From what I understand, the CG of full-sized fixed-wing airplanes need to be forward of the wing's center of lift for stability. But the CG of a helicopter must be directly below the rotors since it doesn't have a horizontal stabilizer to counteract the pitching moment.

So, where is the CG in a tiltrotor airplane (the kind that has its engines on the wings, such as the V-22 or the AW-609)?