AL­BA­TROSSES ‘CHEAT’. MUCH OF THEIR PROPUL­SION COMES FROM THEIR ABIL­ITY TO RIDE THE WIND AND WAVES.

BBC Wildlife Magazine - - Science Of Flight -

the same ‘runway’, un­able to cope with land­ing nearby, and I’ve also watched be­calmed al­ba­trosses pad­dling around in the Southern Ocean like big ducks wait­ing to be thrown bread. Al­ba­trosses are hardly all-rounders.

The al­ba­tross wing-shape and flight style are, more­over, com­par­a­tively sim­ple. The wings are long, nar­row and pointed, a shape de­scribed as a high as­pect ra­tio (as­pect ra­tio is the ra­tio of wing length to width). They are also held out rigid – in­deed al­ba­trosses have spe­cially mod­i­fied joints that ‘lock’ them in po­si­tion. Long wings are good for lift, too (the lift force pro­duced by the aero­foil shape adds up all along their length), and nar­row wings are great at re­duc­ing drag.

CREA­TURES OF HABI­TAT

Drag is the force that coun­ter­acts for­ward propul­sion, and it comes in two main forms. For­ward move­ment gen­er­ates fric­tion against the air, but very nar­row wings will nat­u­rally gen­er­ate less fric­tion than broad ones. At the same time, the move­ment of wings through air creates tur­bu­lence and ed­dies, which add to the drag – but, once again, nar­row wings re­duce this. Such a wing shape is per­fect in un­clut­tered places, in­clud­ing the open ocean, where ma­noeu­vra­bil­ity is not a prime con­cern.

Al­ba­trosses also ‘cheat’. Much of their propul­sion is not self-gen­er­ated, but comes from their abil­ity to ride the wind and waves and har­ness their power. They do this in two ways: first, they al­low up­drafts hit­ting the tops of waves to hoist them up (a wind speed of 10m/s is the­o­ret­i­cally able to lift them to 20m), so that they can glide down. And sec­ond, they glide up­wards into head­winds, gain­ing en­ergy purely from vari­a­tion in hor­i­zon­tal wind strength over the ocean.

So al­ba­trosses travel ef­fort­lessly, yet with­out strong winds they are pretty help­less. They are very much crea­tures of habi­tat. Does that really make them great fly­ers?

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