On that CIA "Zoom Climb"

[publius]

I'll take that as a "no" to the question I asked you, Thee. Thanks.

 

[org]

Publius, I missed that reference to the cg shift. You're right, that's a huge change. It still wouldn't create an instant pitchup. When you're moving 500,000 plus pounds, nothing occurs instantly, especially when the tail is still attached. I'd have to think that by the time the pitch through the vertical the climb would have exceeded 3000 ft.

Also, as I said before, any instant large pitch change would have taken the wings off.

 

[publius]

So org, just to be clear, you're saying that a 42 second, 3000 foot climb sounds plausible to you after the loss of the nose?

How many seconds does it take to rotate the transport aircraft you're typed in from rolling attitude to takeoff attitude when you reach decision speed?

 

[org]

To me it sounds possible. If the wings didn't come off, it indicates to me that the rotation rate was NOT instantaneous or close to it. A figure (2 seconds ?) to 45 degrees was given. If the airplane made it to 45 degrees pitch without losing the wings and tail, it wouldn't take long for a pretty formidable upward vector to be generated. If you get 500,000 pounds going up at even 250K at 45 degrees, the wings could come off and the junk would continue up for quite a while. 3000 feet of climb isn't that much at jet speeds. As for the effect of the nose being gone, ???. At that point inertia is more of a factor than aerodynamics anyway. What used to be an airplane is now so much mass on a ballistic arc, possibly influenced by what used to be wings and a tail, possibly not. Possibly it would go farther without wings than with, after the initial pitch up.

I have no idea how fast the aircraft can be rotated at liftoff, since you don't apply max deflection on the controls anyway. Recommended target rotation for the B727, DC8, and A300 are all about 3 degrees per second. This is really not applicable anyway, since liftoff isn't at 340K. I guess I don't know what you're getting at here.

 

[publius]

If the wings didn't come off, it indicates to me that the rotation rate was NOT instantaneous or close to it. A figure (2 seconds ?) to 45 degrees was given.

Pitching up 45 degrees in two seconds strikes me as pretty close to instantaneous. It also strikes me as fast enough to produce airflow separation, and maybe fast enough to rip off the tail. It's also too fast to change the velocity vector of all that mass very much. Sure, it would be pointed upward, but as you pointed out, some things don't happen all that fast. It would still be going ahead for a little bit before it started climbing, even if the nose were rapidly pointed skyward.


What I was getting at is, a partial deflection of the elevator at decision speed is enough to produce a rotation rate of a few degrees per second. Makes me wonder how many ft-lbs of torque that partial deflection is producing. Something considerably less than 6 million, would be my guess.

 

[org]

Publius, I can't argue any of these things. Everything I've suggested was (or should have been) prefaced by "if". If this happened, that happened. I don't know what happened, but I THINK it's possible that the airplane climbed (or arced) as described.

Maybe I'm right, maybe you're right. Maybe we're both partly right. However, I don't think a missile shot down Flight 800. The logistics just don't fit. The human ability to keep a secret doesn't work. The capabilities of small missiles don't fit. The damage inflicted doesn't fit. Maybe a bomb, maybe a fuel tank explosion.

All my opinion, of course.

 

[publius]

I agree that those are good reasons to doubt that a missile took the plane down. I have my doubts about that as well. Like I said before, maybe a bomb, and maybe even a wire in a fuel tank, but this thread isn't about those things.

This thread is about what would happen to a 747 that lost its nose, for whatever reason.

I think it probably would take less than 2 seconds to pitch up 45 degrees, and less than 4 seconds to pitch up 90, and less than 6 seconds to pitch all the way over to 135, in the unlikely event that it made it that far. People on the ground wouldn't see it climb. They'd see it do a very rapid vertical circle.

It probably never made it that far. It pitched up very abruptly for those first couple of seconds before stalling/spinning/disintegrating (take your pick).

I just don't see how a sustained 40 second climb would be possible, since that would necessarily involve pointing the aircraft skyward for at the least several seconds. I don't think TWA 800 could be pointed in any one direction for as long as several seconds once the nose was gone.

 

[publius]

Looking back through the thread, I think I've found where we really differ, org.

The airplane pitches up, increasing the angle of attack initially and it goes up until it either stalls or breaks up.

I've bolded the key word. I don't think the pitching would ever stop. I can't see any reason it would. Can you?

If the pitching didn't stop, the angle of attack would increase until the plane stalled/spun/broke up.

It would be gaining altitude for that entire time, but I can't see that entire time lasting more than a couple of seconds. That brings me to:

When you're moving 500,000 plus pounds, nothing occurs instantly, especially when the tail is still attached.

You've got a little more than 10 times the number of flight hours I do, including, apparently, time in transport jets. You must have encountered clear air turbulence. I have, but only as a passenger. The beverage cart beside me levitated about 2 1/2 feet, then came crashing back down, all in less time than it took you to read that. In other incidents, as you are no doubt aware, passengers who don't pay heed to the advice that you buckle up while in your seat have found themselves flung against the ceiling and injured during a CAT encounter. These are all really big, heavy passenger liners I'm talking about, and they hit an air pocket and just DROP for lack of a better word, instantly.

Things can happen to really big planes really fast. Those planes that went into the WTC towers were also destroyed instantly. All it takes is a huge amount of force. Like 6 million foot pounds.

 

[artherd]

"All it takes is a huge amount of force. Like 6 million foot pounds."

You do have a very good point here. Things can happen to even big aircraft in a big hurry.

Just because the control surfaces create a sloppier 'feel' as aircraft tend to get bigger, does not mean they are less vulnerable to physics.

A CG change to 11 feet AFT of COL would definately be catastrophic. How would it behave? Depends on a thousand other factors I am not aware of. It could really almost 'go either way'. Is it likely it stabaly zoom climbed for 42+ seconds? no. Is it possible some freak set of circumstances allowed it to do just that? Sure it is! I wouldn't bet my lunch money though.

 

[publius]

I can't think of any circumstance, freaky or otherwise, that would stop the pitching.

Can anyone name one, even an extremely far-fetched one?

 

[publius]

On a lighter note,

Just because the control surfaces create a sloppier 'feel' as aircraft tend to get bigger, does not mean they are less vulnerable to physics.

It's the designers who create that "feel."

Most of my multiengine time is in the venerable Beech 18. I say venerable because that's a nice way to describe an airplane that was really old when I was born. It's not all that big, has 900 horsepower, and carries a ton or so. Talk about sloppy! With a heavy load, those little rudders don't do a thing unless you've got the engines run up pretty high.

Makes for an interesting crosswind landing. The only really good way to get it pointed straight is to add some power on your upwind engine. Yeah, there's a really good way to keep the oily side down.

I flew the 18s with a guy who had thousands of hours in DC 3s and 6s, which are more or less the same plane, only bigger and much bigger, respectively. A big difference, according to my buddy: that big ol' tail on the DC 3 is actually effective. You stomp, and something happens! Imagine that. A bigger airplane, but not as sloppy.

 

[org]

Publius, when I said the angle of attack would increase initially. I was referring to the fact that sometime before the vertical, the airplane either came apart or stalled. That initial pitchup could generate a higher angle of attack and climb vector. The longer before stall or breakup, the more climb. After either of those events, pitch and angle of attack are meaningless, all there is left to determine how high it went was inertia.

Turbulance is movement of the airmass. Maneuvering is movement within the air mass. Technically, this was maneuvering.

I agree that the pitch probably never reached the vertical. Big jets don't do loops, even with the nose on. That's why I said "initial."

 

[UnknownSailor]

I remember reading about that, but I can't remember where. You got a link?

That's something I heard on Art Bell, when he interviewed Cdr. Donaldson on air on Coast to Coast AM.

I will look for a link, but I can say with a good degree of certainty that it is in the twa800.com site, somewhere, since Cdr. Donaldson was associated with that site until he passed away.

 

[publius]

That initial pitchup could generate a higher angle of attack and climb vector. The longer before stall or breakup, the more climb.

That's true. I just think forces like those mentioned would mean that the initial pitchup would result in an almost immediate stall/spin/breakup. The CG was in its normal position, a foot in front of the COL, then, suddenly, it was 11 feet behind the COL. A tail section designed to pull down hard enough to resist the torque from the CG being 1 foot in front of the COL suddenly has to push up hard enough to resist the new torque from the CG being 11 feet behind the COL.

Seems to me that has to result in the aircraft pitching up really dramatically, and with only the badly overwhelmed tail to resist that pitching, it would pitch right through the critical angle of attack very quickly, and that'd be that.

Turbulance is movement of the airmass. Maneuvering is movement within the air mass.

True again. My only point with the CAT reference was that it is possible for something as big as a 747 to just drop quite a ways in almost no time at all. I realize that the wind causes it, not the flight controls, but the point remains: something that big can move down quickly enough that a person who is not strapped in can wind up hitting the ceiling.

Unknown Sailor, thanks. I'll go have a look. Never checked out that site before.

 

[HABU]

You guys can argue the finer points of aerodynamics all you want to. I simply hope that Capt. Ray Lahr can expose the .gov for the baffoons they can be.

If he does, I doubt that the media will take it very far.

 

[publius]

It's not really a fine point, HABU, more of a fundamental one. Like if I said that a dramatic climb would produce a dramatic reduction in groundspeed, but the radar data don't show that.

 

[Leatherneck]

I'm with org on this one. Publius's theory assumes that the CofL remains static, when in fact, beyond a certain AOA, the whole notion of COL is meaningless, and the wing is no longer a lifting body. Don't forget, in your theory of non-stop pitch-up. you neglect to consider the AOA of the horizontal stabilizer, which is roughly the same as the wing unless structural failure occurs. So the tail force vectors shift from downward to neutral to upward as the airplane pitches up. It's not unreasonable to assume that the whole pitch-up process slows at some point, allowing the new, somewhat stable "flight condition" to carry the mass upward almost ballistically. How long is reasonable? I don't know, but 42 seconds seems too long.

BTW, some guys from our live-fire test shop were involved in the test planning and analysis; the ullage mixtures were varied only slightly, not extensively, so not all potential conditions inside the tank were emulated in test. And Jet A-1 fumes can be explosive under certain conditions of temperature, pressure and richness.

TC
TFL Survivor

 

[JJohnston015]

First, my "credentials" : private pilot, about 300 hours, with some tailwheel and aerobatic time. Civil Engineer, with some knowledge of inertia, load paths, stress distribution, shear & moment, etc.

All talk of pitch-up aside... As I understand it, the main wing spar in the 747 is very close to, and in fact, makes up some of the structure of the center fuel tank. For those who don't know, the main spar is the "backbone" of the wing. It runs from wingtip to tip, it's more or less I-shaped (like a beam in a building or bridge), and it's generally located at the thickest point of the wing (thickest point = tallest ("deepest") spar = maximum bending strength). In a cantilever wing (no braces like many small planes have), there are large bending stresses at the root of the wing (the wings want to fold "up").

I find it very difficult to believe that after an explosion powerful enough to blow off the entire fuselage forward of the wing occurred in such close proximity to the center section of the spar, that the spar could have been in any condition to take any bending loads at all. I'm forced to think that the wings would have folded up immediately, and would not even have been able to take 1G, much less the more-than-1G associated with a sudden pitch-up and resulting zoom.

 

[publius]

Publius's theory assumes that the CofL remains static, when in fact, beyond a certain AOA, the whole notion of COL is meaningless, and the wing is no longer a lifting body.

I'm not ignoring that at all. In fact, that's my point! It's true that the center of lift does move with a changing angle of attack, but it doesn't move much. In any case, the AOA you're talking about is called the critical angle of attack, and it's the angle beyond which the wing stalls. All I'm saying is that flight 800's wings would have reached that angle, and reached it very quickly, long before any noticeable climb could occur. Like I said, a couple of seconds.

Don't forget, in your theory of non-stop pitch-up. you neglect to consider the AOA of the horizontal stabilizer, which is roughly the same as the wing unless structural failure occurs. So the tail force vectors shift from downward to neutral to upward as the airplane pitches up.

That's true, the tail would be experiencing an increasing angle of attack during the couple of seconds I'm talking about, resulting in some lift on the tail of the plane. The reason I think that would not matter is because the tail was never designed to resist the sudden application of that much force.

It's not unreasonable to assume that the whole pitch-up process slows at some point, allowing the new, somewhat stable "flight condition" to carry the mass upward almost ballistically.

Let's get back to the see-saw with the heavy guy and the guy wearing the weight belt for a second here. Recall that the weight belt is the horizontal stabilizer, always pulling down because that heavy guy is on the other end. In an airplane, the heavy guy is on the nose end for purposes of stall recovery and stability. The CG is forward of the COL.

What happens when the wing stalls, and there is no longer a COL? The heavy guy wins. The nose pitches down, and recovery is possible.

With the CG behind the COL, it's like putting extra weights on that smaller guy. When the wing stalls, the tail drops. Ouch! If you don't tie down your cargo in your old Beech 18, it can happen to you! Once that happens, no stable flight condition is possible.

The CG on flight 800 didn't just shift a little bit. It shifted a LOT, and it wound up behind the COL, exerting 6 million foot pounds of nose-up torque in the process, and it did it, presumably, really fast. Once a nose starts coming off, my guess would be it comes all the way off very fast, and until that time, it weighs what it weighs, in this case, something like 80,000 pounds, or roughly 14% of the weight of the whole plane (just from memory, I already looked up those numbers twice for this thread, so go back and find 'em yourself if you want 'em ).

 

[publius]

DJJ,

You might be right. On the other hand, the tail is usually the weakest part of conventional airplanes. They come off in high-g situations much more often. Of course, most of the time, there hasn't been an explosion.

Still, those wings are damn strong. I've seen videos of them testing them, during which they bent one until it broke. It bent a long, long way beyond what I expected, then snapped with a sound that completely overloaded the poor microphone they used.

I'm not sure if I'd bet on the wings or the tail of 800 coming off first. I'd just bet on one, followed pretty quickly by the other, and all within maybe 10 seconds.

 

[Sergeant Bob]

publius

Still, those wings are damn strong. I've seen videos of them testing them, during which they bent one until it broke. It bent a long, long way beyond what I expected, then snapped with a sound that completely overloaded the poor microphone they used.

I saw that video too. It was on Discovery Channel "Wings". The 747 has an amazingly strong wing!
I can't remember how much deflection it could withstand, but IIRC it was way beyond the design specifications.

 

[publius]

I think I actually saw it on Government Broadcasting Service, not Discovery. I haven't had cable TV since August 24, 1992 (hurricane Andrew snapped my cable line on that day, and soon afterwards I moved very far away from where any cables exist.) In any case, probably different specials, but almost certainly the same Boeing file video.