When I sit down and sketch a wing out of my head, I think I’ve got a handle on how wing feathers work and which go on top of which, in which direction, but when I study the real thing, I find it ain’t necessarily so!
Wings have a huge variety of feather patterns between different types of birds. The size and shape of each “patch” of feathers differs, as well as the type and texture of the feathers. Griffins are supposed to have eagle wings, but I think bird of prey wing undersides are less interesting looking than the underside of a chicken’s wings!
These are a few sketches I drew of various different common bird’s wing undersides. These are all “life” drawings, from real birds. I use these as reference to come up with my own made up feather patterns.

Top left is a mallard duck.
Top right is a chicken.
Bottom left is a Towhee.
Bottom right is a dove.

I think the humble chicken’s wing is the prettiest!