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