Stall speed in climbing turn
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I still believe the statement "the outer wing has a higher angle of bank in a climbing turn" is incorrect.
More forward speed gives a lower 'relative airflow' which equals higher AOA.
If the foregoing were changed to read: Less forward speed gives a lower 'relative airflow' which equals higher AOA. I would agree with it.
Do a Hover - it avoids G
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Well said DAR.
I find it quite surprising that professional pilots can have so many varied views about the basics of flight.
Mind you so far as the RAF is concerned AP129 was riddled with errors in 1955.
The current AP3456 is a much better animal. But we are talking half a century later.
I find it quite surprising that professional pilots can have so many varied views about the basics of flight.
Mind you so far as the RAF is concerned AP129 was riddled with errors in 1955.
The current AP3456 is a much better animal. But we are talking half a century later.
Last edited by John Farley; 19th May 2012 at 13:31.
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DAR
I was entirely with you on this one, but I think I get what the others are talking about.
If you climb 1000ft in a turn, both wings have climbed 1000ft, but the outer has flown further to do it.
This gives a different angle of incidence on each wing, as shown in background noise's diagram.
"In the most extreme, were the turn to be so tight that its pivot point was the inner wings wing tip, that wing tip would have zero relative airflow, and therefore an apparently infinate AoA."
No, because the aircraft is climbing.
This situation is exactly the reality of a helicopter in a hover. The air is flowing vertically downward through the disc. The airflow at the rotor head centre is actually giving reverse or negative AoA rather than infinite AoA.
At the exact centre of the disc, the airflow is from vertically above, ie -90 minus blade angle and stalled.
As you move outward along the blade, the blade's motion produces a tilt in the relative airflow from vertically above the blade steadily more towards coming from the direction of travel, and at some point you will find the blade unstalls and produces downward lift.
At some point further along the blade, the AoA reaches 0degrees or directly down the chord line.
As you move yet further along the blade, the AoA finally becomes positive, ie from below the chord line, and produces upward lift. This is produced in greater and greater quantities as you move along the blade to the tip.
If the blade/wing was infinitely long, then the max AoA at the tip would approach the blade angle.
The AoA at the centre of the rotor/or tip of inner wing in your example is 90degrees minus the blade angle/or aircraft nose up plus wing mounting angle.
That is, as you say an extreme example compared to fixed wing aircraft in a turn, but it makes the point.
This would give a greater angle of attack on the outer wing if we didn't effectively alter the shape of the wings with ailerons to balance the Lift to maintain a steady state.
Edit:
I'm slightly traumatised to find that I have been persuaded to the other view just as JF has waded in agreeing with my earlier view!
I was entirely with you on this one, but I think I get what the others are talking about.
If you climb 1000ft in a turn, both wings have climbed 1000ft, but the outer has flown further to do it.
This gives a different angle of incidence on each wing, as shown in background noise's diagram.
"In the most extreme, were the turn to be so tight that its pivot point was the inner wings wing tip, that wing tip would have zero relative airflow, and therefore an apparently infinate AoA."
No, because the aircraft is climbing.
This situation is exactly the reality of a helicopter in a hover. The air is flowing vertically downward through the disc. The airflow at the rotor head centre is actually giving reverse or negative AoA rather than infinite AoA.
At the exact centre of the disc, the airflow is from vertically above, ie -90 minus blade angle and stalled.
As you move outward along the blade, the blade's motion produces a tilt in the relative airflow from vertically above the blade steadily more towards coming from the direction of travel, and at some point you will find the blade unstalls and produces downward lift.
At some point further along the blade, the AoA reaches 0degrees or directly down the chord line.
As you move yet further along the blade, the AoA finally becomes positive, ie from below the chord line, and produces upward lift. This is produced in greater and greater quantities as you move along the blade to the tip.
If the blade/wing was infinitely long, then the max AoA at the tip would approach the blade angle.
The AoA at the centre of the rotor/or tip of inner wing in your example is 90degrees minus the blade angle/or aircraft nose up plus wing mounting angle.
That is, as you say an extreme example compared to fixed wing aircraft in a turn, but it makes the point.
This would give a greater angle of attack on the outer wing if we didn't effectively alter the shape of the wings with ailerons to balance the Lift to maintain a steady state.
Edit:
I'm slightly traumatised to find that I have been persuaded to the other view just as JF has waded in agreeing with my earlier view!
Last edited by Tourist; 19th May 2012 at 15:58.
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This gives a different angle of incidence on each wing,
No, because the aircraft is climbing
Though aileron application can affect AoA, it's probably better for this discussion to exclude that factor, as it is certainly different for different aircraft, and there is no common rule there. My experience with the subtle changes in roll contorl and stability following the installation of a STOL kit leading edge cuff on a Cessna wing have shown me the affect on roll control, and dihedral effect made by changing and displacing a part of the leading edge radius downward.
The center of lift in a rotor disc, and the change in that center of lift postion based upon forward speed do bear some similarity to this discussion, but I think are different enough to not be effectively relevent to this discussion. I do agree that there are widely varied AoA's along the blade span though. Some blades have considerable washout to compensate for this.
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I was unable to reply earlier so forgive me for digging things up again.
Tourist...
I think we need to define some things here and get an understanding of what they actually mean because there are a lot of terms being thrown around and I don't think we all know exactly what they mean - nomenclature if you will. The text and images below are from one of my aerodynamics textbooks.
According to this picture (http://i.imgur.com/1q1cL.jpg), the definitions are - Fundamentals of Aerodynamics, John D. Anderson, Jr., Chapter 4.2:
The mean camber line is the locus of points halfway between the upper and lower surfaces as measured perpendicular to the mean camber line itself. The most forward and rearward points of the mean camber line are the leading and trailing edges, respectively. The straight line connecting the leading and trailing edges is the chord line of the airfoil, and the precise distance from the leading to the trailing edge measured along the chord line is simply designated the chord c of the airfoil. The camber is the maximum distance between the mean camber line and the chord line, measured perpendicular to the chord line. The thickness is the distance between the upper and lower surfaces, also measured perpendicular to the chord line. The shape of the airfoil at the leading edge is usually circular, with a leading-edge radius of approximately 0.02c. The shapes of all standard NACA airfoils are generated by specifying the shape of the mean camber line and then wrapping a specified symmetrical thickness distribution around the mean camber line.
Something to note is that the chord line, as defined above, is the geometric chord line - based on the clean wing profile. When you look at a Cl vs AoA graph - the AoA is the geometric angle of attack (which is the angle between the geometric chord line and the relative wind) as shown in this picture - http://i.imgur.com/orLUQ.jpg. Therefore, when analyzing the aerodynamics involved here we must proceed with the understanding that the geometric angle of attack does not change with deflection of the ailerons. Also of note is this: if you look at the lift equation you will see a surface area variable. Since fowler flaps increase the surface area of the wing (increasing lift) you would think that the surface area variable in the equation would change - but that's not the case. The increase in surface area of the wing is taken into account completely by the change in coefficient of lift - which is why you see a substantial increase in Cl for fowler flaps compared to other variants of trailing edge flaps.
Going back to the problem - you can't call it "what you want" as you say if you're trying to explain something clearly for everyone to understand. As soon as you start using words that mean something different to someone else, you will never accomplish the task of effectively explaining a phenomenon. It only makes sense to use the nomenclature that is used by engineers and aerodynamicists since they are the ones who have made it possible for us to discuss this topic with some degree of accuracy and clarity.
Yes, pilots are taught that it's all about AoA and airspeed which works somewhat well for pilots to understand and effectively use, however, it's not the full picture and really not true at all. When you're trying to discuss the topic in-depth, and considering this is the Flight Testing forum, we must talk about this using the most correct terms as possible.
So, no the angle of attack (geometric) isn't changing. Just like the Cl changes when the flaps are deflected, the Cl changes when anything about the airfoil changes! That includes the deflection of the ailerons, speed brakes, spoilers, etc. It gets even more complicated than that since the airfoil shape usually never remains constant across the whole wing (tapered wings, washout, etc), among other factors. When you deflect the ailerons you're essentially decreasing/increasing the Cl for the entire wing (since there is usually one Cl figure for the entire wing). Looking back at post #27 I explained a bit about downwash and how that was changing the lift of the wing. It essentially comes down to the upwash/downwash of the wing which tells you how the airfoil will behave and how the airplane will fly. Then all the complicated theories and theorems and laws, etc all try to explain how and a little bit about why this happens.
EDIT: Here is one page out of the Airplane Upset Recovery Training Aid (Airplane Upset Recovery Training Aid | Flight Safety Foundation). It contributes to what I was saying.
https://www.box.com/s/8ca4f81bcf9abe9f4be2
Tourist...
You can call it what you like, ie downwash etc, but at the end of the day lift is all about AoA and airspeed, and if the airspeed has increased then the AoA has to reduce to stop a roll.
According to this picture (http://i.imgur.com/1q1cL.jpg), the definitions are - Fundamentals of Aerodynamics, John D. Anderson, Jr., Chapter 4.2:
The mean camber line is the locus of points halfway between the upper and lower surfaces as measured perpendicular to the mean camber line itself. The most forward and rearward points of the mean camber line are the leading and trailing edges, respectively. The straight line connecting the leading and trailing edges is the chord line of the airfoil, and the precise distance from the leading to the trailing edge measured along the chord line is simply designated the chord c of the airfoil. The camber is the maximum distance between the mean camber line and the chord line, measured perpendicular to the chord line. The thickness is the distance between the upper and lower surfaces, also measured perpendicular to the chord line. The shape of the airfoil at the leading edge is usually circular, with a leading-edge radius of approximately 0.02c. The shapes of all standard NACA airfoils are generated by specifying the shape of the mean camber line and then wrapping a specified symmetrical thickness distribution around the mean camber line.
Something to note is that the chord line, as defined above, is the geometric chord line - based on the clean wing profile. When you look at a Cl vs AoA graph - the AoA is the geometric angle of attack (which is the angle between the geometric chord line and the relative wind) as shown in this picture - http://i.imgur.com/orLUQ.jpg. Therefore, when analyzing the aerodynamics involved here we must proceed with the understanding that the geometric angle of attack does not change with deflection of the ailerons. Also of note is this: if you look at the lift equation you will see a surface area variable. Since fowler flaps increase the surface area of the wing (increasing lift) you would think that the surface area variable in the equation would change - but that's not the case. The increase in surface area of the wing is taken into account completely by the change in coefficient of lift - which is why you see a substantial increase in Cl for fowler flaps compared to other variants of trailing edge flaps.
Going back to the problem - you can't call it "what you want" as you say if you're trying to explain something clearly for everyone to understand. As soon as you start using words that mean something different to someone else, you will never accomplish the task of effectively explaining a phenomenon. It only makes sense to use the nomenclature that is used by engineers and aerodynamicists since they are the ones who have made it possible for us to discuss this topic with some degree of accuracy and clarity.
Yes, pilots are taught that it's all about AoA and airspeed which works somewhat well for pilots to understand and effectively use, however, it's not the full picture and really not true at all. When you're trying to discuss the topic in-depth, and considering this is the Flight Testing forum, we must talk about this using the most correct terms as possible.
So, no the angle of attack (geometric) isn't changing. Just like the Cl changes when the flaps are deflected, the Cl changes when anything about the airfoil changes! That includes the deflection of the ailerons, speed brakes, spoilers, etc. It gets even more complicated than that since the airfoil shape usually never remains constant across the whole wing (tapered wings, washout, etc), among other factors. When you deflect the ailerons you're essentially decreasing/increasing the Cl for the entire wing (since there is usually one Cl figure for the entire wing). Looking back at post #27 I explained a bit about downwash and how that was changing the lift of the wing. It essentially comes down to the upwash/downwash of the wing which tells you how the airfoil will behave and how the airplane will fly. Then all the complicated theories and theorems and laws, etc all try to explain how and a little bit about why this happens.
EDIT: Here is one page out of the Airplane Upset Recovery Training Aid (Airplane Upset Recovery Training Aid | Flight Safety Foundation). It contributes to what I was saying.
https://www.box.com/s/8ca4f81bcf9abe9f4be2
Last edited by italia458; 26th May 2012 at 04:07.
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Yes, I will freely admit that my misuse of terms has not been helpful, however that does not make my points invalid.
You can say that aileron movement does not change the geometric angle of attack, however that is just how our engineers have decided to resolve it for standardisation.
If an engineer came across a solid wing, (ie no hinge or aileron) in the shape of "our wing" but with the aileron deflected downwards and was asked to work out the chord line he would come up with a different result than if he was given a wing in the shape of "our wing" with the aileron level.
Equally, if you have wing warping, to say that the chord line is unchanging is no more valid than to say that the Cl is unchanging.
There are many different and equally valid/imperfect ways to look at lift, and to suggest that one must do it in a particular way is not reasonable.
My point was, that the outside wing in a stable climbing turn has higher speed, therefore needs to lose lift somehow.
If you want, you can say it reduces it's Cl to do this rather than AoA, but the point still stands, and I think it is merely semantics.
You can say that aileron movement does not change the geometric angle of attack, however that is just how our engineers have decided to resolve it for standardisation.
If an engineer came across a solid wing, (ie no hinge or aileron) in the shape of "our wing" but with the aileron deflected downwards and was asked to work out the chord line he would come up with a different result than if he was given a wing in the shape of "our wing" with the aileron level.
Equally, if you have wing warping, to say that the chord line is unchanging is no more valid than to say that the Cl is unchanging.
There are many different and equally valid/imperfect ways to look at lift, and to suggest that one must do it in a particular way is not reasonable.
My point was, that the outside wing in a stable climbing turn has higher speed, therefore needs to lose lift somehow.
If you want, you can say it reduces it's Cl to do this rather than AoA, but the point still stands, and I think it is merely semantics.
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Tourist...
You agree you've used incorrect terms and yet you still argue that your points are valid?
The problem here is not a 'language' problem. If you were to talk English to a Russian-only speaking person, you would not be able to communicate because you have a completely different word to describe the same thing as the Russian. That's not the problem here. You are using terms which you, I and most people on this forum have the same, roughly speaking, definition for. As I pointed out before, many pilots are taught that it's ONLY about angle of attack and speed to make lift and so from that it's easy to see that you need to change angle of attack to change lift at the same speed. But that's not true. Saying it's all about AoA and speed only works if you're going to analyse a few, very specific, flight conditions where you could accurately describe changes in lift with AoA or speed. However, when you try to describe a complicated flight profile, such as a climbing turn around the stall speed regime, you can't accurately describe what's happening with just AoA and speed. But people do just that. They know what the outcome is, ie: the wing stays at a particular bank while in a turn, so since the outside wing is traveling faster, it MUST be at a lower AoA.... problem solved! <---- That is exactly how misinformation gets passed along.
I would never tell a student something that I know to be wrong. I have no respect for the attitude of, "I know this isn't totally correct but it makes sense and the correct way is far too complicated, so I'm going to teach it incorrectly".
Here is a perfect example of misinformation that gets passed on, in this case due to ignorance and not willfully. I've been told many times by people that they just did a barrel roll. Everytime I ask them to describe what they did and everytime they describe an aileron roll. I thought for the longest time too that an aileron roll was a barrel roll - I think we have the entertainment industry to blame for this one!
http://www.pprune.org/tech-log/48589...rel-rolls.html
You're trying to 'bend' the way that airfoils are normally designed so as to fit your description. I would say 'yes' to what you said, but that's not the way that airfoils are designed! How does this prove your point? I don't think you understand why it's incorrect to describe the condition we're discussing in this thread the way you have.
You can't say that since the chord line is changing (or unchanging as you used) the Cl is changing. They are two completely separate things. A change in the chord line does not mean that there is a change in the angle of attack or a change in the Cl, or anything else. If 'Cl' was the same as 'chord line', it would be spelt this way: chord line.
I completely agree with you that this is all 'semantics'... but, ironically, I don't think you have the same interpretation of semantics as I do! The definition of semantics: the meaning, or an interpretation of the meaning, of a word, sign, sentence, etc. If you think that you don't need to have the same interpretation of the meaning of the words being used to discuss aerodynamics, then I don't think we're going to come to an agreement here!
I will freely admit that my misuse of terms has not been helpful, however that does not make my points invalid.
The problem here is not a 'language' problem. If you were to talk English to a Russian-only speaking person, you would not be able to communicate because you have a completely different word to describe the same thing as the Russian. That's not the problem here. You are using terms which you, I and most people on this forum have the same, roughly speaking, definition for. As I pointed out before, many pilots are taught that it's ONLY about angle of attack and speed to make lift and so from that it's easy to see that you need to change angle of attack to change lift at the same speed. But that's not true. Saying it's all about AoA and speed only works if you're going to analyse a few, very specific, flight conditions where you could accurately describe changes in lift with AoA or speed. However, when you try to describe a complicated flight profile, such as a climbing turn around the stall speed regime, you can't accurately describe what's happening with just AoA and speed. But people do just that. They know what the outcome is, ie: the wing stays at a particular bank while in a turn, so since the outside wing is traveling faster, it MUST be at a lower AoA.... problem solved! <---- That is exactly how misinformation gets passed along.
I would never tell a student something that I know to be wrong. I have no respect for the attitude of, "I know this isn't totally correct but it makes sense and the correct way is far too complicated, so I'm going to teach it incorrectly".
Here is a perfect example of misinformation that gets passed on, in this case due to ignorance and not willfully. I've been told many times by people that they just did a barrel roll. Everytime I ask them to describe what they did and everytime they describe an aileron roll. I thought for the longest time too that an aileron roll was a barrel roll - I think we have the entertainment industry to blame for this one!
http://www.pprune.org/tech-log/48589...rel-rolls.html
If an engineer came across a solid wing, (ie no hinge or aileron) in the shape of "our wing" but with the aileron deflected downwards and was asked to work out the chord line he would come up with a different result than if he was given a wing in the shape of "our wing" with the aileron level.
Equally, if you have wing warping, to say that the chord line is unchanging is no more valid than to say that the Cl is unchanging.
I completely agree with you that this is all 'semantics'... but, ironically, I don't think you have the same interpretation of semantics as I do! The definition of semantics: the meaning, or an interpretation of the meaning, of a word, sign, sentence, etc. If you think that you don't need to have the same interpretation of the meaning of the words being used to discuss aerodynamics, then I don't think we're going to come to an agreement here!
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The laws of Physics, in this universe, seem to be a constant at levels we can observe.
An alien from mars would see the same effects happen.
They might not, however, resolve things into the same terms and planes of reference.
A small example of this is the different way that we draw the force diagrams for propellors vs rotor blades.
Because the people who did the original work were not conversing, they resolved them differently.
That does not make either of them wrong.
You say "You're trying to 'bend' the way that airfoils are normally designed so as to fit your description. I would say 'yes' to what you said, but that's not the way that airfoils are designed! How does this prove your point? I don't think you understand why it's incorrect to describe the condition we're discussing in this thread the way you have."
No.
You can't have it both ways.
The laws of physics don't care that some people decided to say that the chord line stays contant when ailerons are moved purely for there own ease of discussion and calculation.
The simple fact is that if an engineer with no prior knowledge was asked to calculate the chord line of two wings, one with an upturned trailing edge, and one with a downturned trailing edge then he would give a different answer to each.
That is all an aileron is.
One of the basic tennets of any science is that it must be demonstrable and repeatable by different observers, not just ones primed by prior knowledge into saying a standard answer.
It is perfectly reasonable to say that aileron movement causes a change of chord line.
"A change in the chord line does not mean that there is a change in the angle of attack or a change in the Cl, or anything else. If 'Cl' was the same as 'chord line', it would be spelt this way: chord line."
If two wings which are mounted at the same angle of incidence on one fuselage have their chord lines differentially altered by the use of ailerons, then a change in the chord line does mean that there is a change in AoA.
This is all beside the point anyway.
Consider an aircraft with no ailerons in a climbing turn.
With no ailerons, both wings must have the same Cl and Area.
The outer wing will have greater airspeed and greater AoA, and the situation will be unstable, ie the angle of bank will increase.
Ailerons are required to reduce the lift on the outer wing, whether we call that by changing the Cl or by changing the AoA via the change in Chord line.
That is my point.
The fact that my terminology has not been precise is not helpfull, I admit, but that does not make my point invalid.
"I would never tell a student something that I know to be wrong. I have no respect for the attitude of, "I know this isn't totally correct but it makes sense and the correct way is far too complicated, so I'm going to teach it incorrectly". "
Think about it reasonably.
Every scientist in every field throughout history has always proved to be wrong.
Every single one.
Copernicus
Newton
Einstein
Closer to the truth than the previous generation perhaps, but basically just iterating closer to the truth.
That is not the same as "right"
To imagine that we are currently the generation that finally got everything correct is just a little unlikely, and frankly arrogant beyond belief.
We know that what we currently believe about aerodynamics is a reasonable approximation, and enough to be going on with, but if you think that the leading minds of our generation, let alone anybody chatting on here about what they read (from one of the many books which don't fully agree on the basics, let alone the minutia) know anything but an approximation then you are deluded.
What you teach your students is just an approximation. Get used to it.
An alien from mars would see the same effects happen.
They might not, however, resolve things into the same terms and planes of reference.
A small example of this is the different way that we draw the force diagrams for propellors vs rotor blades.
Because the people who did the original work were not conversing, they resolved them differently.
That does not make either of them wrong.
You say "You're trying to 'bend' the way that airfoils are normally designed so as to fit your description. I would say 'yes' to what you said, but that's not the way that airfoils are designed! How does this prove your point? I don't think you understand why it's incorrect to describe the condition we're discussing in this thread the way you have."
No.
You can't have it both ways.
The laws of physics don't care that some people decided to say that the chord line stays contant when ailerons are moved purely for there own ease of discussion and calculation.
The simple fact is that if an engineer with no prior knowledge was asked to calculate the chord line of two wings, one with an upturned trailing edge, and one with a downturned trailing edge then he would give a different answer to each.
That is all an aileron is.
One of the basic tennets of any science is that it must be demonstrable and repeatable by different observers, not just ones primed by prior knowledge into saying a standard answer.
It is perfectly reasonable to say that aileron movement causes a change of chord line.
"A change in the chord line does not mean that there is a change in the angle of attack or a change in the Cl, or anything else. If 'Cl' was the same as 'chord line', it would be spelt this way: chord line."
If two wings which are mounted at the same angle of incidence on one fuselage have their chord lines differentially altered by the use of ailerons, then a change in the chord line does mean that there is a change in AoA.
This is all beside the point anyway.
Consider an aircraft with no ailerons in a climbing turn.
With no ailerons, both wings must have the same Cl and Area.
The outer wing will have greater airspeed and greater AoA, and the situation will be unstable, ie the angle of bank will increase.
Ailerons are required to reduce the lift on the outer wing, whether we call that by changing the Cl or by changing the AoA via the change in Chord line.
That is my point.
The fact that my terminology has not been precise is not helpfull, I admit, but that does not make my point invalid.
"I would never tell a student something that I know to be wrong. I have no respect for the attitude of, "I know this isn't totally correct but it makes sense and the correct way is far too complicated, so I'm going to teach it incorrectly". "
Think about it reasonably.
Every scientist in every field throughout history has always proved to be wrong.
Every single one.
Copernicus
Newton
Einstein
Closer to the truth than the previous generation perhaps, but basically just iterating closer to the truth.
That is not the same as "right"
To imagine that we are currently the generation that finally got everything correct is just a little unlikely, and frankly arrogant beyond belief.
We know that what we currently believe about aerodynamics is a reasonable approximation, and enough to be going on with, but if you think that the leading minds of our generation, let alone anybody chatting on here about what they read (from one of the many books which don't fully agree on the basics, let alone the minutia) know anything but an approximation then you are deluded.
What you teach your students is just an approximation. Get used to it.
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Oh, and incidentally, that is a barrel roll.
An aileron roll does not keep positive G
A barrel roll can be anywhere from a loop 1 degree from the vertical to just far enough off an aileron role to maintain positive G,
Role and pull equals barrel
Roll equals aileron
If you fly a helical path describing the inside of a tube, then you are flying a barrel roll.
Duh.
An aileron roll does not keep positive G
A barrel roll can be anywhere from a loop 1 degree from the vertical to just far enough off an aileron role to maintain positive G,
Role and pull equals barrel
Roll equals aileron
If you fly a helical path describing the inside of a tube, then you are flying a barrel roll.
Duh.
Last edited by Tourist; 9th Jun 2012 at 18:44.
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This might help -- http://www.bruceair.com/aerobatics/aerobatics.htm
The key part is where it says: "A barrel roll is a combination of a loop and a roll".
The key part is where it says: "A barrel roll is a combination of a loop and a roll".
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Perhaps picking up a basic aerobatics book might help you both understand it a bit better.
I just took this picture from the Basic Aerobatics book by Geza Szurovy and Mike Goulian.
http://i.imgur.com/O5te7.jpg
I just took this picture from the Basic Aerobatics book by Geza Szurovy and Mike Goulian.
http://i.imgur.com/O5te7.jpg
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Originally Posted by pull what
Can anyone shed some light on how there is an increase in the stalling speed in a climbing turn. I cannot see how there can be an increase unless there is an increase in wing loading and I cannot see how wing loading is increased if there is no back pressure on the CC, am I missing something here?
If you don't apply back pressure then the AoA won't change, and since stall depends only on AoA you won't ever get any closer or further away from a stall, no matter what manoeuvre you fly.
I cannot see how there can be an increase unless there is an increase in wing loading and I cannot see how wing loading is increased if there is no back pressure on the CC
This is what happens in a spiral dive.
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If you enter a turn hands off then wing loading increases due solely to an increase in airspeed.
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You haven't touched the pitch trim, so the trimmed AoA stays the same.
If the aircraft is in a turn then:
a. it's not accelerating downwards. It's descending, but at a constant rate, to first order. Therefore the vertical component of all the forces matches the weight of the airplane
b. it's acclerating sideways (or it wouldn't be in a turn). Assuming the attitude has some semblance of normality, i.e. nose first and tail last, then most of the force causing the sideways acceleration comes from the wings too - a.k.a lift vector tilted over etc.
Therefore the total lift force generated by the wings is larger than in level flight (i.e. an increase in wing loading)
Since the AoA is the same (inherent pitch stability of an airplane yada yada yada) the extra lift must be caused by an increase in the airspeed. Lift equation and all that.
This is to first order and ignores:
1. Trim changes caused by adding or reducing power, neither of which is necessary to go from level flight to a descending spiral turn.
2. What Denker calls the "long tail effect" - that in a steeply banked small radius turn the elevator has increased angle of attack, and becomes more effective at supporting the tail (or less effective at pulling it down). The nose tends to drop more than it otherwise would, the trimmed angle of attack (of the main wing) decreases and the aircraft actually speeds up in a spiral dive. It gets further away from a stall.
If you want to look into item 2 in more detail, google for "stick free manoeuvre point" and compare it with the "stick-free neutral point". This is an interesting place to start:
http://www.flightlab.net/Flightlab.n...u%232BA152.pdf
If the aircraft is in a turn then:
a. it's not accelerating downwards. It's descending, but at a constant rate, to first order. Therefore the vertical component of all the forces matches the weight of the airplane
b. it's acclerating sideways (or it wouldn't be in a turn). Assuming the attitude has some semblance of normality, i.e. nose first and tail last, then most of the force causing the sideways acceleration comes from the wings too - a.k.a lift vector tilted over etc.
Therefore the total lift force generated by the wings is larger than in level flight (i.e. an increase in wing loading)
Since the AoA is the same (inherent pitch stability of an airplane yada yada yada) the extra lift must be caused by an increase in the airspeed. Lift equation and all that.
This is to first order and ignores:
1. Trim changes caused by adding or reducing power, neither of which is necessary to go from level flight to a descending spiral turn.
2. What Denker calls the "long tail effect" - that in a steeply banked small radius turn the elevator has increased angle of attack, and becomes more effective at supporting the tail (or less effective at pulling it down). The nose tends to drop more than it otherwise would, the trimmed angle of attack (of the main wing) decreases and the aircraft actually speeds up in a spiral dive. It gets further away from a stall.
If you want to look into item 2 in more detail, google for "stick free manoeuvre point" and compare it with the "stick-free neutral point". This is an interesting place to start:
http://www.flightlab.net/Flightlab.n...u%232BA152.pdf
Last edited by photofly; 2nd Mar 2013 at 02:08.
