Research pick: Acer: Legends of the fall - "Study of the flight of the Acer negundo samara"

Plants have a wide range of seed dispersal techniques. Some seeds are embedded in delicious fruit that animals eat and pass intact seeds elsewhere. Some simply fall to the ground but are harvested by animals that carry them off and even bury them in the ground. Other seeds are wrapped in bristly or sticky cases that cling on to passing fur and fall off or are rubbed off some distance away. Some plants overhang water and have seeds that float away on the country to find themselves beached elsewhere. Others have evolved tiny flying machines that allow the wind to carry their offspring away.

In the latter, category, the plants we know as maples and sycamores have evolved winged seeds. Once detached from the tree, these seeds spin as they fall and that rotation extends the time they are in the air allowing the wing to carry them large away from their parent tree. Technically, such a flying system is known as a “pararotor”.

Research from a team in Argentina published in the International Journal of Aerodynamics has taken a look at the flight path of the seed of the native North American species Acer negundo, the boxelder maple, also known as the Manitoba maple or simply the box elder. This species’ winged seeds, known as samara, hang from the tree on stems with pairs of seeds attached to each other and flat, wing-like protuberances jutting out below.

The team describes this flying seed configuration as an aerodynamic rotary decelerator and suggests that its unique flying abilities represent natural inspiration for researchers and engineers working on rotator wing design. Indeed, it seems no coincidence that in some parts of the world, the winged seeds of sycamores and related trees are colloquially referred to as “helicopters”. The concentrated load and thin wing of a samara, represent a simple engineering feat on the part of nature that might be exploited in the design of novel aerodynamic decelerators, the team suggests. Samara-type artificial decelerators have applications as novel parachutes for skydivers and space probes, and unmanned aerial vehicles (UAVs).

The researchers have characterised the flight of samara by nutation (spinning) angle, falling, and rotation velocities. They then used this data to model and simulate the flight path with a view to using these to better understand how the structure and shape of such seeds give them their particular aerodynamic characteristics.

Porritiello, F., Nadal Mora, V. and Piechocki, J. (2022) ‘Study of the flight of the Acer negundo samara’, Int. J. Aerodynamics, Vol. 7, No. 3, pp.224–235.