Fig. 21. Regions of positive and negative vorticity during the translation of two wings following `clap and fling'. R_n1 and R_n2 denote regions of negative vorticity, R_p1 and R_p2 denote regions of positive vorticity. The two wings are initially clapped together and rotate apart along their trailing edges. This rotation creates two large leading edge vortices. Towards the end of rotation, the wings begin to translate apart. During translation, two weak trailing edge vortices begin to form. In this diagram, the wings are moving away from each other at a constant speed and angle of attack. The leading edge vortices (denoted by R_n1 and R_p1) are stronger than the trailing edge vortices (denoted by R_n2 and R_p2). This vortical asymmetry results in larger lift forces than in the symmetrical case without fling.