Flight initiation is an area that remains unexplored amongst today's nano-scaled, flapping-wing, robotic insects. To understand mechanical principles of ground-to-air transitions at this particular scale, we investigate the biomechanics of the fruit fly Drosophila melanogaster during takeoff. Building upon a prior framework (G.M. Card et al., 2008), we analyze the insect's pre-flight motion, and its impact in directionality control. Using a rigid multi-body system comprised by one central body and six legs, we are able to estimate forces from joint kinematics. The approach provides a mathematical framework for studying tradeoffs between directionality control and dynamic stability during flight initiation.