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 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: Gravitational gliding by potential energy storage can only be partly used instead of electric energy storage in application now. The large lift coefficient is propitious to get a good velocity factor. The larger the initial velocity, the longer the gliding endurance that can be obtained. So, in order to get a good gliding performance, it is advantageous for solar aircraft to be designed with the range of lift coefficients as broad as possible. The lower the initial altitude, the longer the gliding endurance that can be sustained by unit altitude. Below 4 km, aircraft can glide more than 3600 s during vertical altitude of descending 1 km, while, given the same vertical distance, aircraft can only glide fewer than 1000 s above 22 km. The gravitational gliding by potential energy storage can only be partly used instead of electric energy storage. Because there always is a great wind between the altitude of 8 and 12 km, the issues with turbulence and wind for the altitudes recommended would render this mode unfeasible.
Research on characteristics of gravitational gliding for high-altitude solar-powered unmanned aerial vehicles
Charakteristik des Gravitations-Gleitfluges von durch Solarenergie angetriebenen, unbemannten Luftfahrzeugen in der Hochatmosphäre
2013
13 Seiten, 10 Bilder, 2 Tabellen, 30 Quellen
Article (Journal)
English
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