Scott V- If there was a straight duck flank feather, I wouldn't like to tie it.
Try tying one using the tip of the flank feather. Stack a couple, position them, hold sides firmly, take three loose wraps. Make sure the thread wraps back on the feather just a little . Tighten the thread and the feather sides should roll in to make a nice cupped effect.
I'm leaving to fish here in a bit . PM me if it don't work and I'll get into detail or pictures If need be.
I'm sure some tie with just the sides of the feather but for me it is time consuming.
JungleJimJigs is a duck feather master. Illinoisgiller