ballpark. According to some info, radar shows that Flight 77 did a downward spiral, turning almost a complete circle and dropping the last 7000 feet in two-and-a-half minutes.

It clipped light poles on the way in. According to one analysis: Assuming that the ground at the base of the poles was elevated 18 feet relative to the Pentagon's foundation, and that the poles were clipped at a height of 20 feet, the aircraft's wings were 38 feet higher than the foundation at 600 feet before impact. Assuming that the plane's wings were at an average elevation of 8 feet upon impact, the plane would have lost 30 feet of altitude in 600 feet of travel, averaging one foot of altitude for each 20 feet traveled.

Hopefully this is enough info to give a ballpark answer.

Thanks a bunch,
Ty

So where does this pilot suggest the 757 ended up if it did not crash into the Pentagon? Does he/she believe in some sort of conspiracy theory?

First, a warm welcome to the forum! And second, your associate with a differing point of view needs to find a new hobby. Hopefully a hobby that falls far more within his realm of comprehension. Ground Effect? Really? Is that the new term the "truthers" are tossing about these days?

Ground Effect is a useful term associated with takeoff and landing (low speed). But it has ZERO meaning when applied to a meteoric object hurtling itself inbound at throttles forward at a sharp downward angle. Not even a hiccup would be expected due to such. Just tell him that ground effect is no force field...

The only part of your post that has me concerned is your posting all the forensics. Please do not waste your time at that level. The Pentagon got hit by one of our own airliners. Enough said.

quote: "second, your associate with a differing point of view needs to find a new hobby" unquote:



LOL!

Yes. The issue arose in a forum thread alledging "irrefutable proof" that the plane flew over the Pentagon instead of crashing into it. Utter nonsense to me but if they had irrefutable proof I thought it worth a look. Turns out they don't know irrefutable proof from nonsense. I'm not sure if he believes the flyover theory himself or if he prefers the hologram theory that also arose in that thread. There are a few "true believers" on the thread who dismiss all actual evidence as fabricated. The only reason I am still engaged in the debate is because there are also fence-sitters and I feel somewhat obligated to present a defense of the "official story" as they refer to it.

And of course he and others occasionally bring 911 Pilots For Truth into the argument as proof that

a) the plane couldn't have been flying at 460 knots because that's 110 knots over "rated speed" or something to that effect. I saw on Boeing's site that the 757 had a cruising speed of .8 mach which converted to 515 knots more or less so don't know what they'r referring to

b) ground effect would have made the hit impossible

c) Hani Hanjour, the terrorist, lacked the needed skill to pilot the plane into the Pentagon

and

d) if Hani was piloting the plane then the FAA should have his pilot's license on file since all pilots must be licensed.

I like the last argument the best

Hi bernoulli,

Thanks for the reply. As indicated in my other reply the only reason I am still engaged in the debate, to the extent that I am, is to provide another perspective for the fence-sitters and casual viewers of the thread. I can deal with most of the nonsense but when they start getting technical with aviation theory I am unqualified.

I appreciate your reply. OK if I link to this thread from that one? I don't think he will actually bother creating an account and engaging in a discussing here. In his opinion you are already a "disinformation agent" because you accept the official story.

Thanks again,
Ty

Oh I almost forgot- welcome to the forums thallstd.

I just can not understand how people can believe these conspiracy theories. I find it particularly disturbing when American people blame their own government for 9/11. I can't take them seriously.

Whenever an event like this happens, certain people like to believe everything other than the truth and no matter what you say to them or how good the evidence is, they only believe in their wacky ideas. It's something I will never understand.

Please do. But, remind him that he doesn't have to register here to read, but to post. But you should also remind him that should he choose to register here and post his theory, he will get challenged by professionals who will find his theory silly, if not bordering on insanity.

I think Popular Science magazine pretty much debunked every nut case scenario, but the "truthers" don't want to hear it, regardless of the evidence. They made up their minds beforehand, so no point in arguing with them...

Well, I'm not qualified to comment on any conspiracy theories, but ground effect essentially reduces induced drag when an aircraft is close to the ground. Induced drag decreases as speed increases, so at 460knots, induced drag would be very little anyway. Nevertheless, ground effect would still help the aircraft go faster.

I'm not sure what the Vne or Vmo is on the 757, but its unlikely that someone attempting to fly an airliner into a building is overly worried about undue stress on the airframe. Also, diving towards a building and flying into it at full throttle is a sure-fire way of getting a fair bit of speed up.

Sounds to me like these conspiracy theorists are using aviation lingo to try and fool *I mean, convince* non-believers into thinking the government had something to do with it.

Exactly!