Samara of the sycamore autorotates due to curved shape.


“Winged seeds or fruits…can be placed into one of two categories—plane-winged, in which the seed coat or fruit wall grows more or less symmetrically with respect to its longitudinal axis and generates a linear gliding flight, and autogyroscopically winged, in which lift is created by wings on the propagule that permit autorotation during free-fall…The behavior of autogyroscopic seeds and fruits is remarkably similar to that of a helicopter and results from the combination of angle of attack and sideslip generated by the slightly curved blade of fruit wing or seed wing. The local speeds developed at the tip of the wing are relatively high and, together with the corresponding moments, produce great dynamic stability. When viewed from above and below, the rotating wing sweeps out a shallow conical section with an area Ap (Figure 9.10). The angle subtending the longitudinal axis of the fruit or seed and the horizontal plane is the coning angle ß, the equilibrium condition between the centrifugal forces acting on the rotating wing (which produce a turning moment tending to force the wing into a horizontal position) and aerodynamic forces (which tend to displace the wing into the vertical position). Thus the coning angle is the result of moments due to centrifugal and aerodynamic forces.” (Niklas 1992:461,463)

Plant Biomechanics: An Engineering Approach to Plant Form and FunctionJanuary 8, 1992
Karl J. Niklas

“European maples and sycamores have an even more economical design. They are equipped with only a single wing, sprouting from one side. The balance between the weight of the seed and the length of the wing is so accurately matched that these seeds also spinEven in a light breeze their tiny spinning helicopters can travel for very long distances across thecountryside.” (Attenborough 1995:19)

The Private Life of PlantsOctober 28, 2016
David Attenborough

Sycamore MapleAcer pseudoplatanusSpecies