Methods and Systems for Transitioning an Aerial Vehicle Between Hover Flight and Crosswind Flight

Abstract

A method includes operating an aerial vehicle in a hover-flight orientation. The aerial vehicle is connected to a tether that defines a tether sphere having a radius based on a length of the tether, and the tether is connected to a ground station. The method includes positioning the aerial vehicle at a first location that is substantially on the tether sphere. The method includes transitioning the aerial vehicle from the hover-flight orientation to a forward-flight orientation, such that the aerial vehicle moves from the tether sphere. And the method includes operating the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent to a second location that is substantially on the tether sphere. The first and second locations are substantially downwind of the ground station.

1 . A method comprising:
 operating an aerial vehicle in a hover-flight orientation, wherein the aerial vehicle is connected to a tether, wherein the tether is connected to a ground station;   while the aerial vehicle is in the hover-flight orientation, positioning the aerial vehicle at a first location that is substantially downwind of the ground station;   transitioning the aerial vehicle from the hover-flight orientation to a forward-flight orientation, such that a tension of the tether is reduced; and   operating the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent to a second location that is substantially downwind of the ground station.   
     
     
         2 . The method of  claim 1 , wherein the aerial vehicle has attached flow during the ascent. 
     
     
         3 . The method of  claim 1 , wherein operating the aerial vehicle in the forward-flight orientation to ascend at the angle of ascent to the second location comprises selecting a maximum angle of ascent, such that the aerial vehicle has attached flow during the ascent. 
     
     
         4 . The method of  claim 3 , wherein operating the aerial vehicle in the forward-flight orientation to ascend at the angle of ascent to the second location comprises adjusting a pitch angle of the aerial vehicle based on the maximum angle of ascent. 
     
     
         5 . The method of  claim 3 , wherein operating the aerial vehicle in the forward-flight orientation to ascend at the angle of ascent to the second location comprises adjusting thrust of the aerial vehicle based on the maximum angle of ascent. 
     
     
         6 . The method of  claim 1 , wherein the tension of the tether increases during the ascent. 
     
     
         7 . The method of  claim 1 , wherein the aerial vehicle comprises a global positioning system (GPS) receiver, and wherein operating the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent comprises monitoring the ascent of the aerial vehicle with the GPS receiver. 
     
     
         8 . The method of  claim 1 , wherein the aerial vehicle comprises at least one pitot tube, and wherein operating the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent comprises monitoring an angle of attack of the aerial vehicle or a side slip of the aerial vehicle during the ascent with the at least one pitot tube. 
     
     
         9 . The method of  claim 1 , wherein the second location is substantially upwind of the first location. 
     
     
         10 . The method of  claim 1 , wherein the tether does not contact the ground. 
     
     
         11 . The method of  claim 1 , wherein a bottom of the tether remains above a predetermined altitude. 
     
     
         12 . The method of  claim 1 , further comprising transitioning the aerial vehicle from the forward-flight orientation to a crosswind-flight orientation. 
     
     
         13 . The method of  claim 12 , wherein the tension of the tether in the forward-flight orientation is less than the tension of the tether in the crosswind-flight orientation. 
     
     
         14 . The method of  claim 1 , wherein the tension of tether in the forward-flight orientation is less than the tension of the tether in the hover-flight orientation. 
     
     
         15 . A system comprising:
 a tether connected to a ground station;   an aerial vehicle connected to the tether; and   a control system configured to:
 operate the aerial vehicle in a hover-flight orientation; 
 while the aerial vehicle is in the hover-flight orientation, position the aerial vehicle at a first location that is substantially downwind of the ground station; 
 transition the aerial vehicle from the hover-flight orientation to a forward-flight orientation, such that a tension of the tether is reduced; and 
 operate the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent to a second location that is substantially downwind of the ground station. 
   
     
     
         16 . The system of  claim 15 , wherein the control system is further configured to select a maximum angle of ascent, such that the aerial vehicle has attached flow during the ascent. 
     
     
         17 . The system of  claim 15 , wherein the control system is further configured to operate the aerial vehicle, such that the tether does not contact the ground. 
     
     
         18 . The system of  claim 15 , wherein the control system is further configured to operate the aerial vehicle, such that a bottom of the tether remains above a predetermined altitude. 
     
     
         19 . The system of  claim 15 , wherein the control system is further configured to transition the aerial vehicle from the forward-flight orientation to a crosswind-flight orientation. 
     
     
         20 . A non-transitory computer readable medium having stored therein instructions executable by a computing device to cause the computing device to perform functions, the functions comprising:
 operating an aerial vehicle in a hover-flight orientation, wherein the aerial vehicle is connected to a tether, wherein the tether is connected to a ground station;   while the aerial vehicle is in the hover-flight orientation, positioning the aerial vehicle at a first location that is substantially downwind of the ground station;   transitioning the aerial vehicle from the hover-flight orientation to a forward-flight orientation, such that a tension of the tether is reduced; and   operating the aerial vehicle in the forward-flight orientation to ascend at an angle of ascent to a second location that is substantially downwind of the ground station.