Curving to fly; synthetic evolution of helicopter seeds finds sweet-spot in wing curvature for optimal lift

Nature has invented ingenious aerodynamic design solutions, some of which are critical for plants as wind dispersal of seeds/fruits is coupled to their flight performance. This formulates into an optimization problem for plants: large seed wings can lead to increased lift and more efficient dispersion, but are costly for the tree to build and can more easily be trapped in the canopy. Double winged seeds/fruits separate from their tree when a specific level of dessication is reached, and autorotate as they descend to the ground. This leads to the question: how is the change in the wing curvature of seeds/fruits as they dessicate linked to flight performance ? To answer this, we develop a theoretical model that suggests the existence of an optimal wing curvature that yields maximal lift. To further understand the interplay between flow optimality and geometry, we perform a synthetic seed evolution by deploying 3D printing of seeds that we use in flight experiments, where we span the design space of wing curvature and seed/fruit weight. Our results confirm that there is a sweet-spot in curvature for lift similar to observations in nature, which highlights the importance of not curving too much or too little for helicopter seeds to fly.