Embry Riddle Aeronautical University, Blackbird

Team Blackbird 12’
System Design
Team Members:
Inacio Diaz, Ryan Hoffman, Jake Neighbors, Ramiro Perez, Justin Peterson, Mark Schoeni, Maxwell Seifert,
Terik Weekes
Faculty Advisor:
Dr. Richard Stansbury
Submitted:
May 24, 2012
Abstract
This document provides an explanation of Blackbird's 2012 SUAS system design and implementation. The goal
of the Blackbird group is to design and operate a robust Unmanned Aerial System utilized for reconnaissance or
search and rescue. Blackbird's goal for the 2012 SUAS competition is to provide a foundation in which future
teams can build upon. The new airframe, "Agent Grey", is very robust and capable of carrying a larger and
heavier payload than what is being flown this year. The ground station imaging software is very easily adapted
to new image/video systems. Each system utilized this year is very stable and adaptable so that future
Blackbird members will be able to improve upon systems or develop new systems with limited concern about
system compatibility.
Table of Contents
Abstract ....................................................................................................................................................................0
I.
Introduction ......................................................................................................................................................2
Design Methodology ............................................................................................................................................2
Mission Analysis ...................................................................................................................................................2
II.
System Design...................................................................................................................................................3
Autopilot/DataLink ...............................................................................................................................................3
Ground Control Station ........................................................................................................................................5
RCTransmitter/Receiver .......................................................................................................................................6
Camera/CameraDataLink .....................................................................................................................................6
Blackbird Airframe: "Agent" .................................................................................................................................7
III.
Failure Mode Analysis................................................................................................................................ 11
IV.
Test and Evaluation Results ....................................................................................................................... 12
Autopilot/DataLink ............................................................................................................................................ 12
RCTransmitter/Receiver .................................................................................................................................... 13
Camera/CameraDataLink .................................................................................................................................. 13
Payload Workflow ............................................................................................................................................. 16
Figure 1. Lab test bench used to determine workflow. ........................................................................................ 16
Figure 2: Payload Monitor Overview ..................................................................................................................... 17
Figure 3: Target Classifier overview ...................................................................................................................... 17
V.
Mission/Flight Operations ............................................................................................................................. 18
VI.
Safety ......................................................................................................................................................... 19
System Safety .................................................................................................................................................... 19
Operational Safety ............................................................................................................................................. 19
I.
References ......................................................................................................... Error! Bookmark not defined.
I.
Introduction
Design Methodology
When given the task of the 2012 SUAS mission, the team members of Blackbird employed a combination of
system design methodology, aircraft design, research and development and previous experience. Learning
from past successes and failures, the team was able to identify a major issue that too much effort had gone
into attempting to create the newest and best of each sub-system while the over-all mission requirements
became slightly out of focus. The Blackbird team of 2012 made the mission the priority and the system and
sub-systems tools to accomplish the mission.
UAS design requires a specific method to system design. This is true for mini aerial vehicles in which the
payload is a significant percentage of the aircraft’s weight, such as the ones competing in the SUAS
competition. The rationale of this statement comes from the fact that an aircraft is designed and optimized
around its intended mission, which is to carry and maneuver a payload that is also designed and optimized to
accomplish the mission. During the design of the payload sub-systems, changes are expected. These changes
must be anticipated and planned for while the aircraft is being designed and built in parallel with its subsystems.
In order to successfully complete this design challenge, the members of Blackbird adopted an agile design
approach. The team's method included the allowance of system and sub-system changes or replacements due
to required alterations to another sub-system. That is, not only were the advantages and disadvantages listed
and discussed, but the final design was still dynamic and agile. The method allowed for the implementation of
“backup” sub-system designs in the case that a particular design for a sub-system was deemed impractical. By
employing this more agile system design process, the team was able to replace inadequate sub-system designs
without major changes to the overall system.
Mission Analysis
In order to have a complete a mission, the system must first be able to withstand and perform in certain
environmental conditions. The UAS will be able to operate after 10hrs exposure to 100°F. The plane will be able
to fly and maintain communications in fog with a visibility of at least 2mi. The system must also be able to
function within an electromagnetic field with emissions typical of a military base. Though not flight critical, the
plane will be able to be transported to and from the flight area within the allotted time.
The mission will be completed in less than 40 minutes. The plane will be able to take off in crosswinds of 8kts
with gusts up to 12kts. The plane will be able to maintain steady, controlled flight within ±100ft path error and
±50ft altitude error. The plane will contain flight within the allowed fly-zone. The UAS will be capable of
autonomously navigating waypoints in order. The system will overfly targets while navigating to waypoints and
will record all 6 required characteristics. The system will be able to identify targets as small as 2ft by 2ft with an
alphanumeric as small as 1ft by 1ft with 2in thick lines. The system will be able to identify an off-path target
that can be as far as 250ft off-path at 200ft altitude. The system will be capable of autonomously searching for
targets. The system is also capable of altering search patterns in flight.
For operational effectiveness, the ground station will be able to be seen in bright sunlight. The ground station
will be capable of reporting that the plane is within the no-fly boundaries. It will also report required telemetry
such as altitude and KIAS.
Blackbird's previous SUAS successes have been due to the team's dedication to complete practice missions. For
this reason, the system will complete as many practice missions as possible before the competition. The team
will be trained with each member capable of multiple flight operation roles in case of personnel unavailability.
II.
System Design
The system is comprised of two main sub-systems, the ground station and the airframe. There are smaller subsystems within the two main sub-systems. A system diagram is provided in Figure 1, below. A detailed
description of each subsystem is provided in the subsequent paragraphs.
Figure 1: System Diagram
Autopilot/DataLink
Several factors were considered when selecting an autopilot. The first are the cost and size constraints for the
autopilot. Two low cost open source autopilots were compared to the expensive Cloudcap Piccolo System. A
comparison of the various, constraints can be seen in Table 1, on the following page.
Table 1: Autopilot Cost and Size Constraints
Autopilot
Piccolo II/SL
Case Weight
Size
Implementation Cost
Yes
7.7 oz, 3.9oz 5.6” x 1.8” x 2.4” $6000 +
Paparazzi YAPA
No
.28 oz
3.15” x1.57”
$750
Paparazzi TWOG No
.28 oz
1.57” x 1.18”
$750
Paparazzi Lisa M
No
.4 oz
2.36” x 1.18”
$650
Adupilot Mega
No
1.58 oz
3.7”x1.6”
$450
Although the Paparazzi and Ardupilot are physically smaller, their various peripherals add significant size and
bulk to a completed autopilot system; however, the lack of an RF shielded case vastly increases the
interference from external sources to the autopilot’s internal components. This has been tested and discovered
to be the source of many different “mysterious” failures and malfunctions. The tests are further discussed in
the Tests and Evaluations section.
The sensor and telemetry options, as seen in Table 2, of the Paparazzi "Yet Another Paparazzi Autopilot" (YAPA)
and "Tiny Without GPS" (TWOG). Autopilots were the most diverse of all the autopilots considered. The
modularity of the YAPA and TWOG allowed the team to test many sensors to isolate and replace faulty and
poorly performing hardware. This has led to several essential system improvements compared to the Piccolo
autopilot, such as a significantly faster GPS lock time and ability to power RF modems on and off independently
of the YAPA autopilot board. These improvements can reduce mission time by several minutes.
Table 2: Autopilot Sensor and Telemetry Options
Autopilot
Piccolo II/SL
IMU
Crista
Air Data
Pitot-Static
Modem
900MHz
GPS options
4Hz
Magnetometer
No
Paparazzi YAPA
Various User Selectable User Selectable 2Hz, 4Hz, 10Hz Various
Paparazzi Lisa M ASPRIN
Barometer
User Selectable 2Hz, 4Hz, 10Hz No
Adupilot Mega
Pitot-Static
Xbee
ARDU
4Hz, 10Hz
Yes
The YAPA and ground station system, itself, satisfies many mission requirements. These requirements include
displaying desired aircraft telemetry, no fly zones and search areas, flying autonomously while navigating to
waypoints, displaying desired aircraft telemetry, manual override, return home and flight termination.
The TWOG and YAPA, which can be seen on the following page in Figure 2, were evaluated in the laboratory.
The TWOG proved difficult to utilize due to the small PicoBlade connectors which it uses. These proved
unreliable due to the high gauge wire which needed to be used to connect the sensors. This unreliability
presented a significant risk and would reduce the system's operational capability.
Figure 2: Left: TWOG Right: YAPA
The on-board autopilot communicates with a ground station software implemented using a Linux based
computer. The on-board autopilot supplies a wireless serial output. Different versions of Xbees are available
with ranges from 300’ to 1.6mi. Table 3, below, shows the multiple Xbee solutions available. A 100mW XbeePro
900MHz XSC was chosen to be the datalink for the YAPA because it fulfills the mission requirements. A 5dBi
antenna was chosen for the ground station and a less powerful 3.1dBi for the aircraft, which will perform
better than the 1.6mi estimate for a 4.2 dBi of gain.
Table 3: Data Links Considered.
Modem
Xbee Pro XSC 900Mhz
Xbee Pro Series 1 2.4ghz
Max Stream Xtend 900Mhz
Output Power
100mW
60mW
1000mW
Reciever Sensitivity
-106dBm
-92dBm
-110dBm
Estimated Range
1.6 mi
300’
14 mi
The second data link which could be used is a 900MHz Max-Stream Xtend modem, shown in Figure 3, below.
The Max-Stream has a maximum output power of 1,000mW. This modem is less susceptible to interference;
however, because of the modem’s high output power and low frequency it may reduce the reliability of various
components. Servo jitter would be introduced due to interference on the pulse with modulation (PWM) lines;
this may make the aircraft difficult to control and can only be resolved with proper shielding or ferrite cores.
Data and power lines to various components would also be affected by this interference.
Figure 3: Top: Xbee 100mW Module
Bottom: Xtend 1000mW module
The more powerful modem is not currently in use because the system can complete all requirements for the
mission, however if additional range is needed the system would require additional shielding against radio
interference, which adds additional maintenance, weight and testing.
Ground Control Station
The System possesses a ground station capable of handling all necessary mission related tasks. The ground
control station is comprised of two major subsystems, Autopilot control and Payload. Autopilot control is the
most crucial and is operated by a single UAV operator. The operator uses the Paparazzi Ground Control Station
(GCS) to re-task and monitor the aircraft in flight. Paparazzi’s GCS is an effective piece of software and its
telemetry is sent to the payload operator’s software.
The payload operations are shared between two separate operators. The first operator monitors the incoming
video streams for targets as well as retrieving the image files. The second operator uses the camera viewing
software. The software sorts and groups the images, which allows the operator to quickly process target
images. This configuration was decided after multiple laboratory simulated missions to reduce operator
workload, this is further discussed in the Test and Evaluations section.
RC Transmitter/Receiver
The mission requires a radio control system that will allow manual control at the extent of the mission field.
The RC link also has to operate on a frequency that is different than any of the other data links, so that there is
never interference of the safety pilot's control. A 72MHz radio and receiver were chosen because it operates
on a legal, common remote control (RC) frequency that is known for being able to achieve adequate range. The
final radio and module were chosen to be a Futaba T9 Cap and FP-TK-FM, respectively. The chosen radio
module is the most powerful, legal 72MHz transmitter currently on the market. The choice of the radio and
module is further discussed in the "Safety" section.
The aircraft’s RC receiver can either use Pulse Position Modulation (PPM) or Pulse Coded Modulation (PCM).
PPM signal has the advantage that degradation in the RC link can be determined by evaluating jitter; however
PCM will simply fail without warning once it has gone out of RC range. PPM was selected as the modulation for
all RC transmissions.
Two different Manual override methods were considered an external multiplexer or using the YAPA’s PPM
input. The two systems have a fundamental difference; first the multiplexer will not indicate loss in RC signal
and cannot monitor RC signal strength. The Paparazzi can estimate the signal strength from the PPM and upon
loss of link can automatically return home or perform any routine of preprogrammed actions.
With initial flight testing the multiplexer was used; however, once the paparazzi was evaluated as a stable
platform, the team transitioned to testing the YAPA’s onboard PPM capabilities.
Camera/Camera Data Link
The team decided not to have a gimballing camera system and instead use to cameras to overcome the
limitation of the cameras field of view. A pair of 1 mega pixel Axis M1054's cameras are used as part of the
imaging system. A breakdown of the cameras specifics is given in table 4. The cameras are mounted such that
their field of view will overlap approximately 25 degrees. The cameras will be able to see 59 degrees off either
side. Using two cameras allow the team to increase the scan rate and reduce the amount of time the plane has
to be in the air. By not having a gimbal system on the plane the team reduces the risk of mechanical failure
that could compromise the mission. Fixed camera also reduce the complexity of the imaging operator’s tasks
by allowing the operator to focus solely on spotting and processing targets and not controlling a gimballing
system.
Table 4: Axis Camera Data Specs
AXIS M1054
Image sensor
Lens
Field of view
Light sensitivity
Shutter time
Resolution
Frame rate
Video streaming
Progressive scan RGB CMOS
2.9 mm
84 degrees
100000 lux
1/24500 to 1/6
1280x800 to 160x90
30 fps (Motion JPEG and H.264)
H.264 ; Motion JPEG ; MPEG-4
The camera data link solution chosen for this system is the Ubiquity 2.4 GHz Bullet. Table 5 below shows specs
for Ubiquity 2.4 Bullet. The Ubiquity Bullets are paired with a Hyperlink 2.4GHz YAGI antenna on the ground
that is used to receive video stream and photos. The Hyperlink antenna provides the team with wide beam
width reducing the likelihood that the video stream will be lost if the antenna is not directly pointed at the
plane.
Table 5: Ubiquity M2 Bullet
Ubiquity
Processor Specs
Memory Information
Networking Interface
RF Connector
Enclosure size
Weight
Enclosure
Characteristics
Power Method
Operating Temperature
Operating Humidity
Shock and Vibration
Max Power
consumption
Atheros MIPS 24KC, 400MHZ
32MB SDRAM, 8MB Flash
1 x 10/100 Base-TX (Cat 5, RJ-45)
Ethernet
Integrated N-type Male Jack
15.2x3.7x3.1 cm (length width height)
.18 kg
Outdoor UV Stabilized Plastic
24 V
Passive Power over Ethernet
40C to 80C
5 to 95% Condensing
7 Watts
2.4GHz File Retrieval System
Extra points will be awarded to retrieve the file from on ground. In order to do so a system which introduces
the least complexity to operations should be employed. There are two options which employ technology
already in use by Team Blackbird.
An additional 2.4GHz Ubiquity bullet modem will be used to automatically connect to the 2.4GHz ground
network and act as a bridge allowing an operator to manually access the file. This is the most reliable solution
which uses a well-tested hardware and RF combination which has similar reliability to the video data link.
Blackbird Airframe: "Agent"
After discussing the payload system design and all potential backup systems including larger antenna, extra
batteries, switches, controller boards and cameras, the team's airframe designer and aerodynamicist used the
potential payload options to design a solution which will fit all possibilities.
Figure 4: Render of“Agent Blue” Airframe
The airframe was selected in response to the following criteria the ability to carry a DSLR camera payload,
ability to be hand launched and a highly stable and slow platform.
Figure 5: XFLR 6 Model
The aircraft was designed using the digital DATCOM methodology in conjunction with XFLR 6,seen in Figure 5,
and Surfaces analysis. A 5/8 scale prototype, “Orange”, was produced which verified the aircraft’s stability and
was extensively tested. Although the aircraft has excellent phugoid and dutch roll dampening, the weight and
balance of the aircraft may cause the aircraft to become spirally divergent, based on the Eigen Value Pole
placement, as seen in Figure 6.
Figure 6: Eigen Value Pole Placement of Longitudinal (Left) and Lateral Dynamic Modes (Right)
A low aspect ratio swept wing planform was selected in order fit the deepest potential payload, a canon DSLR
which was 4”tall with the lens. As a result a 20% thick airfoil is used in the root and spans approximately 32” of
the wing span, this allowed for an extremely roomy 32” x 10” x 4 cavity which can be used to a wide variety of
components, should the system change during testing.
The system is hand launched and can be recovered via belly landing; the aircraft possesses a folding propeller
which folds avoiding breakages. A general overview of the aircrafts dimensions are in Table 6, seen below.
Table 6: Aircraft Parameters
Gross Weight
Wing Span
Aspect Ratio
Length
Battery Type
Construction
Color Schemes
Maximum Endurance
Stall Speed
Cruise Speed
13.5 lb. (Grey) 11.5lb. (Blue)
80”
4
61”
2-3 4S Lithium Polymer or 3 5S A123
Carbon And Fiberglass Reinforced EPS Foam
#1 Orange and Grey, #2 White and Blue
40+ min
< 15 KCAS
25-35 KIAS
The aircraft can be broken into 4 distinct sections to allow for the complete aircraft to be stowed within the
trunk of a small sedan for flight tests.
Figure 7: Right: Fully assembled aircraft Left: aircraft stowed in Vehicle,
After performing flight tests, the team noticed that the motor/prop combination was an insufficient source of
thrust at takeoff and at cruise. New prop/motor combinations were analyzed using the "excel sheet" Prop
Power Calculator. Wind tunnel tests were also performed to verify the results of the Prop Power Calculator's
estimates at velocities of interest. These results can be seen in the “Test and Evaluations “section.
Flight testing of the first full scale aircraft “Grey” also showed a sudden loss of lateral stability and flight control
at high angles of attack. This characteristic is often referred to as tip stall. The safety pilot was instructed to
perform a few maneuvers. It was observed that the plane also experienced tip stall under flight conditions with
significant side slip, or crosswind. Agent’s wing planform resembles the wing-bodies of flying wings, name...
was referenced. Two solutions were provided by this book.
The first was to move the CG forward which reduces the maximum angle of attack attained in sudden pitch up.
This was impractical since the only way to do so was to add ballast in the nose and would simply make the
problem less prevalent. The second solution was to add wing fences. The wing fences effectively reduced the
wing’s aspect ratio at high angles of attack delaying stall and eliminating wing tip stall by generating vortices at
the half span. This can clearly be heard at high angles of attack as a loud hiss.
Figure 8: Wing Fences at Half Span Which Eliminated Wingtip Stall
The Aircraft also has a stall speed which is far lower than its theoretical 18kt for a 13.5lb aircraft, in flight
testing the stall was lower than 15kt. Which can likely by attributed to strong vortices produced by the
planform’s low aspect ratio and wing fences.
III.
Failure Mode Analysis
Failure Mode Analysis for the Blackbird system is very particular due to the system design and mission
requirements. Each sub-system is dependent upon another sub-system. At least three sub-systems must
remain in working in order before the simplest mission requirements is met. The interdependent nature of the
overall system can be seen in the Failure Flow Diagram, below.
Figure 9: Failure Flow Diagram
Due to the fact that all mission requirements rely on flight, the airframe is the most important of the subsystems. Its failure would render all other systems useless and would be catastrophic for the mission. The
mission also requires manual control and proper termination. These requirements make the RC system the
second most important sub-system. Its failure would render every system other than the airframe useless and
would be cause for automatic disqualification. It could be argued that a failed RC link would also cause the
airframe to be destroyed. It is very likely, though, that due to the stabilizing aerodynamics of the plane, its low
stall speed and material design, that the plane would be flight ready immediately after an RC failure assuming
it struck no obstacles during its flight termination.
The mission requires autonomous navigation, searching as well as real-time system parameter reports to the
judges. This ranks the autopilot and ground control station software third and fourth, respectively, in subsystem importance. If the autopilot failed, the plane would lose autonomy, ending the mission. If the ground
station software failed, the judges would require the plane to regain communications with a working ground
station or terminate the flight.
The mission requires the location of ground targets from the air. This requires the camera and camera data link
systems. The camera is useless without its data link; therefore, the camera data link and camera systems are
ranked fifth and sixth, respectively, in importance. Finally the least important system has been determined to
be the targeting software. Although a large portion of mission performance is based on this sub-system
working properly, no other systems are dependent upon it. The fact that this system was labeled least
important shows how important it is that the entire system work properly in order to complete a mission.
Based on past experiences, the team spent limited time analyzing potential failures and solutions to those
failures. Instead the group employed their dynamic systems engineering approach and had backup sub-systems
in mind for any high risk solutions. As for the lower risk potential incidents, the team has taken a field testing
approach as opposed to an analytical and lab testing approach. Blackbird, throughout the years, has noticed
that if a risk is not obvious (classified as high risk or catastrophic), it is likely that flight tests and practice
missions will provide more insight to the probability of certain risks and even identify new, unforeseen risks.
This method has proven true as can be seen in the “Test and Evaluation” section in which it can be seen that all
of the problems identified were identified during field testing or flight tests and were resolved using the
backup system or small modifications.
IV.
Test and Evaluation Results
Autopilot/DataLink
During the first few flight tests with the airframe and integrated Paparazzi, the team experienced IMU failures
on multiple occasions. It appeared that the IMU would quit reporting when the throttle was wide open. The
first assumption was that the EMF from the motor was causing enough interference for the I2C IMU to quit.
Wire shielding was then added to the motor wires as well as the IMU wires. The problem persisted on the
following flight test.
After some research, a lab experiment showed that when the 72MHz signal was transmitted horizontally with
respect to the IMU, the input voltage oscillated from ± 1.5V with respect to the 3V baseline voltage. It was
discovered that a transmission signal could alter, not only signal voltages, but input voltages as well. Online
research and consultation with professors showed that this problem could be solved by soldering the IMU
directly to the Paparazzi board. The rationale behind this solution is that the board's power was less disturbed
by the radio signal because it drew more current. The IMU power, though, was able to drop below the power
provided by the autopilot board because it was has a low current draw. By decreasing the length of the IMU
power cable to, essentially zero, the team was able to adequately decrease the transmitter's effect on the IMU
input voltage.
Once the IMU became a reliable component, tuning began on the autopilot. One of the main advantages of the
Paparazzi is that its gains are originally set such that it will stabilize a plane without any custom tuning. This
proved true during our first autopilot test. When the plane was “turned over” to the autopilot, it reacted by
stabilizing the plane and commanding low surface deflections, minimizing the potential for a crash. After a few
test flights, Agent Grey was able to be tuned to react to waypoints and flight plans that would be adequate for
the competition's navigation, search and surveillance missions.
RC Transmitter/Receiver
Originally, a Hitec Spectra Pro 72MHz module was chosen as Blackbird's transmitter module. During field range
tests, the module proved inadequate due to its range of less than 0.25mi. Upon interference, a weak RC link
can render an aircraft into an uncontrollable and dangerous item posing risk to persons and property.
After referencing the FCCID number on the FCC's website, the team discovered that the module had
insufficient output power of 0.026W. Further research showed that there is a Futaba module that has 0.7W
output power. A few available modules and their output powers are shown in Table 7, below. It was a clear
choice to purchase the higher power module for testing. Ground testing on this module showed that it
produced a reliable signal with no servo jitter at 0.75 miles with a large building between the transmitter and
receiver. Over 20 hours of flight operations have been executed using this module with no report of
interference/servo jitter.
Table 7: Transmitter output powers.
Module
Hitec Spectra Pro
Futaba TK-FM
Futaba TP-TM
Hitec STD
Futaba TP-FSM
Output Power
26mW
700mW
450mW
110mW
188mW
The aircraft’s RC receiver can either use Pulse Position Modulation (PPM) or Pulse Coded Modulation (PCM).
PPM signal has the advantage that degradation in the RC link can be determined by evaluating jitter; however
PCM will simply fail without warning once it has gone out of RC range. PPM was selected as the modulation for
all RC transmissions.
Camera/Camera Data Link
Blackbird has bench tested two surveillance system options. The first being a low altitude, high velocity, low
resolution solution. The second is a high altitude, low velocity, high resolution solution. Only the first, though,
has been field tested. There was discussion between team members as to which system would be used. It was
a debate whether the complexity of the higher resolution system would be worth the benefit to this specific
mission. An analysis was done between the two camera systems at various altitudes Table 8 to determine what
aerodynamic characteristics the airframe would require.
Table 8: Camera Operating Conditions
Camera
Canon DSLR
Axis 1MP
Altitude (ft)
700.00
300.00
Velocity (ft/s)
25.00
35.00
Target Size (ft)
4.00
4.00
Using the expected download or streaming data speeds of both cameras, each system was given an optimal
altitude and velocity range. These two performance characteristics Table 9 were analyzed to ensure that they
were reasonable for an airframe that could incorporate these systems.
Table 9: Camera technical parameters
Specifications
Horizontal
Vertical
Camera
Mega
Pixels
Shutter
Time (s)
Aspect
Ratio
Resolution
(pixels)
View Angle
(deg)
Resolution
(pixels)
View Angle
(deg)
DSLR 18MP
17.92
0.0001
1.67
5184.00
50.00
3456.00
30.00
Axis 1MP
1.00
0.0100
1.78
1280.00
75.00
720.00
42.19
Since both systems were feasible, a design analysis was done to determine the resolution of targets and the
speed at which the ground could be scanned using each system. Table 10, below, shows the results of the
camera systems that have been compared.
Table 10: Camera Analysis results
Camera
Pixels per Target
Pixels per Inch
Performance
Horizontal Vertical Horizontal Vertical Scan Rate (ft2/s) Image Blur (in)
18 MP DSLR
68
56
1.42
1.15
13097
0.05
Axis 1MP
21
16
0.43
0.34
12032
7.01
Based on the data above, it was determined that, although, the high resolution option would be ideal, it was
not worth the added complexity for this year's competition. The added complexity includes an onboard
computer for image processing, attitude/picture time sync, decreased accuracy of target location due to quick
attitude changes at such a high altitude and that the team did not have the software personnel to guarantee a
completed system.
As mentioned in the “System Design” section, the original video link was to be a 5.8GHz transmitter/receiver.
The team had previously used a 2.4GHz video link and was looking to change to a 5.8GHz link in order to
prevent creating a network on the plane itself. In order to prove that the 5.8GHz system could work as well as
the 2.4GHz system, range tests were designed.
The range test of the two systems was to take place on a long stretch of road with little traffic and line of sight
between the transmitter and receiver. Although the choice to go with the low altitude, high velocity, and lower
resolution surveillance system had already been made, the range test was designed to provide valid data for
the current system as well as the anticipated higher resolution system. Since video is typically transmitted via
UDP and images are typically transmitted via TCP, the test would incorporate both transmission protocols.
Unfortunately, the 5.8GHz equipment did not perform to its' expected range and quality as expected from
Ubiquiti's data sheets. The results of the range test are presented in Figure 10 and Figure 11, below.
35000
30000
Bandwidth
25000
20000
Run One
15000
Run two
10000
Run Three
5000
0
0.5
1
1.5
Miles
Figure 10: TCP Range Test
200000
180000
160000
Bandwidth
140000
120000
100000
100 mb/sec
80000
60000
50 mb/sec
40000
20000
0
0.5
1
1.5
Miles
Figure 11: UDP Range Test
As part of Blackbird's agile and dynamic design method, the system was adaptable to work with the planned
5.8GHZ or previously implemented 2.4GHz backup video link. The main change to the system, as a whole, was
that the file retrieval system would have to operate on the same frequency as the camera data link.
An additional concern was brought up during flight testing by the ground station operators. They reported that
it was difficult to keep the ground antenna pointed at the plane so that it transmitted quality video. Research
was done on higher gain antennas and a 12dBi Yagi antenna was purchased with a similar gain pattern to the
tested patch antenna. The antenna pattern is shown in Figure 12, on the following page.
Figure 12: Antenna Gain Patterns of 12dBi Yagi Antenna
This higher gain antenna has not been fully range tested, but has been observed to outperform the 2.4GHz
system that was used by Blackbird in the past.
Payload Workflow
Figure 13: Lab Test Bench
Full simulated missions were carried out in lab by using a camera to view a simulated live stream form a
computer using Google Earth, as seen above in Figure 13. This is done with a working autopilot in Software in
the Loop simulation. By testing several different application layouts using this method the following workflow
and layouts were selected.
Figure 14: Payload Monitor Overview
The Payload monitor views the live incoming UDP streams using open CV in a wx-widgets python window from
the two separate cameras on an Ubuntu OS machine. When the operator presses the capture button a full
resolution Jpeg photograph is requested from a camera and paired with the aircraft’s current attitude and GPS
Coordinates. This photo is then given a unique name and saved in folder that is synchronized across the ground
station network using Rsync.
Figure 15: Target Classifier overview
The viewer is a Cocoa application on a Macintosh OSX machine. The captured Images actively update and can
be selected for viewing. When a target is identified the user simply clicks the target and drags the mouse in the
orientation of the target, the user then types the letter the software automatically identifies the colors clicked
and assigns a generic color name. Using a ground plane transformation equation the target‘s GPS coordinates
are Identified. Repeat Targets are automatically grouped and the best image is selected by the user. When the
Target Classifier’s user is satisfied the targets are then exported to the format identified by the rules.
V.
Mission/Flight Operations
Preflight
The first stage of pre-flight the system is powered without radio transmission allowing the aircraft to obtain a
GPS lock without starting the mission. Once the timer starts the crew chief immediately powers on the radios
allowing the ground station operators to connect via the wireless RF link to the aircraft. At this point the crew
chief and secondary payload operator wait for a go-ahead. After the go-ahead is given the secondary operator
and crew chief launch the aircraft.
Flight
The immediately after takeoff the aircraft will go to its 200ft standby circular flight block waiting for
instructions from the ground control operator to initiate. Waypoint searches the autopilot is next instructed to
into a waypoint course. This course is listed as a new block of waypoints in the ground control station.
After the waypoint course is completed the aircraft will be commanded to a flight block to initiate off path
target search. The payload operators will identify and classify the off path target as the actionable intelligence.
The team expects to see the off path target with the current camera layout. The aircraft will return to standby
and be commanded to go to enter the search area. There are three flight blocks which may be for the target
search, the first is a target sweep, second a road and runway sweep and the final is a variation of the second.
The aircraft is then commanded to enter the extended search area where a second group of similar flight
blocks are used. The final two Flight blocks pertain to the popup target. The popup target will be assigned two
flight blocks each different routes. The wifi challenge will be a 200ft circle until the secondary payload operator
can connect and retrieve the file.
Landing
Landing is achieved by commanding the aircraft to calculated glide slope for two waypoints before landing. The
aircraft kill’s its motor for the after the first waypoint. Once the aircraft has landed the Ground control
operator will command the aircraft to be killed, then the Crew Chief will un-power all modems on the aircraft
and Motor Controller. Once all transmissions are ended mission ends.
Expected Outcomes
With the current design of the system the team expects to be able to maneuver the waypoints and be able to
spot 80% percent of the targets including off path targets in the first search area and relay their location to
within 100 feet. It is expected that with the current imaging system the team will be able to identify four out of
five of the targets characteristics those been background color, alpha numeric color, alpha numeric and
orientation of target. It is expected that the system will be able to locate pop-up targets due to past successes
and an improved camera system. The system is also expected to be able to download the file from the network
in the third search area. The flight is expected to be done fully autonomous from take-off to landing.
VI.
Safety
System Safety
Safety is the most important mission requirement. In order to conduct a safe mission, the plane will remain
below the maximum weight covered by AMA policy, fly at velocities less than 100KIAS and fly below 750 ft.
MSL to minimize energy available to cause damage or injury. The plane will also fly above a minimum altitude
of 100 ft. MSL so that the safety pilot has time to react in the event that manual override is necessary. The
plane must be able to controlled by a safety pilot at any point during the mission. Additionally, the UAS must
be able to accommodate the flight termination requirements stated in the 2012 SUAS rules document.
The UAS must be prepared as to avoid an accident, to the best of the team's ability. This entails securing all
attachments and parts, having bright colors on the bottom of the plane that are easily seen by the safety pilot
and complying with the 2007 AMA National Model Aircraft Safety Code. Additional flight readiness procedures
are detailed in the "Preflight" section within the "Flight/Mission Operations" section, below.
In the event of an accidental ground interaction, precautions were taken to minimize collateral damage such as
a fire. The plane was designed to be able to withstand hard landings. This, combined with the plane's natural
stability and low stall speed give the team confidence in the UAS's safety in the event of a flight termination or
crash. Additionally, the team has bright colored batteries that can be easily located if they are dislodged from
the fuselage in a crash.
Operational Safety
The flight crew is in charge of all safety procedures and will enforce safety policies and carry out checklist that
will ensure the safety of the system as well as the safety of all people and property. The flight crew will also be
tasked with keeping all noise to a minimum so that the spotter, flight director, and safety pilot can
communicate flawlessly.
Preflight Procedure
Preflight checklist are performed by the crew chief to ensure that the aircraft is flight ready and poses no risk
to bystanders and property. The checklist has the crew chief asses the aircraft structural frame, propellers
structural integrity and check that all control surface hinges are not obstructed. Before any electronics are
turned on the crew chief must also clear the flight line of any personal not part of the flight line crew which
consist of the safety pilot, Throwers. The flight director will convene with the flight line crew after everyone has
been cleared to update the flight line crew on the flight plan. After the flight director has cleared the flight line
the crew chief will begin the pre-flight readiness checklist.
During Heads up Flight
The safety pilot is in charge spotting for the flight director who will be operating the autopilot. No one on the
team is allowed to speak to either the safety pilot or flight director except for the target imaging operator. A
member of the flight crew will man the antenna for imaging while the rest of the flight crew is in charge of
keeping an eye on the aircraft while it is in the air as well as keeping the flight line clear. Although the safety
pilot may take over the plane whenever he feels it is not in control of the flight director, The flight director has
final say on where the aircraft will fly and whether it will be landed or terminated.
Landing
Once the flight director has decided to land the aircraft flight crew must ensure the flight line is clear and
communicate to bystanders where the plane will be coming from and where it will land. Once it has touched
ground the flight crew will disarm the engine and the crew chief will carry the plane back to the judges for
observation.
I.
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