can someone give me the 411 on stalling and that such?
My flight instructor asked me the other day why a airplane stalls.  I replied with,  "A airplane stalls when the thrust is not fast enough to keep the airplane afloat"  He stared at me with a half strangled look and told me to look it up online and tell him why they really stall. 

btw I am on my 3 hour of flying


spirit

Wait a second, I just skimmed over that aritcle and it doesn't mention stalls. . Still some good info in there though. I'll try my best to explain it. It all has to do with angle of attack. Lets walk through a controlled stall shall we? flying along at 3000' MSL, you pull the power back to flight idle. Maintain altitude for as long as you can. keep the nose up. do whatever you can to keep from descending. Soon you find yourself descending anyway, and your airspeed is falling all the time. Notice that the slower you go, the quicker you descend. pretty soon you hit that magic number, 56KIAS (in a 1968 C172E anyway) or so and the stall horn goes off. the planes shudders a little, the nose goes over and you increase power and gradually return to level flight. No what happened when the stall horn went off? The wings of the airplane no longer had enough air flowing over them to create lift, so the plane stopped flying and started falling. This would be a lot easier to understand if I had some pictures to show you. I suggest you do an internet search, or try the AOPA site for more info, but I hope my drawn out explanation at least helped. Remember, it is important that you really understand this, don't just quote me, or a book, but really understand it. You will be a safer pilot for it. good luck with your training, I'm about to solo myself.

There are key words your instructor is looking for, the main one being "critical angle of attack"  The critical AoA is the angle at which the air flowing over the top of the wing seperates from the surface in a manner that causes an abrupt decrease in lift.  Air flows in much the same way as water does... if you let the water run out of a faucit and place your fingertip in the stream even at 90 degrees you will notice that it "bends" the stream as it goes around your fingertip.  This is just what air does over the top of the wing.  But, at a certain point the air doesn't have enough energy to make as drastic of a change in direction.  Thus it begins to get turbulent and seperates causing the stall.

AoA as you may know now is the angle between the chord of the wing (drawn from trailing edge to leading edge and the relative wind. 

Thrust only has an indirect relationship with the stall... you can be going mach 2 in your Cessnan 150 and still cause the wings to stall.  (it'll be a very spectacular event to watch from the ground as the wing vaporizes... but theoretically possible)  The faster you go (straight and level) the lower the AoA... the slower you go the higher the AoA is needed to maintain level flight.  Also, the heavier you are the greater the AoA needs to be and vise verse.  This applies to turning because you now have centrifugal force pulling the plane to the outside and are continuously changing direction/momentum.   That's why you will need to add power/airspeed in steep turns.

Next time he asks you say that the wing stalls when the actual angle of attack exceeds the critical angle of attack for that configuration.  Also being able to draw out a sketch of the coefficient of lift graph helps to understand this as well and will really impress your instructor.


Hope it helps and my lack of sleep today hasn't made everything I just said nonsense. :p

This technical stuff about critical angle of attack is all very well in theory. This might impress your flight instructor & be what he/she wants to hear but it's perfectly possible for an aircraft to fly under control & without stalling when the the wing is way beyond what would nomally be regarded as a critical angle of attack. Watch any air display by an aerobatic pilot in something like an Extra or Pitts Special & you will see what I mean. So far I've seen no mention of power to weight ratio.

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He could be flying over the Dead Sea, or Death Valley. o_O

Yes, but if he was at 3000 MSL, he would be at 3000+ AGL, so it would be all right.

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Exactly.. If a plane is hanging on it's thrust (or it's prop) it wouldn't matter if the wings fell off (as far as lift goes). They could have stalled long ago.

Let's say a jet fighter has a stall speed of 150kias. If it has enough thrust, it could very well climb straight up at 149.9kias with the wings fully stalled acting ONLY as stabilizing control surfaces.

Right... 3000' AGL. I was at the end of a 12 hour shift, mistakes were made. . Mobius posted the type of drawings I was thinking of. It was an illustration like that in a book that really helped me understand stalls. Everyone else explained it much better than I did.

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I think the turbulence you felt was just turbulence... unless you flew in a complete circle and passed through your airplane's own "wake".
  Everyone here is happy to help, and most of us know what we're talking about, but if you're paying an instructor to teach you about flying, ask him these questions.
If he's being vague with his answers or dismissive about your newbie questions, get another instructor. Otherwise, you'll just waste your time and money.

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Good advice. It'll be much easier for him/her to explain sitting in front of you...

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Quite so & theory is all very well but you only fully understand it once you've actually done it. If you have a good instructor they will demonstrate all you need to know. I've had a good practical understanding of aerodynamics from a very early age when I first started building & flying model aeroplanes. I'm no scientist & if you'd asked me to explain it in technical terms I couldn't. I feel that I've always known & some of these drawings & explanations only confuse me. I sometimes wonder if the people attempting to explain these things in textbooks actually know what they're talking about.

I look on it in much the same way as driving a car. You play it by the book until you've passed your test but only really start leaming how to drive once you've passed it & thrown the book out of the window. Please note that I'm not suggesting that anyone actually does that where flying is concerned but it's the best comparison I can think of.

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And he's being paid to teach this stuff- a little theory is needed just to comprehend what's going on in flight. Were I the instructor, I'd try to explain it first, then say: "Go look it up later".
But whatever.I guess as long as a student learns to recognize an incipient stall, it doesn't matter too much if they fully grasp the physics involved.

Wow, this really exploded into some interesting arguments... well, I don't know that they're really arguments per-say... but still stimulating to the mind nonetheless. lol

As I said in my original post... everyone's point can still be true given the whole "critical angle of attack" statement earlier. 

Hagar wrote, "it's perfectly possible for an aircraft to fly under control & without stalling when the the wing is way beyond what would nomally be regarded as a critical angle of attack. "

Well, I wouldn't really say that the airplanes are not stalled... in fact, even in snap rolls they are in a stalled condition.  As for vertical maneuvers... to be super-picky the wing isn't stalled as (at least with vertical lines) the wings have nearly 0 AoA.  Now, the airplanes you mentioned like the Extra have a symmetrical airfoil, so it isn't creating any lift... but airflow is still pretty much laminar.  And when you do hang on the prop, then accelerate vertically... the wings are still un-stalled.  A stalled condition refers to disrupted/seperated airflow over the wing.  Vertical lines are done on nearly 0-degree AoA.  No seperation, just SLOW.

If you're familiar with Remote Control airplanes maneuvers such as the Harrier are performed with a fully stalled wing.  Now, the majority of the "lift" is from the fan up front, but those wings are still helping out.  In fact, this maneuver is the perfect example as to what happens when an airplane gets behind the power curve.  At the RPM required for this maneuver... the airplane can still fly just great S&L... to recover from Harrier you just lower the nose, no power adjustment even needed.  More on that later.

Now, when it comes to converting this "critical AoA" to an airspeed is a completly different storry and that seems to be the true culprit to your conversation, not the critical AoA itself. lol 



The original question was only about the stall itself... not control.  And, regardless of what any engineer tells you the actual critical AoA is... there is still a definate point when the airflow over the top of the wing becomes turbulent and seperates... thus your stall.  As I remember it, this critical AoA remains constant within the configuration of the airfoil with regard to speed. 


The problem you get into with jets and thrust, though, is the whole issue of being behind the power curve.   I'm sure many of you like myself have experienced this very problem in flight sim...  you find yourself too slow and stalling, then cram on full power and find that you're STILL DESCENDING even when everything is spool'd up at max RPM.  There is a certain AoA range of the wing when it's screaming for attention... may not even be in a stall... but is getting close.  When this happen, something has got to give... and the easiest thing to change is your AoA... lower the nose, reduce the drag, and the engines will help you out more. 

Try it up at altitude in something like a Hornet... the greater the thrust/weight ratio, the shorter this period of being behind the curve will last.  If you're doing that in a heavy 747 you may as well kiss your butt good-bye unless you've got 4,000 feet to spare!




Also, if you want to understand aerodynamics more, and really visualize it... I recommend buying some cheap RC plane (electric) that's ready to fly and play around with the wing and some smoke.  Heck, even a small plastic model and an incense stick works wonders for actually visualizing the airflow over the wing.  It's great to actually SEE the stall and see where the laminar flow starts to transition to turbulent and seperate from the airfoil. 

Now, take all this with a grain of salt as I haven't taken an aerodynamics classes in 2 years! haha  So if you know I'm saying something Bss Ackwards, slap me upside the head!  :p

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Velocity isn't the same as speed. Speed is a scalar quantity, velocity is a vector. For example, in straight and level flight, you move the throttle from idle to full power, and the speed will increase. However, if on the other hand you put in a control input you change the aircraft direction of movement, which is its velocity (effectively an acceleration).

(Wikipedia does a good explanation = http://en.wikipedia.org/wiki/Velocity

For example in a full power, steep turn at around 5G, I can stall my normal aircraft (into the heavy buffet) at about 135kts, yet in a similar configuration in straight and level flight the aircraft full stalls around 60 to 70kts...

Power can also change the stall speed on some aircraft (ie props) as the prop provides an increase in the airflow over the wing. Its not something we practice so I can't really give an example of how much of a difference it makes (not very much)...


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Very much the same now. We are taught 3 stalls: Clean, the finals turn stall (configured, low power, overbanked and pulling round the corner), and the approach (configured, simulating trying to extend the approach with too little power set). These are all taught before first solo, which is all in the circuit, and if you entered a spin you'd be 1) being a buffoon, and 2) pulling the Handle to vacate the aircraft! We are then taught spinning (erect and inverted) before going solo outside the circuit.

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That might be so in the RAF Charlie & I wouild expect nothing less. What about normal civil training to PPL standard that I was referring to? I can't see that being anywhere near as comprehensive & not sure you would even have to do stall recovery before being sent solo now.

I still think this is purely academic & not helping spirit1flyer who asked a simple question. My advice on that would be to ask his instructor & take no notice of us lot trying to prove how clever we all are.

Try it in a Tomahawk (Piper).. When my instructor demonstrated spin recovery.. we went right  into a spin.. IN THE OPPOSITE DIRECTION

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Mmm, my first 20 hours or so were at a civvy school, and  I'm fairly sure we were taught the stall recovery pre-solo (being an RAF sponsored course I expect this would be the case as. To notot teach it could be considered negligent in the event of a poor little 18 year old stoofing it in on finals).

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We do it in a similar fashion - our minimum (intentional!)stalling height is 5000ft AGL, even with the seats, and would technically give a 2000ft window in which to recover the aircraft in the event of a departure from controlled flight before the mandatory minimum abandonment height.

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I was once offered a demonstration in a C152! I politely declined...

Hagar wrote: Quote:


I used to say that if I owned a plane, I'd disable the stall-horn . A lot of the fun flying for me is at or near stall speed. I  REALLY enjoy tossing a plane around in slow-flight. If you can master Dutch Rolls, right at stall-speed, you're more than prepared to land a plane in a gusty, unpredictable cross-wind. And, if you take off from grass fields with obstacles.. requiring a rigid V-x climb.. the stall horn can get annoying. I thought.. geez.. if you cant feel a stall coming on by now you shouldn't be flying..

An equal wise, vetran instructor told me it would all but void my insurance and promised me that at some point, climbing out in IMC that I'll be fiddling with the radios or something and that horn will remind me I had neglected the attitude indicator and/or airspeed indicator.. You'd be surprised how quickly a plane will get "out of shape" when you can hardly see the wing-tips.

One day during my preflight, I found the stall horn didn't work, so I told my instructor, and he said, "just don't stall".   So Spirit, tell your instructor you just don't ever plan on stalling. 

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I've heard similar stories about Tomahawks... they seem a little unfriendly in a fully-developed stall, from what I've heard. Other than that, they're wonderful trainer/sport planes.
Most interesting tale was of a CFI and student who found themselves in a deep stall; the heavier of the two had to crawl up onto the glareshield to get the CG forward enough for the nose to come down.

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Just as long as you don't rely on it as even the simplest mechanical device can go wrong & the calibration or positioning of the actuator switch might vary considerably on different aircraft, even the same type. Some might work better than others or have a habit of sticking. I think this was one of the reasons for my boss not liking the idea, especially on a basic trainer. Far better to be able to recognise an impending stall without depending on a instrument.

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True. However any safety net is better than none. I can think of a couple of scenarios where the stall warner may very easily make the difference between landing safely and ending up a crumpled heap in the ground (particularly if there is cloud around! )

[edit] I notice Brett's mentioned this above. The stall warner could be the difference between regaining control before the stall, or pointing at the ground in rapid time 

When you're peripheral vision is loaded with a nice mixture of terra-firma and blue.. it mixes well enough with your other senses to feel a stall coming in plenty of time. I'd be more than happy to never hear a stall horn in that situation.. It's that darn IMC stuff.. THAT'S when I'm glad it's there. The stall you enter then could very well be because you're banking some 60 degrees and didn't even now it. That kinda stall has a much smaller recovery window.

(I'm picturing Hagar setting a wheelbarrow on it's rests and trying to figure out what that blasted noise was    )

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Thankfully I don't have any hours on wheelbarrows!

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Funny thing: the first airplane I ever controlled was a Tomahawk; took my "discovery" flight in one way back when. Very much like any other low-wing Piper, only with superb visibility . Didn't try any stalls that day. I guess the bottom line is that it's just a little more unforgiving if you push the bottom of the envelope...

BTW, that "Red Barrows" pic is one of the silliest things I've ever seen... but do they do formation "barrowbatics"? I'd like to see that...