Dave,
I understand that in the laminar flow environment of a university wind tunnel critical spacing of the propellers ensures perfect reversal of the induced swirl.
(unless i found a way to break the tunnel by not securing the turbulence generator boards
) In the real world of turbulence, gusts, manouvres, tired pilots, etc without ducting to force this you will need to use a large amount of tip washout to at least minimise BVI.
In practice, i just don't see the advantage. Leishman comments that it is only really applicable for high disk loading, which we
aim to avoid in helicopters - right? Even so similar diameter disks have the advantage of the rear rotor drawing in clean (laminar) air from outside of the front rotor. For your concept I just don't get what the benefit is.
If we are agreed that critical spacing is of interest only to PhD students trying to expand the capabilities of CFD software modelling, then forget trying to cram in the prop-rotors ahead and astern the wing. Space them out nicely so that you can have a nice simple vectoring system - consisting of sprockets and chains (like Harrier). Trust me simple solutions work - every time! (I'm used to having to justify why i want to redesign castings and repackage layouts to the money men).
What i mean by "transition" is that at some point your concept must go from its very power hungry, hence time limited, hover to its real comfort zone of high speed cruise. It is designed for >300mph high speed, right? Otherwise, why not just put down an order for "son of X2"? Your nice pictures of laminar flow stream tubes will become a jumble of lines where that wing is partly stalled and our PhD students have a field day seeing whose CFD code gets the closest to right answer. You could eat even more payload with a wing swivel mechanism. You could provide a self stowing helium balloon...
The point is that the Chinook development team faced similar problems and opted to put the rear rotor up out of the way of the messy front rotor outwash. If you want to see a 21st century bi-plane, look up the Quickie Q2 then see whether the rear wing is the low or high wing.
Perhaps i have laboured my points too strongly for your tastes. But my honest opinion just has to be that this concept is just too complex to be competetive...
