[secant0give]

It’s been established that it was, not tail heavy, it was not pilot error, it was not radio failure. It was not incorrect incidence, the throttle wasn’t opened up suddenly, control rates were set reasonably for this type of model.

Kieran It could be that the fin is too small. I.e. the Centre of lateral area is too far forward. Here’s a couple of Pics showing the changes I made from the original plan.
You can see that I moved the wing back slightly as well as made the fuse bigger at the front. The design was probably already pretty close to the money with having the minimum sized fin. Which makes sense from a drag reduction point of view, after all it is a pylon model.
I’ve enlarged the lateral area in front of the C of G by quite a bit by making the fuse taller and moving the wing back a little so I could get the ESC in up front.

   

The Wing is also a little bigger in span, than the original design, which doesn’t help with Lateral Stability.

   

The other thing I don’t like is that the tail is just a little lower than the wing. I don’t like the idea of the tail being in the down wash of the wing. Even tho’ the insidence angle is zero the wake of the wing can have the air flowing
At a slightly different angle and this may upset things in Pitch ?? The original design had the wing and tail in line. I had moved the wing up, by probably just the wrong amount.

   

The model survived with out too much damage so I guess the next step is surgial removal of the tail group and repositioning it higher, further back and the enlargenment of the fin.