What exactly is "stall"

[Brett_Henderson]

I have a genuine question.  Do wing tips stall earlier on swept-wing aircraft because of the "sweep"; or because of the taper ?

Also (and this is pure speculation), I think that stalling (especially an accelerated stall) is rarer in higher-performance, bigger and faster aircraft because the gap between the top of MCA and the onset of stall is larger. Maybe not so much proportionally larger; but definately a bigger chunk of the ASI's arc. Not to mention that pilots are more experienced.

[Hagar]

[quote]I have a genuine question.

[C]

I've done a little research to refresh my memory of this phenomenon. As I recall, the BAC One Eleven was being tested at a rearward CoG. Once it had entered the "deep stall" condition it seems obvious that a highly skilled & experienced test pilot like Mike Lithgow & crew would have tried everything in their power to recover from it, including a wide variety of power settings & control inputs plus deploying the anti-spin parachute carried during this sort of testing. It seems likely that the aircraft ended up in a 'flat spin' from which recovery turned out to be impossible.

From a little reading around, it appears the aircraft was in a "stable" stalled state all the way to the ground, sadly with a fatal RoD...

It's also worth considering that AoA is measured from the relative wind OTTOL mentioned & not necessarily from the horizontal as is shown in most textbooks

At last. I'm glad someone's mentioned that...

[OTTOL]

Fatal TU154 crash August 2006[/url]
Three previous fatal accidents with the same type of aircraft have been attributed to the "deep stall".

.

Welp...let me rephrase that with a little more emphasis on some key words.

..... very few, if any modern jets fall victim to stall related accidents during normal operations and day-to-day flying........

You are correct. This is a recent "deep stall", jet accident. I think that a forty year old design that was "a bad knock-off of a mediocre design" (even back in 68', when it was new) is a weak example though.
Although I sympathize with and respect your personal experience regarding the early designs, these examples are dated and IMO don't have a real bearing on the bulk of the current airline fleet today.
The TU154 is severely underpowered and the wing is a flying aerodynamic history class. (Iran Air flies them here into Kuwait. They have wing fences the size of roadside billboards!!) The fact of the matter is; the only reason the aircraft is still flying is one of economics (they're cheap to buy and operate) not resilient design attributes.
I have to admit, most of my practical experience on T-Tail, swept-wing aircraft is with Learjets. I may be living in a bit of a vacuum by that distinction. Nonetheless, all of my stall-training has emphasized the violent roll which can occur as a result of tip stall and subsequent loss of aileron authority.
.....But....

[Hagar]

Fatal TU154 crash August 2006[/url]
Three previous fatal accidents with the same type of aircraft have been attributed to the "deep stall".

.

Welp...let me rephrase that with a little more emphasis on some key words.

..... very few, if any modern jets fall victim to stall related accidents during normal operations and day-to-day flying........

You are correct. This is a recent "deep stall", jet accident. I think that a forty year old design that was "a bad knock-off of a mediocre design" (even back in 68', when it was new) is a weak example though.
Although I sympathize with and respect your personal experience regarding the early designs, these examples are dated and IMO don't have a real bearing on the bulk of the current airline fleet today.

I respect your opinion OTTOL as you are the commercial pilot. I have no practical experience even with the early jet airliners. My comments are based on what I've learned or been told over the last 50 years or so.

Although it's an old design, production of the Tu 154 ended in 2006 according to Wikipedia so that makes it a current type in my book. The Tu 134 is still very popular & many are still in regular service. http://www.tupolev.ru/English/Show.asp?SectionID=144

I have little knowledge of, or interest in, modern jet airliners but note that the T-tailed swept-wing designs are still very popular today, especially the smaller bizjets & medium-range types. It's possible the winglets now in vogue have gone a long way to overcoming the airflow problems over swept wingtips. You would know better than me if there have been similar aerodynamic improvements to overcome the deep stall problem or whether they still rely on audible warnings & stick-shakers.

PS.

Oddly enough, the best example that I could find of this was this one that chornedsnorkack eluded to. http://www.airdisaster.com/news/0106/22/news.shtml Quote:

The interim report contained a wealth of details from the plane's flight data recorder and cockpit voice recorder, showing that the crew was incorrect in saying that the plane had experienced a "dual engine flameout," and that the crew took the opposite action to recover from an aircraft stall than action that is taught to every beginner pilot. That suggests that the crew did not recognize that the plane was, in effect, stalling.

I understand that compressor stall can be experienced with this type of aircraft in a deep stall condition. This obviously makes a serious situation even worse & could explain why the loss of power was not immediately recognised for what it was.

[OTTOL]

Although it's an old design, production of the Tu 154 ended in 2006 according to Wikipedia so that makes it a current type in my book. The Tu 134 is still very popular & many are still in regular service. http://www.tupolev.ru/English/Show.asp?SectionID=144

.

They still manufacture the Ural motorcycle (a bad rip-off of a late 30's BMW design) over there. Sure, the Ural may still get you to work (most of the time) but it's far from a good example of a motorcycle by which current bikes can be measured. This is just another example of the previously mentioned point. Economics drives the production of the Ural (zero development, tooling and employee training costs) in the same manner that it drove the production of the Tupolev.
The bottom line; if you do a little research (even look at your own quoted article) pilot error is, overwhelmingly, the key cause of the majority of accidents today.

From your article....

The latest data from the MAK (Interstate Aviation Committee) reports that Flight 612 had step-climbed to 12,400 m (41,000ft). Maximum allowed weight at 12,100 m is 85t for the TU154. Take-off weight must have been around 93.5t, given the distance from Anapa to St. Petersburg and with 160 passengers. This would mean a weight of about 88t at the time of the crash .

The thunderstorm was reported as having been a heavy one, reaching up to 12-15 km. It looked like the aircraft had stalled and entered a flat spin when it encountered turbulence at a low indicated airspeed (IAS), because it was way too high up for its weight. This was confirmed two weeks later in a statement by the Ukrainian Attorney General.

Crew error and compressibility (and the crew's lack of knowledge of its affects) are the culprits IMO.

Look, I'm not looking for an argument here. And although I appreciate the Kudos, I don't need my ego padded either. The reason I argue my point so vehemently is that I hate to see a false idea or rumor perpetuated. Airplanes don't just fall out of the sky. The crew usually has to do something terribly wrong to create these circumstances. And any modern, high-performance airplane can fall victim to crew complacency. The fact of the matter is; all too often an aircraft is given an undeserved "bad rap."

[chornedsnorkack]

A plane with zero forward airspeed still cannot drop out of the sky at any high speed.

What would you define as "any high speed"?

Well, let

[Hagar]

Look, I'm not looking for an argument here. And although I appreciate the Kudos, I don't need my ego padded either. The reason I argue my point so vehemently is that I hate to see a false idea or rumor perpetuated. Airplanes don't just fall out of the sky. The crew usually has to do something terribly wrong to create these circumstances. And any modern, high-performance airplane can fall victim to crew complacency. The fact of the matter is; all too often an aircraft is given an undeserved "bad rap."

I have no wish to appear patronising or to cause offence. I happen to find this subject interesting & I'm simply expressing my opinion. If you call that argument so be it. I call it discussion.

I agree that a lot of these accidents are due to pilot error & most likely caused either by complacency or inadequate training. What worries me is that the stall doesn't seem to be fully understood by a large number of pilots flying regularly today. I think this is demonstrated by some of the comments in this thread & other similar topics. I'm not convinced that some instructors understand it themselves. This brings into question the basic training methods used by flying schools.

[Brett_Henderson]

I agree that a lot of these accidents are due to pilot error & most likely caused either by complacency or inadequate training.

Unless there's an airframe or engine failure/malfunction..It's statistically certain that 100% of stall related accidents in certified airframes are pilot error.

I have no wish to appear patronising or to cause offence. I happen to find this subject interesting & I'm simply expressing my opinion. If you call that argument so be it. I call it discussion.  

Interesting.

What worries me is that the stall doesn't seem to be fully understood by a large number of pilots flying regularly today. I think this is demonstrated by some of the comments in this thread & other similar topics. I'm not convinced that some instructors understand it themselves. This brings into question the basic training methods used by flying schools.

Being that, as far as I know, I'm the only CFI posting in this (and other) threads... and for my learning's sake, as well as the sake of challenging specifics ... I'm compelled to ask, "What exactly do you mean ?"

[Hagar]

Being that, as far as I know, I'm the only CFI posting in this (and other) threads... and for my learning's sake, as well as the sake of challenging specifics ... I'm compelled to ask, "What exactly do you mean ?"

Please don't think my comments were aimed at you Brett. I could possibly have phrased it better but in previous discussions on the subject on this forum both you & Sean have confirmed the type of instruction to be found in a typical flight school today. It worries me that what used to be an honourable & respected profession is now seen in the majority of cases as a standby until something better comes along. There are obviously dedicated professional flight instructors still around but I get the impression these are now in the minority.

As you pointed out earlier, this topic has little to do with answers & is more like provocative thumb wrestling. I don't mind a sensible & informed discussion but a lot of chornedsnorkack's argument seems based on flawed theory.

[Brett_Henderson]

I didn't think it was directed at me specifically, but after a couple of reads, I wasn't quite sure. I could have better phrased my post as well, but I didn't want to over-think it and get patronising or offensive either

[OTTOL]

My apologies Hagar. My comment wasn't directed at you but actually meant to be a clarification of my own stance in this.....uh....debate....

[Brett_Henderson]

If you want to get into a real mental wrestling mach; let's start a new thread about lift. You would be surprised (maybe not) at how misunderstood that one is. ....by the majority of the aviation community!!

Here, Ottol..  Read these five pages and if you like.. post it back into active discussion  ;)



http://www.simviation.com/cgi-bin/yabb2 ... 1148281582

[Hagar]

[quote]I didn't think it was directed at me specifically, but after a couple of reads, I wasn't quite sure. I could have better phrased my post as well, but I didn't want to over-think it and get patronising or offensive either

[chornedsnorkack]

And notice that while, at least, the pilots and instructors of "aircraft" have some certification, training, experience and knowledge requirements, those are not applicable to ultralights.

By FAR Part 103, a person does not need to meet ANY requirements of licencing, training, experience, knowledge, medical condition or age to fly an "ultralight".

By the same FAR Part 103, an ultralight does not need to be registered in any manner, nor bear any markings.

The airframe of an ultralight does not need to meet any certification requirements. Which implies that a person does not need to meet any requirements of knowledge or age to build an ultralight, or design an ultralight.

Verifying the empty weight is a simple matter of weighing. Verifying the fuel volume - ditto.

But how does one establish the exact stall speed? If you stall, and happily recover, at 25 knots, you should never have taken off to begin with...