Alex,
Thanks for the links, all of which I have seen but somehow forgot!
The bubble winglets are attractive from a structural point of view because I think there is enough base area to attach them with double sided tape and no mods to the wing. I'm actually thinking of 3D printing them hollow and completely closed in one piece with a very thin wall so they will weigh virtually nothing.
What I don't know is how high they would need to be made to work. I arbitrarily chose 25mm high for my Depron ones but it would be nice to reduce this a bit for the bubble version. Also is the bubble the same width as height i.e. 1/4 circular looking on the rear? I don't have a lot of time to sort this so don't really want to have to do another Depron trial if I can get away with it.
Your help appreciated.
Malcolm