Biomedical Engineering Reference
In-Depth Information
by a cicada, and a single-bladed rotary-wing
vehicle (typically called a
monocopter
) inspired by
a maple seed. The size, mass, and performance
requirements of the NAV were intended to push
the limits of aerodynamics, propulsion systems,
and electronics. The vehicle based on the hum-
mingbird was selected for further development
in Phase 2 of the program. The final prototype
was capable of stable, controllable flight indoors
as well as outdoors, with an onboard camera and
a fuselage fairing that made it look like a real
hummingbird. The prototype met all of the
original specifications except for the gross mass.
However, all the components were commercially
available and it is expected that developing
components specifically optimized for this
application will enable a significant reduction in
gross mass.
The Air Force Research Laboratory has also
released a future-vision plan that describes a fully
autonomous robotic bird by the year 2015 and a
fully autonomous robotic insect by 2030. Several
research groups are currently investigating a
variety of issues related to such vehicles, specifi-
cally focusing on flapping-wing aerodynamics,
wing aeroelasticity, gust response, stability, and
control as well as autonomous flight.
Bioinspiration and biomimetics form a com-
mon theme of many of these micro and nano air
vehicles (referred to as
microflyers
), for two key
reasons. The first reason is the belief that a
microflyer performing a surveillance mission
can remain undetected by looking like a real
bird or insect and literally
hiding in plain sight
.
The second reason is that by virtue of their size,
microflyers fall in a size regime that is naturally
populated by large insects and small birds. It is
believed that by copying several of the charac-
teristics of these natural fliers, man- made micro-
flyers can improve several aspects of their
performance such as flight endurance, maneu-
verability, and gust tolerance. However, it is
important to caution against blindly copying
biological systems without properly under-
standing their function. It is quite tempting to
TABLE 5.1
Key MAV design requirements.
Maximum dimension
<15.24 cm
Take-off mass
<100 g
Range
Up to 10 km
Endurance (loiter time)
60 min
Payload mass
20 g
Maximum flight speed
15 m/s
relay video and audio information back to the
operator. In this way, the MAVs would enhance
the situational awareness of the soldier. Other
possible civilian applications of MAVs included
sensing of biological/chemical agents in an
accident zone without risk to the human
operator, fire rescue, traffic monitoring, mobile
communications links, and civil structure
inspection. Responses to this solicitation
included several fixed-wing MAVs such as the
MicroStar by Lockheed Martin and the Black
Widow by Aerovironment. Rotary-wing MAVs
included the LuMAV by Lutronix Inc. In general,
it was observed that the fixed-wing MAVs
outperformed the rotary-wing MAVs in terms of
cruise speed, range, and endurance. However,
the major advantage of the rotary-wing MAVs is
their hover and low speed capability, which is
very useful for surveillance indoors or in
confined areas. The key design requirements for
a MAV as described by this solicitation are listed
in
Table 5.1
. Note that these specifications are
very stringent; over the years, the term
MAV
in
published literature has been used to refer to
unmanned aerial vehicles with a range of
dimensions, from palm-sized to meter-sized.
Recently, DARPA released specifications for
the
nano air vehicle
(NAV) program
[4]
. The goal
of this program was to develop a vehicle even
smaller than the MAV specifications. The gross
mass of the NAV was specified as 10 g, with a
payload of 2 g. Configurations that were selected
for Phase 1 of this program were a coaxial heli-
copter, a flapping-wing vehicle inspired by a
hummingbird, a flapping-wing vehicle inspired
