I have a Vector Flight Edge 540 that I want to use in basic patten contests. I have about 8 flights on it. It seems to behave very well except on the backside of a horizontal eight. As I come over the top of the first loop then straight down, when I add down elevator to start the second loop, it wants to roll out of the maneuver. Not snap, just roll. I can keep it going with aileron, but it shouldn't be doing that. It rolls to the same direction each time. I don't seem to have the problem while doing a reverse outside loop.

The throws for each elevator half are the same. There is no flexing as down elevator is in tension on the control rods. My elevator throws are very low as you don't need much with this plane. My cg is as specified by the manufacturer. Incidences at the wingtips are within 0.5 degrees.

I can't figure out why I am not having trouble with anything else except for starting the second loop of the horizontal eight. Any ideas??

Thanks.