In this work we consider the problem of performing an optimal transition maneuver focusing on a particular class of V/STOL aerial vehicles in which a change of the attitude allows to switch between the hovering flight configuration towards the more efficient level flight configuration. In particular we consider both the minimum time and the minimum energy optimal control problems in which the aircraft has to reach a certain desired flight speed starting from a hover (i.e. zero flight speed) initial condition. Explicit approximate solutions, to be used as computationally efficient bounds for the problems under investigation, are derived and compared to numerical solutions which are instead obtained using a direct collocation method based on pseudo-spectral approximation.