Editing Dynamic soaring (section)

==Basic mechanism==
While different flight patterns can be employed in dynamic soaring, the simplest is a closed loop across the shear layer between two airmasses in relative movement, e.g. stationary air in a valley, and a layer of wind above the valley. The gain in speed can be explained in terms of airspeed and groundspeed:
* As the glider begins the loop, say in a stationary airmass, groundspeed and airspeed are the same.
* The glider enters the moving airmass nearly head-on, which increases the glider's airspeed.  
* The glider then turns 180°, where it is able to maintain most of its airspeed due to momentum. This must happen immediately, or groundspeed will be lost. The glider's groundspeed, first crosswind, then downwind, as it turns, is now higher, as the tailwind has accelerated the glider.
* The loop continues with the glider re-entering the stationary airmass and turning around, maintaining the now higher airspeed and groundspeed.
* Each cycle results in higher speeds, up to a point where drag prevents additional increase. 
The energy is extracted by using the velocity difference between the two airmasses to lift the flying object to a higher altitude (or to reverse the descent respectively) after the transfer between the airmasses.
[[File:Dynamic Soaring Animated Diagram.gif|right|450px|Dynamic Soaring Loop]]

In practice, there is a [[turbulent]] mixing layer between the moving and stationary air mass. In addition, [[drag (physics)|drag]] forces are continually slowing the plane. Since higher speed gives rise to higher drag forces, there is a maximum speed that can be attained. Typically around 10 times the windspeed for efficient glider designs.

When seabirds perform dynamic soaring, the [[wind gradient]]s are much less pronounced, so the energy extraction is comparably smaller.  Instead of flying in circles as glider pilots do, birds commonly execute a series of half circles in opposite directions, in a zigzag pattern.  An initial climb though the gradient while facing into the wind causes it to gain airspeed.  It then makes an 180° turn and dives back through the same gradient but in the downwind direction, which again causes it to gain airspeed.  It then makes an 180° turn at low altitude, in the other direction, to face back up into the wind... and the cycle repeats.  By repeating the manoeuvre over and over it can make progress laterally to the wind while maintaining its airspeed, which enables it to travel in a cross-wind direction indefinitely.

<!-- There is some speed lost during the climb, as the bird trades speed for altitude, and some speed gained by diving as the reverse happens.  <<  Obviously. Should this even be mentioned ? -->  
As drag is slowing the bird, dynamic soaring is a tradeoff between speed lost to drag, and speed gained by moving through the wind gradient. At some point, climbing higher carries no additional benefit, as the wind gradient lessens with altitude.