Overbanking tendency

[Black_Dawn]

In my years of flying, I've always believed that during a turn, the lift was equal on both wings. Recently I've found in the FAA-H-8033-3B pag. 3-13, a description of overbanking tendency due to a faster travelling outside wing in respect to the inside wing during a turn, so you have to counteract by opposite aileron when the desired bank angle is reached. Being now some years that I retired from flying, so I could be wrong, I can't recall to have ever used such a maneuver during a turn. I did some research in aerodynamics books, but did not find anything about this tendency. Could someone shed light on this aerodynamic fact.

[B2N2]

FAA publications are not always 100% correct they’re just the least amount of wrong.
As far as I’ve always understood is that overbanking tendency is a function of static/dynamic stability inherent to the design and the amount of bank used in the turn.

For instance a C172 will slowly roll wings level from a shallow banked turn while it will steepen the bank in a steep turn.
So it displays positive static stability up to a certain bank angle.
Past that bank angle you need a bit of opposite aileron.

[Black_Dawn]

Hi B2N2
what about the difference of lift during a turn, is it wrong?

[B2N2]

Aerodynamically speaking it is correct

https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1200x675/image_cb2e7d7160467826334da12e7ba0bf3a9aa4fd24.jpeg
Can’t find a better picture but visualize a line from the wingtip down to the ground or an imaginary point. This forms a cone shape with the (in this image) right wing higher in the cone then the lower.
So the higher wing has a longer distance to cover.
If your airplane would display static instability or even neutral it would have a overbanking tendency.
Since all GA trainers display stability it’s an academic subject rather then a practical issue unless you’re doing in excess of 45-50 degree banked turns.
As a CFI this is fun and easy to demonstrate after an appropriate ground lesson.

[Black_Dawn]

So, if I've understood right, the right wing has more lift (being faster) and I've to counteract the overbanking tendency with opposite aileron. Is that correct?

[vilas]

But not in FBW. The flight control computers will hold the bank and AoA for you.

[wiggy]

Black_Dawn

It’s a heck of a long time since I’ve taught this but if we are talking at ab-initio level certainly I’d be careful of overthinking this…and as has been mentioned characteristics of the aircraft may enter into it…

All your average blogs or bloggess really needs to know is that they should select the attitude required for the turn (30 degree, 45 degree, whatever) and around the aircraft goes with the pilot making making small and appropriate control inputs to maintain the target bank..(and pitch A/R)

I’m a bit :hmm: about the implication in one post that the effect is more pronounced at high angles of bank, maybe that’s an aircraft specific thing…..

[Black_Dawn]

Sorry, but I don't understand if there is a difference of lift between the wings during a turn or it is only evident in steep turns.

[fitliker]

Not an issue in most training aircraft until you get passed 50 degrees of bank , at 55 degrees of bank you are holding aileron to stop the roll . Most pilots never look at the yoke in a steep bank . But if you glance for just a moment at the yoke position you will see just how much opposite aileron you are using to maintain a steep turn at 55 degrees of bank . To hold that attitude you will have to hold up the wing . With the ball centred of course !

[farsouth]

Not quite sure about the explanation of the higher wing travelling faster, therefore creating more lift, and this effect being greater the higher the bank angle . . .
If you look at the two extremes, a flat, rudder only turn would result in the highest difference between the wing speeds through the air, and the closer you get to a 90deg bank, the less the difference between the wing speeds - as the hypothetical cone that B2N2 refers to becomes closer to a cylinder!

[Black_Dawn]

here is a video by an instructor showing a steep turn without touching the yoke. Maybe because he didn't get passed 50 degrees of bank. It seems the wings are producing the same lift. So I'm confused!
from time 1:44
Steep turn

[dash34]

Glider pilots know that their aircraft have a pronounced tendency to overbank if not corrected with aileron and rudder.

[sablatnic]

Black_Dawn

That is absolutely correct when flying slower and or long winged aircraft, especially gliders, but you just correct for what the aircraft does. Not doing anything the aircraft will end in a death spiral, graveyard spiral, have seen several names for it.
Thermalling in a glider you will end up with rudder into the turn, and ailerons out of the turn. (Cross controlled).
Gliders won't turn on ailerons alone because of adverse yaw. I have tried, holding the camera with my hands, the stick with the knees, and no feets free for the rudder - not possible, way better to leave the stick to itself those few moments a picture takes.

[POBJOY]

Oh, I thought you got wings near vertical with the power ON and nose slightly UP to give a bit of fuselage lift, and kept pulling, ensuring if in a suitably strong Cessna (like a 180) you had the Top tank selected so the power stayed ON. A small touch of flap can help. Not recommended for NDB holds or CAA IR renewal.

[ChrisJ800]

Isnt that why planes have dihedral to counteract overbanking? The inner wing is flatter to the airflow therefore produces more lift to self level...

[B-757]

.. Easy way to visualize the aerodynamics in a turn is to look at a Nascar racetrack ..The curves are tilted..The outer wheels of the racecar have to cover more distance around the curves, therefore they must be spinning at a slightly different speed than the inner wheels.. Same thing with the wings of an airplane in a turn, therefore there must be a difference in lift..

[Black_Dawn]

B-757
what you say is clear. I quote you "Same thing with the wings of an airplane in a turn, therefore there must be a difference in lift", so how do you explain the video I posted: the aircraft is in a 45 degrees bank steady, the pilot isn't touching the controls ( they are in neutral position) and the aircraft keeps going steady in the banked attitude without rolling; this give me the idea that the wings are producing the same amount of lift even in a turn. Am I missing something?

[washoutt]

Doesn't a trim deflection alter the equal shape of the wings? So the inside wing may have slightly more lift than the outer one or the outer one slightly less. Dash 34 is right, I remember that from my gliding days.

[Black_Dawn]

washoutt
I don't understand how could possibly the trim, which is acting on the elevator, alter the shape of the wings?

[wiggy]

I fear the discussion is headed down a rabbit hole but as a point of order I think the reference was to trim in roll (aileron and/or spoiler trim)…

FWIW I spent umpteen years flying around (gliders, fast pointy things, bigger things, some with FBW) and like you say in your OP I don’t recall ever having to consciously nudge or remind myself to apply out of turn spoiler/aileron…I don’t deny the aerodynamics theory behind this but I suspect like many I just (tried) to waggle the controls around to achieve the desired attitude/result…

[Black_Dawn]

Hi Wiggy, I agree with you. Just to end the question, I would paraphrase freely Sikorsky's famous bumblebee quote: we, pilots, turn the aircraft without caring or knowing how lift behaves on the wings.

[boguing]

The difference in speed between the inner and outer wings will disappoint. In a 40' span aircraft at 80kts in a Rate 1 turn the outer is (averagely) going 0.62kts faster than the inner. Roughly 0.8% difference in lift.

[sablatnic]

It is actually a bit over 1.6% - lift is the speed squared, but it doesn't do much difference in your example. In a glider with 50' - 80' span and a speed of 35 - 40 kts it is however very real, but again, it isn't a problem, you see the bank increase and the yaw string go sideways, and correct with a bit of rudder and opposite stick.

[boguing]

Oops. Schoolboy error... and I knew there was something wrong as I looked at my scribble, but couldn't see it for looking.

[Less Hair]

Another reason to have pilots begin on gliders before moving up the magenta line.

[blind pew]

Called spiral instability which most aircraft suffer from except paragliders at relatively low bank angles..above roughly 40 degrees they go into a locked in spiral with nasty outcomes.

[Deskscribbler]

It's a curious mix of the original poster's "outer wing faster", vs. the dihedral which will tend to return things to wings level. Other things affecting it are the size of the fin and directional stability and even the wetted area above and below the CofG.

[Vessbot]

The difference in wing speeds, as a percentage of the turn radius becomes larger the more steeply you're banked (and the turn becomes smaller.) But this reverses past a certain point, where at very high banks, the wings are nearly on top of each other, and the relative difference shrinks again.

This is only one aerodynamic effect, and there are other minor ones that, as people above have said, there's no pressing need to understand, and can be simply counteracted by use of the controls while maintaining the desired bank, and essentially treated as turbulence or other aberrant minor upsets. For example, is the long-tail effect, where even though the CG of the plane (and the ball, or IRS) is perfectly balanced on the path of the turn circle, the vertical stabilizer is flying outside the circle and sees a relative wind coming from the outside, and therefore produces a yaw (and roll) toward the outside.

Dihedral, by itself, has nothing to do with this though. There is no physical process by which the projected wing area over the ground, effects the amount of lift. Dihedral effect is a response to sideslip and not bank, and will therefore only act on the plane if sideslip occurs.

[Deskscribbler]

Sideslip does build during a spiral dive though? The spiral tendency being partly a balance between directional stability reducing sideslip and the dihedral trying to use said sideslip to roll more wings level? So an aircraft with more directional stability will have a greater spiral divergence tendency (all others equal), and an aircraft with more dihedral less of a spiral divergence tendency (all others equal)? Worst being an aircraft with strong directional stability (big fin) and lesser dihedral?

[Vessbot]

Sideslip may or may not develop, that's a function of a host of external factors, as well as the rudder response (or non-response, or over-response) to them. Any effect that the dihedral has is a result of this sideslip, and not of the bank angle. If you're over-ruddering the turn (ball to the outside) then dihedral will tend to increase the bank, not return it to level.

Anyway, there's a common misconception of dihedral's function (It's looking now, that that's not what you meant, but the poster a few replies from the top certainly did with "The inner wing is flatter to the airflow") that says that the inner wing's bigger projected area over the ground, somehow translates to an aerodynamic significance. And this is not true: you can have a plane with (ridiculously exaggerated for effect) 45 degree dihedral at 45 degrees of bank, so the inner wing projects 100% of its area over the ground, while the outer wing projects 0%; and as long as there is no sideslip (ball is in the middle, airflow is straight down the fuselage) this fact has zero bearing on any force on the airplane.

[Locked door]

All aircraft are different.

Fly the output (ie make it do what you want).

Some types need opposite aileron, others don’t. Except in a stall turn, then they all do.

(standing by for incoming………)

[blind pew]

Incoming..symmetrical airfoil..if you get it right!

[fitliker]

Using aileron in a stall turn can induce a spin very nicely and quite quickly . A cruel Method to introduce spins to newbies :)

[FullOppositeRudder]

All aircraft are different.

Fly the output (ie make it do what you want).

That's certainly been my experience.

Not to put a dampener on the discussion however - it's all been most interesting - and informative. May it continue please ...

[punkalouver]

I definitely have seen this tendency when doing a steep turn. I don’t want to say that all light aircraft have this characteristic, but I have seen it.

I happened to read the other day that had a description about this phenomenon.....

Proficiency: Take it to the bank - AOPA (https://www.aopa.org/news-and-media/all-news/2020/may/pilot/proficiency-anatomy-of-a-turn)

"Overbanking tendency. In a coordinated turn, the aircraft moves along a cone so that, in any given amount of time, the outer wing moves faster through the air than the inside wing. The differential velocity means that the outer wing, with more lift than the inside wing, tends to roll the aircraft more deeply into the turn—so it is necessary to hold aileron against the turn. The wider the wingspan, the more noticeable the overbanking tendency becomes, so glider pilots know it well."

There is a bit of a diagram in the article for explanation.

[wiggy]

fitliker

Must be another aircraft differences thing then because it was very much needed on the JP :bored:

[B2N2]

Have we figured it out yet?
:8

[zzuf]

I don't think it can be figured out before an accurate sideslip angle for the noted symptoms is given.

[FullWings]

I can hold a 45deg banked turn in my glider at ~55kts, and due to the span the outer tip is going some 33% faster than the inner one. It has always amazed me that there is very little, if any overbanking tendency; I suspect there are many other things at play, not limited to wing flex, fin/fuselage effects, rudder deflection, etc.

I agree with Locked Door about flying the output - apply control inputs to achieve your desired attitude...

[boguing]

One fairly important thing not mentioned so far is that the AoA of the inner wing is higher, and to an extent will restore the lift lost through lower speed.

[Vessbot]

Can you expand on the AOA being higher? I'm not seeing it. Are you talking about the roll-in, or the steady part of the turn?

[FullWings]

Sounds like roll damping/subsidence, which is a dynamic effect. In a steady state turn AoA is the same across the wing but the airspeed differs from one end to the other.

[boguing]

In the very simplest terms, the wing foil itself has to be pitched up to the approaching air to generate lift. Separate the angle of flow into the horizontal and vertical components. The horizontal component is the wing's speed and makes drag, and vertical could be said to be the amount of air needed to deliver the lift. Now take the two wings of a turning aircraft. The same amount of air must be coming up vertically to each wing, but one is travelling faster. Recombine the two sets of vectors for each wing.

[Vessbot]

Boguing,

I see where you're coming from. For a propeller, there is the rotational component, (in-plane with the disk) that increases in magnitude at a further-out radius; and the forward component, which is the same at all stations. The resultant of those two is the relative wind, which changes angle due to the change of the rotational component's magnitude. (Notice that so far, I have not brought the chordline into the picture. All we're concerned with, is the relative wind and the components that go into it. Without referencing the chordline, we understand the change in relative wind. But this changing relative wind is why the twisting chordline changes along with it, to keep AOA the same.)

But the analogy from this, doesn't carry. For the (wings of) the plane in a turn, there is no motion component analogous to the forward component of the prop. The plane is moving forward, of course, but THAT IS the rotational component. The whole picture is turned up 90 degrees. If you simplify it down to look at a plane doing a zero-bank turn with rudder only, different stations along the wing are moving at different speeds, but the direction does not change. It is precisely horizontal. There is no motion 90 degrees to that, to add and come up with a resultant at an angle.

If you remove the zero-bank simplification and look at a normal banked turn, the path of the wings sweeps out a cone instead of a disk, but the relative wind at each station still comes from the horizon...with no component from above or from below. Upon rereading your post, this could have been a lot more succinctly put to say "there is no vertical component." Anyway. There is no relative wind change, therefore there is no AOA change. (Of course most planes have washout that varies the AOA, but this is mirrored left vs right.)

[boguing]

There can't be an angle (of attack) without a vertical component. There may not be one for the aircraft as a whole, but there is for its wing.

If this weren't the case how would you explain the tip stall of an incipient spin?

[FullWings]

Or if you’re taxying around in a circle on a wingtip wheel, does the AoA vary along the wing? No? Take the ground away - does it change anything?

The best non-mathematical description of AoA that I’ve seen is that it’s the difference between where the wing is pointing and where it’s going. For an aircraft in a steady banked turn, this is the same all along the wing, otherwise it would be rolling...

[Vessbot]

boguing,

"There can't be an angle (of attack) without a vertical component."

This is not true. Look at at a simple plane, flying at a mid speed and mid AOA, straight and level. There is no vertical component, but there is an AOA.

"If this weren't the case how would you explain the tip stall of an incipient spin?"

In this case there is a vertical component. But there doesn't have to be.

[boguing]

I've asked MadFltScientist (and would like to ask Genghis the Engineer but his pms box is full...) to chip in on the AoA point I may foolishly be trying to make.

[derdere]

That’s is what’s called spiral mode of the aircraft. Aircraft can have stable or unstable spiral mode. If it’s stable when you bank the aircraft and let it go it tends to recover itself from the bank over time. On the other hand, if it’s unstable, then bank of the aircraft gradually increases and ends up with what’s known as graveyard spiral.

It’s very closely related with dihedral effect. If aircraft has high wings or delta wings or wings that has positive dihedral (upward wingtips) then it’s tend to be more spirally stable. Meaning it will recover from the banks.

There is a tradeoff between spiral stability and dutch roll stability. The more spirally stable an aircraft is the more nasty dutch roll it has and vice versa. The spiral stability is not regarded as important as the other stability modes. And if there needs to be a tradeoff between spiral mode and dutch roll, the spiral stability is out of the window. And the reason for that is, even if it’s unstable it grows very slowly and by the time it becomes dangerous pilot already corrects it.

I have seen quite some aircraft that are spirally unstable. But hardly see one that is unstable in dutch roll.

[Banana Joe]

In addition to the outboard wing traveling at a greater speed (thus generating more lift), the sideways component of the relative airflow in a sideslip contributes to create overbanking tendency.

The sideways component flows around the fuselage from inboard wing's root, decreasing the angle of attack of the inboard wing, flows under the fuselage and then flows in an upward direction at the root of the outboard wing, increasing its angle of attack.

Quite a bit of a mouthful to write without an illustration available.
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/771x386/image_b08027970d20798149f32a753553e7132c880be9.png

On a high wing aircraft, the sideways component contributes to lateral stability.
https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/771x386/image_a908052d80ffc1e40fbfb47e725edae99edf5392.png

These images are taken from OAA PPL collection ebook.