Compliant wing designs have the potential of improving flapping wing Micro-Air Vehicles (MAVs). Designing compliant wings requires a detailed understanding of the effect of compliance on the generation of thrust and lift forces. The low force and high-frequency measurements associated with these forces necessitated a new versatile test stand design that uses a 250 g load cell along with a rigid linear air bearing to minimize friction and the dynamic behavior of the test stand while isolating only the stationary thrust or lift force associated with drag generated by the wing. Moreover, this stand is relatively inexpensive and hence can be easily utilized by wing designers to optimize the wing compliance and shape. The frequency response of the wing is accurately resolved, along with wing compliance on the thrust and lift profiles. The effects of the thrust and lift force generated as a function of flapping frequency were also determined. A semi-empirical aerodynamic model of the thrust and lift generated by the flapping wing MAV on the new test stand was developed and used to evaluate the measurements. This model accounted for the drag force and the effects of the wing compliance. There was good correlation between the model predictions and experimental measurements. Also, the increase in average thrust due to increased wing compliance was experimentally quantified for the first time using the new test stand. Thus, our measurements for the first time reveal the detrimental influence of excessive compliance on drag forces during high frequency operation. In addition, we were also able to observe the useful effect of compliance on the generation of extra thrust at the beginning and end of upstrokes and downstrokes of the flapping motion.

Successful realization of a flapping wing micro-air vehicle (MAV) requires development of a light weight drive mechanism that can convert the continuous rotary motion of the motor into oscillatory flapping motion of the wings. The drive mechanism should have low weight to maximize the payload and battery capacity. It should also have high power transmission efficiency to maximize the operational range and to minimize weight of the motor. In order to make flapping wing MAVs attractive in search, rescue, and recovery efforts, they should be disposable from the cost point of view. Injection molded compliant drive mechanisms are an attractive design option because of manufacturing scalability and reduction in the number of parts. However, realizing compliant drive mechanism using injection molding requires use of multipiece multigate molds. Molding process constraints need to be considered during the design stage to successfully realize the drive mechanism. This paper describes an approach for determining the drive mechanism shape and size that meets both the design and molding requirements. The novel aspects of this work include (1) minimizing the number of mold pieces and (2) the use of sacrificial shape elements to reduce the impact of the weld-lines on the structural performance. The design generated by the approach described in this paper was utilized to realize an operational flapping wing MAV.

Flapping wing motion produces positive lift in the down stroke and negative lift in the upstroke under zero forward velocity. Large birds frequently exhibit flight behavior where their wings are folded during the upstroke, thus lowering the air resistance as the wing is moved upwards. The result is reduced magnitude of negative lift produced during the upstroke, relative to the positive lift produced in the down stroke, where the wings are unfolded and the area is increased. We expect that by incorporating this style of upstroke wing folding into miniature air vehicle (MAV) platforms, beneficial flight properties would arise. Specifically, a portion of the wings' overall lift will be generated by upstroke folding and downstroke unfolding, even at zero forward velocity. Such a capability will reduce the reliance on aerodynamic lift produced due to the forward motion of the MAV. This in turn would reduce the minimum flight-sustaining forward velocity and thus enhance MAV maneuverability by allowing for a reduced turning radius.Incorporating wing folding into a miniature air vehicle platform presents a unique challenge due to strict weight constraints present at small sizes.Using actuators to accomplish folding actively is not feasible due to the added weight of the actuators and the need for an on-board control system to synchronize the folding with the wing flapping motion. Therefore, the folding motion must be accomplished passively, since this is currently the only viable option in miniature MAVs. We have developed a passive, spatially distributed, one-way folding mechanism. This mechanism has been incorporated into a flying MAV testbed, and has successfully shown that the flapping wing MAV with folding wings is capable of flying at reduced forward velocity, while maintaining the payload carrying capacity.