Thank you for your question. Your most recent edit points to where your misunderstanding stems. Relative Wind is a function of flight path relative to the airfoil chord line. It is how the airflow interacts with the wing surface. Your frame of reference is the airfoil, not the ground. Align the Relative Wind with the flight path of the airfoil/wing. For big picture understandings, we can consider this roughly the same as the flight path of the aircraft with a little consideration given to how the wing is angled on the fuselage (Angle of Incidence).
It is the same concept whether the Relative Wind/Flight Path were parallel, perpendicular, or at an angle to the ground. It is true whether the aircraft is flying horizontally, vertically, inverted, straight up, or straight down. This is even true in a loop. The flight path (therefore the Relative Wind) would be roughly the tangent of the loop. Or, even if the airfoil/wing is spinning in circles in front of, above, or to either side the aircraft. Do some research on P-factor, auto-rotation, and vortex ring state. After all, propellers and rotors are airfoil with chord lines and angles of attack.
You are assuming that the aircraft’s flight path changes with attitude. Your blue arrows all represent the Relative Wind if the aircraft airfoil chord lines were relatively parallel to its flight path. That is only true in the first diagram. In the second and third diagrams, the chord line of the airfoil is not parallel to the flight path. The flight path in all three diagrams is from left to right, parallel to the top and bottom of the page.
In the first diagram, the airfoil is flying level into the Relative Wind created by the movement of the aircraft through the airmass. In the second and third diagram, the aircraft’s flight path has not changed. The airfoil’s position in the Relative Wind has changed. This could be caused by a sudden change in attitude. The aircraft’s flight path would not change until aerodynamics and power plant thrust overcomes the aircraft’s momentum. It could also be caused by the reduction of power necessitating an increase in nose up pitch in order to maintain level flight. For instance, pulling back on the control yoke abruptly and violently would change your attitude before it would change your flight path. Also, doing straight and level slow-flight would cause you to fly with your nose in an abnormally nose high pitch attitude.
To use your example of fighter planes and acrobatic planes, let’s look at some real world examples. If you ever watch a fighter plane rapidly change pitch, you will notice fog or clouds form just aft of the leading edge of the wing. This visible moisture is not visible when the aircraft is flying straight and level in unaccelerated flight. It only happens when the aircraft abruptly changes attitude. No matter how it looks, the aircraft’s change in flight path is not as abrupt as its change in attitude. In the case of an abrupt pitch nose up, the angle of attack will abruptly change until the aircraft’s flight path realigns itself to the new attitude.
Don’t make the ground or the horizon your frame of reference for Relative Wind. Don’t even use the direction of flight based on the aircraft’s longitudinal axis. Make your frame of reference the path of flight of the chord line of the airfoil through the airmass. The way the airmass hits or the air molecules interact with the airfoil/wings determines the Angle of Attack.
Relative wind is opposite of the aircrafts 3-dimensionally path or track of flight regardless of its attitude. If the aircrafts path of flight is straight up, straight down is the direction of its Relative Wind. You can extrapolate the same point to a banking aircraft. Relative wind is depicted as horizontal to simplify the imagery of a complex subject. It is similar to the fact that most maps and sectionals are printed with North at the top regardless of which direction you are actually facing. If you are confused, just turn the paper to orient it correctly.
Try this with your diagrams with your blue lines removed. If you are flying straight and level in unaccelerated flight, the first diagram would represent your Angle of Attack. If you were to reduce power to slow your airspeed while maintaining the same attitude, you would start to descend in altitude. The second diagram would represent this if you turn it to keep the airfoil chord line parallel to your frame of reference (the actual ground) in your visual field. If you were to bring the power to idle while maintaining the same attitude, you would descend at a faster vertical speed. The third diagram would represent this if you were to turn it so that the airfoil chord line remains parallel to your frame of reference (the actual ground) in your visual field.
To understand this from the frame of reference of the airmass, think of yourself as a human shaped air molecule either stationary or moving at a different speed or direction than the airfoil. Your feet are pointing toward the earth and your head toward the sky. If the airfoil from the previous paragraph strikes you while in level flight like in diagram one, the leading edge would hit you right in the gut. If the airfoil were to strike you while in a descent or in nose-up attitude level flight at a slower airspeed like in diagram two, the underside of the airfoil would hit you in the forehead. If you increase the descent rate while maintaining a level attitude or increase nose up pitch in straight and level slow flight like in diagram three, more of the underside of the airfoil would hit you on the top of your head.
