Hahahah you like that? Just havin some fun. But in all seriousness, the AoA that a wing stalls at will never change due to altitude. Thats why its called the critical angle of attack. Now true airspeed will change as you get higher. However the critcal angle of attack wont. Now i think once mach comes into play things do get squirrily.

Airspeed Tape says: "Would you like to Stall or encounter Super-Sonic buffeting!?"

The threads at pprune.org have become so bloated that it's now hard to find, but some of the well-informed discussions about af447 indicate that there is a real issue about the quality of training for stall recovery in real life. There are multiple perceived problems but apparently one of them is that even the full motion simulators are unsuitable for training for recovery from some stalls because they cannot reproduce accurately all the phenomena of flight outside the envelope of normal flight. If that is correct then it would be odd if fsx can do so accurately.

Sorry if off topic...but regarding this AF447 stuff I thought these big airliners had tables and such for erratic/lost airspeed indications. Stuff like fly this pitch with this N1 at this approximate altitude and you should be level/climbing/decending. Not my thing to speculate on the crash yet though.

Sorry if off topic...but regarding this AF447 stuff I thought these big airliners had tables and such for erratic/lost airspeed indications. Stuff like fly this pitch with this N1 at this approximate altitude and you should be level/climbing/decending. Not my thing to speculate on the crash yet though.

HI Patric,They most certainly do and for the Airbus family it's in the QRH. Next to the smoke checklist it's one of the longest also. regards,

Sorry if off topic...but regarding this AF447 stuff I thought these big airliners had tables and such for erratic/lost airspeed indications. Stuff like fly this pitch with this N1 at this approximate altitude and you should be level/climbing/decending. Not my thing to speculate on the crash yet though.

In relatively smooth air that is true, you can indeed set the controls to expected positions for level flight and your aircraft will indeed fly level or whatever. In fact, if you ever fly an older aeroplane, you'll often find that the paint on the trim controls will be worn in such a way that you can actually tell where the trim should be for various stages of flight and sometimes trim controls will even rest in those positions more easily than on other settings because of wear on the linkages making the controls more inclined to sit in those detents.But all that stuff goes out of the window if you are in the middle of a thunderstorm with no visible horizon from which to initialise such settings, and even then it is no guarantee that you will stay level. If you've ever flown through a thunderstorm (I did once and I don't recommend it, I came very close to deciding to make a forced landing just to get down out of it), then you will know that it is very easy to find one wing in a massive updraft or downdraft, where the aeroplane is being flung about like a rag doll. And when it is like that, you find yourself putting full control deflections on just to keep the thing from going inverted - I'm not kidding, it really is that bad. Any pilot who was prepared to sit there with the aircraft trimmed for level flight and assume it was going to level off in those circumstances is a very trusting soul indeed!Al

Airspeed Tape says: "Would you like to Stall or encounter Super-Sonic buffeting!?"

Your point. Im well aware of that. However critical AOA doesnt change.

Hi Guys,I just thought I would chime in a correct some of you arm chair pilots. Here is from my ATPL book: "As speed increases the wing gets closer to its leading pressure wave and the streamline pattern is affected a short distance ahead, so must approach the wing a steeper angle. This change in the streamline pattern accentuates the adverse pressure gradient near the leading edge and flow separation occurs at a reduced angle of attack". All this is caused by the compressability effect.Matthew Kubanda If you doubt any of this please feel free to write to Oxford Aviation Training. Here is a little reading: http://www.ukfsc.co....uary%202011.pdfHave a good day

Hahahah you like that? Just havin some fun. But in all seriousness, the AoA that a wing stalls at will never change due to altitude.

*ahem* read the post, by FirstOfficerA320, above this one.

Thats why its called the critical angle of attack. Now true airspeed will change as you get higher. However the critcal angle of attack wont. Now i think once mach comes into play things do get squirrily.

You realize the effect of compressibility comes in at Mach 0.3? It's all fine if you fly a small Cessna at 70 kts to assume the stall AoA is constant, but when you get into flying anything faster you need to understand that stall AoA reduces with altitude.WHY does it reduce with altitude? Mach.Mach dictates compressibility (the air is a fluid after all; Dr. Vaos can elaborate). As the air temperature reduces, so too does the relative speed of sound. As you approach the speed of sound, a shock-wave builds in front of the wing/aircraft. At Mach 0.9999 the air is as compressed as it can be made. At Mach 1, the aircraft is flying so fast through the air that the air ahead of the aircraft is not being displaced before the aircraft goes through it. The effect of doing this causes the sonic bang, as the air is forced over the aircraft and can then release this energy as sound once the aircraft is through this area, and the air can "relax" again.What has this got to do with stall AoA?As Martin's quote says, it affects the relative direction of the wind at the leading edge of the wing.A simple way to explain it is thus: At slow speeds, the air is compressed ahead of the aircraft, and starts to move around the aircraft as the aircraft moves through the air. The air can flow nicely over the wing, and everything is good.As the aircraft flies faster, the air is increasingly forced to get out of the way. This is the result of compressibility, and starts at Mach 0.3.As the air is being forced out of the way, it is less inclined to follow the shape of the wing. This is fine for level flight, as the boundary layer remains attached to the wing, and the wing keeps producing lift (to certain limits - I won't get into Mach buffet, etc. as that is beyond the scope of this discussion).Now, assume that we demand more lift from the wing. We do this by increasing the Angle of Attack. This causes the wing to create more lift, but again, there is a limit. The actual limit depends on airspeed (TAS!), and altitude.Why is altitude important? As we climb, the air rarefies (gets less dense), so for a given IAS we have a higher TAS (the air that is present is hitting the aircraft at a higher velocity).Time for a diagram:This drawing is suitable for flight at low altitude. Let's say 3000 ft. We can pitch our nose up to e.g. +12 degrees of pitch, and bring the speed right back to Cl_MAX (the point of maximum lift), and remain in controlled level flight at very low speed. Now, if we reduce speed further, or, we increase the pitch angle, we exceed Cl_MAX, the wing generates less lift, and we start to descend. If we exceed Cl_MAX by much then we stall completely, and we really start to fall out of the sky (note I'm ignoring any effects of the stall - all that is important is that the wing has stopped producing any meaningful lift and we're going down, fast).Now try this same experiment at high altitude.You should be aware that stall speed increases with altitude? I saw a nice photo of a 737 NG at FL400 where stall was at 260 kts and overspeed at 300.Now, if we try and fly at our 3000 ft stall speed of 120 kts at FL400, we are clearly much slower than the displayed stall speed of 260 kts. You would argue it is obvious we will stall, but you would also argue the stall AoA will be the same as at lower altitude.Going back to maintaining level flight... if we slowed our aircraft to 260 kts at FL400, we could not achieve a pitch angle of +12 degrees as we did at 3000 ft, even though we are at the maximum lift angle of attack (known as alpha max). You could probably get the nose up to +5 degrees of pitch at 260 kts and maintain level flight at FL400. If you pitch up any more, you will exceed alpha max, and stall. Note that at low altitude our Cl_MAX was +12 degrees, and now it is only +5 degrees...Due to the effect of compressibility, and the fact the air is being forced out of the way, it is less inclined to want to follow the curvature of the wing. The result is that once we get to +5 degrees of pitch in level flight at slow speed, we have reached Cl_MAX for that air density (and thus altitude). Simultaneously, our stall alpha has reduced by an equal amount. We try and push the wing beyond +5 degrees of alpha, and the air, now hitting a steeper curved section of the wing, is not going to be so kind as to keep following the curvature of the wing, so it breaks away, and our wing loses lift. If we keep pushing it (+7 degrees and rising) the lift will just fall off, and we fall out of the sky.There is a very cool video of the 747-8i stall testing. Watch that it very suddenly starts losing altitude for a very small increase in pitch. You will also like to note that the pitch attitude this occurs at is far lower than anything you see a 747 achieving at takeoff!!!I conclude therefore, that stall AoA at high altitude is lower than that at low altitude, and you sir, are very wrong.Here is that video I just mentioned. Undeniable proof. 1:35. Just note he has the flaps/slats out so stall speed is reduced/stall alpha is increased. Enjoy. ;)http://blog.seattlepi.com/aerospace/2011/01/06/video-shows-boeing-747-8-tail-drag-stall-tests/Best regards,Robin.

Brilliant.Point - Robin.

You will want to read this, too.Remember, as altitude increases, air density decreases!! This is why I say with increasing altitude stall AoA reduces.http://www.grc.nasa.gov/WWW/k-12/airplane/lifteq.htmlBest regards,Robin.

Thanks for yhe write up but the very first post i explicitly said.......it all gets squrrily when mach comes into play. Hence getting faster. I dont need a write up about mach buffet or the coffin corner or how air density decreases with altitude. Do i stand correct? Sure of course. However i was joking with the all caps thread. I said that a long time ago. But it seems that stall aoa decreases with an increase in tas rather than altitude.....or the correlation is strong when comparing critical aoa with the increase in speed rather than altitude.....and altitude only plays a part because is the reason our true airspeed increases. So it still seems that speed.....not altitude is the reason out stall aoa decreases......or shoukd j say altitude plays an indirect part in the decrease in stalling aoa. But to say altiude alone is the reason why is wrong. Especially on a flight sim forum where people soak this stuff up who have never been ij the fron seat of a real plane.

* sigh *Lift is TAS dependent, not IAS dependent (and it is amazing how many don't understand the difference). Lift is also affected by air density. You can see how all these parameters work together in the lift equation that I also linked to.Please, get several books on aerodynamics and explore the NASA Glenn pages, and read.

But to say altiude alone is the reason why is wrong.

Umm.... I didn't. I was quite clear that the role altitude plays is that the air density reduces. It is AIR DENSITY that is a key factor!From the NASA link you clearly didn't read (or understand):

Lift depends on the density of the air, the square of the velocity, the air's viscosity and compressibility, the surface area over which the air flows, the shape of the body, and the body's inclination to the flow.

There are multiple factors at work, simultaneously. The relationship and effects are complex.Best regards,Robin.

Thanks for yhe write up but the very first post i explicitly said.......it all gets squrrily when mach comes into play. Hence getting faster. I dont need a write up about mach buffet or the coffin corner or how air density decreases with altitude. Do i stand correct? Sure of course. However i was joking with the all caps thread. I said that a long time ago. But it seems that stall aoa decreases with an increase in tas rather than altitude.....or the correlation is strong when comparing critical aoa with the increase in speed rather than altitude.....and altitude only plays a part because is the reason our true airspeed increases. So it still seems that speed.....not altitude is the reason out stall aoa decreases......or shoukd j say altitude plays an indirect part in the decrease in stalling aoa. But to say altiude alone is the reason why is wrong. Especially on a flight sim forum where people soak this stuff up who have never been ij the fron seat of a real plane.

Hi Mathew,Since you're working towards your ATP and already hold a PPL I thoght you where smart enough to spell properly. I've never seen "squrrily" in my books, but it must be an american thing. Now here is the really interesting bit. You know it changes with speed yet you still comment like small children. Here is a tip for you: Keep the blue side up! (but not too much)Good day,

Hi Mathew,Since you're working towards your ATP and already hold a PPL I thoght you where smart enough to spell properly. I've never seen "squrrily" in my books, but it must be an american thing. Now here is the really interesting bit. You know it changes with speed yet you still comment like small children. Here is a tip for you: Keep the blue side up! (but not too much)Good day,

Yeah sorry for typing on my phone........its just as easy as a fullsized keyboard. Squirilly is just as expression and im sure we can agree that its not even a real word. The whole "American thing" was uncalled form i already said that i stand corrected about the main prinicple of it all However i get this whiole write up about how airspeed and graphs and air density and it al comes down to speed decreasing aoa and not altitude. Thats at least what i got out of the whole thing. Like i said...ill be sure to carry a fullsized keyboard with me where ever i go and to not use expressions.......wow seriously guys. All this started out with a joke with all caps and a very broad explination of aoa.

it al comes down to speed decreasing aoa and not altitude.

No. Speed does NOT decrease AoA.As I clearly stated before, TAS determines lift, NOT IAS!!!! IAS measures the PRESSURE of the air entering the pitot tube. Lower air density, lower pressure, thus lower reading on the IAS display. TAS however must increase with altitude (as a result of reducing air density), and is a measure the velocity of what air remains. The actual molecules of air are hitting the aircraft at higher and higher speeds, and must do so in order for the wing to continue generating sufficient lift as the air gets thinner.It is this fact that the air flow is increasing in velocity (and more critically, relative to local speed of sound) as the air density reduces that means the stall AoA reduces, because the air flow is less able to follow the curvature of the wing. The separation of the boundary layer *IS* what a stall is. Behind the separated airflow is turbulence and drag, and results in an *increase* in the relative pressure over the top surface of the wing, reducing lift. The speed at which this happens increases merely as a symptom. It is NOT a cause!I really should sit and write a book.From your profile:

PPL in the USA.Working towards my ATP...that's a long term goal i might add.

Yes... VERY long term...Best regards,Robin.