TWCobra
Senior Member.
The claim:
Pilots for 9/11 truth have published several videos claiming that airliners travelling slightly above the Design Dive Speed; known as Vd, are subject to structural failure. This assertion, amongst others, forms the basis of this video;
The video itself takes numerous licences with what it states; which will be addressed later, but for now let us concentrate on their claims about the ramifications of flying faster than Vd.
The specific claim at 5.00 is that Egypt Air 990 suffered structural failure at 425 KEAS. (Vd+5).
(EAS is Equivalent Air Speed, is a value mainly used by test pilots to equate the aerodynamic loads on an aircraft at different altitudes and speeds to a speed at sea level, where the air is thickest.)
This claim is completely without merit and contradicts the NTSB report into the incident as discussed in this post. Analysis of the FDR data shows that the 767 suffered no structural failure at Vd+23 knots or 443 KEAS whilst pulling 2.1G, with split elevators.
Research has uncovered another incident of a Easyjet 737-700, G-EZJK^ which pitched down during a test flight whilst flying at 15,000 ft. The aircraft had its hydraulic flight controls turned off as part of the test. The AAIB investigation into the incident finds that the aircraft, which has a Vd of 380 KEAS, recovered slightly below 6000 feet after achieving 429 KCAS which converts to 424 KEAS, or Vd+44 knots.
The aircraft, according to the report, landed undamaged and continues to fly in Brazil for GOL airlines^ as PR-VBI. During the recovery this aircraft pulled ~1.7G at ~420KEAS.
Another 737 did go much further past Vd before it unfortunately broke up. The report of the Adam Air Flight 574 crash on New Years Day 2007 in Indonesia shows that whilst descending in a tight spiral dive after the pilots mishandled problems with the aircraft's navigational equipment and lost spatial awareness, the aircraft broke up whilst pulling 3.5G (max G limit 2.5) whilst flying at 495 KCAS at 12,000ft.
This aircraft was a 737-400 which has a Vd of 400 knots. The KEAS value at the point of breakup is 480 or Vd+80.
Pilots for 9/11 truth make these videos in an attempt to push their claim that UA 175, a United Airlines 767-200 was in some way modified to achieve the highest speed reported by the several studies that were done into UA175, that of ~508 KEAS or VD+88. They claim it is not possible for an unmodified 767 to survive at these speeds.
EA990, a 767-300 was undamaged @Vd +23/2.1G and split elevators (Which caused massive twisting loads on the tailplane).
G-EZJK, a 737-700 was undamaged @Vd +44/1.7G and recoverable with hydraulic controls switched off.
Adam Air 574, a 737-400 did not break up till reaching Vd+80 and pulling 3.5G. There is no indication of structural failure before that point.
None of this data proves that UA175 could get to Vd+88 and survive. However UA175 did not reach Vd+80 until about 5 seconds before impact with the South Tower of the WTC. It was in a slight descent and rolling towards 38 degrees of bank. The G force in that scenario would be slightly over 1G.
I have gone through this research because UA175 has interested me since I learned of the speeds it reached. It should be noted that the range of speeds obtained from the various studies is 437-510 kts Groundspeed.
All of the best case studies indicate the aircraft should have easily survived, some are below the Vd+23 of EA 990. The highest speed is right on the limits of believability, however none of the alternate theories; modified, guided, holographic; are credible.
One thing that has been proved however is that Boeing build damn strong aeroplanes.
Pilots for 9/11 truth have published several videos claiming that airliners travelling slightly above the Design Dive Speed; known as Vd, are subject to structural failure. This assertion, amongst others, forms the basis of this video;
The video itself takes numerous licences with what it states; which will be addressed later, but for now let us concentrate on their claims about the ramifications of flying faster than Vd.
The specific claim at 5.00 is that Egypt Air 990 suffered structural failure at 425 KEAS. (Vd+5).
(EAS is Equivalent Air Speed, is a value mainly used by test pilots to equate the aerodynamic loads on an aircraft at different altitudes and speeds to a speed at sea level, where the air is thickest.)
This claim is completely without merit and contradicts the NTSB report into the incident as discussed in this post. Analysis of the FDR data shows that the 767 suffered no structural failure at Vd+23 knots or 443 KEAS whilst pulling 2.1G, with split elevators.
Research has uncovered another incident of a Easyjet 737-700, G-EZJK^ which pitched down during a test flight whilst flying at 15,000 ft. The aircraft had its hydraulic flight controls turned off as part of the test. The AAIB investigation into the incident finds that the aircraft, which has a Vd of 380 KEAS, recovered slightly below 6000 feet after achieving 429 KCAS which converts to 424 KEAS, or Vd+44 knots.
The aircraft, according to the report, landed undamaged and continues to fly in Brazil for GOL airlines^ as PR-VBI. During the recovery this aircraft pulled ~1.7G at ~420KEAS.
Another 737 did go much further past Vd before it unfortunately broke up. The report of the Adam Air Flight 574 crash on New Years Day 2007 in Indonesia shows that whilst descending in a tight spiral dive after the pilots mishandled problems with the aircraft's navigational equipment and lost spatial awareness, the aircraft broke up whilst pulling 3.5G (max G limit 2.5) whilst flying at 495 KCAS at 12,000ft.
This aircraft was a 737-400 which has a Vd of 400 knots. The KEAS value at the point of breakup is 480 or Vd+80.
Pilots for 9/11 truth make these videos in an attempt to push their claim that UA 175, a United Airlines 767-200 was in some way modified to achieve the highest speed reported by the several studies that were done into UA175, that of ~508 KEAS or VD+88. They claim it is not possible for an unmodified 767 to survive at these speeds.
EA990, a 767-300 was undamaged @Vd +23/2.1G and split elevators (Which caused massive twisting loads on the tailplane).
G-EZJK, a 737-700 was undamaged @Vd +44/1.7G and recoverable with hydraulic controls switched off.
Adam Air 574, a 737-400 did not break up till reaching Vd+80 and pulling 3.5G. There is no indication of structural failure before that point.
None of this data proves that UA175 could get to Vd+88 and survive. However UA175 did not reach Vd+80 until about 5 seconds before impact with the South Tower of the WTC. It was in a slight descent and rolling towards 38 degrees of bank. The G force in that scenario would be slightly over 1G.
I have gone through this research because UA175 has interested me since I learned of the speeds it reached. It should be noted that the range of speeds obtained from the various studies is 437-510 kts Groundspeed.
All of the best case studies indicate the aircraft should have easily survived, some are below the Vd+23 of EA 990. The highest speed is right on the limits of believability, however none of the alternate theories; modified, guided, holographic; are credible.
One thing that has been proved however is that Boeing build damn strong aeroplanes.
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