Brian,

Very sorry to hear No. 2 went in with such a catastrophic failure. I remember what it feels like from Flight 19 of my No 1 last year and wouldn't wish it on anyone.

While there aren't many positives, I sense the last couple of failures have eliminated some potential causes and draw us closer to the likely cause. A couple of observations:
-- The failures aren't associated with high stress antics, mine failed pushing through an outside radius into the down line of a triangle, Brians not dissimilar, and same for two others I have talked to people about.
-- The crutch treats the symptom, not the cause. One down in Oz failed at the rear, but was repairable. A crutch was added in the rear and 3/4 of the way up to the back of the canopy, but not all the way. It subsequently failed as Brian's did, ahead of the crutch and behind the canopy opening.
-- The structural materal subscribes to Peter P's egg shell theory. When intact it is fine, when is is compromised a tiny bit it can fail completely. It seems to fail first in compression, which you see in the minor buckling/wrinkling of the surface, and once that happens all strength is gone.
-- Brian has now (expensively) isolated the hinge issue -- even with the exposed Robarts with lever arm embedded in soft balsa construction replaced it has failed.

So my guess is it points to the mass balance issue on some of the stock rudders, and there is a combination of airspeed well within the flight envelope, and perhaps a vibration that kicks it off in IC ones, that starts the death flutter. I don't know a lot about flutter but I assume it is some undamped natural frquency based vibration. The pulsing of the flutter down the fuz finds any weakness and Bang!

The lessons (aside from an aversion to flying Composites!) may well be:
-- Replace the stock rudder ala Eric H and others, and hinge it traditionally.
-- The crutch has to be one structural piece from the stab tubes through to well into the canopy area, with formers to stop any deformation of the oval structure. And as we have seen, that includes tying the crutch tightly to the rear former and through to the servo tray/rear wing brace.


An expensive set of lessons.

David