Micro Air Vehicle Club Focusing on French Competition

Aug. 1, 2007
This tiny ornithopter's longest dimension is only 5.2 inches. (To see a larger version, click on the image.)
This tiny ornithopter's longest dimension is only 5.2 inches. (To see a larger version, click on the image.)
The VTOL plane has a different paint scheme on each side so the RC pilot can determine its orientation when it's in flight. (To see a larger version, click on the image.)
The VTOL plane has a different paint scheme on each side so the RC pilot can determine its orientation when it's in flight. (To see a larger version, click on the image.)
UA's vertical takeoff MAV takes a flight around a lab in the Aerospace and Mechanical Engineering Building. The contra-rotating propellers are visible at the nose, just above the two electric motors. The plane's batteries include the two rectangular objects near the leading edge of the wing and a third battery that powers the radio, which is the black device in the middle of the wing. (Photos by Matt Brailey)
UA's vertical takeoff MAV takes a flight around a lab in the Aerospace and Mechanical Engineering Building. The contra-rotating propellers are visible at the nose, just above the two electric motors. The plane's batteries include the two rectangular objects near the leading edge of the wing and a third battery that powers the radio, which is the black device in the middle of the wing. (Photos by Matt Brailey)
The fixed wing MAV flies autonomously. (To see a larger version, click on the image.)
The fixed wing MAV flies autonomously. (To see a larger version, click on the image.)

Members of UA's Micro Air Vehicle club are spending thousands of man-hours this summer hunched over computers, assembling tiny circuits, and fabricating lilliputian flying machines from high-tech composite materials.

All the research, building and testing, which is being done in a third-floor Aerospace and Mechanical Engineering (AME) lab, is directed toward the US-European MAV07 Conference and Flight Competition that will be held in Toulouse, France from September 15 to 21.

MAVs are tiny, radio-controlled airplanes designed for reconnaissance. They can be invaluable for search-and-rescue, law enforcement, military surveillance, or similar tasks.

Three years ago UA's MAV team took first prize for successfully flying the smallest MAV at the French event.

But much has changed since then in the US-European Competition, said AME post doc Roman Krashanitsa, who conducts research with UA Professor Sergey Shkarayev, the MAV club's advisor and one of the world's foremost authorities on MAV technology.

"The rules are getting more and more complicated each year," Krashanitsa said. "This year, for instance, we have to perform seven separate sub-missions for autonomous flight."

That's why UA is sending two airplanes, an ornithopter, and six students to the competition. (Ornithopters are mechanical birds that use flapping wings for lift and propulsion.)

The competition will include an indoor event, in which a vertical takeoff (VTOL) plane will fly into a room to grab video images of targets, and an outdoor event, in which a conventional, fixed-wing plane will scour the countryside for targets. Meanwhile, UA's ornithopter will attempt to establish a world record as smallest mechanized bird to successfully demonstrate continuous, controllable flight for more than a minute.

The Indoor Competition
The VTOL plane will have to prove that it can land and take off from a 1-meter-diameter platform.

Then it will need to fly through a 1-meter-square window into a 3-cubic-meter room to identify one target on a table and another on the wall, all the while avoiding obstacles, explained UA MAV President Gavin Ananda Krishnan, an AME undergraduate student.

"We'll have a miniature video camera onboard and that's how we will see the target," he said. "Since the plane will be out of sight, we are going to have video-display goggles and a computer monitor so the pilot, who is controlling the plane by radio control, can navigate by seeing what the plane's camera sees."

The Outdoor Competition
The outdoor contest involves identifying targets on the ground. The team will have exact GPS coordinates for some targets, but others will be in a zone that the plane will search.

For the outdoor competition, the conventional plane will fly autonomously — entirely by itself, without human intervention, other than to receive GPS coordinates from an operator on the ground.

"The guy sitting at the computer can designate where to go," Krishnan said. "The airplane will then select a route and decide how to use its control surfaces to get there."

Krishnan explained that it's like having a tiny electronic pilot inside the plane. "We're telling the plane where to go, but the 'electronic pilot' may do something different from how we would fly it. But he will still get there."

In another part of the competition, the plane will drop a paint ball to simulate "sensor deployment."

"We have to drop a paint ball into a circle or bin," Krishnan explained. "Our score would depend on how close the paintball is to the target. And when we return from any of these missions, we are required to fly through two arcs made of balloons.

Fixed Wing Specs
The conventional, fixed-wing plane has a 12-inch wingspan and is powered by a tiny electric motor.

"This plane has very good airframe technology," Krashanitsa said. "It's very reliable and it has very good aerodynamics. It's also very rugged. We can drop it from a height of 60 meters and the airplane will be still intact and able to fly."

UA's MAVs had flat wings in the previous years, but this year's model has a 5-degree dihedral, which helps with roll stability, Krishnan said.

"All small airplanes are well known for their inherent instability," Krashanitsa added. "So this is why we have to counteract it with some structural modifications. That's why we went through several configurations of the wing and fuselage design during the past year. We selected the best one after (former master's student) Motoyuki Aki did a lot of wind tunnel testing in the AME slow-speed wind tunnel." (AME master's student Bill Silin did similar wind tunnel testing for ornithopter wings.)

"But the major change this year was switching to a more advanced autopilot and making modifications in the autopilot and electronics," Krashanitsa added.

VTOL Specs
The VTOL plane has a composite wing and two propellers that spin in opposite directions to neutralize torque that would otherwise create control problems.

"With contra-rotating propellers, there are no gyroscopic moments and that helps a lot with stability," Krashanitsa said.

The plane also is equipped with gyroscopes on all three channels of control to further enhance stability, making it easier to fly, land and take off.

Currently, the VTOL plane can only hover like a helicopter, but the next step is to make it transition to level flight so that it can fly quickly to a target like a conventional airplane and then transition back to helicopter mode to hover near the target, Krishnan explained.

Building the contra-rotating props — each of which is powered by a separate electric motor — involved the complicated process of running one driveshaft through the center of the other motor and its driveshaft. "This has to be done within 2 hundredths of a millimeter tolerance," Silin noted. "We machined some of the parts for this."

Performance Challenges
The batteries that power the two motors on the VTOL plane are built into its wings. The entire plane weighs 160 grams or about 5 ounces.

The fixed-wing airplane tips the scales at about 180 grams when equipped with an autopilot.

"Both planes have very high wing loading," Silin said. "So we have to maintain a minimum speed or else they will stall." And when they stall, they fall like rocks.

"That's why we fly as high as possible," Krishnan said. "This gives us space to recover from a stall before we hit the ground."

The fixed-wing plane cruises between about 15 to 34 mph and stalls when the airspeed falls to around 5 mph.

Ornithopter Competition
Although there is no official competition for ornithopters at the French meet this year, enthusiasts will attempt to establish a world record for the smallest ornithopter that can demonstrate at least one minute of controllable flight.

UA's entry is hummingbird size, with its longest dimension measuring only 5.2 inches.

To keep it small and light, the ornithopter uses a special radio tuned to 900 megahertz. This allows it to use tiny antennas made from fine wire, which make it look more like a giant insect than a tiny hummingbird. The ornithopter's receiver weighs only half a gram, compared to the more conventional RC radios on the VTOL and fixed-wing planes that weigh about 7 grams each.

MAV Club Promotes Learning and Fun
UA's MAV club includes graduate students who are working on thesis projects related to MAVs as well as undergrads who are eager to learn all they can about radio-controlled airplanes.

"The club is where undergraduates can gain new skills like soldering, working with electronics, and working with airframes," Krashanitsa said. "You can learn a lot in the club. It's also a good place for Dr. Shakarayev to recruit graduate students.

"It's like a graduate student farm club," Silin joked.

"It's also fun," Krishnan added. "The main reason I joined and my other friends did is because we like RC planes. And seeing these fly and having the liberty to use this lab to build them is a great opportunity to get hands-on experience. You can apply what you learn in class right away, which is a lot more fun than just studying theory without applying it."

The experience gained through the club also helps undergrads find engineering jobs during the summer, Krishnan said.

The club has about 20 members, many of whom have internships with local engineering companies this summer. "So they join us and work in the lab at night or early in the morning," Krishnan said.

"This is how technology develops, in labs like this," Krashanitsa added. "And they're getting experience first hand. That's why all those industrial companies are interested in hiring our people."

While the club has mainly focused on airframe research in the past and been heavily oriented toward aerospace and mechanical engineering, things are changing as the planes move more toward autonomous flight, electronics and computers. "We're now trying to recruit more electrical and computer engineering students to help us with this end of the research," Krishnan said.

UA MAV Sponsors
UA's MAV Club is sponsored by Lockheed-Martin, Plantraco, Bob Selman Micro RC, and the Air Force Research Lab at Eglin AFB.

 

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