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757/767 Disintegration Point  
User currently offlineIFEMaster From , joined Dec 1969, posts, RR:
Posted (8 years 1 month 3 weeks 4 days 13 hours ago) and read 3593 times:

After some short but intense discussion on a now deleted thread yesterday, I started wondering about the physical capabilities and margins for 757s and 767s. So for those who are clued in, I have some questions...

What is the maximum tested airspeed for these types?
What is the maximum tested nose up/nose down angles?
What is the maximum tested bank angle?
What combinations of these were tested (such as a high speed sharp bank while in a nose-down attitude)?
Are prototypes ever tested to the point of destruction?

My curiosity is peaked by learning that a wing fairing detached from the UA 767 that hit the WTC - possibly because of the speed and bank angle?

9 replies: All unread, jump to last
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 1, posted (8 years 1 month 3 weeks 4 days 12 hours ago) and read 3585 times:

Quoting IFEMaster (Thread starter):
My curiosity is peaked by learning that a wing fairing detached from the UA 767 that hit the WTC - possibly because of the speed and bank angle?

Analys of the tapes has showed that the planes (or at least one of them) were pushing 400 knots. With that kind of overspeed it seems likely that stuff would start falling off.

On a related note it seems dumb to push overspeed when you can do enough damage with 250 knots. But I guess that wasn't the foremost thing on their minds...



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMX757 From United States of America, joined Aug 2005, 628 posts, RR: 12
Reply 2, posted (8 years 1 month 3 weeks 4 days 10 hours ago) and read 3524 times:

Quoting Starlionblue (Reply 1):
Analys of the tapes has showed that the planes (or at least one of them) were pushing 400 knots. With that kind of overspeed it seems likely that stuff would start falling off.

Do you know if it was 400 knots IAS or 400 knots GS?



Is it broke...? Yeah I'll fix it.
User currently offlineDw747400 From United States of America, joined Aug 2001, 1254 posts, RR: 1
Reply 3, posted (8 years 1 month 3 weeks 4 days 9 hours ago) and read 3508 times:

Quoting MX757 (Reply 2):

Do you know if it was 400 knots IAS or 400 knots GS?

It doesn't make much difference at that altitude, unless the winds are extremely high (I don't believe they were).



CFI--Certfied Freakin Idiot
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 4, posted (8 years 1 month 3 weeks 4 days 9 hours ago) and read 3500 times:

Quoting Dw747400 (Reply 3):
Quoting MX757 (Reply 2):

Do you know if it was 400 knots IAS or 400 knots GS?

It doesn't make much difference at that altitude, unless the winds are extremely high (I don't believe they were).

Sorry should have been clear: I don't know. But as Dw747400 says, the altitude is low enough it doesn't matter much.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAreopagus From United States of America, joined Sep 2001, 1368 posts, RR: 1
Reply 5, posted (8 years 1 month 3 weeks 4 days 8 hours ago) and read 3444 times:

Quoting Starlionblue (Reply 1):
Analys of the tapes has showed that the planes (or at least one of them) were pushing 400 knots.

Not that it makes much difference, as Dw747400 stated, but:
If "the tapes" were from the black boxes, then the datum is airspeed. But if "the tapes" are videotapes shot by people on the ground, the datum is ground speed. I believe I read that the speed estimates came from ground video.


User currently offlineBobster2 From , joined Dec 1969, posts, RR:
Reply 6, posted (8 years 1 month 3 weeks 4 days 4 hours ago) and read 3378 times:

Quoting Starlionblue (Reply 1):
the planes (or at least one of them) were pushing 400 knots.

Some excerpts from the NY Times, 2/23/02:

"... new calculations showing that the passenger jet that hit the south tower had been flying as fast as 586 miles an hour, about 100 miles an hour faster than the other hijacked plane."

"The speed of the two planes at impact has been painstakingly estimated using a mix of video, radar and even the recorded sounds of the planes passing overhead."

"... In fact, the United plane was moving so fast that it was at risk of breaking up in midair as it made a final turn toward the south tower, traveling at a speed far exceeding the 767-200 design limit for that altitude, a Boeing official said."

"'These guys exceeded even the emergency dive speed,' said Liz Verdier, a Boeing spokeswoman. 'It's off the chart.'"

"... The M.I.T. analysis, by Eduardo Kausel, a professor of civil and environmental engineering, found that the United plane was traveling an estimated 537 m.p.h., while the American plane, the first to hit, was traveling 429 m.p.h."

"The Federal Bureau of Investigation said the government's analysis put the speeds at 586 m.p.h. for the United flight and 494 m.p.h. for the American one."

"... Flying a Boeing 767 straight ahead at 1,000 to 1,500 feet would not be too difficult, even at more than 580 m.p.h., and it would most likely not threaten the structural integrity of the plane, a half a dozen pilots and a Boeing spokeswoman said."

"But accurately turning the plane at that speed and maintaining the proper pitch, or up and down movement, is difficult, the pilots said, particularly for a novice pilot, and turning at that speed would have put excessive stress on the plane."


User currently offlineMich From United States of America, joined Feb 2006, 36 posts, RR: 0
Reply 7, posted (8 years 1 month 3 weeks 4 days ago) and read 3293 times:

Quoting Bobster2 (Reply 6):
"... In fact, the United plane was moving so fast that it was at risk of breaking up in midair as it made a final turn toward the south tower, traveling at a speed far exceeding the 767-200 design limit for that altitude, a Boeing official said."

What are the g loads at this point of a airplane 762, at or above structural integrity ..?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 8, posted (8 years 1 month 3 weeks 3 days 16 hours ago) and read 3212 times:

Quoting Mich (Reply 7):

What are the g loads at this point of a airplane 762, at or above structural integrity ..?

Approved G loads in clean configuration are on the order of +2.5 to -1.0. Certification is 50% more, so +3.75 to -1.5.

My guess is that we're not so much talking about snapping the wings as about stuff ripped off from the wings. But that's just a guess.


BTW Thx for the research Bobster2.

[Edited 2006-02-24 14:47:47]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1606 posts, RR: 52
Reply 9, posted (8 years 1 month 3 weeks 3 days 11 hours ago) and read 3143 times:
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Quoting Bobster2 (Reply 6):
"... new calculations showing that the passenger jet that hit the south tower had been flying as fast as 586 miles an hour, about 100 miles an hour faster than the other hijacked plane."



Quoting Bobster2 (Reply 6):
"'These guys exceeded even the emergency dive speed,' said Liz Verdier, a Boeing spokeswoman. 'It's off the chart.'"

586 mph is 509 KTAS, which at Sea Level is M=.77

From the 767 TCDS (A1NM):
Airspeed Limits: VD = 420 KCAS to 17,854 ft/.91M above 23,000 ft, linear variation between these points.

As KTAS = KIAS (which is more or less KCAS) at Sea Level, they were in excess of the dive speed for the aircraft. However, aircraft are designed with a 50% safety factor on loads (Ultimate Load = 1.5 * Limit Load).


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