Friday, 8 February 2013

ON EAGLE'S WINGS



Wedge-tail eagle

Thirty years had slipped by since Bruce was instructing air force pilots in World War II and even on this scorching summer afternoon in 1975 he couldn't resist going gliding at Waikerie, South Australia. He must have been keen to brave the 42 degree heat and climb into the cabin of a Blanik TE glider. 
Blanik TE glider

 Finally airborne and released from the tug he searched for promise of lift and found a wedge-tail eagle hooking into a thermal so Bruce gave chase. Up, up,  round and round they went, until finally the thermal faded approaching icy cirrus clouds and Bruce was only too glad to break off the chase, get down to warm up and collect his Gold 'C' Height Award for reaching something like 13,000 feet of altitude.                                                                                                                                                                                       

Bruce knew what he was doing but how did the eagle know how to climb so well?

 When an aerofoil creates lift it also creates induced drag due to the higher pressure air under the wing leaking around the wing tip to the lower pressure above, causing an energy-sapping wing tip vortex. 


The eagle has been specially equipped with adjustable wingtip feathers which it can fold up to form a winglet that blocks the vortex, increasing lift efficiency.




Aeronautical engineers have known of this phenomenon for decades, incorporating tip tanks in various models, but finally we now see wide-bodied airliners like this Airbus A380 fitted with winglets to improve fuel economy, lessen the danger of wake turbulence for following aircraft, and improve noise abatement.
It’s yet another ‘stroke of genius’ we've copied from nature's Master Designer, except we’ve missed the adjustable feature – that’s just too clever.

Special thanks to our neighbour Bruce Berry, Port Macquarie, NSW
Photo credits:
BlanikTE/soaringcafe.com                                                                                                                                                                                                                                                                                                      wedgetail / wedgetail eagle / aussiebirdlife.com                                                                                                                                            Airbus / aeronews.net


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1 comment:

  1. Discovery Safari with Mr. K8 February 2013 at 14:32

    We publish IOPNA's as laminated posters with larger print for the enjoyment of the elderly. Mr. Bruce Berry told me of his experience on that blistering day all those years ago and then to prove it, produced the barograph etching, duly signed by the instructor on the day!
    Researching the remarkable design of the eagle I discovered that their eyesight is so special that they can even see thermals with their infra-red and ultraviolet detection. Mr. Berry's reply? "That's cheating!"
    It looks like eagles deserve another article some day.

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