visventis.org

Here’s some footage of our first test day:

It was fairly windy so the kite (only 3.5m²) was generating a huge amount of force, easily enough to pull a large man over, but our frame, firmly tethered to the ground, made it possible to control at these high speeds. You can see that the kite is very manoeuvrable using this system.

There are some issues with the design which meant that the tethers kept coming off the pulleys, causing wear, with the cable (500lb breaking tension without wear) then snapping, as shown at the end of the video. This happened several times, and we even switched to a much smaller kite for part of the test, which flew well too. We hope to fix these issues with some simple mods to the frame. The next step is then to fit a generator and demonstrate power production.

Which brings me on to my final point. We really need more skilled volunteers who are willing to spend a little time helping push this project, which is not only great fun but also potentially very valuable to our target beneficiaries–impoverished people in off-grid communities in the developing world–forward. If you’re interested in helping, please drop us a line.

Saturday 2nd June 2012 was a significant day in the history of Visventis. Olly and I satisfied ourselves that the rig we have built can control a kite. We were lucky with the weather and the wind was strong enough to easily launch the kites, and we could control them with the steering bar. This is the critical factor that we wanted to prove before moving to the next stage of the project. Success!

The rig parts about to be assembled.

There were inevitable teething troubles particularly since we have built the rig with a philosophy of keeping everything as simple and cheap as possible. After all, the idea is that future rigs will be constructed by poor people with limited resources. The kite lines kept jumping off the pulleys which caused them to get frayed and break. This was expected, but we were hoping that it would not be serious enough to force us to have to construct tether guides.

There had been concern that the inability of the steering bar to move backwards and forwards would cause problems by preventing the kite reacting to changing wind, but we are now satisfied that it will not.

Here is how it works.

Robert about to mount the support beam and chair onto the support post.

Robert with the steering bar.

Securing the rig to the ground

The pilot's view of the kite about to be launched.

The kite flying.

Home time after a good day.

Removing the chains that stop the support ring twisting.

All packed up and ready to go.

More photos and video footage will be posted soon. We thank Paul, the farm owner, for allowing us to use his land for this test.

The next phase of the project is to get a generator attached. Olly and I are very much part time on this project, so now that we are far more confident that the basic idea is good we need to step up our efforts to find more volunteers to help. Hopefully the above photos adequately illustrate how our concept works and you will be inspired to contribute. Please contact us and/or spread the news.

A visualization of the carousel in action.

Recently we met another kite power enthusiast, Phil Anderson, here in Cambridge. We asked him to write about his own ideas. So here he is:

“The “Carousel” is a semi-physical model of a small scale vertical axis kite generator. The image above shows five kites tracking around a prescribed path as the legs of carousel turn beneath them. Each  kite rotates on its tether to face into the apparent wind, that is, the vector addition of the wind and the kite velocity. Within the model, the tension on each tether is calculated from the kite’s apparent wind and the kite pointing vector, assuming a realistic function for lift, drag and slew.

“Two aspects of the schematic should be noted. Firstly the kites appear to make a complete revolution on their tether during each cycle. This is important because it exactly counters the rotation  of the carousel which would otherwise cause the tether to become increasingly twisted. Although a design incorporating a swivel on the tether is possible, adding control lines (i.e. having a three- or four-line tether), makes swivel-decoupling unwieldy.

“Secondly, the flight orbit generates torque on the carousel by a combination of alternating between the power-zone and window-edge feather (as for other designs) coupled to the phase of the orbit to the phase of the carousel: the kites are acting at an angle to the arm of carousel for most of the orbit.

“The physical basis of the model provides an estimate of the total power per kite integrated over a revolution of the carousel for any given orbit. This power estimate can be used as a metric for the efficiency of the orbit; the orbit itself is a parametric function and the power metric is used to optimise the function for a given wind speed.”

Thanks, Phil!

Credits: cmogle

If you are around next Wednesday (20th July 2011) and you want to have a glimpse of power-kites and how powerful and fun they are, just come over in Midsummer Common, around 18:30 to take part or take a look. It will be fun.

More info about the event on the groupspace page.

P.S.: If you’ve got a kite, just bring it alone. More kites, more fun.