I think differently. The two speeds aren't necessarily the same.
Vy is the point where there is the greatest excess power. It is the difference between two independent curves ie power available & power required.
Vg occurs at the best L/D ratio ie minimum drag, a different curve from the other two. Min drag is just that. The lift required is being obtained for the least amount of drag.
Power available changes with speed.
Power required is derived from Thrust required x TAS. This the same as Drag x TAS. Multiplying the two together gives a different curve to the original Drag curve.
For the sake of argument, change the engine characteristics slightly and the power available can change, leading to a different point between Power Avail. & Power required curves where they're furthest apart.
This hasn't necessarily changed V min drag so hasn't changed Vg.
Last edited by Tinstaafl; 25th Aug 2004 at 19:17.