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ŀNorth Carolina State University Aerial Robotics Club

Monday, May 24, 2010

The North Carolina State Aerial Robotics Club is entering the ArcWulf Unmanned

Aircraft System (UAS) into the 2010 Association for Unmanned Vehicle Systems

International (AUVSI) Student UAS competition. ArcWulf is a 26-pound fixed wing

aircraft with an 8 foot wingspan. It is controlled using a commercial off-the-shelf (COTS)

Piccolo LT autopilot and an imagery payload consisting of a flight computer and a Nikon

D60 camera. The Piccolo, flight computer and camera run on a 11.1V Lithium Polymer

(LiPo) battery and the control surfaces run off a 4.8V Nickel Metal Hydride (NiMH)

batteries. A 4 stroke glow fuel engine is used for the engine to power the 26 pound

ArcWulf. The camera orientation is nadir pointed by the autopilot, while the flight

computer handles the camera control. The imagery system provides high-resolution still

imagery of the search area with a geo-referenced downlink to a trailer based ground

station for real-time data analysis. A safety pilot uses 2.4 GHz Spektrum RC

communication system for manual control of the aircraft if necessary, while the autopilot

command and control link operates at 900 MHz. The imagery link uses the 5 GHz 802.11a

communication standard. Operational procedures are used to keep all personnel safe

during missions.

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North Carolina State University Aerial Robotics Club 2

Table of Contents

I. System Design Overview ............................................................................................................. 3

II. Vehicle ...................................................................................................................................... 4

A. Engine .................................................................................................................................................................. 4

B. Electrical System .................................................................................................................................................. 5

C. Batteries ............................................................................................................................................................... 5

III. Autopilot ................................................................................................................................... 5

A. Flight Algorithm .................................................................................................................................................. 6

B. Peripherals ............................................................................................................................................................ 6

C. Safety Switch ....................................................................................................................................................... 6

D. Flight Path ............................................................................................................................................................ 7

E. Gimbal Control Features ...................................................................................................................................... 7

IV. Imagery .................................................................................................................................... 7

A. Imagery System Overview ................................................................................................................................... 7

B. Onboard Imagery System Workflow ................................................................................................................... 8

C. Camera ................................................................................................................................................................. 8

D. Gimbal.................................................................................................................................................................. 8

E. Onboard Computer ............................................................................................................................................... 9

F. Autonomous Tracking Antenna ........................................................................................................................... 9

G. Ground Station Imagery Workflow...................................................................................................................... 9

H. Imagery Viewer Overview ................................................................................................................................. 10

I. Imagery Viewer Details ..................................................................................................................................... 11

V. Mission Planning ...................................................................................................................... 11

VI. Operations............................................................................................................................... 12

A. Safety ................................................................................................................................................................. 12

B. Flight Line Crew ................................................................................................................................................ 13

C. Trailer Crew ....................................................................................................................................................... 13

VII. Flight Testing and Evaluation .................................................................................................... 13

Appendix 1- Aircraft Systems Communication Flow ............................................................................ 15

Appendix 2-Image Collection and Data Processing Pipeline ................................................................... 16

Appendix 3-Flight Line Setup ............................................................................................................ 17

Appendix 4-Go/No-Go Criteria .......................................................................................................... 18

Appendix 5-Failure Mode Effect Analysis ........................................................................................... 19


I. System Design Overview

The NCSU Aerial Robotics club began with the 8’ Telemaster design because it has proven to be

simple to build, easy to fly, and a stable imagery platform. The fuselage has been significantly

widened and strengthened to fulfill the derived requirement of carrying a 10-pound systems

payload. The relatively simple construction of the Telemaster allows for timely repairs or

construction of a backup aircraft should a crash occur. The landing gear is modified and designed

to fail prior to causing permanent damage to the fuselage in the event of a hard landing.

The autopilot portion of any autonomous vehicle is often the most important for ensuring reliable

and safe operation of the vehicle. The Piccolo LT autopilot was selected for its reliability, ease of

use and its ability to meet all autonomous mission goals.

Safety was a critical factor in the design and construction of ArcWulf. Failure Mode Effect

Analysis (FMEA) was conducted to help improve standard operating procedures. Redundant

systems are used for telemetry and manual control of the aircraft. Finally, the system was

designed to be as reusable and robust as possible with the understanding that hard landings

would likely occur.

The imagery system was redesigned from previous years to better fulfill mission objectives.

Since the targets are not moving, still photography is used as it provides superior resolution to

what could be achieved through full motion video. A high resolution Digital Single-Lens Reflex

(DSLR) camera mounted in a custom two-axis, orthorectifying gimbal was chosen as the basis

for the imagery platform. The gimbal is designed to point off-axis of nadir to capture targets that

are not directly under the path of flight. It was determined that a flight computer based on readily

available, reliable and inexpensive ITX form factor hardware would be used to collect the

images onboard the aircraft and send them to the ground. The images and embedded telemetry

would be sent to the ground over a fast, high-powered 5 GHz 802.11a wireless link capable of

rapidly transmitting high resolution photos. An auto-tracking antenna is installed on the ground

to maintain high wireless signal strength.

The entire software library was rebuilt for higher performance and ease of use. A multi-pronged

software system was built allowing one main program to display the images while several

smaller programs perform enhancement tasks on the pictures. This allowed additional features to

be added in a modular fashion, reducing the time spent developing. The resulting software is

operable on a high-end desktop, but with the added capability of being distributed across several

laptops if available.

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II. Vehicle

Figure 1 – ArcWulf Front Fuselage Layout

The fuselage has been widened and made taller than stock to add clearance between the ground

and the camera lens, and a 5.5”x 11” x 4” camera bay has been cut in the fuselage to allow for

the external mounting of the gimbal and camera. A carbon fiber spar has been added to the stock

eight foot wing to account for increased wing loading due to the added payload weight. The wing

brace that attaches the wing to the fuselage is now removable for quick and easy access to the

payload. An Ethernet port is installed in the fuselage to allow quick access to the computer for

troubleshooting and fast download of any remaining images in the queue once the plane has

landed. The landing gear has been changed from the stock tail dragger configuration to a tricycle

landing gear to improve ground handling. As a result of this change, the C.G has moved further

forward to balance the aircraft while on the ground. The main landing gear is constructed of 1/8”

thick 3003 aluminum sheet for dampening on landing. The soft temper of the alloy allows the

landing gear to bend and subsequently fail prior to the fuselage in cases of hard landings. Finally,

the engine and all payload components are vibration mounted to reduce the effects of piston

engine vibration.

Figure 2 – Removable Wing Brace (Right), Main Landing Gear and Ethernet Port (Left)

A. Engine

The NCSU UAS uses a four-stroke O.S FS120III engine in conjunction with a 24oz fuel tank. A

four-stroke engine was chosen over the two-stroke engine used in previous years because of the

added reliability, lessened vibration, and higher takeoff and landing performance. The FS120III


engine also provides 38% greater fuel economy than comparable two-stroke engines, translating

to a 25 minutes flight time with a 5-minute reserve. A tachometer is now installed on the engine

to provide the safety pilot enough warning to land the plane should the engine fail mid-flight.

The tachometer also aids the Piccolo in controlling airspeed when auto-landing the ArcWulf.

B. Electrical System

The NCSU ArcWulf relies on two primary power buses, a 12 V bus and a 5 V bus. The 5 V bus

is exclusively used to power the control surface servos, R/C receiver, and safety switch. The

onboard computer and camera payload is powered by the 12 V bus, thereby isolating payload

power from the critical R/C power bus. Linear voltage regulators are used to convert 12 V power

to 5 V power for gimbal payload servos. A power distribution unit is located in the tail section of

the aircraft. The switch panel in the tail allows the operators to switch easily between ground

power and flight power and turn individual system components on and off without having to

reach near the spinning propeller. All internal connections are made using locking and keyed

connectors that have proved reliable over hundreds of flight test hours at NCSU.

C. Batteries

ArcWulf relies on two batteries for flight operations. A 4.8V, 2000 mAh Nickel-Metal Hydride

battery powers the 5 V bus while an 11.1 V, 5000 mAh Lithium Polymer battery powers the 12

V payload bus. Our system has demonstrated the ability to provide over 45 minutes of battery

life across both power rails under flight conditions. Battery voltages are monitored by the

autopilot operator during flight and the plane is landed if the voltage drops below a safety

threshold.

III. Autopilot

NCSU’s autopilot, a Cloud Cap Technology’s Piccolo LT, is capable of the following:

• Navigating by GPS waypoints

• Receiving commands mid-flight

• Providing telemetry to peripherals

• Providing telemetry to ground station

Three years of experience with this autopilot has shown the Piccolo to be a reliable and rugged

component that is easy to tune for the Telemaster aircraft and performs the required mission

well.


A. Flight Algorithm

The Piccolo LT uses a six-degree of freedom inertial measurement unit, global positioning

system, and air pressure sensors to maintain good reference to the aircraft attitude during flight.

The Piccolo controls the aircraft based on aircraft geometry and gains provided by the NCSU

autopilot operator. Measurement of the geometry is done in the lab, while gains are calibrated

during flight tests after base assessments using the provided AVL modeling software. The design

of the aircraft produces stable flight characteristics that expedite the tuning of the Piccolo. Once

properly tuned, the Piccolo LT achieves stable flight characteristics that improve the ability of

the Telemaster to serve as a solid and stable imagery platform.

B. Peripherals

The autopilot system interfaces with both the aircraft and imagery sub-systems. This interface is

simplified through the use of a wiring harness that allows a single plug to connect the autopilot

to the aircraft. The antennas and pitot-static tubes are connected separately. The GPS antenna is

mounted on the tail boom of the aircraft separating it from interference with a ground plane to

increase the antenna’s sensitivity and RFI resistance. Pitot and static probes are mounted 22” out

on the left and right wings respectively and several inches away from the leading edge of the

wing to avoid the slipstream of the propeller. A 900 MHz telemetry antenna is connected to the

Piccolo and exits the top of the aircraft. This half-wave antenna improves sensitivity over the

quarter-wave antenna used in previous years. Telemetry from the Piccolo is transmitted over the

900 MHz link to the Cloud Cap ground station. The ground station makes the telemetry available

across the network to provide support for the autonomous tracking antenna.

A magnetometer provides supplemental information on the heading of the aircraft. This enables

the aircraft to determine its heading while stationary and determine actual heading of the aircraft

rather than the track of the aircraft. This capability allows the aircraft to perform wheeled take-

off and landing and allows imagery software to correct for crabbing in the photographs during

windy conditions.

C. Safety Switch

Servo commands coming from the autopilot are fed into a safety switch box. This box is

controlled by the RC link that switches control of the aircraft between the autopilot and the

safety pilot. The primary function of the safety switch is to allow the human pilot to take control

of the plane regardless of the autopilot’s status. A system schematic for this setup is located in

Appendix 1. In the event of a loss of connection to the plane for 30 seconds, the safety switch

defaults the control surfaces and throttle to preset failsafe conditions.


D. Flight Path

The Piccolo is controlled by the Piccolo Command Center run on a computer in the ground

station trailer. This software easily allows the operator to designate GPS waypoints as well as

view telemetry from the aircraft. Waypoints can be added, removed, or moved during flight to

change the flight path as desired. It also allows for Software-in-the-Loop (SIL) and Hardware-in-

the-Loop (HIL) simulation. Both of the functions are valuable in the training of operators and the

verification of the Piccolo control gains.

E. Gimbal Control Features

After some research, it was determined that a simple plug-in could be written to control the

gimbal for the DSLR camera.

Figure 3 – Camera Gimbal Plug-in Interface

Figure 3 above shows the user interface for the camera gimbal plug-in. The “Stow” button

commands the gimbal to a position that puts the lens as far from the ground as possible to help

protect it during landings. The “Auto-Stow” feature automatically repositions the gimbal to this

“farthest from ground” position when the aircraft is in a “non-flying” state as defined by the

Piccolo and points the camera nadir while in flight mode. A non-flying state is defined by the

Piccolo as preflight, take-off, and landing. The Nadir button points the camera straight down for

taking orthographic pictures of the ground and is the primary mode used for imaging the search

area. The arrow gives the user a graphical feedback of the current roll of the gimbal relative to

the earth. The Angle and Offset features allow for photographing an off-center target. Using the

Angle feature keeps the camera at a constant angle offset with respect to its normal nadir

condition. The Orbit feature allows simple targeting of the “Pop-up” target when orbited by the

vehicle by keeping the camera aimed at a single point on the ground. These features are

sufficient for all competition and testing purposes.

IV. Imagery

A. Imagery System Overview

The basic goal of the NCSU imagery system is to acquire the best possible photos of the mission

area and transmit them to the ground station in real time. On the ground, our operators are


equipped with custom tools for imagery analysis, which enable them to rapidly search for and

identify targets. The system is designed for redundancy and reliability, with care taken to ensure

that the system continues to function with the failure of certain error-prone systems such as the

real-time data transmission link. The following subsections detail each of the components of the

onboard and ground-based systems.

B. Onboard Imagery System Workflow

The onboard portion of the NCSU imagery system consists of a high-resolution digital still

camera, an onboard computer which provides the interface between the camera, autopilot, and a

high-powered 5 GHz 802.11a wireless networking card, and a stabilizing gimbal mount. The

camera is controlled over a USB 2.0 connection using the PTP protocol, while autopilot

telemetry is received from the payload serial port of the Piccolo autopilot. Onboard software

commands the camera to take a photo and downloads the image data. Next, the software embeds

the latest autopilot telemetry packet into the image header and transmits the image to a ground

station computer connected to the wireless network. Image acquisition and transmission are

executed in parallel. Each image is also archived onboard to a Solid State Disk, ensuring that the

imagery data will be recorded regardless of the performance of the wireless link.

C. Camera

The NCSU imagery system is built around a Nikon D60 Digital Single Lens Reflex (DSLR)

camera. The DSLR design and quality lens enable faster shutter speeds and improved image

quality over smaller cameras with the same sensor resolution. At the camera’s native resolution

of 10.2 megapixels (3872 x 2592 pixels) the camera delivers more than 36 times more pixels

across the image compared to a 640x480 Sony Block Camera or webcam.

D. Gimbal

The D60 is mounted in a stabilized nadir-pointing camera mount. It was designed in SolidWorks

and printed using the university’s 3D printer to reduce the overall weight of the design, decrease

the time needed to construct, and increase the precision of the final product. This camera mount

primarily functions to point the camera towards the ground, reducing perspective distortion

caused by changes in aircraft attitude. The gimbal is vibration mounted to the fuselage using

rubber isolators. The gimbal servos are driven directly by the Piccolo, using the Piccolo

Command Center plug-in detailed above to enable ‘stare’, ‘stow’, and ‘roll’ modes.

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Figure 4 – Gimbal Mount SolidWorks Model

E. Onboard Computer

The onboard computer was selected to provide a compromise between performance, peripheral

availability, size, and power requirements. The final configuration is based on an Intel Atom

Dual Core processor operating at 1.6 GHz. An Ubiquiti XtremeRange5 5 GHz long-range

802.11a wireless card provides 25 dBi of transmit power through a 6 dBi omnidirectional

antenna. The 5 GHz frequency band was selected to provide sufficient frequency clearance from

the 900 MHz autopilot communication link and the 2.4 GHz RC link. A side benefit is the

availability of smaller high-gain antennas for both the ground and airborne systems. Flight tests

indicate a nominal data rate of approximately 10 Mb/s can be maintained throughout a

competition flight profile, resulting in a download rate of about one image every three seconds.

All transmissions between the aircraft and ground are conducted using the SSH2 protocol.

Although there is a small computational penalty for encrypting traffic, the benefits of enhanced

data security is high enough to our group that encryption is seen as a benefit and is included in

the data transfer.

F. Autonomous Tracking Antenna

To maintain a Wi-Fi link with the plane while it is in motion, the ground station 16 dBi 5 GHz

antenna is mounted on a two-axis gimbal. The gimbal motors are connected to an h-bridge driver

which is controlled by an Atmega168 microcontroller. Two linear potentiometers are also

attached to each motor. The Atmega168 monitors the analog signals of the potentiometers to

determine the position of the antenna. An additional program running on a computer in the

trailer interfaces with the Atmega168 through a serial USB connection. This program was

written in C using the libproj4 library to compute the GPS location of the plane using telemetry

data being streamed over the network in the trailer. The plane’s GPS coordinates are then

converted to spherical coordinates, which are sent to the Atmega168. The Atmega168 then uses

a proportional–integral–derivative (PID) control interface comparing the old spherical

coordinates to the new. This PID allows the antenna to track the plane smoothly.


In the case of a networking failure, the auto-tracking antenna has a manual mode. In this mode,

the user controls the antenna with a modified remote control transmitter. The user has full range

of motion of the antenna, and this mode can be activated by simply flipping a switch on the

antenna. Overall, this system enables real-time tracking of the plane in flight and provides an

optimal link in order to download images as quickly as possible.

G. Ground Station Imagery Workflow

Once the images arrive on the ground, the receiving application corrects for lens distortion and

generates down-sampled (lower-resolution, smaller size) versions of the original image. The

images and associated metadata from the autopilot are inserted into a database. Both the images

and the database are stored on a four-disk redundant (RAID 1+0) array to guarantee performance

and reliability on the flight line. All intermediate images are stored to the database, including the

raw image as transmitted from the aircraft and the undistorted, down-sampled images. Images in

the database can be searched and sorted by flight, location, and any of the other telemetry fields

(altitude, aircraft attitude, etc.). This allows analysis applications to efficiently select the best

images for display to the user or compare images of the same scene between flights.

Figure 5 – (Left to Right) 10 MP (D60), 3 MP, 0.3 MP (Webcam)

H. Imagery Viewer Overview

The images and data are loaded by an imagery viewer application, which may be run on the same

machine as the database or on a separate machine connected to the server using gigabit-Ethernet.

The imagery viewer application provides the operator with the tools required to complete the key

identification and location tasks required by the mission goals. Images are displayed in their

approximate locations and orientations, as recorded by the autopilot telemetry packet at the time

the image was acquired. As new images are loaded into the database, the view is automatically

updated to include new images. The viewer provides familiar pan-zoom functionality, just as in

common commercial applications.


Figure 6 – Imagery Viewer Screenshot

Additional features are implemented to support the specific requirements of the competition.

These include target tagging and characteristic identification. Target tagging is the registration of

the GPS location and the orientation of the target. The interface allows characteristic

identification to be entered including shape, primary color, secondary color, and alphanumeric.

At the conclusion of the mission, the operator can then generate a document that includes all

targeting information as per the request for proposal.

I. Imagery Viewer Details

The images captured by the camera are very high-resolution. Modern high-end graphics

hardware is leveraged to display many images at the same time without sacrificing performance.

Manual imagery analysis is severely hampered by sluggish response in the viewer. Most of the

time this is caused by overflowing the image (texture) memory on the graphics card, resulting in

slow ‘swapping’ of data between the graphics card and system memory. Our software attempts

to minimize this problem by intelligently loading the minimum resolution image (from the

selection of down-sampled images stored on the server) required to display the scene. The

caching strategy uses the distance from the ‘eye point’ of the viewer to each individual image in

order to select the appropriate image to load. Each image is ranked in terms of priority, and a

limited number of high-resolution images are loaded in order of priority. If the operator zooms

out so that all images are visible, the viewer will load the smallest thumbnail version of each

image. As the operator zooms in towards an individual image, the viewer will begin to display

fewer higher-resolution images corresponding to the smaller viewing area selected.

V. Mission Planning

Mission planning for the NC State UAS is a flight-critical task developed prior to the aircraft

leaving the hangar. The system is prepared for flight and weather limits are verified. Once the

aircraft is at the field, the autopilot operator and flight test director verify the wind direction and

an autonomous takeoff and landing flight plan is created that accounts for proper runway usage.

The autopilot operator then discusses the mission with the imagery operators. Prior to takeoff,

the flight plan and runway direction are briefed with the entire mission team.


While the aircraft is in flight, waypoints are manually changed to accommodate search area

changes and to ensure adequate search area coverage. Also, changes may occur to the flight plan

in order to produce a more accurate autonomous landing pattern. All changes to the aircrafts

flight plan are relayed to the safety pilot via the flight test director prior to the aircraft being

commanded to execute the new parameters. In the event of an emergent waypoint, the autopilot

operator can command the aircraft to orbit the new waypoint. Upon reaching the orbit, the

operator will then command the gimbal to lock to the center waypoint. The lock command

compensates for altitude changes and orbit radius. This avoids the possibility of photographing a

ring without ever seeing the center.

The no fly zones are displayed on the Piccolo Command Center screen in red and are manually

entered prior to flying the aircraft by the autopilot operator.

VI. Operations

A. Safety

UAS are complex systems and safety is a major concern during any UAS operations. Good

engineering practices were used in the construction of ArcWulf to help reduce the probability of

catastrophic structural or electrical failures that could pose a risk to operators and potential

spectators. NCSU uses extensive Standard Operational Procedures (SOP’s) before, during and

after each flight to help mitigate the remaining risk.

NCSU maintains a separation of approximately 10 feet between the trailer and the flight line to

help ensure the safety of the ground crew while also being close enough to maintain good

communication between the trailer crew and the flight line crew. An established chain of

command reduces communication errors between the trailer and the flight line.

Figure 7 – Chain of Command Flow Diagram

Mission objectives are defined clearly prior to each flight test, and operators are briefed on their

duties before each flight. A FMEA and a Hazard Analysis were conducted based on possible

failures and past failures experienced by the club. This data is used to improve checklists and

procedures, thus improving safety of the system.


B. Flight Line Crew

Flight Test Director: The flight test director is in charge of all flight test operations and the

overall safety of the operators and the aircraft. The director‘s roles include pre-mission briefings,

taxi and takeoff allowances, and autonomous handover procedures. In addition, the director

ensures all checklists are followed and information is passed smoothly between the trailer and

the flight line. Finally, the flight test director is in charge of performing mission debriefing’s and

updating SOP’s to improve mission performance.

Safety Pilot: The safety pilot has primary responsible for the safety of the flight crew and

spectators during all phases of flight. There is a defined hand-off procedure for transitioning

from manual to autonomous control that involves the Safety Pilot and the Autopilot Operator. In

the event of an autopilot failure or unexpected aircraft behavior the safety pilot is responsible for

taking manual control of the aircraft. The safety pilot has the final decision on if the aircraft is

unsafe to land near the flight crew in which case they will use their best judgment to land the

aircraft in the least risky manner.

Scribe: A scribe is placed on the flight line that assists with running checklists and verifying the

aircrafts speed and altitude. This position may be replaced by the flight test director during

minimum crew operations.

C. Trailer Crew

Autopilot Operator: The autopilot operator is responsible for autonomous flight planes, waypoint

navigation, and autonomous takeoff and landing. The operator verifies the aircraft position

during all phases of flight and alerts the flight test director to the status of the aircraft.

Imagery Operator: The imagery operations team is responsible for ensuring pictures are received

from the aircraft and analyzed.

Antenna Operator: The antenna operator is responsible for ensuring the ground station antenna is

properly tracking the aircraft at all times. If the antenna fails to autonomously track the aircraft,

manual control of the antenna can be used to maintain an adequate wireless link.

VII. Flight Testing and Evaluation

The NCSU Aerial Robotics Club has flown the system 53 separate times since the 2009

Competition. Over the course of these flights, the ArcWulf accumulated 9.5 hours of total flight

time. Of that time, 4.38 hours were flown autonomously. 10 autonomous takeoffs and 6

autonomous landings were successfully completed. The ArcWulf experienced two major crashes

that resulted in an end to flight testing until significant repairs could be made. On 11/8/2009, an

engine malfunction caused the plane to lose power over the tree line, resulting in a broken

fuselage and minor damage to the wing. 60 man hours of repairs were made within a week and

flight testing continued within a month. The second major crash occurred on 3/14/2010 when


the landing gear caught on a fence during an autonomous landing attempt, resulting in

catastrophic damage to the fuselage. A second fuselage was in the process of being built as a

backup starting in mid-January, so this body was made the primary fuselage and completed so

that flight testing could resume as soon as possible. Flight testing resumed after roughly 250

man hours.

Over the 2009-2010 flight test season, 100% of the identified targets met or exceeded threshold

standards as per the request for proposal. The average distance error in GPS location was 79.96

feet. From a maximum altitude of roughly 500 ft AGL, the imagery team can discern useful

target information such as primary color, secondary color, alphanumeric, target shape, and

heading. However, the optimum height for target recognition is 350 ft AGL.

North Carolina State University Aerial Robotics Club

Appendix 1- Aircraft Systems Communication Flow


Aircraft Systems Communication Flow

15


Appendix 2-Image Collection and Data Processing Pipeline


Appendix 3-Flight Line Setup


Flight Line Setup

17


Appendix 4-Go/No-Go Criteria

The NCSU UAS shall not fly under the following conditions:

1. If there is any perceptible precipitation.

2. If there is any indication of thunder or lightning within 5 miles of the field.

3. If sustained winds exceed 15 kts, or the sustained crosswind component exceeds 8 kts.

4. If another vehicle, manned or unmanned, is operating within line of sight of the field.

5. If non flight-critical personnel cross the flight line.

6. If the aircraft fails to range test beyond 100 feet on the primary R/C link with all wireless

devices operational.

7. Any indication of poor or unreliable engine performance.

8. Any indication of inoperative flight control surfaces.

9. Any indication of poor nose wheel steering.

10. If a GPS lock cannot be obtained.

The NCSU UAS may fly under the following conditions

1. An inoperative 5GHz imagery data link

2. An inoperative 900 MHz autopilot data link with an operative 5 GHz data link


Appendix 5-Failure Mode Effect Analysis

Failure Symptom Action Status

RC Receiver

System

Malfunction

Erratic

aircraft

behavior

1. Safety pilot defaults to

autonomous control Mission Failure, Recoverable

2. If problem continues, safety

pilot turns off autopilot

transmitter when system is a

safe distance away from

ground personnel. This initiates

flight termination.

Catastrophic

Autopilot

Malfunction

Erratic

aircraft

behavior

1. Safety pilot switches to

manual control Mission Failure, Recoverable

Loss of

Autopilot

Uplink

Indicated on

Command

Center

1. If less than 30 seconds,

aircraft continues previous

flight path

Mission Continues

2. If greater than 30 seconds,

aircraft goes to lost comms

waypoint

Mission Failure, Recoverable

3. If, after 1 minute, link is not

established, Safety pilot takes

manual control


Loss of GPS

Signal

Indicated on

Command

Center

1. Aircraft continues on inertial

navigation for 30 seconds Mission Continues

2. If no signal after 30 seconds,

safety pilot takes control Mission Failure, Recoverable

Loss of

Camera

Downlink

Real-time

image

transmission

stops

1. NCSU relies on onboard

data storage Mission Continues

One servo

dies

Erratic

aircraft

behavior

1. Autopilot attempts to fly

aircraft without servo Mission Continues

2. If flight control is

unacceptable, manual control is

engaged, and the safety pilot

attempts landing in a safe area.


3. Turn off transmitter,

initiating hard-over Catastrophic

Engine dies Indicated on

Command

Center


manual control, initiates

emergency landing procedure



Failure Mode Effects

Analysis (Continued)

Vehicle

breaks in-

flight

Falling

debris, erratic

behavior


manual control Mission Failure, Recoverable

2. If flight control is

unacceptable, manual control is

engaged, and the safety pilot

attempts landing in a safe area.


3. Turn off transmitter,

initiating hard-over procedure Catastrophic

4.8v Servo

Battery Low

Indicated on

Command

Center


manual control and when

practical


12v System

Battery Low

Indicated on

Command

Center


manual control and lands when

able


3.3v Camera

Battery Low

Loss of image

capture

1. Auto land initiated as no

more images can be captured Mission Failure, Recoverable

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