Chamonix
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A330 Thin Speed Margins?

Sat Mar 26, 2011 7:23 pm

Quoting http://www.economist.com/blogs/babbage/2011/03/aviation_accidents

At 10,600 metres, a fully loaded Airbus 330 cruises (for reasons of fuel economy) just below this critical point in its flight envelope—with probably no more than 25 knots (46 kph) between stalling (through flying too slow) and breaking up in a shockwave-induced dive (through flying too fast).
 
Mir
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RE: A330 Thin Speed Margins?

Sat Mar 26, 2011 8:15 pm

No thinner than any other large airliner, really.

At some point, this morbid fascination with the A330 is going to have to stop. We still don't know exactly what happened to AF447, and apart from the defective air data sensor issue (which has been well-addressed), I haven't seen anything that would lead me to believe that the situation would have been different had it been a 777, 340 or 747. If you lose all your airspeed indications in cruise, and you're flying through a severe thunderstorm, you're going to have problems.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Pihero
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RE: A330 Thin Speed Margins?

Sat Mar 26, 2011 9:05 pm

Quoting Mir (Reply 1):

At some point, this morbid fascination with the A330 is going to have to stop.

I agree, especially when the article is so full of errors, mistakes and misrepresentations : there's never been proof of a "mesoscale convective system" and certainly not anything even remotely indicative of a possibility of a masking phenomenon : The situation was, basically, normal for a lightly active ITCZ.
The last sentence of the article is proof that the writer hasn't got a clue on physics or flight mechanics : "By all accounts, it had literally fallen out of the sky as if its wings had melted...
...by an alien death ray, I'd guess.
Contrail designer
 
mandala499
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RE: A330 Thin Speed Margins?

Sat Mar 26, 2011 10:17 pm

OK, let me keep this short, simple, and blunt.

Quoting Chamonix (Thread starter):
At 10,600 metres, a fully loaded Airbus 330 cruises (for reasons of fuel economy) just below this critical point in its flight envelope—with probably no more than 25 knots (46 kph) between stalling (through flying too slow) and breaking up in a shockwave-induced dive (through flying too fast).

My remark: BALONEY!!!!!!!
But wait... what's your point anyway? You're just putting something from the article... what is it do you want to discuss?

Let's get some facts straight...
1. The maximum operating speed, if exceeded, does not mean the aircraft breaking up in a shockwave-induced dive! It just means your plane starts to vibrate due to shockwaves forming. The breakup, will happen at a much higher speed. The high speed protection sets in at a speed higher than the Maximum Operating Speed (when in normal law).
2. Let us get some more FACTS into this: Assuming Cruising at M0.82 @ FL350, @ 200Tons @ 40%CG.. If you maintain 0.82M, you don't stall unless you're pulling a turn causing a 1.75G load on the aircraft. For straight and level:
High speed Mach Buffet onset at 0.86M
Slow speed stall buffet starts at 0.58M

If you want to speak numbers...
The operating range at the given scenario above, is 290kts - 460kts for true airspeed.
But since pilots fly using indicated airspeed, the range is 170kts - 290kts indicated. Hey, that's a 120kts indicated airspeed range!

THIN????? You gotta be kidding me!

Wait... why do I bother.. here are some pics:

View Large View Medium
Click here for bigger photo!

Photo © John Richard Thomson


See, it's more than 25kts margin between the 2 ends. And that's at FL370... which should mean a smaller coffin corner.

WAIT! LET'S GO HIGHER! To FL410!

View Large View Medium
Click here for bigger photo!

Photo © John Richard Thomson



See the margin is MORE than 25kts!

I have great respect for the economist, but, for aviation physics and technical operations, I don't.

Quoting Pihero (Reply 2):
The last sentence of the article is proof that the writer hasn't got a clue on physics or flight mechanics

INDEED !
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
PGNCS
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RE: A330 Thin Speed Margins?

Sat Mar 26, 2011 11:34 pm

Quoting Mir (Reply 1):
No thinner than any other large airliner, really.

Thank you, Mir.

Quoting Pihero (Reply 2):
Quoting Mir (Reply 1):

At some point, this morbid fascination with the A330 is going to have to stop.

I agree, especially when the article is so full of errors, mistakes and misrepresentations : there's never been proof of a "mesoscale convective system" and certainly not anything even remotely indicative of a possibility of a masking phenomenon : The situation was, basically, normal for a lightly active ITCZ.
The last sentence of the article is proof that the writer hasn't got a clue on physics or flight mechanics : "By all accounts, it had literally fallen out of the sky as if its wings had melted...
...by an alien death ray, I'd guess.

Thank you, too, Pihero. The essence of the article: we have nothing new to say about AF447. Beyond that there's nothing but sensationalism and supposition.

As if the wings had melted...give me a break. 
Quoting mandala499 (Reply 3):
But wait... what's your point anyway? You're just putting something from the article... what is it do you want to discuss?

Yes, I too would like to know the point behind this thread. What is it that is up for discussion that mandala499 and Pihero haven't addressed? I'm all in favor of learning new things, but this seems to be nothing but a link to a sensationalist article regurgitating known facts with unproven theories with a random quotation extracted from it.
 
Fly2HMO
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 2:56 am

This applies to EVERY plane out there at altitude. Super high flying aircraft like the SR-71 and U-2 had even less of a margin to play with.

http://en.wikipedia.org/wiki/Coffin_corner_%28aviation%29
 
tdscanuck
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 4:12 am

Quoting Chamonix (Thread starter):
with probably no more than 25 knots (46 kph) between stalling (through flying too slow) and breaking up in a shockwave-induced dive (through flying too fast).

25 knots is pretty good at the upper end of the flight envelope...I've certainly seen it tighter. And if you go outside it's hardly a catastrophe (since there's margin built in), you just reduce altitude.

Quoting mandala499 (Reply 3):
1. The maximum operating speed, if exceeded, does not mean the aircraft breaking up in a shockwave-induced dive! It just means your plane starts to vibrate due to shockwaves forming. The breakup, will happen at a much higher speed.

There are several airliners that don't even start vibrating at Mmo...from a piloting point of view, it's just a number to be avoided.

Tom.
 
Mir
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 4:30 am

Quoting Pihero (Reply 2):
The last sentence of the article is proof that the writer hasn't got a clue on physics or flight mechanics : "By all accounts, it had literally fallen out of the sky as if its wings had melted...

Which accounts are they talking about? We know that there were problems with air data sensors in other 330s, and we know that there were instrumentation problems. Other than that, we know jack diddly about what was going on on that airplane. So if the author knows of some accounts of what made the plane fall out of the sky (or if it even did fall out of the sky), he should probably contact the investigation teams - I'm sure they'd be very interested in hearing them.

Quoting mandala499 (Reply 3):
See the margin is MORE than 25kts!

Looks like a good 45 knot margin to me.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
wilco737
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 8:32 am

Ah well, another article saying the 330 is unsafe... If I go to FL 330 with a MTOW 744 then you don't have a lot of margin as well. That's what aerodynamics are about. The closer you get to max altitude, the less speed margin you have. If you go above max altitude: bad idea....

wilco737
  
 
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Faro
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 10:05 am

out of curiousity, are there any recorded incidents/accidents attributed to airspeed excursions in the cruise? Apart from CAL 006, in which the excursion was a consequence and not a primary cause, I can think of none. Presumably powerful gusts above say FL 320 are a very rare occurrence unless you are in a CB.

Faro
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wilco737
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 10:32 am

Quoting faro (Reply 9):
Presumably powerful gusts above say FL 320 are a very rare occurrence unless you are in a CB.

Maybe not powerful gusts, but quick changes of wind which let the speed drop or rise pretty quickly or sudden change in air pressure, mountain waves etc etc.... It can happen, even at high altitudes.

wilco737
  
 
aviopic
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 11:02 am

Quoting mandala499 (Reply 3):
But since pilots fly using indicated airspeed, the range is 170kts - 290kts indicated. Hey, that's a 120kts indicated airspeed range!
THIN????? You gotta be kidding me!
Quoting tdscanuck (Reply 6):
25 knots is pretty good at the upper end of the flight envelope...I've certainly seen it tighter.

I am no pilot but I've seen it as thin as 15 kts on a 74 flight and always thought it was something expected as a function of physics(I still do).
But how come the opinion of 2 pilots ? is so different ?
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ferpe
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RE: A330 Thin Speed Margins?

Sun Mar 27, 2011 11:09 am

I've been flying into the transonic range and passt M1 in military figthers, depending on aircraft it is outright un-eventfull to a bit of a bumpy ride. If you are pulling g it can be more exciting   as when you pass often there is a pitch-up followed by the typical nose-heavyness of supersonic 50% aerodynamic centre flying. Once over M1 it is very plain sailing, almost boring.

My question is why would a civil airliner have a dramatic consequence of overspeeding? There is at least ,12 of Mach to pass before you have truly supersonic aerodynamics and given the airliners wing slender ratio (being massive compared to a fighter) I just don't think you would be able to get full supersonic flow on the wings, you hit MASSIVE drag and buffeting before that. Those hughe wide wings would just generate a barn-door of transonic drag > M0,9. Furhter, the pitching moment could go a bit roller-coaster but I doubt you can get into the trouble the economist is describing, you would have to loose the tail for that.

The buffeting and wing-drops/pitch undulations are very clear signals you are overspeeding to any pilot and you would just raise the nose slightly and ease back on the throttle. Of course the 330 could have some nasty habit and throw you of a bit but I doubt it, I expect a lot of drag (basically a drag wall) and nervousness. Anyone who knows more?

About the worst thing that can happen to a modern aircraft would be structural failure due to shock-wave overstressing of the airframe, any dive generating by nose-heavyness (Mach tuck) should be easy to counter. There is no tale of something falling of the A/C like and engine or so but who knows. IMHO I doubt they fell out of the sky due solely to overspeed.

On the stall side I expect the aircraft to be normal as well, perhaps you could get into a spin if you have sideslip when you enter stall, especially if you wrestle with a thunderstorm and pull a bit of G + sideslip. But then if the guys were military trained getting out of a spin should be straight forward and you have plenty of time to analyse and engage anti-spin rudder/stick.

If the pilots had only civil cert training this can be a new and unpleasant/difficult experience to analyse and do the right thing to get out of (never had any deep stall or spin training when I took my civil certs).

A late spin after some entry into overspeed followed by overcorrection and stall could make them "fall out of the sky", especially if they had no military fighter experience. Should this be the case (spin) this is about one of the oldest problems in the history of flight.

All the above assumes the FBW is in direct law as you have no airspeed info.

[Edited 2011-03-27 04:19:14]

[Edited 2011-03-27 05:19:15]
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tdscanuck
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RE: A330 Thin Speed Margins?

Mon Mar 28, 2011 5:07 pm

Quoting ferpe (Reply 12):
My question is why would a civil airliner have a dramatic consequence of overspeeding?

Some civil airliners don't have enough pitch authority to overcome Mach tuck...if you get them into a fast dive, they can't pull out of it.

Tom.
 
ferpe
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RE: A330 Thin Speed Margins?

Mon Mar 28, 2011 6:24 pm

Quoting tdscanuck (Reply 13):
Some civil airliners don't have enough pitch authority to overcome Mach tuck...if you get them into a fast dive, they can't pull out of it.

Oops, sounds weird and dangerous. Would assume it is then rather servo stall (hydraulics are not strong enough to cant stabilizer) then not enough surface.

To what Mach do they get and what would be the effect of cut back on the throttles? The big fans must generate a lot of drag then?
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travelavnut
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RE: A330 Thin Speed Margins?

Mon Mar 28, 2011 8:20 pm

Quoting tdscanuck (Reply 13):

Could that situation be over come by using the landig gear or spoilers to lose speed? Granted they stay on the airplane of course  
Live From Amsterdam!
 
Mir
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RE: A330 Thin Speed Margins?

Mon Mar 28, 2011 10:53 pm

Quoting travelavnut (Reply 15):
Could that situation be over come by using the landig gear or spoilers to lose speed? Granted they stay on the airplane of course

Probably not the gear, but I had the same question about the speedbrakes.

-Mir
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brons2
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RE: A330 Thin Speed Margins?

Mon Mar 28, 2011 11:23 pm

Quoting tdscanuck (Reply 13):
Some civil airliners don't have enough pitch authority to overcome Mach tuck...if you get them into a fast dive, they can't pull out of it.

There was an incident that I posted a while back on Tech/Ops about a UK based crew getting a 737 in a mach tuck dive on a positioning flight. While they were able to recover, they lost 10,000 feet in the process and accelerated the aircraft to 440kts. It's in the NTSB database somewhere.
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Speedbird741
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RE: A330 Thin Speed Margins?

Tue Mar 29, 2011 12:11 am

Quoting Mir (Reply 1):
this morbid fascination with the A330 is going to have to stop

Why should there not be such a fascination? The fact is there were two A330-200 (GE) accidents in a relatively narrow time frame, of which the final (conclusive) reports are yet to be released. Although they seem to have nothing to do with each other, it is natural that people become irrationally fascinated with that particular aircraft. I would never hesitate about flying an A332. However, I am honest in saying that AF447 crosses my mind each and every time I or a family member flies in one.

Quoting travelavnut (Reply 15):
spoilers to lose speed?

Could spoilers even maintain their integrity at such levels of speed an vibration?

Speedbird741
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Mir
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RE: A330 Thin Speed Margins?

Tue Mar 29, 2011 2:05 am

Quoting Speedbird741 (Reply 18):
Why should there not be such a fascination?

Because it leads to blatant mistruths like those in the article cited by the OP. And then you get people who treat those things as though they're gospel, and draw all sorts of crazy conclusions from them.

Quoting Speedbird741 (Reply 18):
it is natural that people become irrationally fascinated with that particular aircraft.

I agree that it's natural. But that doesn't mean it's good, and I'd hope that enough time would have passed since AF447 that cooler heads would have prevailed.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
tdscanuck
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RE: A330 Thin Speed Margins?

Tue Mar 29, 2011 4:29 am

Quoting Ferpe (Reply 14):
Oops, sounds weird and dangerous.

Not really...there's a reason it's called the operating envelope. You're not supposed to operate outside it. If you go outside it, you're now a test pilot. If you go past where the test pilots took it (which is well beyond the certified envelope) you're out where "there be dragons" and there is zero guarantee/requirement/expectation that the aircraft operate properly. *All* aircraft have portions of the flight envelope where you're going to die...it's just a matter of how hard you have to work to get to those parts of the envelope.

Quoting Ferpe (Reply 14):
Would assume it is then rather servo stall (hydraulics are not strong enough to cant stabilizer) then not enough surface.

Yes, it's a control surface blowdown problem...the aerodynamic forces are so high that the hydraulics can't generate enough deflection to get enough nose up pitch authority.

Quoting Ferpe (Reply 14):
To what Mach do they get and what would be the effect of cut back on the throttles? The big fans must generate a lot of drag then?

I'm not sure what the exact number is...well in excess of M0.9, I'm sure. Cutting back on the throttles would cause an initial nose-down pitch, which might actually hurt you. Even at idle, the engines do generate some positive thrust (they won't actually slow you down, just reduce acceleration).

Quoting travelavnut (Reply 15):
Could that situation be over come by using the landig gear or spoilers to lose speed? Granted they stay on the airplane of course  

Landing gear, assuming they stay on, would cause a nose down pitch, exacerbating the problem. Speedbrakes should help, but I'm not sure how much deflection you'd get at those speeds.

Quoting Speedbird741 (Reply 18):
Could spoilers even maintain their integrity at such levels of speed an vibration?

Maybe, maybe not...there's no requirement for them to operate at that speed, so I doubt the analysis even exists.

Tom.
 
prebennorholm
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 12:39 am

Quoting tdscanuck (Reply 20):
If you go past where the test pilots took it (which is well beyond the certified envelope) you're out where "there be dragons" and there is zero guarantee/requirement/expectation that the aircraft operate properly.

Every airliner is certified with an MMO - max Mach operational.

For certification the airliner must demonstrate a test where it recovers in a safe manner from an overspeed to MMO + M0.07.

There was a video some years ago about the A380 test when it was taken out to M0.96 in a shallow dive (A380 MMO = 0.89). The chief test pilot told that it was a rather demanding test since they of course had to demonstrate M0.96, but they didn't want to get anywhere near M0.97.

If memory serves me well, then during the first such test flight some composite streamlining panels behind the MLG failed and had to be reinforces in production. Or maybe I'm dreaming things up - it's too long time ago.
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MD-90
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 2:41 am

I know they were horsing around and not being responsible, which is what led to the engine problems, but how narrow did the operating envelope get when the Pinnacle crew took their CRJ up to 410 and stalled?
 
tdscanuck
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 5:01 am

Quoting MD-90 (Reply 22):
I know they were horsing around and not being responsible, which is what led to the engine problems, but how narrow did the operating envelope get when the Pinnacle crew took their CRJ up to 410 and stalled?

It went to zero...that's why they stalled. That's not what did them in though...they core locked the engines, killing all chance of a restart, then didn't notify ATC of what they'd done and how much trouble they were in until it was too late to do anything about it.

Quoting prebennorholm (Reply 21):
Every airliner is certified with an MMO - max Mach operational.
For certification the airliner must demonstrate a test where it recovers in a safe manner from an overspeed to MMO + M0.07.

Exactly. The test pilots have to take it out just beyond Md, which it outside Mmo+0.07. If you take it beyond Md, don't blame the OEM when the plane doesn't work.

Tom.
 
travelavnut
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 9:10 am

Quoting prebennorholm (Reply 21):
If memory serves me well, then during the first such test flight some composite streamlining panels behind the MLG failed and had to be reinforces in production. Or maybe I'm dreaming things up - it's too long time ago.

That's correct, I saw the Discovery Channel documentary yesterday. Things were certainly shaking at that speed!

Quoting tdscanuck (Reply 23):
...they core locked the engines, killing all chance of a restart

Excuse my ignorance, but what exactly does core locking the engine entail?
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chuchoteur
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 9:28 am

Quoting prebennorholm (Reply 21):
There was a video some years ago about the A380 test when it was taken out to M0.96 in a shallow dive (A380 MMO = 0.89). The chief test pilot told that it was a rather demanding test since they of course had to demonstrate M0.96, but they didn't want to get anywhere near M0.97.

Actually had a social chat with said chief pilot a while back when he was presenting at a conference.
They didn't want to exceed M0.97 so they were pretty meticulous about the way they ran the test. Apparently they went up to M0.96, then jumped up to M1 and beyond.

Cut the test short, came back down, analysis showed that a very localised supersonic shockwave occured right in the pitot area, the probes had to be recalibrated. interesting to know that bits of the A380 have actually gone supersonic :P
 
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Starlionblue
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 11:03 am

Quoting travelavnut (Reply 24):
Quoting tdscanuck (Reply 23):
...they core locked the engines, killing all chance of a restart

Excuse my ignorance, but what exactly does core locking the engine entail?

I had to look it up. As I read the explanations online, if airflow is stopped/disrupted in the core in certain ways, cooling stops and core components can expand to such dimensions that they no longer "fit", meaning the engine seizes up and can't be "unstuck".
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
mandala499
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 11:12 am

Quoting tdscanuck (Reply 20):
Even at idle, the engines do generate some positive thrust (they won't actually slow you down, just reduce acceleration).

They generate some thrust at idle, but that doesn't mean they couldn't cause drag in a high speed dive. In the good old days of the EPR (unlike today's artificial EPR)... an EPR of less than one means there's higher pressure at the intakes than at the exhaust, meaning the engines were holding the plane back despite the idle thrust... ie. it's pushing less air than it is receiving... in theory anyways. Same goes with a prop.

Dive a 732 steep enough in idle power and EPR goes to 0.9* instead of 1.**.

Quoting tdscanuck (Reply 20):
Speedbrakes should help, but I'm not sure how much deflection you'd get at those speeds.

Any deflection to cause drag in such a dive wouldn't hurt. Old-timers were taught that the use of speedbrakes in uncontrolled speed dive, should pull the nose up... whether one can pull up and slow down before terra firma is a different story altogether though.   
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Chamonix
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 12:26 pm

 
ferpe
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 4:32 pm

Quoting chuchoteur (Reply 25):
interesting to know that bits of the A380 have actually gone supersonic :P

I don't want to be picky and I don't know if I am right but I think the A380 wing is done in such a way that one have an area on the inner section that goes supersonic even in normal flight, it then slows down to subsonic speed before the flap area in a mild series of shock-waves.

What you mean is that major portions of the airframe has gone supersonic, well if they do there should be some pretty wild buffeting on this whale looking beauty. (thickness to lenght ratio must be a awfull  )

[Edited 2011-03-30 09:42:33]
Non French in France
 
Pihero
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 4:54 pm

Quoting Chamonix (Reply 28):
I think it made Mach1

No, it did not according to the NTSB report : "Although the captain said that the airplane exceeded Vmo twice and also decelerated below 100 KIAS during the dive, all three crew members said that they did not hear the overspeed warning and that the stall warning stickshaker did not activate. Examination of the reliable recorded airspeed data points showed that the Vmo limitation was not exceeded during the descent."
The limitation at altitude is Mmo = .92 M.
A 747, and for that's worth, any transport jet isn't built for speed 
The report here

[Edited 2011-03-30 10:03:47]

[Edited 2011-03-30 10:04:22]
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chuchoteur
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RE: A330 Thin Speed Margins?

Wed Mar 30, 2011 5:34 pm

Quoting Ferpe (Reply 29):
I don't know if I am right but I think the A380 wing is done in such a way that one have an area on the inner section that goes supersonic even in normal flight, it then slows down to subsonic speed before the flap area in a mild series of shock-waves.

What you mean is that major portions of the airframe has gone supersonic, well if they do there should be some pretty wild buffeting on this whale looking beauty. (thickness to lenght ratio must be a awfull )

... haven't heard anything about a section of the A380 wing profile having supersonic flow... as far as I understood it, the supersonic shockwave beyond MMO was a localised phenomenon around the front nose section, and was rather unimpressive from the inside (i.e. no wild buffeting or banging), so I guess the rest of aircraft is pretty much subsonic whatever happens  
 
tdscanuck
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RE: A330 Thin Speed Margins?

Thu Mar 31, 2011 5:38 am

Quoting travelavnut (Reply 24):
Excuse my ignorance, but what exactly does core locking the engine entail?

It's basically what Starlionblue said:

Quoting Starlionblue (Reply 26):
As I read the explanations online, if airflow is stopped/disrupted in the core in certain ways, cooling stops and core components can expand to such dimensions that they no longer "fit", meaning the engine seizes up and can't be "unstuck".

A lot of engine components have very tight clearances and a lot of the rotating bits are air cooled. It all plays nice together since the temperature of a running engine moves fairly smoothly. If you stall/surge the engine or otherwise screw up the cooling airflow, you get big temperature gradients and you can lose clearance in some parts of the engine. Once the parts get stuck the engine stops windmilling, drag goes up, and your chance of a restart plummets to zero.

Quoting Ferpe (Reply 29):
I don't want to be picky and I don't know if I am right but I think the A380 wing is done in such a way that one have an area on the inner section that goes supersonic even in normal flight, it then slows down to subsonic speed before the flap area in a mild series of shock-waves.

I'm not aware of any large jet airliner since, at least, the 707 that didn't have supersonic flow over some portion of the top of the airfoil when it's out near Mmo. Most modern designs use supercritical airfoils that have some supersonic flow on the top surface even at normal cruise speed.

Tom.
 
Pihero
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RE: A330 Thin Speed Margins?

Thu Mar 31, 2011 9:32 am

Quoting tdscanuck (Reply 32):
I'm not aware of any large jet airliner since, at least, the 707 that didn't have supersonic flow over some portion of the top of the airfoil when it's out near Mmo. Most modern designs use supercritical airfoils that have some supersonic flow on the top surface even at normal cruise speed.

  
I you looked well, there is an amateur fim and a thread on another site : in some rather rare conditions of light and humidity, a small shock wave can be seen. The sequence was taken from a pax window on a 777.
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