The vg's on our Navajo are used for a gross weight increase. In other words, the normal PA31-350 has a max takeoff weight of 7000#. The vg's increase our t/o weight to 7368#. Our single engine roc is vastly improved over stock, as is single engine climb, vmc (minimum control seed single engine). Overall I can think of no reason not to install them except for being cash strapped.
Tony Wright
