Stalling?

[beaky]

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

You should get yourself some sort of flight training manual that explains all of this more simply... a lot of good info here, but I wouldn't be surprised if you understand stalls less now than when you first asked....
You may not haven taken any ground school lessons yet, but don't wait for that to get the book(s)  you'll need- ask your CFI what text they'll be using in ground school, get a copy ASAP, and start reading it.
 
For example, from my copy of the Jeppesen Private Pilot Manual:

A stall is caused by the separation of airflow from the wing's upper surface. This results in a rapid decrease in lift. For a given airplane, a stall always occurs at the same angle, regardless of airspeed, flight attitude, or weight...you can stall an airplane at any airspeed, in any flight attitude, or at any weight.

[beaky]

another question,   What makes that turbulence you feel when you level out, after going through a 45 degree "or more" bank?

spirit

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.

[Hagar]

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.

Indeed & take no notice of me. I'm just being my usual pedantic self by pointing out that things are not always according to the book. You need to know what it says in the book you're expected to answer questions on.

[C]

[quote]

[Staiduk]

Indeed & take no notice of me. I'm just being my usual pedantic self by pointing out that things are not always according to the book. You need to know what it says in the book you're expected to answer questions on.

The fun thing about flight theory is it's just uncertain enough to have some really ripping arguments.

[Hagar]

The fun thing about flight theory is it's just uncertain enough to have some really ripping arguments.

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.

[Brett_Henderson]

Charlie wrote:

But a stall speed can only be quote for a certain parameter, such as the two most quoted examples, the clean stall in S&L, power off, flight, and "dirty", ie configured (gear and flap), power off.  

For any discussion about stalls.. the configuration is a given or constant (flaps/no-flaps .. gear/no-gear). My 150kias airspeed could have been any configuration.. doesn't matter.  I could have said, "150kias clean"  or  "135kias flaps and gear down" and just said stalling occured at 0.01 less.

Charlie wrote"

Any change in an aircrafts velocity will vary the speed at which the wing stalls.

I'm not sure what you mean here.. An aircraft's velocity(speed) doesn't  change its stall speed... Nor does its power setting.

Now I'm getting confused  :P

[beaky]

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

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.

[Nexus]

Speaking of stalls. This is what my ground examiner wrote on the white board before a flight, I guess to ease us up abit

The definition of a Nanosecond: Time delay built into the stall warning system
 

[Boss_BlueAngels]

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

[Hagar]

To be honest I think all this textbook stuff is pretty academic & most of the advanced stuff still makes my head spin. The main point is in knowing what would cause a stall in circumstances most likely to be experienced in a conventional trainer like the Cessna that you're learning on. More important is learning how to recognise an impending stall & take remedial action if it ever happened. I believe that stalls are not actually carried out during basic training now which I've always thought is a mistake. When I was learning to fly in 1961 stalling & spinning were part of the normal training & had to be done before a pupil was sent solo. Consequently you knew exactly what it was all about without needing to look in a book.

[C]

[quote]

I'm not sure what you mean here.. An aircraft's velocity(speed) doesn't

[Brett_Henderson]

I undestand the physics of velocity as it applies to a vector. And under certain sets of circumstances (like this discussion) velocity and speed are

[Hagar]

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.

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.

[Mobius]

Yes, in the US we are taught the same three stalls, however it's done at a safe altitude, and spins are avoided as we don't have very good ejection seats in a C172.  We also have to demonstrate stalls during the checkride, and I just took my BFR and I had to do all three stalls there too.  We don't have to practice spins though, a 172 is pretty docile and it is difficult to get it into a spin, my instructor tried to show me what it was like, but he wasn't able to atually make it spin.