We show that a Fell bundle $\B =\{B_t\}_{t\in \F}$, over an arbitrary free group $\F$, is amenable, whenever it is orthogonal (in the sense that $B_x^*B_y=0$, if $x$ and $y$ are distinct generators of $\F$) and \ss (in the sense that $B_{ts}$ coincides with the closed linear span of $B_tB_s$, when the multiplication ``${ts}$'' involves no cancelation).