6 Flexible Energy Harvesting/Storage Structures for Flapping Wing Air Vehicles 41 Fig. 6.3 Testing results for regular wings. (a) Achievable amplitude with full amplitude commanded. (b) Modeled and measured thrust at full commanded amplitude. (c) Achievable amplitude with half amplitude commanded. (d) Modeled and measured thrust at half commanded amplitude multifunctional wings. When the amplitude correction is applied the agreement is greater until 3 Hz in both the case of the flexible wing and the multifunctional wing when full flapping amplitude is demanded. After 3 Hz there is a departure between the model and the measured values as there appears to be saturation of the thrust values. The departure starts a bit sooner for the multifunctional wings. When the commanded amplitude is half of the full range, the servos are able to largely follow the commanded signal and the results collapse on top of each other, however, the measured results actually outperform the models slightly as seen in Figs. 6.3d and 6.4d. What is notable is that the thrust generated by the stiffer wings is higher than the thrust generated at 2 Hz as seen in Fig. 6.5. This changes at all frequencies above this as it seems that the amplitude effects and stiffness saturate the thrust produced. 6.3.2 Predicted Effects from Integrating Flexible Solar Cells and Batteries into Wings for FWAVs Using the experimental results, it was then possible to predict the effects on flight time from integrating the solar cells and batteries into the wings. To perform this analysis, the payload capacity of the platform with solar cells and batteries were predicted from the test stand aerodynamic lift and thrust measurements. The resulting payload capacity was assumed to be used to carry conventional LiPo batteries in order to predict the flight time. The results are shown in Table 6.1. It is interesting to note that integrating the flexible ultrathin galvanic cell batteries and flexible solar cells produce similar increases in flight time of approximately 3.4 , but that the combination can produce a potential increase of17.4 .
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