This post was written by David Walker on the old CUSF website.
My final year project was on building a guided rocket using canards during which I was fortunate enough to get access to a large wind tunnel for a week at very short notice. This proved extremely enlightening as the aerodynamics were much more complicated than I had been assuming.
Firstly the lift from the canards was much lower than anticipated based on 2D values (see graph). This was due to the extremely low aspect ratio (span/chord) of the canards, this meant the flow was dominated by the tip vortex. Due to the pressure differential between the top and bottom of the aerofoil a vortex is generated at the tip (see diagram) this vortex induces downwash which reduces the effective angle of attack delaying stall (the canards stalled above 30°) and reducing lift.
However the lift forces back calculated from the rolling moment are much lower again. To explain this requires consideration of how the vortices interact with the aft fins. As can be seen in the diagram below the vortices generated by the canards resulting in an opposing roll moment from the aft fins. Source: The Effect of Tail Fin Parameters on the Induced Roll of a Canard-Controlled Missile By Melissa McDaniel, Christine Evans and Dan Lesieutre.
My full report can be read here: Final report