URBANA, Ill. (May 1, 2012) – By the virtue of their size and speed, birds are uniquely capable of efficient flight while flapping their wings and while gliding. Researchers at the University of Illinois at Urbana-Champaign have duplicated the control functions that allow birds to successfully perform a soft landing-in this case, perching on a human hand.
"We believe we have the first demonstration of autonomous/robotic flight of a bird-like micro aerial vehicle (MAV) perching on a human hand," stated Soon-Jo Chung, an assistant professor in the Department of Aerospace Engineering at Illinois.
Because the wings of ornithopters-birds or aircraft with flapping wings-are inherently capable of being reoriented, this capability can be used for controlling and maneuvering the aircraft in a gliding phase, thereby eliminating the need for additional traditional actuators. Gliding is an effective way to conserve energy while soaring, descending, and landing.
"The driving philosophy behind the work is that the maneuverability and control efficiency of avian flight can be replicated by applying their actuation and control principles to advanced MAVs designed on the size scale of small birds," explained Aditya Paranjape, a postdoctoral scholar working on this project. The result is based on his PhD thesis and a series of journal papers with Chung.
"We have developed an articulated-wing-based concept for an agile robotic aircraft inspired by birds," Paranjape added. "Of all maneuvers executed by flapping wing aircraft in a gliding phase, a perched landing is arguably the most challenging."
Perching is routinely used by birds to land on objects such as tree branches, power wires, or building ledges. According to the researchers, there are two factors that make perching challenging to engineer: 1) the maneuver's duration is very short, on the same order as the aircraft dynamics, and 2) a high level of position accuracy is required for a successful perched landing.
"Our aerial robot concept lacks a vertical tail for improved agility, similar to birds, which renders it dynamically unstable and exacerbates both of these factors," Paranjape said. "We choose a perching maneuver to demonstrate the capabilities of our articulated-winged aircraft concept, novel guidance algorithms, and control design. In particular, the ability to perform perched landings on a human hand endows our robot with the ability to operate around humans."
A typical perching maneuver consists of two phases-a gliding phase to bring the bird to a suitable position with respect to the landing spot, and a rapid pitch up (usually to a post-stall angle of attack) accompanied by an instantaneous climb and rapid deceleration. The researchers noted that the success of the maneuver can be severely impeded by the lateral-directional motion (yaw and roll), particularly when the perched landing has to be accomplished on a small surface such as an electric pole or a human palm. In the absence of a vertical tail, wing articulation is a promising capability which can be used for both longitudinal and lateral-directional control.
Chung, who joined the Illinois' faculty in 2009, brought with him a vision for developing aircraft that mimic the autonomy and agility of bats.
"There's a lot to learn from bio systems," Chung said. "Bats can fly with damaged wings. They are so agile and highly maneuverable; they can make rapid 180-degree turns autonomously and they can fly indoors without colliding with obstacles. These qualities are desirable for small aircraft that could be used in surveillance, particularly in urban settings where obstacles hamper movement and satellite control is blocked."
The MAV project was funded by the Air Force Office of Scientific Research.