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.
Wow, a chance to reply to pg! Yes, it could and has been done. Glider pilot Helmut Reichmann describes the technique for how to do this in a glider in his book, "Cross-Country Soaring". He has also performed the maneuver a couple of times.
You have to be flying in an area where there is strong wind shear, which means a sharp difference in wind speed with altitude. You could detect such wind shear when climbing or descending through it, either with GPS or by watching the ground and seeing how much you drift in relation to it. Cloud movements are another option. You also need a very maneuverable and aerodynamically efficient plane, so you won't lose a lot of energy from the sharp banking maneuvers required.
So assume that the wind speed increases sharply with altitude, maybe around 20 knots over 100 meters of altitude. You start out flying the same direction as the wind and then sharply dive 100-200 meters down into the space where the wind is weaker. This turns part of your altitude into kinetic energy, so your ground speed increases by about 100-150 kph. But due to the change in wind speed, your airspeed velocity has changed less than it would in dead air. So your total energy has increased. You can then make a sharp (>120 degree) turn in the direction you want to go, so you face partly into the wind again. You then sharply pull up, gaining about 100 meters of altitude and losing some of your velocity. The relative wind speed has increased with altitude, so your kinetic energy loss in relation to the air from pulling up is less than it would be in dead air. Overall, you have gained velocity, moved the aircraft and maintained your altitude "for free".
This process can be repeated, and you can keep doing it (albeit with some nausea, unless you're used to these sharp maneuvers) as long as there is sufficient wind shear. It will be easier to move perpendicular to the wind direction than directly with or against the wind, but the energy (altitude, velocity) you gain from this maneuver could be used to glide in any direction.
I don't want to make any grand claims that this technique can be used for anything practical (i.e. passenger transport). Glider pilots don't use it in competitions, because there are lots of techniques for moving around without an engine that are a lot better and easier to exploit. (You can gain altitude in thermals, ridge lift or mountain waves - and translated to horsepowers, a thermal carrying a 500kg glider upwards by 3m/s is a very powerful engine). But the technique is very cool as an intellectual curiosity.
[Edit: Actually, it's interesting that the authors mention possible applications for this to robotic aircraft. I'm sure you could make a robotic glider that used the meteorological principles that glider pilots use to move around without engines. The "Albatross" technique would only be a small part of this - glider pilots have extensively studied techniques for moving around without an engine, and there are lots of them. Glider pilots manage >100kph average velocities over >500km journeys on days with good weather, and robotic aircraft could in principle do the same].
There isn't a direct glider analogy to being "in irons" (you can always dive to gain airspeed, assuming you have any altitude to lose of course - not having any altitude would mean you are guaranteed to crash, since gliding is basically flying slightly downhill all the time).
But there are plenty of ways to get in trouble when gliding, most notably flying into an area where there aren't any sources of lift. This means you can't gain any more altitude, and you'll gradually lose your remaining altitude and probably have to land in a field or something.
Per the sister comment it seems this is a known technique in glider circles, but a more interesting question is what sort of sensors would be required to capture airflow information such that an aircraft on autopilot could do it. Or more specifically as the authors of the paper suggest, a UAV.
If the flight modality could be maintained without net energy input then any energy collection on the wings in the form of solar panels could be used for sensors in the payload.
The flight planning aspect can be done. In ways it has been done by gliders. The real difficulty is convincing a very conservative industry to change.
The mechanical/aerodynamic aspect is much more difficult, but some people are making real progress here (see the synergy homebuilt). Still, we don't have a cost effective way to change the shape of a wing like a bird does. So we're stuck making some (though not as much as is currently standard) tradeoffs. As mentioned int he article, the albatross has a L/D of 20, which is certainly achievable with current technology
Again, the big trouble is convincing a conservative industry to change. They're still not catching up with canard wing designs from the 1970's.
EDIT: As marvin points out gliders use different techniques. As you might expect you'll get the best results using an ensemble technique - take advantage of thermals when possible, use wind where possible, plan for most fuel efficient altitude/temperatures, etc.
You're certainly correct. I was getting L/D and glide ratio mixed up. Further I was thinking about the state of the art in small aircraft - the Cessna 172 or Cirrus SR22. Neither particularly good in this respect.
L/D and glide ratio are equal numbers. It's a matter of basic geometry. While different concepts, they'll always be the same value for a given aircraft.
Our results reveal an evolutionary adaptation to an extreme environment, and may support recent biologically inspired research on robotic aircraft that might utilize albatrosses' flight technique for engineless propulsion.
There has been an RC glider community doing dynamic soaring probably for decades, it's easy to find videos on youtube.
Basically it's just extracting energy from the wind velocity difference.
Of course you could use it at much larger scales, like a huge UAV dynamically soaring high up if the winds are in different directions at different altitudes.
Rc gliders do it behind a ridge, taking advantage of big wind speed differences caused by the ridge. It's pretty fantastic to see in a video or in real life.
But I'm not sure whether it translates to generalized flying at high altitude - is there enough windshear without a close-by hill for this to work? Can it work in any direction?
I think my jaw dropped the first time I came across videos of RC gliders doing 400+ mph. No motor. 400 mph. Here's one clocked at 399. Others on YouTube show over 450
Wow at last we can have our flying cars that don't need fuel... Just kidding.
Can a minimally powered aircraft on mars or venus do this without spending a dime on fuel or panels for flight? That would be a cool technology demonstration getting the whole world shocked. And we could throw all kinds of exotic material like carbon fiber and thin strong foils and kites coz getting these beasts there would be way more costlier than building them. I see very interesting short term future possibilities for this. Maybe even an X-Prize for this would help.
How can this be an "evolutionary adaptation" is beyond my understanding. How can a genetic mutation lead to such complex flight strategy? Anyone can clue me out? Or is it just another irresponsable "just-so story"? [1]
Albatrosses have for years been known to use the flight pattern of leeward dives, windward climbs to move around, which is what this paper describes. Those two movements are the only things you need to gain energy when there is wind shear, so I don't see any reason that this isn't an evolutionary adaption. Birds using this technique use less energy when moving around, which is a clear benefit.
I've noticed that most people who have trouble grasping evolution are making two mistakes: they tend to look from a given adaption back in into time for a rather simple linear path to describe the adaption, and they don't grasp the shear number of iterations that occurred and the massive number of random adaptions that failed.
Soaring flight seems pretty easy to evolve to me. Any soaring ability will be an advantage to a bird, who can use less energy to fly. This just takes it to an extreme. Each little step along the way provides an advantage, which is exactly the kind of situation that evolution is able to take advantage of.
At a broad level, one mechanism that's fairly well documented is selecting more for gliding-oriented versus flapping-oriented wing and muscle structure, which may coevolve with behavior and habitat. I do agree that there are a lot of evolutionary explanations that are more like "it's plausible that it'd be this" than actually proven, though.
It can be an instinct; an innate behavior that is not learned, such as a bear preparing for hibernation, or certain birds migrating in fixed patterns. When animals display these specific behaviors even in the absence of instruction from their parents or other members of their species, then it must be genetic, even though it's probably not known how that would work specifically.
The accusation of a "just-so story" is made against a claim of how an adaptation came about. But that's not happening here, they just state that it is an evolutionary adaptation, without a theory of how it was acquired.
Wouldn't this technically be gliding rather than flying? I had thought that by definition it was only flight if you could produce enough thrust to maintain velocity and altitude in still air.
