UA's MAV team has developed an autopilot that is much simpler and smaller than conventional ones. It was built with help from two French MAV enthusiasts, and the team hopes to eventually commercialize it.
Autopilots are computers that fly airplanes without human intervention.
UA's autopilot was designed to fly Micro Air Vehciles (MAVs), which are tiny airplanes — some have wingspans of less than six inches. They carry video cameras and are designed for reconnaissance missions. They can be used for search-and-rescue, law enforcement, military surveillance, or in any situation where sending in a human observer might be too costly or dangerous.
Commercial autopilots often have an accelerometer to measure acceleration, a pitot tube to measure airspeed, a magnetometer to measure the plane's heading, and a barometer to measure altitude.
UA's autopilot has none of these.
Instead, it has just two sensors, an infrared sensor that detects the difference between sky and ground and measures the plane's attitude toward the ground (whether it's diving, climbing or banking) and a 4 Hz GPS to measure altitude and the plane's location.
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Less is More with MAV Autopilots
"A lot of autopilots use inertial sensors, accelerometers or gyros," said A.J. Kochevar, president of UA's MAV club and an aerospace engineering senior. "On a small airframe like ours, they're susceptible to exceeding their maximum sensing rate. If that happens, the autopilot doesn't know where the airplane really is in the world as far as pitch and roll are concerned."
That means it crashes.
UA's autopilot has proven very reliable and robust. It has flown autonomously (hands-off by humans) in 35 mph winds. Modelers who fly radio-controlled airplanes find it extremely difficult to keep a tiny plane in the air at these wind speeds.
"It's remarkable how well the plane flies in autonomous mode," Kochevar said. "You wouldn't know the difference between it being flown by autopilot or by a human, if you saw it in the air."
The plane also is very maneuverable when flown by autopilot and can turn 180 degrees in 50 feet.
The UA team began developing the device last September, after meeting up with two French MAV enthusiasts at the 4th International Micro Aerial Vehicle Meeting in Toulouse, France.
"We found that the autopilot we took to France was less than satisfactory, and we met a group of guys who thought their airplane was less than satisfactory," Kochevar said. "So we decided to collaborate. We helped them with aerodynamics and they helped us with avionics."
Two Microprocessors do the Work
The autopilot includes two processors. There's an 8-bit microcontroller that handles the communications needed to fly the airplane and a 128-bit microcontroller that does the navigation.
"The hardware for our autopilot is really trivial," Kochevar explained. "This has been basically a software problem."
"The reason autopilots cost a ton of money is because their software is very sophisticated," he added. "So that's where the time and energy goes — to create reliable software that always works, that gives you what you want and that flies the airplane responsively and that doesn't fail or corrupt."
The software is written in C programming language. The GPS route the plane will fly is fed into the software, which is compiled on a laptop at the launch site. Then the compiled software files are loaded into the autopilot memory.
"We've really worked to design software that will mimic the plane's flight characteristics," Kochevar said. "It really 'understands' the aerodynamics and the action it needs to take to respond in various situations."
The first autopilot weighed in at 12 grams (0.42 ounces), but it has now been pared down to eight grams (0.28 ounces). "With the next revisions, the weight should drop to 5 grams (0.18 ounces)," Kochevar said. While this drop in weight may seem trivial, it's a huge weight savings for a small plane that's powered by a tiny electric motor.
Autopilot is Part of the Big Picture
The autopilot is part of the larger MAV development program at UA, which is focusing on development of a prototype Autonomous Micro Aerial Vehicle system.
The system will include a ground station with communication tools, including uplinks and downlinks for real-time data collection and in-flight mission programming and adjustment. It also will include the autopilot system and an inter-aircraft communication system.
The GPS navigation system will be able to store several waypoints and will be capable of changing its target destination while flying. It will also be able to set up in-flight circular and oval loitering patterns.
The MAV system will have a range of at least 4 miles when unobstructed views are possible.
"Based on the success of this system, the extension for the multi-MAV flight system, and integration of other sensors (chemical, IR, etc.) will follow," said Sergey Shkarayev, who is directing UA's MAV program in the Aerospace and Mechanical Engineering Department.
