Welcome to the future of unmanned flight.
The ability of unmanned aerial vehicles to collect information over battlefields has changed warfare. But what if those same abilities could be applied indoors? Enter the Nano Aerial Vehicles program, a Pentagon research effort led by the Defense Advanced Research Projects Agency. The idea is simple: Create a small unmanned aerial vehicle that can observe unobtrusively from inside a building, hovering to ensure steady camera images. In 2006, DARPA commissioned AeroVironment to create a tiny UAV that fits these criteria—by flying like a hummingbird.
The company today released its final product of the contract: the Nano Hummingbird. The handmade prototype aircraft has a 6.5-inch wingspan and weighs less than an AA battery, including batteries, motors, communications and video camera. This pint-sized surveillance craft may pave the way for future indoor fliers.
"The idea was not to create a robotic hummingbird," says Matt Keennon, AeroVironment's NAV project manager. "We wanted to make something that emulated the flight dynamics of a hummingbird.... As far as we know, this is a new form of man-made flight." The company says it's the first two-wing, flapping aircraft that carries its own energy source and can hover and fly forward.
The craft does not simply use the bird's biological blueprint, swapping muscles with actuators. Researchers combed many natural and man-made designs to perfect the flapping motion that keeps its NAV in the air. One crucial trick to the bird's quick, precise flight is the way it modulates its wings to go any direction and speed. The speed of the beating wings changes the thrust; changing the angle at which the wings move the air can slide the craft left and right, or twist to up and down. (Click here to see a PDF of his patent, filed last year.) "Flapping wings make more sense the smaller your craft gets," Keennon says. "Larger birds are very efficient in forward flight, but they need a running start to take off, and they can't hover."
Small craft have little mass, granting them the ability to react quickly—useful when adjusting to gusts of wind or dodging obstacles. But the real gold ring is the ability to fly inside a building to capture images that identify targets, collect intel, locate hostages or (in civilian uses) gather courtroom-ready evidence. AeroVironment's craft is not ready for these prime-time missions—it's just a one-off prototype, after all—but the lessons the researchers have learned about power conservation, weight reduction and motor efficiency will be integrated into future products. This little bird is a pioneer.
However, don't start scrutinizing every bird that flits by your window for camera holes. Several technologies must be mastered before nano-UAVs can fly indoor missions, Keennon says. Buildings cause massive disruptions in air flow, so a future indoor flier will need small sensors that help the craft automatically adjust to this turbulence. Keennon says hummingbirds use their vision to help stay stable, and future NAVs could do the same.
Flying indoors is another tricky environment. No controller, no matter how skilled, can safely operate a UAV inside an unknown building based on limited camera imagery. So some automatic collision-avoidance system will be needed to ensure the craft doesn't crash. But perhaps the biggest limitation, Keennon says, is the need for the NAV to capture and transmit video in real time. "Video transmission will always be a big chunk of the power budget," he says. He says that as commercial cellphones and other personal devices drive down the size of communications electronics, the size of surveillance NAVs will likewise shrink, possibly to the size of bumblebees.
So the NAV program comes to an end—"We're out of time and money," Keennon says—but the trend of the ever-shrinking UAV may just be starting. "The end result may not be what you are looking at now," Keennon says. "This might help us do something more imaginative in five or 10 years.... The capabilities will continue to get more impressive."
The Nano Hummingbird met or surpassed the following DARPA milestones:
1. Demonstrate precision hover flight within a virtual 2-meter diameter sphere for one minute.
2. Demonstrate hover stability in a wind gust flight that requires the aircraft to hover and tolerate a two-meter per second (five miles per hour) wind gust from the side, without drifting downwind more than one meter.
3. Demonstrate a continuous hover endurance of 8 minutes with no external power source.
4. Fly and demonstrate controlled, transition flight from hover to 11-mph fast forward flight and back to hover flight.
5. Demonstrate flying from outdoors to indoors, and back outdoors through a normal-size doorway.
6. Demonstrate flying indoors "heads-down," where the pilot operates the aircraft looking only at the live video image stream from the aircraft, without looking at or hearing the aircraft directly.
7. Fly the aircraft in hover and fast forward flight with bird-shaped body and bird-shaped wings.