Flight has always captured the human imagination. For thousands of years, we have tried to replicate the birds in the sky, and we have tried to understand how they soar above the earth. The Wright Brothers accomplished the former goal in 1903 — but it was not until this year that the latter was achieved. Now, a team of Stanford engineers led by engineering professor David Lentink has created a easures the aerodynamic forces of flying objects. This invention is the first of its kind, and it represents a breakthrough in the study of biomechanics.
The new machine, called the aerodynamic force platform (AFP), answers age-old questions about aerodynamics while also serving practical purposes. In addition to studying the flight of birds, the device will contribute to the development of man-made aircrafts, including small drones. What makes the AFP unique — and extraordinarily accurate — is the way its design circumvents previous challenges in calculating the forces that keep birds aloft.
Previous methods of studying the aerodynamic forces involved in bird flight have been fairly inaccurate and plagued with difficulties. Until now, the most common strategy had been to measure the airflow over a wing in order to approximate lift — the force component that keeps objects airborne. But the resulting calculations are disrupted by turbulence and only hold true at low speeds. Furthermore, this type of study requires precise measurements of birds’ wingbeat strengths. To gather these measurements, every bird would have to be killed and dissected so that its mass and exerted force could be measured.
The Stanford team has invented a device without any of these drawbacks. The AFP takes the form of a thin carbon-fiber box in which a bird can fly. Instead of measuring airflow, it calculates aerodynamic forces directly by measuring air pressure changes. When the animal beats its wings, it forcibly relocates the air around it, causing pressure changes that push and pull on the walls of the enclosure. This motion activates delicate sensors within, which provide the most accurate measurements to date of in-flight aerodynamic forces.
This new machine is already adding to our knowledge of flight mechanics. Most recently, it was used to confirm a long-held theory about avian wingbeats: Birds generate no lift during their upstrokes, but produce double the amount of lift necessary to stay aloft on each of their downstrokes. Flying birds, therefore, do not produce the same amount of lift at all times. Instead, a rapidly oscillating force keeps them in the air. Soon, the AFP may be tested on the fastest fliers of all, hummingbirds, whose wingbeats are so rapid that they resemble those of insects rather than those of other birds.
Lentink’s AFP holds great relevance outside the field of aerodynamic research as well. In particular, it may eventually be used to test small drones. These unmanned aerial vehicles have garnered substantial attention in the past year, largely for their military applications overseas. Already, smaller cousins of the Predator and Global Hawk, two American Air Force drones, are being used in the United States. Small drones may be employed in fields from agriculture to science — they could dust crops, take photographs, survey geography, deliver packages, or monitor traffic. They have even been suggested as search-and-rescue aircrafts, which could spot people stranded in the snow or the ocean.
It takes aerodynamic finesse to make a small-scale drone, and AFPs might help with the fine-tuning. While paving the road for a better understanding of flight, inventors like Lentink and his colleagues are helping the next generation of aircrafts take to the skies.
Cover Image: Art by Casey McLaughlin.