Conference Session C5
Paper# 2260
The Predator of the Sky; the Avenger Drone
Grigoriy Mishkov (grm29@pitt.edu), Thomas Stimmel (tas131@pitt.edu)
Abstract— The Avenger Drone is being used by the military
as a stealth weapon. This newer, more improved drone uses
cutting edge technology. The body of the General Atomics
Avenger Drone is designed in a specific manner to reduce its
radar signal. This body also includes a state of the art turbo
fan engine. Finally, this unmanned aircraft provides the
ability of entering enemy airspace without the risk of losing
American lives. The stealth capabilities and weapons of the
Avenger Drone derives from its body and the specification
wherewithal built. The Avenger Drone’s body is designed
explicitly to avoid and reduce radar signature. The aircraft
also has a Pratt & Whitney’s [UTX] PW545B
engine[PW545B]. The engine is a turbofan design. This
engine is different from other jet engines because it receives
a significant amount of power from the creation of hot gas
under pressure. Finally, drones that are being used in
warfare, such as the Avenger Drone, bring up ethical
considerations.
in a new plane; one that is cheaper, stealthier, and safer.
This spawned the birth of the drone.
The concept of an aerial drone is not a new idea, as
airplanes since the seventies have had primitive autopilot
features, but within the past several years, the popularity of
the drones has grown exponentially. This is the direct result
of better technology which greatly improved a drone’s
performance.
The demand for a drone stems from the
inadequacy of humans not the machines. Humans cannot
withstand great g forces that occur when turning, nor can
they fly a plane for a long time without tiring. Furthermore,
a remote controlled drone gives the ability of changing the
pilot without grounding the vehicle and eliminates the
chance of a pilot’s life being lost. The General Atomics
Avenger Drone is leading the pack with technology
exceeding its predecessors in all aspects.
Key Words—Drone, Radar Cross Section(RCS), Radar,
Stealth, Turbofan Engine, Warfare
The design process for any aircraft follows numerous
considerations. The first consideration is who is going to
pilot the plane and what its intended purpose is. The first
airplanes required humans to be directly within the aircraft
to pilot the vehicle. This in turn led to the design of the
aircraft with the human element being as fundamental as the
purpose of the plane itself. On the other hand, a vehicle that
removes the direct human element from being present in the
aircraft allows for greater versatility in design. The design of
the first Predator A Drone was to create a drone
reconnaissance vehicle [1]. Following its predecessor, the
Predator B Drone, next drone in the predator family,
followed in the same style of design but was made larger in
order to increase its weapon capabilities. The Predator B
Drone was designed to become a more military action
orientated vehicle while keeping the surveillance aspect
intact within the vehicle [1]. Finally, the General Atomics
Avenger Drone, also known as Predator C Drone, follows a
similar pattern in the drone aspect, but was designed for a
different purpose. The General Atomics Avenger Drone
features a different type of body, engine, weapons bay, and
purpose. The designing of any aircraft that has wide spread
use is a telltale sign of a trend that is to occur within
aviation. The United States Air force trained over 350
remote control pilots in 2011, which is more than the
combined numbers of fighter and bomber pilots trained in
the same period of time [2].
The design of an aircraft is a direct correlation to the
purpose of the aircraft. The design of the previous drones
was specifically designed as reconnaissance vehicles, but the
General Atomics Avenger Drone was designed first as a
fighter drone and second as a reconnaissance vehicle. The
FIGHTER DRONE
DRONE WARFARE
War has been fought between mankind since the dawn of its
creation. The methods humans use to fight wars have
changed continuously over time, from the use of steel to the
use of napalm; new technologies are developed daily. War
technology and research now take up a considerable segment
of a nation’s budget. A significant portion of this budget is
in the funding and maintaining of an air force. From the start
of its introduction, aerial warfare became an integral part in
war. The first planes used in war were used as scouts but
were later transformed into deadly weapons by the addition
of mounted guns and the ability of dropping bombs from
beneath them. World War I introduced the concept of aerial
warfare and created the principles of aerial combat. Fights
between opposing planes soon became a reality for the
young pilots who flew the planes with the risk of dying
looming over their heads with every flight. As the war
progressed, the planes were designed with better engines and
built with better materials giving their pilots a greater chance
of coming out the victor. Constant improvements lead to an
aeronautical race between nations. This race is still going on
to this day with the United States being one of the strongest
contenders for air supremacy.
The modern day air race is all about cutting a nation’s
losses. Cutting the cost of making a plane without
sacrificing performance, reducing radar detection, and trying
to eliminate the chance of losing lives are all aspects of
designing a plane. Factoring this into one machine resulted
University of Pittsburgh
Swanson School of Engineering
April 14, 2012
1
Grigoriy Mishkov
Thomas Stimmel
General Atomics Avenger Drone features a payload that is
similar to the previous versions, but where previous versions
of the predator class had their payloads attached to the wings
of the drone, the General Atomics Avenger Drone has an
internal weapons bay like other modern stealth planes [1].
This weapons bay has a weight capacity of 3,000 pounds,
and with a wingspan of 66 feet, the Predator C Drone has the
option to carry another 3,000 pounds on its wings at a cost of
losing some of its stealth capabilities [1]. The Predator B can
only hold 3,850 pounds of ordinance total while the Atomics
Drone can hold nearly double the amount [1]. The General
Atomics Avenger Drone also differs itself from former
drones by utilizing a turbofan jet engine instead of a
propeller [1]. The move from a propeller powered to a jet
engine powered aircraft also reveals the motives of the
creation of an aircraft. The movement from a propeller
reduces the total operational hours of an aircraft. For
example, the Predator B has 30+ hours of operational time
compared the General Atomics Avenger Drone which only
has 18-20 hours [1]. Finally, the body of the General
Atomics Avenger Drone was designed to have a reduced
radar signature, a move that is different from the previous
versions.
signal for only 10% of its total operational time. The wave
that the receiver picks up is the backscattered signal of the
wave. This is called a radar echo. With the information
given by the echo on hand, the radar device is capable of
calculating the distance of an object by using equation (1).
R
ct
2
(1)[3]
This variable R is the distance from the station to the
aircraft. The constant c is the speed of light. The change in t
is the time it takes to send the radar pulse and to receive the
incoming echo [3]. Unfortunately the distance does not give
us the location, but computing the azimuth and elevation
angles gives us the precise location [3].
Furthermore, when an electromagnetic wave impinges
upon an object it creates fields that scatter from the surface
as well as introducing other fields that occur from following
the contours of the object [3]. The text book Radar Cross
Section explains the creation of the fields, “The total field at
an observation point due to radiation by induced fields over
the surface of the target obstacle is composed of the incident
and scattered fields. Presumably, the incident field is known,
and all that need be done is to subtract it from the total field
in order to obtain the field scattered by the body” [3]. The
creation of these fields depends upon the geometric surface
of the object. Designing any vehicle with a reduced radar
signature; the object needs to be created in such a fashion as
to limit the scattered field produced by the body. To reduce
the scattered field of the body is to reduce the likelihood of
the radar device receiving an echo from the radar station.
This leads to the term of a radar cross section. A radar cross
section is defined directly as, “a measure of power scattered
in a given direction when a target is illuminated by an
incident wave” [3]. Equation (2) is the equation used to find
power flux assuming the object is far from the incoming
signal to remove any near field effects from the equation.
DESIGNED FOR A PURPOSE
The General Atomics Drone was designed from the
beginning with the exact purpose of having a reduced radar
signature [1]. The purpose of this design was to create an
aircraft that would be able to actually act as the first wave of
an attack. The design of any aircraft that is to have a reduced
radar signature starts at the initial phases of the design
process [3]. The methods used to reduce radar signature for
the General Atomics Avenger Drone requires a fundamental
understanding on how radar works and how the signature of
an object is reduced.
The introduction of radar to find and locate aircraft
started during World War II [3]. Radar is composed of two
components; an electric and a magnetic component. These
two key components form the definition of radar as being an
electromagnetic wave. These two aspects, remote from any
radiation or reflection, are perfectly perpendicular to each
other. They both are sinusoidal and reach a peak and zero at
the same time [3]. Radar functions as a great method of
detection for several reasons. Radar emits its own energy
and thusly is an active device instead of a passive locating
tool [3]. Utilizing the principle of how radar works allows
the distance of an object to be found as well as its location
within space. Radar works by sending an electromagnetic
wave into a specific part of space. If the wave interacts with
any object in the normal direction of the radar device, the
device picks up the signal and computes the data giving an
accurate location and distance of said object. Look at Figure
1 for a visual representation of this process. Waiting and
picking up the back scattered signals involves 90% of the
operation of a radar device. Most radar devices only send a
Ps 
PI
4R 2
(2)[3]
The variable Ps is the power flux that a radar device
receives after interacting with an object within a certain
distance of space R. Power flux is the received radar waves
that bounced back to the device. The variable σ, is the cross
section of the object. The variable P I is power of the radar
signal that was sent. We then solve for the cross section σ
and the equation then looks like equation (3).
  4R 2
2
Ps
PI
(3)[3]
Grigoriy Mishkov
Thomas Stimmel
This equation shows the radar cross section is
fundamentally a ratio of scattered power density to incident
power density [3]. The equation also shows that the cross
section captures a σ*P I amount of power. Radar Cross
Section is there for a function of the following variables:
 Position of transmitter relative to target;
 Position of receiver relative to target;
 Target geometry and material composition;
 Angular orientation of target relative to transmitter and
receiver;
 Frequency or wavelength;
 Transmitter polarization;
 Receiver polarization [3].
becoming undetectable. This cannot be done for all viewing
angles as there will be angles in which the angle of incidence
will be normal to the surface. This will result in high echoes
to occur at these points. A caveat, the shaping techniques
that will be discussed, will only apply to monostatic radar
devices. However, if bistatic radar devices are used, the
methods noted will have to be changed dramatically.
Luckily, most radar devices currently being used are
monostatic so the methods being described are for the
majority of radar devices [3].
The first topic to discuss is that most radar devices view
the bottom and the front part of an aerial object. This leads
to the placement of large Radar Cross Sections in the back
and top of the plane. The threat section of an object is
generally defined as ±45̊ in Azimuth and ±20 in elevation.
A visual representative of the threat section is shown Figure
2. The object of any shaping methods is to first and
foremost reduce the radar cross section with in these sectors
of the object to a minimum.
FIGURE 1
DIAGRAM SHOWING AN INTUITIVE DEFINITION FOR RADAR CROSS SECTION
[3]
To reduce the radar signature or more aptly to reduce
the Radar Cross Section, various factors need to be changed
in order to decrease the radar signature of an object. Since
the incoming signal, nor any variable dependent upon the
incoming signal cannot be changed; the only factors that can
reduce the Radar Cross Section is the composition of the
object as well as its geometry. The geometry of an object has
a greater impact on the radar cross section when aircraft are
involved then the material composition. Material
composition of the object plays only a small roll in reducing
an object’s radar signature while changing the geometry can
reduce the Radar Cross Section by 90% and higher [3]. This
is the main reason why the creators of the General Atomics
Avenger Drone focused mainly on its shape while designing
it.
A fundamental knowledge of how radar operates is
important to understand how the changing of the geometry
will change the Radar Cross Section. There are various
methods of reducing the Radar Cross Section of an object,
the principle method utilized within the General Atomics
Drone is referred to as shaping [3]. Shaping is the process of
orienting the edges and surfaces of the object to deflect
scattered fields away from the radar system, thereby
FIGURE 2
DIAGRAM SHOWING THE THREAT SECTORS OF AN AIRPLANE [3]
The main type of scattering that occurs is defined as
specular scattering. Specular scattering is a scattering where
the angle of reflection is equal to the angle of incidence. To
reduce this type of radar signature, the object must have no
surface normal to the radar device. This can be
accomplished by utilizing planar surfaces while avoiding
double and single curved surfaces. This is the primary
method of reducing the Radar Cross Section of an object.
A saucer or object with the type of body as a UFO is
similar to the design of a General Atomics Avenger. Figure
3 will show the design of the Avenger Drone from a side
view. While it is not a saucer, it does have a large center
body with the body thinning out on the sides. This leads to
only a curved edge specular flash occurring on the sides of
the plane. Overall, the body is clean and simple with
minimal discontinuities [3]. The only issue with this type of
body is the flash that occurs on the edges of the plane. This
could be leaving a large signature which minimizes the
desired reduction.
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Grigoriy Mishkov
Thomas Stimmel
plane features sharp edges as well as little curves to reduce
the chance of creating a surface normal to the radar device.
FIGURE 3
SIDE VIEW OF THE GENERAL ATOMICS AVENGER DRONE [1]
All of these topics combine to design the General
Atomic Avenger Drone. The design of the aircraft shows
considerable thought into the reduction of the radar signature
[1]. The first noteworthy part of the drone’s design is the
engine placement. The engine is first and foremost placed in
the back and on the top of the vehicle. The intake of the
engine is placed in a manner of being protected by the front
of the plane. The hump in the beginning blocks the incoming
radar waves to remove any harsh edges that would occur if
the engine was unprotected. The second interesting feature
of the engine is the declination of the engine to taper off at
the end. This tapering off is a sure sign of Radar Cross
Section reduction. The logic behind utilizing this method is
that any plane cut perpendicular to the azimuth plane creates
an echo [3]. This tapering is showcased in Figure 4 as the
backscatter pattern showcases less normal backscatter
patterns occurring.
FIGURE 5
ELLIPSE(A) AND SHAPED(B) AIR PLANE MODELS [3]
The graphs in Figure 6 show the backscatter patterns of
the ellipse plane on top and the shaped plane on bottom. The
pattern is viewed, as in the example of Figure 4, as occurring
on the normal direction of the plane. The large black area of
the graph shows the normal vectors occurring in a large
portion straight back to the radar device. The shaped plane
shows the backscatter pattern as occurring all in directions
not normal to the radar device.
FIGURE 4
RCS BACKSCATTER SPIKES ARE SHOWN WHEN VIEWED AT NORMAL
INCIDENCE[3]
FIGURE 6
ELLIPSE(A) AND SHAPED(B) AIR PLANE BACKSCATTER RADAR CROSS
SECTION [3]
Finally, the position of the stabilizer fins follows that of
a model plane that is designed for greater radar signature
reduction. Figure 5 showcases the design of a radar reducing
airplane on the bottom of the figure and a regular ellipse
based commercial plane on top. The ellipse plane holds a
continuous egg shape over the whole body. The shaped
This principle method of reducing a Radar Cross
Section is by the shaping of the body to create a surface that
will reduce the surface normal of the body.
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Grigoriy Mishkov
Thomas Stimmel
Minimizing the Radar Cross Section is a key component
when dealing with a stealth plane because it is physically
impossible to completely remove a cross section. However,
the smaller the Radar Cross Section is, the more powerful
the radar device has to be to detect it. As radar waves
interact with an object and backscatter back to the radar
device, the angle of reflection remains generally constant.
Since the radar wave is reflected at an angle, the wave has a
probability of never coming back to the radar device. A
smaller cross section forces the waves to scatter in directions
that are not normal, reducing the probability of being picked
up. Table I demonstrates this concept.
The inlet of a jet engine is responsible for several
factors and depends highly upon the thrust and performance
desired from the engine. The purpose of the inlet is to
provide the compressor air at a high stagnation pressure.
Modern design practices dictate that the inlet should allow
air into the compressor at a Mach number of .45 [5]. This
means that even for subsonic aircrafts, the inlet must provide
adequate retardation of air. This is accomplished by either
creating a ‘fat’ or a ‘thin’ lower lip on the fan’s blade. The
‘fat’ lower lip increases the flow of air, while the ‘thin’
lowers the amount [5]. Computer simulations are generally
used to provide the best mix between these two to create the
perfect version that will work in regard to the situation
needed.
The compressor, as the name suggests, compresses air.
There are two major classes of compressors used in engines
today; the centrifugal and the axial. In the centrifugal
compressor, air is compressed around the axis and
centrifuged to the outer axis. Axial compressors work in a
similar fashion; the enthalpy increase occurs around the
rotating rotors. The kinetic and static pressures are increased
because of this. Centrifugal compressors hold several
advantages and are generally used in smaller engines. They
are more rugged and deliver more pressure. Axial
compressors hold the advantage that they require less fuel
and have a smaller cross section compared to the inlet cross
section than the centrifugal compressor.
The combustor is the part of the engine that combusts
the fuel. Fuel is sprayed into a central flame stabilized
region. In this region the droplets vaporize and then begin to
combust. The vaporized gas is mixed in with the compressed
air from the compressor. A good combustor is designed to
achieve complete burning while keeping the pressure from
dropping. The mixing of the air is accomplished to remove
hotspots from within the engine. However, too much mixing
results in a pressure drop.
The turbine is partially related to the axial compressor
operating in reverse. The turbine is designed to convert some
of the power from the high pressure and kinetic energy of
the air to turn the compressor. Only some of the energy is
used to power the compressor.
The nozzle of an engine is used to accelerate the high
pressure gas that is coming from the turbine to the ambient
pressure. Thrust and momentum are produced by the result
of mixing pressurized air with a fuel that is then ignited.
This ignited mixture expands rapidly and is forced out of the
engine’s back. More energy flows out of the back then what
comes in, pushing the plane forward through Newton’s third
law.
TABLE I
TABLE SHOWCASING THE EFFECTS OF CROSS SECTION REDUCTION [3]
Utilizing this fact, the Avenger Drone gains its stealth
capabilities. Radar devices are unable to see it when it is at
certain heights and greatly reduces the detection range.
Reducing the detection range is an important aspect in any
form of attack. It takes time to scramble fighter planes to
intercept another plane and missile systems on the ground.
Since the method of detecting an object does not solely rely
upon the Radar Cross Section another important feature in
the design of the General Atomics Avenger Drone is its
engine.
JETTING ACROSS
An important feature of the General Atomics Avenger Drone
is the engine that provides the mechanical energy of the
vehicle. This engine is a Pratt & Whitney's [UTX] PW545B
turbofan engine. Figure 7 shows the basic insides of a
turbofan engine. This engine provides 4,800 pounds of
installed thrust [4]. It also gives the drone a cruising speed of
648 km/h and a max speed of 740 km/h. Finally, the drone
carries about 9,000 pounds of fuel that gives it a total
operational timeframe of 20 hours [1].
Understanding how an engine functions also reveals
aspects about a vehicle. The basic premise behind a jet
engine is that thrust is generated by the rearward momentum
of a stream of gas [5]. The basic components included in
every turbofan jet engine are an inlet, a compressor, a
combustor, a turbine, and a nozzle.
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Grigoriy Mishkov
Thomas Stimmel
All of these specific features were included into the
drone. The General Atomics Avenger Drone is an
engineering marvel. This feat of an accomplishment had to
involve multiple fields of engineering all working in unison
to produce this aircraft. The shaping of the aircraft had to
occur with the use of aeronautical engineers as well as radar
cross section specialists. The use and placement of a jet
engine showcases that various mechanical as well as
chemical engineers were involved in the engine process. The
need for a new engine was not present as seeing that an
engine capable of satisfying the technical aspects already
existed.
This drone represents a part of the future of the United
States Air Force. This drone also represents the future of
engineering as one field of engineering can no longer
encompass all the different technical aspects needed in the
design of a mechanical vehicle. An engineer’s work does
not only stay in their field of engineering but rather shared
with the world. Engineers have a deep impact on the global
society as a result. Constantly trying to improve a world
with problems, an engineer is faced with a choice; to let the
world continue the way it is or make it a better place to live
for all. The Avenger Drone is a perfect example of multiple
engineers wanting to make a difference in the world.
FIGURE 7
DIAGRAM SHOWCASING INNER COMPONENTS OF A JET ENGINE [6]
Designing a new engine for a vehicle is not necessary
when a new plane is designed. Picking an engine that fits the
customs needs needed for a specific purpose is just as useful
[7]. Since the General Atomics Avenger Drone uses an
already existing engine, it raises the question why one was
not designed for it.
One of the main facets of the design of the General
Atomics Avenger Drone was the reduced detection ability.
Radar is not the only method used to locate and target an
aircraft. Heat signatures as well as noise are also used to
find and bring targets down. A heat signature is hard to hide
in any kind of aircraft that utilizes a jet engine. However, the
design of the drone leads to considering that the back of the
engine is curved down and leaves only a small opening to
vent out the exhaust. A long engine body as well as a flat
nozzle mimics the engine types of the b-2 fortress bomber.
Another issue that gives away aircraft is the sound of
their engines. A jet engine produces a great deal of sound.
Previous types of engines created more sound then the
turbofan engines of today. Since the introduction of
turbofans the noise engines produce has been reduced.
NASA conducted research on the location as well as
reduction of jet noise. The study was performed on
commercial turbofan jet engines. Research has showed that
much of the noise created by the engine occurred within the
combustor as well as the nozzle of the engine [8]. The
General Atomics Avenger Drone uses a commercial turbo
fan jet engine. Commercial turbo fan jet engines are
designed to make less noise. This is a probable reason for
utilization of this turbo fan jet engine in the Avenger Drone.
ETHICS OF DRONE WARFARE
The Avenger Drone offers many advantages in the form
of a first strike weapon but at what cost? Drone warfare is a
very controversial part of war. One of the more argued
points about drone warfare amongst analysts is the topic of
pilot performance. A drone is able to save lives by
retrieving recognizance information in an area that would be
deemed too dangerous for an actual pilot without putting an
actual human being at risk. At the same time, the drone’s
pilot is not physically there and will not be able to make the
same life or death split decisions as if he was. Sadly, even
though the pilot is not there, he still feels the repercussions
for his actions. A study constructed by the Air Force
reported that 28% of drone pilots who have been flying for
long periods reported experiencing symptoms of burnout [9].
The severity of the feeling was proportional to the amount of
fly time.
Another major topic in drone warfare is the fact that
drones have killed civilians in the past and are figured to do
the same in the future. Since the pilot’s eyes are that of a
camera lens on the drone, there is a chance of them
mistaking a civilian as a target. Since Obama took office the
CIA has used drones to kill 400 to 500 militants while
reporting roughly only 20 of those killed were civilians. The
Pakistani officials have told a different story. They have
reported in the year of 2009 alone, drone strikes have killed
roughly 700 civilians while only 14 were terrorist leaders
[10]. This begs the question if the drone’s operators have
become inclined to shoot more often. Despite multiple levels
COGS WORKING TOGETHER
The creation of a plane stems from the perceived need of an
aircraft that needs to accomplish certain parameters [7].
Looking at the technical aspects of a plane as well as the
features that it holds allows insight into why the aircraft was
created and what goals they set in mind for the aircraft. The
General Atomics Avenger Drone was designed to include
stealth capabilities. The Radar Cross Section of the drone is
seen to be minimalized because its body geometry.
Furthermore, the weapon capabilities of the drone have been
increased over its previous processors. Finally, the speed of
the plane was increased at a cost of total operational time.
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Grigoriy Mishkov
Thomas Stimmel
of the military confirming the attacks, mistakes are still
made. Does controlling a drone, possibly thousands of miles
away, leads to a loss of the sense of responsibility? With a
pilot present in the seat, he is responsible for the attack; with
a drone operator multiple analysts confirm an attack before it
occurs.
The last point for drone warfare focuses on the fact that
drones are cheaper to build than any modern fighter jet. A
country would be capable of creating more units if they
choose to go with drones over jets. With a larger unit count,
the possibly of a prolonged war becomes a real concern. A
destroyed drone does not take the same toll on a country like
a physical dead body. Life cannot be replaced while a drone
can be rebuilt. This fact could lead to warfare occurring
more frequently as well as prolonging conflicts; as humans
are no longer lost, only machines.
Drone warfare has the ability of saving a pilot’s life but
at a great cost. Drones unintentionally put innocent civilian
lives at risk by reducing responsibility and by taking
psychological tolls on their pilots. It dehumanizes warfare
as a direct result. Drones can only be the future if the pros
out-weight the cons. The future of peace and war lies with
engineers and the decisions they make.
ACKNOWLEDGMENTS
We would like to thank our co-chair, Roger, for helping us
with the planning. We would also like to thank the staff at
the University of Pittsburgh for making the writing process
self-explanatory and helping us along the way.
REFERENCES
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