GREAT!!!!! Would love to see the video of the flight! and the beach!!!! Have been thinking of bringing my bird to the beach for a video shoot.

My best guess just looking at your supplied pix, as I said before was probably just the "trim" bends, the V shapes bend in the middle of the push rod, was your issue. that might have been removing the stiffness you need to prevent the surface from flapping..... "Flutter".... Shoot you could have even rigged your camera on board and tried to induce a mild case of the flutters and see what was happening during your flight.

As I said before with my US40 I had flutter and I did two things to try and prevent it. Fill the gaps between your surfaces, You got that covered with the SPAD design.

I also moved my control rods closer to the end of the control horn which helped with the leverage of the control rods on the surfaces. It stiffened the controls just a little... My bird has been clocked at 118MPH so there is little room for play... I also tend to fly a little low..... 3 to 4 foot passes of the field and some in the 2 foot range and one on film at 2 inches... That didn't last too long as the prop split in half.... Now if only I could find the cure to that....