That B'zar looks stunning
so, I will admit that I made a mistake with the Thornback... by building it at 85%, I don't think I have done the kite justice as to how good it probably is at full scale.
IME when scaling a kite down you need to add a bit of depth to the sail (more billow / longer standoff). The Thornback is a pretty flat sail by modern standards to begin with so will almost certainly need it.
I imagine scaled down it will get pretty skittish, the original plan was only a .85 size kite to begin with (150cm leading edge) even though it feels bigger.
As for building for someone, this is something I would do very selectively and with strings attached (I've discussed this with a specific person who reads this forum on occasion and the circumstances are different than what you are asking).
Since the question was about the Thornback and since I remember someone getting niggly about building for someone else a while back...
I'd just like to say as the author of that plan any amateur kite builder has my permission to do what they like with the plan including charging someone else for building it.
Anyone who wants to complain saying that's commercial use should understand that the plan was put under cc solely to deter commercial kitemakers i.e. factories from knocking it off. You know, the kind of outfit that pushes 'Revs' on ebay...
