Autonomous Launch & Land - Lifter Kites

gordon_sp · August 29, 2021, 4:04pm

I would like to describe my latest version of autonomous launch and land of a large lifter kite. In the example below I have combined this with an LTA balloon frame though it could easily be combined with other methods of launch assist such as “lever-arm” “telescoping rods” or “scissor lifts”.
The kite rests on a frame of LTA balloons and is secured by stays at the corners so that it is spread out. Similarly the LTA balloon frame is secured in place by four lines at each corner. These two sets of four lines are gathered together by means of transfer pulleys to two wind/unwind stations.

During launch, the LTA balloon frame lifts the kite to an acceptable launching height (30-60 meters) at which point the balloon frame is prevented from rising further. The kite separates from the frame and the frame is lowered back to the ground. The kite continues to rise to the operating height. The four corner lines are still attached, but remain slack.
During landing, the kite is reeled in with the main tether and the four lines at the corners are wound up on the take-up reel so that the kite remains spread out. The taut lines ensure that the kite is precisely located and resting on top of the balloon frame, ready for the next launch.
There is little chance that the four slack lines can become entangled since the lifter kite is always maintained in a stable position. This stands in contrast to the nose line of the Skysails system which must avoid entanglement while the kite performs figure-of-eight maneuvers.
A single skin kite has the greatest lift/weight ratio of all kites. It is also the least expensive. It is scaleable to very large sizes, but must be controlled at all times. A kite control unit can control the kite in the air and I believe that a system of anchoring lines can control it near and on the ground. This will provide a truly autonomous launch and land system.

gordon_sp · June 8, 2023, 1:01pm

On further thought it might be possible to combine both the wind/unwind stands into one device, separated by clutches, so that all the functions can be performed at the same time. The sequence is as follows:
1. Both clutches are engaged and the kite and lifting frame are lifted to a suitable launch height (approximately 50 M).
2. Lifting frame clutch is released and the kite continues to be lifted to the operating height.
3. Motor is reversed, lifting frame clutch is engaged and the kite clutch is released. The motor lowers the lifting frame aback to the ground position.
4. For landing the kite, only the kite clutch is engaged and the kite is lowered to the starting position on the ground.
As a further refinement we can divide each reel into two sections, so that the root of one is slightly larger than the other. We do this in order to increase the length of the leading auxiliary lines in both the kite and lifting frame, so that when the kite separates from the lifting frame, they are both tilted in an optimum angle of attack to catch the wind. When the kite and the lifting frame are on the ground they are completely horizontal.

Since both the lifting frame and the kite are restrained at all times this system lends itself to full autonomous control. If the wind dies down, then the act of retraction causes an effective wind force on the kite and it is controllable while being retracted. The whole launch/land operation can be performed with the main tether fully extended. In this way we do not require a wind/unwind system for this tether resulting in considerable savings.
I consider launch and land with a restrained kite to be considerably more reliable than launch land systems with a crosswind kite. The analogy is a conventional wind turbine which autonomously turns to face the wind when wind direction changes. No human interaction is required.