bearfoil

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

Tailspin Turtle

Or for simple folk... Note that the ground speed for the given pitch angle, angle of attack, and 10,000 fpm rate of descent is about twice the BEA number...

Garrison

Whew! Thanks a million. But what do you mean about 10,000 fpm being twice the BEA number? It is the BEA number.

gums

Yeah, Tailspin, just show for the impact velocities BEA has published.

I also got the same numbers using an AoA of 40+/- and pitch of 16 and vertical of 10,000 feet per minute

For Garrison: He says the groundspeed, not the vertical velocity. He is also using some numbers from early in the description of the descent. I am using the ones at impact, which are very specific in the report.

bearfoil

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

I am still stuck on Flight Path, ok? Ballistic flightpath. Not "line of Flight" when there is none.

Ballistic. Some few seconds after 2:10:04, Aero was out the door, and Rocketry wandered in. Ballistic.

Rocketman? Where fore art Thou?

Garrison

Well, that's the point. The numbers BEA gives for the steady-state descent are incompatible with the groundspeed at impact. Either something changed at low altitude, or the numbers are not reliable.

bearfoil

I think, as above, what went out the glass ("changed at altitude") was aeronautics, at ~ FL360.

One cannot fly a brick, no matter the architecture. And Stall is a point in time, once broken, Stall is left behind. It is Flight, Stall, or NOT Flight. At no time can two of the above be happening concurrently. One at a time. "Breaking the Stall" is misleading, what one does, is become airborne again. "Take off".

How's that for pedantic. Garrison, you are a writer, does that work for you?

Barkeep, two aspirin and an ROC cokola, boy howdy.

mm43

The graphic I put up on the previous page is using the BEA's data at impact. You are not telling me they read that data out incorrectly?

bearfoil

mm43

and my velocity was low by 11knots. Apologies, and good night.

Machinbird

Smilin_Ed (Another USN guy)
And also the single most useful instrument in recovering from a stall. Otherwise, at low speed, how do you know how much to push the nose down? Suppose you are actually inverted? Which way do you pull (push) then?

I didn't always look at my AOA while flying my Navy jet, but if I was maneuvering, it was definitely in my scan. If you ever get AOA in your airliner, try real hard to use it. You don't need it in cruise of course, but when you start to dirty up, you can observe the beneficial effects of slats and flaps very clearly, and with a little practice, you can tell when you need some flap to fly slower.

How to best mechanize AOA presentation has some contention, but it is probably time to develop a standard for airliners. It would be silly to have to train to recognize different types of presentations for each aircraft you fly.
A little bit of software and some free space on your PFD should be all most jet aircraft will need.

The AOA gauge directly answers the question, "How close am I to stalling the aircraft. " You can accurately fly an aircraft below stall speed in a ballistic trajectory and not stall the aircraft if you mind your AOA. (Of course, you do need some control authority-this doesn't work with tail slides.)

I'm also thinking the first two "beeps" of stall warning on AF447 were quite possibly caused by the g incurred in the initial pull up! It will be interesting to see the pitch rates developed.

JD-EE

deSitter, two comments about that link about demanding all A330s be grounded:
1) It's Speigel, which news service does not have a sterling reputation for their handling of this crisis, so far.
2) The A330 has a safety record that any earlier airliners more than a few years older than the A330 can only dream about. Shutting it down on a 1 in a million accident is past foolish. It's damn foolish.

I'm tempted to add a third item - it's Spiegel.

Garrison

I wish there were some aero guys contributing to this thread. It's interesting, and revealing, that a bunch of Airbus pilots hunched over their keyboards in the safety of their homes can argue so long and hard about the meaning of the various "laws"; imagine trying to figure it out in a cockpit headed toward the ocean. But the laws that really count in the end are the laws of nature and physics, and I think a lot of the commentary here has been lacking in understanding of the aerodynamics of a stalled airplane. It's much more complicated than just "brick". It appears that the wing is providing sufficient downwash, in spite of being "stalled," to keep a download on the horizontal stabilizer. If it were not, the airplane would pitch down naturally, because it is a conventionally configured airplane, it's not in a spin, its CG is not excessively far aft, and that's what they do. So the stabilizer is actually working. Furthermore, the wing, although largely stalled -- but note that the ailerons continue to be effective -- is still producing a lot of lift -- probably a CL of 1.0 at least -- but just with a ton of drag to go along with it. It's the drag that's making the airplane sink -- not lack of lift.

I'm just an amateur at this, but I've talked with a few experts and they all agree that it's highly unlikely that the airplane was in a stable "deep" stall. Much more probable that it was being held nose-high by its own wing and stabilizer.

Machinbird

Bearfoil
Bear, I used to fly a brick-like object aboard ship routinely. The secret was maintaining control. Well, that and lots of thrust too.

Garrison

mm43
No no, your graphic is great (don't quite agree about pitot behavior, but that's a small matter when they're frozen anyway) but if you compare it with Turtle's you see that the two sets of numbers are incompatible. So either some of the numbers are wrong to start with, or the flight conditions changed as the airplane neared the surface.

Tailspin Turtle

My bad. The BEA report doesn't give an angle of attack at impact. Solving for it:

bearfoil

Hello, bingo.

mm43

Two graphics showing exactly the same data, just in different ways.

Garrison

mm43
You mean your graphic and his second one. Agreed. I'm talking about the differences between his first one and his second one, which are quite significant.

Tailspin Turtle

Consider my first graphic to be the general case on the way down and the second to depict the flight condition at impact with the difference being the angle of attack. Of course, the actual angle of attack at impact will be dependent on surface wind speed and direction, but it was clearly much more than 40 degrees for the stated rate of descent and ground speed at impact and might even have been more than 61 degrees.

Graybeard

The modern jetliner gets its vertical speed from the IRU, Inertial Reference Unit. The IRU measures in 3 axes, as that's how the plane travels. It is apparent that all the velocity was in the Z axis, so the plane was dropping at 10,912 fpm, or 107 knots. There must have been near zero horizontal velocity when the plane hit.

AOA vane has physical stops. It has to be 35-40 degrees, so greater than 40 degrees AOA can only be calculated from the IRU, which data has apparently not been released, and the BEA are quoting AOA only from the vanes. I'm betting real AOA at the end was 100-120 degrees.