On 9/11 The Reported airspeed of United flight 175 was 510 knots near sea level. At 22,000 ft the equivalent speed/stress is 722 knots or mach 1.19

Thus Spoke Mainer

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Mar 6, 2012
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A little off topic, but this post reminded me of a story my dad likes to tell.

He was in the Navy (Norfolk, VA) some time around when stuff was still warm with Cuba (during or shortly after the Cuban missile crisis). He was an airplane mechanic, primarily working on the F4.

For whatever reason, they got a sudden request for a few F4s to be over Cuba "ASAP." He said flight time wheels up in Norfolk, VA to air space over Cuba was right around 30 minutes. MUCH faster than the published "max speed" of the F4 says should have been possible.
Fish, speaking of aviation, can you re-post that corkscrew landing you made a few years ago?
 

WeR0206

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A little off topic, but this post reminded me of a story my dad likes to tell.

He was in the Navy (Norfolk, VA) some time around when stuff was still warm with Cuba (during or shortly after the Cuban missile crisis). He was an airplane mechanic, primarily working on the F4.

For whatever reason, they got a sudden request for a few F4s to be over Cuba "ASAP." He said flight time wheels up in Norfolk, VA to air space over Cuba was right around 30 minutes. MUCH faster than the published "max speed" of the F4 says should have been possible.
The true max operating speeds of military planes is never really disclosed publicly but that’s not true for civilian planes. I highly doubt the F4 went 150 knots over the max safe operating speed. Also the aerodynamics, impacts of dynamic pressure, and stress limits of a fighter jet are far different than a commercial 767. Apples to oranges

This chart lays out the limits of the airframe:
wMoFVbr.png
 
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BoulderFish

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Oct 31, 2016
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I highly doubt the F4 went 150 knots over the max safe operating speed. Also the aerodynamics, impacts of dynamic pressure, and stress limits of a fighter jet are far different than a commercial 767. Apples to oranges

You apparently haven't seen the new Top Gun movie!

Seriously though:
1. I have no reason to doubt the story (there is no known incentive for my father to make it up).
2. While the actual max speed of the F4 was classified at the time of course, at this point there is probably public record of the flights somewhere. It's not exactly something that could be hidden or denied after that point.
3. Yes I know it's apples to oranges compared to a commercial jet - That's why the post started with, "A little off topic..."
 
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WeR0206

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You apparently haven't seen the new Top Gun movie!

Seriously though:
1. I have no reason to doubt the story (there is no known incentive for my father to make it up).
2. While the actual max speed of the F4 was classified at the time of course, at this point there is probably public record of the flights somewhere. It's not exactly something that could be hidden or denied after that point.
3. Yes I know it's apples to oranges compared to a commercial jet - That's why the post started with, "A little off topic..."
I’ve seen it twice actually! Saw it the day it came out in IMAX.
 

McCloudersportLion

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I love how when they do Q'y gaslight propaganda and it's always "Barack Obama, the Clintons, Joe Biden r kiddy rapers" - no dummy you put Obama at the very front because he is more liked and doesn't have the same smelly kiddy reaper smell as the others ya listed. Clumsy ass misdirection and gaslighting.
 

WeR0206

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Comment from another board:

It would, in all likelihood, be impossible for a large transport category jet to even reach an airspeed of 500 knots at an altitude that low. Drag increases with the square of the airspeed and the transsonic region presents some additional challenges on top of that.

A 767 should have sufficient thrust to accelerate past Vmo at low altitude, but Vmo for a 76- is 360 knots at MSL, a long way away from 500. Even if structural and powerplant failures due to overstress weren't an issue, it's safe to say that a 76- would be drag-limited from reaching anywhere near 500 knots in level flight.

With respect to failure modes, there are structural concerns, skin integrity concerns, powerplant concerns, and Mach tuck, and one or more of these would be encountered long before you had a chance to read 500 on the Airspeed Indicator.

  1. Bending of the airframe - going sufficiently fast will induce the various aerodynamic structures on the aircraft the generate forces and turning moments in excess of what the structure was designed to handle, leading to plastic deformation (and possibly outright failure if the stresses are sufficiently large)
  2. Control surface flutter - this is probably less of a concern in fly-by-wire and hydraulically-actuated control surfaces than for free control surfaces, but at sufficiently high speeds, air particles will strike the control surfaces with sufficient force to displace them and cause them flutter (ailerons are by far the most susceptible to this and the infamous control column "buzz" is caused by this). Sufficiently aggravated flutter has caused control surface separation in several fatal accidents.
  3. Skin integrity - sufficient suction over the top of the wings has been known to cause material, rivets, and inspection panels to separate and compromise the surface. Probably less of a concern for a stressed aluminium metal or composite skin than for a canvas skin.
  4. Mach tuck - the center of pressure moves rearward along the wing chord when the aircraft enters the transsonic regime (the exact speed and characteristics of this shift differ by aircraft) and causes nose-down pitching moments, which may become impossible to overcome. This effect is aggravated in a conventional tailplane arrangement by the generation of standing shockwaves and the subsequent change in airflow separation characteristics.
  5. Powerplant failure - reaching 500 knots would require the powerplant to generate tremendous amounts of thrust, requiring a much greater displacement of air through the compressors (and turbines) and a much hotter burn in the combustion chamber. The resulting engine rotational speeds and temperatures would ruin the engine for further use, if not cause it experience an outright structural failure. There's a pretty infamous case of an Egyptian MiG-25 overflying the Sinai Peninsula at Mach 3+ (the Foxbat was rated for a maximum of 2.8); the engines were toast afterwards.
Though not necessarily a failure mode, something to watch out for in fast-travelling swept-wing aircraft with large wingspans is the possibility the aerodynamic forces might twist the wingtips to the point where aileron functionality is reversed from normal.

Lastly, the control difficulties at such a high speed would stem more from the fact that the control surfaces (especially ailerons) become much more effective at higher speeds (less displacement is necessary in order to generate the forces necessary). Ordinarily, this might lead to an aircraft that is responsive bordering on twitchy and would require very light control inputs, but the story is a bit more complicated in an aircraft like the 76- due to the role played by the envelope protection software and the hydraulic actuation system.
 

WeR0206

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IOW the airframe would receive the same amount of stress going an airspeed of 510 knots at sea level as it would going mach 1.2 at 22,000 feet. The plane would break apart before it would reach these speeds.

At sea level These planes would become incontrollable at around 380 knots airspeed and start to break apart after around 420ish knots (see below V-G diagram). Because of this fact commercial pilots with thousands of hrs say 510 knots at sea level is impossible especially with a mostly level flight path. Even the concord jet can’t go 510 knots at sea level. But some dudes who trained on a single engine cessna going 60 knots pulled this feat off hitting a 200 ft wide target going an impossible speed? It’s absurd.

I guess boeing built 757 and 767’s capable of supersonic flights at altitude and still controllable enough to hit a 208 ft wide target with a 25 foot margin of error on either side?? That’s amazing!!

If you don’t believe me you can do the EAS calculations yourself. Dynamic pressure is dynamic pressure and math doesn’t lie.

Either the speed data obtained by numerous sources is inaccurate and therefore flight safety is in jeopardy (major ramifications for the airline industry) or what actually hit those buildings isn’t what we were told. Either way the story told by the 9/11 commission is a lie.

For a real life comparison Egyptian air flight 990 went straight down and at 22,000 feet it achieved its maximum speed of 603 knots (425 knots equivalent at sea level) or mach .99 then broke apart shortly after that as commercial airliners aren’t designed for that stress and it hit denser air. These planes cant handle super sonic speeds. They break apart first.

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Note the red failure zone starts at 420 knots at sea level:
wMoFVbr.png


Pilots for 9/11 truth:

In this video ^^^ at around the 25 min mark Ross “Rusty” Aimer who has 30,000 hours and has captained one of the actual planes used on 9/11 (United 175) said 510 knots at sea level is impossible due to air density and air frame integrity. Also The only way they would have the slightest chance of hitting their targets would be if they approached at landing speed which is around 130 knots. Otherwise it’d be like trying to park your car in your garage going 150 mph.
The people who responded to this below quora seem to know what I’m pointing out in the OP


“Vmo at sea level is 360 knots, 412 MPH. Go any faster and bad things are likely to happen. You can probably push Vmo by 10%, to 450MPH, but 500MPH is more like 20% and probably enough to cause significant issues with stability, control, and structural integrity.”
———————
“At sea level, it will usually be around 400 mph, or 360 knots for heavily-built transport airplanes.

Fly any faster than that at sea level and you risk a break-up.

Even rockets are built with limited strength, so they have to observe speed limitations during certain phases of their climb through the atmosphere to contain the aerodynamic forces on their bodies.”

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