"In reply to your comments, I refered to actual measurements as taken at the GC 2007 and have you included the aluminium rudderstock in your 12.64 kg ?"

Yes of course, in F18 weight of rudders is for the full system.

For memory, Viper at GC 2007 was prototype ... i think take it like references isn't fair ..

Now GC is finish, we could tell 8 Viper 2-up was present, 7 finish in the 8 th ... mens isn't enough for explain that.