Nano Air Vehicles
Present Engineering
Challenges


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AeroVironment has for the first time achieved controlled precision hovering and fast-forward flight of a two-wing, flapping-wing aircraft that carries its own energy source and relies only on its flapping wings for propulsion and control.

When the Monrovia, CA firm AeroVironment unveiled its prototype "nano-hummingbird" in February 2011, it did so with great fanfare.

In developing the miniature drone, the company had overcome some not-so-small engineering hurdles. In fact, one milestone had never before been achieved: controlled precision hovering and fast-forward flight of a two-wing, flapping wing aircraft that carries its own energy source, and uses only the flapping wings for propulsion and control.

The achievement was the result of the Phase II contract awarded by the Defense Advanced Research Projects Agency (DARPA) to AeroVironment to design and build a flying prototype "hummingbird-like" aircraft for the Nano Air Vehicle (NAV) program. DARPA defines NAVs "as airborne vehicles no larger than 7.5 cm in length, width, or height, capable of performing a useful military mission at an affordable cost, and gross takeoff weight (GTOW) of less than or equal to 10 grams."

The military has great plans for NAVS for defense purposes. Equipped with a video camera or a sensor, NAVs are envisioned for a multitude of roles, including surveillance, reconnaissance, targeting, battle damage assessment, air or artillery spotting, detection of mines, and jamming enemy communications.

AeroVironment demonstrates the maneuverability of its prototype Nano Hummingbird. Photo credit: AeroVironment

AeroViroment's nano-humming bird is truly an engineering marvel, measuring only 16 cm (6.5 in) tip-to-tip and with a total flying weight of 19 g (0.66 oz.). It is capable of climbing and descending vertically; flying sideways left and right; flying forward and backward; rotating clockwise and counter-clockwise ?all while under remote control and carrying a video camera payload.

However, even with a working prototype, there are still many technology challenges that need to be solved before NAVs are ready to take on real military missions. The key areas of ongoing research include propulsion and energy storage; aerodynamics at low Reynolds numbers; guidance, navigation, sensors, and communications systems; and advanced manufacturing techniques.

Propulsion and Energy Storage

Propulsion and energy storage systems for NAVs require a highly efficient power source with sufficient energy and power density to fly for sustainable time periods. Even more challenging is the requirement for dense energy storage that can be efficiently converted to thrust in order to propel the vehicle as well as power all the subsystems. Some designs employ a dual functionality power source that is also used as a structural component, thus enabling a significant reduction in size while serving to maximize flight durations.

Aerodynamics

Aerodynamic design challenges for NAVs are driven by low "Reynolds number" physics (<15,000). Natural fliers such as birds and insects operate at very low Reynolds numbers compared to a typical aircraft and have inspired research designs with flapping wings like Aerovironment's hummingbird, insects, and even maple tree seeds. The severe space limitations of the NAV make the aerodynamic challenge even greater than that overcome by the NAVs larger predecessor, the miniature air vehicle (MAV).

Guidance, Navigation, Sensors, and Communications

Another major technical challenge is the integration of navigation, guidance, and control sensors onto a single chip at the nanoscale to meet the restrictive size, weight, and power requirements of the NAV vehicle design. Furthermore, NAVs may be required to operate autonomously, in concert with others via a network, or travel in "swarms," making the challenge even more complex due to increased processing and sensory requirements of functions.

Advanced Manufacturing

Designing and building a NAV requires revolutionary manufacturing technologies and innovative subsystem packaging and configuration layout to integrate nanoscale components into the airframe itself. This was a key component of the DARPA NAV program, which included the requirement to demonstrate a clear process to integrate other subsystems into the airframe and show the capability to manufacture the system.

Tom Ricci is the owner of Ricci Communications.

However, even with a working prototype, there are still many technology challenges that need to be solved before NAVs are ready to take on real military missions.

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August 2011

by Tom Ricci, ASME.org