March 2013 Archive

Rear Line Loads

3/7/13

We’ve been curious about the distribution of rear line loads, and have recently been collecting load data from both lines. The result is a bit of a surprise. As expected, the “top” rear line has a higher load, but the difference between the top and bottom lines is smaller than anticipated: typically only a few kgf, out of a total rear line load of up to 120 kgf.

The top attached histogram shows the distribution of the total rear line loads. The second histogram shows the difference between the right and left lines when on a starboard tack, and the third histogram shows the same for port tack. This data comprises the entire test on March 5 during which the […more]

K2 Test – Mar 5

3/6/13

We took K2 out today in blustery conditions with winds from the South. We flew the same 50 sqm kite as yesterday, with this morning’s new bridle. The bridle distributed the load in such a way that the kite looked very flat, and we decided both that this bridle was not an improvement and that it was too windy for such a large kite. We then launched the 18 sqm kite with the unusual planform, which we had not yet flown in sufficient wind. The 18 sqm kite performed very well, and we hit a top speed of 33 knots with 3 crew. Attached kite closeups are mostly of this kite. We will try […more]

True Wind Error Sensitivity

3/5/13

We have dramatically improved our true wind estimates by using better sensors that we have on hand. To decide which sensors to use in the future, we have graphed the effect of each type of sensor error on the true wind estimate. Using these values, we can predict the level of true wind accuracy that we can expect from candidate sensors. One thing that these plots make obvious is that small errors in apparent wind speed (lower-right plot) lead to very large errors in estimated true wind angle. Thus, it makes sense to keep our current GPS compass (with approximately 1 degree error), but to choose a new wind sensor with a very high windspeed accuracy.

The group of four […more]