Yoke deflection, load factor & stall

[gismo]

In a steep bank, the tail on a Cessna 172 at slow speeds is way out back behind the CG which is tangent to the turn's flight path. This means the local airflow strikes the elevator more from below than in straight and level flight, robbing it of authority. It's less capable of causing a stall, even though it may, but the yoke will be further back. The loss of authority can be replaced with additional power.

I'm not sure I'm following you here. In a coordinated turn the airflow over the tail (excluding the rather slight variation from one side to the other due to different radii) is the same as it would be in straight/level flight if you increased the weight of the airplane to match the load in the turn. The tail in that level flight would be lower than it would be at the original weight just as the tail will fly a slightly greater radius than the main wing in the turn. The AoA on the wing and the tail and the elevator authority would be the same in the turn and loaded level flight. In both cases the relative wind would indeed be coming more from below but that's exactly why a given amount of nose up elevator produces a specific AoA (with the same CG). When you raise the elevator the airplane rotates about the CG until the AoA decreases on the tail until the downward force decreases enough to balance the pitch couple (torque on the lateral axis). The absolute tail downforce changes slightly unless the CG matches the location of the aerodynamic center.

 

[bbchien]

This is an example of a guy with no experience trying to do this theoretically. Lance you efforts were magnificent. I think.like MAKG, that Swave needs to go out and do some dual.

Now he's thinking about inverted stalls. Like you're going to do that in a 172. Are we now going to consider a Pitts? When does this stop? Is the Xmas tree down yet?

 

[dtuuri]

I'm not sure I'm following you here.

You can see what I'm describing by taking a ballpoint pen and "flying" it around the top of a coffee cup. Place a tab of paper under the clip to simulate the horizontal tail surface and bank it near 90° (for drama). Make it lag as far as you can with the "propeller" end in contact with the cup. It'll be obvious that there's a tendancy for the relative wind to flow from the outside of the turn, so more up deflection is required to get the job done. That's fine--until the elevator hits the stop. If you were in straight and level under a similar load, like you describe, the relative wind would be coming from the horizon not from below it (the elevator) like in the steep turn. So, there is more 'authority' in straight flight than in a bank.

dtuuri

 

[gismo]

You can see what I'm describing by taking a ballpoint pen and "flying" it around the top of a coffee cup. Place a tab of paper under the clip to simulate the horizontal tail surface and bank it near 90° (for drama). Make it lag as far as you can with the "propeller" end in contact with the cup. It'll be obvious that there's a tendancy for the relative wind to flow from the outside of the turn, so more up deflection is required to get the job done. That's fine--until the elevator hits the stop. If you were in straight and level under a similar load, like you describe, the relative wind would be coming from the horizon not from below it (the elevator) like in the steep turn. So, there is more 'authority' in straight flight than in a bank.

dtuuri

Still don't see it. The relative wind doesn't know about "centrifugal force" and I'm pretty certain that if the airplane is generating 2000 lb of lift at 100 KCAS the airflow over the wings and tail is identical whether or not the plane is turning. Yes if you put the spinner on a circle and make the angle between the line from nose to tail tangent to that circle, the tail will be flying a circle with greater radius. But I believe a better mental image has the airplane's CG or AC on the "primary" circle and the tail could be on a bigger or smaller circle depending on the configuration. A low wing airplane with a T tail (Lance, Tomahawk, etc) would put the tail on a smaller circle than the wing unless the AoA exceeded the angle between the wing's chord and the line from wing to tail. In any case with any non-aerobatic bank angle in a 172 the difference between the radii is going to be awfully small and for the most part inconsequential.

 

[dtuuri]

Still don't see it.

If the horizontal tail surface is where the CG is then the relative wind is like a plane in straight and level flight--directly from in front. Slide it back from there on a long boom (fuselage) and it rides in a crosswind from the outside. The tighter the turn the more pronounced, slow and steep being the greatest.

Yes, the tail follows a wider radius, but that's irrelevant. Even a T-tail high enough to have the same radius as the CG would still experience a cross-flow from the outside. Imagine the T-tail parallel with the wing (which is located at the CG and tangent to the turn); being behind, but on the same arc, the flow is still from the outside.

Have you ever gone up to demonstrate how the stalling speed is higher in a steep bank only to find the airplane absolutely refuses to stall like the books claim it should? I have. Yet some accidents are clearly caused that way. Perhaps those pilots used more prop blast than in my failed demos, offsetting the loss of elevator authority due to the boom effect.

dtuuri

 

[Richard_SWave]

Now he's thinking about inverted stalls. Like you're going to do that in a 172. Are we now going to consider a Pitts?

What's so wrong with that? I said very clearly that I thought an aerobatic airplane that really I have no experience. You'll say now that until I get to fly on one so I have no right to know anything or what? Instead it would be useful to help more than you like to comment meaningless.

I asked it about inverted stall exactly because I don't have the possibility to practice them too soon. If you don't want to help, no problem, but please don't write for the sake of adding useless comments.

 

[EdFred]

What is your "in the air" experience?

 

[MAKG1]

What's so wrong with that? I said very clearly that I thought an aerobatic airplane that really I have no experience. You'll say now that until I get to fly on one so I have no right to know anything or what? Instead it would be useful to help more than you like to comment meaningless.

I asked it about inverted stall exactly because I don't have the possibility to practice them too soon. If you don't want to help, no problem, but please don't write for the sake of adding useless comments.

Nothing is "wrong" with it, but you're seriously handicapping yourself without it. I work regularly with aerodynamicists and simulation experts. Understanding the stall in detail is an exercise in turbulent boundary layers. That's a heroic calculation at best, but you're treating it like a back-of-the-envelope trivial calculation. In real life, these things are done in wind tunnels and by test pilots.

 

[Richard_SWave]

Understanding the stall in detail is an exercise in turbulent boundary layers. That's a heroic calculation at best, but you're treating it like a back-of-the-envelope trivial calculation.

I think any aerobatic pilot with some experience can tell me, if he wants, how an aircraft reacts when you push the yoke all the way and if it's the same behaviour as for a normal stall. As you can see, I got some answers here. All I wanted is help from those ppl if it's the same for an inverted stall.

 

[LDJones]

Inverted behavior will be far different from normal behavior since the wing is designed for normal flight. Inverted aren't you flying more on impact lift and brute force than Bernoulli?

 

[RoscoeT]

I think any aerobatic pilot with some experience can tell me, if he wants, how an aircraft reacts when you push the yoke all the way and if it's the same behaviour as for a normal stall. As you can see, I got some answers here. All I wanted is help from those ppl if it's the same for an inverted stall.

Dude stop the endless arguing with experienced pilots on the internet and just get some experience. You are way over thinking everything and your questions will become self-evident as you get more experience. How many hours do you have right now?

To answer your question - the laws of physics don't change just because you stall an airplane under negative G vs. positive G. Spam cans likely don't have the down elevator authority to stall at negative G, but aerobatic airplanes do. Why do you bring up negative G stalls? A stall is a stall. The airplane doesn't care whether you pull or push.

 

[flyingron]

Pilots tend to think that lift pretty much falls to zero when the wing stalls but if you look at a typical trainer coefficient of lift vs AoA curve you'll see that the C of L barely drops as the AoA increases slightly beyond the critical AoA. What actually happens that creates that "bottom dropping out" feeling is that when the wing stalls the slight decrease in wing lift causes the lift to be less than what's needed to offset the airplane's weight and as the wing drops, the AoA is increased because the direction of the relative wind shifts due to the wings downward motion.

I do not believe lift falls to zero. I know all that. In fact, the lift curve is pretty symmetrical about the stall point. The stall is the place where it changes direction.

My argument was DTURI's bizarre statement that you "run out of elevator, the nose drops, INCREASING AOA and causing a stail." He still hasn't explained it.

I'm not talking about the AIRPLANE sinking, I'm trying to understand how running out of UP elevator authority where the nose then drops (the NOSE MIND YOU NOT THE AIRPLANE) causes any INCREASE in AOA.

 

[Richard_SWave]

Spam cans likely don't have the down elevator authority to stall at negative G, but aerobatic airplanes do.

That finally answers a question, thanks God that among some of your insults and useless comments I've finally managed to get some answers about what interested me.

 

[flyingron]

An extreme example would be a whip stall.

Nope. A whip stall would cause the nose to continue to rise and increase AOA.
It's not what you described in your message.

I can bank left, yet turn right. It takes more lift to go down than go up--due to the upward component of thrust. You can enter a stall maintaining straight and level flight at a constant weight and increasing angle of attack, but have no increase in lift--it's still just enough to balance weight (or less due to the upward component of thrust).

You seem to have a basic lack of physics. You use lift and CLIMB as if they are synonyms. If you increase AOA there IS an increase in lift. You may not climb depending on what other forces are in play.

The CG is at the end of the turn's radius. The tail (and spinner) are not.

Ture.

The tail goes around like a telephone pole sticking out of the bed of your truck. A flag on the end would be blown to the inside of the turn.

Negative. The relative wind is the direction the flag is moving which due to the fact that the truck is sitting with four wheels on the ground (let's assume), the "relative" wind is still mostly along the longitudinal axis of the truck/pole. However, the free end of that flag wants to continue in a straight line while the force of the truck tires are forcing the truck to turn. The flag will tend towards the OUTSIDE of the turn.

 

[dtuuri]

Nope. A whip stall would cause the nose to continue to rise and increase AOA.
It's not what you described in your message.

Perhaps an illustration would help you out: http://www.youtube.com/watch?v=Ee4PYDOBDNM

You seem to have a basic lack of physics. You use lift and CLIMB as if they are synonyms. If you increase AOA there IS an increase in lift. You may not climb depending on what other forces are in play.

There is an increase in lift coefficient, not necessarily lift.

The relative wind is the direction the flag is moving which due to the fact that the truck is sitting with four wheels on the ground (let's assume), the "relative" wind is still mostly along the longitudinal axis of the truck/pole. However, the free end of that flag wants to continue in a straight line while the force of the truck tires are forcing the truck to turn. The flag will tend towards the OUTSIDE of the turn.

Go try it and you'll see. I'll wait.

dtuuri

 

[RoscoeT]

That finally answers a question, thanks God that among some of your insults and useless comments I've finally managed to get some answers about what interested me.

I don't think I said anything insulting, but you need to understand that you're coming across as a bit argumentative. And considering your (apparently very low, though non-admitted) experience level compared with others here, you should take many of the comments for what they are worth, leave it at that, and stop worrying about intellectualizing such theoretical minutia when you'll get a much better sense of all this through experience. Maybe you are simply earnestly trying to understand flight dynamics and simply asking more questions, rather than questioning the accuracy of what some are stating. Hard to tell sometimes on a forum like this.

Why are some airplanes (I think aerobatic planes) more likely to have a hard wingover if you pull hard on yoke and have an accelerated stall? Is the fact that they get more uncoordinated when you pitch up? Or is there a design factor? I figure out this won't happen if the pilot kept it perfectly coordinated, right?

Airplanes are all different. Some airplanes are designed (by various means) to allow the inboard wing section to stall before the wingtips. This builds in stability into the stall. Other airplanes (and not just aerobatic ones) have a wing design that stalls all at once, rather than progressively across the length of the wing. These airplanes may display more of the "hard wingover" that you describe. I assume you are simply describing the serverity and sharpness of a wing drop during a stall. You can prevent wing-drop during straight and level stalls in most airplanes (even aerobatic ones) through proper coordination and rudder use during the stall. During turning stalls, many will roll sharply even if you are perfectly coordinated. The AoA between both wings during a coordinated turn is not equal, which causes a wing-drop during a coordinated turning stall.

And don't go pushing hard on the yoke just because you may not have the elevator authority to stall at negative G. Depending on your speed, you still may have plenty of elevator authority to overstress the airplane. Keep in mind that many non-utility category airplanes have negative G limits under 2 negative G. That's not much.

 

[Richard_SWave]

Maybe you are simply earnestly trying to understand flight dynamics and simply asking more questions, rather than questioning the accuracy of what some are stating.

That's right.

During turning stalls, many will roll sharply even if you are perfectly coordinated. The AoA between both wings during a coordinated turn is not equal, which causes a wing-drop during a coordinated turning stall.

This is interesting, but a little confusing for me. I hope it causes just a wingdrop and not further an incipient spin. I guess if coordinated flight is not enough to prevent a wingdrop in a turning stall, is it necessary a little opposite rudder if you want to keep it straight?
I was thaught to keep the ball centered even when I practiced stall during turns.

 

[MAKG1]

There are some OK figures in the PHAK (and probably some better ones in Rod Machado's book) about the balance of forces in a turn. But BE CAREFUL accepting aerodynamics from pilots without question. You can be a very good pilot with a mediocre understanding of aero. As an example, witness the above argument about which way a "flag" tied to the back of an airplane would blow in a turn. Neither party apparently realized all functional aircraft have just such a flag attached, called a "vertical stabilizer" and that there are multiple types of turns. Rudder correction to a coordinated turn is a direct measurement of which way the wind is blowing on the tail. Not all turns require inside rudder. A common example is a departure (full power, climbing as fast as possible) turn to the left.

An airplane is a dirty system that really doesn't lend itself well to simplification. For instance, the rudder doesn't really just yaw the aircraft, but will roll it as well.

 

[RoscoeT]

This is interesting, but a little confusing for me. I hope it causes just a wingdrop and not further an incipient spin. I guess if coordinated flight is not enough to prevent a wingdrop in a turning stall, is it necessary a little opposite rudder if you want to keep it straight? I was thaught to keep the ball centered even when I practiced stall during turns.

Realize that a dropping wing does NOT necessarily mean the airplane is entering an incipient spin. Many equate a wing drop with a spin entry. Not necessarily. You can react with rudder to more quickly control the wing drop, but it's virtually impossible to produce a spin entry in an airplane if you stall with the ball centered, even if a wing snaps over hard. As soon as you release back pressure and unstall the wing, you will be able to use the ailerons to level the airplane. It's just that DURING the stall, the rudder can be used to control the severity of the wing drop, and is good technique. But rudder would only be REQUIRED to recover from an actual spin entry. A spin requires a substantial amount of yaw to produce enough lift differential between both wings to produce a spin. If you are flying with the ball in the center, there is very little yawing force present, and you will not spin.

Go up with an instructor and do some turning (accelerated) stalls with the ball centered. When it stalls and drops a wing, keep the yoke back and keep the ailerons and rudder neutral. The airplane may wallow around, but it will not spin. I assume you have not done spin training yet. When you do, you will see the difference between a "wallowing" stall, a spiral, and an actual spin.

 

[Richard_SWave]

Ok, I thought The AoA between both wings during a coordinated turn is not equal, which causes a wing-drop during a coordinated turning stall is enough to induce an incipient spin.

Actually I've done few spins during my PPL training, but far not addressed so detailed. Actually it was more my theoretical lack of understanding here, practicing them it would be hard to figure out exactly what causes what.

 

[RoscoeT]

Ok, I thought The AoA between both wings during a coordinated turn is not equal, which causes a wing-drop during a coordinated turning stall is enough to induce an incipient spin.

Yes, lift differential causes the wing drop during a coordinated accelerated stall, but without a significant yawing force, the dynamics just don't get set up such that the airplane settles into autorotation associated with an actual spin. You know it's an autorotating spin (and not a spiral) when bringing the yoke/stick forward from the aft position does not slow or stop the rotation. You also know it's a spin if applying aileron opposite the direction of roll aggravates the rotation.

In reality, you may not know whether you've got a simple wing drop, a spiral, or an autorotating spin unless you actually wait to see what happens. If you stall with the ball centered, and hold neutral rudder and aileron and full aft elevator and WAIT...what you will observe will not be an autorotating spin. But this is academic. At low altitude, you will not sit there and wait to see what happens. You want to recover the airplane ASAP with as little altitude loss as possible. The recovery inputs between a simple wing drop and an actual spin entry are the same - neutral aileron, full rudder opposite the roll, move the elevator to break the stall, neutralize rudder, then level wings (if required) with aileron only after the stall is broken and a little airspeed is regained.

Much of the dynamics are lost on students in the PPL training environment, since you are trained to recover the airplane at the FIRST indication of a stall. Unless you do spin training, this does not allow things to develop to the point of showing the student what is actually happening. And this, of course, leads right into the whole stall prevention vs. spin training debate.

 

[Richard_SWave]

The recovery inputs between a simple wing drop and an actual spin entry are the same - neutral aileron, full rudder opposite the roll

For an incipient spin entry I understand, but why full rudder opposite the roll for a simple wing drop? Before you apply that the ball is centered, when you apply it the ball will offset, thus yaw and actually you force it to enter a spin opposite way, am I right or what am I missing?

 

[RoscoeT]

For an incipient spin entry I understand, but why full rudder opposite the roll for a simple wing drop? Before you apply that the ball is centered, when you apply it the ball will offset, thus yaw and actually you force it to enter a spin opposite way, am I right or what am I missing?

You must understand that it's a very quick, momentary rudder application-and-neutralize movement. If your wing is dropping, full rudder will stop the drop quicker than a small rudder input. Yawing the airplane against the wing drop quickly equalizes the AoA between both wings, and the roll stops. It doesn't matter what the ball momentarily says. And skid balls have flaws anyway. Unless mounted perfectly on the exact roll axis of the airplane, they're really only giving you a perfect indication when the airplane is not in the process of rolling. You will be a better pilot if you learn not to worship the ball, but rather feel in your seat whether you are coordinated or not. This lets you keep your eyeballs outside the cockpit where they belong, and gives you a better "feel" for the airplane, which will make you a better "stick-and-rudder" pilot.

And you will only enter a spin in the opposite direction if you keep holding the dern rudder input after the roll stops WHILE maintaining too much aft stick/yoke. In other words, only if you are hamfooted/fisted. Once you've moved the elevator forward and broken the stall, all continued rudder input will do at that point is yaw the airplane severely. It won't spin unless you are still holding too much elevator.

Ever do falling leaf maneuvers? The very quick rudder inputs involved in controlling wing drop will make much more sense if you do those.

 

[Richard_SWave]

Watching leaf maneuvers and reading your post it makes some sense, however, I figure out the recommended technique is to keep coordinated, unstall, and after that you roll level using ailerons. At least this is what I was thaught. If it's wrong, please let me know.

 

[EdFred]

How many flight hours do you have? What ratings?

 

[Richard_SWave]

About 120 hrs, PPL, if you insist so much. Heading towards CPL.

 

[RoscoeT]

I figure out the recommended technique is to keep coordinated, unstall, and after that you roll level using ailerons.

The term "coordination" is completely meaningless and should not be applied or thought of while the airplane is stalled. "Coordination" applies to unstalled flight, and simply means that the airplane's total lift vector is perfectly perpendicular to the wings of the airplane, regardless of its bank attitude. The objective during a stall is to return to straight-and-level flight ASAP. Again, coordination during a stall is meaningless, and you shouldn't even consider "coordination" in this context. Max efficiency stall recovery may require a quick full rudder input. That does not mean you are "uncoordinated", or that you are doing something wrong. Once the airplane has departed controlled flight, you need to put any thought of "coordination" out of your mind. You need to look out the windshield and do whatever is required to recover the airplane as quickly as possible.

I should stop, I've said enough.

 

[MAKG1]

Watching leaf maneuvers and reading your post it makes some sense, however, I figure out the recommended technique is to keep coordinated, unstall, and after that you roll level using ailerons. At least this is what I was thaught. If it's wrong, please let me know.

No. The recommended "maneuver" is PARE. It's in your POH and in the PTS. You're still a student pilot, aren't you?

Power to idle
Ailerons neutral
Rudder opposite rotation/roll
Elevator forward

Do NOT use aileron to correct a dipped wing. You can stall the upward pointing aileron (which is the OUTSIDE one under these circumstances), for a really fun ride. It's really fun for power-on stalls in a 182 (which seem to always dip wings during high power stalls, due to the really strong P-factor).

 

[MAKG1]

The term "coordination" is completely meaningless and should not be applied or thought of while the airplane is stalled. "Coordination" applies to unstalled flight, and simply means that the airplane's total lift vector is perfectly perpendicular to the wings of the airplane, regardless of its bank attitude. The objective during a stall is to return to straight-and-level flight ASAP. Again, coordination during a stall is meaningless, and you shouldn't even consider "coordination" in this context. Max efficiency stall recovery may require a quick full rudder input. That does not mean you are "uncoordinated", or that you are doing something wrong. Once the airplane has departed controlled flight, you need to put any thought of "coordination" out of your mind. You need to look out the windshield and do whatever is required to recover the airplane as quickly as possible.

I should stop, I've said enough.

Actually, coordination is about the total WEIGHT vector. Weight is not antiparallel to lift during climbs, descents, or turns as it is during straight and level flight. And we measure it with a ball level.

 

[RoscoeT]

Actually, coordination is about the total WEIGHT vector. Weight is not antiparallel to lift during climbs, descents, or turns as it is during straight and level flight. And we measure it with a ball level.

Weight and lift vector ARE the same thing in relation to the lateral axis (along the wings) of the airplane, which is all that counts. You're adding an irrelevant vertical axis (as viewed from the side of the airplane). I'll cancel this confusing double negative above and say yes...weight and lift are NOT parallel during climbs and descents, and ARE for straight and level. But that is unrelated to coordination. These lift and weight vectors, though not always parallel to each other in the vertical axis (as viewed from the side), are always PERPENDICULAR to the wings (lateral axis) when in coordinated flight, as I originally stated.

 

[Richard_SWave]

No. The recommended "maneuver" is PARE. It's in your POH and in the PTS. You're still a student pilot, aren't you?

Power to idle
Ailerons neutral
Rudder opposite rotation/roll
Elevator forward

I know it as a spin recovery technique, not as a stall recovery one. For stall, I was not thaught to use rudder opposite rotation/roll. I was just thaught to keep coordinated i.e. ball/butt in the middle.
There's no stall recovery technique in PTS, POH, at least I can't find it. I would appreciate to point me a link.

 

[RoscoeT]

I know it as a spin recovery technique, not as a stall recovery one. For stall, I was not thaught to use rudder opposite rotation/roll. I was just thaught to keep coordinated i.e. ball/butt in the middle.

OK I lied about being done. So what if you F-up a plain old straight ahead power-on stall so bad that you actually DO produce a spin entry. This happens. Like I said, you may not know if you're simply dropping a wing or spinning at first unless you have a lot more experience than you have. If you don't use rudder, and are actually in an incipient spin, not using opposite rudder will drill you a big hole in the ground.

 

[Richard_SWave]

When I did it, there was an obvious difference between an incipient spin and just a simple wing drop. It was pretty obvious that the wing drop was more like a slow roll towards the lower wing unlike incipient spin which clearly bring the aircraft into a lower attitude and hard rolling towards lower wing and was not going to cease on its own so easily.

 

[RoscoeT]

When I did it, there was an obvious difference between an incipient spin and just a simple wing drop. It was pretty obvious that the wing drop it was more like slow a slow roll towards the lower wing unlike incipient spin which clearly bring the aircraft into a lower attitude and hard rolling towards lower wing and was not going to cease so easily.

If you're good enough to recognize the difference, then why not use rudder to minimize the wing drop during a stall? You don't NEED opposite rudder if it's just a stall, but you won't depart so far from level flight it you do use rudder. If instructors are afraid of students getting themselves into spins by practicing stalls on their own, then they should question the wisdom of letting them do power-on stall practice on their own period, without spin training. Lots of power, aft stick/yoke, and hamfisted right aileron can produce a spin in many airplanes, even if you don't use the rudder.

 

[Richard_SWave]

If you're good enough to recognize the difference, then why not use rudder to minimize the wing drop during a stall?

Because you might induce one on the other part if you misappreciate just how much rudder is needed.

As long as you stalled coordinated, there is no need to use opposite rudder because you can't enter a spin towards lower wing cause you were coordinated and not necessary to introduce opposite rudder cause you might make it worse to spin opposite way if misappreciate how much is needed.

If you encounter an inadvertenly power-on stall during departure and the plane has the obvious tendency to roll hard it is a must to bring opposite rudder to avoid a spin towards the lower wing if you can't make sure you were perfectly coordinated when the stall happened and not sure if it's just a simple wingdrop or an incipient spin.

At least in a C172, it is pretty obvious if you need rudder. Usually it has no tendency to enter spins especially if you use to fly coordinated. And if it wants, there is gross difference between them. Badsically, use PARE if it's a spin, use standard stall recovery if it'a stall. How do you figure out? It is pretty obvious what is it. At least if you are familiar with those two maneuvers in the airplane you use to fly.

then they should question the wisdom of letting them do power-on stall practice on their own period, without spin training.

Where's the risk if you keep it centered/coordinated/butt/ball in the middle as they use to teach us?

Please anyone here show me where is rudder included in power-on, power-off standard STALL recoveries. (POH, PTS etc.) If so, me, my instructor and many others are profoundly wrong.

 

[RoscoeT]

As long as you stalled coordinated, there is no need to use opposite rudder because you can't enter a spin towards lower wing

Sure you can in some airplanes if you're power-on and mishandle the ailerons after the stall (as in an inappropriate repsonse to a wing drop), even if you were working hard on being coordinated while approaching the stall. Not all airplanes are as benign as the 172 that you have your 120 hrs in. I think I'm starting to come back to my original impression that you are only here to show us how exceedingly knowledgeable and experienced you are after a whole 120 hrs of flight time in 172's.

Where's the risk if you keep it centered/coordinated/butt/ball in the middle as they use to teach us?

Mistakes. http://www.youtube.com/watch?v=WKIk-dqml6U&feature=youtu.be

 

[dtuuri]

BE CAREFUL accepting aerodynamics from pilots without question. You can be a very good pilot with a mediocre understanding of aero. As an example, witness the above argument about which way a "flag" tied to the back of an airplane would blow in a turn. Neither party apparently realized all functional aircraft have just such a flag attached, called a "vertical stabilizer" and that there are multiple types of turns. Rudder correction to a coordinated turn is a direct measurement of which way the wind is blowing on the tail.

THIS party realizes it. He can point to an unimpeachable source to back him up too: Stick and Rudder, page 221.

​

THIS pilot has a couple thousand hours legally teaching these things to mostly primary students too.

dtuuri

 

[Richard_SWave]

Sure you can in some airplanes if you're power-on and mishandle the ailerons after the stall

Right, keep the ailerons neutral, don't pick up the wing using them. If you don't respect this it is obviously your fault. We don't assume here the pilot makes others mistakes, because if so, we can assume even he can make a mistake entering a stall when skidding and he'll end up in a spin.

And I guess you meant with after the stall, after stall entry during stall, not after the stall recovery. After stall, the ailerons are the way to level the wing.

Please anyone here show me where is rudder included in power-on, power-off standard STALL recoveries. (POH, PTS etc.) If so, me, my instructor and many others are profoundly wrong.

Still looking for it. Is there a requirement to arrest any roll and to keep wings level during stall using rudder? If so, please let me know.

P.S. I'm out for today, sorry but I have to go. Looking forward for your help. Thanks!

 

[dtuuri]

After stall, the ailerons are the way to level the wing.

That's apparently what the captain on Colgan Air in Buffalo thought too. Check out the control wheel excursions after the stall on the FDR traces:

http://dms.ntsb.gov/public/47000-47499/47271/417236.pdf​

Although use of "coordinated controls" sounds good in a book, in the real world most pilots use rudder pedals for foot rests unfortunately. Use your feet first, then maybe a little aileron--not much though.

dtuuri

 

[gismo]

If the horizontal tail surface is where the CG is then the relative wind is like a plane in straight and level flight--directly from in front. Slide it back from there on a long boom (fuselage) and it rides in a crosswind from the outside. The tighter the turn the more pronounced, slow and steep being the greatest.

Yes, the tail follows a wider radius, but that's irrelevant. Even a T-tail high enough to have the same radius as the CG would still experience a cross-flow from the outside. Imagine the T-tail parallel with the wing (which is located at the CG and tangent to the turn); being behind, but on the same arc, the flow is still from the outside.

I'm stuck with the concept that as long as the tail is flying the same arc as the wing, the angle between a tangent to the circle will have the same angle to the tail a and wing as they have when generating the same amount of lift in level flight. To me that means the "authority" of the elevator would be the same in either case. That said it wouldn't surprise me if the "authority" of the elevator is reduced at higher weights.