He refers to them as "nature's fighter jets" and has devoted his life's work and an entire lab to monitor their every move. Thus is the relationship existing between Dr. Michael Dickinson and the objects of his attention—fruit flies. Career pursuits aside, Dr. Dickinson's connection to the insects is one he predicts will eventually lead to the development of flying robots capable of performing various covert tasks, such as spying and surveillance.

An AFRL-sponsored bioengineer, Dr. Dickinson has been working with colleagues to unravel the mystery of how a fly's brain controls its muscles during precision flight. "They make lightning-fast 90° turns, take off or land upside down, and even carry twice their body weight," observes Dr. Dickinson from his uniquely dedicated lab facility at the California Institute of Technology (Pasadena). "I've spent a lot of time with folks in the lab trying to figure out the basic aerodynamics of insect flight," he explains.

ImageUntil recently, scientists did not understand how insects could get airborne, let alone fly as well as they do. The conventional laws of aerodynamics dictate that a fly's tiny wings are too small to create enough lift to support its body weight. Based on these same conventions, scientists had long assumed that the viscosity of the air, and not inertia, was the fly's greater force to overcome in executing in-flight turns. Dr. Dickinson's research team evidenced that the long-standing rules of steady-state aerodynamics, which irrefutably govern the flight of airplanes and birds, are simply not applicable to insects that flap their wings approximately 200 times per second. Specifically, the team's research revealed that to generate the forces that allow them to turn, fruit flies make subtle changes in both the tilt of their wings (relative to the ground) and the motion range of each wing flap. They then use their wings to create an opposing, twisting force that prevents them from spinning out of control.

To gain insight regarding these anomalies, Dr. Dickinson and his team created a unique test arena known as the Fly-O-Vision. The Fly-O-Vision is essentially a fruit fly flight simulator that allows scientists to track a fly's wing motions as it responds to a changing visual landscape (see figure). The Fly- O-Vision's high-speed, infrared video cameras captured the wing and body motions of fruit flies as they performed rapid 90° turns, called saccades. The researchers then analyzed the threedimensional wing and body positions of the fly as it executed turns at a speed faster than a human can blink. Dr. Dickinson's team concluded that fruit flies perform banked turns resembling those executed by larger flies, whose turns must primarily overcome inertia rather than friction.

To facilitate a better understanding of the aerodynamic forces generated by flies, the team built a huge model of the wings of a fruit fly. Aptly dubbed "Robofly," the device mimics the atmospheric effects of a fruit fly's 1 mm wings flapping in the air. In order to quantify the aerodynamic forces acting on the insect's wings, the team also constructed (and immersed in a 2-ton tank of mineral oil) a 15 in. dynamically scaled robotic wing, which flaps and rotates at one-hundredth the rate of an actual fly's wing. Six motors move the robotic wing back and forth in precise, computer-controlled motions. Air bubbles pumped into the tank indicate the aerodynamic flow patterns on the wing, and sensors measure the wing's forces during each phase of its motion.

Using these unique instruments to dissect the complex aerodynamics of fruit fly motion, Dr. Dickinson determined that a fruit fly executes a series of wing motions in order to turn. The fly first generates sufficient torque to accelerate into the turn. As it nears its desired turn angle, the fly then actively counteracts its own rotational inertia by producing torque in the opposite direction, thus halting the rotation of its body. Once the fly has achieved its desired turn angle, it then buzzes flawlessly through the turn and off in another direction. "They're arguably the most aerodynamically sophisticated of all flying animals," Dr. Dickinson asserts.

Although the researchers performed these experiments on tiny fruit flies, they speculate that their results will help scientists understand the flight dynamics of nearly all insects, particularly since the important balance of inertia and friction changes according to the size of the insect. Dr. Dickinson's research results also provide insight into the design of biomimetic flying devices, which could prove beneficial to future military operations

Lt Col Sharon A. Heise and Mr. John Malthaner, of the Air Force Research Laboratory's Air Force Office of Scientific Research, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm . Reference document OSR-H-05-04.