THE PHYSICS OF FLIGHT; a thread for CIT

[Dave Rogers]

Isn't this sort of the same argument by some truthers on the maneuvers and flight speed of the 9/11 planes performed by inexperienced pilots at a denser altitude?

In so far as your question makes sense, no it isn't. Truthers argue that physically possible maneuvers such as a 330 degree diving turn could not have been performed by an inexperienced pilot, but that physically impossible maneuvers such as an 11g pull-out and climb could have been performed by an experienced pilot.

What exactly do you mean by "a denser altitude"?

Dave

 

[Homeland Insurgency]

In so far as your question makes sense, no it isn't. Truthers argue that physically possible maneuvers such as a 330 degree diving turn could not have been performed by an inexperienced pilot, but that physically impossible maneuvers such as an 11g pull-out and climb could have been performed by an experienced pilot.

What exactly do you mean by "a denser altitude"?

Dave

http://www.netaces.org/flightdynamics/flightdynamics.htm

Aircraft engines produce different amount of thrust at different altitudes, and some planes’ engines are optimized at different altitudes than others.

Drag is the resistance of air against the surfaces of your plane. It will always be directed opposite the direction of travel. Because air is less dense at higher altitude, drag decreases at altitude.

 

[Dave Rogers]

Let me put it differently. We're discussing the CIT hypothesis that flight 77 could have pulled up sharply enough to have overflown the Pentagon. You're commenting on a maneuver carried out by Hani Hanjour as he descended to a low enough level to hit the Pentagon, in other words at a higher altitude, where the air is less dense. Is that what you meant by "a denser altitude"?

Dave

 

[X]

Thank you everybody for the feedback so far. Some very good points have been brought forward.

The only thing I found with a cursory read is in 2.4 you have it spelled "seperated," kind of a pet peeve of mine, though you have it properly spelled in the section header.

Bugger. I thought I'd caught all of those.

I might add a comment that a flat plate actually makes a decent wing, provided you have a nice sharp trailing edge and operate in a narrow range of alpha. It's not the shape that creates lift, it's the angle of attack -- the shape optimizes and gives you control. Example, paper airplanes work just fine.

Also some additional discussion of the boundary layer might be in order. Many aircraft (I'm sure you know, I'm just stuck on Lecture Mode, sorry) deliberately create a turbulent boundary layer, but provided this is still attached to the aerfoil this is not a problem, indeed is usually a benefit. The advantages are that the turbulent boundary layer doesn't separate as quickly, and as a result drag decreases, trading more skin friction for a lesser wake. This is why golf balls and oranges are particularly good projectiles, too.

I thought about that.
Ultimately, I felt it would have been more than was required. Not that that stopped me in other areas.

I'll see what I can come up with and add it to the PDF.

In the image (Figure 6), there are two angles labeled alpha (α). One is the angle of attack as defined by the angle between the chord and the free-stream velocity, and the other I figured out had to be the angle between the chord and D (drag). When I first looked at this, for some reason I read the smaller alpha as being the angle between the chord and the top surface of the wing.

The second alpha is between the chord line and the direction of drag. It is the same as the angle of attack (look at the letter Z, the angles between the horizontal lines and angled lines are the same, it's a geometry thing), so they showed this by labeling it alpha.


Dave Rogers: I think Homeland Insurgency means a lower altitude when he refers to "denser altitude". He seems to be referring to the increased drag brought on by the more dense air at lower altitudes, and appears to be suggesting this makes some of the supposed maneuvers impossible.


Hokulele: I will make a post here announcing when I have completed the PDF. At that time, I will tell people how to go about getting a copy. (I haven't decided how to work that, yet.)



And finally, one more point:

I never showed the calculations for bank angle. Overlooked that, it seems. I will add those later today and incorporate them in the PDF.

 

[Homeland Insurgency]

Let me put it differently. We're discussing the CIT hypothesis that flight 77 could have pulled up sharply enough to have overflown the Pentagon. You're commenting on a maneuver carried out by Hani Hanjour as he descended to a low enough level to hit the Pentagon, in other words at a higher altitude, where the air is less dense. Is that what you meant by "a denser altitude"?

Dave

Not just the maneuver carried out by Hani Hanjour. I'm talking in general about the past claims of truthers on the limitations of airliners and the counter of debunkers on just how much they can perform past their rated limitations. Truthers in the past have commented on the flight speeds claimed in the official version of the planes that hit the towers as well as the claimed maneuver carried out by Hani Hanjour.

Then what happened? It wasn't debunked? The flight speed of 175 challenged? Gravey's airshow videos of just how much an airliner can do?

Back and forth.

 

[R.Mackey]

Not back and forth, because the position of conspiracists is based on stupidity, not physics.

UA 175's speed was considerably less than that of Egypt Air 990's, and at higher altitude, in a lower drag configuration. Diving from 20,000 feet pretty much moots any potential engine inlet performance issues.

 

[Dave Rogers]

Not just the maneuver carried out by Hani Hanjour. I'm talking in general about the past claims of truthers on the limitations of airliners and the counter of debunkers on just how much they can perform past their rated limitations. Truthers in the past have commented on the flight speeds claimed in the official version of the planes that hit the towers as well as the claimed maneuver carried out by Hani Hanjour.

OK, I see what you're getting at. It was the "denser altitudes" bit that threw me, because all these maneuvers took place - in fact, everything involving hijacked airliners (except perhaps the final crash of flight 93 - can anyone remind me of the ground level in Shanksville) took place - at higher altitudes than the supposed Pentagon pull-up, where the air is less dense.

As far as I'm aware, then, there are perhaps four areas of dispute:

(1) Flight 175 exceeding its rated maximum speed shortly before hitting WTC1. A question for X, then: Could you address the question of how an airplane gains speed as a result of a dive, for the benefit of those to whom it isn't obvious? This would explain how 175 could have achieved that speed. The other issue is how long its airframe could have survived the stresses imposed by that speed; as yet, I've seen no evidence that airframe failure would have been expected in the conditions experienced.

(2) Hanjour's turn. Was this within the limits of what's physically possible? I've seen no evidence to the contrary, in fact it appears to have been well within the capabilities of the airframe. The only question is whether Hanjour was capable of executing the turn.

(3) Flight 77 missing the VDOT antenna and still being able to strike the light poles.

(4) Flight 77 being physically able to overfly the Pentagon after striking the light poles.

I hope X will carry on from his excellent introductory summary to consider those four specific points.

There may also be a debate over the final actions of flight 93, but it seems rather futile to discuss whether an airframe was capable of surviving maneuvers that led almost immediately to its total destruction in a crash.

Dave

 

[Hokulele]

The second alpha is between the chord line and the direction of drag. It is the same as the angle of attack (look at the letter Z, the angles between the horizontal lines and angled lines are the same, it's a geometry thing), so they showed this by labeling it alpha.

Yup, that's what I was thinking, which is why I resketched it to satisfy myself. After 10:00pm, I sometimes travel at a "denser altitude".

 

[Horatius]

Not just the maneuver carried out by Hani Hanjour. I'm talking in general about the past claims of truthers on the limitations of airliners and the counter of debunkers on just how much they can perform past their rated limitations. Truthers in the past have commented on the flight speeds claimed in the official version of the planes that hit the towers as well as the claimed maneuver carried out by Hani Hanjour.

Then what happened? It wasn't debunked? The flight speed of 175 challenged? Gravey's airshow videos of just how much an airliner can do?

Back and forth.

Except that the truthers were wrong in both cases, but they were wrong for different reasons.

Flight manoeuvres can be grouped into three general classes:

1) Things that planes can do, and should do.

2) Things that planes can do, but shouldn't do.

3) Things that planes can't do.

Number 1 encompasses all the normal plane activities: Take off, landing, cruising, normal rate turns and the like.

Number 2 encompasses things that may be physically possible, but which are inadvisable in normal operations: Excessive speed, hard turns, steep dives and ascents. You can do them if necessary, but most pilots will spend a lot of time and effort avoiding these actions.

Number 3 encompasses anything else that will cause a complete failure: structural failure, hitting the ground, or whatever.


Hani Hanjour's manoeuvres fall into category 2, but the truthers insist they are category 3. Conversely, truthers argue the manoeuvres needed for the NoC flightpath are category 1 or 2, but they are actually category 3.

That's why they are wrong in both cases.

 

[Reheat]

Excellent X, just great. You ought to put it somewhere on the 'net accessible for those interested.

(1) Flight 175 exceeding its rated maximum speed shortly before hitting WTC1. A question for X, then: Could you address the question of how an airplane gains speed as a result of a dive, for the benefit of those to whom it isn't obvious? This would explain how 175 could have achieved that speed. The other issue is how long its airframe could have survived the stresses imposed by that speed; as yet, I've seen no evidence that airframe failure would have been expected in the conditions experienced.

We will never get a definitive answer on the speed issue. As far as I know, it is unknown even to the manufacturer just how much an Boeing airframe can endure. What we do know is that the aircraft doesn't just break up at high speed, it tends to shed panels, the engines may stall or it may came become difficult to control. Opinions are about all we're likely to get.

(2) Hanjour's turn. Was this within the limits of what's physically possible? I've seen no evidence to the contrary, in fact it appears to have been well within the capabilities of the airframe. The only question is whether Hanjour was capable of executing the turn.

I dare say every aircraft that flies more than just a few minutes does the type of turn Hani did in AA77. It was a simple descending turn, not a dive as terrorist loyalists like to call it. There was nothing extraordinary about it at all.

(3) Flight 77 missing the VDOT antenna and still being able to strike the light poles.

If one uses the proper figures it's no problem at all.

(4) Flight 77 being physically able to overfly the Pentagon after striking the light poles.

It was unable to do this because it crashed into the building. The wings were no doubt damaged and parts were shed, but it was flyable for the second or two that it needed.

There may also be a debate over the final actions of flight 93, but it seems rather futile to discuss whether an airframe was capable of surviving maneuvers that led almost immediately to its total destruction in a crash.

One could say this about all of the aircraft, not just 93. They went beyond normal limits for a few seconds in their final phase. Boeing builds tough aircraft. Heck, look at the KC-135 fleet. Most of those aircraft are older than Beachnut and still flying!

 

[Homeland Insurgency]

Except that the truthers were wrong in both cases, but they were wrong for different reasons.

Flight manoeuvres can be grouped into three general classes:

1) Things that planes can do, and should do.

2) Things that planes can do, but shouldn't do.

3) Things that planes can't do.

Number 1 encompasses all the normal plane activities: Take off, landing, cruising, normal rate turns and the like.

Number 2 encompasses things that may be physically possible, but which are inadvisable in normal operations: Excessive speed, hard turns, steep dives and ascents. You can do them if necessary, but most pilots will spend a lot of time and effort avoiding these actions.

Number 3 encompasses anything else that will cause a complete failure: structural failure, hitting the ground, or whatever.


Hani Hanjour's manoeuvres fall into category 2, but the truthers insist they are category 3. Conversely, truthers argue the manoeuvres needed for the NoC flightpath are category 1 or 2, but they are actually category 3.

That's why they are wrong in both cases.

That's your opinion. Here's another...



And a few more...

 

[R.Mackey]

Stunning idiocy.

747's have exceeded Mach 1 and landed safely.

NIST discusses the spread in estimates in NCSTAR1-2B. All the measurements cited are consistent within their experimental errors. All of them.

ETA: In response to the second video, the 747 described above performed this feat with one of four engines failed, and the other three at ordinary cruising power. Gravity provides all the thrust you need. Joe Keith is spectacularly stupid.

Welcome to eighteen months ago.

 

[Bobert]

They will simply argue that because The Government has infinite technology, the flyover could've been done by a magical aircraft capable of defying inertia.

To anyone unfamiliar with the CIT they would read the above and think that it was a complete joke yet it isnt at all far from what the CIT has already said.

 

[Bobert]

Wait a second where is the See-Saw?

 

[Horatius]

That's your opinion. Here's another...



And a few more...

You imply we are being inconsistent in our attitudes; I explain why that isn't so; you respond by posting a YouTube video that amounts to a non sequitur.


Please, do try to not be such a stereotype.

 

[ElMondoHummus]

Tiny nitpick

Boeing builds tough aircraft. Heck, look at the KC-135 fleet. Most of those aircraft are older than Beachnut and still flying!

Not possible. They're jets, not prop-driven.

Yipes!...

 

[rwguinn]

Not possible. They're jets, not prop-driven.

Yipes!...

I quite agree. I know for a fact there is no fabric-and-dope on the surfaces!
And absolutely no wax and feathers!

 

[bje]

I am sure I am not exaggerating to say CIT's next stunt will be to claim that ALL planes can fly safely with just one wing:

 

[Gravy]

Thanks, X. Had I read your treatise earlier, I could have spared myself a lot of ill-advised experimenting.

 

[Gravy]

I am sure I am not exaggerating to say CIT's next stunt will be to claim that ALL planes can fly safely with just one wing:

That is just...wow!