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A330 Thin Speed Margins?  
User currently offlineChamonix From France, joined Mar 2011, 424 posts, RR: 2
Posted (3 years 8 months 4 weeks 1 day 12 hours ago) and read 6423 times:
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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).

33 replies: All unread, showing first 25:
 
User currently offlineMir From United States of America, joined Jan 2004, 21864 posts, RR: 55
Reply 1, posted (3 years 8 months 4 weeks 1 day 11 hours ago) and read 6392 times:

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
User currently offlinePihero From France, joined Jan 2005, 4670 posts, RR: 77
Reply 2, posted (3 years 8 months 4 weeks 1 day 10 hours ago) and read 6343 times:
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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
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6965 posts, RR: 76
Reply 3, posted (3 years 8 months 4 weeks 1 day 9 hours ago) and read 6296 times:

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 !
User currently offlinePGNCS From United States of America, joined Apr 2007, 2858 posts, RR: 48
Reply 4, posted (3 years 8 months 4 weeks 1 day 8 hours ago) and read 6233 times:

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.


User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 5, posted (3 years 8 months 4 weeks 1 day 5 hours ago) and read 6127 times:

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


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (3 years 8 months 4 weeks 1 day 3 hours ago) and read 6091 times:

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.


User currently offlineMir From United States of America, joined Jan 2004, 21864 posts, RR: 55
Reply 7, posted (3 years 8 months 4 weeks 1 day 3 hours ago) and read 6081 times:

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
User currently offlineWilco737 From Greenland, joined Jun 2004, 9118 posts, RR: 76
Reply 8, posted (3 years 8 months 4 weeks 23 hours ago) and read 6009 times:
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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
  



It it's not Boeing, I am not going.
User currently offlinefaro From Egypt, joined Aug 2007, 1613 posts, RR: 0
Reply 9, posted (3 years 8 months 4 weeks 21 hours ago) and read 5961 times:

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



The chalice not my son
User currently offlineWilco737 From Greenland, joined Jun 2004, 9118 posts, RR: 76
Reply 10, posted (3 years 8 months 4 weeks 21 hours ago) and read 5947 times:
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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
  



It it's not Boeing, I am not going.
User currently offlineAviopic From Netherlands, joined Mar 2004, 2681 posts, RR: 41
Reply 11, posted (3 years 8 months 4 weeks 20 hours ago) and read 5922 times:

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 ?



The truth lives in one’s mind, it doesn’t really exist
User currently offlineferpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 12, posted (3 years 8 months 4 weeks 20 hours ago) and read 5919 times:

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]


Non French in France
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (3 years 8 months 3 weeks 6 days 14 hours ago) and read 5470 times:

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.


User currently offlineFerpe From France, joined Nov 2010, 2805 posts, RR: 59
Reply 14, posted (3 years 8 months 3 weeks 6 days 13 hours ago) and read 5432 times:

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?



Non French in France
User currently offlinetravelavnut From Netherlands, joined May 2010, 1667 posts, RR: 7
Reply 15, posted (3 years 8 months 3 weeks 6 days 11 hours ago) and read 5364 times:

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!
User currently offlineMir From United States of America, joined Jan 2004, 21864 posts, RR: 55
Reply 16, posted (3 years 8 months 3 weeks 6 days 9 hours ago) and read 5284 times:

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



7 billion, one nation, imagination...it's a beautiful day
User currently offlinebrons2 From United States of America, joined Sep 2001, 3017 posts, RR: 4
Reply 17, posted (3 years 8 months 3 weeks 6 days 8 hours ago) and read 5268 times:

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.



Firings, if well done, are good for employee morale.
User currently offlineSpeedbird741 From Portugal, joined Aug 2008, 654 posts, RR: 0
Reply 18, posted (3 years 8 months 3 weeks 6 days 7 hours ago) and read 5237 times:

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



Boa noite Faro, Air Portugal 257 climbing flight level 340
User currently offlineMir From United States of America, joined Jan 2004, 21864 posts, RR: 55
Reply 19, posted (3 years 8 months 3 weeks 6 days 5 hours ago) and read 5191 times:

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
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 20, posted (3 years 8 months 3 weeks 6 days 3 hours ago) and read 5143 times:

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.


User currently offlineprebennorholm From Denmark, joined Mar 2000, 6537 posts, RR: 54
Reply 21, posted (3 years 8 months 3 weeks 5 days 7 hours ago) and read 4829 times:

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.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineMD-90 From United States of America, joined Jan 2000, 8508 posts, RR: 12
Reply 22, posted (3 years 8 months 3 weeks 5 days 5 hours ago) and read 4799 times:

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?

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 23, posted (3 years 8 months 3 weeks 5 days 2 hours ago) and read 4755 times:

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.


User currently offlinetravelavnut From Netherlands, joined May 2010, 1667 posts, RR: 7
Reply 24, posted (3 years 8 months 3 weeks 4 days 22 hours ago) and read 4700 times:

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?



Live From Amsterdam!
25 chuchoteur : 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 p
26 Starlionblue : 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 component
27 Post contains images mandala499 : 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
28 Post contains links Chamonix : I think it made Mach1 http://en.wikipedia.org/wiki/File:747-CA006-1.png
29 Post contains images Ferpe : 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 th
30 Post contains links and images Pihero : 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 dur
31 Post contains images chuchoteur : ... haven't heard anything about a section of the A380 wing profile having supersonic flow... as far as I understood it, the supersonic shockwave bey
32 tdscanuck : It's basically what Starlionblue said: A lot of engine components have very tight clearances and a lot of the rotating bits are air cooled. It all pl
33 Post contains images Pihero : 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 ca
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