AF 447 Search to resume

[mm43]

Equatorial North Atlantic and South Atlantic WX

PJ2;

There is currently a 2 - 2.5m significant swell running in the search area, but the forecast is for that to decrease to around 1m in the next 72 hours. Full meteo details are available as follows:-

(a) Significant wave prognosis H0 - H+78 in 6H increments
Navy Hydrographic Center

(b) Mean wave period prognosis H0 - H+78 in 6H increments
Navy Hydrographic Center

(c) Wind at 10m prognosis H0 - H+78 in 6H increments
Navy Hydrographic Center

(d) Mean Sea Level Pressure prognosis H0 - H+78 in 6H increments
Navy Hydrographic Center

All the above, and other features can be accessed through:-

DIRETORIA DE HIDROGRAFIA E NAVEGAÇÃO

- click on "English" and then navigate through the menus.

EDIT:: Click on "Continuous" then ">>" to get the animation to run.
------------------------------

At the time of this message, the "Anne Candies" is still berthed at Recife.

mm43

[Kalium Chloride]

Seabed Worker departed from Recife at 05:00 local, bound for the search zone. The Anne Candies is expected to depart tonight or tomorrow morning, latest.

[PJ2]

mm43;

Thank you very kindly - will keep an interested watch.

PJ2

[mm43]

Update: "Seabed Worker" & "Anne Candies"

Seabed Worker Dep Recife: 2010-03-29 0820z, Last Country: Cape Verde, Dest: Sea
Anne Candies Dep Recife: 2010-03-29 1920z, Last Country: Trinidad, Dest: Sea

I don't expect we will get any further information on the progress of the search unless there is a press release by the BEA.

Edit :: It would appear that the BEA intend to give updates on the search progress, e.g. their information release of yesterday - Information, 29/03/2010 - which is welcome.

mm43

[HarryMann]

I don’t think either that such a wing would stall at 6.5 degrees of AoA, but I would rather think that a level flight at such AoA/attitude is unsustainable due to the lack of available thrust versus the tremendous increase in drag in a low air density environment.

Any change in stall AoA from ground level would be almost entirely due to Mach effects, not the altitude density. The low drag cruise bucket would be at quite a high Cl
Perhaps you should be thinking and talking in terms of Cl rather than AoA, because that's what really matters

[p51guy]

AOA is gospel at low altitudes. Someone said CI is mach sensitive. I sense the BS sensor going off. Can that be interpreted as coefficient of lift? I don't know.
AOA will take care of you on approach, LRC, and keep you from getting slow anywhere else. AOA is the only important information you need. If it is accurate the rest isn't important. Air France might have made good use of it that night.

[BOAC]

Originally Posted by P51

I sense the BS sensor going off.

- actually that is the optician's sensor going off - it was written as Cl which of course is Mach sensitive.

[p51guy]

It must be a UK thing. Googling it doesn't work.

[p51guy]

My next guess is "see eye", probably wrong too.

[BOAC]

Try CL.....

[HazelNuts39]

195 000 000 responses ...

[ChristiaanJ]

Typing "Lift coefficient Cl" (capital C lowercase L) cuts that down to less than 59000 responses.
Then take your pick from the first few.

CJ

[jcjeant]

Hi,

Just readed this:

Air France 447: The Probable Cause
About the author:
About Ellis Traub

What do you think ?

[lomapaseo]

Hi,

Just readed this:

Air France 447: The Probable Cause
About the author:
About Ellis Traub

What do you think ?

Worthless.

Now what do you think ?

[BOAC]

To spare P51 mucho Googling

CL = CL(M=0) / (1 - M2)1/2 where M=Mach number

[Chris Scott]

Capt Traub's paper on jet inertia and horizontal vortices

jcjeant,
Don't take lomapaseo's riposte too hard. On the other hand, wasn't it you who were complaining (23rd March) about thread drift, after a discussion on possible use of AoA in recovery?

Have read through (Capt) Ellis Traub's 1966 piece once and, in case it helps anyone, am prepared to give one retired line-pilot's opinion on it. But it doesn't cast any new light on the AF447 inquiry.

Traub explained the inertia characteristics of the large jet transport well, bearing in mind that Eastern had only been flying them about six years; other US carriers not more than eight. Eastern, Wikipedia says, had lost a DC-8 in 1964, due to "degradation of aircraft stability characteristics in turbulence because of abnormal longitudinal trim component positions." This was reckoned to have happened while climbing through about 16000 ft.

For me, his argument weakens from the bottom of page 7. He poses a scenario where a horizontal vortex forms at 28000 ft, about 20 miles in diameter, with a circumferential velocity of about 300 kts. The transiting aircraft flies through one side, experiencing a rapid increase in headwind-component (to 300 kts). IAS is 280 on entry, and the pilot initially tries to maintain IAS or Mach by raising the nose. This is unsuccessful.

Traub argues that the uncontrollable rise in speed leads to the centre of pressure (lift) moving forward, leading to the pilot trimming forwards to counteract. My recollection is that, certainly on the early jets, an over-speed in Mach leads to the centre of pressure moving aft (causing Mach "tuck").

He also argues that the shock wave at the nose leads to unreliable airspeed/Mach indications, because the pitot tubes are mounted aft of the nose (unlike supersonic experimental aircraft).

During the vortex transit (about 2 minutes), he suggests that ground speed could have reduced to zero. Considering the TAS and G/S on entry were about 450 kts (my guess), and because of the aircraft inertia he is describing, I think that is a considerable exaggeration. But, on the other hand, we don't need to have ground speed as low as that to be in trouble...

Reduction in thrust (of engines mounted below the wing) increases the trim problem, in his scenario.

The aircraft emerges from the vortex with (a) massive loss of airspeed; (b) severe nose-down trim. He argues that the ensuing dive would be difficult to recover without eventually over-speeding and/or applying too much normal acceleration (pulling too hard). Fair enough. (The latter was Bernard Ziegler's main argument for removing the pilot option of "pulling" more than 2·5g on fly-by-wire Airbuses, but this does not apply if the FBW system has been sufficiently degraded.)

The paper may be badly flawed, but Traub's basic jet-inertia argument is universally recognised in relation to downbursts/microbursts close to the ground, and often practised in the simulator.

Whether the high-altitude, horizontal vortex he described is now a known phenomenon I don't know. but doubt it would be found in the vicinity of ITF (ITCZ) convective storm cells. If it did, the BEA and others would know.

[jcjeant]

Hi,

Don't take lomapaseo's riposte too hard. On the other hand, wasn't it you who were complaining (23rd March) about thread drift, after a discussion on possible use of AoA in recovery?

No problems with it .. my turtle shell protects me

In fact I gave up the fight after seeing the following messages after my rant about the off topic

Thank you for your analysis this seems to be OK

[HazelNuts39]

Coriolis

Originally Posted by Chris Scott;#637

Whether the high-altitude, horizontal vortex he described is now a known phenomenon I don't know. but doubt it would be found in the vicinity of ITF (ITCZ) convective storm cells.

For whoever is sufficiently interested in this topic: Go to Wikipedia, search for ‘Coriolis’, then go to ‘Coriolis effect in meteorology’

Cyclones rarely form along the equator due to the weak Coriolis effect present in this region.

regards,
HN39

[mm43]

Coriolis

Having had a closer look at the 0215z Satellite IR image (nominal time of scan 0208z), and using some image editing software, I have come to the conclusion that the mesoscale event that AF447 appears to have entered was of the reverse coriolis type. Due to the closeness to the equator, the coriolis effect was possibly modified by the surface winds as the rotation in the updraft commenced. That statement is not necessarily true as observations have often shown a change of rotation direction as altitude increases - particularly in low latitudes.

The image in question shows a marked tendril circling in a clockwise direction from the southern edge. That being the case, the head wind that Ellis Traub based his thesis on, was in the AF447 case, a tail wind. It is worth mentioning that the 0215z Satellite IR image probably recorded events 10,000ft or more above FL350, and the apparent tendril could have been feeding the core of the mesoscale system, while the updraft flowed outwards as anvil cloud at our altitude of interest.

Having made the above points, I wouldn't be putting bets on exactly was happening, except to to say that at about 50,000ft the IR image indicates a clockwise rotation.

mm43

[HazelNuts39]

Mach, CL and AoA

BOAC;
Thank you for reminding me of the Prandtl-Glauert transformation:

Originally Posted by BOAC; #636

CL = CL(M=0) / (1 - M2)1/2 where M=Mach number

I must shamefully admit to having neglected this sofar. All AoA’s I gave are based on the cL-AoA relation established from a M=0.815 maneuver, without correcting for Mach change. Although there is some doubt as to applying P.-G. in the transsonic flow likely to exist at M=0.815 (see Wikipedia quotation below), if I apply that correction, the numbers I gave earlier change as follows:

Originally Posted by HazelNuts39; #611

If we assume that the CBT’s VLS is defined by the stall, but alphaProt and alphaMax are somehow ‘adjusted’ for buffet boundary, we could estimate alphaMax(stall) as either:
VLS/1.18 = 181kt; alpha = 7.7 degrees, or –
VLS/1.23 = 174kt; alpha = 8.5 degrees.

The revised numbers are:
VLS/1.18 = 181kt; M = 0.55; alpha = 11.5 degrees, or –
VLS/1.23 = 174kt; M = 0.53; alpha = 12.7 degrees.

Originally Posted by PJ2; #510

For 212k kg, FL350 the pitch attitude at AlphaProt is almost 9deg;

The PFD shows 204 kt CAS; pitch attitude 8.3 degrees, while the QF72 data after applying the P.-G. transformation result in 8.4 degrees

From Wikipedia; Prandtl-Glauert transformation:

This correction factor works well for all Mach numbers 0.3 < M < 0.7
It should be noted that since this correction factor is derived from linearized equations, the pressures calculated is always less in magnitude than the actual pressures within the fluid.

regards,
HN39