Tiny insects like dragonfly flaps in an inclined stroke plane, which derives most of its vertical force from the downstroke. Dipole and its induced jet are unique to inclined stroke plane flapping, which transfer a linear momentum downward, causing a lift on the flapping wing. The study on the single isolated wing in hover, showed the dipole jet to have optimum downward momentum and spread for the stroke plane angle used by dragonflies. Further, the study on the inclined stroke plane wings in the ground effect showed the role of dipole jet and its ability to enhance vertical force generation in certain cases.

Consequently, the current study is designed to study the tandem wing configuration in the class of inclined stroke plane flapping wings in hover. In the study, the inter-plane distances between the flapping wings are systematically reduced for four different stroke plane angles. This study reveals the fundamental flow physics of this class of flow with the dominant lift enhancement mechanism in play. Interestingly, the study also reveals a few cases to have force variation of double the flapping period, and a case of aperiodic force trace. Further, comparing the cycle average force with the single isolated wing shows the maximum vertical force production for the in-phase stroking of flapping wings. The higher stroke plane angles were identified to produce sustainable high vertical force for the range of inter-plane distances considered. Moreover, the shedding pattern is found to have distinctive regimes of similar dipole interaction, as the inter-plane distance is reduced. In addition to the above, some interesting features of the dipole jet can be identified from the tandem wing configuration.