John, I just got back to this forum after a long absence and finding your design disclosed on the CAFE site (and discussed on the homebuilt airplanes forum ) Firstly it is good to see the actual hardware and see that it is also technically feasible and in fact quite beautiful so congratulations on both scores . There are a few 'buts' though which come to mind .
Your voluminous descriptions and observations are hard to summarize or respond to but I will try to add some hopefully useful comments .
"Biplane interference" -- it has long been realized that biplanes can be favourable for reducing induced drag -there is nothing mysterious about that (it has to do with the streamtube being influenced by the wing not being a circle equal to span as Prandtl determined but a 'racetrack' shape having a parallel section inserted equal to the wing gap and therefore dealing with a bigger volume and hence mass flow of air so needing to deflect it less to get the same momentum reaction that we call lift . Newtonian physics is dafe still . Nenandovich in France published a series of papers showing such effects and various other SAE and AIAA papers over the years have followed suit --one man powered aircraft intended to use the concept and was in fact a joined wing well before Wolkovitch . The tip feathers of a soaring bird are an example of non planar multiplane and the Swiss tip grid is another application --Francis Rogallo did work for NACA on multi element airfoil arrays along with others over the years (nobody called homely old biplanes 'non planar wings' back then )
Your computer flow simulations a few posts back look somehow wrong --the upper one shows negative lift and strong upwash from the rear airfoil with little overall lift while the lower one at least shows some overall flow deflection and therefore lift -- the descriptions are opposite to this as far as I can tell (?) Wolkovitch designed a staggered tandem wing aircraft for Vought that had in effect a huge T tail and calculated induced drag only 0.6 of the Prandtl value --this was the predeccesor to his joined wing work when he realized how relatively unsupported the rear wing was and joining the two tips by sweeping them together solved the structural issue --when I met him in 1990 and had that paper with me he gave a wry smile and asmitted that this was how he came upon the concept (not the 'married man's hang glider' as he quoted --this was I think to 'freshen' the idea in terms of patent life )
In one post you compared the efficiency of a 'towed' vehicle ( a barge on a tow way pulled by a horse) as against a vehicle 'pushing' on a fluid -- indeed the reality is that not only do you scrub the air with the wetted surface of the aircraft as you would also if pulling it via a cable from the ground like a glider being winch launched but you also scrub ,at much higher velocity, the wetted area of the propeller in the act of thowing air rearwards (and the power absorbed being proportional to the cube of local airspeed means that tiny spinning surface absorbs the whole of the power of the engine with the lift reaction created then indirectly propelling the rest of the aircraft . This is undoubtedly inefficient and results in the wake of the aircraft being composed of one highspeed blast going going rearwards accompanied by another lot of air going forwards which is the wake of the aircraft itself (as seen by a stationary observer in a balloon basket as you pass )
the "ideal' aircraft would leave no wake in effect like being pulled by a cable from in front but adding enough power to cancel out the drag which was leaving energy in the wake --seen as forward moving air to the observer. Goldschmied attempted to get to that condition for bodies (airships and submerged torpedoes,submarines and then fuselages)
Bouyant bodies create no induced drag by needing no lift but flight requires lift and still faces the very large ( 66%) cost of induced power to stay airborne at least power point and 50% at best L/D -- a huge penalty as compared to a rolling or floating vehicle . To reduce that cost significantly will require some form of Goldschmied like wake energizing for the wing itself --in fact a propelling wing rather than one that is dragged along by a discrete propulsion system elsewhere .
This too has been known for decades -- every flying creature uses in fact a self propelling wing --we call it flapping .
The nature of flapping flight is that the wing can generate thrust at a maximum at the wing tips --where the local drag is the highest due to tip vortex and along the span the plunging velocity drops so that there is a net drag on the inboard part of the wing -- a combined plunge anf flap could match the local drag and wing thrust to give the ideal of a constant wake velocity along the span much like the ideal downwash distribution . Migrating birds exploit tip vortex energy recovery by flying in formation and 'unwinding' each other's tip flow ( they in effect 'surf' the upwash that occurrs outside the span --the start of the tip vortex roll up )
I suspect you are hoping to realize a similar sort of gain with the Synergy wing -- it is somewhat related to the spiroid winglet, the "C" wing or the tip tail configuration as well as the Whitcomb winglet in geometric terms and effect -- I would question how much value this will be in cruise UNLESS you can operate at a very high Cl which implies some sort of very high lift system or ideally variable geometry -- since induced drag is so low at higher speeds (without climbing into the stratosphere like commercial jets ) the potential gains are only small --gliders can get a net benefit by 'cheating' the span rule for 15Metre class and by spending half their time at very high Cls when thermalling --for the usual lightplane the performance benefits are minimal if any . (handling might improve and climb rate )
I don't agree that the Synergy is 'revolutionary' or breaks new ground conceptually but it is a fresh look and welcome in terms of experimentation --it is NOT novel in configuration though ( several papers on the joined wing sensorcraft depict a 'gull rear winged' joined wing with the same curious gap in the rear wing with the rear wing returning to the body via a pair of fins --jet engines are nestled in the 'armpit' region -- Several tip fin joined plus twin finned but long span configurations also exist -- Wolkovitch's design with twin turboprops at the fin(s) and rear wing intersection is an example and I think Rutan might have sketched something similar .
The big gap in the rear wing, or tail, cannot fail to increase induced drag regardless of the direction of the lift vector --the flow is so far from the wing tip that the flow will be essentialy "2D" and the danger is that very high local changes in Cl will threaten separation of flow from yaw inputs --leading to flow breakdown from the fins spreading to the wing and hence giving rolling and pitching moments . I don't like the look of it in that respect --at least a wing fence might be needed .
The Ligeti Stratos crashed (twice) due to interactions from the tip fins and the pitch surfaces --once in a flat inverted spin and the next in a crosswind take off -- destabilizing (or rather being super stable but uncontrollable) when inverted is a consequence of the highly loaded trim surfaces on canards and close coupled joined wings,tandems, staggered biplanes (flying flea included) and the geometric shift of CG and lift centre --make sure you have a tailchute ( in your case from one or both booms I guess ) and do some captive 'free flight' model tests at unusual attitudes on a car mounted rig or the like (that will get around your distaste for wind tunnels as well !)
I'll wind this up before the link expires Again..) Might post again after some more thought.
Good luck with further test flying.