Learn From the Experts - Or Not

By Erik Minty

Autonomous Underwater Vehicles (AUVs) are the latest rage _ it seems like everyone wants to build one. But if you wanted to build a really great one (not knocking the heroics of Pete by any means ...) where would you turn? Well, take a look at the oldest swimmers around. Fish, right? That's just what they're doing at MIT _ figuring that nobody knows about swimming better than a fish, they've built an AUV with a swishing tail to reduce drag caused by vortices.

So moving on to more exciting places, if you wanted to build a flying machine, you would look at _ guess who? _ birds! Let's go back a century or so. Two bright young chaps named Wilbur and Orville (have you heard of these guys?) happened to be avid bird-watchers. Looking closely, they noticed that in order to turn, birds would "warp" their outside wing. No small surprise to them, that when they flew the first "official" airplane, they used a technique called "wing-warping" to provide lateral control. Now, modern aircraft don't use exactly the same technique, but the theory is identical.

Let's look at a favourite topic of mine _ soaring. Birds are inherently lazy, so if they can sit in a rising pocket of air instead of flapping their wings, guess where they'll be? So if I'm up there looking for thermals (slightly more urgency here, since my wings don't flap too well) what do I look for? You got it _ birds! Funnily enough, since I don't make a terrible loud noise (gliders are funny that way) they tend to be awfully friendly to me, and generally fit me right into their "pattern." Gulls especially display superior airmanship (although they make up for it with other deficiencies, as I will explain later). They all circle the thermal in the same direction, and are pretty good at staying out of each other's way when joining in. I've seen a few glider pilots who should take some etiquette lessons from gulls!

Let's take a quick diversion back to aerodynamics theory. Ever watch birds landing? Take a close look someday. They'll approach their "landing site," stretch the backs of their wings waaaay down, and right at the end they'll give a few forward pushes. All of this helps them to slow down of course, but by stretching out their wings, they increase the curvature or "camber" of the wing, which increases lift. This prevents them from dropping out of the sky when they slow down. (Granted, some gulls have been known to make much less-than-graceful landings, but they make up for their "lack of technique" with their superior airmanship. And besides, it can be fun to watch gulls trying to make tricky landings. I think their wings are too long and their feet too big.)

We can apply most of this to airplanes. On approach to land, pilots generally lower "flaps," located inboard on the trailing edge of each wing. This increases the overall camber of the wing, which has two effects: increasing lift, and increasing drag. The increased drag helps the pilot to slow down without having to pitch the nose high (which would make it difficult to see the runway), and provides an extra margin of lift which enables the pilot to fly at such a reduced speed without dropping out of the sky. Which is always nice.

But you can't learn everything from the experts. (Note to first years: this is also true about life in general, which explains why you sometimes get blank looks from senior students when you ask them to help you out with a "really simple" ENSC-125 problem.) Have you ever seen any of those old black-and-white silent screen movies with all kinds of crazy people crashing in all kinds of wild and wonderful flying machines (which we, in all our infinite wisdom of hindsight, know before they "take off" will not work)? Please keep in mind as you laugh at these people, that many of them were just as clever _ if not more so _ than you and I. But a lot of these crazy ideas for flying machines over the centuries have come from watching birds (which, as you may remember, is exactly what the Wright Brothers did!) People have tried to glue feathers to themselves, strap wings to their arms, and even build an automatic wing-flapping machine! And if you really think about it, for people trying to learn how to fly by watching "the experts," it all makes at least a little bit of sense.

Now admittedly ducks are pretty good, but I would really recommend against the idea of taking lessons on formation flying from a goose. It is with tremendously good reason that a formation of geese is termed a "gaggle." If they're not running into each other or biting each other's tails, they're straggling all over the sky! And if one goose gets slightly out of formation, the whole thing falls apart! You can also tell how effective a gaggle is by the amount of chatter. Ducks make lots of noise when flying in formation _ this is communication. Geese occasionally squawk at each other, but it really sounds more like they're hassling each other, rather than trying to keep formation. (Snowbirds, of course, are a completely different story. Nobody flies formations like them ...)

So we can learn a lot from nature's experts, but don't go completely overboard. Ol' Mother Nature sure has some pretty great ideas, but the unfortunate thing is that we as Engineers can't use them all. What we have to do is use our brains a little, pick and choose among the ideas we can use, and discard the rest. And don't expect the Pentagon to start fitting their Stealth bombers with goose feathers.

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