Thanks, I have that part right then but I'm missing the AOA part. I'm thinking backwards, advancing blade teeters up and angle from the blade chord line to relative wind also increases. What am I not getting?
First think of vertical autorotation where there is no dissymmetry of lift and lift is equal on both sides. Hence teetering isn't really needed. Also 2/rev vibrations are largely gone because no teetering is happening and thus no application of law of conservation of angular momentum (ice skater raising her arms "in" to spin faster causing acceleration twice (2/rev), one at 3 O clock, one at 9 O clock)
In this case, angle of attack is high (stalled) close to the root (slow speed due to rotation) and low towards the tip of the blade because of faster speed from rotation. The regions of the disc are 1) stall, 2) driving, 3) driven and between stall and driving region there is an area of equilibrium where it transitions. Also between driving and driven region there is an area of equilibrium where transition happens.
The main reason for angle of attack to be high at the root and low at the tip is rotational speed. In the driving region the twist of the blade also contributes to a more positive angle of attack and helicopter blade designers play funky with this area to gain some advantages for their stated mission and spread the load more evenly across but for our purposes we just let nature do its thing because designing twist or [washout] isn't worth the effort for us.
To get a fuller picture of this, crack open your Rotorcraft Flying Handbook and look at page 3-9 onwards and read that carefully. Fairly simple and clear. Its the helicopter private pilot section but its the same concepts. Teetering 2 blade fixed pitch semi-rigid rotors are the simplest implementation of rotors from the helicopter point of view.
Once you understand and can visualize that in vertical autorotation these 3 regions have different AoA because primarily of rotational speed difference from root to the tip, you are then ready to go to autorotation in forward flight.
In forward flight, the airfoil path of advancing (and teetering up/rising) blade results in relative wind (resultant relative wind) that gives us a smaller angle of attack and airfoil path of retreating (and teetering down/falling) blade results in relative wind that gives us a larger angle of attack. A visual of this is attached in one of the pictures.
Don't need to do all the math and vectors. Just think that when at 3 O clock position the advancing blade starts to rise up (because this is where it sees the fastest wind speed and thus higher lift), the resultant relative wind also starts to come from "more above" because the airfoil has started to add a vertical rise path in its motion in addition to circulating forward in its in-plane path. Similarly, when the retreating blade at 9 O clock starts to go down (because this is where it sees the slowest wind speed and thus least lift), the resultant relative wind also starts to come from "more down". If you can visualize that, you can make sense of it.
Another way to think of this is, as in vertical autorotation you saw that the rotating blade has high angle of attack at the root and low at the tip due to rotational velocity producing different speeds. Well when advancing blade sees "additional speed" due to forward motion it then follows by same logic that it will inevitably see even lower angle of attack compared to its retreating brother which sees the opposite because its tip is now subtracting the forward velocity and slowing down. Awesome nature always looking for symmetry does the job for us.
Now we know from our 9th grade Physics that acceleration is a change in speed or direction (change in velocity). At 3 O' Clock and 9 O' Clock these blades are "both" accelerating due to law of conservation of angular momentum as they teeter up or down (doesn't matter). Their center of gravity is moving inwards slightly. That acceleration twice in one revolution is 2/rev hits you get and is directly the result of equalizing the difference in lift between the blades. You feel that most at 12 O Clock and 6 O Clock because that is how rotational systems work due to gyroscopic precession (90 degrees later effect)
Hope this helps.