# Wind Dispersal of Natural and Biomimetic Maple Samaras
## 5 Discussion  
New information is needed to understand the dynamics of wind dispersal. Here, we designed a series of biomimetic maple samaras, and tested their ability to 'fly' in a series of laboratory and field experiments. With still-air laboratory experiments, we showed that the biomimetic samaras exhibited similar descent properties (i.e., descent speed and rotation) as the natural samaras. From field experiments, we found that the natural samara traveled the greatest distances with the wind, yet also exhibited the most variability. Our field experiments also supported the assertion that wind speed has a strong impact on dispersal. We calculated a windage coefficient via Equation (3) to capture the effect of wind and showed that it is an effective metric for predicting dispersal distance.  
Figure 5: Descent speed (\(v_{d}\)) as a function of wing loading (\(W/S\)) for the natural and artificial Norway maple seeds. Mean and standard deviation are shown in both variables. The gray lines represent descent speed as a function of wing loading for constant descent factors (\(DF\)), based on Equation (6), adapted from [21]. The natural and artificial samaras are on the same descent factor curve, likely due to similar shapes.  
The shape of the artificial samaras was developed heuristically, varying the depths of each segment until the desired behavior was observed. However, the locations of the center of mass of the natural and artificial samaras are nearly identical. This relationship has been more closely investigated, using balsa wood prototypes [39], which showed that descent speed and rotational velocity are closely related to the location of the center of mass. The separation of the center of mass and the center of fluid forcing contributes to the rotation of a samara [30; 40].  
From the observed behaviors, the natural and artificial samaras both showed approximately equivalent descent factors, \(DF\approx 3\), as shown in Figure 5. According to [21], the descent factor is a measure of aerodynamic efficacy relating the wing loading, descent velocity, and fluid density of a samara. The measured result that the natural and artificial samaras have the same descent factor is likely due to their similar morphology, and suggests that differences in descent speed may be related to differences in samara weight.  
During the high wind trials, the landing distribution shows a significant bias to the right of downwind (Figure 4a). This may be due to temporally localized turbulent gusts, which were biased to the right of the mean wind direction during the trial duration (Figure 4b). This is consistent with the high variability of the wind direction during this trial.  
Our results indicate that for some samaras, the windage was estimated to be greater than 1 (see Figure 6a). While a windage value of greater than 1 might at first glance seem puzzling, seeds are capable of various aerial movements, including tumbling and gilding relative to the moving air [41; 42; 43], which could lead to average horizontal speeds that exceed that of the wind itself. The sensitivity of these effects to local conditions, and the spatiotemporal variability of the conditions themselves (turbulence), may also contribute to the observed dispersal patterns.