  This work answers positively the question whether non-stop flights are
possible for maintaining constant the pose of cable-suspended objects. Such a
counterintuitive answer paves the way for a paradigm shift where energetically
efficient fixed-wing flying carriers can replace the inefficient multirotor
carriers that have been used so far in precise cooperative cable-suspended
aerial manipulation.
  First, we show that one or two flying carriers alone cannot perform non-stop
flights while maintaining a constant pose of the suspended object. Instead, we
prove that three flying carriers can achieve this task provided that the
orientation of the load at the equilibrium is such that the components of the
cable forces that balance the external force (typically gravity) do not belong
to the plane of the cable anchoring points on the load. Numerical tests are
presented in support of the analytical results.
