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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 9th May 2011, 20:40
  #1021 (permalink)  
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Salute!

First the beacons:

- if they are using pulse code modulation or a variation of the spread spectrum technology, it's very easy to find the thing even with s/n approaching 1:1 Witness GPS with all the stuff basically on a single frequency. Same with your cellphones and such. You just have to know the "chip" sequence and rate.

Some of the RF gurus here can explain it better than I.

Second, about the pitch excursion theories:

- Doesn't take much to lose half your groundspeed in ten seconds if you are climbing at 10 or 15 degrees and not having motors going full grunt. Just a few degrees of flight path change at a reduced power setting will do the trick - think higher AoA and resulting increased drag.

If the air data went FUBAR and the jet thot it was going faster than it was actually going, I can see the thing climbing until reaching the AoA "protection". Unless the power was increased (unlikely}, a very rapid speed bleedoff would occur. The folks in the other incident being mentioned either took immediate action or the body rates were low enuff for the flight control system to counter the excursion (gotta find out more about that incident, but it sounds hairy). Not the "test flight" crash, but the two planes flying close together when one went yahoo.

- If you look at the jet I flew, we could reach 40 or 50 degrees AoA before the stability issue came to play. From then on we had little or no pitch authority commanding a nose down attitude or gee. Remember we were flying at a very rear C.G. So if we got real slow, real fast at a steep climb, then we didn't have enuff control authority to get the nose down. We "parked" and then started down at a great rate. Wasn't some violent "snap roll" or "nose slice" or "pitch up" ( also flew the VooDoo and it had the violent pitch up LOC). We couldn't enter the deep stall on purpose at pitch attitudes of 5 or 10 or 20 degrees without being real slow and with some harsh rolling or skidding commanded by the pilot.

So I can see entry to a stall or even a stall/spin if the jet started an extreme climb.
++++++++++++++++++++++
I feel most of us wish to discover the root cause of this accident, then come up with some procedures by the crew to mitigate the situation. If we have to change the flight control "laws" while we're at it, then so be it.

Contrary to popular belief, the Viper FBW system had several modes that changed the priority of the air data, body rate, AoA, and gee inputs. Nevertheless, the system was way less complicated and had zero inputs from the autopilot to bias the basic control laws - it acted as a very limited "pilot" command when seen by the computers. More on the autopilot later upon request, but it wasn't quad redundant and was basically a device to reduce workload while pulling out an approach chart or cruising along to and from the target.

later,

Gums sends...

-
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Old 9th May 2011, 20:51
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Originally Posted by Machinbird View Post
RR_NDB
I believe the technique you are referring to is a phase lock loop system.
Phase-locked loop - Wikipedia, the free encyclopedia
Real electronic black magic. No doubt the EE folk will have more to say.
Real EE black magic = kalman filters (especially when extended). PLL is the simple case.

Once I thought I got all the math and completely understood how they worked, whilst the elders advised just treating it as black magic... now, I am older and wiser and know how little I knew
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Old 9th May 2011, 20:54
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Retired F4 - The 330 has a big wing and two powerful engines. Cruise power settings are modest in comparison to other types such as the 320
Imagine the folowing scenario- pitots ice up generating an overspeed. The aircraft pitches up and the athr retards the power to idle,add in a powerful upcurrent as a cb is penetrated adding to the pitch up. The aircraft has a lot of energy and due to the big wing a lot of manouvrability at altitude Whilst the crew is reacting to the autopilot dropping out and the aircraft fbw law degrading the aircraft stalls. If the aircraft has been cruising at 15-20kt above VLS and assuming a rapid decelleration the crew may have had only ten seconds or less to counter the stall but having penetrated a cb they are still in an updraft. The aircraft continues to climb. The crew pitch down to counteract the stall but the speedtape is still showing an overspeed. VLS is now overlaying the Barbers pole and the crew struggle to interpret what what has happened.Their computerised FBW protected aircraft had turned against them.
The cockpit is full of warning chimes and the ecam is full of failure messages due to the icing up of the ADR. The aircraft exits the CB core and is still in a
stalled condition but now is in the downdraft of the CB and it rapidly descends towards the sea and to their demise
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Old 9th May 2011, 20:57
  #1024 (permalink)  
 
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Speed/height trade

Originally Posted by RetiredF4
Flying at FL 350 with a still heavy aircraft, how much climb could be produced even with full power?
The mass doesn't enter into the equation. I see gums answered most of the questions you raised. Here is just a graph illustrating speed traded for height at constant total energy: Zoom Climb
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Old 9th May 2011, 20:59
  #1025 (permalink)  
 
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Signals 20 dB or more below the noise floor can detected using this method!

Gums,

Some tutorial info:

DK8KW Longwave Information (Slow-CW)
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Old 9th May 2011, 21:21
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Speed/height trade
Quote:
Originally Posted by RetiredF4
Flying at FL 350 with a still heavy aircraft, how much climb could be produced even with full power?
The mass doesn't enter into the equation. I see gums answered most of the questions you raised. Here is just a graph illustrating speed traded for height at constant total energy: Zoom Climb
Do i understand the graph correct?

Flying S&L at FL 350 with 470 TKAS, i can zoom the A330 to FL430 by trading 250 Kts of my TAS, provided thrust equals drag? To initiate this zoom, how much additional drag would be produced and how would that effect the result, if thrust is not increased?

What would be the rate of climb and AOA? We discussed the possibility of a sudden pitchup-scenario, not an easy and gentle climbing maneuver, which the graph probably represents, didn´t we?

Why does the mass not enter into a "useful" equation? I´m aware of the title "Constant TE Thrust=drag", bat higher mass means higher drag, therefore higher thrust to maintain TE (drag=thrust) is necessary, isn´t it?

At what altitude would the speed be below stall-speed and what would the stall speed be?
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Old 9th May 2011, 21:36
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Originally Posted by RetiredF4 View Post
Why does the mass not enter into a "useful" equation?
Trade kinetic energy 1/2 m v^2 for gravitational potential energy mgh - the m's cancel.
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Old 9th May 2011, 21:37
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Noise

Originally Posted by RR_NDB
Signals 20 dB or more below the noise floor can detected using this method!
I think you are confusing wide-band vs. in-band noise. Note that I said in answer to DJ77 in post 1005, that a traditional detection starts with a narrow band filter. This accepts and compares only the signal and noise that is within 100-200Hz of the target signal; the bandwidth of a 10ms pulse being about 100Hz .

The pictures you have shown appear to be of signals that are at least 10 and maybe 20db above the in-band noise (I don't know what the color scale is for those images). Your sonograms are performing the narrow-band filter operation, by using an FFT to break the spectrum into narrow slices, then separately displaying each slice.

gums points out correctly that GPS works at very low SNR; but GPS uses a long pseudo-random code that an auto-correlation algorithm can detect. Unfortunately, these old pingers just send a 10msec tone burst. One can certainly do better using techniques possible with a DSP than with the traditional detector, but I'm certain that the performance of a system like GPS, which uses engineered signals, cannot be exceeded when the signal is a tone burst filling only 1% of time (10msec/1sec).
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Old 9th May 2011, 21:41
  #1029 (permalink)  
 
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SaturnV,

Tim Vasquez's paper is indeed an impressive document. As I don't have to remind you, he did not entirely rule out the possibility of what he calls a "Warm sink" by the northern face of that Cb, which I guess marks the "front" of what the French still call le "Front Inter-Tropique". I suppose that this warm sink would amount to a downward kink in the tropopause. And we all know what flying in and out of the "trop" can be like.

The increase in SAT would lower the Mach for a given TAS. The wind would change, and the BEA commented that there was a weak jetstream of 280/85 at latitude 10N to the west of track. This MIGHT indicate a switch from very light headwind to a tailwind on the north side of the ITCZ. The downdraft also might cause loss of performance. The engine thrust would be lower for a given N1. Turbulence would be inevitable. The combination of all these factorss might present significant handling problems, even without the loss of reliable IAS/Mach indications.

Vasquez's flight-profile suffers slightly from lack of available data: I refer particularly to the isotherms, which he had to draw perfectly horizontal. Interestingly, the altitude scale is for true altitudes, and he shows AF447 at 35000ft on the -43C isotherm. On his modified SKEW-T for the "most probable" case (Fig 11), he has substituted a true altitude scale for the scale of pressure (millibars) on the vertical axis. The diagonal isothermic lines show -43C as being at about 37000ft, which I interpret as being the true altitude at FL350 (due to the ISA deviation).

If you suddenly encounter even warmer air (albeit only affecting the higher levels not the whole atmosphere below you), you need to climb even higher to maintain FL350...

Chris
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Old 9th May 2011, 21:51
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Takata

.13 Medical and Pathological Information
Sailors from the Frigate Ventôse recovered about thirty bodies. A visual examination of the bodies showed that they were clothed and relatively well preserved.
This would contradict most of the press releases (still today summaries):
1. Many bodies were recovered by the French Navy (about 3/5th by Ventôse);
2. They were clothed and well preserved



A bit confused by this. Unable to spot the difference, or are my eyes failing me?
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Old 9th May 2011, 22:43
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promani;
were clothed and relatively well preserved
The facts associated with that statement are most likely (from my experience) somewhat different, i.e.

"ballonné et endommagé par la morsure de requin étrange"
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Old 9th May 2011, 22:56
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auv-ee;
... the signal is a tone burst filling only 1% of time (10msec/1sec).
Not a good basis for PLL capture, bearing in mind that the ULB oscillator is most likely R/C with inherent phase shifting and possibly small frequency changes as the battery voltage drops.
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Old 9th May 2011, 23:00
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mm43
"ballonné et endommagé par la morsure de requin étrange"

"bloated and harmed by the bite of strange shark", is my translation. You could be right.
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Old 9th May 2011, 23:00
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Originally Posted by RetiredF4
Flying S&L at FL 350 with 470 TKAS, i can zoom the A330 to FL430 by trading 250 Kts of my TAS, provided thrust equals drag?
Yes.
What would be the rate of climb and AOA?
You control AoA with the elevator, that changes your load factor, which determines the rate of change of rate of climb. In other words, if n=load factor, c=rate of climb, and t=time, then dc/dt=(n-1)*g
At what altitude would the speed be below stall-speed and what would the stall speed be?
That depends on how you use the elevator, i.o.w. how much 'g' you apply.

Last edited by HazelNuts39; 9th May 2011 at 23:25.
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Old 9th May 2011, 23:04
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Originally Posted by mm43
auv-ee;
Quote:
" ... the signal is a tone burst filling only 1% of time (10msec/1sec)."
Not a good basis for PLL capture, bearing in mind that the ULB oscillator is most likely R/C with inherent phase shifting and possibly small frequency changes as the battery voltage drops.
I assume we are in agreement. That's another way to put the point I was trying to make.
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Old 9th May 2011, 23:07
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promani;
bloated and harmed by the bite of strange shark
"bloated and damaged from the odd shark bite" seems slightly clearer!
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Old 9th May 2011, 23:14
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auv-ee;
I assume we are in agreement.
"Singing from the same song sheet" is another way to put it.
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Old 9th May 2011, 23:23
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Google Earth

The terrain patterns shown in the LKP maps here are different from the terrain depictions in "regular" Google Earth. Can anyone explain?
For example, the abbyssal plane described for the final debris location looks like very broken/steep terrain in Goole Earth, not a flat sandy bottom.
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Old 9th May 2011, 23:31
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Originally Posted by mm43
Not a good basis for PLL capture, bearing in mind that the ULB oscillator is most likely R/C with inherent phase shifting and possibly small frequency changes as the battery voltage drops.
However, I should point out that an uncertain frequency is one problem that can be aided with improved signal processing. In the traditional detector one would make the filter bandwidth wide enough to be sure to include the maximum drift of the signal, thereby including more noise. With DSP techniques, it's easier to simultaneously track multiple narrow bands to find one that has a signal. This is likely part of RR_NDB's point.
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Old 9th May 2011, 23:44
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Googleearth

Originally Posted by [FONT=Arial
KTVaughan[/FONT]]The terrain patterns shown in the LKP maps here are different from the terrain depictions in "regular" Google Earth. Can anyone explain?
For example, the abbyssal plane described for the final debris location looks like very broken/steep terrain in Goole Earth, not a flat sandy bottom.


Others may know better, but...

Not much of the ocean bottom has been mapped at high resolution, and in many areas only by sparse tracks-of-opportunity from passing ships having deep fathometers. Most of the topography that Googleearth uses is based on sea surface altitude data collected from satellites. It turns out that dense mass under the ocean (sea-mounts and such) draws water toward itself, thus raising the sea surface slightly. This is a reasonable analog for water depth where there is no other information, but it is not very precise. Where Google has better bathymetry data, they include that.

Introduction to Physical Oceanography : Chapter 3 - The Physical Setting - Measuring the Depth of the Ocean

The maps that BEA is using are based on multi-beam bathymetry collected during Phase 2 (I think, someone will correct if it was collected at some other time).
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