AeroVironment has captured the imagination of a worldwide audience with news of a major extension of its activities into nano air vehicles (NAVs).
Ever since human beings first discovered the basic principles of lift and the importance of wing shapes, the necessary muscle power and control movements of birds defeated all attempts to emulate the mechanical process of using wing flapping to beat gravity. The hummingbird’s amazing ability to conduct a perfectly stable hover has long fascinated students of aerodynamics, especially when slow-motion film footage displays the complexity and perfection of its ultrahigh-speed wing flapping movements.
In 2009, under DARPA's NAV Program, AeroVironment achieved a technological milestone never achieved before by building and flying a wing-flapping air vehicle, carrying its own energy source and using only two flapping wings for propulsion and control. The vehicle could climb and descend vertically, fly sideways, left and right, as well as forward and backward, all under remote control. The vehicle weighed 10 g.
Work for the NAV Program has involved developing new flapping-wing designs, low Reynolds number physics, navigation in complex environments, and the ability to communicate over significant distances. AeroVironment has subsequently developed expertise in new aerodynamic design tools to achieve high lift-to-drag airfoils, lightweight, efficient propulsion and power subsystems, and advanced manufacturing and innovative subsystem packaging and configuration layouts.
Continuing work includes developing conformal, multifunctional structural hardware and strong, light, robust aerodynamic lifting surfaces for efficient flight at low Reynolds numbers. In addition, researchers are studying advanced technologies to enable collision avoidance and navigation systems for use in GPS-denied indoor and outdoor environments, as well as improving efficiency and stability in hovering flight and during the deployment or emplacement of sensors.
Following the initial success of test flights of the flapping system, the company has further developed the flapping flight mechanisms and improved system-wide efficiency, and it has demonstrated the transition from hover to fast forward flight and back to hover.
The original technical goal was to achieve free flight with controlled hovering in a 4 m³ space. The aircraft alone would generate all lift and control forces through the use of only two moving aerodynamic parts—the flapping wings. No additional wings, tails, propellers, or other devices could be used to facilitate lift or control.
The aircraft itself had to be no bigger than 6 in and able to carry all necessary systems onboard, including energy sources and flight control sensor. The company has now tested over 90 different wing designs, many flapping mechanisms as well as many control configurations, most of which are manipulations of the wing dynamics and tail-less design. The configuration is inherently unstable and only an automatic control system prevents it tumbling out of control.
During early trials, some tails and thrusters were added to research various control algorithms, but once this had been established the extra control structures were removed and all control was focused on the wings, which are the only active components on the air vehicle.
According to Matt Keenon, AeroVironment’s Project Manager and Principal Investigator on the NAV Project, “We knew our biggest challenge would initially be to develop a viable propulsion system, and after that, the control system would be the next extreme challenge. Both systems were extremely difficult and required an intense combination of creative, scientific, and artistic problem-solving skills.”
Work on Phase II of the project continued through 2010 and subsequently the Hummingbird air vehicle was improved and refined, so that by 2011 a high degree of confidence was achieved in being able to fly the NAV indoors and outside, including flying it through doors and down corridors into a workshop and office environment.
All this was done using a tiny onboard TV camera within the 19-g NAV monitored by an operator using simple controls to fly the MAV using the camera’s forward vision as a guide. The NAV can hover for up to 8 min and is almost impossible to identify in flight as anything but a real bird.