Given to Fly

Alight - Herring Gull LandingI never get tired of watching birds fly. It’s something that’s always entranced me: a warbler flitting between sun-dappled leaves, a gull wheeling lazily against the clear blue of a Manitoba summer sky, or the subtle whisper of an owl’s feathers as it returns to roost.

My fascination with flight started at an early age, much to the consternation of my parents who had to cart me off to the hospital to get my foot x-rayed after an ill-fated attempt to get airborne from the top of a ladder with willow branches strapped to my arms.

I’m pleased to report that there was no permanent damage and I now have a much better grasp on the mechanics of avian flight.

Physicists and biologists alike are still trying to sort out all of the details; but we get the general gist of how it works and much of that knowledge has resulted in the air travel we enjoy today.

A bird in the air has two forces to contend with: gravity (the inexorable force the earth exerts on everything, drawing us back to its core) and drag (the force of the air that pushes back against us whenever we try to move through it). In order to keep itself aloft, the wings of a bird must produce enough lift to counter gravity and reduce drag.

 

Much of that is achieved through the shape the wing. It takes a lot of energy to flap all the time to produce enough thrust to keep you up and moving forward, so having wings that can generate lift and reduce drag as you glide are a beneficial adaptation. Wings aren’t flat, whether they are on a bird or a plane. Diagram explaining how cambered wings create liftFlat wings don’t create lift. Air moving around a symmetrical wing passes over and under its surface at the same speed on both sides. However, if you curve the wing and create a cambered airfoil, then you’re getting somewhere. With a cambered wing, the air passing over the top moves much faster than the air passing below the wing. This creates a pressure differential, with lower pressure above the wing, where air is being swept away and high pressure below where air is piling up, pushing the wing and the bird attached to it, up into the sky. There wasn’t much camber to my willow branches, hence the crash landing.

 

Diagram explaning how the angle of attack of a wing can affect liftAnother way increase that pressure differential is to tilt the leading edge of the wing up, dropping the flight feathers down and building up more air underneath. However, you can go too far with this. Tilt more than about 15o and the airstream separates from the upper surface of the wing, creating turbulence, stalling the bird out. They use this to their advantage when landing, like the gull in the image above. To control the stall, most birds can raise their equivalent of a thumb called the alula. This nub of bone with usually about three feathers on it (you can just see it sticking up behind the top of the gull’s wing in the picture) can split the airstream at the leading edge, forcing it back over the surface of the wing.

 

 

 

Once they’ve vanquished gravity, there’s still the matter of drag threatening to push them back to the ground. Flapping, of course, will keep you moving; but there are several design considerations that birds have made over millenia of evolution.Β  Birds that do a lot of gliding (e.g. gulls) have long, tapered wings that concentrate any vortices that might form at the wing tips (turbulence caused by the feathers slicing through the air) into two small areas that are as far apart as possible, reducing what is called ‘pressure drag’. Soaring birds, like hawks and Sandhill Cranes, take a different approach, spreading out their primary feathers like fingers, splitting up the wingtip vortices and reducing their impact.

If you found wrapping your head around all that was a bit of a challenge (like I did the first time I had to teach it), understanding what’s going on when a bird is flapping will give you a veritable headache. Things get complicated as the wing starts to move and lift and thrust start happening simultaneously. In a nutshell, however, the lift is generated by the curve in the part of the wing closest to the body, while the tips of the primaries produce the thrust, creating momentum that propels the bird through the air with a grace that always amazes me.

Sometimes taking a phenomenon apart and learning how each component works destroys the magic of the whole thing; but I haven’t found that to be the case with the flight of birds. Understanding the forces that make it possible for them to shed the earth’s shackles only makes it all the more remarkable.

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18 thoughts on “Given to Fly

  1. Oh wow — you explained it so well — I UNDERSTAND ! Bet that first flight at Kittyhawk would have been longer if the Wright Bros. had tweaked the design of those wings so they were wider at the front.

    Thanks so much … and no, it doesn’t take away any of the magic. πŸ™‚

    • I’m happy to know it made sense, Sybil. When I had to teach flight mechanics to my chordates class this year, it took a few readings to wrap my head around the whole thing. A good diagram made all the difference, though.

      It’s funny that you should mention airplanes. Now that I know how they work, I’m actually more nervous to fly. It just blows me away that just moving air over the right shaped surface at a fast enough speed will get you off the ground. Still doesn’t take away from the magic.

  2. Thanks for the lesson. I realize that the more I learn about any of nature’s creatures, the more I am amazed at the complexity of their bio-mechanics, which govern their movement, and their instinct, which governs most of their behavior. Each creature is amazing in its own right.

    • Thanks, Jo Ann. I know what you mean. I just taught course on chordate zoology and another on human anatomy/physiology and I was blown away by the complexity of life (even after all of my years studying it). There’s something new to learn everyday that only makes my appreciation of nature that much more complete. I’m glad I can share that with you.

  3. What a wonderful post… Thanks so much for sharing! And I agree, I don’t think it destroys any of the magic, magnificence, and elegance of birds’ flight β€” I remain ever-captivated. β™₯

      • There’s a wonderful quote that’s escaping me at the moment… About truly KNOWING things (which is perfect for your posts), but for now:

        The possession of knowledge does not kill the sense of wonder and mystery. There is always more mystery. -Anais Nin πŸ™‚

  4. I can close my eyes, let my arms transform into massive wings and I swear I know how flying feels, the air pushing and swirling as I swoop – like I’ve done it before! But I never understood so well how it works. Your description, as always is clear and your illustrations are excellent. The featured artwork, however is the kicker – just beautiful!

    • Hi Cindy. I meant to reply to this just as I got the message and was predictably distracted (squirrel). Anyway, thanks for the lovely visual. We already know what happened when I tried to move past my imagination πŸ™‚ Good thing the ladder wasn’t overly high.

      I’m very glad my explanation of the mechanics of the whole thing made sense. When I first had to wrap my head around the concept so that I could teach it to my students, I’d feared that I’d hit the one subject that I wouldn’t be able to master. So, I started to draw it out. Made all the difference.

      The featured artwork is definitely one of my favourites too, thanks πŸ™‚

  5. I love watching sea birds fly – pelicans skimming inches above the water or seagulls negotiating the complex air currents…it’s complete artistry. And if you’re lucky enough to look up just as a bird flies by, you can see the sunlight pick out the prehistoric structure of the wings. I try to take photos of birds in flight – I usually make a muddle of things, but sometimes I almost capture them and it makes all the effort worthwhile!

    • I love watching seabirds too, especially the pelicans that we lovingly call the ‘Lake Winnipeg Air Force’ around here. They really are something I never get tired of watching. Keep taking pictures. Even if they don’t turn out perfectly, it’s a wonderful way to feel connected with these amazing creatures. Thanks for stopping by and sharing your experience with me.

  6. Nice post! Nice combination of natural beauty and the world of physics which always amazes. Bernoulli’s lift-force is simple once you understand it, but difficult to get your head around when watching a several-ton aircraft leave the ground at slow air speed.

    We watched a northern cardinal hover like a hummingbird while hunting for his next meal on my tomatoes. I wished I could have seen it in slow motion. Beautiful.

    • Thanks, Shannon. I agree, Bernoulli’s principle is relatively easy to get once you spend some time with it, however, it still blows me away every time I’m in an airplane. I almost wish I didn’t understand how it worked. I find it a little scary now πŸ™‚

      Your cardinal experience sounds amazing. The don’t usually make it this far west. I was treated to a show of a bald eagle swooping down to catch a fish the other day and it really is amazing when you consider all the forces in play. I lost of love of physics when I started university, but now I think I’m getting it back, just in a different context.

  7. At least you had the good sense to make wings of some sort! I recall a similar childhood experience, but without wings, just flapping arms. Your artwork is so graceful, Heather. I agree, knowing more about what makes it possible for birds to fly doesn’t take away from the wonder of it all.

    • Thanks, Cait! Willow branches, unfortunately did not make very good wings πŸ™‚ I hope you weren’t injured in your adventure. As for the artwork, sometimes, I’m just lucky and manage to capture a photo that is so easy to work with.

  8. Heather, I am dong an assignment for my education class, and need to use an image on your site. Can I? Is there a certain way you need me to cite it if I can?

    • You know what never mind, my husband found something I can use. Your site is fantastic! The way you explain things makes such great sense, better than reading it out of a textbook or other places.

    • Hi EmmaLee. Thanks very much for your kind words. It’s high praise to hear from an education student that I’m doing a good job explaining things. Please forgive me accidentally flagging your last comment. I’m still getting used to the mobile version of Word Press.

      I’m glad you found an image you could use. Thanks for asking. I’m curious to know more about how one of my images was going to be helpful for you. It always helps to learn more about what I’ve done well and what can be improved.

      Thanks for reading and good luck with your assignment.

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