This is a model of a 50s/60s Lotus racing car wheel, famous for its "wobbly web". The web was essentially designed as a deformed cylinder of material, like the closure of a draw-string bag. The splines of the loft are 6-period circular waves, and only the outer one needed laying out, the others are just scaled copies. It's identical in concept to a suggestion that Henry offered to model a wave washer, and although I've used seven profiles, that's overkill for a chute, I'd reckon. The file is an example of what three profiles can do, very exaggerated. Adjust the height of the two smaller circles to adjust the shape.