Reference of position of each joints and links

A description of characteristics for the wing's formula and the body's
formula.

body a1 and body a2 are fixed.
wing a1 and wing a2 are fixed to the body y1.
wing w1 is fixed to the wing a2.

each angle of the formula is able to calculate by the position of a1.y.
(a2 is origin)

wing e1,e2 to always point towards target wing w1. ("Look at"
constraint)
wing o4 to always point towards target wing e1.
wing y5 to always point towards target wing e2.

wing e1a copy the rotation of e1 on the center w1.
wing e2a copy the rotation of e2 on the center w1.
wing o4a copy the rotation of o4 on the center w1.
wing y5a copy the rotation of y5 on the center w1.