for the wing to hit 90 when the rotation hits 0 try 90-thisComp.layer("Plane").transform.rotation
to flip the value from -90 to 90 try -thisComp.layer("Plane").transform.rotation
“thisComp.layer(“Plane”).transform.rotation” is the code you get when you drag the pickwip to plane’s rotation.
and of course all of that is on the code should be on the scale of the wings.
Good Luck!