A turbomachinery engine includes an unducted rotor assembly, a low-pressure turbine, a low-pressure shaft, a gearbox, and an engine correlation parameter. The unducted rotor assembly includes a plurality of rotor blades arranged in a single row and defining a blade diameter. The gearbox includes an input, an output, and a gear ratio. The input of the gearbox is coupled to the low-pressure shaft (which is coupled to the LPT), and the output of the gearbox is coupled to the unducted rotor assembly. The engine correlation parameter is greater than 0.17 and less than 0.83. The engine correlation parameter equals D/N/GR, where D is the blade tip diameter measured in feet, N is the stage count of the low-pressure turbine, and GR is the gear ratio of the gearbox. The unducted propulsor assembly optionally includes a disk loading within a range of 60-180 HP/ft 2 at a takeoff flight condition.