Tuesday, March 29, 2011

There'll be an exam on this!


The albatross was immortalized in Samual Taylor Coleridge's famous poem, The Rime of the Ancient Mariner but these birds have always been watched by sailors. They don't so much as fly as soar across the waves in a swoopping flight pattern upwind in wind speeds of 10 to 20 knots.


Albatrosses spend the majority of their long lives above the ocean. By the age of 50, an albatross has typically flown at least 1.5 million miles. The adults routinely fly hundreds of miles to gether food before returning to feed their chicks. The lucky ones make it, the unlucky die trying to grab the bait on the miles of long hooked fishing lines. Their wingspans can reach up to 12 feet but they rarely flap their wings


Phil Richardson, a retired oceanographer but still at Woods Hole Oceanographic Institution, has studied the aerodynamics of the birds which can fly in any direction including into the wind without losing speed or steadiness in flight and with no wing flapping.


With his knowledge of sailing, gliding and his work with the movement of ocean currents, he began to look closely at the albatross.


Richardson came up with a theory involving the interaction between wind and ocean. In the trough of waves, there is little wind, because the waves block it. But above the waves and their troughs, winds blow briskly across the ocean in thin layers. Lower layers are slowed by air-sea friction near the ocean surface, but winds speeds increase as you go farther from the surface and higher up.


He concluded that albatrosses needed a minimum wind speed of 7 knots to soar and calculated that they could soar upwind at a speed of 12 knots. An albatross ascending from a wave trough at an angle would encounter progressively faster winds increasing its speed in the air as a burst of kinetic energy that enables it to climb to heights of 10 to 15 metres. (Hello, are you still with me) It then makes a tight turn downwind and swoops into another wave trough, adding airspeed as it descends through the wind sheer into progressively slower winds. Each addition of airspeed balances the loss of energy caused by drag on the bird. The albatross keeps up this cycle and each swoop cycle takes about 10 seconds. (a heck of a lot shorter than it took me to understand this).




This phenomenon is called dynamic soaring and glider pilots know it well. Richardson still didn't know how they flew upwind but being a sailor it came to him that the birds were tacking as ship's sails do. He went back to his model and calculated that the fastest course upwind for an albatross is to tack about 30 degrees to the right and left of the wind. He observed that the birds climb upwind but often dive perpendicular to the wind to maximize their average velocity in an upwind direction. (WAKE UP, this is interesting)


Of course the military are interested in all forms of flight dynamics at a small scale, using bird, bat and insect flight as models for the development of autonomous drones for use in war zones. They already have them but want better ones, don't they always?




"Great albatross! The meanest birds

Spring up and flit away,

While thou must toil to gain a flight,

And spread those pinions gray;

But when they once are fairly poised,

Far o'er each chirping thing

Thour sailest wide to other lands,

E'en sleeping on the wing."


Perserverando by Charles Godfrey Leland

13 comments:

Andrew said...

Is that what is called long line fishing? Banned. But still happens I suppose. Bad!

Davo said...

So, what's the question (always remembering that i can still remember the 60 hours in those sleek glassfibre thingos that don't flap wings .. well, sometimes, but not often).

Jayne said...

They are the marathon runner of the skies...except they look nicer and don't suffer from Jogger's Nipple.

River said...

Now there's an exam I'm sure to fail. I'd be too fascinated watching the birds to pay attention to details.

JahTeh said...

Andrew, the long lines have baited hooks and string out for miles in the ocean. They hook turtles, dolphins, birds and even whales have had lines and hooks in their flesh. They should be banned.

Davo, a new world's record of 468 miles per hour was set using an albatross-sized glider but I don't think a Davo sized one would do as well.

Jayne, jogger's nipple suggests a gentle irritation but you and I know that we would be suffering from slam-dunk boob.

River, the researcher has taken to photography to concentrate on the beauty of seabirds. I love nothing better than to be at the beach with lots of birds.

Link said...

Have you seen the film/doco"Travelling Birds"? I saw it for the fourth time the other night. It's fabulous. Birds are one of the more interesting things about life.

JahTeh said...

Link, I have the DVD but haven't watched it yet. I'm waiting for the machine to be hooked up to the bigger tv to get the full enjoyment. At the moment my technician is brawling with his mobile company so I dare not interrupt the fight which has gone on for over a week now.

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