Spy Flies – Micromechanical Insects
A micro air vehicle (MAV), or micro aerial vehicle (once called by The
Washington Post Robobugs), is a class of unmanned aerial
vehicles (UAV) that has a size restriction and may be autonomous.
Modern craft can be as small as 15cms. Development is driven by
commercial, research, government, and military purposes; with insect-
sized aircraft reportedly expected in the future.
If a country is at war in an unfamiliar territory, and the battle is about
to begin, enemy ground troops are positioning themselves to form an
attack on our army, located just 2 miles (3.2 km) away. However, the
enemy doesn't know that its every move is being monitored by robotic
insects equipped with tiny cameras, flying overhead. These tiny robotic
flyers, called micro air vehicles (MAVs), will be able to buzz over
enemy territory nearly unnoticed by the enemy troops below. Few
would even look twice at these dime-sized flying robots.
The small craft allows remote observation of hazardous environments
inaccessible to ground vehicles. MAVs have been built for hobby
purposes, such as aerial robotics contests and aerial photography.
The U.S. Department of Defense is spending millions of dollars to
develop these MAVs. They are the perfect way to keep soldiers out of
harm's way during reconnaissance missions. Today, gathering
reconnaissance during battle typically involves putting either small
teams of soldiers or large aircraft in harm's way. At the same time,
satellite imagery is not immediately accessible by a ground soldier.
The Defense Advance Research Projects Agency (DARPA) is funding
several research teams to develop MAVs no larger than 6 inches (15
cm) in length, width and height. These tiny aircraft will be an order of
magnitude smaller than any unmanned aerial vehicle (UAV) developed
to date.
One class of these MAVs is being designed to mimic the flying motions
of certain insects, including flies, bees and dragonflies. In this article,
we will focus on these bug-like MAVs. You will learn how flies fly, how
machines can be built to mimic their movements and where these tiny
aerial devices will be deployed.
Learning to Fly
Flies have a lot to teach us about aviation that can't be learned from
studying fixed-wing aircraft. For years, there was little known about
the mechanics of insect flight, yet they are the world's oldest group of
aviators, sometimes called nature's fighter jets. You may have heard
about how bumblebees can't fly according to conventional
aerodynamics. That's because the principles behind insect flight are far
different from those behind fixed-wing airplane flight.
"Engineers say they can prove that a bumblebee can't fly," saidMichael
Dickinson, a biologist at the University of California, Berkeley. "And if
you apply the theory of fixed wing aircraft to insects, you do calculate
that they can't fly. You have to use something different."
Dickinson is part of the Micromechanical Flying Insect (MFI) Project,
which is developing small flying robots using the flight principles of
insects. The project is in cooperation with DARPA. The MFI Project is
proposing a robotic insect that is about 10 to 25 millimeters (0.39 to
0.98 inches) in width, which is much smaller than DARPA's size limit of
6 inches (15 cm), and will use flapping wings to fly. The project's goal
is to recreate the flight of a blowfly.
You know that airplanes generate lift due to the air travelling faster
over the top of the wing than along the bottom of the wing. This is
called steady-state aerodynamics. The same principle cannot be
applied to flies or bees, because their wings are in constant motion.
"Unlike fixed-wing aircraft with their steady, almost inviscid (without
viscosity) flow dynamics, insects fly in a sea of vortices, surrounded by
tiny eddies and whirlwinds that are created when they move their
wings," said Z. Jane Wang, a physicist at Cornell University's College
of Engineering. An eddy is whirlpool of air that is created by the wing,
and the air in the eddy is flowing in the opposite direction of the main
current of air.
The vortices created by insect wings keep the insects aloft. Dickinson's
group outlines these three principles to explain how insects gain lift
and stay airborne:
Delayed stall - The insect sweeps its wing forward at a high angle of
attack, cutting through the air at a steeper angle than a typical
airplane wing. At such steep angles, a fixed-wing aircraft would stall,
lose lift and the amount of drag on the wing would increase. An insect
wing creates a leading-edge vortex that sits on the surface of the wing
to create lift.
Rotational circulation - At the end of a stroke, the insect wing rotates
backward, creating backspin that lifts the insect up, similar to the way
backspin can lift a tennis ball.
Wake capture - As the wing moves through the air, it leaves whirlpools
or vortices of air behind it. When the insect rotates its wing for a
return stroke, it cuts into its own wake, capturing enough energy to
keep itself aloft. Dickinson says that insects can get lift from the wake
even after the wing stops.
"It would be real spiffy if we could exploit these mechanisms, too, by
building an insect robot. But you can't build them now based on known
principles -- you have to fundamentally rethink the problem,"
Dickinson said. In the next section, you will learn how researchers are
taking these principles and applying them to the creation of robotic
flying insects.
Preparing for flight
There are at least two DARPA-funded MAV projects that have been
inspired by the principles of insect flight. While Michael Dickinson is
creating the micromechanical flying insect at Berkeley, Robert
Michelson, a research engineer at the Georgia Institute of Technology,
is working on the Entomopter. Let's take a closer look at both projects.
Entomopter
In July 2000, the United States Patent Office awarded a patent to
Georgia Tech Research Corporation for Michelson's invention of the
Entomopter, also called a multimodal electromechanical insect. The
Entomopter is being designed for possible indoor operations, according
to U.S. Patent Number 6,082,671. It will mimic the fight of an insect
by flapping its wings to generate lift. In addition, researchers are
studying ways for the Entomopter to navigate hallways and ventilation
systems and crawl under doors.
Let's look at the basic parts of the Entomopter:
Fuselage - Just like in larger aircraft, this is the hull of the machine
and houses the power source and primary fuel tank. All other
components of the Entomopter are attached to the fuselage.
Wings - There are two wings, front and rear, which are pivotally
coupled to the fuselage in an X configuration. These wings are made
out of a thin film. Stiff but flexible veins are attached to the wings at
the fuselage junction to give the wings the curve they need to
generate lift on both the upstroke and the downstroke.
Reciprocating Chemical Muscle (RCM) - A compact, noncombustive
engine is attached to the wings to create a flapping motion.
Sensors - There are sensors for looking forward, downward and
sideways.
Camera - The prototype lacks a mini-camera, but the final version
could carry a camera or an olfactory sensor. This sensor would detect
odors, and the Entomopter would track the odors to their point of
origin.
Surface steering mechanism - This aids in navigation when the
Entomopter is used in ground missions.
Legs/feet - Also called surface locomotors, these parts provide anti-roll
inertia and auxiliary fuel storage.
The Entomopter is powered by a chemical reaction. A monopropellant
is injected into the body, causing a chemical reaction that releases a
gas. The gas pressure that builds up pushes a piston in the fuselage.
This piston is connected to the pivotally coupled wings, causing them
to flap rapidly. Some of the gas is exhausted through vents in the wing
and can be used to change the lift on either wing so the vehicle can
turn.
Currently, the Entomopter has a 10-inch (25-cm) wingspan. "The next
step is to shrink the RCM device down to bug size," said Michelson.
In a vehicle the size of a house fly, every part must perform multiple
tasks. For example, a radio antenna attached to the back of the
vehicle may also act as a stabilizer for navigation. The legs could store
fuel for adjustment of the vehicle's weight and balance during flight.
Airborne
Considering the amount of money that the U.S. military is pumping
into MAV (micro air vehicle) projects, it's likely that the first use of
these robotic bugs will be as spy flies. DARPA envisions a spy fly that
could be used for reconnaissance missions and controlled by soldiers
on the ground. This small flying vehicle would not only relay images of
troop movements, but it could also be used to detect biological,
chemical or nuclear weapons.
Additionally, the robotic insect would be able to land on an enemy
vehicle and place an electronic tag on it so it could be more easily
targeted.
The military would like an MAV that has a range of approximately 6.2
miles (10 km), flies in day or night and can stay airborne for
approximately one hour. DARPA officials say that the ideal speed for
an MAV is 22 to 45 mph (35.4 to 72.4 kph). It would be controlled
from a ground station, which would employ directional antennas and
maintain continuous contact with the MAV.
Robotic flies could also be well-suited as a new generation of
interplanetary explorers. The Georgia Tech Research Institute (GTRI)
has received funding from the NASA Institute for Advanced
Concepts (NIAC) to study the idea using the Entomopter as a
flying Mars surveyor. In March 2001, NASA funded the second phase
of the study in anticipation of future Mars micro-missions.
Advantages
Entomopters offer several advantages over larger surveyors. They
would be able to land, takeoff, hover and perform more difficult
maneuvers in flight. Their ability to crawl and fly also gives them an
advantage in exploring other planets.
Most likely, NASA would send dozens of these surveillance vehicles to
explore other planets. Entomopter developer Rob Michelson said that
the Mars version of the Entomopter would have to be sized up to have
a wingspan of about 1 meter in order to fly in the thin atmosphere of
Mars.
Researchers say that these tiny flying robots would also be valuable in
the aftermath of natural disasters, such as earthquakes, tornadoes or
landslides. Their small size and ability to fly and hover make them
useful for searching for people buried in rubble.
They could fly between crevices that humans and larger machines are
unable to navigate. Other uses include traffic monitoring, border
surveillance, wildlife surveys, power-line inspection and real-estate
aerial photography.
Spy flies are yet another example of how technology is aiding humans
in performing dangerous tasks, allowing the humans to stay out of
harm's way.
Credits: http://digitink.blogspot.com/