What causes stalls?

Ryanb said:
I think you missed the point Ron. @ktup-flyer stated that if both thrust and lift are taken away, the aircraft will stall (which is true), not one or the other as you made it seem. If both are reduced, the aircraft's AOA will increase trying to maintain sufficient altitude, which will induce a stall.
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"taking away" lift could also be a reduction in angle of attack. If you take away thrust sumultaneously, you simply use gravity to keep the airplane moving. So taking away both thrust and lift isn't stalling the airplane, it's making it into a lawn dart.
 
MauleSkinner said:
"taking away" lift could also be a reduction in angle of attack. If you take away thrust sumultaneously, you simply use gravity to keep the airplane moving. So taking away both thrust and lift isn't stalling the airplane, it's making it into a lawn dart.
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Yes it's called gliding, but the point was, that if both factors are removed and the AOA is not reduced, a stall will occur.
 
flyingron said:
Precisely, it is not the speed or any of the forces that make the stall, it's increasing the AOA that causes the stall.
Why stall "speeds" are important is they are a yardstick that says "you'll stall inceasing AOA trying to maintain altitude at a speed less than this."
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Righto!
 
Ryanb said:
Yes it's called gliding, but the point was, that if both factors are removed and AOA is not reduced, a stall will occur.
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Wrong again...it's called a ballistic trajectory.
The wing is still generating lift in a stall, just not enough to support the airplane.
 
Ryanb said:
Yes it's called gliding, but the point was, that if both factors are removed and the AOA is not reduced, a stall will occur.
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If lift is reduced it is because the AOA has been decreased, unless the airplane is already stalled.
To talk in terms of "reducing lift will 'eventually' make the airplane stall" makes no sense. The four forces diagram is a red herring.
 
dmspilot said:
To talk in terms of "reducing lift will 'eventually' make the airplane stall" makes no sense.
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I didn't say that. I said without reducing AOA, the airplane will stall, not reducing lift.

This is what I assumed tup-flyer was intending to say or at least the way I gathered it.
 
Ryanb said:
I didn't say that. I said without reducing AOA, the airplane will stall, not reducing lift.

This is what I assumed tup-flyer was intending to say.
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You also made no mention of increasing AOA.

I prefer to go with what people say, rather than making assumptions about what they mean...especially without stating those assumptions as part of my response.
 
PPC1052 said:
To me the interesting question is what events precipitate a pilot stalling their aircraft. I understand what a stall is, and I suspect the vast majority of pilots do, too. But what I don't understand it how pilots get themselves tripped up to let it happen. Obviously, something is occurring that some pilots are not aware of that is catching them by surprise. What is it? Sure, overloading the wings by pulling too hard when turning base to final due to overshooting is one way. But it can't be the only one.
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This is the same place I'm at. Nobody intends to crash by stalling. So what surprises them?
 
bflynn said:
This seems a good argumentative question for the board

We all know that stalls occur when the airfoil exceeds the critical angle of attack. But how does that happen? What affects it? Under what conditions can a stall happen when the airplane is not already at low speed? How can the airplane stall at speeds between Vso and say 1.2 times Vso?
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Besides the usual things like angle of bank, G's, CG and all that other stuff that changes the speed at which the stall occurs is inertia. Sudden, abrupt control input like jerking the the yoke/stick back can change the AOA like right now, but inertia keeps the plane from slowing down like right now.
 
Ryanb said:
It's not absolutely wrong. @ktup-flyer stated that if both thrust and lift are taken away, the aircraft will stall (which is true), not one or the other as you made it seem. If both are reduced, the aircraft's AOA will increase trying to maintain sufficient altitude, which will induce a stall.
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Not if you point the nose down. Less lift less thrust, but not stalled, just decscending.
 
SoonerAviator said:
I think the think that always required me to contemplate the scientific-side of the stall was related to load factor. It's easy to see how getting slow and having less airflow over the wings can cause a stall (i.e. slow flight, approach/departure stalls). However, I was always much less confident in knowing how hard I could pull on the elevator in a 45/60-degree bank before I got close to the critical AOA that would cause a stall, which is generally likened with to the "overshooting the base-to-final turn" scenario. Practicing stalls while straight-n-level is easy, and the recovery is relatively simple as well. I don't know of anyone who practices steep-turn accelerated entry to stalls, aside from aerobatic pilots, which makes recognition and avoidance much more difficult without AoA or even G-load instruments as a visual reminder.
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I do steep turn stalls in my airplane on occasion. Done wings level pitch up accelerated stalls as well.

No need for an AoA or G meter. The aircraft provides ample warning in the form of a buffet 5-6 kts prior. Either abort or continue to pull and let it stall. Recovery is the same as a level flight stall except for reducing the AoB. Increased altitude loss vs straight and level is negligible.

You should also already have a number in the back of your head for a 60 degree AoB stall. For my Glasair, I know if I stay above 70 KIAS (1.4 x stall speed), I can do 60 degrees no problem. Since I'm never below 80 kts in the pattern, it's not an issue.
 
MauleSkinner said:
Wrong again...it's called a ballistic trajectory.
The wing is still generating lift in a stall, just not enough to support the airplane.
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A wing that is not stalled may not be enough to support the airplane too.

No need for an AoA or G meter. The aircraft provides ample warning in the form of a buffet 5-6 kts prior.
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A G meter won't tell you anything about stalls. AOA gives you a hint to the margin above stall but as you state many airframes will give you aerodynamic feedback of the impending stall. The FAA doesn't require a stall warning horn in aircraft that do this (the Navion is also one). Even the 172 which has a horn gives you a bit of aerodynamic warning but it doesn't shudder like the Navion does approach stall.
 
bflynn said:
This is the same place I'm at. Nobody intends to crash by stalling. So what surprises them?
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Because, there's no direct indication of the one thing that causes a wing to stall... exceeding a specific angle of attack. We have all of these other rules for trying to figure out when it might based on indirect data, but the ONE THING that would let you know it's about to happen, we don't have (The oft-joked about Angle Of Attack indicator).
 
flyingron said:
A G meter won't tell you anything about stalls.
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AOA can be estimated from airspeed, weight, and G-load using a set of baseline values for the aircraft in question.
 
MAKG1 said:
I thought it's when you ran out of fairy dust or you stopped thinking happy thoughts.
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Well, speaking only for myself, I have the most trouble near class M stars.
 
Velocity173 said:
For my Glasair, I know if I stay above 70 KIAS (1.4 x stall speed), I can do 60 degrees no problem
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Interesting. The math for a 60 degree turn says that it adds a 1.41 factor to the stall speed, using sqrt (1/cos(bank angle)). If you're doing these at 70 kts, you are right at stalling. That might be what you're saying.
 
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Removed lift doesn't equate to a stall. You can go way negative on the AOA as well.
 
bflynn said:
Interesting. The math for a 60 degree turn says that it adds a 1.41 factor to the stall speed, using sqrt (1/cos(bank angle)). If you're doing these at 70 kts, you are right at stalling. That might be what you're saying.
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A 60 degree AoB equates to a 40 % increase in level flight stall speed. My Glasair stalls at around 50 kts clean so about 70 kts in 60 degrees. So yeah, I want to see at least that speed in a steep turn to avoid stalling. Like I said though, 80 kts is what I do on final anyway so I'll never be close unless I somehow got very distracted.
 
Velocity173 said:
A 60 degree AoB equates to a 40 % increase in level flight stall speed. My Glasair stalls at around 50 kts clean so about 70 kts in 60 degrees. So yeah, I want to see at least that speed in a steep turn to avoid stalling. Like I said though, 80 kts is what I do on final anyway so I'll never be close unless I somehow got very distracted.
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Correct, but most pilots don't practice accelerated stalls. Also, you can make inferences and run the math in your head to guestimate what the critical airspeed will be to cause a stall at a 56-degree bank . . . but isn't it more fool-proof to look at an AoA indicator? I suppose they could create a new AoA-adjusted colored arc to the IAS so that the bottom of the green/white arc moves with AoA. I'm not saying that pilots shouldn't have a general idea of what those critical IAS are for 30-45-60 banks, but in the end it's always going to be less accurate than an AoA indicator.
 
SoonerAviator said:
Correct, but most pilots don't practice accelerated stalls. Also, you can make inferences and run the math in your head to guestimate what the critical airspeed will be to cause a stall at a 56-degree bank . . . but isn't it more fool-proof to look at an AoA indicator? I suppose they could create a new AoA-adjusted colored arc to the IAS so that the bottom of the green/white arc moves with AoA. I'm not saying that pilots shouldn't have a general idea of what those critical IAS are for 30-45-60 banks, but in the end it's always going to be less accurate than an AoA indicator.
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As I've said, if one doesn't understand the relationship between AoB and increase in stall speed, then perhaps they need an AoA indicator. A decent stall horn or light will provide the same warning though. Every small GA aircraft I've flown has a pre stall buffet that should give sufficient warning prior to stall.

As far as an AoA being accurate, Maui's last landing vid is proof that book speed will work just as well. His blue donut was illuminated for almost the entire 80-90 kt range on his vid. Book speed for an SR22 is 83 KIAS with full flaps. That was a solid blue donut in his vid. So, the majority of flying that we do in GA doesn't require an AoA to be safe.
 
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SoonerAviator said:
Correct, but most pilots don't practice accelerated stalls. Also, you can make inferences and run the math in your head to guestimate what the critical airspeed will be to cause a stall at a 56-degree bank . . . but isn't it more fool-proof to look at an AoA indicator? I suppose they could create a new AoA-adjusted colored arc to the IAS so that the bottom of the green/white arc moves with AoA. I'm not saying that pilots shouldn't have a general idea of what those critical IAS are for 30-45-60 banks, but in the end it's always going to be less accurate than an AoA indicator.
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I believe he is saying that he is set up to never unintentionally practice accelerated stalls. There's no math in your head, it's just another number.

BTW, 45 degrees is 1.19, call it 1.2 for ease.
 
bflynn said:
I believe he is saying that he is set up to never unintentionally practice accelerated stalls. There's no math in your head, it's just another number.

BTW, 45 degrees is 1.19, call it 1.2 for ease.
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Exactly. My Glasair is far less forgiving and I manuver it far more aggressively than your typical certified SE GA aircraft. It has no stall warning devices at all and I have never come close to stalling unintentionally. It's about knowing your aircraft and what AoB vs speed you need to stay out of.
 
PPC1052 said:
To me the interesting question is what events precipitate a pilot stalling their aircraft. I understand what a stall is, and I suspect the vast majority of pilots do, too. But what I don't understand it how pilots get themselves tripped up to let it happen. Obviously, something is occurring that some pilots are not aware of that is catching them by surprise. What is it? Sure, overloading the wings by pulling too hard when turning base to final due to overshooting is one way. But it can't be the only one.
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I suspect that many people accidentally stall airplanes due to the way pilots typically train for stalls. Other than some basic exposure to what a stall is under some structured conditions defined by the PTS or ACS there typically isn't a ton of time spent on stalls or the recognition of them while learning to fly.

I've ridden with several different rated pilots (people who should know better) who clearly did not understand the basic concepts of stalls outside of what happens in the training environment on a flight review or a checkride. A power on or power off stall was no problem in any of the cases I can recall. Most of the time these guys failed to recognize (feel or see) some of the warning signs that could lead up to a stall when not presented with a textbook airplane configuration. Things such as slow airspeed, high sink rate, buffet, mushy controls, etc. occurred until it was nearly too late and I either helped out or said something. Most or all of the incidents occurred in the traffic pattern too, which coincides with where we seem to see a lot of loss of control accidents.
 
bflynn said:
I believe he is saying that he is set up to never unintentionally practice accelerated stalls. There's no math in your head, it's just another number.

BTW, 45 degrees is 1.19, call it 1.2 for ease.
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Lol, I understand his point. However, for many pilots, remembering "another number" that corresponds to 45-degrees bank, and "another number" than corresponds to 60-degrees bank, then you find yourself banking at 53-degrees and pick a number in between those two "another numbers" you memorized and try to multiply 1.2-1.4 by the stall speed, but wait, I've only got 20-degrees of flaps instead of 30, so the stall speed is higher than the bottom of the white arc, with a conversion to CAS in there somewhere . . . see where I'm going? If you want to apply 40% to your stall speed, and you know that number by heart for every configuration you might be in, while simultaneously communicating with ATC in a busy traffic environment, great. The AoA/stall horn/buffet should all provide that information to you in an instant without having to account for several variables (gear position, IAS/CAS, flaps, etc). One would hope that the buffet/mushy controls gets someone's attention, but with the number of low-altitude LOC accidents, it apparently isn't enough for many.

I'm not saying that an AoA is going to automatically save all of GA from that type of accident, I'm just saying it would provide more instantaneous information than trying to make inferences and incorporate fudge factors when it comes to predicting stalls. Of course practicing for these situations is always better in terms of training, but there's likely a sense of disconnect when practicing accelerated stalls in a made-up scenario at 3K' AGL versus 500' AGL in the pattern. If many pilots aren't practicing accelerated stalls or incipient spins, they don't have much of a catalogue of knowledge with which to draw from regarding speeds/buffeting when they never operate near that limit of the envelope.
 
saddletramp said:
One of the major causes of low altitude stall/spin accidents are from "buzzing". A pilot attempts to show off to people on the ground, flies low, pulls too many G's. & the rest is history.

Other common ones: Divided attention during the approach & taking off beyond the density altitude of the aircraft. It will fly in ground effect giving a false sense that it's going to climb, then stalls out.

Yes, the major cause is the nut behind the wheel.
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Loss of control and stalls are two different things
 
Whaaaa??? This is an odd question for a pilot board.

A stall occurs when airflow is separated from the wing at critical angle of attack. It can happen at any airspeed and attitude. Case in point: What's the most common place to stall an aerobatic airplane while flying a loop? It's not the initial pull or the final 1/4 of the loop. It's the backside - the third quarter. Pull the nose toward the ground too hard as you come back through the horizon, and shudder...there goes the stall.

Oh, and you get maximum troll points for this thread, OP. ;)
 
luvflyin said:
Besides the usual things like angle of bank, G's, CG and all that other stuff that changes the speed at which the stall occurs is inertia.
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As long as everyone is being pedantic here I want to clairify that in my understanding CG does not affect the stall speed. CG location affects the aircraft's stability. Specfically, a center of gravity too far aft will cause the plane to become unstable while a center of gravity too far forward will result in the pilot running out of elevator travel before fully flaring.

bobmrg said:
As the angle of attack nears the critical angle the boundary layer begins to separate from the wing surface at the trailing edge.
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It should be noted that not all airfoils stall at the trailing edge first. It is possible for some airfoils to develop leading edge stall
 
I guarantee that my 180's stall speed is higher when the CG is out of the aft limit. Get slow and the tail starts to drop, increasing the AOA involuntarily. Eye opening.

I'm interested in the turning stall comments about reducing angle of bank. That's a topic to discuss.
 
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