Abstract
Dynamic soaring is a special flying technique designed to allow UAVs (unmanned aerial vehicles) to extract energy from wind gradient field and enable UAVs to increase the endurance. In order to figure out the energy-extraction mechanisms in dynamic soaring, a noninertial wind relative reference frame of aircraft is built. In the noninertial frame, there is an inertial force which is created by gradient wind field. When the wind gradient(GW)and the components of airspeed(vzvx)are positive, inertial force(F)makes positive work to the aircraft. In the meantime, an equilibrium position theory of dynamic soaring is proposed. At the equilibrium positions, the increased potential energy is greater than the wasted kinetic energy when the aircraft is flying upwards. The mechanical energy is increased in this way, and the aircraft can store energy for flight. According to the extreme value theory, contour line figures of the maximum function and the component of airspeed(vz)are obtained to find out the aircraft’s lifting balance allowance in dynamic soaring. Moreover, this equilibrium position theory can also help to conduct an aircraft to acquire energy from the environment constantly.
Highlights
Long endurance flight is a key design criterion for unmanned aerial vehicle [1]
The paper presents an equilibrium position theory of dynamic soaring which is the forces balance during the flight
The aircraft stays in a certain speed without kinetic energy loss
Summary
The UAVs’ flight endurance can be improved by the progress in power capacity and aerodynamic and engine design [2], but not all such means are equal Another important alternative for enhancing UAV flight endurance is to seek energy from flight environment. Moving air is called gradient wind, in which wind speed varies with altitude In this paper, both the size of the wandering albatrosses with its 3.3 m wing span and its flight performance are taken as a reference model against the dynamic soaring performance of a small UAV. There should be some positions of forces balance in the course of flight At these points, the aircraft stays in a certain speed, with no kinetic energy loss.
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