As the winged liquid fly-back booster (LFBB) is one of the partially reusable space transportation systems considered within the German future space launcher technology research program ASTRA. The regarded system consists of two booster stages, which are attached to the expendable Ariane 5 core stage at an upgraded future technology level. The main area of interest of the presented aerodynamic study is the return flight after the staging procedure which dominates the layout of the LFBB. The present paper discusses the aerodynamic refinement of an existing LFBB design, focussing on its longitudinal stability and trim. Detailed aerodynamic parameter studies are performed based on Euler calculations. Force measurements and selected Navier-Stokes simulations confirm this approach. They point out that a LFBB configuration may be designed primarily based on Euler simulations. The discussion of the numerical results and their comparison with experimental results shows that it is possible to adapt the originally given LFBB proposal in a way that it allows a nearly indifferent flight along the complete return trajectory and that it additionally enables a very robust trim behaviour.