Sky Monsters
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biology + medicine
Sky Monsters
All photos courtesy of Professor Gerritsen
by Nancy Falxa-Raymond
Building “Herkie” - A Model Pterosaur
T
wo years ago, Professor Margot Gerritsen, Assistant Professor of Petroleum Engineering and, by courtesy, of Mechanical Engineering, undertook the challenge of creating a functional replica of an ancient giant, flying lizard called the pterosaur for a documentary by National Geographic. The Stanford-National Geographic Pterosaur Replica Project was conducted primarily at Stanford, under Gerritsen’s lead in collaboration with pterosaur flight expert and engineer Jim Cunningham. The project team included scientists, graduate students, engineers, paleontologists and paleoartists. The group’s efforts culminated in “Sky Monsters,” an educational documentary featuring the team’s working pterosaur model. In the process, they gained fascinating insights into the flight mechanisms of one of the world’s first flying animals.
Flight of the Pterosaurs The pterosaur, which lived between 210 and 65 million years ago, was one of the earliest creatures to fly--second only to insects. For 70 million years, it had a distinct advantage over its competitors as the only flying animal in the world. The enormous lizards were effective predators, sometimes grabbing fish out of the water on the fly. Fossilized landing tracks reveal how well the
16 stanford scientific
pterosaur could control its flight. Some scientists believe that by flapping its wings to brake, the pterosaur was able to slow itself down before it landed, eliminating the need for a running landing like that of birds today. Paleontologists disagree on the exact mechanism by which the pterosaur achieved takeoff. Some argue that the lizard took a running start, whereas others contend the enormous animal stepped off the edge of a cliff or out of a tree. One caveat with the latter theory is that the edge of a cliff might not have always been available when the pterosaur needed to escape from a predator. This consideration is especially important given that the fossilized tracks show the pterosaur walked on four legs, and may have been an awkward animal on the ground, dependent on flight for survival. Additional fossil evidence reveals the pterosaur’s unique skeletal structure was adapted to flight. Its bones were extremely lightweight, with very thin walls and air-filled inner cavities. While its fourth finger was lengthened dramatically to support its entire wing, it lacked a fifth finger. The dinosaur also had massive flapping muscles to propel its body and its large, long head and neck. Along with the so-called megafinger and flight muscles, a layered wing membrane added to its vital flight adaptations.
biology
Gerritsen beams after Herkie lands successfully.
The wing was composed of layers of fibers, muscle, blood vessels, and an outer layer of UV-protected skin with a hair-like covering. Early pterosaurs had long tails, but in later species the tail was reduced, leaving the wings to bear the burden of flight.
Building “Herkie:” A Model Pterosaur “No one really knew how pterosaurs flew, and we still know little,” says Gerritsen. “What we tried to do was understand their flight mechanics better by building and playing.” She and her team built multiple models in attempts to build a realistic, flyable replica of the pterosaur species Anhanguera piscator, beginning with a simple remote-controlled glider and ending with an eleven pound, three-meter wingspan pterosaur dubbed “Hercules,” or “Herkie” for short, a nickname conceived by Gerritsen’s six yearold son. Herkie utilized the latest miniature technology, including a lightweight lithium battery, a telemetry - data acquisition - system, an onboard wireless camera, a microprocessor to automatically control the head’s position during flight, and 8 to 12 lightweight and powerful servos to control wing, tail and head motions.
+ based on a late and more sophisticated pterosaur, medicine the team encountered difficulty when emulating the pterosaur’s brain. Herkie was controlled by remote control instead of by a computer. Thus, its flight relied on a person’s reflexes and only slow adjustments to the position of the head, tail, and wings were possible. In order to fly, Herkie’s wings could move back and forth, rotate, and twist asymmetrically, but could not flap up and down (although flapping was attempted in a later model). The wrists were able to sweep and rotate, and the movement of the tail was also controlled by remote. In total, twelve different motors were used. Gerritsen and her team members, in particular sail designers Steve Collie and Peter Heppel, used their knowledge of sails to build pterosaur-like wings. Assisted by Ph.D. student Axel Strang, they reinforced layers of thin carbon fibers with Kevlar tape in order to replicate the pterosaur’s flexible and nearly unbreakable megafinger. They even replicated the physical properties of the megafinger that allowed it to be bendable in certain directions, but not in others. In addition to being functioning mechanical structures, the wings needed specific properties of elasticity and rigidity. The inner wing was quite stretchy while the outer wing was not. The wings were rigid in one direction and had some elasticity in the other direction. The first model featured wings of sailcloth, which were later strengthened with nylon fibers. By allowing for a transfer of forces along the wing, the nylon fibers Gerritsen and her team used fossil evidence to create a realistic pterosaur model that mimicked the bones, joints, and wing membrane of the real animal. The megafinger seen here is usually referred to as a lengthened fourth finger but is sometimes called a lengthened fifth finger.
Pterosaur fossils guided Margot Gerritsen and her team as they built their pterosaur model. The bones, the joints, and the wing membrane in the model are all in the same places that they were in the real animal. Gerritsen says the team followed a simple principle: “We won’t move things, and we won’t cheat.”
“Early pterosaurs could have been stuffed and flown like a well-designed paper airplane. Later ones became much more sophisticated fliers.” Unlike their predecessors, Gerritsen’s team claims to have built a model that was as “true to paleontology” as possible. The design was primarily based on the almost complete fossil skeleton of an A. piscator that lived in Brazil about 110 million years ago. “Most people start from an airplane design, something they know flies. We followed the known or deduced paleontological constraints on joint movements and position. This made it exceedingly hard for us because these pterosaurs are not very stable fliers. Early pterosaurs could have been stuffed and flown like a well-designed paper airplane. Later ones became much more sophisticated fliers,” Gerritsen says. As the pterosaur evolved it became a more efficient flier, using its brain to constantly adjust its wings. Because the project was
layout design:Jessie Tao
volume iv 17
biology + medicine
Herkie is ready for cartop testing.
Launching Herkie The RC plane carries Herkie to the sky.
were more lifelike. Another critical component of the pterosaur model was the head. During flight, it was necessary for the head to face into the wind at all times to reduce drag. After completion and “car-top” testing –carrying the model atop a car to determine the behavior of wings under the lifting force of flight-- the pterosaur model was carried underneath a remote-controlled airplane to a height of 700 feet where it was released in the air and expected to glide back down. Herkie crashed on its first filmed test-run, but was not completely destroyed due to an installed emergency parachute. After a night of repair work, Herkie was able to resume flight the following morning and flew successfully several times.
The Challenge of Getting Herkie off the Ground For the documentary, the National Geographic team requested a lifelike head and fur on Herkie’s wings. This made Herkie two to three pounds heavier. Gerritsen and her team were worried the extra weight would hinder the success of the model’s flight. “They just wanted it to look good, which made it very difficult for us. We’d rather not have dressed Herkie up. It was a real struggle,” Gerritsen recounts. The extra dressing is in fact why the model crashed on the first test-run. Getting paleontologists and engineers to see eye to eye was another challenge. Gerritsen and the engineers on her team saw the project as a preliminary exploration into pterosaur flight. They wanted to work quickly to prepare a working model for the documentary. The paleontologists, however, prioritized scientific debate over building a model. They disagreed about the pterosaur’s leg position during flight, wing stroke, and the location where the wings were attached on its body. Since current fossil evidence gave no precise answer to these questions, the team had to pick a design and begin working. “The debates went on too long at the beginning. At some point we had to just start building in order to finish the project in time for the movie,” Gerritsen says. With a three-meter wingspan, Herkie was 58% of the size of an average grown adult A. piscator. If the model was built to the true scale, it would have been too big to lift under a remote controlled airplane and tests flights would have been much more difficult. With Herkie’s dimensions, the team was able to run twenty test
18 stanford scientific
The RC plane leaves Herkie to glide on his own.
flights before filming the documentary.
The Flying Success of Herkie ”Sky Monsters” aired in late January this year, inspiring awe at the sight of an ancient flying bird across thousands of homes. Since its broadcast, Gerritsen has been working on a traveling exhibition for natural history museums. She envisions a “very hands on” exhibit that describes the evolution of flight, and features models from the project and a virtual animation that would allow a person to “fly” on a screen as a pterosaur. While much progress has been made, questions remain unanswered. Pterosaurs grew up to at least a 10-meter wingspan— how was an animal this large able to fly? When its body grew larger relative to the surface area of its wings, the pterosaur would have reached a limit to its body size. Paleontologists continue to debate what that limit is. The sophisticated wing membrane helped to alleviate the pterosaur’s problem, but not much more is known. “It’s like one big puzzle. But not a very well defined puzzle,” she acknowledges. One day, Gerritsen hopes engineers may be able to use information about unique pterosaur wing membranes in modern flight designs, although she admits we are far away from that. To continue unveiling the pterosaur’s flight mechanism, the next step does not involve sailcloth or nylon fibers, but computer simulations, she says. From physical flight to byte, the StanfordNational Geographic Pterosaur Replica Project’s findings are bringing paleontologists closer to discovering the mystery behind the pterosaur’s soar. S Nancy Falxa-Raymond is a junior majoring in History, with a minor in Biology. She enjoys paleobiology and the New York Metropolitans. To Learn More Stanford-National Geographic Pterosaur Replica Project. http://pterosaur.stanford.edu/] More about pterosaurs. http://www.projectexploration.org/news_121803.htm
Sky Monsters
All photos courtesy of Professor Gerritsen
by Nancy Falxa-Raymond
Building “Herkie” - A Model Pterosaur
T
wo years ago, Professor Margot Gerritsen, Assistant Professor of Petroleum Engineering and, by courtesy, of Mechanical Engineering, undertook the challenge of creating a functional replica of an ancient giant, flying lizard called the pterosaur for a documentary by National Geographic. The Stanford-National Geographic Pterosaur Replica Project was conducted primarily at Stanford, under Gerritsen’s lead in collaboration with pterosaur flight expert and engineer Jim Cunningham. The project team included scientists, graduate students, engineers, paleontologists and paleoartists. The group’s efforts culminated in “Sky Monsters,” an educational documentary featuring the team’s working pterosaur model. In the process, they gained fascinating insights into the flight mechanisms of one of the world’s first flying animals.
Flight of the Pterosaurs The pterosaur, which lived between 210 and 65 million years ago, was one of the earliest creatures to fly--second only to insects. For 70 million years, it had a distinct advantage over its competitors as the only flying animal in the world. The enormous lizards were effective predators, sometimes grabbing fish out of the water on the fly. Fossilized landing tracks reveal how well the
16 stanford scientific
pterosaur could control its flight. Some scientists believe that by flapping its wings to brake, the pterosaur was able to slow itself down before it landed, eliminating the need for a running landing like that of birds today. Paleontologists disagree on the exact mechanism by which the pterosaur achieved takeoff. Some argue that the lizard took a running start, whereas others contend the enormous animal stepped off the edge of a cliff or out of a tree. One caveat with the latter theory is that the edge of a cliff might not have always been available when the pterosaur needed to escape from a predator. This consideration is especially important given that the fossilized tracks show the pterosaur walked on four legs, and may have been an awkward animal on the ground, dependent on flight for survival. Additional fossil evidence reveals the pterosaur’s unique skeletal structure was adapted to flight. Its bones were extremely lightweight, with very thin walls and air-filled inner cavities. While its fourth finger was lengthened dramatically to support its entire wing, it lacked a fifth finger. The dinosaur also had massive flapping muscles to propel its body and its large, long head and neck. Along with the so-called megafinger and flight muscles, a layered wing membrane added to its vital flight adaptations.
biology
Gerritsen beams after Herkie lands successfully.
The wing was composed of layers of fibers, muscle, blood vessels, and an outer layer of UV-protected skin with a hair-like covering. Early pterosaurs had long tails, but in later species the tail was reduced, leaving the wings to bear the burden of flight.
Building “Herkie:” A Model Pterosaur “No one really knew how pterosaurs flew, and we still know little,” says Gerritsen. “What we tried to do was understand their flight mechanics better by building and playing.” She and her team built multiple models in attempts to build a realistic, flyable replica of the pterosaur species Anhanguera piscator, beginning with a simple remote-controlled glider and ending with an eleven pound, three-meter wingspan pterosaur dubbed “Hercules,” or “Herkie” for short, a nickname conceived by Gerritsen’s six yearold son. Herkie utilized the latest miniature technology, including a lightweight lithium battery, a telemetry - data acquisition - system, an onboard wireless camera, a microprocessor to automatically control the head’s position during flight, and 8 to 12 lightweight and powerful servos to control wing, tail and head motions.
+ based on a late and more sophisticated pterosaur, medicine the team encountered difficulty when emulating the pterosaur’s brain. Herkie was controlled by remote control instead of by a computer. Thus, its flight relied on a person’s reflexes and only slow adjustments to the position of the head, tail, and wings were possible. In order to fly, Herkie’s wings could move back and forth, rotate, and twist asymmetrically, but could not flap up and down (although flapping was attempted in a later model). The wrists were able to sweep and rotate, and the movement of the tail was also controlled by remote. In total, twelve different motors were used. Gerritsen and her team members, in particular sail designers Steve Collie and Peter Heppel, used their knowledge of sails to build pterosaur-like wings. Assisted by Ph.D. student Axel Strang, they reinforced layers of thin carbon fibers with Kevlar tape in order to replicate the pterosaur’s flexible and nearly unbreakable megafinger. They even replicated the physical properties of the megafinger that allowed it to be bendable in certain directions, but not in others. In addition to being functioning mechanical structures, the wings needed specific properties of elasticity and rigidity. The inner wing was quite stretchy while the outer wing was not. The wings were rigid in one direction and had some elasticity in the other direction. The first model featured wings of sailcloth, which were later strengthened with nylon fibers. By allowing for a transfer of forces along the wing, the nylon fibers Gerritsen and her team used fossil evidence to create a realistic pterosaur model that mimicked the bones, joints, and wing membrane of the real animal. The megafinger seen here is usually referred to as a lengthened fourth finger but is sometimes called a lengthened fifth finger.
Pterosaur fossils guided Margot Gerritsen and her team as they built their pterosaur model. The bones, the joints, and the wing membrane in the model are all in the same places that they were in the real animal. Gerritsen says the team followed a simple principle: “We won’t move things, and we won’t cheat.”
“Early pterosaurs could have been stuffed and flown like a well-designed paper airplane. Later ones became much more sophisticated fliers.” Unlike their predecessors, Gerritsen’s team claims to have built a model that was as “true to paleontology” as possible. The design was primarily based on the almost complete fossil skeleton of an A. piscator that lived in Brazil about 110 million years ago. “Most people start from an airplane design, something they know flies. We followed the known or deduced paleontological constraints on joint movements and position. This made it exceedingly hard for us because these pterosaurs are not very stable fliers. Early pterosaurs could have been stuffed and flown like a well-designed paper airplane. Later ones became much more sophisticated fliers,” Gerritsen says. As the pterosaur evolved it became a more efficient flier, using its brain to constantly adjust its wings. Because the project was
layout design:Jessie Tao
volume iv 17
biology + medicine
Herkie is ready for cartop testing.
Launching Herkie The RC plane carries Herkie to the sky.
were more lifelike. Another critical component of the pterosaur model was the head. During flight, it was necessary for the head to face into the wind at all times to reduce drag. After completion and “car-top” testing –carrying the model atop a car to determine the behavior of wings under the lifting force of flight-- the pterosaur model was carried underneath a remote-controlled airplane to a height of 700 feet where it was released in the air and expected to glide back down. Herkie crashed on its first filmed test-run, but was not completely destroyed due to an installed emergency parachute. After a night of repair work, Herkie was able to resume flight the following morning and flew successfully several times.
The Challenge of Getting Herkie off the Ground For the documentary, the National Geographic team requested a lifelike head and fur on Herkie’s wings. This made Herkie two to three pounds heavier. Gerritsen and her team were worried the extra weight would hinder the success of the model’s flight. “They just wanted it to look good, which made it very difficult for us. We’d rather not have dressed Herkie up. It was a real struggle,” Gerritsen recounts. The extra dressing is in fact why the model crashed on the first test-run. Getting paleontologists and engineers to see eye to eye was another challenge. Gerritsen and the engineers on her team saw the project as a preliminary exploration into pterosaur flight. They wanted to work quickly to prepare a working model for the documentary. The paleontologists, however, prioritized scientific debate over building a model. They disagreed about the pterosaur’s leg position during flight, wing stroke, and the location where the wings were attached on its body. Since current fossil evidence gave no precise answer to these questions, the team had to pick a design and begin working. “The debates went on too long at the beginning. At some point we had to just start building in order to finish the project in time for the movie,” Gerritsen says. With a three-meter wingspan, Herkie was 58% of the size of an average grown adult A. piscator. If the model was built to the true scale, it would have been too big to lift under a remote controlled airplane and tests flights would have been much more difficult. With Herkie’s dimensions, the team was able to run twenty test
18 stanford scientific
The RC plane leaves Herkie to glide on his own.
flights before filming the documentary.
The Flying Success of Herkie ”Sky Monsters” aired in late January this year, inspiring awe at the sight of an ancient flying bird across thousands of homes. Since its broadcast, Gerritsen has been working on a traveling exhibition for natural history museums. She envisions a “very hands on” exhibit that describes the evolution of flight, and features models from the project and a virtual animation that would allow a person to “fly” on a screen as a pterosaur. While much progress has been made, questions remain unanswered. Pterosaurs grew up to at least a 10-meter wingspan— how was an animal this large able to fly? When its body grew larger relative to the surface area of its wings, the pterosaur would have reached a limit to its body size. Paleontologists continue to debate what that limit is. The sophisticated wing membrane helped to alleviate the pterosaur’s problem, but not much more is known. “It’s like one big puzzle. But not a very well defined puzzle,” she acknowledges. One day, Gerritsen hopes engineers may be able to use information about unique pterosaur wing membranes in modern flight designs, although she admits we are far away from that. To continue unveiling the pterosaur’s flight mechanism, the next step does not involve sailcloth or nylon fibers, but computer simulations, she says. From physical flight to byte, the StanfordNational Geographic Pterosaur Replica Project’s findings are bringing paleontologists closer to discovering the mystery behind the pterosaur’s soar. S Nancy Falxa-Raymond is a junior majoring in History, with a minor in Biology. She enjoys paleobiology and the New York Metropolitans. To Learn More Stanford-National Geographic Pterosaur Replica Project. http://pterosaur.stanford.edu/] More about pterosaurs. http://www.projectexploration.org/news_121803.htm
