emulation of natural flight with biomimetic wings

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Mechanical Engineering Session A4


2040

University of Pittsburgh

Swanson School of Engineering

3/01
/ 2012

1

E
MULATION

OF

NATURAL

FLIGHT

WITH

BIOMIMETIC

WINGS


Eric Belski

(
etb14@pitt.edu
),
Mitchel Refosco

(
mir43@pitt.edu
)


Abstract

Flapping

micro air vehicles are miniscule,
unmanned aircraft that operate through the use of flapping
wings in the same way that
certain animals do
.
Utilizing
biomimetic design, flapping micro air vehicles are able to
operate with higher efficiency than manned air
craft or
aircraft powered by propellers or rotors. In mimicking the
wing motions of
flying creatures,
micro air vehicles also
maneuver with a precision and accuracy close to that
observed in the species they emulate.


The wing systems found on cutting
-
edge micro air
vehicles are made possible through extensive study in the
field of bionics. This study of the application of biological
methods and processes to engineered designs is not
responsible for just flapping micro air vehicles; countless
designs i
n many fields have stemmed from what scientists
have observed in nature. It is
insect

wings, though, that
have provided important insight into making biomimetic
wings possible and effective. By studying the aerodynamics
of
insect

wings and replicating the

most efficient and
powerful motions made by them, biomimetic wings have
been successfully incorporated into complex designs that
allow for deft maneuverability of small aircraft. Engineers’
continued understanding of biomimetic wing design and
their use o
n flapping micro air vehicles will result in even
more advanced micro

aircraft.

Key Words

AeroVironment,
Biomimetic
, Flapping wings,

Micro Air Vehicle (MAV), Unmanned Aerial Vehicle (UAV)

A

H
ISTORY OF
H
UMAN
F
LIGHT

Over one hundred years ago, Orville and Wilbur Wright
became the first to sustain controlled
heavier
-
than
-
air
human
flight

[1]
. This fated accomplishment had more of an impact
on aviation than any other. It rapidly ushered in decades of
frenzied research i
nto the mysteries of the sky and what
could be done in it; it set precedents for how aircraft should
be built to best conquer the clouds and beyond. The Wright
brothers’ earliest craft ignited a worldwide search for
airborne dominance. For transportation,
for warfare, for the
sake of being up, the world ha
s since been looking for the
nex
t best plane. Over and over again, someone has found it.
Generations of aircraft have come and gone since the Wright
brothers’
, while those preceding it have come closer and

closer to obscurity
.

The Earliest Flight

Roughly 2600 years ago, the Greek scientist, philosopher
and
mathematician Archytas built a device he knew as “The
Pigeon”. Powered by steam, this bird
-
shaped mechanical
model was purportedly able to fly
200 meter
s.

Such a design
took great inspiration from nature. Its name reflects this, as
does
Roman author
Aulus Gellius’ description of its
source
of power as being “a concealed aura or spirit”

[2].

Later, yet
still ancient, aircraft began to tend away from this
o
bvious
emulation of nature. Chinese lanterns from the third century
BC were constructed with oil lamps enclosed in large paper
bags. They wer
e able to float through the air

and were used
in war to scare enemy troops with the illusion of divinity

[3]
.
This
design would later influence hot air balloons
and other
lighter
-
than
-
air craft; these rely on control of gases to stay
buoyant in the atmosphere. They found success and
popularity in the
1700’
s and onward, with many
monumental aviation firsts occurring in
steerable balloons
(dirigibles). The first controlled, sustained lighter
-
than
-
air
flight occurred in 1852 when Henri Giffard flew 15 miles in
his hydrogen
-
filled, steam engine
-
driven dirigible

[4]
.


Modern Flight


At the same

time, heavier
-
than
-
air cra
ft were

first being
investigated.
These were at first primarily gliders with
lightweight skeletons and no
on
-
board
propulsion. The
Wright brothers’ earliest designs were gliders.

By 1903, they
had fixed engines to their craft and extensively studied
aerody
namics in a homemade wind tunnel.

In this wind
tunnel, the Wright brothers tested the effectiveness of
over
200 different fixed wings
.

Their first flight in the famous
“Wright Flyer”
,

a craft honed through careful study of
fixed
wing design
,
lasted for jus
t seconds

[1]
.


Since 1903, the year of the first flight by the Wright
Flyer, airplanes have evolved in
an interesting

way. Modern
aircraft are

huge
, with wingspans often exceeding 75 meters
.
They can carry almost anything to almost an
y
where. They
can

travel faster than sound

itself.

Yet modern aircraft look
for inspiration to a model that was never perfect, or even
close.
P
roblems that have plagued aircraft for
generations
-

instability, inefficiency
, sluggish control
-

are problems that
stem from fixed

wings and
cannot be solved with design that
is fundamentally inferior to that of another model; Nature.


It is a craft of

a
completely different
kind

that will
revolutionize
human

flight and follow
modern

mastodons of
air travel; this craft is one of
modest size and silence. This
craft is one that ignores the way
modern
planes fly
, with
fixed wings,

and embraces the way nature always has
,

with
flapping

wings
. This craft is the flapping micro air vehicle.

U
NDERSTANDING
N
ATURAL
F
LIGHT

Flapping micro air
vehicles
(FMAVs)
are miniscule,
unmanned aircraft that operate through the use of flapping
wings in the same way that bird
s and insects do
.
Typically, a
micro air vehicle, and more specifically a FMAV, is defined



Belski



Refosco

2

by the Defense Research Projects Agency (DA
RPA) as
having a maximum dimension of 15 cm and a maximum
weight of 100 grams

[
5
]
.

Utilizing biomimetic design,
FMAVs

are able to operate with higher efficiency

and
maneuverability

than
fixed
-
wing craft. The biomimetic
design inherent in FMAVs

and vital to

their success

is a
product of bionics, the study of the application of biological
methods and processes
to engineered designs

[6]
.

Bird Wing Dynamics

Birds have made the sky their home for
millions of years [7
].
Certain physiological
attributes

have enabled this mastery of
the air. Hollow yet unyielding bones make them
extraordinarily light, and

allow the wing to take a permanent
camber
.
Because of this, birds’ wings continuously produce
lift and enable extended periods of gliding. While not
gli
ding, the motion of the wings can be described as having
three distinct control methods. One is flapping; this is up
-
and
-
down motion of the wing. It provides the majority of the
thrust (forward force). Increasing thrust increases forward
velocity.

Increasi
ng forward velocity
increases

lift, a result
of higher pressure air flowing under the wing and lower
pressure air flowing over the wing.
Another is twist; this is
the act of changing the pitch of the wing

during flight. In
doing this, a bird can further co
ntrol lift during flapping and
gliding. The third aspect of control that birds have over their
wings is folding
. This is bending of the wing on the upstroke
to decrease wingspan and drag

[8]
.


Depending on a bird’s size and other physiological
factors
,
its

frequency of flaps may be drastically different
from the average bird’s. Large birds, for example, flap
slowly relative to smaller birds.
The Streaked Shearwater
(
Calonectris leucomelas
) has been observed to flap with a
frequency of 7.5 Hz while begi
nning flight from rest on the
surface of water and then with a lower frequency of 4.2 Hz
throughout cruising flight.


Hummi
ngbirds, in contrast, flap
much more often to allow for their characteristic
maneuverability and the ability to hover. The Ruby
-
throa
ted
hummingbird (
Archilochus colubris
) flaps with a frequency
of about 55 Hz

[6]
. This allows it to hover at will,

an ability
not had by other birds but desirable in FMAVs.


Insect Wing Dynamics

Insect wings, in contrast to bird wings, are not rigid
ly
cambered
. They deform elastically during flapping
,

meaning
that the
incredibly thin
wings are constantly changing shape.
This phenomenon produces large amounts of lift,
comparable to that produced by camber of birds’ wings

[5]
.
An insect’s flapping motion
is
also
different from that of a
bird’s.

Insect wings do twist, and they do flap, but they do
not fold. This is because where birds have joints within the
ir

wing
s
, an insect’s is a continuous
skeleton of veins. These
veins provide strength to keep the film

of the wing from
being destroyed by rapid motion

[9]
.




Instead of being up
-
and
-
down, the flap of an insect wing
is

more

in the horizontal direction

and is dependent on
precisely controlled
twisting
and high flap frequency
to
control lift and maneuver
ability

[5]
.



FIGURE

1

F
IGURE OF
I
NSECT
W
ING
F
LIGHT
P
ATH
[5]


Insects thus rely less on forward motion; it is not needed to
stay airborne. Hovering

is completely possible for
many
insects, and can be deftly controlled

for graceful movement
in any
directi
on.
The frequency of insect wing flaps is higher
than the frequency of bird flaps. Male mosquitos’ flap
frequency is 450
-
600 Hz.
Smaller insects’ fl
ap frequencies
can

actually

surpass this

[9]
.


However,
continuous flapping

in one spot

has drastic
effects on the nearby air
, which actually aid

the insect in
producing lift
. Cornell University professor Z. Jane
Wang

explains that
"Unlike fixed
-
wing aircraft with their
steady, almost inviscid (without viscosity) flow dynamics,
insects fly i
n a sea of vortices, surrounded by tiny eddies and
whirlwinds that are cre
ated when they move their wings

[10].

This
chaotically
swirling air
helps to keep

insects aloft

because it is of lower pressure than the air below the wing

[11
]
.


A
NALYZING
W
ING
D
YNAMICS

Despite the thorough understanding of bird and insect wing
dynamics that the study of bionics has provided
,
the infancy
of FMAVs means that
little research

has been done in the
past into
mechanizing the
flapping wing design that defines
them
. Cons
equently, research is
presently
being conducted
to further understand the properties of
mechanical
flapping
wing
-
powered flight.

FMAVs often operate under conditions
not perfectly consistent with those that actual animals are
found and studied in. To know
how to develop mechanical
flapping wings, specific conditions, especially those that
animals are not studied in, must be reproduced with test
devices and computer simulation.

Table
-
Based Flapping Wing Test Setup

One apparatus which emulates
insect wing kin
ematics

is a
biomimetic flapping wing test setup.
A specific table
-



Belski



Refosco

3

mounted device, c
reated in 2008
,
tests the thrust produced
by various insect wing emulations. In order to do this,
a
mo
tor drives a scotch yoke
, which produces oscillatory
motion of attache
d wings.




FIGURE

2

A

TABLE
-
M
OUNTED
D
EVICE
T
HAT
T
ESTS
W
INGS
[5]



The motion of these wings is multi
-
dimensional, involving
both horizontal back
-
and
-
forth motion and
passively
changing pitch.
This means that during a half
-
stroke, which
is either one
back

stroke or one
forth

stroke of the wing in
the horizontal plane, the pitch stays constant. As the wing
comes to the end of its
half
-
stroke

the pitch
of the wing
flips
to have an identical pitch in the successive
stroke
.



FIGURE

3

A

F
IGURE
T
HAT
I
LLUSTRATES THE
P
ITCH
C
HANGE
.

S
IDE
V
IEW OF THE
W
ING
[5]


Sensors attached to the base of the wings collect data which
quantify the thrust produced by the wings
. This device is
helpful because
the
frequency of
the
stroke

and

its

pitch
angle can be altered t
o produce optimum thrust. The data
collected from this testing can be factored into the wings of
FMAVs

to produce the most efficient flap pattern

and angle
of pitch

[
5
]
.


Computer Simulation

Another method of analyzing the nuances of flapping
-
wing
design i
s through computer simulation. Computational Fluid
Dynamics (CFD)
are

able to provide insight into the
pressures surrounding the wings at different points in the
wings’ flap cycle. These pressures describe the amount of
lift the wings produce and the other

dynamic forces present,
such as wake produced by previous flaps. CFD also models
environmental factors, such as wind, which can drastically
affect the stability of the FMAV.

CFD shows that FMAVs
are resistant to these environmental factors because dynamic

forces produced by the flapping motion of the wings
themselves disrupt the force of the environmental factors

[12
]
.





FIGURE

4

P
RESSURE
C
ONTOURS
ON A
V
IRTUAL
C
YLINDRICAL
S
URFACE AT
2.0

CM FROM THE
W
ING
B
ASE
[11]

Wind Tunnel Testing

Testing of the aerodynamic forces on FMAVs cannot only
be performed by computer modeling; real experimental data
also needs to be collected in order to verify the theoretical
computer results. Wind tunnel testing gives insight into the
laminar and turbulen
t flow around the flapping wings at
various
velocities. A
ir

will

flow slowly past the wings as
they flap and the pressures that are generated
and the wakes
produced can be observed. This combination of data is
compared against the computer models to confir
m the
accuracy of the formulas that generate the data.
Additionally, testing in a wind tunnel details the differing
thrust
s

that four
-
wing and two
-
wing FMAVs
produce and
the affect body angle has on these thrusts. Results from wind
Plane of Symmetry

-
1 1

Pressure

(non
-
dimensional




Belski



Refosco

4

tunnel testing at Chiba
University show that two winged
FMAVs produce greater thrust than four winged FMAVs
when the body angle of the craft exceeds thirty degrees from
the horizontal. Increasing wind velocity and flapping
frequency also produce more l
ift

[
12
]
. The factors

observed
through wind tunnel exper
imentation help to enhance
FMAVs’ flight by maximizing the performance of the
flapping wings.

C
OMBINING
A
SPECTS OF
D
IFFERING
W
ING
D
ESIGN

What is known about bird and insect wing dynamics through
biological study

can be co
mpared to what has been found
through experimental and computational testing to find the
most desirable wing design
s

for FMAVs.

It is important to
realize, however, that certain wing aspects are more
effective in specific contexts.
Four
-
winged FMAVs, for
e
xample, while not as common as two
-
winged FMAVs,
produce more lift when the body of the craft is inclined less
than thirty degrees from the horizontal

[12
]
. This was
discovered through extensive wind tunnel testing. Most
FMAVs, though, employ two
-
winged

de
sign with very
specific qualities in mind. Each desirable quality, such as the
ability to hover and combat disruptive environmental
factors, can be achieved by incorporating aspects of either
bird wings or insect wings. In order to hover and remain
lightwe
ight, for example, two
-
winged FMAV wings emulate
shorter, horizontally
-
flapping insect wings instead of longer,
more massive and vertically
-
flapping bird wings. The ability
to elastically deform, which produces large amounts of lift,
is also desirable in F
MAV wings, an
d is inspired by insect
wings.
Due to the desired specifications and needs of
FMAVs, emulating insects is more
desirable

than mimicking
birds
.

D
ESIGNING A
B
IOMIMETIC
W
ING

Biomimetic wings, by definition, are designed to imitate
natural
wings.

In the specific case of FMAV wings, insects
are the models to which wing designers look. There are three
main components of FMAV wings that these designers must
consider and coordinate to make a successful design: the
film, which is responsible for aerody
namic performance, the
frame of the wing, which provides th
e wing its shape and
dictates the degree to which it can deform, and the spring
system that reduces inertial loads on the body of the FMAV

[5]
.

Biomimetic Film

The film that covers an FMAV’s wings
is vital to the craft’s
flight. Every aspect of its design must be carefully
planned
to ensure that proper lift and other aerodynamic forces are
produced. To do this, CFD is used in conjuncture with wind
tunnel testing to examine film material candidates.
Specif
ically, polyethylene and mylar have been identified as
desirable film choices. Both are plastics, and both are used
in sheet form to cover the wing’s frame.




FIGURE

5

D
IFFERING
W
ING
D
ESIGNS
[5]


In both CFD modeling and wind tunnel testing, these two
materials showed differing yet acceptable approximate
Reynold’s numbers

[5]
. A Reynold’s number is a ratio of
inertial forces (forces created by the rapid back
-
and
-
forth
motion of the wing on the body

of the FMAV) to viscous
forces. Viscous forces include turbulent flow (chaotic,
random motion of air) and laminar flow (ordered motion of
air).
As for insects, turbulent flow is desirable for FMAVs.
At Reynolds numbers of 2300 and above, turbulent flow is

predominant. FMAVs are thus able to produce high lift by
flying in the midst of leading
-
edge vortices created by
preceding flaps
, just as insects do
.

Ideally, FMAV wings
would produce Reynold’s numbers between 1,000 and
100,000

[5]
.
Polyethylene
-
covered w
ings
with thickness of
0.03mm have

been shown to produce Reynold’s numbers
ranging from 2500 to 4700 in wind tunnel testing. Mylar
wings
with thickness of 0.12mm
produced similar results.

Both were found to be acceptable based on experimentally
found Reyno
ld’s numbers. However, the thicker mylar
-
covered wings produced more lift than the polyethylene
-
covered wings, and were in
this experiment more favorable

[12]
.


Wing Framework

The frame of biomimetic wings found on FMAVs is also
very important to the FMAV’
s success. It must be light
enough to not hinder the wing’s
intended
motion, but strong
enough to withstand the inertial forces produced by high
frequency flapping. Also considered in design of the frame
is how the frame flexes during strokes.
This is affe
cted by



Belski



Refosco

5

differing material and structure type.
An open frame, one
w
ithout

envelopment of the film

on the four edges of the
wing
, was found
in table
-
based tests to

produce higher thrust
from frequencies ranging from 5.5
-
10 Hz

than a closed
frame design, whi
ch is characterized by complete enclosure
of the film

on its four edges
.




FIGURE

6

M
ODEL OF AN
O
PEN
S
HAPE
W
ING

[5]




FIGURE

7

M
ODEL OF A
C
ARBON
C
OMPOSITE
W
ING

[5]



A f
rame made of 0.3mm

carbon
composite

formed to an
open shape was found in
table
-
based tests to produce more
power than 0.508mm aluminum designs at flap frequencies
of 8
-
10 Hz.

However, the aluminum frame produced higher
thrust at all frequencies tested and more power at all
frequencies above 10 Hz

[5]
.

Comparing these two materi
als
reveals
open
carbon composite frames to be acceptable, but
open
aluminum frames to be superior

at the flap

frequencies

FMAVs typically require for flight
.

In testing done at the
University of California at Berkeley, an FMAV was flown at
various flap fr
equencies ranging to more than 30 Hz without
using more power than was available from its power source

[6]
. FMAVs strive to maintain flap frequencies of this
magnitude to best match the frequencies at which insects fly.



Combating Inertial Forces

Because of the high frequency with which FMAV wings
flap, resulting inertial forces pose problems for the motors
that power them.
As the wings come to the end of each
stroke, the motor, without assistance from a spring system,
would be subjected to damagin
g strain while attempting to
reverse the motion of the wings. The addition of a torsion
spring damping system alleviates enough stress to allow the
motor to operate with high efficiency and less power
consumption.
One example of this

system
, tested at the
University of Maryland,

includes a carbon fiber flexing rod
that provides torsional forc
e. This

connects to the shaft of
the wing and the actuator that controls pitching of the wing.
This carbon fiber rod conserves energy at the end of each
stroke by helpi
ng to reverse the horizontal flapping motion
and pitch

[5]
. This energy conservation occurs because
as
the rod
is bent during the course of a stroke, it stores energy.
At the end of the stroke, this energy is released and the rod
conforms to its equilibriu
m state. This process occurs
constantly, with the rod bending and unbending during every
stroke.




FIGURE

8

F
IXTURE
N
EAR
B
ASE OF
W
ING
I
LLUSTRATING
C
ARBON
F
IBER
F
LEX
R
OD
[5]



Another example of an FMAV
-
utilized torsion spring
damping system is eviden
t on the Sparrow II, developed at
the University of Delaware. This system contains two
springs per wing

that function with the same purpose as the
carbon fiber rod used in the previous example. One spring is
attached at the joint of the wing where flapping

motion
originates. This spring conserves energy by deforming
during each stroke and then returning to its equilibrium state
momentarily during the middle of the stroke. The second
spring is located further along the wing shaft, past the joint
at which fla
p occurs
. It is responsible for
helping the motor
to control

pitch
.

The spring is compressed as the wing flaps,
and releases energy at the apex of each stroke.






Belski



Refosco

6


FIGURE

9

F
IXTURE
N
EAR
B
ASE OF
W
ING
I
LLUSTRATING
S
PRING
D
AMPING
S
YSTEM
W
ITH
S
PRINGS
[
13
]


Each of these systems performs the same function. For the
sake of simplicity, though, the carbon fiber rod system is
preferable.

S
UPPORTING
A

B
IOMIMETIC
W
ING

Biomimetic wings rely on
many facets of
careful
engineering to
function properly. Perfect wings, however,
are not enough to give FMAVs flight. They must be
coordinated with other systems to make their host craft
functional.
Counteracting wing
-
produced vibrations and
endeavoring to select appropriate motor and batterie
s are
central to this concern.


Counteracting Vibrations

Rapid wing movement produces constant and potentially
detrimental vibration of the FMAV. When constructing an
FMAV, certain design aspects separate from wing design are
implemented

to fight these
.
Ke
y to this is a sturdy
internal
frame
. This
directly integrates

all of the FMAV’s
components other than the
moving ends of the
wings
themselves, which must remain secure yet unhindered from
ideal motion.
Attaching FMAV components must be done
carefully to e
nsure that damaging vibrations do not loosen
connections. For this reason, and because of the small scale
of FMAVs, assembly of these craft is vigilantly done by
hand

[14]
.

Motor and Battery

An FMAV’s motor and battery do not directly provide lift or
cont
rol. However, they play a very crucial role in moving
the wings, which do

provide lift
.

A

test
apparatus used in
studies at the University of Maryland employed “a Hacker
B20 26L brushless motor, which was controlled by a
Phoenix PHX
-
10 sensorless speed con
troller in combination
with a Grand Wing Serv0
-
Tech (GWP) microprocessor
precision pulse generator [
5
].”
The various controls and
sensors that regulate FMAV motors serve the purpose of
making sure each wing stroke is of the right amplitude, but
the same f
requency. This means that the wings beat at
variable speeds but always maintain the same number of
strokes per second.
This motor setup is consistent with those
used in actual FMAVs, though there is differentiation of
specific motors used by different mod
els. All, though, are
small and electric. Both of these qualities cut the weight of
the
motor and its noise production

without compromising
power output

[5]
.

The minimum power output required for
an FMAV’s successful flight differs based on its specific,
i
ndividual specifications

and expectations of it
. Testing done
at Georgia’s Institute of Technology revealed power
consumption by one FMAV to be 0.65 Watts. This was
comfortably lower than the maximum power output of 0.
75
Watts for the tested motor

[
15
]
. Si
milarly sized motors
produce similar power.


The batteries used by FMAVs are, like the motor, very
important. Not only must they have
long life; they cannot
put too much strain on other systems with excessive weight.
Ideally, FMAV batteries would allow

for their host craft to
fly for about 60 minutes. This

is long enough for intended
use to realistically be complete. As of 2005, most did not
achieve this flight time; they allowed for less than 20
minutes of flight because of constraints on weight

[5]
.





The power output of FMAV motors is important

because
without sufficient power, maneuverability significantly
decreases
. So are the life of the batteries that make them
work and the weights of both components.

Each of these has
a direct correlation to the flight time and therefore
effectiveness of FMAVs.

The placement and positioning of
these parts is something that engineers must also factor into
the design of FMAVs.

Fastening these parts to the FMAV’s
interna
l frame securely but without throwing off the balance
of the craft is essential. Having any concentration of mass to
either side of the center of the FMAV can cause failure
, as
the wings flap in tandem and cannot compensate for the
permanent unsteadiness

[
15]
.

A
ERO
V
IRONMENT

S
H
UMMINGBIRD

AeroEnvironment
, a California engineering firm, makes use
of biomimetic wings in its
Nano Hummingbird
.

Named one
of the “50 Best Inventions of 2011” by TIME magazine, this
innovative
FMAV

was designed and created for

Defen
se
Research Projects Agency (DARPA).
Since 2006, the
project has received
$4 million in funding from this
organization.
The
Nano Hummingbird
, according to
AeroVironment,


met all, and exceeded many, of the Phase
II technical milestones set out

by DARPA:


T
ABLE

1

S
PECIFICATIONS OF THE

FMAV

H
UMMINGBIRD
[14]



Demonstrate precision hover flight.



Demonstrate hover stability in a wind gust flight which
required the aircraft to hover and tolerate a two
-
meter
per second (five miles per hour) wind gust from the
side,

without drifting downwind more than one meter.




Belski



Refosco

7



Demonstrate a continuous hover endurance of eight
minutes with no external power source.



Fly and demonstrate controlled, transition flight from
hover to 11 miles per hour fast forward flight and back
to hover

flight.



Demonstrate flying from outdoors to indoors and back
outdoors through a normal
-
size doorway.



Demonstrate flying indoors 'heads
-
down' where the
pilot operates the aircraft only looking at the live video
image stream from the aircraft, without
looking at or
hearing the aircraft directly.



Fly the aircraft in hover and fast forward flight with
bird
-
shaped body and bird
-
shaped wings.



These requirements, which were met by the FMAV, attest to
the capabilities and expectations of flapping
-
winged fli
ght.
Used by the U.S. military for incognito surveillance
purposes, the Nano Hummingbird ironically remains the
most publically known example
of an FMAV.
Unfortunately, though, its current use by the military also
limits the amount of technical detail that

can be found about
it. What is known about the Nano Hummingbird
,

from what
little has been made public
,

is that it is a very advanced and
fine
-
tuned product of biomimetic wing design. Weighing
just two
-
thirds of an ounce

and with a wingspan of 6.5
inches
,

the craft can be equipped with a protective shell
,

amazingly emulative of a live hummingbird
,

as well as a
live
-
feed video camera. This technology can be used
by a

pilot to operate the FMAV without being in its immediate
vicinity
, up to kilometer away
. Mo
re impressive and relevant
to biomimetic wing design, though, is the flawless workings
of the craft during flight. It can hover flawlessly for
more
than eleven minutes. It can deftly operate

around objects and
through tight spaces. It can even be programme
d to
autonomously perform tricky aerobatic maneuvers such as a
360 degree lateral flip.

Such a move attests to the control
available with flapping winged
-
design

[14]
.




FIGURE

10

H
UMMINGBIRD
FMAV

[14]


The Nano Hummingbird is a promising example of
biomimetic wing design used by an FMAV. Its capabilities
have amazed both the general public and
those

that truly
understand

and appreciate

the work that has gone into its
design.

With it and other FMAVs, as evidenced by the Nano
Hummingbird’s funding by D
ARPA, surveillance missions
can more easily be completed. These small craft, equipped
with a video camera as the Nano Hummingbird has been, are
perfect for incognito operation.


T
HE
E
THICS
A
ND

F
UTURE
OF
FMAV
S

FMAVs currently only serve one purpose outside
of
laboratories and te
sting facilities: surveillance.
And though
they are incapable of directly inflicting physical harm,
military use of FMAVs, like DARPA’s use of the Nano
Hummingbird, can lead to
harmful conflict.
This distinction
between doing and enab
ling clouds the issue of whether or
not FMAVs are ethical

in their present application
.



Some maintain that FMAV design and use is not only
ethical, but
essential
. Bradley Strawser, in the
Journal of
Military Ethics
,
explains:

“I

contend that in certain contexts
UAV employment is not only ethically permissible, but is, in
fact, ethically obligatory. The basis of this claim rests upon
what I call the principle of unnecessary risk (PUR). PUR
proceeds as follows: If X gives Y an orde
r to accomplish
good goal G, then X has an obligation, o
ther things being
equal, to choose a means to accomplish G that does not
violate the demands of justice, make the world worse, or
expose Y to potentially lethal risk unless incurring such risk
aids in

the accomplishment of G in some way that cannot be
gained via less risky means. That is, it is wrong to command
someone to take on
unnecessary

potentially lethal risks in an
effort to carry out a just action for some good; any
potentially lethal risk incu
rred must be justified by some
strong countervailing reason.

[16]
” Another argument for
FMAVs’ ethical benefit is that they accomplish the same
goals that other means can, but with fewer resources.
Deployment of an FMAV
to survey an area
is cheaper than
se
nding a much larger UAV, or a manned aircraft. If a job is
to be done that can be done by an FMAV, it is ethical to save
resources by employing this
craft
.



However, others argue that FMAVs are unethical. This is
to be expected, especially at this poi
nt in their development,
as
they

are only practically used by the military. Future
development of FMAVs may

change the realm in which
they are useful, and thus the opinions of those who doubt
their ethical value.

Making them

capable of traveling long
range
s
and at lower cost
may make them more viable
in

civil
and commercial applications.

FMAVs could, for example,
be used in environmental monitoring (e.g. pollution and
weather applications), forest fire monitoring, traffic
monitoring, precision agriculture a
nd disaster relief

[17]
.
Increasing the number of roles that FMAVs play outside of
military surveillance will undoubtedly make them more
ethically acceptable and generally helpful.




Belski



Refosco

8

T
HAT

S
A

F
LAP

Flapping micro air vehicles promise to revolutionize human

flight by emulating the oldest model that can be looked to;
Nature.

This
mimicry

is manifested in their wing design.
Utilizing flapping wings instead of the fixed
-
wing design so
common on
conventional aircraft

for over a hundred years
,
FMAVs exhibit amaz
ing flight characteristics. They can
move in any direction and hover like the animals they take
inspiration from. Years of research into avian flight, but
more importantly insect flight, provide the basis for the
design of biomimetic wings. Supplementing t
his with
insightful computer simulation and actual aerodynamic
testin
g has allowed for the

design and implementation of
flapping wings on FMAVs. Continued advancement of these
already amazing engineering marvels will expand FMAV
applications and undoubtedl
y serve the world well.

R
EFERENCES

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[12
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A
C
KNOWLEDGEMENTS

We would like to ackn
owledge our parents who inspired our
interest in engineering. Also we would like to acknowledge
the professors who are distributing knowledge so academic
pursuits like the one discussed in this paper can occur.