Scientists and engineers are incorporating principles of flight utilized by birds to create better unmanned airborne vehicles (UAVs). Animal flight is highly unsteady and complex compared to mechanical flight. The more complicated articulation of the living wing also makes this type of flight more essentially three-dimensional than conventional flying machines. So far, the main use of UAVs has been by the US military, the NASA is also co founding recent research on the subject at the University of Florida (UF). The current generation of UAVs has been spectacularly useful in the wars in Afghanistan and Iraq---taking the Army brass by surprise and causing production to be quickly ramped up as combat infantry on the ground makes evermore requests for UAV support. However, the current generation of UAVs is designed to fly high above the ground.

The UF research is designed to create UAVs that will be more maneuverable than the current generation, allowing them to fly close to the ground and, for example, bring special sensors close in to investigate a particular individual building suspected of harboring the manufacture of chemical or biological weapons. The new generation of UAVs would be designed to be able to fly down a street with buildings on both sides, turn a corner, fly between two buildings, etc.

As Rick Lind, a UF assistant professor of mechanical and aerospace engineering who heads the project explained, this will require the ability to do sharp turns, spins, and dives. To accomplish this, the new UAVs will have wings similar to those of a seagull---able to undergo drastic changes of shape during flight.

This idea came from mechanical and aerospace engineering doctoral student Mujahid Abdulrahim. He was impressed with the way seagulls could hover, dive, and then quickly climb to regain their altitude again. Photographs by Abdulrahim showed the gulls’ wings flexing both their shoulder and elbow joints to alter their flight patterns.

He incorporated structures analogous to a gull’s elbow and shoulder into the latest UAV prototype. With the UAV wings in a position analogous to a gulls’ wings with the elbows down, the UAV becomes less stable but highly maneuverable. With the “mechanical elbows” straight, the UAV glides very well. With the UAV wings in a position analogous to a gull’s wings with the elbows up, it is very easy to control and can be utilized to land the craft in a relatively small area. The motors in the UAV can move the wings from the down position to the up position (during flight) in 12 seconds. Abdulrahim says this is fast enough to make the craft maneuverable in a city landscape.

The UAV can complete three 360° rolls in one second---three times as many as an F-16. No human piloted plane would ever be designed with the ability to do three 360° rolls in one second because that would kill the pilot. In general, jet fighter design has been bumping up against the fairly immovable constraint of what the human body can withstand. This is one of the main reasons that when the U. S. Air Force announced that it was going to develop the F-35, it also said that this would be the last human-piloted jet fighter.

For awhile, there was understandable resistance against UAVs in the Air Force. Being in charge of employees enhances the power of bureaucrats, and in the air force, pilots are very prestigious employees. Being in charge of a bunch of flying machines will not seem to have the same importance. But the stellar performance of UAVs in Iraq and Afghanistan has caused any potential remaining resistance inside the Air Force to crumble.

Recently, the Air Force tried to retrofit the current state-of-the-art American fighter, the F-22 to perform ground reconnaissance in Iraq using sensors. However, the Predator UAV, costing about 5% as much as an F-22, ended up doing the job better. To be fair, the F-22 was never designed for ground sensor mission. Still, the incident is telling in a way. Grown sensor missions are mainly what we need---at least right now.

And even more promising model for UAVs the seagulls may be bats. Because bat wings are so flexible and highly articulated, bats have more lift, less drag, and greater maneuverability than birds. In contrast to man-made machines, bats fly very slowly, have highly compliant aerodynamic surfaces, and are very unsteady.

Two Brown University professors, Kenneth Breuer, a professor of engineering at who studied mechanical aerodynamics earlier in his career and Sharon Swartz, an associate professor in ecology and evolutionary biology, have collaborated to greatly advance the understanding of bat flight. Some of their findings were published in a study titled “Direct Measurements of the Kinematics and Dynamics of Bat Flight."

A bat wing has more than 24 joints---all independent of each other. A thin, flexible membrane encompasses the entire wing. The bones of a bat wing also go through a large degree of deformation during flight. The extremely flexible articulation of the bat’s wing allows a bat to make a 180° turn in less than half the distance of a wingspan. During the 180° turn, the turning rate exceeds 200° per second.

Bat wings are architecturally and mechanically more complex than those of other any other flying animal, resulting in more maneuverable flight with unique kinematics. (Kinematics is the branch of mechanics that studies the motion of a body or a system of bodies without consideration given to its mass or the forces acting on it. This is in contrast to dynamics, the branch of mechanics that is concerned with the effects of forces on the motion of a body or system of bodies, especially of forces that do not originate within the system itself.)

To better understand how the wings of bats function, Breuer and Swartz first set up videos shot from four angles simultaneously. Reflective markers were placed on joints, bones, and the wing membrane. Analysis of the videos helped the researchers understand how complex movements of the wing strokes related to the overall flight speed, body position, and angle of attack of the bats. After taking a series of ordinary videos, the research team injected a fine mist of aerosol particles into the area where the bats would fly. As the bat flew by, a laser imager imaging device captured the position, speed, and direction of the particles in her wake (all the tests bats were female).

The study revealed that unlike birds or insects, bats draw their wings into their bodies during the upstroke and then extend them out during the downstroke. In a sense, they are rowing rather than flying.

Another area of study is the development of a swarming capability for UAVs. A thousand starlings, flying together in a flock, are able to maneuver easily. The path of the group’s flight changes from moment to moment with no central control. Researchers are copying some of their subtle and effective control methods to help large numbers of UAVs flying near each other without collisions. Swarms (of bees for example) are more complex than flocks because they incorporate stigmergy---their form of communication between individuals. This results in even greater coordination.

Flying robots however, are capable of forming a system with much more complex and effective coordination. In a recent BBC Focus Magazine article, Professor Owen Holland talked about such a system he is building, which he describes as a “gridswarm” (the name of the particular gridswarm he is now developing is “Ultraswarm”---a group of miniature robot helicopters linked together computationally to create an indoor flying cluster computer.

“Imagine a large group of small unmanned autonomous aerial vehicles that can fly with the agility of a flock of starlings in a city square at dusk. Imagine linking their onboard computers together across a short range, high-bandwidth wireless network and configuring them to form an enormous distributed parallel computer. Imagine using this huge computational resource to process sensory data gathered by this swarm, and to direct its collective actions. You have now grasped the idea of a flying gridswarm.”

Although the article focuses on civilian applications, the application to military UAVs is obvious and will clearly becoming soon.

"New UAV designed to maneuver in tight spaces;" OE Magazine, the SPIE Magazine of Photonics Technologies and Applications; http://oemagazine.com/newscast/2005/082405_newscast01.html

"Predator Kicks F-22 Ass," Strategy Page http://www.strategypage.com/htmw/htecm/articles/20070131.aspx

"Bats in flight reveal unexpected aerodynamics," Physorg.com, (their source: Brown University)

http://www.physorg.com/news88359720.html.

"Direct Measurements of the Kinematics and Dynamics of Bat Flight," by Xiaodong Tian, Jose Iriarte, Kevin Middleton, Ricardo Galvao, Emily Israeli, Abigail Roemer, Allyce Sullivan&, Arnold Song, Sharon Swartz and Kenneth Breuer, Brown University, Providence, RI 02912, http://microfluids.engin.brown.edu/Breuer_Papers/Conferences/AIAA-2006-2865-552.pdf.

"UAV; Killer Swarms: The New Generation," by David Hambling, DefenseTech.org, http://www.defensetech.org/archives/002651.html