Commercial pilot with small experience with gliders here. I can not be sure, as I lack the scientific background, but I think this study is missing the important contribution of waves in the way albatrosses gain energy from the wind.
If you watch videos of sea birds, you´ll see that they try to fly close to cliffs or wave crests, that way they take advantage of the upward currents generated.
When albatrosses turn windward I´ll bet something that they are aiming for the upward current created by a big wave. I don´t think they can do something like this with weak winds or no sea to take advantage.
Gliders and paragliders routinely use upward currents to stay for hours in the air(altitudes 50.000´, see http://en.wikipedia.org/wiki/Perlan_Project). This currents can be generated by mountains or by the air heated close to the ground that climbs as a bubble (and tops as a typical summer cotton cloud or in a Super thunderstorm..).
Small ascending currents are even able to stop the descend of a 60Ton commercial airplane while crossing them. But are to thin (a 100 yards in diameter or less for small clouds) to be usable by fast and heavy jets.
Maybe they are not suitable for commercial flights but could be used for small drone fleets loaded of scientific instruments. They would only need a small electrical motor(for those moments with out wind), solar panels and enough battery to fly the way Albatrosses do, and of course the AI to maneuver.
edit: After reading some comments and the study again, I see that I missed the point. I realize that it´s possible for a small "plane" to use the wind gradient to soar.
With commercial planes you don´t look for it, but you have to avoid it!, if you are flying at your approach speed (lets say 140 kts) with 20 kts head wind and you suddenly find wind shear of 20 kts tail wind, you´ll find yourself with some 40 kts less of speed and fully into stall. The opposite is used (as I understand) by the albatrosses to win total energy.
Is still not usable for larger planes as wind gradient is thin and very close to the ground.
Strong jet streams are used every day by commercial flights to cross oceans. The routes are changed along the winds. For example USA to Europe flights will flight with the jet stream(and save more than an hour of flight time), and Europe to USA flights will avoid it. All routes are based on the weather reports and previsions.
I really would like to hear Elon Musk take on electric planes. He claims he has some calculations on electrical high altitude planes, that would be awesome and ground braking.
Actually the paper specifically rules out energy gain due to surface effects.
" The total energy begins to increase during the windward climb. At the top of the trajectory, the energy gain does not come to a stop, but continues to increase. The total energy finally reaches its maximum value during the leeward descent, after the bird has already started to loose altitude."
True, I missunderstood the point. They are basically using the wind to "push" them and increase total energy, once they get the "push" of strong altitude winds, they dive to convert that fast ground speed into air speed(kinetic energy), and then pull again against the wind to receive another push. Any way the wind gradient is too thin and close to the ground to be of any use for a commercial plane.
Maybe it could be done in a jet stream. Just the same principle but coming in and out of a jet stream instead.
Maybe they are not suitable for commercial flights but could be used for small drone fleets loaded of scientific instruments. They would only need a small electrical motor(for those moments with out wind), solar panels and enough battery to fly the way Albatrosses do, and of course the AI to maneuver.
edit: After reading some comments and the study again, I see that I missed the point. I realize that it´s possible for a small "plane" to use the wind gradient to soar. With commercial planes you don´t look for it, but you have to avoid it!, if you are flying at your approach speed (lets say 140 kts) with 20 kts head wind and you suddenly find wind shear of 20 kts tail wind, you´ll find yourself with some 40 kts less of speed and fully into stall. The opposite is used (as I understand) by the albatrosses to win total energy. Is still not usable for larger planes as wind gradient is thin and very close to the ground. Strong jet streams are used every day by commercial flights to cross oceans. The routes are changed along the winds. For example USA to Europe flights will flight with the jet stream(and save more than an hour of flight time), and Europe to USA flights will avoid it. All routes are based on the weather reports and previsions.
I really would like to hear Elon Musk take on electric planes. He claims he has some calculations on electrical high altitude planes, that would be awesome and ground braking.