  Experiments and global linear stability analysis are used to obtain the
critical flow rate below which the highly stretched capillary jet generated
when a Newtonian liquid issues from a vertically oriented tube, is no longer
steady. The theoretical description, based on the one-dimensional mass and
momentum equations retaining the exact expression of the interfacial curvature,
accurately predicts the onset of jet self-excited oscillations experimentally
observed for wide ranges of liquid viscosity and nozzle diameter. Our analysis,
which extends the work by Sauter & Buggisch (2005), reveals the essential
stabilizing role played by the axial curvature of the jet, being the latter
effect especially relevant for injectors with a large enough diameter. Our
findings allow us to conclude that, surprisingly, the size of the steady
threads produced at a given distance from the exit can be reduced by increasing
the nozzle diameter.
