Winds have been very strong and gusty here for the last few days since the start of WWKW. KAP conditions have not been ideal, however the higher winds have given me a chance to experiment with an idea I’ve been wanting to try for a while that will allow my Levitation to adapt to varying wind conditions.
The 9ft Levitation delta has become my primary kite for moderate to high winds from 15 MPH and above. (My Jones 7ft Rok is my primary kite for lighter winds up to ~15 MPH but that's another topic). For winds between 15 and 20 MPH, I’ll typically use the Levitation with a standard length spreader spar which is 46.75 inches long. For higher wind conditions I’ll use a shorter spreader (39.5 inches) which extends the wind range up to 30MPH+ and significantly reduces the amount of pull and provides a more stable, pleasant flight. Additional discussion of the dynamic spreader spar can be found here:http://arch.ced.berkeley.edu/kap/discuss/index.php?p=/discussion/3398/extending-levitation-delta-upper-wind-range#Item_29
The short spar works well as long as the winds stay consistently above approx. 20 MPH, however, it doesn’t provide the desired lift in lighter winds.
I’ve been working on a dynamic spreader spar that adjusts its length based on the wind conditions. I’ve only had a few hours of flight time with this, but it looks favorable that it will allow the Levitation to be flown from ~5MPH to 30MPH+ with a single spreader spar configuration. The dynamic spreader is basically a spring loaded telescoping graphic tube that keeps a constant spreader tension on the kite wings. At low wind speeds the spreader is fully extended maximizing wing surface area and lift. As the wind increases, the spreader is compressed resulting in a swept wing profile reducing surface area and line pull.
The dynamic spreader I’m using is an initial prototype and is constructed from graphic arrow shafts (roughly equivalent to P200 tubes). The uncompressed spreader length is 46.75 inches in light winds (length of stock spreader) and compresses down to approx. 42 inches in winds up to 30MPH. Its compression limit is set to 39.5 inches which it will reach in winds above 30MPH. The spring tension can be adjusted to provide different amounts of compression for a given wind speed.
With the current settings, I’ve been able to fly very comfortably in winds from approximately 15 MPH to 30 MPH with a line pull between approximately 2.5 and 12.5 lbs.
The dynamic spreader weighs 38 grams. The stock fiberglass spreader that comes with the Levitation weighs 67 grams.
Here are a few videos and photos showing more detail:Basic operation video.Launch and flight video showing the spreader compress as the wind increases.
Picture: No spreader compression (light wind flying, standard 46.75 inch length spreader)
Picture: Medium compression (winds up to 30MPH, 3.5 inch compression)
Picture: Full spreader compression (winds greater then 30MPH, 7.25 inch compression)Additional pictures and videos showing construction details and operation can be found on my Flickr site.
I plan on developing this further over the summer. It would be interesting to see how this could be applied to other types of kites.