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									Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

University of Colorado Department of Aerospace Engineering Sciences Senior Projects – ASEN 4018

Solar Unmanned Aerial Vehicle (SUAV) Project Definition Document (PDD)

Document History
Release Version 1 2 3 4 Final Date 9/4/08 9/9/08 Description of Top Level Changes Baseline draft Revised Draft PM Name R. Kramer R. Kramer

Approval
Name Customer Advisor #1 Advisor #2 CC Affiliation Approved Date

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Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

Project Definition Document
Aerospace Engineering Senior Projects (ASEN 4018 & 4028)

1. Information
1.1. 1.2. Project Title
Solar Unmanned Aerial Vehicle (SUAV)

Project Customers
Martin Dunn Associate Professor Mechanical Engineering Sciences University of Colorado at Boulder Boulder, CO 80309-0429 (303) 492-6542 Martin.dunn@colorado.edu

Kurt Maute Associate Professor H. Joseph Smead Fellow Aerospace Engineering Sciences University of Colorado at Boulder Boulder, CO 80309-0429 (303) 735-2103 maute@colorado.edu

1.3.

Group Members
Byron Young youngb@colorado.EDU 720-480-4605 Nathan Lawson Nathan.Lawson@Colorado.EDU 303-807-2369 Ryan Nowakowski nowakowr@gmail.com 303-502-0267 Parker Keegan Parker.Keegan@colorado.edu 509-710-0953 Sheldon Coutinho sheldon.coutinho@colorado.edu 720-352-5418

Ryan Kramer ryan.kramer@colorado.EDU 303-506-0134 Brendan Roberts brendan.roberts@colorado.EDU 303-638-4706 Kevin Weber Kevin.weber@colorado.EDU 719-339-5569 Brandon Yonko Brandon.Yonko@colorado.edu 925-683-8539 Noah Moore mooren@colorado.edu 303-718-7805

1.4.

Other Interested Students
None.

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2. Background and Context
Unmanned Aerial Vehicles (UAV’s) currently operating are limited by their relatively low flight time. This forces the aircraft to periodically return to earth, thereby limiting the scope of potential missions. A UAV with a dramatically increased endurance will allow for a broader range of application. This includes such tasks as communications relays, climate/weather observations, surveillance and reconnaissance, or other scientific research capabilities. These UAV’s will be significantly cheaper than satellites, and have the added capability to land for repairs or calibrations. A novel and efficient way to increase an aircraft’s endurance is by harvesting energy from the environment by the use of a photo-voltaic system. This project aims to modify and test an existing aircraft partially powered by an integrated solar/electric system with the goal of significantly increasing flight time. Generally, the more flexible a solar cell, the less efficient the cell performs. As a design solution, this project will attempt to integrate solar cells into the structure of the aircraft and attempt to minimize the added weight problematic in other solar aircraft. As load bearing devices, the solar cells are required to supplement the power and carry a measurable load without compromising wing integrity or the aerodynamics of the craft. The additional mass is justified as it provides a net energy increase in the system. If high efficiency solar cells can be used effectively, long endurance and perhaps even perpetual flights will be more feasible. Mechanically, this aircraft will be tested to ensure that the wings and other structural components can withstand the stresses and strains exerted during flight. The plane will fly by radio control with partial autonomy as a stretch goal. The aircraft will also need to be designed such that the processors, motors, and servos receive the correct and highly optimized amounts of power at the correct voltages.

3. Goal
The goal of this project is to modify a high performance sailplane by the addition of a structurally integrated photovoltaic system in order to extend the standard endurance of the aircraft by 250%. This will be accomplished through the inclusion of wing integrated solar panels and, if possible, batteries.

4. Objectives
4.1. Overall Objective
The overall objective is to increase the endurance of an existing high performance sailplane by the integration of photovoltaic energy harvesting.

4.2.

Flight Endurance
Through the inclusion of a photovoltaic system and extended battery storage, this aircraft’s endurance shall be increased over the unmodified aircraft. An existing design shall be modified from an OTS model electric sailplane. Extending this endurance enables the aircraft to potentially fly through a solar period by relying on the energy collected by the solar panels. Application of energy harvesting on a kit airplane provides a basis for improving larger scale aircraft.

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4.3.

Altitude
This craft will fly at typical operating altitudes of Radio Controlled UAV with limitations imposed by FAA regulations. R/C aircraft are required to fly under 400 ft AGL. Testing can be done at the higher altitudes if FAA permission is granted.

4.4.

Structurally Integrated Photovoltaic System
The photovoltaic system, consisting of solar cells and casing, will be integrated into the structure of the wing such that it serves as a load bearing member while maintaining wing flexibility to preserve aerodynamic performance. Including the solar cells as part of the structure will reduce the empty weight of the aircraft, thereby improving the aircraft’s performance. The energy collected with the photovoltaic cells will be utilized by the aircraft and excess energy will be stored in a battery system.

4.5.

Structurally Integrated Battery System
A thin film battery system, consisting of battery and casing, will be integrated into the structure of the wing such that it acts as a load bearing member of the aircraft. Incorporating a thin film battery system into the structure of the wing will reduce the overall weight of the aircraft. The battery system will be controlled and monitored by a Maximum Power Point Tracker (MPPT) to ensure proper charging within the battery limitations, based on solar power influx.

4.6.

Control System
At any point in the flight, the aircraft will have the ability to be manually controlled by a certified RC pilot. A supplemental autopilot system may be used to assist with horizontal stability as well as navigation during cruise to account for pilot limitations. This system will have a fail-safe mode that reverts to R/C control.

4.7.

Wireless Communication/Data Acquisition
The aircraft will downlink critical control system flight data. Additional data may be downlinked as needed. The aircraft will store all other measurements via onboard data storage. If the airplane is no longer visible to the R/C pilot, additional flight data will be necessarily transmitted. This information will be used to determine when to land the aircraft based on battery charge.

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5. Functional Block Diagram

6. System Operational Timeline
The diagram below shows a simplified timeline for flight operations. During each of these periods, the team will need to produce procedures detailing how to correctly operate the flight to ensure the aircraft’s and operator’s safety.

7. Project Requirements (0.PRJ)
7.1. Aircraft Configuration (0.PRJ.1)
The aircraft shall be of a fixed-wing, standard configuration and shall be purchased as a kit. The kit that will be modified shall be a TBD sailplane with a wingspan of at least three meters and a TBD weight range. The wing will be designed or modified to account for the additional structural rigidity and weight added by the solar cells and the batteries.

7.1.1. Objective

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Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

7.1.2. Discussion In order to achieve the simplest, lightest, and most efficient design, a fixed wing configuration shall be utilized. The additional complexity and weight added by a rotary system or other non-fixed configuration was determined to be detrimental to the objectives of the aircraft. A kit plane will expedite the design, build, and test processes. 7.1.3.Method of Verification The dimensions specified shall be measured for accuracy.

7.2.

Structurally Integrated Solar Cells (0.PRJ.2)
The photo-voltaic cells shall be integrated into the wing structure. The cells shall be loaded to TBD% of their structural capacity.

7.2.1. Objective

7.2.2. Discussion The structural weight of the aircraft will be reduced by applying a load to the solar cells, thereby improving performance. Loading them to TBD% of their structural capacity leaves a TBD safety factor so that the aircraft can be flown in various conditions. 7.2.3.Method of Verification The loads applied to the solar cells shall be verified with strain sensors placed on the cells. These strains will be compared to those predicted by an analytical model to determine if the solar cells are loaded to the predicted values.

7.3.

Structurally Integrated Batteries (0.PRJ.3)
Thin-film lithium polymer batteries shall be implemented into the structure or surface of the wing such that they carry a component of the aerodynamic load. These batteries will be loaded to TBD% of their structural capacity.

7.3.1. Objective

7.3.2. Discussion Using batteries as a structural component of the aircraft will reduce the amount of additional structure required by the wing and will relocate the cells from the fuselage. This will maximize volume for other equipment or payloads. 7.3.3.Method of Verification Strain sensors shall be applied to the batteries to determine their structural contribution to the wing. The batteries shall be simplified and modeled analytically, and the stress applied to the battery cells will be predicted and compared to experimental results.

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Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

7.4.

Endurance (0.PRJ.4)
The endurance of the aircraft shall be improved by 250% over the original aircraft through the addition of: a photo-voltaic system, thin film batteries, and lithium polymer battery cells.

7.4.1.Objective

7.4.2. Discussion The preliminary analysis predicts an expected worst case scenario increase in endurance of 250% from baseline, without the addition of extra battery storage. 7.4.3.Method of Verification The aircraft power will be exhausted on a static test platform to determine the baseline endurance value. After the addition of the photo-voltaic system and extra battery storage capability, the aircraft’s endurance will be measured again to determine the success or failure of this requirement. The aircraft can be flight tested to confirm endurance predictions.

7.5.

Battery Endurance (0.PRJ.5)
The aircraft shall have enough energy storage capacity to fly throughout a nighttime period of 8-12 hours without any solar power input.

7.5.1.Objective

7.5.2. Discussion The aircraft should have the capability to sustain flight through a night cycle. 7.5.3.Method of Verification This requirement shall be tested on the ground simulating flight without solar power input to determine if the energy storage capacity is sufficient to power the aircraft through the night.

7.6.

Maneuverability (0.PRJ.7)
The aircraft shall be maneuverable enough to perform at most a TBD banked turn, and achieve TBD pitch. No rolls or vertical maneuvers will be required.

7.6.1.Objective

7.6.2. Discussion The ability to perform basic maneuvers while in flight will allow for course corrections and varying flight patterns. The aircraft must be reasonably maneuverable for ease of takeoff and landing. 7.6.3.Method of Verification Sensors can be mounted to the fuselage to measure relevant accelerations. The banked turn should yield an approximate TBD vertical force. The pitch can be determined through straight flight and a trigonometric breakdown of gravity.

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Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

7.7.

Propulsion (0.PRJ.8)
The aircraft’s propulsive system shall provide TBD thrust to sustain cruise.

7.7.1.Objective

7.7.2. Discussion To convert the electricity collected via the solar panels into propulsion, an electric motor shall drive a propeller. 7.7.3.Method of Verification Sensors will be used to measure the thrust and verify our thrust to weight ratio. The motor will be statically tested on the ground.

7.8.

Wireless Communication/Data Acquisition (0.PRJ.9)
The aircraft shall transmit data such as battery voltage and strain data to a ground station. Additional data shall be stored in onboard memory for post-flight download and analysis.

7.8.1.Objective

7.8.2. Discussion Communication between the aircraft and a ground station must be maintained for the duration of the flight. If a visual of the aircraft is lost, then GPS coordinates will need to be sent and received. Transmission of the battery voltage will be essential to knowing the state of charge of the battery. 7.8.3.Method of Verification Real time battery voltage and strain data shall be observed from the ground. Additional telemetry items will be analyzed after the flight, and stored on the aircraft.

7.9.

Aerodynamic Performance (0.PRJ.10)
The aircraft shall achieve a TBD L/D.

7.9.1.Objective

7.9.2. Discussion Given the project’s critical power requirements, the losses due to aerodynamics must be minimized. Tentative parameters ranging from 50 and above are given for typical high aspect ratio sailplanes. 7.9.3.Method of verification The drag can be calculated by observing the thrust and lift can be assumed equal to the weight in steady level flight. The amount of power required by the motor will also be closely monitored to verify our power to weight ratio.

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AES-SRP-2008-SUAV

7.10.

Structural Performance (0.PRJ.11)
The aircraft shall achieve a TBD safety factor for each component as well as a TBD for the entire aircraft.

7.10.1. Objective

7.10.2. Discussion Due to the nature of the aircraft, a high aspect ratio will likely be chosen. As a result, thorough structural testing is especially important as extreme wing flexing will be fatal to the solar panels. Ideally, several failure modes will be tested, including loading a wing to failure in order to achieve a safety factor of 1.4. This safety factor will have to be low to minimize the structural weight, while high enough to make the aircraft capable of emergency maneuvers. 7.10.3. Method of Verification A test wing shall be tested to ensure that safety factor and strain measurements are acceptable. The flight wings shall be outfitted with strain sensors to analyze their inflight properties.

8. Top Level System Requirements
8.1. Airworthy Aircraft
At an absolute minimum, this team will have to produce an airworthy aircraft. 8.1.2.Discussion The aircraft will not be designed from scratch, but will be modified from a prefabricated aircraft. 8.1.3.Method of Verification Completion of takeoff, cruise, and landing will successfully fulfill this requirement. 8.1.1. Objective

8.2.

Utilization of Solar Energy
Power collected from the solar cells shall be either put to use immediately or stored in a battery system for later use.

8.2.1. Objective

8.2.2.Discussion The use of solar cells is what differentiates this project from other UAVs. Utilizing this power collection method is a basic and reasonable system requirement. 8.2.3.Method of Verification Static ground tests shall be conducted to determine energy usage and aircraft performance in flight under optimal conditions.

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Project Definition Document Aerospace Senior Projects (ASEN 4018 & 4028)

AES-SRP-2008-SUAV

9. Minimum Requirements for Success
Success will be judged by an increase of 250% to the endurance of the stock aircraft or equivalent energy produced and stored by the power system.

10. Deliverables
10.1. Aircraft
An aircraft shall be produced that shall fly in a pre-specified pattern, utilize energy collected with solar cells, and land. This will be achieved while meeting all the requirements set forth in this document.

10.2.

Ground Station

The ground station will function as a transmitter and receiver. This will consist of a computer and communications hardware that will prepare and operate the aircraft. The ground station function and hardware will comply with all of the requirements listed above, including remotely commanding the aircraft, and displaying onboard telemetry.

10.3.

Radio Controller

This project will need to provide a radio controller capable of manually assuming control of the aircraft at any point in the flight, overriding the autopilot.

10.4.

Battery Charging Hardware

The batteries will be fully charged on the ground before a flight to maximize the flight duration. They will also utilize in flight charging from the solar panels.

11. Technical Risks
11.1. Risk #1 (0.RSK.1) Link Loss

11.1.1. Due to the nature of the mission of SUAV, loss of radio contact with the aircraft may be encountered. In the situation where the aircraft is relatively high, loosing control of the aircraft could pose a threat to the safety of the aircraft as well as observers on the ground. 11.1.2. In order to mitigate this risk, highly robust and proven radio control methods will be implemented to minimize the risk of link loss. In the event that contact is lost, an emergency program will be activated which may include any of the following: navigating the aircraft back to a ‘rendezvous point’, shutting down all systems and deploying a parachute, land the aircraft at a pre determined destination, etc.

11.2.

Risk #2 (0.RSK.2) Power Malfunction

11.2.1. Because SUAV has numerous onboard systems that depend greatly on the collection and distribution of power, any power malfunction, including a loss of power or a sudden surge in power could compromise the aircraft.

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11.2.2. In order to mitigate this risk, several power regulation techniques will be employed. These include implementation of a Maximum Power Point Tracker (MPPT) and a minimum ‘emergency’ power reserve that is not to be exceeded.

11.3.

Risk #3 (0.RSK.3) Structural Failure

11.3.1. SUAV is distinct from other UAVs in that it must integrate a solar electric system (including photovoltaic cells and batteries) into the structure of the aircraft. Therefore, the ability of the aircraft to gather power and to function is directly dependent on the structural integrity of the airframe. For example, if the wing flexes beyond a certain tolerance causing damage to integrated PV infrastructure, an otherwise small and/or inconsequential crack in the wing may wreak havoc on subsequently affected systems. Thusly, maintaining structural integrity is of paramount importance. 11.3.2. In order to mitigate this risk, special attention must be paid to ensuring high structural tolerance. This can be achieved by rigorously testing the airframe, particularly those parts that house delicate electronics, and engineering the structure to high factors of safety.

11.4.

Risk #4 (0.RSK.4) Budget Constraints

11.4.1. Solar Cells, especially space grade cells, are notoriously expensive. It is possible that our aircraft will have to be specifically designed around the amount of solar cells we can afford. 11.4.2. Many systems, such as the communication system, the autopilot, and some of the composite structural components, may be too expensive for the budget provided by the customer. 11.4.3. The cost of the cells and other components can be scaled by scaling the size of the airplane. The size of the airplane will be budget dependant.

12. Engineering Expertise
Technical Expertise
Structural Design

Application
Development of detailed solid 3D models of system components. Will also help construct and assemble the aircraft, as well as design the actuator layout for the control surfaces. Designs and selects the solar panels, the battery, the charge controllers, and other voltage regulators. Determines the most appropriate control system, as well as the gains required to make the aircraft stable. Develops software required to control all electronic systems, such as the battery controller, and the servo and speed controllers.

Member (Tentative)
Parker Keegan (Lead) Ryan Nowakowski

Power Design

Brandon Yonko (Lead) Noah Moore Nathan Lawson (Lead) Byron Young

Controls/Autonomy

Software/Programming

Noah Moore

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Wireless Communications

Electronic Design

Data transmission to the ground, as well as ground based commanding, such as setting waypoints. Determines the optimal energy acquisition/storage/distribution, and implements integrated circuit design. Aerodynamic design of the aircraft Controls the motor and propeller selection. Coordinates reports and presentations, group meetings, facilitates communication between subsystems, and aids in subsystems that need additional assistance. Uses a system wide perspective to determine weight and power requirements for each subsystem to maintain the aircraft within its performance requirements.

Ryan Nowakowski Brendan Roberts (Lead) Brandon Yonko Sheldon Coutinho (Lead) Kevin Weber Kevin Weber

Aerodynamic Design Propulsion Design

Project Manager

Ryan Kramer

Systems Engineer

Byron Young (Lead) Parker Keegan

13. Resources
13.1. Facilities
The project will have access to the Senior Design Laboratory, the Aerospace Machine Shop, the ITLL Manufacturing Center, the ITLL wind tunnel, the ITLL Electronics Center and a TBD test area (possibly the model aircraft field next the Boulder reservoir).

13.2.

Additional Advisors

The group is in the process of finding advisors concerning specific aspects of the design, including people currently working in the field. Having an advisor for the electronics aspect (charging and discharging the batteries) would be extremely helpful.

13.3.

Funding

Currently, the project is funded by the customer’s research grant. If these funds are insufficient, we will likely also apply for funding through EEF or other external funding opportunities such as the Undergraduate Research Opportunity Program, the Engineering Excellence Fund, the W.M. Keck Foundation, the National Science Foundation and others.

13.4. References
    "AC Propulsion's Solar Electric Powered SoLong UAV." AC Propulsion. 5 June 2008. <www.acpropulsion.com/solong/acp_solong_solar_uav_2005-0605.pdf>. "Advanced Aircraft Analysis." DARcoporation. <http://www.darcorp.com/software/aaa/>. AstroFlight. <http://www.astroflight.com/>.

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               

"Charging Lithium-Ion Batteries." BatteryUniversity. Mar. 2006. <http://batteryuniversity.com/partone-12.htm>. Eagle Tree Systems. <http://www.eagletreesystems.com/>. HoverHobbies. <http://hoverhobbies.com/>. Kontronik. <http://www.kontronikusa.com/>. "Lithium Sulfur Rechargeable Battery Data Sheet." SION Power, Inc. 28 Sept. 2005. <http://sionpower.com/pdf/sion_product_spec.pdf>. "Main Page." Paparazzi. <http://paparazzi.enac.fr/wiki/index.php/main_page>. MicroPilot. 30 Aug 2008.<http://www.micropilot.com/>. Microstrain: Microminiature Sensors. <http://www.microstrain.com/>. Neumotors. <http://www.neumotors.com>. Northeast Sailplane Products. <http://nesail.com/>. PeakEff: An Internet Database For Logging Motor Performance.<http://www.peakeff.com/>. RoyMech. 14 June 2008. <http://www.roymech.co.uk/>. The Sailplane Shop. <http://sailplaneshop.com/>. SoaringUSA. <http://www.soaringusa.com>. Tower Hobbies. <http://www.towerhobbies.com/>. "UIUC Airfoil Coordinates Database - Version 2.0 (over 1550 airfoils)." 19 Feb. 2008.<http://www.ae.uiuc.edu/mselig/ads/coord_database.html>. XOAR. <http://www.xoarintl.com/>.



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14. Acknowledgements
14.1. Customer contacts
Our customer is Professor Kurt Maute, who provided invaluable advice concerning this PDD. He helped to drastically scale down this project so that it is much more attainable as a yearlong project.

14.2.

Technical Contacts

Stephanie Golmon provided advice concerning the technical aspects of our solar panels as well as what energy values we can expect to receive from our cells. She will as be helping to obtain solar cells, as well as technical expertise concerning how we can apply these cells to our design.

14.3.

Faculty Members

We have yet to be assigned any faculty PAB contacts, but will utilize them as soon as they become available.

14.4.
None

Graduate Students Undergraduate Students Others

14.5. 14.6.

None, but will try to utilize as many as are willing to help.

Robert Breaux has provided advice concerning our aircraft kit, as well as preliminary motor selection.

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15. Relevant Acronyms
                       AES – Aerospace Engineering Sciences AGL – Above Ground Level ASEN – Aerospace Engineering DC – Direct Current EEF – Engineering Excellence Fund FAA – Federal Aircraft Administration GPS – Global Positioning System ITLL – Integrated Teaching and Learning Laboratory L/D – Lift to Drag Ratio MPPT – Maximum Power Point Tracker P/W – Power to Weight Ratio PAB – Project Advisor Board PDD – Project Definition Document PIC – Proportional Integrated Controller PRJ – Project PV – Photovoltaic R/C – Radio Control RSK - Risk SOC – State of Charge SRP – Senior Project SUAV – Solar Unmanned Aerial Vehicle TBD – To Be Decided UAV – Unmanned Aerial Vehicle

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