I too am so sorry to see the failure.

I keep looking at all of the photos and all of the fixes for clues why some are failing and some are not. There is not a large amount of data to work with.

I fitted logitudinal formers before I flew both of mine. My buddy did not. None have failed and we have been snapping them in FAI ubknowns etc, to our hearts content.

I have postulated that the rudder "death dance" could be a culprit. That made me put on two new lightweight rudders. He did the same.

I noted that in mine the logitudinal former is glued to the former in front of the stab. Thus making continuous force transference to the stab tubes etc. Could or would this make the difference? I don't know.

I did note that all of the ones that I know are using at least the lighter rudders. Could it simply be that the mass of the somewhat heavy stabs and the heavy rudder could be too much for the narrow neck just before the fin? This would be even heavier if rear elevator servos were used.

In any event, if I were building another IMPACT I would put a former lengthways from a balsa sternpost, glue it with sub-formers to the stab-tubes, and extend it past the narrow part of the fusealge.

I would, and have, run another former at an angle from 2/3 of the way up the sternpost, again, through the narrow section.

I would run 1/4" square strips all the way from the front to the sternpost and crossgrain sheet between them with 1/16" balsa. (I did this on #2)

Regards,

Eric.