Research on characteristics of gravitational gliding for high-altitude solar-powered unmanned aerial vehicles

Abstract

Gravitational gliding during night without electric power is an efficient method to enhance the endurance of high-altitude solar-powered unmanned aerial vehicles. The properties of the maximum endurance path of gravitational gliding are studied in this article. The maximum endurance path problem is formulated as the problem of the maximum endurance can be sustained by unit altitude difference with the constraints of dynamic equations and aerodynamic parameters. The maximum endurance path is generated by Gauss pseudo-spectral method, and a new way to estimate co-state variables in Hamiltonian is proposed. In order to analyze the sensitivity of initial altitude and velocity of solar unmanned aerial vehicles with its endurance performance, the lift coefficient in the interval [0.4, 1.2] and flight envelopes between 0 and 30 km are investigated. The results are as follows: first, the broad range of lift coefficients can improve solar aircrafts' long-endurance performance; second, the lower the initial altitude, the longer the gliding endurance can be sustained by unit altitude difference; third, it is possible for a solar-powered unmanned aerial vehicle to keep aloft during the whole night just by gravitational potential energy storage, but the issues with turbulence and wind would render this mode of unlimited endurance unfeasible. Thus, gravitational gliding by potential energy storage can only be partly used instead of electric energy storage in application now.

Reviews of methods to extract and store energy for solar-powered aircraft

“…Motivated by his ideas, the properties of the maximum endurance path of gravitational gliding have been studied in Ref. [66], and a new energy management strategy has been proposed in Ref. [67], other relative works about the energy stored by gravitational potential for bird and UAV can be seen in [136,137].…”

“…Besides, there are also several other methods in consideration, such as to extract energy from wind shear [59][60][61][62][63] and store energy by gravitational potential [64][65][66][67] for solar-powered aircrafts. Although lots of works have been done, it is still not a simple task for the designers of solarpowered aircraft to select a particular technique from a number of existing techniques, since each technique has certain advantages and disadvantages with respect to different performance indices to fulfill the special requirements.…”

Power Management Strategy by Enhancing the Mission Profile Configuration of Solar-Powered Aircraft

“…By adopting the proposed power management strategy, UAV operations at a lower altitude may avoid the highly volatile wind region. A comparison of the power ratio performance of the proposed power management strategy and that of various approaches [3,9,12] is listed in Table 3. The concept of the proposed strategy significantly improves the power ratio by at least 30.84% relative to the other approaches for perpetual solar-powered UAV missions.…”

“…Moreover, an appropriate trajectory control in gravitational gliding during nighttime has been considered an efficient method to enhance flight endurance. The energy stored as gravitational potential energy and gained in height is used by the UAV to glide at night without any electrical power supply [3,9].…”

Analysis of the Hybrid Power System for High-Altitude Unmanned Aircraft

“…Gao et al from National University of Defense Technology studied the high-altitude long-endurance flight based on energy extraction from wind shear and put forward the idea of dynamics simulation. However, the idea requires the infrastructure for monitoring wind field [7,21].…”