Instructors teaching full rudder to "pick up" dropped wing.
Forward stick isn't going to help you when you're inverted . . . But I digress.
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You could use the flick roll manoeuvre at the top of a loop to make it a roll off the top. Good fun for 20 year old trainee pilots...
Nowadays on some modern types if it all gets too hard you can just push a button (or pull a lever) that will release a big parachute to sort it all out for you.
Yep, I certainly recommend checking out lift coefficient vs angle of attack plots with different control surface or flap deflections to see that the stall AoA is reduced with downwards control/flap deflection.
If the stall has progressed to a wing drop I would suggest that even if you reckon your aileron isn't as stalled as the rest of the wing (which is a big if), then the rapidly increasing upward flow because of the drop will be pushing it past that point pretty quickly. A flap is not just a flap when it's hurtling downwards at a great rate, surely.
But then once the wing-drop has gotten into it's stride the only thing that will do any good is unstalling the wing anyway - using ailerons won't be any worse than using rudder. If fact using the ailerons will recamber the wing such that it will "unstall" in the vicinity of the ailons a lttle soon, where as if the aeroplane has any dihederal the yaw from any anti-rudder input will increase the angle of attack of the dropped wing and delay the "unstalling" (due to the geometry of yaw and dihederal).
PDR
Originally Posted by Cuban 8
As a former Aerodynamicist, I think it is important to re-iterate the points that Taylor G and Bookworm have made.
The Cl/AoA debate is an issue of definition. By convention in aerodynamics, the chord line of an aerofoil is defined for it's clean configuration with nothing "hanging out". As we begin to deploy trailing edge high lift devices, we are indeed modifying the characteristics of the aerofoil - the most significant change being the introduction of a greater camber. Commensurate with this, the aerofoil's true chord is also modified - but by convention, the reference chord remains that for the clean aerofoil. Thus, on a characteristic Cl/AoA plot, it appears that the aerofoil stalls at a lower AoA, but with a greater Clmax. In reality, the AoA at which the aerofoil stalls is usually greater than for a clean aerofoil. A secondary effect of this is very beneficial to use as pilots - the pitch angle at which we a achieve a given AoA is reduced.
The same principle is true for Fowler slotted flaps and similar devices. The effect of such devices on a Cl/AoA plot often look too good to be true compared to other trailing edge devices, in that they offer a relatively large increase in Clmax. However, you have to consider that Fowler slotted flaps are also significantly increasing the aerofoil wetted area, but this fact is not reflected in the calculations - the aerofoil reference area remains that for the clean aerofoil. The increased area is hence absorbed into the increased Clmax the devices offer, slightly misleading!
Of course, day to day, the theory offered by BEagle is all we really need to know. However, when your really trying to understand what is going on, such simplifications can be misleading.
Rgds
Cuban_8
The Cl/AoA debate is an issue of definition. By convention in aerodynamics, the chord line of an aerofoil is defined for it's clean configuration with nothing "hanging out". As we begin to deploy trailing edge high lift devices, we are indeed modifying the characteristics of the aerofoil - the most significant change being the introduction of a greater camber. Commensurate with this, the aerofoil's true chord is also modified - but by convention, the reference chord remains that for the clean aerofoil. Thus, on a characteristic Cl/AoA plot, it appears that the aerofoil stalls at a lower AoA, but with a greater Clmax. In reality, the AoA at which the aerofoil stalls is usually greater than for a clean aerofoil. A secondary effect of this is very beneficial to use as pilots - the pitch angle at which we a achieve a given AoA is reduced.
The same principle is true for Fowler slotted flaps and similar devices. The effect of such devices on a Cl/AoA plot often look too good to be true compared to other trailing edge devices, in that they offer a relatively large increase in Clmax. However, you have to consider that Fowler slotted flaps are also significantly increasing the aerofoil wetted area, but this fact is not reflected in the calculations - the aerofoil reference area remains that for the clean aerofoil. The increased area is hence absorbed into the increased Clmax the devices offer, slightly misleading!
Of course, day to day, the theory offered by BEagle is all we really need to know. However, when your really trying to understand what is going on, such simplifications can be misleading.
Rgds
Cuban_8
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Just to be clear, the actual stalling AoA does not "increase" or "decrease" - the stalling angle of the chord line in relation to the relative airflow remains the same. You are simply changing the camber/chord line by dropping the trailing edge.
This is the bit I'm trying to understand: are you referring to positive aileron? That is, left wing drops, apply left aileron to reduce camber of left wing (and AoA) in the hope it will unstall sooner?
As for dihedral effect, my understanding is when a wing stalls and drops, the aircraft yaws into the dropped wing as a result of induced drag. This causes a brief side-slip in the opposite direction (skid). The higher wing will now be moving into the sideslip - which increases its AoA and causes the lift vector to move further aft, compounding the yaw and causing the aircraft to roll further to the left.
The only way to break the yaw-roll cycle in the incipient stage is to apply opposite rudder to not only bring the aircraft back into balance, but change the relative airflow of the dropped wing to reduce its AoA. This happens when the dropped wing moves forward (and has nothing to do with "increasing the speed of the wing to increase lift", as the wing is already stalled!).
If I am missing something - and I'm not trying to be smart - then I'm very open to re-education.
As an aside, I know from experience it is entirely possible to ride a stall - stick all the way back - wings level for hundreds of feet of lost altitude simply by dancing on the rudder to keep the aircraft in balance. It works. I've done it. No aileron. All rudder.
Originally Posted by PDR1
But then once the wing-drop has gotten into it's stride the only thing that will do any good is unstalling the wing anyway - using ailerons won't be any worse than using rudder. If fact using the ailerons will recamber the wing such that it will "unstall" in the vicinity of the ailons a lttle soon, where as if the aeroplane has any dihederal the yaw from any anti-rudder input will increase the angle of attack of the dropped wing and delay the "unstalling" (due to the geometry of yaw and dihederal).
As for dihedral effect, my understanding is when a wing stalls and drops, the aircraft yaws into the dropped wing as a result of induced drag. This causes a brief side-slip in the opposite direction (skid). The higher wing will now be moving into the sideslip - which increases its AoA and causes the lift vector to move further aft, compounding the yaw and causing the aircraft to roll further to the left.
The only way to break the yaw-roll cycle in the incipient stage is to apply opposite rudder to not only bring the aircraft back into balance, but change the relative airflow of the dropped wing to reduce its AoA. This happens when the dropped wing moves forward (and has nothing to do with "increasing the speed of the wing to increase lift", as the wing is already stalled!).
If I am missing something - and I'm not trying to be smart - then I'm very open to re-education.
As an aside, I know from experience it is entirely possible to ride a stall - stick all the way back - wings level for hundreds of feet of lost altitude simply by dancing on the rudder to keep the aircraft in balance. It works. I've done it. No aileron. All rudder.
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Hello
I have not read all 4 pages of the topic but just the first post.
Applying large amounts of rudder in order to keep wings level is correct procedure when stalling. It is large amount of ailerons that should be banned.
Where do I have this knowledge from ?
I was on several flights with one of the best pilots there is : chief test pilot for an aircraft manufacturer and former chief test pilot instructor.
A/C was SET.
When approaching stall, he wanted to see on which side the particular aircraft would bank. Afterwards, on the ground, some small adjustments were made. But during the test, he would make large inputs, up to full rudder, in order to keep level for as long as possible.
HOWEVER there really is no point other than test flight in doing this !
If a student or inexperienced pilot (in this case meaning someone without extensive aerobatics experience) tries to do it and mixes up the foot side, or puts too much foot, he will end up in a spin.
Whereas he could just have pushed on the stick with a few degrees of bank : who cares ? He will level the wings with the ailerons once the stall is recovered.
I have not read all 4 pages of the topic but just the first post.
Applying large amounts of rudder in order to keep wings level is correct procedure when stalling. It is large amount of ailerons that should be banned.
Where do I have this knowledge from ?
I was on several flights with one of the best pilots there is : chief test pilot for an aircraft manufacturer and former chief test pilot instructor.
A/C was SET.
When approaching stall, he wanted to see on which side the particular aircraft would bank. Afterwards, on the ground, some small adjustments were made. But during the test, he would make large inputs, up to full rudder, in order to keep level for as long as possible.
HOWEVER there really is no point other than test flight in doing this !
If a student or inexperienced pilot (in this case meaning someone without extensive aerobatics experience) tries to do it and mixes up the foot side, or puts too much foot, he will end up in a spin.
Whereas he could just have pushed on the stick with a few degrees of bank : who cares ? He will level the wings with the ailerons once the stall is recovered.
And while we're here - another similar depressingly common myth/misunderstanding is the idea that deflecting an aileron downwards increases the angle of attack of that part of a wing and risks stalling it of the wing is close to it's stalling AoA. This is not true. A lowered aileron is just a flap, and no one says "if you're close to the stall for <deity's> sake down't lower the flaps because you'll stall the wings!"
So if you were very close to stall and then extended flaps without changing the pitch I think I may very well be saying "for <rude word>ing <deity's> sake you need to lower the nose captain if you are extending flap now!
In simple S&L un-accelerated stalling of an aircraft in landing configuration you have a lower nose attitude compared to the clean stalling attitude, if you were to raise the nose of a dirty configuration to a similar position for clean stall, the wings would be even more stalled.
Have a look at Aerodynamics for Naval Aviators (in my 1965 revision, page 39 and 40)
Notice how the max lift point actually reduces significantly for flap extension.
FWIW, a C172 has something like Fowler style flaps
I agree that in a sense yes ailerons are just asymmetric flaps. The difference however is in their use. Typically extending flaps involves lowering the pitch attitude to produce the same lift. Similarly it allows slower flight before reaching the critical angle (ie a lower stall speed) by increasing lift and drag. What it doesn't do is allow the aircraft to stall at a similar or higher AoA (or for simple stalls at a higher or similar pitch attitude).
The ailerons are not being used in the same way as flaps. The aircraft attitude is not being changed to account for the aileron's change to the effective shape of the aerofoil. If you have an outer wing near the point of stall and without changing its relative motion to the airflow, deflect the aileron down, you are pushing it closer to the stall.
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I would have agree with the jonkster. And it's pretty easy to demonstrate a departure of control by using opposite aileron at the point of stall.
Have a look at this video and see what the pilot does with the yoke right at the point of stall:
Let's not forget the primary function of a basic flap - as opposed to an aileron - is to increase the surface area of the wing to increase lift for the same speed - the penalty being drag. The change in chord line merely facilitates a lower nose attitude for a better view during approach.
As far as I'm aware, ailerons (not flaperons) do not change the lift coefficient of the wing in the same manner flaps do. In addition, there seems to be a bit of confusion about the reference point of AoA in relation to flaps. Flaps change the chord line, so if you do not alter the point of reference of AoA for a clean wing, then of course the AoA of the wing as a whole will decrease. But the stalling AoA of the chord line in reference to the relative airflow is still the same.
As for the application of flaps at the point of stall, this has been addressed by at least one person who claims to have tried it in a Chippy: http://www.pprune.org/questions/2027...-stalling.html
Have a look at this video and see what the pilot does with the yoke right at the point of stall:
Let's not forget the primary function of a basic flap - as opposed to an aileron - is to increase the surface area of the wing to increase lift for the same speed - the penalty being drag. The change in chord line merely facilitates a lower nose attitude for a better view during approach.
As far as I'm aware, ailerons (not flaperons) do not change the lift coefficient of the wing in the same manner flaps do. In addition, there seems to be a bit of confusion about the reference point of AoA in relation to flaps. Flaps change the chord line, so if you do not alter the point of reference of AoA for a clean wing, then of course the AoA of the wing as a whole will decrease. But the stalling AoA of the chord line in reference to the relative airflow is still the same.
As for the application of flaps at the point of stall, this has been addressed by at least one person who claims to have tried it in a Chippy: http://www.pprune.org/questions/2027...-stalling.html
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Something to be considered - I was fortunate enough to start my flying career in gliders and so was exposed to proper spin training from the start. Funnily enough, the military also taught full spin recoveries ... but I also went all the way through the GA world to CPL without doing a single one. If you'd like to experience the reality of what all of this theoretical talk is about, go for a couple of flights with your local gliding club: Unusual Attitude and Spin Training for non- Glider pilots (UAS)
As far as I'm aware, ailerons (not flaperons) do not change the lift coefficient of the wing in the same manner flaps do. In addition, there seems to be a bit of confusion about the reference point of AoA in relation to flaps. Flaps change the chord line, so if you do not alter the point of reference of AoA for a clean wing, then of course the AoA of the wing as a whole will decrease. But the stalling AoA of the chord line in reference to the relative airflow is still the same.
A simple aileron is just like a simple flap as far as the aerodynamics of the aerofoil is concerned.
Airflow separation results from adverse pressure gradient. Deflecting that flap or aileron increases the negative Cp near the leading edge therefore that adverse pressure gradient will increase so ....
Someone kindly provided the usual charts from wind tunnel data where we retain the chord line of the aerofoil with nil flap or control surface deflection. That is my usual reference.
Some calculations we do are via the so-called thin aerofoil theory where we change the chord line to follow the deflected trailing edge. A fine theory but generally doesn't lead us to a calculation of stalling angle of attack, at least not a realistic one.
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Originally Posted by djpil
Airflow separation results from adverse pressure gradient. Deflecting that flap or aileron increases the negative Cp near the leading edge therefore that adverse pressure gradient will increase so ....
I get that. And I get that more camber = more lift = more drag. And that reducing XTE (trailing edge position) increases Cl.
But then once the wing-drop has gotten into it's stride the only thing that will do any good is unstalling the wing anyway - using ailerons won't be any worse than using rudder. If fact using the ailerons will recamber the wing such that it will "unstall" in the vicinity of the ailons a lttle soon, where as if the aeroplane has any dihederal the yaw from any anti-rudder input will increase the angle of attack of the dropped wing and delay the "unstalling" (due to the geometry of yaw and dihederal).
And in reality - as demonstrated in the video I posted - opposite aileron at the point of stall can actually facilitate a wing drop.
I know I am only referring to basic GA type aircraft, but for the purposes of this conversation, that's what most of us fly. Also, most of us have done a few stalls and spins in our time and at least in my experience, wing drop at the point of stall can be countered through use of opposite rudder, whilst opposite aileron has the reverse (and undesired) effect.
My point is, I can't see how "ailerons won't be any worse than using rudder" when experience has taught me that's not the case. That's just my experience in what few types I've stalled and spun, including those with dihedral (Piper's etc). Even an aero trainer like the Decathlon has a small amount of dihedral.
I know you guys do this for a living, so what is it I'm missing?
Just me but I would avoid saying "pick up the wing" with rudder. I would prefer to say in a stall, control yaw with rudder and keep ailerons neutral.
Use ailerons to return to wings level once the stall is broken.
Pretty sure "out spin" aileron at stall (ie aileron that you would think would stop the wing dropping) will actually help make a nice positive spin entry in Chipmunks if I recall correctly. (Someone with more recent time on them please correct me if this wrong!)
It has been a long time but in a Citabria, I recall talking students through stalling in a climbing left turn with a bit of power with a little too much rudder and holding off bank with aileron. (This simulating at altitude what might happen in real life trying to make a unplanned landing site due weather or maybe rough running engine, turning onto final and needing to stretch the glide and the pilot unconciously is avoiding banking too steeply because they are low to the ground so they skid the final turn around on rudder).
I recall it makes for a quite sharp spin entry and a loss of several hundred feet in a blink. The Citabria normally has a very good manners and a gentle predictable spin entry from a simple unaccelerated stall.
Teaching people it is OK to use ailerons to keep wings level in a stall is something I would feel very wrong about doing. On some aircraft it works fine but it is not a good habit to have people get into.
Use ailerons to return to wings level once the stall is broken.
Pretty sure "out spin" aileron at stall (ie aileron that you would think would stop the wing dropping) will actually help make a nice positive spin entry in Chipmunks if I recall correctly. (Someone with more recent time on them please correct me if this wrong!)
It has been a long time but in a Citabria, I recall talking students through stalling in a climbing left turn with a bit of power with a little too much rudder and holding off bank with aileron. (This simulating at altitude what might happen in real life trying to make a unplanned landing site due weather or maybe rough running engine, turning onto final and needing to stretch the glide and the pilot unconciously is avoiding banking too steeply because they are low to the ground so they skid the final turn around on rudder).
I recall it makes for a quite sharp spin entry and a loss of several hundred feet in a blink. The Citabria normally has a very good manners and a gentle predictable spin entry from a simple unaccelerated stall.
Teaching people it is OK to use ailerons to keep wings level in a stall is something I would feel very wrong about doing. On some aircraft it works fine but it is not a good habit to have people get into.
Is not that the whole point of washout?
And in reality - as demonstrated in the video I posted - opposite aileron at the point of stall can actually facilitate a wing drop.
I know I am only referring to basic GA type aircraft, but for the purposes of this conversation, that's what most of us fly. Also, most of us have done a few stalls and spins in our time and at least in my experience, wing drop at the point of stall can be countered through use of opposite rudder, whilst opposite aileron has the reverse (and undesired) effect.
I know I am only referring to basic GA type aircraft, but for the purposes of this conversation, that's what most of us fly. Also, most of us have done a few stalls and spins in our time and at least in my experience, wing drop at the point of stall can be countered through use of opposite rudder, whilst opposite aileron has the reverse (and undesired) effect.
As you say, most of the aeroplanes we fly were certified to older or very old standards so I like to stick to that script.
(Fairly new certification requirements of FAR 23 etc do require the aileron to be effective the normal sense throughout the stall - saw some video yesterday of flight tests of a new type showing exactly that.)
I know you guys do this for a living, so what is it I'm missing?
Last edited by djpil; 4th Mar 2017 at 04:53. Reason: missed a )
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Thanks for the links. The "Falling Leaf" manoeuvre is what I was referring to earlier about using rudder at the stall to prevent a wing drop.
Unfortunately, I'm nowhere near Avalon
Just described the Mallard incident, I believe.
Unfortunately, I'm nowhere near Avalon
Originally Posted by jonkster
I recall it makes for a quite sharp spin entry and a loss of several hundred feet in a blink.
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A very good video on upset recovery, stalling, and most importantly, Stalling while Skidding, and slipping.
Not once is anything mentioned anywhere about picking up a wing drop, let alone using aileron or rudder to pick it up. Slipping at the point of stall is nothing to worry about, Skidding on the other hand will kill you at low level. and both are demonstrated here.
https://youtu.be/ovXZxwUN-ZI
skip to about 20 mins for the skidding slipping stuff.
"Keep your ball centred or your balls are gonna be all over the ground" - Josh
Not once is anything mentioned anywhere about picking up a wing drop, let alone using aileron or rudder to pick it up. Slipping at the point of stall is nothing to worry about, Skidding on the other hand will kill you at low level. and both are demonstrated here.
https://youtu.be/ovXZxwUN-ZI
skip to about 20 mins for the skidding slipping stuff.
"Keep your ball centred or your balls are gonna be all over the ground" - Josh
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They may not say it, but they certainly do it: 00:35 for example.
And those slipping turns at 22.00+ where the aircraft remains stable in the stall (no spin entry) - that's all opposite rudder.
Just sayin'.
And those slipping turns at 22.00+ where the aircraft remains stable in the stall (no spin entry) - that's all opposite rudder.
Just sayin'.
yes exactly! The bit you point out is with the aircraft cross controlled but not yawing, it is slipping (due excess rudder) but basically tracking in a straight line. You can do that in a Citabria (in the video a Decathalon) and it won't bite. Similar to how you would side slip to lose height on final.
If however you are cross controlled and yawing due excess rudder (ie skidding) and it will bite. Similar to trying to skid it around on a base/final turn and avoiding too much bank. Stall then in the Citabria (and Decathalon in the video) it enters a spin really smartly.
Why I suggest saying use rudder to control yaw NOT to "pick up a dropped wing".
If however you are cross controlled and yawing due excess rudder (ie skidding) and it will bite. Similar to trying to skid it around on a base/final turn and avoiding too much bank. Stall then in the Citabria (and Decathalon in the video) it enters a spin really smartly.
Why I suggest saying use rudder to control yaw NOT to "pick up a dropped wing".