Cul de canard Cul de canard Cul de canard (CDC) (French for "duck bottom") are the feathers from the back of a duck directly around the preen gland (uropygial gland); they are very buoyant due to preen oil produced by the preen gland. They are used when tying dry flies for fly fishing. They owe their buoyancy to their proximity to the ducks preen gland which secretes an oil distributed by the duck as a cleaning and waterproofing measure. It is unnecessary for the angler to add additional oil by way of floatant. Flies incorporating CDC are easy to dress requiring no floatant
Canard (aeronautics) affect the wing lift distribution unfavorably, so the differences in overall lift and induced drag are not obvious and they depend on the details of the design. A danger associated with an insufficiently loaded canard—i.e. when the center of gravity is too far aft—is that when approaching stall, the main wing may stall first. This causes the rear of the craft to drop, deepening the stall and sometimes preventing recovery. To ensure safe pitch stability in the stall, the canard must stall first, so the wing must always stay below its maximum lift capability. Hence, the wing must be larger