Aerodynamix

From what I understand from my own research on this topic, you're basically right. The main issue is that the airflow over the main wing must remain the same at all angles of attack to keep the aicraft stable and predictable. With the canard slightly above the main wing, the canard's wake is always above the main wing and never/rarely flows below it. If the canard were below the main wing, the canard's wake during straight and level cruise would be below the main wing which is ok but as soon as the aricraft pitched up to climb or from turbulence, the canard's wake would strike the leading edge of the main wing and interfere with the airflow over the main wing and likely cause some undesireable effects. As far as the undercarriage is concerned, a low or mid main wing is desireable since the gear can be attatched to it relatively simply and retracts can retract inward into the fuselage. If the wing were high, the gear would be attached to the fuselage, have a narrower track, and be a little less stable on the ground.

Hi there. This is my first post on The Canard Zone and my handle "Aerodynamix" is the same I use to post on other forums. Before I answer your question, I feel the need to point out that I have no formal training in aerodynamics and every thing I know I have learned myself over the past decade. Second, aside from some very basic experience with working wood, ceconite, aluminum, and composites, I have never actually built a manned aircraft before. Thirdly, I am not a fully trained pilot. I have started training but due to my current financial situation and a certain medical issue, I don't feel it necessary to continue at this point in time. Also, as Jon mentioned there are several CFD (Computational Fluid Dynamics) programs available and I have used several of them including X-Plane but I feel that there is still room for error and their version of your aircraft should not be taken as gold. Ok, on to your question. The aerodynamic center of a wing or any control surface varies slightly depending on the airfoil you use, however, the rule of thumb is to use an imaginary line spanning from the root to tip at 25% of the wing's chord, measured from the leading edge toward the trailing edge. A wing with a constant chord (Hershey bar) planform (wing shape as viewed from above) with no sweep, it is easy to figure out the Aerodynamic Center (AKA: Center of Pressure). On a swept wing, either fore or aft, the AC can be calculated as: (RootChord + TipChord) / 2 = MAC (Mean Aerodynamic Center) Note that this formula only works when the leading edge and trailing edge is completely straight and not curved like the wing on a Spitfire or Concorde. So at whatever span the MAC happens to be on, just draw an imaginary line parallel to the fuselage center line and where that line intersects the 25% chord line (from root to tip), that's where your Center of Pressure is and that's where your airplane will balance and where all moment arms (horizontal tail or canard or both!) will be measured from. I hope this helped and I'm always open to constructive critisizm when it comes to fine-tuning my knowledge of everything aviation related so everyone, feel free to correct me if necessary.