Hi folks,

I'll pass on all the comments so far, but I won't see him again until Tuesday.
Turns out that he was going to use a 9x4 prop.
Remember that my sketch is not a scale drawing, done purely from memory in just a few minutes, so please don't take it too literally.
Possibly you are right that the rudders will work in an adverse manner, if they do he will accept that, but not before trying it. The same goes for airfoil shape, but this is his starting point. Remember it's made of polystyrene and will cost virtually nothing!
In fact he will accept any shortcomings it may have, and if he fails to rectify them after a few attempts he will scrap it, and move on to something else.
Believe me, he is very much a thinker.