Since hindsight is always 20/20, and now we thankfully have 2020 in hindsight, it’s time to celebrate. In particular, to celebrate a commercially irrelevant but wondrous technology that might allow humans to fly through the air under our own power, like birds. This is the stuff of dreams.
One of the few virtues of the “Wonder Woman 1984” film I saw recently is that it shows a woman flying up in the air like a bird or a plane, just like 50 years ago we saw Superman fly through the air. Last month, I saw dozens of real human beings fly many stories into the air, lifted aloft from their surfboards by airfoil-kites powered by wind. Amazing to see and, I imagine, amazing to experience. But the age-old dream of human flight is simpler: Can people fly in calm air, using their own power?
Like a Bird
The fact that birds fly shows that we might be able to, too. We’re just heavier, so it’s harder, which is in fact a very general rule. Insects can fly with wings even tinier than their tiny bodies, but big birds like albatrosses and condors need wings way bigger than their bodies. Fortunately, that relation is such a simple, universal concept — weight per unit area — that with a little physics, we can calculate how much harder it might be for people to fly than condors. Then maybe, with some clever materials and design, we might bridge the gap. We might redo the Icarus story, using carbon fiber instead of wax and feathers.
Let’s say a condor weighs roughly 15 kilograms and a human 60, making a nice round ratio of 1:4 in weight. The heavier-is-harder principle, called wing-loading, is based on body area. It says it will be twice as hard (square root of four) for us to fly, all else remaining equal.
So before getting to new stuff, let’s see what might actually remain equal. Condors and humans are both warm-blooded vertebrates, so it’s a good guess human muscles can generate as much average power-per-weight as condor muscles. And given the aerodynamic elegance that nature has evolved into soaring birds’ wings and feathers, it’s unlikely we humans could do much better than them for either lift or propulsion. So the shape of the next Icarus will have an aerodynamic efficiency at best as good as that of birds. What might be improved by a factor of two?
Birds are made of meat, bones and feathers. Not Kevlar (stronger than tendon), carbon fiber (stiffer than bone) or plastic like Mylar (smoother and lighter than feathers). And they can’t inflate themselves like a balloon to the size of an airplane. So let’s imagine using our fanciest modern materials to build an ultralight mechanical “bird.” The size of an airplane, smooth and tightly-inflated, containing an ultra-light lattice woven entirely and seamlessly from carbon fiber. This wing’s stiffness would mostly come from inflating the plastic.
That would leave the carbon-fiber lattice to accomplish four other goals: deforming in response to wind, to keep the wing from crinkling when bent; stiffening thin parts of the wing which pressurization can’t stiffen; “flapping” and “banking” the wings using human power; and carrying micro-vibrations from wing surfaces into the fingers and toes of the pilot, who would then “feel” the wings’ airflow much like birds do, using nerves in skin and bone.
Designing and building such an intricate, delicate airfoil would be expensive and unprofitable. Clearly, it would only hold its shape on calm days. But it could be built — and it would work. And when that mystical structure exists and is hooked up just right to a strong person pulling and pushing, it will fly like a bird, not a plane. That person will swim through the air.
We know something like that can work because a simpler, clunkier version was done decades ago, on a shoestring no less. In 1979, professional cyclist Bryan Allen piloted the flimsiest and best-designed airplane ever, the Gossamer Albatross, across the English Channel, to win the famous Kremer Prize, barely, on the first try.
He sat inside on a bike-frame, his legs pedaling the propeller. The whole plane weighed half as much as the pilot. It had been designed by aerodynamics genius Dr. Paul MacCready and a dozen crack engineers, one of whom (Stanford professor and venture capitalist Dr. Morton Grosser) wrote the book, “Gossamer Odyssey,” about the project. That plane was constructed like a regular plane, by stretching skin tight over flimsy compressible struts. A tiny breeze could snap it in half.
That single historic episode from four decades ago gives us a crucial data-point. It gives an example of a structure which, just barely, humans can fly for a while on their own. Presumably, every improvement on that structure would translate to less pilot effort. Twice the efficiency would mean half the pilot power, which would mean athletes of normal strength might fly it. Below, I propose four technical innovations that together could provide that improvement in efficiency, so humans might fly.
First, skip the propeller. Propellers spin, which is convenient for motors and drive-shafts. But spinning wastes energy because it moves a little air fast, rather than a lot of air slowly, much like flapping does.
Then, match the drive-train to the human. The drive-train on a bicycle, from foot through shoe through pedal through chain to wheel, is a wonderful way to power spinning wheels. But it isn’t designed to extract the most consistent, stable power from a human body, spread equally over all the muscles. Rowing machines do that better by using the back and arms, but even they still don’t take advantage of the original vertebrate power stroke — spinal twisting. Worse, when rowing, the rower has to clench the fists full-time to grab the oars. An optimum full-body power stroke would open and close the hands in concert with spinal extension and breath.
Let the human feel the airflow. Birds can take advantage of updrafts because they can feel the wind whispering on their feathers. If there were a sensitive vibrational conduit from wing skin to human skin (or fingernail), like thin carbon fibers, our nervous systems could learn to fly by feel.
Finally, gain tension from pressure, not compression. The Gossamer Condor, MacCready’s first attempt at man-powered aircraft that won him his first Kramer Prize in 1977, was built like an old-fashioned plane, with a thin film (plastic) stretched over spars and ribs, which could snap. The more of the film’s tension can be supported by pressurized gas rather than compressed shafts, the lighter and less breakable the structure will be.
I’m a physicist, not a fundraiser. I can’t make the project happen, but I know many innovators could. And I do know I might, just barely, be able to fly in my lifetime if I keep strong and healthy. But someone else will have to take the lead. Any takers?
The views expressed in this article are the author’s own and do not necessarily reflect Fair Observer’s editorial policy.