Canard Drag


Standard methods for parasite drag prediction work quite well for canards: Compute the drag of fuselage, etc., at the desired Reynolds number.
Compute profile drag of the wing based on airfoil data at the appropriate Cl.

The canard profile drag is also computed from airfoil data at CL=CLc.
The tricky part of drag prediction is induced drag which includes most of what is generally termed "trim drag". (A part of the trim drag will also appear as profile drag.)

Given the lift on each of the surfaces, the induced drag may be computed from the expressions derived earlier for multiple lifting surfaces.


e is the overall span efficiency and is given by:

if the surfaces are individually elliptically-loaded.

By twisting the wings in just the right way the induced drag can be reduced from this value somewhat (see Ref. 5) but the preceding equations (which assume an elliptical distribution of lift over each of the surfaces) provide a good practical estimate. This is especially true when structural design is considered: the distribution of wing lift for minimum drag with fixed span carries a large fraction of the total lift on the outboard wing sections, leading to larger bending moments and greater weights. When drag is minimized at fixed weight, the optimal loading is more nearly elliptic.


Results for a particular set of cases is shown below.


Unrelated to canard system drag, the maximum CL of these systems based on total area is shown below. These results are very sensitive to many of the assumed parameters and are included here only as representative results, not general conclusions.