An air turning vane and rail assembly including a pair of rails, a plurality of tabs having a height distance H, a plurality of air turning vanes, each of the turning vanes including a single sheet of metal that is folded in a U-bend to form elongated generally rectangular upper and lower walls, each wall having opposite end edges, the upper wall in end view defining an arc of a first radius of curvature, and the lower wall in end view defining an arc of second radius of curvature greater than the first radius of curvature, and a plurality of crimp spots spaced apart from each other in the lengthwise direction extending transversely through the marginal portions of the upper and lower walls, each two adjacent crimp spots being spaced apart from each other in the lengthwise direction a distance L which is less than the distance H.