LEONARDO’S ROMANCE WITH FLIGHT

Leonardo’s Great Curiosity

Leonardo da Vinci was probably the most curious person in history. Th ere are very few, if any, people who could have filled so many pages with the variety of drawings and notes that Leonardo did. His curiosity kept him very busy. He was a painter, a sculptor, an architect, a military engineer, a designer of weapons and robots, a builder of stage sets and machinery for theatrical spectacles, and a scientist who studied physics, anatomy, and, of course, flight. He is our prime example of l’uomo universale, the universal or renaissance man.

His paintings have been on exhibit and fascinating viewers and scholars for more than 500 years. Some of his work, like the anatomy drawings, changed the way we look at the world. But much, if not most, of his brilliance remained hidden in the pages of his many notebooks until the nineteenth century, while the world struggled through the scientific revolution, unaware that Leonardo had already been there.

Most of the ideas and sketches and studies in his notebooks grew out of work he was doing, or projects he was trying to sell to his patrons. But flight was different. It was something that he did just for himself, and even when it became clear he would never be able to fly himself, he never completely gave up dreaming and drawing.

Leonardo da Vinci’s portrait, drawn by himself.

The one and only drawing of Leonardo’s helicopter.

Part of a design for a mechanical wing.

Looking at Flying Animals

Birds, bugs, and bats: lots of things in our world fly. We see them every day, and envy their freedom. We long to join them in the air, and so did Leonardo. They make flying look so easy. But try as we might, we can’t do it.

Just how do they fly? How can we know?

If this were fifteenth century Italy, Leonardo’s world, we’d be without textbooks and labs and internet, and we could only watch and guess.

That’s what Leonardo did. He watched, intently and endlessly.

But he probably saw these flying animals very differently than we do. Most of us only see blurred wings. His drawings show birds and bugs stopped in mid-flap, each in a different position. Some scholars suggest that he was able to envision a “frame” of their movement in his mind, as if he was seeing not the smooth motion of a movie, as most of us do, but a series of frozen poses. The animated movie director Hayao Miyazaki can do this, which is why his movies look so realistic. In Leonardo’s case, that ability seems to have let him see the wings of birds and insects frozen at each stage of their motion, and understand how they reacted with the air.

The notebooks contain many drawings of flying animals. There are dragonflies, bats, butterflies, a flying fish, and of course the birds. He drew page after page of birds—so many that one whole notebook, the Codex on the Flight of Birds, is devoted to them.

Studies of birds in flight.

Everyone knows that humans can’t fly, but that doesn’t mean flight is impossible. So wrote Leonardo. Look! Th e birds can do it, so it can be done. And if we imitate the birds, and learn their secrets, maybe we will find our own way to fly.

Birds, bugs, and bats all fly with wings. Leonardo thought that if we made wings for ourselves, and if they were the right shape and moved the right way, we would be able to fly too.

So, he spent many hours observing birds and insects fly, and sketched all the various stages of their wing movement. Many of the drawings show what looks like wind; in fact he was showing how the air moved over and around the wing, and how it held the birds up. He saw the animals almost as machines, with bones and muscles and joints that could be reproduced in wood and string and fabric.

And the longer he watched, the more he understood. He began to see how machines could be made to fly.

What Leonardo Discovered

The Wright Brothers are often celebrated as the inventors of flight, but what they actually invented was a way to control the airplane in flight. All of the other knowledge they made use of had been gleaned from others. Engines and propellers already existed. Otto Lilienthal had shown how lift (an upward force acting on an object when the air pressure above the object is lower than that below) was created, Alphonse Pénaud had shown how to create a stable airframe, and George Cayley had proved that airplanes could glide. Th ere were also lots of failures, which taught the Wright Brothers what not to do. Th e brothers just added their own insight to the mountain of knowledge already available.

Leonardo could not do that, because there was almost no one ahead of him. He had to start entirely from scratch.

There were earlier inventors who tried to build wings and fly. Most were “tower-jumpers,” people who strapped on simple wings and leapt from windows and bridges. Others used devices like parachutes, and at least one, Eilmer of Malmesbury, is said to have built a glider. Few, if any, of these attempts succeeded. It was obvious to most people that this was a quick way to die, not to fly. Leonardo would have known that lots of ground testing was needed before making a jump.

What else did he know?

He knew that there is air. And he knew that air can hold things up. He knew that paper, leaves, and handkerchiefs can be wafted up by a breeze, and that they fall very slowly when dropped. To fly, he would need to use this power of air.

He knew that birds and bats and insects fly because they have wings. He knew that there is nothing magical about them. Just as people can only walk if they have legs that are strong and healthy, birds can only fly if they have wings of the right shape and strength.

He knew, from watching hawks, bats, dragonflies, and flying fish, that flapping is not necessary for flight, because all of these animals can rest their wings and glide. He also knew that gliding animals eventually coast down to the ground, unless strong winds waft them up again.

None of this is surprising. Anybody could have seen these things. What is really amazing is what came next.

After years of watching birds, Leonardo learned that it was air flowing around them that holds them up. He had originally thought that flying animals stayed up by pushing down on the air under their wings, the way a person might lift themselves up by pushing down on the arms of a chair. But his wing-testing rig taught him that this was not suffi cient for flight, and could not explain gliding. Among his drawings are several that show the center of gravity of birds, and refer to the way balance affects flight. He knew that bird wings have curved surfaces, and that this was important. Several drawings look like explanations of how lift is made. In fact, some scholars think he discovered what we now know as Bernoulli’s Principle while watching water speed up while flowing through a restriction. From there it was a short step to seeing the same lifting forces that flowing water creates in the currents of air around a wing.

Da Vinci’s visionary ideas sparked innovation and experimentation in the centuries that followed.

Bit by bit, through observation and experiment, Leonardo began to understand the secrets of flight.

Learning by Observation

Leonardo lived at a time when the scientific method was still in its infancy. Scholars no longer accepted received wisdom just because it had been passed down from the ancients. Th ey used more observation to learn things for themselves. But rigorous experiments with hypotheses and controlled variables and statistical analysis of data were still mostly a thing of the future.

Leonardo did a lot of observation. As he watched, he would make guesses about why the things he was seeing happened the way they did. Th e more he watched, the more refined his theory would become, and as he noticed more, he could better judge what must and must not be true.

For example, he knew that birds did not just push air down with their wings, but he also noticed that they twisted them when they wanted to turn. One wing twisted up, and the other down, and the bird turned towards the side of the upturned wing. Why? It must be that the wind is holding that wing down, while the down-twisted wing swings up and forward, he thought, and so it is. Leonardo noticed that birds have small feathers at the front of the wings that look like thumbs, which move as the bird flits about. He guessed that these were to control the flow of air over the wing, and so they are.

Studies showing fluid dynamics and the way air acts like water.

He seems also to have looked for connections or similarities between things. He noticed, for example, that water and air are very similar when they move, or when things move through them. He was the first person to realize that air is a fluid like water. A boat needs a rudder to stay straight when moving; without one, the boat will turn sideways to the wind or the current. So, he realized, a flying machine must need a rudder too. A board with water moving over only one side of it will be pulled toward the current, so birds’ wings are likewise pulled up by strong currents over the tops of their wings. He was very, very close to understanding how the airflow creates a difference in pressure that holds the wing up.

Leonardo also noticed that a man standing in a boat needed to shift his weight to keep the boat balanced, and deduced that by shifting his weight, and therefore the center of gravity, he could control the boat. Could this be done in flight? He watched the birds carefully, and sure enough, they do shift their weight.

These observations let him create an image in his head of what was happening. He often sketched these out. Some of the sketches just show what he actually saw, but the drawings of birds, in particular, are more schematic, showing forces and currents not visible to the eye.

And, of course, he tested these ideas by making models.

Did Leonardo Make Models?

Leonardo was a painter and sculptor, so models were an important part of his work. The models were made to see how light and shadow appeared on a three-dimensional surface, for example, or to ensure that parts of a mold could be taken apart after making a bronze casting. Models allowed him to check ideas and techniques before starting work on the final piece.

Leonardo was also a set designer who made machinery for large theatrical spectacles, including lion and knight automatons which moved on their own like wind-up toys. It is unlikely that he would have been able, let alone allowed, to jump right into building these huge machines without making models first to prove that they would work.

Ropes and pulleys were needed to move mechanical wings.

The wing-testing rig is just such a model. It may be very large as he drew it, but it was still intended only to test whether a wing could produce enough lift to pick a man up off the ground, before he committed himself to designing a whole flying machine.

Much later in his life, he was said to have made many tiny toy birds that flew along strings or rose up on jets of air like balloons do when released.

But it seems clear that he must have made some flying models. Th ere are hints in his notes that he built a small version of the helicopter, powered by a spring, which rose up into the air at least briefly as it spun.

Did he build others? No one can say. The notes he left are not clear about this, and no actual models have been found. But it would have been a simple and natural thing for him to cut bits of scrap paper into the shapes of birds and bats and fly them about his workshop.

If he did, he would have learned the importance of balance. Th e sketches and drawings in his notebooks explore the shapes and structures of wings, but it is hard to imagine that the kite glider, for example, could have occurred to him without some playing with paper and scissors. Neither the glider, nor the other kite-like flying machine drawn on the same page, look quite like anything in nature.

So it seems likely that Leonardo made small models of his flying machines, and learned some of the secrets of flight from them, by actual trial and error.

Testing the Limits of Human Strength

In Leonardo’s day, there were really only four sources of power people could use to do work:

• Animals

• Wind

• Water

• Human strength

Ornithopter wing and harness sketches.

The complete prone ornithopter, shown without fabric on the wings.

There were no others. Leonardo used bows and springs in some of his devices, but bows and springs just store power—they don’t create it.

So when he was designing his flying machines, these were the only options he had.

Birds and bats use animal power to fly, of course, and there had been early dreamers who thought flocks of tethered birds might pull them into the air, but it was clear to Leonardo that this was not realistic. Nor could horses or oxen be used, because of the weight. Wind could power sailboats, but it was not dependable enough to be practical for flight. Water was right out of the question. So that only left human power.

Flight requires a lot of power; much more than you would think. Birds make flying look easy, but think about how muscular they are. Imagine a roasted chicken, for example. Those thick slabs of breast meat? It’s all flight muscle. If humans had chest muscles like that, our pectorals would be more than a foot thick and our chests would bulge out like, well, a chicken’s.

Obviously, we don’t have those muscles. Our arms are barely strong enough to pull us up, let alone flap us into the air.

Leonardo thought our legs might be strong enough to propel a flying machine, and he began thinking about how that might be done. He thought about building an ornithopter, a machine that would fly by flapping its wings like a bird.

Leonardo’s first ornithopter design, with wings like a dragonfly’s.

Articulated flaps and rudders would have been used to control a vehicle in flight.

The first design looked like a large bowl with dragonfly wings at the top. The pilot stood inside a frame with pulleys and pedals to move the wings. In the drawing, the pilot is so small and surrounded he is hardly visible; that ornithopter was clearly much too heavy.

Next, he had the pilot lie prone on a board and move his legs as if climbing stairs. The wings were articulated to both flap and twist, the way birds’ wings do. The design looks quite ingenious and even workable. But there would not be enough power to get off the ground.

He needed to find a way to amplify the pilot’s strength. Ropes and pulleys could multiply the force sent to the wings, but the more pulleys he used, the slower the movement of the flapping. He thought then about double screws, but this had the same diffi culty as the pulleys. A lever could increase the power, but the pilot would need to anchor his feet. Th e flying boat design uses screws and levers.

In the end, Leonardo was forced to admit that human power alone would not be enough. Powered flight was just not possible with the technology of his day. Today, there are human-powered airplanes, ornithopters, and even helicopters, but they fly only because of ultralight modern materials, and at the very limits of human strength.

Did Leonardo Fly Himself?

There is a legend told in the village of Fiesole, in the mountains overlooking Florence, that a giant bird once arose from Monte Ceceri and flew into the distance, never to be seen again.

What was it?

Could it have been Leonardo, testing a flying machine?

On the 18th page of his Codex on the Flight of Birds, Leonardo wrote, “From the mountain that bears the name of the great bird, the famous bird will take its flight and fill the world with its great fame.”*

That mountain would likely be Monte Ceceri, whose name derives from the old Florentine word cecero, meaning “swan.” Monte Ceceri overlooks Florence, and is the highest peak nearby. The summit is open, drops away to an old quarry far below, and is just about perfect for paragliding. If Leonardo ever actually flew one of his machines, this is where he would have launched the “famous bird.”

But flying a lightweight paraglider off the precipice, and leaping with a heavy wood-and-canvas glider, are two very different things. Leonardo would have known he needed a lot of speed to get airborne. That would take a lot of strength, and would require considerable luck, too. He could have had a hapless assistant make the attempt, but it would have been far too dangerous to try himself.

The notebooks tell us he intended to make a flight from the mountain. But did he?

A modern imagining of Leonardo’s ornithopter in flight.

There is a note from towards the end of his burst of work on flying machines, found in the Codex Atlanticus, that laments the futility of many of his efforts. “O Leonardo, perche tanto penate?” he writes. Oh Leonardo, why do you torment yourself so? Leonardo was very tenacious, and kept studying the flight of birds for many more years. But these are not the words of a man who has succeeded in taking to the air.

What Leonardo Didn’t Know

Leonardo learned a lot from observation and trial-and-error. He knew that air is a fluid and that it flows over wings. He knew that birds and insects use a complicated figure-eight motion, and not just up-and-down flapping, to both lift them up and push them forward. He knew that birds, and therefore aircraft too, could glide without flapping. He knew that his machines had to be made much lighter in order to fly.

This kit’s version of Leonardo’s Wing-Testing Rig (page 50). Different wing designs would have been mounted onto the actual device to determine their capability to generate thrust.

But there was a lot he did not know.

He did not know how to get off the ground. His parachute and the gliders were launched by jumping from a high place, but the ornithopters had no landing gear and no way of rising into the air. Small birds use brute strength to leap into flight, but he would have seen larger birds like geese and swans running faster and faster until they had enough speed to get airborne. It seems to have never occurred to Leonardo to add wheels to his machines.

He did not know of any way but flapping to create thrust. Some of his drawings show devices that look like propellers, but they are always windmills; they are turned by the wind, rather than creating wind by turning. So it did not occur to him that he could power his machines by turning a propeller. Though, to be honest, human power would not have been suffi cient to pull his heavily-built aircraft.

But the scope of what he did not know was, surprisingly, quite small. He had most of the knowledge and ideas needed to fly. And with better materials to make very much lighter machines, he could well have succeeded.

Another thing Leonardo never knew: several of his designs have been built in recent years, and successfully flown.

After his death, Leonardo’s notebooks were hidden away by his executors to protect them, and as a result, they were virtually unknown until the nineteenth century. By that time, it was much too late for all of the knowledge and ideas in those thousands of pages to affect the development of technology. But several people have looked at his designs and thought they were practical enough to actually try them out.

In 2002, Robbie Whittall and the University of Liverpool built a hang glider based on Leonardo’s kite glider design, and Whittall’s successful flight was broadcast by the BBC. He had to add a vertical fin, though, to make it stable enough to fly.

In 2003, champion hang glider pilot Judy Leden flew a glider built by Steve Roberts, based on some of Leonardo’s sketches, for an English TV show. She succeeded, but only barely, and said later that first-time pilot Leonardo would have crashed right away.

And in 2000, skydiver Adrian Nicholas built a parachute to Leonardo’s specifications, using only tools and materials that he would have had, and jumped with it from a hot air balloon over South Africa. Not only did it work, but it worked well. Nicholas declared it the smoothest parachute he had ever used. “It took one of the greatest minds who ever lived to design it, but it took 500 years to find a man with a brain small enough to actually go and fly it,” he said.

If only Leonardo had known!

Leonardo’s drawing of the parachute.

Not Giving Up

“Oh Leonardo, why do you torment yourself so?”

By the time of this lament, around the turn of the century in 1500, most of his designing was behind him. He had drawn the helicopter, the parachute, the kite glider, and all of the ornithopters. He had spent a decade and a half trying to devise a machine that would let him rise into the air and fly with the birds, or leap off a mountaintop and soar over the heads of his friends and rivals. But he had not flown, and now he was getting older and it was clear to him that he never would.

But he did not, could not, stop.

“Why do you torment yourself so?”

He had come so far, and he knew so much. If he could not fly, it was not because he did not know how, but because he could not create the means. The technology and materials of the day were too crude and heavy to make lightweight machines with enough strength to be able to carry him aloft. (It has only become possible, barely, in the past few years.) He was frustrated, but he had come too far to completely give up.

And so he carried on with his studies, watching birds and working on the Codex on the Flight of Birds and thinking about flying for two more decades.

Leonardo wrote in one of his anatomical notebooks, “Th ough human ingenuity may make various inventions which, by the help of various machines answering the same end, it will never devise any inventions more beautiful, nor more simple, nor more to the purpose than Nature does; because in her inventions nothing is wanting, and nothing is superfluous, and she needs no counterpoise when she makes limbs proper for motion in the bodies of animals.”**

No flying machine he designed could ever match the perfectly adapted bodies of birds and bats. Nor were human limbs appropriate for flying. But this does not mean that humans cannot devise such machines at all.

Humans, then, would never achieve the beauty and effi ciency of flying animals, but with ingenuity enough, people could still make wings suffi cient for flying. Humans would have to add wood and canvas, rope and pulleys to the weak arms and legs nature had given us.

So, Leonardo did not despair. If he could not find the way to fly, some day some other person surely would.

See page 40 for a functioning parachute model!

The structure of the wings Leonardo envisioned had the long fingers and fabric membranes of bat wings, rather than the feathered wings of birds.

* Translated by E.W. Dickes in 1938.

** Translated by Jean Paul Richter in 1883 from W. An. IV 184a, part of the RL manuscript at Windsor.