You wish to start a turn to the left. So you move the stick (or yoke) left, which causes the aileron on the left wing to move upward and the one on the right wing to move downward. Two things result from this: one desirable, one not.
The good part is that lift from the left wing is reduced, and lift from the right wing is increased, resulting in the left bank that will produce the desired left turn.
The bad part is that the increase in lift from the right wing inevitably also produces an increase in drag (a wing’s lift and drag being more or less inseparable) - and the reduction in lift from the left wing produces a reduction in drag there. This differential change in drag causes the nose of the plane to yaw right - “adverse” to the way you wish to turn.
You deal with this by means of left pressure on the rudder. Indeed, the reason aircraft have rudders is mainly to deal with adverse yaw. The Wrights figured this out in October 1902 - a very significant moment in the development of manned flight.
Your confusion really starts with the earlier post about toy cars and begins to dissipate with this post here.
Cars & boats turn by forcing themselves sideways with what you’re (properly) calling yaw. And eventually that sliding sideways force causes the direction of motion to align with the new direction they’re pointed.
That’s also *almost *what happens when a kid takes a toy car which has non-steering front wheels & makes it turn. He/She applies god-like force to make the tires skid sideways as the car rotates to point in the new direction. Then he/she applies thrust in the new direction to force the car to travel in the new direction. There’s nothing preventing the kid from having the car drive around sideways or on its back the whole time. That’s the gift of being able to apply god-like force in any direction at any time.
All of which is irrelevant to aircraft flight. And as such provides a really lousy framework for thinking about how aircraft turn. So do NOT start from that framework.
Aircraft turn in a much more elegant fashion than a mere boat.
Let’s digress for a moment to your side question: “What does “pull back on the controls” mean?”
The “steering wheel” (AKA yoke) in an airplane controls bank. In aircraft with a joystick (AKA stick), tilting it left or tight accomplishes the same thing. In addition to that left / right action, the yoke / stick also pulls and pushes fore and aft. Which controls pitch, the third dimension. Pull back and the nose pivots upwards in the aircraft’s reference frame. Push forward and it pivots downwards. I reiterate that “up” and “down” here are from the aircraft’s & pilot’s POV, not the outside world. So “up” is towards the top of the tail and “down” is towards the landing wheels.
So when one says “pull back on the controls” they mean to apply a pitch change in the nose upward ( = top-of-tail-ward) direction.
Back to the main question:
Since you say you get vector diagrams let’s try thinking about a simple 2D example.
I’m flying along straight with wings level. I pull back the controls. The nose pitches upwards. The lift vector coming straight out the top of the aircraft is now tilted just a bit backwards versus vertical. which pulls the aircraft into a new path that’s angled upwards a bit versus level.
I keep the same inputs in. The nose continues to rise, the vector tilts backwards more and continues to pull the flight path into an upwards curve.
Assuming lots of engine power, we can keep this situation going all the way up to straight up, over on our back, down the back side, straight back down, then pull out of the vertical dive creating the classic aerobatic “loop”.
What we really did was a 360 degree turn in the vertical dimension. Tilting the lift vector back pulled us around this curved path as surely as if we’d been a rock on a string being spun in the vertical plane. The lift vector pulling towards the center of the circle works just like the string. The result is a curved path through space and a sensation of acceleration directly towards the outside of that curved path, diametrically opposite the line from the aircraft/rock to the center of the circle.
You’ll notice I haven’t mentioned gravity yet. Because gravity is irrelevant to this motion. In an atmosphere with no gravity the same thing would happen. The turning is the result of the lift vector displaced from the instantaneous direction of motion, not from any interaction with gravity.
IOW, the offset lift vector pulls the aircraft around the curved path. And this is the punchline sentence of the whole entire thread. It’s *exactly *the same physics as the leaning bike pulling itself around the curve.
In the real world considering gravity the result is to take what would otherwise be a nice symmetrical circle and squash it into an egg shape. Which you often see in airshow loops that aren’t all that well-flown: the smoke trail looks like an egg or a cursive letter “e” in the sky. True competition aerobatic pilots go to great efforts to offset gravity’s effects, flying an anti-egg shape just enough to offset gravity’s effects and produce, ideally, a truly circular path through space. It ain’t easy.
So far, so good? If not, re-read and ponder some more. Think about the lift vector always in the vertical plane, always pointed directly “up” in the aircraft’s reference frame, but rotating from Earth-up to Earth-sideways to Earth-down to Earth-sideways the other way and finally back to Earth-up.
Now let’s imagine an aircraft going straight again. Let’s say we’re going North. Let’s roll into 90 degrees of, say, left, bank and magically switch off Earth gravity. Now pull back on the pitch controls a bit. What happens? Exactly what I described above about a loop.
The lift vector pulls the aircraft around the turn. First towards West, then South, then East and finally back to North. And just like with the loop above, the result is a curved path through space and a sensation of acceleration directly towards the outside of that curved path, diametrically opposite the line from the aircraft/rock to the center of the circle.
So far so good? If not think about it some more. It’s the same interaction between aircraft, air, and motion / path through space. So it’s the same result (ignoring gravity).
Now let’s do the same “horizontal loop” thing but leave gravity switched on. In our 90 degrees of bank there is no part of the lift vector aimed upwards versus the Earth. It’s all aimed directly into the center of the circle and is spent turning us from N to W to S to E back to N. There is nothing supporting the aircraft in the sky and it will fall like a brick.
The apparent path through the sky when viewed from directly above will still be a circle. In 2D it will be a circle. But viewed from the side in 3D it’ll be a helix, like a coiled spring. By the time we complete 360 degrees of turn and are going North again we’ll be at much lower altitude. The wing and lift vector pulled us in a circle unaffected by gravity and simultaneously gravity pulled us downwards unaffected by the lift vector. The reason the lift vector and gravity didn’t interact is that they are aligned exactly 90 degrees apart by our experimental setup.
So far so good? If not think some more. Draw pictures and wave your arms. It helps.
Now we’re going to put it all together. A conventional banked turn is simply an intermediate case between the vertical loop and the helical descending spiral.
IF we adjust the bank to an intermediate number, say 10 or 30 or 45 degrees off vertical, AND apply the right amount of “aircraft-upward” pitch control, THEN we exactly offset gravity and our coiled spring becomes a closed circle at a single altitude.
If we pull too hard for our bank, we’ll create a helix slowly screwing itself upwards towards higher altitude. If we pull a bit too little for our bank, we’ll create a helix that slowly screws itself downwards toward the ground. And if we pull just right, the helix is a closed circle and we end up after 360 degrees of turn exactly where we started in all 3 dimensions.
The classic vector diagram which Richard Pearse explained in words in post #35 is showing exactly this: With a banked aircraft some of the lift vector is directed inwards towards the center of the curve and creates turning flight. How much vector is directed inwards? Cosine(bank angle).
And some of the lift vector is directed upwards towards the top of the sky (directly away from Earth’s gravity actually) and creates the force to offset gravity and hold altitude constant. How much vector is directed Earth-upwards? Sine(bank angle).
And in a properly flown level turn, the pitch input or control pull is exactly enough so Sine(Bank angle) offsets gravity.
Bottom line:
Flight happens in 3 dimensions where one dimension is special because gravity defines an up and down, versus the other two dimensions which have no such forces and are identical to each other. In an airplane we play off power, speed, 3D direction, and turning (= change in 3D direction) to maneuver in this 1D force field called gravity over this 2D-ish surface called “the ground”.
It’s easier to do than to explain. Many lightplane pilots never really understand this stuff. And they’re the ones who become fatalities when they get into corners where deeply grokking this is necessary to prevent catastrophe.
Aside: Robot Arm & Xema’s discussion about adverse yaw just above is a nuance point about aircraft design. It’s all 100% good and accurate stuff well-explained. But it’s a red herring for your purposes.
Late add: Armed with all that and Robot Arm’s shorter explanation of the bottom line same thing should set you up to read this for more if you care: Banked turn - Wikipedia
I don’t recall that. Which is not to say it never happened, just that I can’t add any corroboration.
I *do *vaguely recall a discussion about whether “down” should be the opposite of the local gravity vector or the direction to the geometric center of the Earth. Which would obviously be the same thing if the Earth was a perfectly symmetrical perfect sphere. Which it is emphatically isn’t either of those things.
To really pick that nit, it should also be a non-rotating symmetrical perfect sphere so we don’t need to include relativistic frame-dragging in our definition of “down”.
I don’t recall enough about the thread to have much hope of searching it up myself. So I didn’t try just now. Good luck.
ETA: Last night falling asleep I gave myself a major :smack: when I remembered that “banking” in aviation is the same as on land. It’s the word “turn” that should be banned.
Of course super fast cars “want to” (have to) bank; the motorcycle circus trick of spiraling up the inside of a sphere is a bank; of course bob sleds bank thrillingly and use what is practically a tunnel; ditto Olympic bicycle speed race tracks.
All of which (turning left or right) is a “2-D” thing, in mental, land-locked space, at one level (my vocabulary is failing me here), but as 3-D as aviation space, where the perfectly matched slopes of the bicycle track or bobsled funnel are traced by the underside of airplane and could be built to order ex-post-facto. (Got a little poetic there, but the mental image I have is clear.)
And now I’m really late.
Interesting enough, the first few hours of training when working on an instrument rating involves learning to recognize and recover from unusual attitudes. The student is wearing a hood that blocks reference to the normal horizon references, while the instructor manipulates the aircraft in an attempt to confuse the student as to the condition (attitude) of the aircraft. One quickly learns which senses are reliable indicators of aircraft attitude and which are absolutely not. Sound is reliable, seat of the pants feeling is not. JFK Jr. should have recognized an engine increasing pitch (sound) even though he most likely did not feel the descending spiral turn. In addition to the engine sound, at least 4 of his primary instruments would have indicated a descent, a couple more would have referenced the turning, but his senses were [del]telling[/del] guarantying him otherwise.
The problem comes because there’s a conflict, and your seat of the pants feelings are absolutely guarantying you that the flight instruments are wrong, and that you’re flying straight and level regardless of those pesky instruments reporting otherwise. It takes training, practice and discipline to overcome the desire to trust your senses and not the instruments when there’s a conflict.
So, why don’t inexperienced pilots who aren’t instrument-trained trust their instruments? I’m pretty sure that flight training would tell you all about this phenomena and tell you to “trust your instruments.”
Well, we’ve all been trusting our sense of balance since before we could walk; it’s hard to train that out of someone.
I had a little bit of practice time under a hood (kind of like a hat with a large visor, so you can only see the instruments). The idea was to learn how to do a 180 turn, so if I accidentally flew into a cloud I could turn around and get back out to where I could see again. I found it to be require very intense concentration, like taking a tough college exam but I couldn’t take a breather between questions. It was getting easier with practice, and I’m sure it gets easier still for pilots who are instrument rated and do it more often. But it’s not something that comes naturally.