Tuesday, October 8, 2019

Chapter 5: Avain Flight

I'll admit, Avian Flight was harder to digest than the other chapters. I learned about lift, the force of acting on a moving airfoil, another cool term, perpendicular to the direction of airflow. In the case for birds, that moving airfoil is a bird's wing. Birds wings' help them create lift with a special curved design in their wing shape, called a wing chord.  There's a bunch of stuff about dynamic pressure that made me feels as if I were in physics class, not a biology book, but it's amazing how everything in science is connected. Birds are so well adapted for flight, every aspect of their body is design to be aerodynamic. Birds' tail-feathers even reduce drag pressure and helps to direct airflow in flight.

Barn Swallow sketch, 9x12 graphite on paper

There's of course hovering, which not all birds can do (hummingbirds can!). The chapter covered aerodynamic power, the type of flapping to create certain speeds, minimum and maximum range speeds, and even types of soaring. 

While all of this info was interesting, I was definitely more interested in the visual aspects of flight, and I really loved how part of the chapter focused on soaring. The book really explain well how birds like our native Turkey Vulture can stay in the air for so long, even on super windy days! I 'm always so scared that one is going to get pushed by a gust of wind into the road and get hurt. What I learned though, was that even our vultures are adapted well to this scenario:

Cornell Lab of Ornithology: Handbook of Bird Biology, Third Ed. Chapter 5, page 163

Cornell Lab of Ornithology: Handbook of Bird Biology, Third Ed. Chapter 5, page 166
When birds like vulture soar, they're wings are not extended to lie completely flat. Instead, they create a dihedral (upturned "V") wing posture to accomplish passive roll stability. If a gust of wind displaces a bird and causes a sideslip velocity downward in one direction, the angle of velocity increases in the opposite wing and effective lift is greater  in the original wing....basically it evens itself out and allows the bird to avoid rolling in mid-air -- This stuff is hard to explain!

Of course, here's a Turkey Vulture to enjoy after all that info about soaring: enjoy!

Turkey Vulture in Flight sketch, 9x12 graphite on paper

This project is made possible by support of the Indiana Arts Commission, a state agency.