AEROSPACE SCIENCES & ELECTRONIC SYSTEMS
Flying into the Future
Miniature flying machines could help with warfare, agriculture and more.
By Amy Stone
IS IT A BIRD? A PLANE? In the case of micro air vehicles -- tiny, self-piloted flying machines -- it's a little of both with some insect and robot characteristics thrown in.
photo by Stanley Leary Robert Michelson's entomopter uses a micropropellant fuel to generate an up and down motion, such as beating wings or scurrying feet. (200-dpi JPEG version - 148k)
While not quite able to leap over a building in a single bound, microflyers (as they are called at the Georgia Institute of Technology) will have some fairly astounding characteristics. Georgia Tech engineers envision that these six-inch machines will be able to fly to a target and feed back or retrieve information in a variety of forms, including visual, chemical and biologic.
Adding to their complexity, microflyers will be able to accomplish their tasks by themselves: they won't rely on humans to provide remote control.
"Microflyers need to be nimble, fearless, safe and survivable in order to be successful," says Dr. Samuel Blankenship, a principal research scientist at the Georgia Tech Research Institute (GTRI) and coordinator of the Georgia Tech Focused Research Program for Microflyers. "The range of applications for a self-piloted, multi-mode tiny machine is truly great."
As with many engineering marvels, the initial applications for the microflyers will be for the military. However, Blankenship sees civilians, such as police and fire officials, scientists and farmers, as the ultimate users of this technology.
As useful as these flyers may be in the future, there are some immediate problems that have to be solved before microflyers are a reality. For example:
Size."You can't just shrink a 747 proportionally down to six inches and expect it to fly," notes Blankenship. Wind, rain, and even air itself, pose different problems to a six-inch flyer than they do to a large jet.
Autonomy.The smaller a system is, the more skittish it acts. Therefore humans -- especially if they are looking through a camera -- will not be able to react in time to control a machine this tiny. Proposed means of making the microflyer autonomous include using a geographic information system (GIS) to provide a map of the terrain or a global positioning system (GPS), which employs a satellite to map the location of the flyer. However, GIS can't include power lines or cars and GPS is useful only outdoors.
Flight Controls.Traditional planes use weighty motors and hydraulic machinery to maneuver control surfaces in the wings and tail. Altered wing design and channelled exhaust may help provide control without extra weight and allow the small aircraft to fly under control at very low speeds not possible with conventional wings and control surfaces.
Power Sources.Since a drop of gasoline has more energy potential than current batteries of the same size, early models will probably use fossil fuels. GTRI researchers have proposed a micropulse jet engine which is not as efficient as a traditional jet turbine engine, but is much simpler.
Weight.All of the components, including the payload, must weigh less than about four ounces.
What Could Microflyers Do?
- Kill harmful insects
- Crawl or fly down smokestacks to measure emissions
- Monitor concentrations of chemical spills
- Look over the next hill in combat situations
- Maneuver through buildings looking for survivors after a disaster
- Fly spy missions, either outside or indoors
- Measure ammonia concentration in agriculture
- Track wild animal herds
To design a microflyer, Georgia Tech is drawing on expertise in aerodynamics, control systems, avionics, sensors, systems integration, electrical engineering and human factors. Tech has supplied initial funding to launch the project so that it will be ready to take off when the Defense Advanced Research Projects Agency (DARPA) announces its funding opportunities.
Also, Georgia Tech has reached out to bring the best minds together on this project: It has partnered with other agencies, such as the Air Force Institute of Technology and the Institute of Defense Analyses, and sponsored a national conference in February 1997, which served as a catalyst for the field.
The First Step: Airborn Microflyers
The initial goal of the microflyer program is to design a machine that can take off, land and follow simple instructions while aloft.
Robert Englar, a principal research engineer at GTRI, is working on a fixed-wing model for the microflyer. By combining an altered wing design that has a rounded trailing edge and channelling the engine exhaust out of the wings through tiny slots, Englar's model employs what is known as the Coanda effect to greatly augment the wing's lift and control without any external moving parts. This results in an aircraft's ability to lift, land and turn, all at very low speeds without complex control devices.
"Traditional planes rely on fast wind speeds to generate lift over their wings and allow them to stay aloft. Our blown model will allow the microflyer to take off and land at much slower speeds and turn while airborne," explains Englar. "This would allow these very small aircraft to fly within buildings, for example."
To change directions, Englar's model uses fluidics devices to control the stream of exhaust. In simplified terms, to turn to the left, the amount of exhaust is increased out of the right wing or reduced from the left. To lift or lower the craft, the quantity of exhaust is manipulated. More exhaust exiting equally through both wings makes the aircraft fly much slower.
graphic by Martin Brooke Stacking microchips and connecting them with light signals allow the chips to perform multiple functions in a small space. This technology may be used in micro air vehicles. (200-dpi JPEG version - 173k)
Robert Michelson, also a GTRI principal research engineer, was inspired by insects for his design. He envisions the microflyer as a multi-mode vehicle -- capable of flying, crawling, and perhaps, swimming.
To fulfill that vision, he has developed a reciprocating chemical muscle (RCM) which uses a monopropellant fuel to generate a reciprocating, or up and down, motion, such as beating wings or scurrying feet. As an added plus, the RCM can generate electricity, which could be used to power sensors for directional or mission purposes.
Resembling a metallic wasp with about a 10-inch wingspan, his prototype (dubbed the entomopter in reference to its insect-like characteristics) flaps its wings as the fuel is injected into the body, enabling it to fly forward. Gas generated as a byproduct of the RCM can be used to change the lift on one wing or the other to allow the otherwise autonomic symmetric wing beating to result in "rolling" of the device so it can turn right or left.
"The next step is to shrink the RCM device down to bug size," says Michelson. "Near-future goals for this model include trimmed, or directed, flight; multi-mode locomotion; and sensors which will enable it to perform simple homing activities."
At such a small scale, every piece of the microflyer has to perform double, or even triple, duty. For example, a radio antenna could also be used as a stabilizer for navigation while the legs could double as receptacles for fuel storage and for adjusting the entomopter's weight and balance during flight. Michelson believes even a "self-consuming" system is possible, in which the microflyer would consume itself to generate energy as it flies. Alternatively, the RCM concept is even amenable to conversion of biomass into usable fuel reactions, so future entomopters may be able to "eat on the run" to extend their mission endurance.
The Next Step: Airborn Potential
To be useful machines, microflyers will have to carry payloads ranging from cameras to chemical sensors. Therefore, other scientists on the Georgia Tech team are examining how to make miniature sensor systems.
The prototype chemical and biologic sensors are basically small chips of glass with optical wave guides fabricated on their surfaces which can trap and manipulate light. On the most basic level, the sensor would have two channels: sensing and reference. When a laser beam is passed under the strips, the phase of the light contained in the guides is altered by the change in refractive index that occurs when the sensing channel interacts with the chemical or biological species it is designed to measure.
The information contained in the light is read after the laser beams passing under the sensing and reference channels are combined to generate a unique interference fringe pattern, which moves past a solid-state detector array in proportion to the phase change that has been caused by the sensing interaction.
graphic by Robert Michelson Reciprocating Chemical Muscle [RCM]-Driven
(200-dpi JPEG version - 305k)
"With this technology, you can design each sensing/reference pair to respond to a particular type of analyte. In some cases, it is possible to design a sensing channel that will respond uniquely to the analyte you want to detect, and in other cases, where unique sensing chemistry is not available, you can design multiple sensing/reference pairs on the same optical chip and use pattern-recognition techniques to sort out which analyte is being measured," explains Dr. Robert Schwerzel, a principal research scientist at GTRI. "We can put up to two dozen channels on a sensor chip to determine what the microflyer is flying through."
Already small (about 1 cm by 2 cm), the sensors will need to be further reduced for the microflyer. For example, the laser and detectors, which currently feed the information to circuit boards in laptop computers, are external to the sensors. Schwerzel and his colleagues, including Nile Hartman, who developed the original concept, and Dr. Dan Campbell, who has developed much of the sensing chemistry, are working on integrating all of these components, including the signal processing electronics, into one small unit.
"An important feature of these sensors is the ability to fabricate thin films of polymers, antibodies, or other chemical reagents on top of the waveguides. These thin films are the key to gathering chemical or biological information in a tiny space," says Schwerzel. "With these integrated-optic sensors, you can use chemical reactions, adsorption into polymers and other means to gather analytical information. Combined, these features make the integrated-optic sensors more specific and sensitive than other monitoring techniques."
A group of researchers in Georgia Tech's School of Electrical and Computer Engineering is working on other types of sensors -- those that would supply visual images and those necessary for communication.
The visual sensors could use active pixel arrays already used in the nose cones of missiles to allow for "real time" processing of images. The trick is, of course, to make the technology tiny enough.
"We're looking at the ultimate level of packaging the components for microflyers," says Dr. Joy Laskar, assistant professor of Electrical and Computer Engineering. "You can't buy these components off the shelf."
Additionally, Laskar and his colleagues are examining how to communicate with the microflyers once they are airborne, how to transfer information that the microflyer gathers and how to keep the information and communications secure -- an important consideration in wartime use.
Therefore, the microflyers won't use a standard cellular frequency band since that is easily jammed or crowded, but will use a higher frequency, which allows for a smaller antenna.
As the initial problems are solved, other specialists will begin work. Amy Mykityshyn, a researcher specializing in human factors, will work on the design of "human/machine interfaces." This area is important because even though the microflyers must operate autonomously after they have been given a task, humans must still play a large role in their missions, including:
Projected Requirements for Microflyers
- Size: less than six inches at largest point.
- Weight: approximately four ounces.
- Speed: up to 50 mph.
- Range: up to 6.2 miles.
- Price: less than $1000 per unit.
- Sturdy: able to hold up in backpacks.
- Use: easy, with minimal training.
identifying tasks for the microflyers, such as specifying the mission objective and the information to be obtained;
servicing the machines by providing logistics support in refueling and repair;
receiving and interpreting the information obtained from the aircraft.
Helping to put together all the parts is Dr. Tom Collins, a senior research engineer in the Electronic Systems Laboratory.
"The integration of all the systems is important -- especially on such a small scale as the microflyer project," notes Collins.
"For example, if one person goes over the weight limit for a component, that weight has to come from someone else's project," continues Collins. "In industry, you'd parcel out weight limits and make people stick to them. However, that's harder to do in research since you're making it up as you go along."
In spite of the many challenges that remain in order to get a microflyer in the air, Blankenship, the project's coordinator, is optimistic.
"We hope to have a machine flying in three years," says Blankenship. "It will cost over $10 million to produce the prototype. We know we're pushing the envelope with this project. However, you have to reach high and employ the push/pull strategy: technical requirements push you to develop new technology and then technology pulls research along."
Further information is available from Dr. Samuel Blankenship, Electronic Systems Laboratory, Georgia Tech Research Institute, Georgia Institute of Technology, Atlanta, GA 30332-0840. (Telephone: 404/894-7311)
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Last updated: Feb. 24, 1998