AF 447 Thread No. 5
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3holelover
In reading your last, I am concerned. BEA have not concluded "There is no problem with the plane, save the iced pitots."
You repeat this in your second to last line.
I submit, with your position especially, that you may be adding to myth, to an incorrect interpretation, and to continued misunderstanding of the process.
You are heading in a direction opposite mine. Some may find that reassuring, I do not. It is better that the public know nothing, than to sheep the "consensus" of a thread with an anonymous population.
In an old, and odd sort of way, I support the mission of BEA. I take the release of the PR note as most destructive of an honored goal.
Agreement (assent) is a cultural artifact. It means nothing in the long term. It supports compromise, rather than the Truth. The best work is done by those who have passion first, and acceptance down the list. In this format, it is the adversary who will move you, not the ally.
In agreement alone, is second best.
In reading your last, I am concerned. BEA have not concluded "There is no problem with the plane, save the iced pitots."
You repeat this in your second to last line.
I submit, with your position especially, that you may be adding to myth, to an incorrect interpretation, and to continued misunderstanding of the process.
You are heading in a direction opposite mine. Some may find that reassuring, I do not. It is better that the public know nothing, than to sheep the "consensus" of a thread with an anonymous population.
In an old, and odd sort of way, I support the mission of BEA. I take the release of the PR note as most destructive of an honored goal.
Agreement (assent) is a cultural artifact. It means nothing in the long term. It supports compromise, rather than the Truth. The best work is done by those who have passion first, and acceptance down the list. In this format, it is the adversary who will move you, not the ally.
In agreement alone, is second best.
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Nav ias discreapancy
Hi Takata:
Just found out why the NAV IAS DISCREAPANCY message might be suspressed.
(Not completely sure, because we don't know the exact ECAM software status but this one is dated 08/NOV/06, so could be valid at that date)
1// The NAV IAS DISCREAPANCY can be triggered by a ADR 1 or ADR 2 IAS FAULT FOR PRIM status (as detected by FCDC1 or 2).
ADR 3 status comes only into view when ADR 3 data switch is out of the normal position)
2// The NAV IAS DISCREAPANCY can be triggered by a FROZEN PITOT Status (as detected by FCDC1 or 2).
But both 1// or 2// conditions to trigger the NAV IAS DISCREAPANCY message can be suspressed by certain system conditions being TRUE.
a/ any Dual or Triple ADR Failures (NAV ADR x+y(+z) FAIL messages not mentioned)
b/ All ADRs INOP [Switched Off] (not mentioned)
c/ NAV ADR DISAGREE present (not before ca. 02:12:00)
d1/ ADR CAS 1 or CAS 2 or CAS 3 NCD(or INValid) for reference 1//: IAS Fault for Prim status
d2/ Any DUAL CAS NCD(or INV) for reference 2//: Frozen pitot status
With this information I need to rethink what I posted before, maybe you could find some justification in your point of view.
Just found out why the NAV IAS DISCREAPANCY message might be suspressed.
(Not completely sure, because we don't know the exact ECAM software status but this one is dated 08/NOV/06, so could be valid at that date)
1// The NAV IAS DISCREAPANCY can be triggered by a ADR 1 or ADR 2 IAS FAULT FOR PRIM status (as detected by FCDC1 or 2).
ADR 3 status comes only into view when ADR 3 data switch is out of the normal position)
2// The NAV IAS DISCREAPANCY can be triggered by a FROZEN PITOT Status (as detected by FCDC1 or 2).
But both 1// or 2// conditions to trigger the NAV IAS DISCREAPANCY message can be suspressed by certain system conditions being TRUE.
a/ any Dual or Triple ADR Failures (NAV ADR x+y(+z) FAIL messages not mentioned)
b/ All ADRs INOP [Switched Off] (not mentioned)
c/ NAV ADR DISAGREE present (not before ca. 02:12:00)
d1/ ADR CAS 1 or CAS 2 or CAS 3 NCD(or INValid) for reference 1//: IAS Fault for Prim status
d2/ Any DUAL CAS NCD(or INV) for reference 2//: Frozen pitot status
With this information I need to rethink what I posted before, maybe you could find some justification in your point of view.
Last edited by A33Zab; 24th Jul 2011 at 19:09.
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henra,
I should clarify that my post #546 was only indicating an initial symbolic notation of the Kinetic energy as a function of speed, with the speeds, which are easy reference points to the BEA text, which mentions the two IAS values 275 and 211. That was a correct notation, and a correct equation. Further calculations based on that equation are correct, as long as as the expansion of the functions include the correct speeds.
But what attracts my attention more in your post, is the TAS values.
I am not sure what considerations you've made in calculating, or getting the TAS. Can you elaborate?
One of the AF 447 BEA reports indicates a TAS of 461 knots at FL350, while yours is 495 knots.
Even further, and more importantly, you're indicating a calculated "delta h" based on the two TAS of 495 and 390, of 4200 ft, and you're reasoning that the larger "height" value (of 4200ft versus 2500ft, a difference of 1700ft) is explicable by the increased drag during the ascent/climb.
You expend further on that in your reply to JD_EE.
JD_EE is pointing out an element that I interpret as being in line with my further explanation bellow. He is also up to something, further in the second 1/2 of his post,
but without elaborating....
In fact if you want to be exact, grity is right. The equilibrium of drag and thrust is only valid for one speed. So when the AC slows down in the climb, the 1g drag decreases. Therefore the thrust of the engines will add some energy to the equation.
However, this Delta of energy is negligable compared to the Deltas in energy state we are talking here. The effects of increased drag by maneuvering and changing bank angles will by far exceed the Excess thrust due to the speed decrease.
It's right that the Thrust and Drag are valid for one speed.
But here is further:
Based on the BEA text, we know 275 knots (FL350), and 211 knots (FL375), were speeds that resulted from Real Time measurements (and/or calculations based on Real Time measurements).
Thus they implicitly include the Real Time AF 447 Thrust and Drag, in Real Time conditions, at FL350, FL375, and the climb/ascent in between. And so should be the TAS.
Also based on the BEA text, we know the delta height of 2500ft, which is also a Real Time measured element, and thus it includes the Thrust and Drag that were present in getting to that height.
Pointing out, or explaining that a calculated approx 4200 ft height's discrepancy of 1700ft is due to Drag, or Thrust, means including Drag or Thrust a second time in the equation. That does not seem to be correct.
So, I think there is a need for a different explanation....
....
The equation bellow, which is a next step from the one I've posted, is correct.
This is to say that the earlier posted warning that
v1^2 - v2^2 is not equal to (v1-v2)^2
was absolutely correct.
I should clarify that my post #546 was only indicating an initial symbolic notation of the Kinetic energy as a function of speed, with the speeds, which are easy reference points to the BEA text, which mentions the two IAS values 275 and 211. That was a correct notation, and a correct equation. Further calculations based on that equation are correct, as long as as the expansion of the functions include the correct speeds.
I am not sure what considerations you've made in calculating, or getting the TAS. Can you elaborate?
One of the AF 447 BEA reports indicates a TAS of 461 knots at FL350, while yours is 495 knots.
Even further, and more importantly, you're indicating a calculated "delta h" based on the two TAS of 495 and 390, of 4200 ft, and you're reasoning that the larger "height" value (of 4200ft versus 2500ft, a difference of 1700ft) is explicable by the increased drag during the ascent/climb.
JD_EE is pointing out an element that I interpret as being in line with my further explanation bellow. He is also up to something, further in the second 1/2 of his post,
but without elaborating....However, this Delta of energy is negligable compared to the Deltas in energy state we are talking here. The effects of increased drag by maneuvering and changing bank angles will by far exceed the Excess thrust due to the speed decrease.
But here is further:
Based on the BEA text, we know 275 knots (FL350), and 211 knots (FL375), were speeds that resulted from Real Time measurements (and/or calculations based on Real Time measurements).
Thus they implicitly include the Real Time AF 447 Thrust and Drag, in Real Time conditions, at FL350, FL375, and the climb/ascent in between. And so should be the TAS.
Also based on the BEA text, we know the delta height of 2500ft, which is also a Real Time measured element, and thus it includes the Thrust and Drag that were present in getting to that height.
Pointing out, or explaining that a calculated approx 4200 ft height's discrepancy of 1700ft is due to Drag, or Thrust, means including Drag or Thrust a second time in the equation. That does not seem to be correct.
So, I think there is a need for a different explanation....
....
The equation bellow, which is a next step from the one I've posted, is correct.
This is to say that the earlier posted warning that
v1^2 - v2^2 is not equal to (v1-v2)^2
was absolutely correct.
Originally Posted by henra Post #612
Between the two calculations I compared there is no doubt about which one is the physically correct one:
it is 1/2(m) v1^2 (Kinetic Energy before the climb) minus 1/2 (m) v2^2 (Kinetic Energy after the climb).
it is 1/2(m) v1^2 (Kinetic Energy before the climb) minus 1/2 (m) v2^2 (Kinetic Energy after the climb).
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airtren
How are the altitudes and "AS" derived by BEA? Inertial? Certainly from the DFDR? How accurate is the "start" Alt.? With great respect, no possibility of gigo?
Perhaps germane is the 'ability' of BEA (or any retrospective) to suss solid data from an airframe that may not have supplied it to the only people who matter? If this is so, and ATF boffins can determine data that would have saved the day, perhaps we should wonder why? No offense intended.
Inherent in any device that can "unwind" a puzzle, is the implied chasm between "best practice" and "Failsafe"? In there also is the "acceptable" risk?
Internist: Knows everything, does nothing
Surgeon: Knows nothing, does everything
Pathologist: Knows everything, does everything, but too late.
How are the altitudes and "AS" derived by BEA? Inertial? Certainly from the DFDR? How accurate is the "start" Alt.? With great respect, no possibility of gigo?
Perhaps germane is the 'ability' of BEA (or any retrospective) to suss solid data from an airframe that may not have supplied it to the only people who matter? If this is so, and ATF boffins can determine data that would have saved the day, perhaps we should wonder why? No offense intended.
Inherent in any device that can "unwind" a puzzle, is the implied chasm between "best practice" and "Failsafe"? In there also is the "acceptable" risk?
Internist: Knows everything, does nothing
Surgeon: Knows nothing, does everything
Pathologist: Knows everything, does everything, but too late.
Last edited by bearfoil; 24th Jul 2011 at 17:02.
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airtren, henra,
the question if the BEA speeds are CAS or TAS are not realy clear for me, up to now I tought CAS
I was not on the search for negligable faktors, just trying to re-calculate the energie for my self (fighting with non metric units as before....)
I think they flow with mach 0.82 at F350 and planed to climb to F375 (flightplan) and in the same moment wanted to reduce the speed to mach 0.80 (turbulence) so they start the climb without more trust....... and then start the UAS event...........
if v2=0 then
v1^2 - v2^2 is equal to (v1-v2)^2 ..... so "dont hang up" uses the second formula just for argumenting how high maximal you can climb before you stand still (V2=0) with given v1....
the question if the BEA speeds are CAS or TAS are not realy clear for me, up to now I tought CAS
I was not on the search for negligable faktors, just trying to re-calculate the energie for my self (fighting with non metric units as before....)
I think they flow with mach 0.82 at F350 and planed to climb to F375 (flightplan) and in the same moment wanted to reduce the speed to mach 0.80 (turbulence) so they start the climb without more trust....... and then start the UAS event...........
if v2=0 then
v1^2 - v2^2 is equal to (v1-v2)^2 ..... so "dont hang up" uses the second formula just for argumenting how high maximal you can climb before you stand still (V2=0) with given v1....
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Originally Posted by airtren
Pointing that Thrust needs to be considered, or explaining that your calculated approx 4200 ft height's discrepancy of 1700ft is due to Drag, or Thrust, means including Drag or Thrust a second time in the equation.
That's not correct.
That's not correct.
Beside speed, altitude is not the only parameter changing during the climb, the flight equilibrum is also changed (thrust/drag ratio).
If no additional power is applied for an altitude change, the aircraft needs more lift; alpha will be increased and airframe will produce more drag. A lesser factor is the loss of thrust at same RPM due to increased flight level.
Consequently, no matter if the calculation is based on IAS or TAS, energy state change is not only due to a single altitude parameter changing while your estimation is only factoring altitude on it.
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And now we need to find out why
From my age and name you can see that I probably lack any special knowledge of modern techniques or -ologies. However..
A Royal Flying Corps pilot was told " not to fly too high or too fast" and he would have seen the effects of flying too low or too slow on the airfield.
Most or many accidents were put down to " Pilot Error" (" No one will ever know...")
By page 31 of David Beaty's "The Human Cost of Aircraft Accidents" ( 1969) he had described three different Pitot/Static accidents - not always the " fault" of the aircraft. He goes on to look at a number of failings of the many humans who then were involved in making the safety of Air Transport even better. Humans are STILL relevant... ( Don't tell HAL.)
Some airlines only had Captains who never made mistakes, were called Sir, and from their Accident Reports, were all rated "Above Average".
Most of the many hundreds of crew members with whom I flew, I would guess, aspired to be just Average, and stay out of the Accident Reports. First names or nicknames were used. It was thought easier to say, "Watch it, Joe.." Rather than " Sir, you are about to hit the sea wall.."
In the crew room of one fleet, built by B., it was joked that Emergency Drills should be done quickly, much more so, than accurately and appropriate. Another fleet, made by a different B. was told that their new aircraft had been so designed that you should sit on you hands and count up to ten before you do anything.
In September 1947 C54 "Robert E. Lee" flew from Newfoundland to Brize Norton, fully automatically. Probably not to today's safety standards, I would guess.
A Royal Flying Corps pilot was told " not to fly too high or too fast" and he would have seen the effects of flying too low or too slow on the airfield.
Most or many accidents were put down to " Pilot Error" (" No one will ever know...")
By page 31 of David Beaty's "The Human Cost of Aircraft Accidents" ( 1969) he had described three different Pitot/Static accidents - not always the " fault" of the aircraft. He goes on to look at a number of failings of the many humans who then were involved in making the safety of Air Transport even better. Humans are STILL relevant... ( Don't tell HAL.)
Some airlines only had Captains who never made mistakes, were called Sir, and from their Accident Reports, were all rated "Above Average".
Most of the many hundreds of crew members with whom I flew, I would guess, aspired to be just Average, and stay out of the Accident Reports. First names or nicknames were used. It was thought easier to say, "Watch it, Joe.." Rather than " Sir, you are about to hit the sea wall.."
In the crew room of one fleet, built by B., it was joked that Emergency Drills should be done quickly, much more so, than accurately and appropriate. Another fleet, made by a different B. was told that their new aircraft had been so designed that you should sit on you hands and count up to ten before you do anything.
In September 1947 C54 "Robert E. Lee" flew from Newfoundland to Brize Norton, fully automatically. Probably not to today's safety standards, I would guess.
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@ChristiaanJ:
What are those >> shaped symbols
In this schematic they stand indeed for OR gates.
Excuses, but didn't find any -OR gate symbol - in my office version.
Will do some edit to mention that.
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What went wrong?
What went wrong?
There is no group more concerned about what happened, or what went wrong with this accident, than the pilot community. They need to glean any lesson that can be learned to avoid it from happening again.
They can't wait for the completion of the up to 2 year period of the formal investigation. They have to continue flying the next day.
The one trigger to all of the following events is entry into a towering cumulo nimbus that reached up to 60,000 feet.
Trying to hand fly an aircraft in turbulent air at altitude for the first time is a difficult task. If not impossible.
The simple remedy until it is all fleshed out is simply avoid the potential trouble spot. And deviate well clear.
There is no group more concerned about what happened, or what went wrong with this accident, than the pilot community. They need to glean any lesson that can be learned to avoid it from happening again.
They can't wait for the completion of the up to 2 year period of the formal investigation. They have to continue flying the next day.
The one trigger to all of the following events is entry into a towering cumulo nimbus that reached up to 60,000 feet.
Trying to hand fly an aircraft in turbulent air at altitude for the first time is a difficult task. If not impossible.
The simple remedy until it is all fleshed out is simply avoid the potential trouble spot. And deviate well clear.
Please wallybird7 do you really think we need another lecture about CBs ?
It may surprise you but be assured that just as every airman AF crews know that you don't venture into the big bad wolf's mouth.
It may surprise you but be assured that just as every airman AF crews know that you don't venture into the big bad wolf's mouth.
Weather or....
With all due respect, Wally, all of us, as pilots and SLF's, have flown thru bad weather. Sometimes we didn't have a choice due to the mission, and I feel most of us avoided obvious bad weather.
Over the past 50 years we learned a lot about weather effects that extend miles and miles from the obvious CB towering cumulus. We learned about mountain waves and CAT and rotor clouds. What a wonderful world it would be to have CAVU every day. Well, I personally like those fair weather cumulus, heh heh. Kinda adds "ambience" to the experience.
There is no doubt that "weather" will play some role in the tragedy. However, the biggest role will be freezing up the air data probes for a system that depends upon them for many functions and "nice to have" features of the jet.
It is interesting to note that several other jets flew thru the same general area and their pitot-static systems didn't go "tits up".
The BEA reports do not indicate severe flight conditions that we pilots would be concerned with. Instead, we have a loss of air data to a sophisticated system, and the subsequent warnings and change of "laws" seem to have played a large role in the pilot reactions.
In short, Wally, I ain't gonna blame flying near some storms over the ocean, or efforts by the crew to "ease the pain" going thru a line of them. In my experience, the storms over the Pacific were nothing compared to the ones over Kansas. I even re-fueled behind a KC-135 a few times in the middle of some of those suckers and it was nothing I would have attempted over Topeka in the summertime.
Over the past 50 years we learned a lot about weather effects that extend miles and miles from the obvious CB towering cumulus. We learned about mountain waves and CAT and rotor clouds. What a wonderful world it would be to have CAVU every day. Well, I personally like those fair weather cumulus, heh heh. Kinda adds "ambience" to the experience.
There is no doubt that "weather" will play some role in the tragedy. However, the biggest role will be freezing up the air data probes for a system that depends upon them for many functions and "nice to have" features of the jet.
It is interesting to note that several other jets flew thru the same general area and their pitot-static systems didn't go "tits up".
The BEA reports do not indicate severe flight conditions that we pilots would be concerned with. Instead, we have a loss of air data to a sophisticated system, and the subsequent warnings and change of "laws" seem to have played a large role in the pilot reactions.
In short, Wally, I ain't gonna blame flying near some storms over the ocean, or efforts by the crew to "ease the pain" going thru a line of them. In my experience, the storms over the Pacific were nothing compared to the ones over Kansas. I even re-fueled behind a KC-135 a few times in the middle of some of those suckers and it was nothing I would have attempted over Topeka in the summertime.
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airtren, let's see if I can be more rigorous without getting into details. That is to say, I'll wave my hands a bit. Hopefully somebody with numbers will then step in.
What really needs to be accounted for is the energy imparted by the engines and the energy removed by drag. In that calculation you use the difference of squares rather than square of differences. Then you add in the energy from the continued thrust Et and subtract the energy lost in drag Ed. In level flight. At FL350 these two figures were roughly balanced. So somebody who knows the engine thrust at FL350 can figure a "static" value for Et and Ed. That allows a modified Ed for the duration of the climb to be estimated. Then we can really figure out of something was holding that plane down or not.
(I played on the back of an envelope and have a suspicion that the plane was indeed in a wind with a downward component of some sort. But it's such a swag I'm not going to publish it. I was pulling numbers out of the air and Wikipoodle.)
What really needs to be accounted for is the energy imparted by the engines and the energy removed by drag. In that calculation you use the difference of squares rather than square of differences. Then you add in the energy from the continued thrust Et and subtract the energy lost in drag Ed. In level flight. At FL350 these two figures were roughly balanced. So somebody who knows the engine thrust at FL350 can figure a "static" value for Et and Ed. That allows a modified Ed for the duration of the climb to be estimated. Then we can really figure out of something was holding that plane down or not.
(I played on the back of an envelope and have a suspicion that the plane was indeed in a wind with a downward component of some sort. But it's such a swag I'm not going to publish it. I was pulling numbers out of the air and Wikipoodle.)
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Hi,
Some interesting documentations (PDF French language!)
AF Simulation décrochage
SIMDecrochage.pdf
A330 Domaine de vol
Domaine-de-vol-A330.pdf
Some interesting documentations (PDF French language!)
AF Simulation décrochage
SIMDecrochage.pdf
A330 Domaine de vol
Domaine-de-vol-A330.pdf
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Please wallybird7 do you really think we need another lecture about CBs ?
Apparently this crew didn't.
Differences to that standard factor may result from temperature differences.
Please note: the BEA value was GS. The calculated one would be speed through the air corrected by density effect. Therefore also a headwind could be a possible explanation for the difference.
Even further, and more importantly, you're indicating a calculated "delta h" based on the two TAS of 495 and 390, of 4200 ft, and you're reasoning that the larger "height" value (of 4200ft versus 2500ft, a difference of 1700ft) is explicable by the increased drag during the ascent/climb.
What I was trying to point out is the fact that any additonal maneuvering (pulling g, thereby increasing induced drag and worse cl/cd of the wing or rolling, thereby increasing drag coefficient due to moving surfaces and induced drag due to resulting g load) will consume kinetic energy thereby reducing the amount which can be converted into altitude for a given speed.
On the other hand flying at 250kts IAS will require less thrust for 1g level flight than 275kts. So after slowing down and leveling off the engines have some excess thrust which would contribute positively to the energy available.
As takata has pointed out that is only partly true as below a certain speed the drag will rise again due to ending up in a less good cl/cd area (higher Alpha) of the wing polar. So at the end you can probably leave excess thrust largely out of the equation.
Based on the BEA text, we know 275 knots (FL350), and 211 knots (FL375), were speeds that resulted from Real Time measurements (and/or calculations based on Real Time measurements).
Pointing out, or explaining that a calculated approx 4200 ft height's discrepancy of 1700ft is due to Drag, or Thrust, means including Drag or Thrust a second time in the equation. That does not seem to be correct.
There are two effects impacting on the drag: even infinte wings used for calculating airfoil qualities have their best cl/cd usually at low AoA. Increasing AoA will deteriorate this ratio. On top of that increasing g will addiotionally increase the induced drag.
Unfortuantely without exact cl/cd curves for the A330 wing it will not be really possible to calculate the net energy loss due to the initial pull up.
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Pardon me for jumping in. Initially, I also thought the PF
screwed up. Though following the discussion and matching the
background of physics to these items, I more or less changed
my mind. The general suggestion is: PF should have initiated
a pitch&power approach. It very well could be he did, with this
as a result.
I did write these articles the last 3-4 weeks, though didn't post,
given my lack of time to keep up with the current thread. Some
of the subjects have been touched in recent posts, though I
keep my writing included, to take care for a complete line of view.
I neither did have time to match all of the raised items with
the actual AF447 figures. Maybe somebody wants to do this.
My apologies about this.
In the, up to now 5 threads, some physics came along. Physics, which are
sometimes so far off, that conclusions drawn on that are totally off. As such I
do give some thoughts how to approach those items.
1. Usage of TAS to calculate Kinetic Energie exchange for height.
====================================
- Since Kinetic Energy is non linear in speed, it's not an option
to consider the change in TAS a suitable parameter for change in
Kinetic Energy. For a zero speed based start to calculate the speed
of a dropping item as function of it's height, that's ok.
Since the Kinetic Energy is the SQR of the speed, the Kinetic
Energy of different perpendicular axis are independent.
- For general exchange of speed into another direction or height
(Potential Energy), the actual inertial speed has to be used,
so at least the ground speed and not TAS. I would even say, groundspeed
corrected with the earths' rotational speed (roughly 1800 m/s). Due
to lack of time, I didn't have the time to think this through for
100%, though I do expect this to be relevant.
This can be understood from the following thought-experiments:
= Assume the windspeed suddenly becomes zero. Will the effective
Kinetic Energy of the airplane change ? Nop.
(The airplane will show reactions after the change, though that's because
the force-field does change).
= Assume with the airplain flies with constant speed, the earth rotation
is suddenly stopped (that would give a mess on the ground, though it's
only a thought experiment). Would the effective Kinetic Energy of
the airplane change ? Nop. When an airplane lifts off, the airplane
starts with a speed related to the ground plus a TAS to generate
sufficient lift to lift off.
- So the Kinetic Energy will be 0.5 * M * SQR (| TAS + WINDSPEED + Vrotation |).
Of course everything in 3D vector calculations. M is the airplane mass. The
bars "| |" represent the calculation of the length of a vector.
- To get an impression how much the effect is. The example assumes
for ease of calculation, all vectors have the same direction. In general,
this is not the real situation:
Kinetic Energy presumed to be "released" from an object bleeding of a 250 m/s TAS back to zero:
0.5 * M * 62500 = 31750 M
Kinetic Energy released from an object bleeding of (TAS) 250 + (Windspeed) 50 +
(V-earth-rotation) 1800 m/s to a TAS of zero (with the same wind/earth-rotational speed):
0.5 * M * 4410000 - 0.5 * M * 4202500 = 103750 * M
So when doing the Ekin calculations properly, around 3 times more Energy
becomes available for height gain. Note: Speeds only intended for example
purposes, these aren't the actual AF447 figures.
Usage of TAS to calculate the energy exchange gave a "suitable" fit
for the AF447 case. Why is the difference so big ? I'll get to that a
little further in this article.
Only vertical speed vs. high, the normal Energy constant formula can be used.
2. Effect FL38 turn on TAS and as such on Stall warning reactivation.
=======================================
Nobody mentioned the potential effect of the 180+ degree turn at FL38 on
the return of the stall warning. Such a turn would have a significant
effect on the experienced windspeed and as such on the TAS.
Once at FL38, the airplanes' Inertial Kinetic Energy would be
reasonable constant during the time it takes for the turn. The TAS
however changes a lot. Depending on the wind direction, up to
twice the windspeed.
Maybe somebody might want to match this aspect with the actual AF447 data.
3. The presumed HS stalled status on the way down.
=====================================
Once the airplane got a reasonable downward vertical speed component,
I don't think the AF447 HS is stalled at all (on the contrary, has super-lift),
Why: Typical aspect with a stall is: release of the boundary layer over
the airfoil AND a sudden increase of the speed vector component opposite
of the intended lift force. On the main wings, both components do influence
each other increase both values after initial upset, significantly.
A situation, with an AoA getting higher than the main wing can handle, starts
very fast.
Now to the HS: The intended "lift" for the A330 HS is downward. The speed vector
of the AF447 HS on it's path down to earth, is also downward. The pressure gradient
is actually pushing the air towards the airfoil. So no reason
at all for boundary separation. More the contrary: Because the downward speed vector
"pushes" the airflow on the airfoil, the tendency to boundary separation will be less.
Another aspect relevant in this, is: The HS airfoil does have to curved surfaces,
bottom side a lot, the upper side just little bit. So both sides of the HS generate
lift, where the downward lift force is significantly higher.
Now back to the AF447 HS on it's downward trajectory. The downward speed
is so high that the upper side of the HS airfoil will have (nearly) complete boundary
layer separation, so the upper airfoil surface is completely stalled. The net effect
is an even greater downward lift vector on the HS.
Or so to say: Because of the huge HS downward lift force, the normally nose heavy
airplane doesn't topple over to a nose down situation.
Because of the high downward HS lift, this airfoil is (together with the VS) perfectly
able to stabilize the aircraft on it's way down and prevent a spin or even a roll.
The above can also be argued from the opposite side. The BEA has reported
the airplane went down in a stable state. This can only be reached when a
configuration with airfoils with sufficient "lift" are present. Since the main wings
are definitely stalled, the stable factor must come from the HS/VS span.
Another reasoning from the other side: The A330 is layed out nose heavy
and with stalled main wings the residual main wing lift vector has moved
aft. Despite that, the aircraft didn't topple over it's nose down. So there MUST
be a force to compensate this nose down tendency. This can only be the
downward lift force of the HS.
4. The correlation between Stall (-warning) and AoA
=====================================
This item has been raised, including the statement, a stall (-warning)
is only a function of AoA. On first glance, this is true. However,
there are more aspects very important for this AF447 situation.
For a buzzer type C152+ stall warning device, the warning goes
of when the AoA approaches the max actual value for that
particular configuration of the aircraft. The buzzer "measures"
the actual critical value itself.
For the stall warning principle on the AF447, the AoA is measured
to calculate the Stall situation based on several assumed aerodynamic
values of the airplane and it's surroundings. As long as these assumptions
are valid, the stall warning is calculated properly. If these base
properties do change, the stall warning calculation fails. I also do
expect these stall warning calculations taking into account aspects
as temperature, actual air pressure, configuration and maybe also the actual speed,
simply because with decreasing air pressure, the stall AoA decreases.
Further in this article why this assumption is important for the AF447 situation.
Pure from the physics, I also do expect this stall warning calculation
to be non-linear, though this is not relevant for this article.
The implications of the above, is that, in case the aerodynamics is
different as expected, the airplane can be stalled, without the
stall warning being triggered.
5. Icing type, super cooled water vs huge "clouds" of ice-xtals.
=======================================
Given the pitot tubes are by far the hottest parts of the airplanes'
outside surface (ok, ok, the engines are hotter), the pitot tubes
did clog up completely and there is no reference at all about icing build
up at the outside of the airplane, it's pretty likely the pitots did
absorb a lot of ice-xtals and not super cooled water freezing up
in the pitots. If the AF447 would have encountered super cooled
water, there would have been a lot of ice accumulated on the airframe.
So much, the windshield would have been covered and probably the aerodynamic
properties of the airplane would have been effected significantly. I
did not see any evidence for this.
Another reason to assume, AF447 went into a cloud of ice-xtals, is
the simpel fact that the air temperature at FL350 is around -55 C and
the lowest possible temperature of super cooled water is around -40 C.
Another reason to assume this is an ice-xtals case, is the mention of the huge
amount of noise in the cockpit. A serious indication the pointy end
got bombarded by ice-xtals.
So in summary the AF447 went into a huge and pretty dense cloud of ice-xtals.
6. Effect of ice-xtal on wing stall.
====================================
The first approximation of ice-xtal polluted air, would be to consider
this type of air as "thick" air. And thicker air gives more lift, so
an increase of lift.
However, there is, pure from the physics, probably another effect. Having
a rough airfoil surface, the boundary layer gets disturbed and lets go
much easier with reduced lift as a consequence.
In the AF447 situation, there is not reason to assume, the wings did get
rough. However, the air is polluted with a huge amount of tiny but solid
and dense particles. So much, that from a pure physics side of the matter,
the boundary layer gets disturbed. And a disturbed boundary layer loosens
up. Simply resulting in slightly reduced lift. A wild guess would be
some 5% maybe 10% maybe even 20% reduction in lift.
Why did AF447 not drop out of the air because of this ?
For these speeds, another aspect might become relevant: The floating
of the wings over the polluted air. However the float based
lifting force is significantly lower then the Airfoil shape based Lift.
And not only significantly lower lifting force, though also creating
significantly more drag, also because of the higher angle of incident
required to get that lifting force. Let me call this aspect a "float-stall".
Some more thought-work in progress about:
- THS run away as result of main wing stall after minimal disturbance.
- Double control loop with run away inside loop.
Just let me know if you guys are interested in this.
And yes, every now and then, physics shows unexpected
behavior, so strange, it's difficult to belief......
Again, my apologies for the rough edges in this writing, I
simply do not have the time to polish this up.
screwed up. Though following the discussion and matching the
background of physics to these items, I more or less changed
my mind. The general suggestion is: PF should have initiated
a pitch&power approach. It very well could be he did, with this
as a result.
I did write these articles the last 3-4 weeks, though didn't post,
given my lack of time to keep up with the current thread. Some
of the subjects have been touched in recent posts, though I
keep my writing included, to take care for a complete line of view.
I neither did have time to match all of the raised items with
the actual AF447 figures. Maybe somebody wants to do this.
My apologies about this.
In the, up to now 5 threads, some physics came along. Physics, which are
sometimes so far off, that conclusions drawn on that are totally off. As such I
do give some thoughts how to approach those items.
1. Usage of TAS to calculate Kinetic Energie exchange for height.
====================================
- Since Kinetic Energy is non linear in speed, it's not an option
to consider the change in TAS a suitable parameter for change in
Kinetic Energy. For a zero speed based start to calculate the speed
of a dropping item as function of it's height, that's ok.
Since the Kinetic Energy is the SQR of the speed, the Kinetic
Energy of different perpendicular axis are independent.
- For general exchange of speed into another direction or height
(Potential Energy), the actual inertial speed has to be used,
so at least the ground speed and not TAS. I would even say, groundspeed
corrected with the earths' rotational speed (roughly 1800 m/s). Due
to lack of time, I didn't have the time to think this through for
100%, though I do expect this to be relevant.
This can be understood from the following thought-experiments:
= Assume the windspeed suddenly becomes zero. Will the effective
Kinetic Energy of the airplane change ? Nop.
(The airplane will show reactions after the change, though that's because
the force-field does change).
= Assume with the airplain flies with constant speed, the earth rotation
is suddenly stopped (that would give a mess on the ground, though it's
only a thought experiment). Would the effective Kinetic Energy of
the airplane change ? Nop. When an airplane lifts off, the airplane
starts with a speed related to the ground plus a TAS to generate
sufficient lift to lift off.
- So the Kinetic Energy will be 0.5 * M * SQR (| TAS + WINDSPEED + Vrotation |).
Of course everything in 3D vector calculations. M is the airplane mass. The
bars "| |" represent the calculation of the length of a vector.
- To get an impression how much the effect is. The example assumes
for ease of calculation, all vectors have the same direction. In general,
this is not the real situation:
Kinetic Energy presumed to be "released" from an object bleeding of a 250 m/s TAS back to zero:
0.5 * M * 62500 = 31750 M
Kinetic Energy released from an object bleeding of (TAS) 250 + (Windspeed) 50 +
(V-earth-rotation) 1800 m/s to a TAS of zero (with the same wind/earth-rotational speed):
0.5 * M * 4410000 - 0.5 * M * 4202500 = 103750 * M
So when doing the Ekin calculations properly, around 3 times more Energy
becomes available for height gain. Note: Speeds only intended for example
purposes, these aren't the actual AF447 figures.
Usage of TAS to calculate the energy exchange gave a "suitable" fit
for the AF447 case. Why is the difference so big ? I'll get to that a
little further in this article.
Only vertical speed vs. high, the normal Energy constant formula can be used.
2. Effect FL38 turn on TAS and as such on Stall warning reactivation.
=======================================
Nobody mentioned the potential effect of the 180+ degree turn at FL38 on
the return of the stall warning. Such a turn would have a significant
effect on the experienced windspeed and as such on the TAS.
Once at FL38, the airplanes' Inertial Kinetic Energy would be
reasonable constant during the time it takes for the turn. The TAS
however changes a lot. Depending on the wind direction, up to
twice the windspeed.
Maybe somebody might want to match this aspect with the actual AF447 data.
3. The presumed HS stalled status on the way down.
=====================================
Once the airplane got a reasonable downward vertical speed component,
I don't think the AF447 HS is stalled at all (on the contrary, has super-lift),
Why: Typical aspect with a stall is: release of the boundary layer over
the airfoil AND a sudden increase of the speed vector component opposite
of the intended lift force. On the main wings, both components do influence
each other increase both values after initial upset, significantly.
A situation, with an AoA getting higher than the main wing can handle, starts
very fast.
Now to the HS: The intended "lift" for the A330 HS is downward. The speed vector
of the AF447 HS on it's path down to earth, is also downward. The pressure gradient
is actually pushing the air towards the airfoil. So no reason
at all for boundary separation. More the contrary: Because the downward speed vector
"pushes" the airflow on the airfoil, the tendency to boundary separation will be less.
Another aspect relevant in this, is: The HS airfoil does have to curved surfaces,
bottom side a lot, the upper side just little bit. So both sides of the HS generate
lift, where the downward lift force is significantly higher.
Now back to the AF447 HS on it's downward trajectory. The downward speed
is so high that the upper side of the HS airfoil will have (nearly) complete boundary
layer separation, so the upper airfoil surface is completely stalled. The net effect
is an even greater downward lift vector on the HS.
Or so to say: Because of the huge HS downward lift force, the normally nose heavy
airplane doesn't topple over to a nose down situation.
Because of the high downward HS lift, this airfoil is (together with the VS) perfectly
able to stabilize the aircraft on it's way down and prevent a spin or even a roll.
The above can also be argued from the opposite side. The BEA has reported
the airplane went down in a stable state. This can only be reached when a
configuration with airfoils with sufficient "lift" are present. Since the main wings
are definitely stalled, the stable factor must come from the HS/VS span.
Another reasoning from the other side: The A330 is layed out nose heavy
and with stalled main wings the residual main wing lift vector has moved
aft. Despite that, the aircraft didn't topple over it's nose down. So there MUST
be a force to compensate this nose down tendency. This can only be the
downward lift force of the HS.
4. The correlation between Stall (-warning) and AoA
=====================================
This item has been raised, including the statement, a stall (-warning)
is only a function of AoA. On first glance, this is true. However,
there are more aspects very important for this AF447 situation.
For a buzzer type C152+ stall warning device, the warning goes
of when the AoA approaches the max actual value for that
particular configuration of the aircraft. The buzzer "measures"
the actual critical value itself.
For the stall warning principle on the AF447, the AoA is measured
to calculate the Stall situation based on several assumed aerodynamic
values of the airplane and it's surroundings. As long as these assumptions
are valid, the stall warning is calculated properly. If these base
properties do change, the stall warning calculation fails. I also do
expect these stall warning calculations taking into account aspects
as temperature, actual air pressure, configuration and maybe also the actual speed,
simply because with decreasing air pressure, the stall AoA decreases.
Further in this article why this assumption is important for the AF447 situation.
Pure from the physics, I also do expect this stall warning calculation
to be non-linear, though this is not relevant for this article.
The implications of the above, is that, in case the aerodynamics is
different as expected, the airplane can be stalled, without the
stall warning being triggered.
5. Icing type, super cooled water vs huge "clouds" of ice-xtals.
=======================================
Given the pitot tubes are by far the hottest parts of the airplanes'
outside surface (ok, ok, the engines are hotter), the pitot tubes
did clog up completely and there is no reference at all about icing build
up at the outside of the airplane, it's pretty likely the pitots did
absorb a lot of ice-xtals and not super cooled water freezing up
in the pitots. If the AF447 would have encountered super cooled
water, there would have been a lot of ice accumulated on the airframe.
So much, the windshield would have been covered and probably the aerodynamic
properties of the airplane would have been effected significantly. I
did not see any evidence for this.
Another reason to assume, AF447 went into a cloud of ice-xtals, is
the simpel fact that the air temperature at FL350 is around -55 C and
the lowest possible temperature of super cooled water is around -40 C.
Another reason to assume this is an ice-xtals case, is the mention of the huge
amount of noise in the cockpit. A serious indication the pointy end
got bombarded by ice-xtals.
So in summary the AF447 went into a huge and pretty dense cloud of ice-xtals.
6. Effect of ice-xtal on wing stall.
====================================
The first approximation of ice-xtal polluted air, would be to consider
this type of air as "thick" air. And thicker air gives more lift, so
an increase of lift.
However, there is, pure from the physics, probably another effect. Having
a rough airfoil surface, the boundary layer gets disturbed and lets go
much easier with reduced lift as a consequence.
In the AF447 situation, there is not reason to assume, the wings did get
rough. However, the air is polluted with a huge amount of tiny but solid
and dense particles. So much, that from a pure physics side of the matter,
the boundary layer gets disturbed. And a disturbed boundary layer loosens
up. Simply resulting in slightly reduced lift. A wild guess would be
some 5% maybe 10% maybe even 20% reduction in lift.
Why did AF447 not drop out of the air because of this ?
For these speeds, another aspect might become relevant: The floating
of the wings over the polluted air. However the float based
lifting force is significantly lower then the Airfoil shape based Lift.
And not only significantly lower lifting force, though also creating
significantly more drag, also because of the higher angle of incident
required to get that lifting force. Let me call this aspect a "float-stall".
Some more thought-work in progress about:
- THS run away as result of main wing stall after minimal disturbance.
- Double control loop with run away inside loop.
Just let me know if you guys are interested in this.
And yes, every now and then, physics shows unexpected
behavior, so strange, it's difficult to belief......
Again, my apologies for the rough edges in this writing, I
simply do not have the time to polish this up.
Join Date: Jun 2009
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wallybird7 said, "Apparently this crew didn't."
That is an assertion not in evidence. How do you know the storm showed on their radar? Was their radar working? Was it employed properly?
By the time the problem appeared on their radar any escape from the storm would have required extreme deviations from their flight plan with no communications to DAKAR.
They did note it at that time and made a deviation towards an area that appeared less risky than plowing on straight ahead.
Now, one might argue that they should have called Atlantico about this. But apparently this happens so often the pilots simply noted the fact and plowed onwards. I wonder what would have happened had they tried to check in at the follow-on control site after DAKAR since their flight plan was not properly forwarded.
But the pesky detail stands - moving aside from the storm at the time they saw it would have required some serious course deviations. At the time they hit it the storm was a very wide solid band.
That is an assertion not in evidence. How do you know the storm showed on their radar? Was their radar working? Was it employed properly?
By the time the problem appeared on their radar any escape from the storm would have required extreme deviations from their flight plan with no communications to DAKAR.
They did note it at that time and made a deviation towards an area that appeared less risky than plowing on straight ahead.
Now, one might argue that they should have called Atlantico about this. But apparently this happens so often the pilots simply noted the fact and plowed onwards. I wonder what would have happened had they tried to check in at the follow-on control site after DAKAR since their flight plan was not properly forwarded.
But the pesky detail stands - moving aside from the storm at the time they saw it would have required some serious course deviations. At the time they hit it the storm was a very wide solid band.
Join Date: Aug 2009
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Hi,
Again we return to the basic questions and answers ..
Radar working .. plane defect ?
Employed properly .. crew error ?
Again .. nothing between ...
Was their radar working? Was it employed properly?
Radar working .. plane defect ?
Employed properly .. crew error ?
Again .. nothing between ...