jgull,
i think you may be on to something. i have changed some components around so the cg is about 3" from the fan-line, and the fan line is about 2 inches above the bottom of the saucer. (the long flat part, i am not talking about the part that extends downward that holds my radio equipment and battery) so the gc is only about 1" below the bottom. the disk is 36" diameter, and the four fan holes are about 11" diameter each. i am hoping this information will help you a bit. while i hardly understood what you said, i caught a little bit. you said according to your equasion, if phi is the distance the cg is below the saucer, and if the value is greater than 0, a slight tilt will increase the moment on the downward side and decrease it on the other side augmenting the situation. so in my thinking, if you gave phi a negative value, a slight tilt would decrease the downward moment on the lower side and increase it on the other side causing positive stability? or would it just cycle the equasion the other way and create the same result? would the solution be to give it completely neutral static stability?

BTW, it does not jsut tilt over to one side, it tilts over, and then tilts the other way much more severely than the 1st time and by about 4 times it is on it's side, it slips out of the air and falls to the ground. this sounds like what you have discovered to me.