SOARING BIRDS - Barn doors vs high aspect ratio

[solidsail]

Does anyone have any thoughts about the different wings used by soaring birds? Eagles and other birds with low aspect ratio wings generally have multiple spread-out feathers at the tip. How do these feathers work? An albatross has a high aspect ratio wing with tapered tip and often flies in ground effect. Is that a clue? Is the low aspect ratio wing better for load carrying?

 

[GregLocock]

An albatross's wing is designed primarily for soaring, an eagle's wing is heavily compromised so that it can lift lambs off the ground.

Cheers

Greg Locock

 

[GraviMan]

Low aspect ratio wings will produce stronger vortices for the same lift force. This is since the same momentum change requires less area to change velocity more. The concept behing tip feathers is to convert this upwash back into thrust. The concept is similar to winglets, but has no real advantages (otherwise we would see lots of multitippede 747s!)

Don't forget that an Eagle has to perform a controlled dive, requiring short span (less inertia for fast turns), while the Albatross operates over a smaller speed range. You'd be suprised how much ornithologists can actually tell you about bird "design"!

Another interesting feature is the trailing edge feathers. At high AOA the trailing edge reduces the tendancy for the flow to reverse (ie stall). The practical upshot is that the aerofoil can be designed to operate more efficiencly, but is more forgiving. Birds are actually not very observant of aircraft...

Mart

 

[franzh]

Just for grins, when I was teaching my sons about RC aircraft in the mid 80's, one of the regulars showed up with a cedar roof shingle with minimal flaps and rudder controls. That son of a gun actually flew better than some of the high dollar composite jewels. I remember some of the aerial dogfights with ribbons, he got more than he lost! Total lifting body!

Wish I took a picture.


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