You've got me as to why it spirals but I would guess it's the channel
acting like a giant rudder against the sweep of the wings.

The one I was working on spiraled also when the angle of the motor
was to steep. I finally got some lift out of it by installing a switch and
then over charging the capacitor to get some more RPM's. I also made
the bridge (canard?) adjustable with a pin to help. Lift is better but still
not what I hoped. I'm done with that now since I used up about 8 batteries
and finally fried the cap.

I also might redesign the bridge and make it bigger. It took some trimming
to get it to fly so anything you come up with to help stabalize it would help.
Now to start on an AA version.

I went back and added the CG to the plans.