The Flying Book

by David Blatner

  The airline later discovered that a series of bizarre errors by the pilots and ground crew, and computer malfunctions caused the airplane to be loaded with 9,144 kilograms of jet fuel—about half the amount required to reach their destination.

  So what happens when all the engines go out? The jet airplane becomes a very large, very expensive glider. The 767 can glide about eleven miles forward for each mile it loses in altitude, but that still only afforded flight 143 about fifteen minutes in the air. Unfortunately, the onboard electronic and hydraulic equipment requires engine power, so the cockpit controls went dark and the flight instruments became very difficult to manage.

  But remember that there are always multiple backup systems in an airplane. In this case, the 767 was fitted with a Ram Air Turbine (RAT), which uses a propeller to provide electrical power: The RAT automatically lowers from the belly of the airplane, and the wind rushing by turns the propeller, which runs a small generator. This system offered just enough hydraulic pressure to move the control surfaces on the wings and tail.

  An aircraft built for gliding (soaring) typically has about a 60-to-1 glide ratio—it will glide 60 feet forward for each foot it descends. Most commercial jet aircraft have approximately a 15-to-1 glide ratio. That is, an airplane flying at 35,000 feet can glide about 525,000 feet (about 100 miles, or 160 km).

  As the 767 glided over the vast Canadian heartland, the pilots calculated that the only airport within their range was the decomissioned Royal Canadian Air Force Base in Gimli, on the west shore of Lake Winnipeg. However, neither the pilots nor air traffic control knew that the airport’s primary runway was now being used for auto racing. Worse, July 23 was the Winnipeg Sport Car Club’s “family day,” and dozens of parents had parked their cars and campers outside the edges of the runway to watch their children race go-carts on the straightaway.

  Without engines, Flight 143 approached the airport silently, but even though it was dusk, people couldn’t help but see the giant wide-body descending on them. Parents and children scattered in every direction as the 767 landed hard, blowing out two tires with explosive force. The main landing gear under the wings had dropped by gravity alone, as it was designed to do in an emergency, but the front gear hadn’t locked into place, and the airplane’s nose bulldozed the asphalt for more than 3,000 feet, trailing a 300-foot shower of sparks.

  Amazingly, not one person on board or on the ground was injured as the airplane scraped to a stop. However, when the crew began the emergency evacuation, they discovered a slight problem: With the nose on the ground, the rear emergency slides dropped to the ground at a near-vertical angle, and several people suffered injuries hitting the tarmac.

  Remember that the space shuttle has no engines when it reenters the Earth’s atmosphere. It doesn’t drop straight down; it glides!

  The Air Canada aircraft had sustained $1 million in damages but was able to fly out only two days after. In fact, the aircraft is still in use and will forever be known as the Gimli Glider.

  Believe it or not, after the Gimli Glider landed, the Air Canada mechanics who were dispatched to drive to the airport and repair the aircraft ran out of fuel en route.

  Birds Do It, Bees Do It…

  Many an elementary school pupil has confounded his or her classmates by declaring, “Scientists have proved that bumblebees can’t fly.” Indeed, scientists have long been mystified because the equations that describe how fixed-wing aircraft lift off the ground don’t seem to work when applied to bugs. But, of course, something holds up these creatures, and the scheme appears to be similar to that used by airplanes. Birds, too, have similarities to airplanes, but as living flyers get smaller they rely on increasingly exotic aerodynamic tricks to wrest themselves into the air, and until very recently these tricks have eluded scientists’ efforts to find them.

  Bird Flight

  Some aspects of bird flight mirror airplane flight almost exactly. In a glide, for example, a bird’s wing acts just like an airplane’s wing: a simple airfoil with a curved top producing lift by deflecting air downward. But where airplanes use engines to create forward thrust, birds flap their wings. The motion is complex, with the bird not only flapping but also twisting and folding its wing during part of the stroke. Scientists have tethered birds in wind tunnels, photographed them with high-speed motion picture cameras, and found that on the upstroke, wings rotate back and up, with the leading edge on top and wingtip feathers open to decrease airflow resistance. On the down-stroke, the leading edge rotates back down and the feathers close, acting as small airfoils, propelling the bird forward.

  A bird is an instrument working according to mathematical law.

  —Leonardo da Vinci, 1505

  A Rüppell’s griffon claimed the bird altitude record in 1975 upon colliding with an airliner at 37,000 feet over Abidjan, Ivory Coast. Although the aircraft survived, the bird was less lucky. However, one expert disputes this record, suggesting that the griffon, which relies on soaring in updrafts for typical flights, may have been sucked up into a thunderstorm and was already dead, frozen, and falling earthward when the airliner hit it. The next highest record goes to a flock of whooper swans that were observed at about 28,000 feet over the Outer Hebrides.

  Birds also turn and twist their wings to maneuver, a process observed by the Wright brothers in their studies of pigeons. In fact, the Wrights modeled the steering mechanism in their first airplane after the twisting motion of a bird’s wing. Soon after, aircraft were designed to roll with ailerons (those panels near the wingtips that can be raised or lowered), as these were much easier to engineer and construct than twistable wings.

  Airplanes, like birds, widen their wings during slow flight, generating more lift in situations such as takeoff and landing. Also, the structures and internal systems of birds (at least of those that fly) are optimized for flight—built strong but light, like the best-designed aircraft. Airplane power systems run fast and hot, burning large quantities of fuel. Birds operate at higher body temperatures than other animals and have racing metabolisms. The metabolic screaming meemie of the bird world, the hummingbird, burns around 4 percent of its body weight per hour. A Boeing 747 burns around 3 percent per hour—over ten tons of fuel.

  Wings aren’t the only things that enable birds to fly; the rest of their bodies must be suited to flying, too. For instance, the pectoral muscles, which drive the wings, may account for as much as one-half of the bird’s weight. And bird bones are hollow. Consider the frigate bird: It has a wingspan of over seven feet, but its skeleton weighs only about four ounces.

  During migration, some birds can fly for distances rivaling the range of some airplanes. The ruby-throated hummingbird, which weighs about as much as a penny, flies nonstop over the Gulf of Mexico, a distance of 620 miles. That’s nothing compared to the four-inch-long blackpoll warbler, which, in its autumn migration from Canada to South America, flies continuously for ninety hours without midair refueling, a feat that puts all airliners to shame.

  Bug Flight

  Insects, which first took to the air about 350 million years ago, were considered by early aerodynamicists to be more or less like tiny birds. But after aerodynamic calculations failed to account for enough lift, twentieth-century scientists tethered insects in wind tunnels and observed that many of them didn’t flap their wings up and down like most birds. Instead, they generally flapped front to back, like a rower with an oar. Plus, aerodynamicists realized that air has a certain viscosity, and if you were the size of a bug, the air would seem thick. The smaller the creature, the thicker the air feels, so small insects like fruit flies can be thought of as swimming in molasses, rather than flying in air.

  Even with this understanding of air viscosity, it wasn’t clear how some insects could pull off the feat of flying. Models of insect flight using supercomputers failed to determine the missing lift sources, so scientists turned to dynamic scaling—constructing large working models of insect wings. The first breakthrough came in the mid-1990s from C
harles Ellington, professor of zoology at the University of Cambridge in England. His lab constructed a large set of mechanical wings based on those of a gray hawkmoth. When the model was set to flapping in a wind tunnel with smoke streams, Ellington was able to observe a vortex—a spinning cylinder of air like a sideways tornado—above the leading edge of the wing.

  Curiously, this type of vortex had been observed in wind tunnel tests of airplane wings, but always as a brief, unstable effect that occurred when the wing’s angle of attack (the angle at which the wing meets the oncoming air) was increased to the point of stall (where the wing begins to lose lift). The vortex would appear at the airplane wing’s leading edge and momentarily increase lift dramatically just before the stall. Ellington found that moths can do what airplanes can’t: hang on the edge of a stall, taking advantage of the added lift of this leading edge vortex and, just before the vortex dissipates, quickly redirect and rotate their stroke to generate the same kind of lift with the wing going the opposite way.

  Insects flap their wings much more often than birds. Ruby-throated hummingbirds click in at 70 beats per second, bees at 200 beats per second, and mosquitos at around 600 beats per second (600 Hz), which produces their irritating whine.

  The bat is the only mammal capable of true flight.

  Unfortunately, this added lift from the delayed stall might be sufficient to explain the aerodynamics of some larger insects, but it still can’t account for the lift from tiny insect wings, which often flutter forward and backward like oars in a figure-eight pattern. Another solution was supplied by Michael Dickinson at the University of California, Berkeley. By immersing a giant set of Plexiglas fruit fly wings in two tons of mineral oil (which would model the relative thickness of the air that the fly swims in), Dickinson’s lab discovered not one but two additional sources of lift exploited by the fruit fly. First, at the end of a wing stroke, the wing quickly rotates, and this flip mimics the backspin on a baseball—lowering the pressure on the top of the wing and generating a small amount of lift. Second, as the wing starts its backward stroke, it encounters the remains of the vortex shed from the previous stroke, which acts like a little headwind, generating even more lift with the faster airflow.

  There are so many different kinds of insects (7,000 new species are found every year), with so many different types of wings, it may take some time before all their aerodynamic tricks are known. In the meantime this new understanding of microaerodynamics has led researchers to begin developing flying microrobots that might someday be used as ultraminiature spy planes.

  Why do jet aircraft fly higher than the highest mountains? First, flying above the troposphere (the lowest layer of the atmosphere, where almost all bad weather can be found) offers a much smoother ride. Second, the higher the aircraft flies, the less dense the air, meaning less drag. On the other hand, thin air has less oxygen to feed jet engines, and fewer air molecules to maintain the airplane’s lift. Plus, The less dense the air the slower the speed of sound, so flying too high forces pilots to fly slower. Each aircraft model has an optimum cruise level based on its design and the amount of fuel it carries. On long international flights, as heavy fuel slowly burns off, pilots will ascend to a higher cruise altitude every two or three hours.

  In America there are two classes of travel: first class, and with children.

  —Humorist Robert Benchley

  If the Wright brothers were alive today Wilbur would have to fire Orville to reduce costs.

  —Herb Kelleher, founder,

  Southwest Airlines, 1994

  The world’s largest paper airplane had a wingspan of forty-five feet, ten inches. Built by students and faculty at Holland’s Delft University of Technology in 1995, it flew (indoors) for 114 feet, six feet less than the Wright brothers’ first powered flight.

  The Skyways

  Between departure and arrival, airplanes must contend with two important factors: the weather and air traffic control. Fortunately, while both the force of nature and the force of human regulation are somewhat mysterious to the passenger, they’re relatively predictable to pilots. Using radar, computers, years of experience, and high-tech navigation and communications equipment, pilots and air traffic control guide airplanes through the clouds along invisible highways in the sky. The following chapters explore the weather, air traffic control, and one of the most important topics to all passengers: turbulence.

  Weather

  Weather affects almost every aspect of flying, but sometimes the effects aren’t what you’d expect. For example, many people would say they prefer flying on warm, sunny days rather than cold, drizzly ones. But in reality, cool weather and light rain can provide less turbulent conditions than clear, hot, sunny days, when air can be more active or unstable.

  And what about those big cotton-ball clouds that rise thousands of feet into the air like giant mushrooms? As harmless as they might seem from the outside, the turbulence inside these clouds (called cumulonimbus) can be so extreme that it can shake a plane like a bean in a child’s rattle. This turbulence is caused by quickly rising warm air, which cools, falls, warms, and then rises again in a cycle. Moisture in the air condenses into rain, which freezes at high altitudes and then falls, only to be caught up in another column of rising air. Soon the ice crystals inside cumulonimbus clouds can grow into hail as big as golf balls and can dent the wings or even crack windows of an airplane.

  The troposphere is the part of our atmosphere from the ground up to about six or seven miles (about 9.6 km)—it fluctuates depending on atmospheric conditions. At the top of the troposphere (where airplanes usually cruise), the temperature is usually around –58 degrees Fahrenheit (-50°C). Above the troposphere is the stratosphere, where the temperature actually rises again—to about 26 degrees Fahrenheit (about –3°C)—because the air at that altitude absorbs more ultraviolet radiation. What we experience as “weather” always occurs in the troposphere (though some large thunderheads sometimes break up into the stratosphere). In the stratosphere, the Sun is always shining.

  Cumulonimbus clouds can develop into thunderstorms, and pilots tend to avoid anything having to do with thunderstorms. In fact, commercial pilots might fly their planes through heavy rain and wind, but pilots will go to any lengths to avoid the core of a thunderstorm (the red areas on a weather radar). Don’t get the wrong idea; it’s unlikely that thunderstorms—or even hurricanes—would cause an airplane to crash, but they cause very expensive damage and incredible stress (to both the airplane and the passengers).

  Storms also introduce three other important weather conditions: lightning, wind shear, and ice.

  Lightning

  Although you might think lightning would be one of the most destructive forces in the sky, the truth is that it has relatively little effect on airplanes. True, one airplane crashed because of lightning in the 1950s. However, since then all airplanes have been fitted with static wicks that dissipate electrical charges, and today lightning strikes an airplane somewhere almost every day without incident. The static wicks, fitted along the trailing edge of the wings and tail, draw off electrical charges that collect on the metal frame. So lightning might hit the airplane in the front and quickly dissipate out the back.

  One of the strangest forms of lightning is ball lightning, which can form inside an airplane and appear to be rolling down the aisle while glowing and sparkling. Ball lightning is so rare that scientists haven’t been able to study it to explain why it happens. Although it’s startling, it has never harmed anyone.

  As a passenger, you don’t have to worry because you cannot touch the metal exterior—you’re completely insulated from the electricity. Lightning could make a direct strike on the fuselage, and the passengers would notice nothing more than a loud bang.

  There are, on average, 45,000 thunderstorms on Earth each day, and lightning strikes 100 times each second.

  Nevertheless, the airplane doesn’t escape completely unscathed. A bolt of lightning momentarily heats the air around i
t to about 50,000°F (about 7,600°C)—hotter than the surface of the Sun—often burning a small hole in the metal skin of the plane, which simply gets patched at the next mechanical inspection. Lightning might destroy an antenna, but that’s one reason why airplanes have more than one.

  Wind Shear

  Sometimes it’s what’s invisible that counts: Wind shear occurs when an airplane travels through air that is blowing in two different directions or speeds within a small area. Wind shear happens frequently at all altitudes—it’s actually one of the main causes of turbulence, and it’s very rarely dangerous. However, when wind shear is severe and occurs at low altitudes, it can be hazardous to airplanes taking off and landing.

  Here’s why: Let’s say a plane is landing at an airport when suddenly it encounters a strong headwind. The airplane gets more lift from the air traveling faster over the wing, so the pilot needs to slow the plane down and bring it to a lower altitude to maintain its path. Then, if the airplane suddenly comes upon a mass of air that is moving in the opposite direction, the headwind becomes a tailwind, the air flowing over the wings slows dramatically, and the aircraft quickly loses altitude. If this happens at several thousand feet, the pilot can quickly regain control, but if it’s within a few hundred feet of landing, the aircraft could fly into the ground.

  This sort of severe low-altitude wind shear happens during microbursts of air that sometime develop under thunderstorms. A microburst is like water pouring out of a faucet into a bathtub filled with water; the air blasts down, hits the ground, spreads out, and bounces back up again. The whole microburst might be only a mile wide and last fifteen or twenty minutes (probably only five minutes of which it’s particularly strong). Some low-altitude microbursts are even strong enough to damage trees and buildings on the ground.