spork wrote:As I'm sure you're aware there are birds that stay aloft without flapping for many many miles with no vertical air currents. They do this using a version of dynamic soaring. All that's required is a healthy wind gradient (even with all air moving horizontally).
Birds are pretty good at grabbing any opportunity that they can get, but I don't think you could ever isolate miles of horizontal windshear without any vertical displacement or mixing. And in real life, the windshear will never be a perfectly even gradient across great horizontal and vertical expanses, even in the middle of an ocean. If a bird flies headlong into increased headwind (or reduced tailwind - same thing, relatively) he can use the newfound kinetic energy to soar higher, and he'll probably be pretty intuitive about changing course to take advantage of the next horizontal gust or gradient.
But soaring birds are vastly more efficient gliders than kiteboarders are, and can therefore take advantage of atmospheric nuances that would be insignificant to a kiter.
spork wrote:I have a hard time believing he got much help from a thermal as I've never seen any evidence of significant thermal activity at 3rd Ave. I have on a couple of occassions seen a shear set up there.
I referred to thermals as a possible source of vertical currents, but in reality, it was almost certainly a rotor or other similar turbulence. I agree that a significant thermal at low altitude, especially over water, wouldn't likely be relevant. And regarding windshear, it is related to a rotor effect anyway in some circumstances. I think you focus on windshear too much. In a gusty environment (usually near geographical obstructions), any windshear near the surface is better characterized as turbulence, and in wide open, steady surface winds, evenly distributed windshear isn't significant enough to turn a kiteboarder into a soarer.
spork wrote:Conditions vary greatly from one place to the next, but I always felt the boosts I got were typically from horizontal wind gusts.
I agree mostly, but 22 seconds of hangtime wasn't just caused by horizontal gusts. And there is almost no such thing as a purely horizontal gust with no vertical displacement involved. You can't have a horizontal gust blasting along the surface without coming from somewhere, going somewhere, and displacing the slow moving air in its way. Gusts at the surface usually tumble down from aloft, due either to a geographically induced rotor, or to vertical mixing caused by temperature induced density differences. Many sailors and kiters would do well to perceive wind and gusts as three-dimensional phenomenon, instead of the conventional two.
spork wrote:I believe you could dynamically soar indefinitely in a strong enough steady wind gradient with proper kite control.
Not when you are doing about 20 kts at a 6:1 glide ratio, sinking at 500 fpm. The energy that you would have to derive from a steady wind gradient to overcome these limitations is totally impractical, unless you could find a steady gradient that is many times the magnitude of any created in earth's atmosphere (without more significant vertical activity).