A flap-flap here and a zoom-zoom there

kw: book reviews, nonfiction, aeronautics, flight

Just about the time I began to drive, I had plans to build a ground-effect "flying" car, vaguely based around a chainsaw engine or two. I was enamored of the one-man "flying jeep" then being touted in Popular Mechanics and other hobbyist journals. Then two things happened. I found that engines with sufficient power to lift me plus a 150-lb (70kg) machine, and appropriate propellors, were as costly as a decent used car; and my Dad pointed out that an auto doesn't need to spend all its energy staying off the ground, that the wheels took care of that. I got an old VW bug for $350, and that was that.

Funny thing is, I'd already "flown", just a tiny bit. My Dad and his business buddy Bill used Bill's small plane (a 4-seater) to make short business trips, and on two or three occasions invited me along—it wasn't hard to get a 10-year-old out of a day of school in the 1950s. One time, Bill invited me to try my hand at the co-pilot's controls. I found out later that he had it on autopilot with those controls "out of the circuit". But for ten minutes, I felt like I was really flying that plane.

My interest in flight was never exceptional, however; I've just had an ordinary person's passing curiosity about the way, and the different ways, that birds and planes fly. Reading Why Don't Jumbo Jets Flap Their Wings: Flying Animals, Flying Machines, and How They are Different by David E. Alexander has answered a great many questions, including many I never thought to ask.

The title question comes first, and in the book it also comes last, in the Epilogue. In short, producing thrust by rotating a propellor or the turbine-compressor of a jet engine is at least twice as efficient as the alternating motion of a flapped wing. Evolution has not produced the wheel-and-axle in any multicellular creatures, so flapping is the only viable alternative for an animal. Yet it is sufficiently capable of being evolved that it did so four times, for insects, pterosaurs, birds, and bats.

Beyond that, the primary differences between muscle-powered and mechanically-powered flight are based on the environments in which they must operate. Airplanes need lots of infrastructure, including at the very least a system of runways, and the modern aviation system includes a large team of flight controllers and an intricate communications system, mainly to keep collisions to a minimum. Helicopters can do without runways, but can't take off or land in confined spaces with contrary, gusty wind.

Flying animals, however, evolved in a world without runways, with variable winds, frequent aerial hazards such as trees and cliffs, and the need to avoid ground- and air-worthy predators. Most of them, if needed, can take off straight up, something only the most costly of aircraft can be engineered to perform.

In eight of the ten chapters, the author goes step by step through the various flight systems and environments, to show where mechanical and natural fliers are similar or different. For example, turning is accomplished differently—ailerons plus a yaw-countering rudder for airplanes, versus twisting wings and banking for a bird. But basic instrumentation can be very similar—all fliers need to see well, so good eyes are a must, and birds or bats can tell changes in elevation by feeling pressure on the middle ear, in a way similar to the variometer used in sailplanes and small "sport" craft. It can be said that the bats' echolocation is similar to radar, but its range is so much smaller that the analogy is pretty weak.

I found the tenth chapter most enlightening, in its historical overviews of human-powered flight and of ornithopters (mechanical flapping fliers). Whereas the Wright brothers produced a working engine-powered airplane in 1903, the first genuine flights by human muscle power (using the human as an engine) were in the 1960s, and the flight of the first ornithopter to successfully lift off, carrying a human, was in 2006, a 103-year lag. That 2:1 efficiency deficit is really severe!

Other topics, including predation (hawking in animals, dogfighting for aircraft), soaring, and vertical flight, fill out the volume. Like many a topic, once you get into it, there's a great deal that one wouldn't have discovered without some digging. I'm always thankful for authors who've dug it out for us.