Studies in telescopic span morphing of HALE UAV

This paper explores the benefits of providing telescopic span morphing in HALE UAV for extending its endurance, while retaining its performance in other flight segments such as climb rate and take-off/landing. An existing methodology for initial sizing and constraint analysis has been used with Global Hawk RQ4-A as the baseline aircraft and a modified Global Hawk with requirement for additional endurance is investigated by morphing due to span extension. The benefits of morphing of HALE UAV for extending its endurance are reported. The telescopic span extensions planned for the Global Hawk lead to an increase in lift-to-drag ratio of the aircraft in morphed configuration. Three morphing configurations are defined in relation to the base configuration in terms of increasing wingspan as a `morphing coefficient'. Two penalties associated with telescopic span morphing are taken into account - weight of the morphing mechanism and fuel volume lost. The effects described above (viz., increased lift-to-drag ratio, reduced available fuel volume and increased empty weight) are factored in to estimate the modified weight of the aircraft and the endurance benefit is evaluated. In order to refine these calculations, bending and shear calculations for the wing are carried out to obtain the weight of the baseline and morphed wing and also the weight of the resized tail to account for the increase in wing reference area, keeping the aircraft stability characteristics the same. It is found that for the same mission profile, as morphing coefficient increases, endurance benefit increases and then decreases. This indicates presence of a limit, beyond which the morphing has no endurance benefit.