Animation Flight School

I’ve been teaching the Animation Mentor Animals & Creatures Class 2 this term, and in particular we’re focused on animating flight (and flying dragons!).  Of course, if you’re going to animate a believable fantasy creature, you need to understand real flying animals, like birds and bats, and I’m going to summarize some ideas and then some great resources below the fold.

The tough thing about animal flight is that much of it is not intuitive.  We tend to assume flight is kind of like swimming through the air, and that the wings work by pushing against the air.  But that’s wrong.  The key to understanding comes from our old friend, physics, via Bernoulli’s principle.  Simply put, Bernoulli found that air pressure drops when air is moving, and the faster it moves, the more the pressure drops.

This is not intuitive at all, but is easy to demonstrate:

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Here we see a piece of paper hanging downwards under the effect of gravity. I’m blowing straight out, just across the top of the paper. The paper magically rises, towards the air stream!  How cool is that?

But there’s no magic – the movement of the air above the paper causes the air pressure in that region to drop. The air pressure below the paper is unchanged.  The result is an air pressure differential, and the higher pressure below literally lifts the paper upwards.

How do creatures get flight out of this?  Through the use of airfoils.  An airplane wing and a bird’s wing (and even individual feathers) are all airfoils. An airfoil is a structure designed so that as air moves across it, the air passing over the top surface moves faster than the air passing below, and the resulting difference in air pressure creates an upward force known as lift.

The Bernoulli principle doesn’t just operate in the vertical direction.  An airplane propeller is also an airfoil, and when rotated creates a low pressure area at it’s leading edge, generating a forward force known as thrust.  Remarkably, the outer portions of a bird’s wing will move in such a way that they also generate thrust, propelling the bird forwards.  Pretty amazing, huh?

What I find fascinating is the staggering variety of solutions that nature has found for these birds and bats to generate lift and thrust.  Despite that variety, there are important commonalities to the way every large animal achieves flight (I say large animals because I want to avoid the extra complexity of insect flight). We need to understand and apply these ideas when we’re animating a bird, or a flying dragon, if it is to look authentic.

Just as Muybridge was commissioned to begin creating his remarkable photographic series of animal locomotion to settle questions about how horses actually move (to the eternal benefit of animators everywhere), we need to study high-speed photography and understand a little physics if we want to understand how flying creatures move.  Fortunately for us, some dedicated folks have put together some great tutorials online, and rather than copy or replicate their good work, I offer a set of superb links.

First is Brendan Body’s fantastic flight tutorial. Brendan was a lead animator on Legend of the Guardians: The Owls of Ga’Hoole, which features fantastic flight animation, and this tutorial is one of the most impressive pieces of internet animation teaching I’ve seen. The rest of Brendan’s fine blog is also worth perusing, and here’s a shortcut to his tutorials.

Next is the Dragon Flight School video from last year’s CTN Expo. It features structure, function, and theory from Dr. Stuart Sumida, and animation application from Simon Otto, Head of Character Animation on the amazing How to Train Your Dragon.

Simon Otto was the lead animator on the eagle in the hand drawn Spirit: Stallion of the Cimmaron, so he came into HtTYD with knowledge of how birds fly. He then spent a couple of years (!) studying flight more deeply, helping develop the characters and their personalities, how each dragon would fly, and so on. The video above is also full of gems about character design, work flow, approaching a shot, and using reference. I only wish it were a two-hour video!

Next is a meaty series of on-line study guides for a college Ornithology course given by Gary Ritchisong at Eastern Kentucky University. This being a college course, it isn’t necessarily light reading, but I think you’ll find it worthwhile.  Plus these links are copiously illustrated with great diagrams and embedded videos.

Introduction to Birds goes into detail on the evolution of birds, and while some of this is peripheral to animating flight, it’s still fascinating, and has several great videos embedded throughout. I particularly think that understanding the skeletal and muscular structure of your flying creature is important, and those subjects are nicely covered here, too.

Bird Flight 1 is pure gold and features great stuff on the origins of animal flight (very useful for thinking about flying/gliding dinosaurs as well as ideas about how an actual dragon might fly).

Bird Flight 2 extends the information about flight, and includes bonus material on bird head movements, climbing, swimming, and diving. The full curriculum of Professor Ritchisong’s course is here.

If you’ve gone though these videos and tutorials and want more, especially a discussion of some of the ways insect flight differs from birds/bats, you can check out this page from the University of Cambridge. Impress your friends with your casual discussion of leading-edge vortices and wake recapture!

I encourage you to return to these tutorials as you animate your flying creatures. It’s too much information to absorb in one sitting (or even several), and the further you go with your animation, the more this information will continue to reveal its usefulness.

Enjoy, and if you know of any other great flight tutorials on the web, or you find some of this difficult to understand, let me know in the comments.

2 Responses to “Animation Flight School”

  1. Yeray Diaz Says:

    Hey Kevin, thanks for the post. The link to the CTN Dragon’s Flight School seems to be broken. I found this version on vimeo

    Not sure if it’s the same one.


  2. Kevin Says:

    Thanks for catching that, Yeray. I’ve fixed it now, and also set the links to open in separate windows. I guess CTN is clearing the old lectures to make room for new ones, but I’m glad they’ve left it up on Vimeo.

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The animation and animation-related musings of Kevin Koch