Thanks for the info chaps. The purpose of it makes sense to me now.
Genghis It's especially reassuring to know that it equates to 81% of the max energy. I realised that there was a safety margin and the wings shouldn't fall off at Vne but it nice to be able to quantify it. I've replaced virtually all of the tail surface control cables on the Auster and had the elevators and rudder painted. If I end up doing the airtest I will be approaching Vne very carefully, feeling for the onset of flutter.
M14P now that I understand the purpose to the Vne check I agree that bizarre was the wrong word and yes, the Cub did need adjustment to the aileron cable tensions.