This work validates through flight tests a previously developed wide-envelope singularity-free aerodynamic framework, called ϕ-theory, for modeling dual-engine tail-sitting flying-wing vehicles for optimization-based control. The ϕ-theory methodology imposes a specific geometry on aerodynamic coefficients that leads to polynomial differential equations of motion amenable to semidefinite programming optimization. Through ϕ-theory, we illustrate a typical predicted longitudinal and lateral flight envelope of a tail-sitting vehicle, which, while commonplace for fixed-wing aircraft in performance textbooks, is a novel figure that generalizes fixed-wing doghouse plots to tail-sitting vehicles. This flight envelope figure suggests a novel, natural and intuitive remote piloting interface that we validate in flight tests. Furthermore, we further validate ϕ-theory through the computation of flight features in simulation and their subsequent observation in flight tests.