Aerodynamics of the Base to Final stall

One way to stay out of trouble is to always be descending on base to final.
There's no extra safety in that at all. Besides suffering an AoA differential in a descending turn, a steady descent is still a 1G load and the turn increases the load factor a bit. The only time the stall speed will fall is in an increasing rate of descent--a pushover--which can't be maintained. You're then faced with a higher load factor to stop that acceleration.
 
But pushing the nose down in a turn decreases AoA (albeit different amounts right to left), giving you more safety margin--and as you note, increases airspeed a tad. We're not talking a siren-blaring Stuka dive here. If you're a little high on base, you need to lose some altitude anyway.

So you've accelerated a little bit...I'd rather be a little fast than too slow in this phase of flight. Reduce power, trim for 65 KIAS or whatever your over-the-fence speed is, and land as normal. I try for a smooth, continuous descent from abeam the numbers, but it's good to have options.
 
But pushing the nose down in a turn decreases AoA (albeit different amounts right to left), giving you more safety margin--and as you note, increases airspeed a tad. We're not talking a siren-blaring Stuka dive here. If you're a little high on base, you need to lose some altitude anyway.

So you've accelerated a little bit...I'd rather be a little fast than too slow in this phase of flight. Reduce power, trim for 65 KIAS or whatever your over-the-fence speed is, and land as normal. I try for a smooth, continuous descent from abeam the numbers, but it's good to have options.


You'll only reduce the load factor if you keep pushing further over; you'd have to have a flight path that curved more and more downward. 1G flight is sustained only when the airplane is moving in a straight line, whether that's upward, level, or downward. A steady-rate, steady-airspeed descent is 1G, and a turn will only increase it. The idea that there's less loading in a descent is false and misleading and could hurt people who believe it.

From https://www.av8n.com/how/htm/motion.html#sec-straight-line-motion

we read:
Force is Not Motion



As simple as these laws are, they are widely misunderstood. For example, there is a widespread misconception that an airplane in a steady climb requires increased upward force and a steady descent requires reduced upward force.3 Remember, lift is a force, and any unbalanced force would cause an acceleration, not steady flight.

In unaccelerated flight (including steady climbs and steady descents), the upward forces (mainly lift) must balance the downward forces (mainly gravity). If the airplane had an unbalanced upward force, it would not climb at a steady rate — it would accelerate upwards with an ever-increasing vertical speed.

Of course, during the transition from level flight to a steady climb an unbalanced vertical force must be applied momentarily, but the force is rather small. A climb rate of 500 fpm corresponds to a vertical velocity component of only 5 knots, so there is not much momentum in the vertical direction. The kinetic energy of ordinary (non-aerobatic) vertical motion is negligible.

In any case, once a steady climb is established, all the forces are in balance.


See that little "3" at the end of the second sentence? That's a footnote that says:

Troublemakers sometimes point out that lift actually is slightly reduced in a steady descent, since part of the weight is being supported by drag. To this I retort: (a) this is an obscure technicality, based on details of the definitions of the four forces (as given in section 4.1); (b) the magnitude of the reduction is negligible in ordinary flying, (c) the lift is reduced for climbs as well as descents — so this technicality certainly does not explain the motion, and (d) when we consider the total upward force, there is no reduction.


Fast approaches and landings are responsible for too many busted airplanes. Airspeed control is one of the toughest skills to learn and maintain. As a former flight instructor, I had to deal with it all the time. Too many want to pad the airspeed to avoid a stall on approach, and end up porpoising, floating, ballooning, or wheelbarrowing. Damage is almost inevitable if the habit continues.
 
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Hell. Just make straight-in approaches. Problem solved.
Beat me to it! Get rid of the whole darned pattern thingy and no more trouble.

Does this happen with overhead break set-ups?
 
Hell. Just make straight-in approaches. Problem solved.

Beat me to it! Get rid of the whole darned pattern thingy and no more trouble.

Does this happen with overhead break set-ups?

LOL!

You'll only reduce the load factor if you keep pushing further over; you'd have to have a flight path that curved more and more downward. 1G flight is sustained only when the airplane is moving in a straight line, whether that's upward, level, or downward. A steady-rate, steady-airspeed descent is 1G, and a turn will only increase it. The idea that there's less loading in a descent is false and misleading and could hurt people who believe it.

What's the wing loading in a straight down steady-rate, steady-state dive? :)

Sure it's 1G pulling on your face toward the ground, but none of the wing lift is being utilized to stay aloft.

You said "straight line downward" counts, in your statement, so I'm just being a pain in your butt here. :)

I understand what you were trying to convey, but the description using G as a way to describe angle of attack, probably confuses some folks, and has some problems, since you can stall a wing at a wide range of G.

With enough thrust you can even maintain a "straight line" completely stalled, but most of us don't have that kind of thrust on board. Heh.

Sorry, just poking at the analogy. I know what you're trying to say.
 
I agree with 331. I've never used an aoa. I learned in an aeronca champ, flew it for 200 hours, then went to a 180 Cessna, lots of them around then, then to a super twenty one Mooney, which had a stall warning but usually only chirped on final.same with the 201, It went full horn just about at touch down . If you KNOW the airplane your flying, like take it to altitude and stall it a lot, etc. you'll find the aoa is in the seat of your pants. I find it amazing that many are getting an instrument ticket with only say, 200 hours total. They don't know much about how to fly, much less tackle a for real instrument approach! I never got an instrument ticket as I believed I would kill myself and maybe others by not spending enough time staying current flying IFR. Many people I knew had no instrument ticket yet flew all over the United States for years! Several pilots I knew that did have one died for the reason I stated. I should add here that I was taught NEVER to " drag it in" which meant you didn't know how to land correctly and you were asking for trouble!
Good advice. However I believe practing 2 g accelerated stalls is a better exercise. 1 g is seat of your pants, but 2 g is a whole different feeling.
 
So guys, now that the conversation is getting very intelligent I want to ask you your thoughts on the published paper by Prof Rogers. What most guys teach is that airflow is blocked in a slip turn and thus causing the base to final stall. However in the original post, it doesn't mention any of that. Have we been teaching the wrong thing?
 
I never noticed it during the first read but the good professor completely ignores something we all know quite well about our typical trainers.

They want to nose down significantly when they stall.

I got to thinking about this when thinking how difficult it is to get the typical Cessna to start a spin from being cross controlled power off. It takes bloody forever and you have to haul back on the yoke.

Thus in the typical stall spin base to final turn in a Cessna, the real trigger for the spin can't be the slow airspeed or the cross controlling by itself. It has to be maintained and you have to PUUUUUUULL to start the spin.

Before that if you quit pulling, you'll just get a wing drop.

This, of course, doesn't cover our less well behaved bretheren aircraft, but in a Cessna trainer... the pull is needed to get rotation started USUALLY. (I'll couch it.)

And that pull... probably has to be from panic. The ground is too close, the stall horn came on, or the airspeed indicator reads way lower than someone expected it to when they looked.

Let the nose fall, like it wants to, and the cross controlling becomes a lot less of an issue instantly.

Thus, the good professor's math is right, and all that. But he forgot that MOST trainers don't really want to
remain stalled in that cross controlled state. They want to pitch down and recover on their own. And they take a hell of a long time to spin. And that requires a heck of a pull without power. The slipstream over the elevator is getting weaker and weaker and weaker.

By the time you're finding yourself with the yoke in your lap and the ailerons and rudder that cross controlled, the airplane gave you enough hints that a Mack truck hitting you probably wouldn't get your attention.

Now your Cirri you fly Maui, I can't speak for. And you can't legally go find out, so if an AoA makes you feel better, I'm not going to argue.

If it's legally capable of spins, I *want* to spin it. Because I want to know what it really takes to get it to go and rotate. A Cessna in the pattern? It's not going to spin easily, you're going to have to force the issue and hold those controls there quite a while to get past a wing drop.

Still doesn't mean it wouldn't scare the hell out of someone who's never seen it, and probably means they MIGHT pull real hard and make things worse. But I think that's the real killer in the docile stuff like Cessnas... the panic pull. It's pretty much a requirement to get rotation started power-off.

Power on, you usually need a climbing turn away from the direction you want to spin to really get any sort of "fast" entry, and it's still not very fast. It'll go left faster than right by far, and some you'll struggle to even get them to go right. All the left turning tendencies work against you. If it's really badly rigged it'll just plow ahead and it won't rotate. You won't have enough right rudder to get the yaw needed to start unless you whipsaw it a bit by accelerating the stall.

So ... how does that relate to what we teach? I don't know, but the good professor forgot to discuss a number of things real trainers do in his discussion of the angle of attack of the wing. Running out of elevator and rudder authority in most trainers is a real thing when trying to get them to spin.
 
Down where you guys fly is it raining airplanes on the approach end of your airfields? Where is all this base to final turn stall focus coming from? Power-out return to airport turns seem more valid. Moose stalls if you're a Cub driver.
 
Maintain they airspeed lest the ground rise up and smite thee.

As far as devices, when I help pilots with problems in the pattern I have a pocket full of sink stoppers.
They become able to fly the airplane by attitude, altimeter, and power setting - and a gorgeous array of sink stoppers covering most everything else.
If you have to have an airspeed indicator to competently land the typical GA, 4 seat aircraft, then you are an airplane driver not a pilot.

Does that mean I sneer at instruments? Hell no. I am an instrument rated pilot.
But there is a basic level of airman-ship that is no longer taught - mostly because the CFI's are not taught during their training.
 
Thus, the good professor's math is right, and all that. But he forgot that MOST trainers don't really want to
remain stalled in that cross controlled state. They want to pitch down and recover on their own. And they take a hell of a long time to spin. And that requires a heck of a pull without power. The slipstream over the elevator is getting weaker and weaker and weaker.

And that docility is where pilots get burned. They learn in a 172, which is hard to get to spin, or in a Warrior or Archer, which doesn't even want to stall. They get their PPL and go and buy something they can afford--an old Champ, maybe, and the first time they skid the thing around the base-to-final like they did the trainer, it kills them.
 
And that docility is where pilots get burned. They learn in a 172, which is hard to get to spin, or in a Warrior or Archer, which doesn't even want to stall. They get their PPL and go and buy something they can afford--an old Champ, maybe, and the first time they skid the thing around the base-to-final like they did the trainer, it kills them.

T'is probably true.

The last guy to auger in because of a low level stall (and probably accelerated) around here owned an Aerostar. Not too forgiving of his high speed low level antics. Killed him while buzzing an airline buddy's house who was literally yelling from the ground at him not to do it.

You just can't make this stuff up.
 
I never noticed it during the first read but the good professor completely ignores something we all know quite well about our typical trainers.

They want to nose down significantly when they stall.

I got to thinking about this when thinking how difficult it is to get the typical Cessna to start a spin from being cross controlled power off. It takes bloody forever and you have to haul back on the yoke.

Thus in the typical stall spin base to final turn in a Cessna, the real trigger for the spin can't be the slow airspeed or the cross controlling by itself. It has to be maintained and you have to PUUUUUUULL to start the spin.

Before that if you quit pulling, you'll just get a wing drop.

This, of course, doesn't cover our less well behaved bretheren aircraft, but in a Cessna trainer... the pull is needed to get rotation started USUALLY. (I'll couch it.)

And that pull... probably has to be from panic. The ground is too close, the stall horn came on, or the airspeed indicator reads way lower than someone expected it to when they looked.

Let the nose fall, like it wants to, and the cross controlling becomes a lot less of an issue instantly.

Thus, the good professor's math is right, and all that. But he forgot that MOST trainers don't really want to
remain stalled in that cross controlled state. They want to pitch down and recover on their own. And they take a hell of a long time to spin. And that requires a heck of a pull without power. The slipstream over the elevator is getting weaker and weaker and weaker.

By the time you're finding yourself with the yoke in your lap and the ailerons and rudder that cross controlled, the airplane gave you enough hints that a Mack truck hitting you probably wouldn't get your attention.

Now your Cirri you fly Maui, I can't speak for. And you can't legally go find out, so if an AoA makes you feel better, I'm not going to argue.

If it's legally capable of spins, I *want* to spin it. Because I want to know what it really takes to get it to go and rotate. A Cessna in the pattern? It's not going to spin easily, you're going to have to force the issue and hold those controls there quite a while to get past a wing drop.

Still doesn't mean it wouldn't scare the hell out of someone who's never seen it, and probably means they MIGHT pull real hard and make things worse. But I think that's the real killer in the docile stuff like Cessnas... the panic pull. It's pretty much a requirement to get rotation started power-off.

Power on, you usually need a climbing turn away from the direction you want to spin to really get any sort of "fast" entry, and it's still not very fast. It'll go left faster than right by far, and some you'll struggle to even get them to go right. All the left turning tendencies work against you. If it's really badly rigged it'll just plow ahead and it won't rotate. You won't have enough right rudder to get the yaw needed to start unless you whipsaw it a bit by accelerating the stall.

So ... how does that relate to what we teach? I don't know, but the good professor forgot to discuss a number of things real trainers do in his discussion of the angle of attack of the wing. Running out of elevator and rudder authority in most trainers is a real thing when trying to get them to spin.
I can't really argue with your thoughts. The professor was looking at the physics of what was going on, and the whole reason I posted it was to get in a debate about what "old school" guys teach which is blocked airflow in a slip causing the stall spin, versus the vector mathematics of relative wind and thus increase in AoA on the descending wing.

Because when I map this out in my lizard brain, you don't need to slip to kill yourself, you can stall it in coordinated flight just by the increase in load factor as the wing can't provide the lift required. Therefore the whole thing about blocked airflow from the fuselage is bunk. I'd like to open the floor (just give me a second while I put on my flack jacket). Am I missing something? Chime in.
 
The professor was looking at the physics of what was going on, and the whole reason I posted it was to get in a debate about what "old school" guys teach which is blocked airflow in a slip causing the stall spin, versus the vector mathematics of relative wind and thus increase in AoA on the descending wing.

Because when I map this out in my lizard brain, you don't need to slip to kill yourself, you can stall it in coordinated flight just by the increase in load factor as the wing can't provide the lift required. Therefore the whole thing about blocked airflow from the fuselage is bunk. I'd like to open the floor (just give me a second while I put on my flack jacket). Am I missing something? Chime in.

The explanation in the paper you posted in your original post is the same explanation I've seen everywhere else, including the 1980 edition of the Flight Training Handbook (and probably older editions as well, which I do not possess). It's not new.

I don't know what you are talking about when you say the industry used to teach blocked airflow during a slip is what causes spins. Slips generally don't cause spins. Do you know the difference between a slip and a skid?
 
The explanation in the paper you posted in your original post is the same explanation I've seen everywhere else, including the 1980 edition of the Flight Training Handbook (and probably older editions as well, which I do not possess). It's not new.

I don't know what you are talking about when you say the industry used to teach blocked airflow during a slip is what causes spins. Slips generally don't cause spins. Do you know the difference between a slip and a skid?
Doh! I meant to say skid. Tired from being up most of the night with new puppies.
Here is the video of which I refer to, what are your thoughts?
 
The explanation in the paper you posted in your original post is the same explanation I've seen everywhere else, including the 1980 edition of the Flight Training Handbook (and probably older editions as well, which I do not possess). It's not new.

I don't know what you are talking about when you say the industry used to teach blocked airflow during a slip is what causes spins. Slips generally don't cause spins. Do you know the difference between a slip and a skid?
In this diagram it shows the same thing. It does not talk about receding airflow and receding velocity causing the rise in AoA. it says relative wind is changed or blocked by the fuselage.http://apstraining.com/traffic-pattern-stalls/
 
T'is probably true.

The last guy to auger in because of a low level stall (and probably accelerated) around here owned an Aerostar. Not too forgiving of his high speed low level antics. Killed him while buzzing an airline buddy's house who was literally yelling from the ground at him not to do it.

You just can't make this stuff up.
If you read the accident report, he had a very high BAC which probably contributed to both the antics and his inability to recover.
 
Ugh. Hadn't read that. Even worse.

https://app.ntsb.gov/pdfgenerator/R...ID=20140319X12053&AKey=1&RType=Final&IType=FA

A 1.75-liter bottle of whiskey was found in the airplane wreckage. A review of the pilot’s Federal Aviation Administration medical records revealed that he had a history of alcohol
dependence but had reportedly been sober for almost 4 years. Toxicological testing revealed that the pilot had a blood alcohol content of 0.252 milligrams of alcohol per deciliter of blood, which was over six times the limit (0.040) Federal Aviation Regulations allowed for pilots operating an aircraft.
 
I never noticed it during the first read but the good professor completely ignores something we all know quite well about our typical trainers.

They want to nose down significantly when they stall.

I got to thinking about this when thinking how difficult it is to get the typical Cessna to start a spin from being cross controlled power off. It takes bloody forever and you have to haul back on the yoke.

Thus in the typical stall spin base to final turn in a Cessna, the real trigger for the spin can't be the slow airspeed or the cross controlling by itself. It has to be maintained and you have to PUUUUUUULL to start the spin.

Before that if you quit pulling, you'll just get a wing drop.

This, of course, doesn't cover our less well behaved bretheren aircraft, but in a Cessna trainer... the pull is needed to get rotation started USUALLY. (I'll couch it.)

And that pull... probably has to be from panic. The ground is too close, the stall horn came on, or the airspeed indicator reads way lower than someone expected it to when they looked.

Let the nose fall, like it wants to, and the cross controlling becomes a lot less of an issue instantly.

Thus, the good professor's math is right, and all that. But he forgot that MOST trainers don't really want to
remain stalled in that cross controlled state. They want to pitch down and recover on their own. And they take a hell of a long time to spin. And that requires a heck of a pull without power. The slipstream over the elevator is getting weaker and weaker and weaker.

By the time you're finding yourself with the yoke in your lap and the ailerons and rudder that cross controlled, the airplane gave you enough hints that a Mack truck hitting you probably wouldn't get your attention.

Now your Cirri you fly Maui, I can't speak for. And you can't legally go find out, so if an AoA makes you feel better, I'm not going to argue.

If it's legally capable of spins, I *want* to spin it. Because I want to know what it really takes to get it to go and rotate. A Cessna in the pattern? It's not going to spin easily, you're going to have to force the issue and hold those controls there quite a while to get past a wing drop.

Still doesn't mean it wouldn't scare the hell out of someone who's never seen it, and probably means they MIGHT pull real hard and make things worse. But I think that's the real killer in the docile stuff like Cessnas... the panic pull. It's pretty much a requirement to get rotation started power-off.

Power on, you usually need a climbing turn away from the direction you want to spin to really get any sort of "fast" entry, and it's still not very fast. It'll go left faster than right by far, and some you'll struggle to even get them to go right. All the left turning tendencies work against you. If it's really badly rigged it'll just plow ahead and it won't rotate. You won't have enough right rudder to get the yaw needed to start unless you whipsaw it a bit by accelerating the stall.

So ... how does that relate to what we teach? I don't know, but the good professor forgot to discuss a number of things real trainers do in his discussion of the angle of attack of the wing. Running out of elevator and rudder authority in most trainers is a real thing when trying to get them to spin.

This is a great point. A CFI once told me that virtually all base to final stall spins are created when a pilot forgets about wind drift, gets blown off a desired ground track(usually blown away from the landing edge of the runway), attempts to correct the now two problems he has( too low relative to the intended landing spot and off course) and pulls back on the yoke, while increasing the bank angle. This is where the pilot gets himself in trouble. The increase in bank of the wings increases the speed at which a stall will occur at the same time as the pilot is decreasing airspeed-- I always use the visual of two hands of a clock to imagine what is happening in this scenario as both hands are moving closer to each other.). At that point, where those two hands cross over, the plane will stall and a spin will happen because one wing has stalled.

My question though that I've never been able to totally figure out in my own mind is, what happens first, the stall or the spin? My understanding as a 320 hour PPL is a spin is created by one wing stalling before the other. Does that mean though, that the other wing has not yet stalled thus meaning the entire plane has not yet stalled or is this just a semantical argument and once one wing has stalled the entire plane is stalled? It's also possible I have all this wrong and if so please help me out!
 
This is a great point. A CFI once told me that virtually all base to final stall spins are created when a pilot forgets about wind drift, gets blown off a desired ground track(usually blown away from the landing edge of the runway), attempts to correct the now two problems he has( too low relative to the intended landing spot and off course) and pulls back on the yoke, while increasing the bank angle. This is where the pilot gets himself in trouble. The increase in bank of the wings increases the speed at which a stall will occur at the same time as the pilot is decreasing airspeed-- I always use the visual of two hands of a clock to imagine what is happening in this scenario as both hands are moving closer to each other.). At that point, where those two hands cross over, the plane will stall and a spin will happen because one wing has stalled.

My question though that I've never been able to totally figure out in my own mind is, what happens first, the stall or the spin? My understanding as a 320 hour PPL is a spin is created by one wing stalling before the other. Does that mean though, that the other wing has not yet stalled thus meaning the entire plane has not yet stalled or is this just a semantical argument and once one wing has stalled the entire plane is stalled? It's also possible I have all this wrong and if so please help me out!
according to the faa, both wings must be stalled before a spin can occur. One wing may be more deeply stalled than the other, or one may resume providing lift after the spin begins.
An airplane must be stalled and yawed in order to enter a spin
from page 14 https://www.faa.gov/regulations_pol...iation/airplane_handbook/media/06_afh_ch4.pdf

This was also a question on my written test. The answer was "both wings must be stalled for a spin to occur".

Even in the picture, they are careful to say "less stalled"
IMG_0016.PNG
 
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according to the faa, both wings must be stalled before a spin can occur. One wing may be more deeply stalled than the other, or one may resume providing lift after the spin begins. from page 14 https://www.faa.gov/regulations_pol...iation/airplane_handbook/media/06_afh_ch4.pdf

This was also a question on my written test. The answer was "both wings must be stalled for a spin to occur".

Even in the picture, they are careful to say "less stalled"
View attachment 50849

Thanks for this. However aerodynamically how can one wing be "less stalled?" Either a wing has stalled and is providing no more lift or it is still providing lift and thus not yet stalled? With respect to a spin-- I get that the wings are not equally producing lift but with respect to the idea of what a stall is--one wing seems to have stalled first.
 
if the load and angle of attack are different between the wings (airfoils)....then the capacity to develop lift will not be equal. An imbalance of lift between the wings....creates roll and pitch changes....and the spin entry.

CL_expdata.jpg
 
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Thanks for this. However aerodynamically how can one wing be "less stalled?" Either a wing has stalled and is providing no more lift or it is still providing lift and thus not yet stalled? With respect to a spin-- I get that the wings are not equally producing lift but with respect to the idea of what a stall is--one wing seems to have stalled first.
This misconception stems from assuming a stall cuts out all lift. It doesn't. As flow separates from the top of the wing, you lose the low pressure zone (it sucks on air, rather than your wing), and you lose somewhere around half the lift in the separated zone. Flow does not separate on the entire wing at once. In a straight wing aircraft, it generally starts at the roots and progresses outward. The two wings need not be symmetrical, and if they aren't, you'll dip a wing. It will get worse if you force additional flow separation at one aileron by trying to correct wing dip with it.
 
This misconception stems from assuming a stall cuts out all lift. It doesn't. As flow separates from the top of the wing, you lose the low pressure zone (it sucks on air, rather than your wing), and you lose somewhere around half the lift in the separated zone. Flow does not separate on the entire wing at once. In a straight wing aircraft, it generally starts at the roots and progresses outward. The two wings need not be symmetrical, and if they aren't, you'll dip a wing. It will get worse if you force additional flow separation at one aileron by trying to correct wing dip with it.

Ok thanks this makes more sense to me.
 
So excuse my ignorance, if I'm on final, with the wind right down the runway, and I'm high, which happens, if I input right rudder, left aileron, I'm I slipping or skidding? What about left rudder, right aileron? Either one succeeds in getting me down faster.
 
So excuse my ignorance, if I'm on final, with the wind right down the runway, and I'm high, which happens, if I input right rudder, left aileron, I'm I slipping or skidding? What about left rudder, right aileron? Either one succeeds in getting me down faster.

In a skidding turn, the rudder is acting in the direction of turn. In a slipping turn, it's acting opposite to the direction of turn.

In other words, highly simplified, to remember which rudder to use in a base to final turn if you're trying to increase the sink rate aerodynamically, "step on the sky"...

Rudder in the direction of the high wing will enter a slip, not a skid, if the controls remain crossed.
 
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