The apparent wind is much much less than 70 knot! The course is so down wind (150 degrees) thay the appparent wind is only around 25 knots at 50 knot speed with a true wind at 40 knot. See forexample http://www.sailingusa.info/true_wind_calculator.htm
WOW. Thanks for the correction, I didn’t realise the course was so far down wind. I’m amazed that a 9m kite can make that much power in only 25kn of wind, I’m flying the wrong kite.
I was WAY off with the 70kn! But the information I found said the course is 140 off the wind. When I used the calculator I got;
"The direction to the apparent-wind is 53.79 degrees off the bow! The speed of the apparent-wind is 35.85 knots!!"
There’s a big difference between 25 and 36 (not nearly as much as 35 and 70,
doh) and 53.79 degrees of the bow (actually the course) is still 36 degrees forward. What’s the normal apparent angle for the average mortal kiter going hard upwind? I really wouldn’t even want to guess. Surely ultimately the speed is limited by how much power can be held and the AOA the kite can pull at. I guess perhaps AOA just limits the speed the kite can fly at and there’s much more to it than that.
To me sailing really fast is sailing upwind (close to the apparent wind). Otherwise you could just fly a parachute straight downwind in a gale and you’re there. I don’t know what the course angle is but check out the apparent wind for this guy. It’s rather forward but he does get up to 126Mph!
There are many classes of speed sailing records, for example, around the world, ocean crossings, 1 Nm and 500m. The kite records are real and are amazing, they’re just short course records. Do it anyway you can but do it on water and powered only by wind. Last year Hydroptère managed an incredible 51kn over a nautical mile on open water. The amazing thing is it looks like there’s not a lot of wind. Again though, they’re sailing very close to the apparent wind.
Kites have a long way to go before they get as close the limits of technology as Hydroptère is. I think these guys (the kiters) will continue smash the records for a few years to come.