Naval Air Weapons Station China Lake, California - A Micro Air Vehicle (MAV) flies over a simulated combat area during an operational test flight. The MAV is in the operational test phase with military Explosive Ordnance Disposal (EOD) teams to evaluate its short-range reconnaissance capabilities.
The term micro air vehicle (MAV) or micro aerial vehicle refers to a new type of remotely controlled aircraft (UAV) that is significantly smaller than similar craft obtainable using state of the art technology as it was in 2007. The target dimension for MAVs today is approximately 15 centimeters (six inches) and development of insect-size aircraft is reportedly expected in the near future. Potential military use is one of the driving factors, although MAVs are also being used commercially and in scientific, police and mapping applications. Another promising area is remote observation of hazardous environments which are inaccessible to ground vehicles. Because these aircraft are often in the same size range as radio-controlled models, they are increasingly within the reach of amateurs, who are making their own MAVs for aerial robotics contests and aerial photography.
Three types of MAVs are under investigation. Airplane-like fixed wing models, bird- or insect- like ornithopter (flapping wing) models, and helicopter-like rotary wing models. Each type has different advantages and disadvantages, different scenarios may call for different types of MAV. Fixed-wing MAVs can currently achieve higher efficiency and longer flight times, so are well suited to tasks that require extended loitering times. Rotary-wings allow hovering and movement in any direction, at the cost of shorter flight time. Flapping wings offer the most potential for miniaturization and maneuvrability, but are currently far inferior to fixed and rotary wing MAVs.
The range of Reynolds number at which they fly is similar to that of an insect or bird (103 - 105). Thus some researchers think that understanding bird flight or insect flight will be useful in designing MAVs.
Practical implementations
The TU Delft University in the Netherlands has developed the (in 2008) smallest ornithopter fitted with a camera, the Delfly Micro, the third version of the Delfly project that started in 2005. (See Delfly.nl for photographs.) This version measures 10 cm and weighs 3 grammes, slightly larger (and noisier) than the dragonfly it was modeled after. The importance of the camera lies in remote control when it is out of sight and eventually completely autonomous flight. This version has, however, not yet been successfully tested outside, although it performs well indoors. Its predecessor, the Delfly II, could fly outside, but was three times the size of this craft. The Delfly II could also hang still in the air and take off and land vertically. Researcher David Lentink of Wageningen University, who participated in all three models, says it would take at least half a century to mimmick the capabilities of insects, with their low energy consumption and multitude of sensors; not only eyes, but also gyroscopes, windsensors and much more. He says fly-size ornithopters should be possible, provided the tail is well designed. Rick Ruijsink of TU Delft says the biggest problem is the weight of the battery. In the Delfly Micro, the lithium-ion battery constitutes a third of the weight, at 1 gramme. Luckily, developments in this area are still going very fast, due to demand in various other (more commercial) fileds.
The next goals are an ornithopter weighing just one gramme with a size of 3 cm and a helicopter model. A helicopter design should be twice as efficient. There are no biological examples of such a design, but Lentink is already looking into the flight of humming birds.
Ruijsink says the purpose of these crafts is on the one hand to learn to understand how insects fly, but also more practical, such as flying through cracks in concrete to search for earthquake victims or exploring a radio-actively infected building.
Robert Wood at Harvard University developed an even smaller ornithopter, at just 3 cm, but this craft is not autonomous in that it gets its power through a wire and is led along a rail.
In early 2008 the United States company Honeywell received FAA approval to operate its MAV, designated as gMAV in the national airspace system on an experimental basis. The gMAV is the fourth MAV to receive such approval. The Honeywell gMAV uses ducted thrust for lift, allowing it to takeoff and land vertically and to hover. It is also capable of "high-speed" forward flight, according to the company, but no performance figures have been released. However, the company states that the machine is light enough to be carried by a man. It was originally developed as part of a DARPA program, and its initial application is expected to be with the police department of Miami-Dade County, Florida.[1]
Although there are currently few MAVs, DARPA has recently announced a program to develop even smaller Nano Air Vehicles (NAVs) with a wingspan of 7.5 centimetres (three inches).
The Washington Post has referred to insect-like versions of MAVs as Robobugs.[2]
MAV07 - The 3rd US-European Competition and Workshop on Micro Air Vehicles and the 7th European Micro Air vehicle Conference and Flight Competition web site.
MAV08 - The 1st US-Asian Demonstration and Assessment of Micro Air and Unmanned Ground Vehicle Technology.
