Maple Seed Microflyer Takes Flight

That innocent-looking maple seed gently floating down to Earth could be a new camera-equipped monocopter developed by scientists from the University of Maryland.

Small enough to fit in your hand and cheap enough for mass production, the monocopter could autonomously explore unstable buildings or hover over a battlefield for days at a time.

"Maple seeds or samara fruit require no power and fall to the ground in the same fashion every time," said Evan Ulrich, a graduate student at the University of Maryland building the new monocopters. "It's extremely efficient."

"Our original idea was to drop them out of an airplane, steer them to a particular place or person, and equip them with a camera or other sensor," said Ulrich.

Since he started designing monocopters in 2005 for his graduate work, Ulrich has built hundreds of monocopter variations. Some weigh less than 10 grams and have a wingspan of seven centimeters (2.8 inches). The largest weigh several times more and have a wingspan of 50 centimeters (19.7 inches).

Each monocopter has a similar shape: a single wing, usually carbon fiber, attached at a right angle to a propeller on one side and an electronics package on the other.

Some monocopter wings can change their angle and alter their speed, but that's far less complicated than trying to design a machine based on the various actuators and power supply needed to power a similarly sized, insect-inspired microflyer.

Each piece can be changed depending on the needs of the designer -- a larger battery for longer flight or a wing optimized for better control, for example. Later versions of the monocopter can be launched from the ground or even out of a person's hand.

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Once its airborne, Ulrich maneuvers the monocopter using a controller with two joysticks. If left at a constant speed, depending on the wing angle, the tiny flyer will hover in a circular pattern, sometimes inches, sometimes feet, in diameter.

For controlled, directional flight, Ulrich varies the monocopter's speed and the wing's angle. Even though it literally flies in circles to get to a particular location, the monocopter can cruise at more than 20 miles per hour.

"I can't fly an RC aircraft or helicopter, but I can fly this," said Ulrich. "I've flown it up next to my advisor's window to get his attention so he will meet with me."

As part of his testing, Ulrich has also attached cameras to the samara fruit flyer. The first cameras were meant to simply monitor the actuators that controlled the wings angle and ensure their proper function. The background on these images tends to be very blurry.

Clear pictures would be easy to produce, says Ulrich, by synching the rotation of the aircraft to the camera. If the camera rotates four times a second, then the camera could be programmed to take a picture at the same time during each rotation.

Other sensors could also be added to the monocopters. Equipped with a laser range finder and a tiny computer, the monocopters could fly autonomously through unstable buildings or insurgent filled caves for minutes to hours at a time, depending on the size of the onboard battery.

Because of their extremely efficient aerodynamic design, a monocopter could even fly for days at a time, if an experienced controller kept it flying in a rising column of hot air, known as a thermal.

A temporary and stationary flying monocopter over a field could provide soldiers with better communication, or provide wildland firefighters with detailed information about the direction and size of an oncoming blaze.

Ulrich hasn't designed the world first monocopter, says Roger Conner of the Smithsonian National Air and Space Museum, but his design, "is by far the most most polished and compact design I've seen."

"It's so simple you could build and drop hundreds of these for not a significant cost," said Conner.

Despite the potential applications for this technology, there are still hurdles ahead for the monocopter.

"The technology is still fairly exotic. I suspect the first application would be a toy, and that once the technology matures there will be an outgrown from there," said Conner.