Posted on 11/16/2001 1:16:03 PM PST by Agent Smith
What's my point? That violent wake turbulence is plausible in this tragedy, BUT should not have knocked the A300 from the sky, and should NOT have knocked off the vertical stabiliser.
Strong vortices can live for quite a while, particularly in clear air. They persist because of the law of conservation of angular momentum; they are annihilated via dissipation, either through contact with the ground or via mixing with calm air, the latter being a much less efficient mechanism.
Vigorous vortices are generated by low speed flight of heavy aircraft -- such as a departing 747. Passing through one is equivalent to encountering shear.
It certainly a phenomenon that's been encountered many times before. Whether it's a causative factor in this case remains to be seen.
The Govt talking heads are saying things in the language of X42 and a lot of posters are reacting to the weasel words.
We have had eight years of the clintons' language meant to misdirect, spin and lie to us about govt events.
If it sounds like spin and weasel words, I am going to take it as that.
The NTSB probably doesn't know yet and neither do I.
I just wish they could be a little more forth coming in the statements, but I recognize that the media dictates the terms.
I think all the focus on the Vertical Stabilizer is also nonsense. All of the airplanes I have ever flown (probably forty or fifty different types--no Airbuses) could be flown without any vertical stabilizer. Some American production airplanes do not even have a vertical stabilizer.
If all that happened was that the vertical stabilizer came off, you could stear the airplane back to a landing with the alierons. There are really two choices here: All this nonesense is an effort to prepare the public and the media for a full court press cover up; or they really don't know what caused this and are trying to figure it out.
It is painfully obvious that something went very wrong with that airplane. Of course, it should have not had any problem with the wake turbulence. Parts should not just fall off. The only real question is what happened, structurally, to that aircraft? Everything else is just window dressing. Something physical happened to that airplane. What was it?
First let me respect your credentials as a high-time pilot, truly. Permit me to go through your points.
The wake turbulance answer is nonsense. There are not sufficient forces to affect structural damage. We do not yet know the amount of force or degree of deflection from the flight path or attitude, or even if there was any. I think we all agree that WT should NOT have caused the VS to separate from the aircraft. I think we all agree. It did, however, separate from the airframe, above the attachment points, indicating failure, as opposed to falling off. This SHOULD NOT have happened. WT may have been the 'last straw'.
There was at least a 15 knot wind (which would have cleared any turbulance out long before the airplane got there) and the hypothetical generator was at least 1 1/2 minutes ahead--there would not have been any turbulance.
Some data indicate the A300's departure path generated an intersection as little as 45 seconds behind and below the departure path of the 747. It is plausible SOME WT would have persisted, and we do not have data on winds aloft.
If you had been right on the tail of the 747 in no wind conditions, wake turbulance is not a structural threat--it bites pilots who are not paying attention and wind up in uncontrollable flying attitudes. It didn't happen this way.
Agreed. The VS should not have failed, all things being normal.
I think all the focus on the Vertical Stabilizer is also nonsense. All of the airplanes I have ever flown (probably forty or fifty different types--no Airbuses) could be flown without any vertical stabilizer. Some American production airplanes do not even have a vertical stabilizer. If all that happened was that the vertical stabilizer came off, you could stear the airplane back to a landing with the alierons.
Other discussion threads have introduced a different plausible scenario. Indeed several aircraft have been successfully flown without a VS in place. But ... Suppose the VS detached from the airframe while the first officer has stepped on the left rudder (appropriately, no pilot error implied) to in part correct for WT. The VS detaches, the yaw moment is to port, and the right wing is generating more lift and roll moment than the left. The WT that had been trying to roll the aircaft to the right now pushes on the wings to roll it to the left (other side of vortex) and encounters an aircraft trying its best already to roll to the left. Without a VS in place, (because it failed, not the pilot) the plane departed controlled flight with no means of recovery.
There are really two choices here: All this nonesense is an effort to prepare the public and the media for a full court press cover up; or they really don't know what caused this and are trying to figure it out. Well, this could all be mechanical and tragic, and the industry, as usual, will try to cover for AA and Airbus and blame the pilot and ATC.
Which ones?
The "wind shadow" that extends in and around a working air foil is pretty large. You can feel it and you will be able to see how it impacts the sails.
The more efficient a foil is, the larger the wind shadow. Foils work because the foil shape warps the fluid and the foil moves to fill he low pressure area created. The thing is, the laminar flow over the surface is what is actually creating the warp. The foil just initiates it. The more efficient the foil, the farther out the laminar flow is attached and the bigger the warp (thus the increased efficiency of the foil).
As the foil moves through the fluid, the fluid "slams shut" behind the warp, and it leaves lots of vortecese (or whatever the plural of vortex is).
This is "wake turbulence" (It can also be seen if you look at the water behind the boat as it moves. Air and water are both fluids, just different viscosities. In fact, it is the differential between the viscosities and the differential between the keel and rudder foils in the water and the sails in the air that make a sailboat work.
Anyway, in the water behind the boat there will be lots of swirls and whirlpools left as the boat passes by. "Wake turbulence".
Move through this turbulence and the foils are tugged this way and that.
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