fluttering of flag
翩 centers on light, graceful fluttering motion, especially of a flag or banner waving in the wind.
翩 combines 羽 (feathers, wings) with 扁, which likely contributes the sound and the idea of something flat and light. Together they suggest the fluttering of feathers or a flag.
The left side 扁 looks like a flat banner, and the right side 羽 is a pair of wings. Imagine a flag fluttering like wings in the breeze.
For ヘン, picture a hen flapping its wings, making the flag flutter: hen -> ヘン.