Since mouse buttons already are assign to:

Left, click in some cockpit buttons/wheels, fire gunner MG...
Right, to pop up windows customization menus...
Wheel click to change mouse cursor behavior when press...

Make sense assign then for another functions?

To use whell as axis maybee work with JoyToKey.

@ Qpassa

To control gunner turrent/MG with mouse cursor hit F-10 first.
The standart sequence to get cotrol is CTRL+O, F-10, SHIFT+F1.

In conf.ini you can change cursor speed.

Sokol1