The Origins of Flight, From Birds to Bugs to Planes

Prepare for takeoff.

By Jonathon Keats|Wednesday, June 12, 2019

When the Wright Brothers took to the skies in 1903, they were relative latecomers — insects already had been buzzing around for 325 million years. But in a little over a century, our species has more than made up for its Earth-bound origins, visiting every planet in the solar system and even penetrating interstellar space.

Paleontologists have found 12 full-body fossils of Archaeopteryx. The one above is known as the Berlin specimen.

Flight of the Archaeopteryx

Two years after Charles Darwin published On the Origin of Species, the discovery of a missing link between dinosaurs and birds gave evolutionary theory a fortuitous credibility boost.

Found in southern Germany, the 150 million-year-old Archaeopteryx fossil combined reptilian and avian features. For the past century and a half, scientists have debated whether it could fly.

It took powerful X-rays to help researchers begin to put together this puzzle. A team of physicists and paleontologists at the European Synchotron Radiation Facility in France produced a 3D model of the creature’s bone structure using a technique called microtomography. The team found adaptations strongly suggestive of powered flight, but the anatomy indicated wing motion must have been weird, more similar to the butterfly stroke of a swimmer than the movement of any modern bird. This rendering shows the most likely flight pattern.

Feathers: Like modern bird plumage, the feathers of Archaeopteryx are asymmetrical, a geometry that can generate aerodynamic lift by pushing air under the wing.

Breast: Archaeopteryx lacked the modern bird’s prominent breastbone, which anchors flight muscles and guides the tendons that facilitate a rapid upstroke. Arm muscles appear to be more broadly distributed in Archaeopteryx, even running along the belly, probably making flying more arduous than it is for modern birds.

Shoulder: The shoulder joint of Archaeopteryx is transitional between those of ancestral dinosaurs and birds. The earlier dinos’ shoulders pointed downward, letting them manipulate prey with their arms. Bird shoulders point up, allowing them to raise their wings above their backs. The sideways orientation of the Archaeopteryx shoulder allowed flapping, but limited the upstroke.

Wing: The arm bones of Archaeopteryx are hollow, likely an essential adaptation for flight because it lightens body weight. In addition, many blood vessels are visible, suggesting vigorous movement — like flapping. Based on arm bone geometry, the flight of Archaeopteryx likely resembled the fluttering of pheasants more than the soaring of hawks.

Tail: Unlike modern birds, Archaeopteryx had vertebrae running through its tail, and asymmetrical tail feathers. The purpose of both remains mysterious.

Wings go way, way back in the fossil record. Insects were flying tens of millions of years before any vertebrates took to the sky.

Insects and the Origin of Flight

Found in practically every niche on all seven continents, insects are the most successful class of animals on the planet. But it wasn’t always like that. Roll back the clock 385 million years, and you’ll find the first bug in the fossil record. The next insects appear a full 60 million years later — in sudden and extreme abundance. Last year, Stanford University researchers provided an explanation for the population explosion: the evolution of flight.

The insects in this second wave were armed with wings, unprecedented appendages that allowed them to escape predators and reach new sources of food high up in trees. It was one of the greatest of all evolutionary breakthroughs — and vertebrates wouldn’t catch on for another 90 million years.

(Click to enlarge.)

Hummingbirds Versus Frigatebirds: Two Extremes of Bird Flight

The frigatebird can fly across oceans. The hummingbird can hover and pivot in any direction. Although both have wings and feathers, and share a recent ancestor, their approach to flight couldn’t be more different. The divergence reveals how flawlessly each is adapted to its niche.

  • The Hummingbird: Hummingbirds can be as small as insects — and size isn’t the only similarity. Whereas ordinary birds pull themselves aloft with just the downstroke of their wings, insects and hummers generate lift in both directions. This ability is the result of their unusual avian anatomy, with enlarged upstroke muscles and the ability to invert their wings, powering a breathtaking 80-stroke-per-second beat.
  • The Frigatebird: With a wingspan over 6 feet and weighing less than 4 pounds, the frigatebird is built for gliding. It can catch an updraft under a cumulus cloud, spiraling to a higher altitude than some planes, and ride the winds without flapping for over 30 miles. Researchers have observed frigatebirds spending months in the air without landing. The endurance fliers even sleep while aloft, in 10-second bursts that add up to a nice, restful 40 minutes a day.

The Weird Vortices of Dandelion Seeds

Dandelion seeds should not be able to stay aloft for miles — but they do. The umbrella-like structures that carry seeds on air currents are made of wispy bristles, and they’re leaky. Only recently have scientists figured out that the leakiness is the secret to dandelions’ success at long-distance unpowered flight. As air passes through the pappus — the technical name for that bristly structure — it generates a vortex like a miniature hurricane, and the updraft provides a little lift. Combined with other aspects of airflow, this so-called separated vortex ring makes the pappus four times more flightworthy than a parachute, ensuring that dandelions continue to sprout everywhere there’s a lawn.

The Wright brothers harnessed physical principles that have applied to every airplane since, balancing two sets of opposing forces, as shown here. (Click to enlarge.)

Major Moments for Flying Humans

  • 1486: Leonardo da Vinci designs an “ornithopter,” based on his observations of birds and bats, to give humans the power to fly by flapping large artificial wings. If Leonardo had built one and tried it, he’d have never left the ground.
  • 1783: The Montgolfier brothers demonstrate the first sustained human flight by launching two people in a hot air balloon. To ensure that the upper atmosphere could support life, the inventors first launch a sheep, a duck and a rooster.
  • 1809: George Cayley publishes On Aerial Navigation, the first serious work on aeronautical engineering. Based on his experiments with gliders, Cayley develops the physics that will eventually lead to airplanes.
  • 1903: The Wright Brothers invent the airplane, achieving the first manned flight in a powered, heavier-than-air flying machine. The Wright Flyer, a small biplane with two engine-driven propellers, stays aloft for a historic 12 seconds. The brothers harness physical principles that have applied to every airplane since, balancing two sets of opposing forces.
  • 1930: Frank Whittle patents the first jet engine. This powers an airplane by igniting compressed gas to generate forward thrust. The Royal Air Force rejects his idea at first, but comes around after Germany deploys its own jet airplanes in World War II.
  • 1936: Ewald Rohlfs demonstrates the Focke-Achgelis Fa 61, an early fully functional helicopter. Its two rotors spin in opposite directions, allowing it to take off and land vertically, fly forward and backward, and hover.
  • 1957: The Soviet Union launches Sputnik 1, the first artificial satellite. Lobbed into lower orbit on a modified intercontinental ballistic missile, Sputnik demonstrates Soviet technical prowess at the height of the Cold War.
  • 1969: Neil Armstrong and Buzz Aldrin are the first humans to land on the moon. After reaching lunar orbit in a computer-controlled rocket, they descend in a craft that Armstrong steers by hand.
  • 1976: Viking 1 and 2 land on Mars. In order to prevent potential contamination, the two landers are heat sterilized for 40 hours before launch, ensuring that the first successful landing on Mars won’t contaminate the Red Planet with Earthly microbes.
  • 2000: Astronaut Bill Shepherd and cosmonauts Yuri Gidzenko and Sergei Krikalev become the first inhabitants of the orbiting International Space Station. Today, after additions, it’s the largest facility built off Earth.
  • 2012: Voyager 1 is the first man-made object to reach interstellar space. Launched in 1977 and guided by computers much simpler than a smartphone, the NASA spacecraft is now more than 13 billion miles from Cape Canaveral.

Envisioning a Practical Personal Flying Vehicle

It sounds simple, yet it’s anything but: Design a personal flying vehicle. Make it quiet and safe, capable of near-vertical takeoff and landing, and efficient enough to transport the pilot 20 miles without recharging. And don’t forget the thrill. With these requirements, Boeing, the major aeronautics corporation widely known for making airplanes, has set out to launch the age of personal flight. The first round of its GoFly competition attracted more than 600 participants from some 30 countries. Here are the visions of three of the Phase 1 winners, who will build their machines and compete in a fly-off this fall.

(Click to enlarge.)

A Helicopter on Mars

The air on Mars has just one hundredth the thickness of Earth’s atmosphere. Even at ground level, it’s a fraction of the density you’d encounter at the top of Mount Everest. So when NASA decided to pack a drone on the upcoming Mars 2020 mission, the Jet Propulsion Laboratory had to design a copter unlike any ever flown on Earth. The two rotors, which spin in opposite directions for stability, turn at 2,800 rpm, up to 10 times the speed of an ordinary helicopter. They’re also much larger and more rigid than usual, each spanning 4 feet, totally overshadowing the 5-inch cube beneath, which is also special. This fuselage is packed with rechargeable lithium-ion batteries that not only turn the two mighty rotors, but also provide heat to protect the copter’s electronics when nighttime temperatures dip to minus 130 degrees Fahrenheit. Yet the most challenging part of flying a drone on Mars has nothing to do with the temperature or atmosphere — it’s the distance to Earth. With a minimum of four minutes to relay a radio signal between the two planets, the copter has to be basically autonomous — able to fly flawlessly, by itself, over terrain no human has ever encountered.

A “rotorcraft” like the one in this rendering is scheduled to launch next July with NASA's Mars 2020 mission.

The Electrically Powered Flight of Ballooning Spiders

Last year at the University of Bristol, scientists levitated spiders with electricity. The experiment was designed to solve one of the great mysteries of the natural world: how certain spider species are able to ascend miles in the sky and travel hundreds of miles over land and sea without the aid of wings. These “ballooning” spiders extrude long strands of silk before ascending. Nobody could work out how these filaments caught sufficient wind to lift the insects and carry them away.

So scientists developed an alternative hypothesis: that spiders ascended on the electrical gradient between earth and sky. (Earth is negatively charged, and the atmosphere is positive. In stormy conditions, the difference can become large enough to produce lightning bolts, but some kind of charge is always present.) The Bristol experiment successfully demonstrated that the negative charge of spider silk is sufficient to repel arachnids off the negatively charged ground beneath their feet — and showed that spiders actually start extruding silk when they feel the electrical gradient increasing.

Flying On An Ionic Wind

Back in 1928, the British Crown granted Thomas Townsend Brown a patent on an antigravity device that promised to revolutionize flight. His invention was based on the observation that a pair of highly charged wires can exert a physical force on their surroundings. Last year, it was finally put to use in a totally new kind of flying machine. Developed by engineers at MIT, the drone has no moving parts and is powered by batteries.

The force Brown observed is now known as an ionic wind. To generate it, a positively charged electrode strips the electrons from the air’s nitrogen atoms, leaving behind positively charged ions that are attracted to a negatively charged electrode a short distance behind. As the ions travel, they collide with air molecules, and these collisions collectively amount to a force propelling the electrodes forward.

To adapt ionic wind to flight, the MIT researchers mounted pairs of electrodes under the wings of a drone, where propellers normally go. Charging the wires to a shocking 40,000 volts, they generated enough thrust to fly their experimental plane across an MIT gymnasium.

Reaching meaningful distances with a significant payload will require more engineering, but the flight has already earned the drone comparisons to the Wright Flyer. Nearly silent and needing no gasoline, the ion drive airplane has the potential to offset some of the biggest environmental impacts of air transportation, revolutionizing flight in ways Brown could scarcely have imagined.

What Makes Bat Flight Special?

In order to roost after a night on the prowl, bats pull off a stunt that no bird or insect has mastered: They flip upside down in mid-flight and grab a branch with their feet. Credit their uniquely flexible wing structure. Whereas bird and insect wings are quite stiff, similar to airplanes, bats have webbed hands with multiple joints, and the webbing is muscular. High-speed videography has revealed that they can control wing shape and rigidity on the fly, allowing them to reach the highest air speed of any vertebrate, and hover at a standstill. Humans are trying to catch up, building planes with soft wings that mimic bat morphology. Engineers hope to better understand bat flight, to maneuver drones more freely and, just maybe, to impress the birds and bees.