Electric UAV Using Regenerative Soaring and Solar Power(project proposal) Abstract: Autonomous Electric Aircraft using no Fuel (Unmanned Aerial Vehicle – UAV) Propeller powered electric UAV takes off on batteries and actively searches for updrafts. After encountering an updraft the UAV switches of the propulsion electric motor and soars. Air passing through the propeller during soaring revolves it and the movement is transmitted to the electric motor. Electro motor works as a generator in this mode. The produced energy recharges batteries and powers the electric equipment of the UAV. Energy gain is improved using solar power. The proposed UAV can stay aloft for long (indefinite) periods of time and can be used in reconnaissance and other applications. The control system of the UAV is responsible for autonomous behavior (searching for updrafts, optimization of flight trajectory with regard to the mission objective and power management, solving critical situations, etc.) and for implementation of the human issued commands. Table of Contents 1 Introduction............................................................................................................................................2 1.1 Outline of the Idea..........................................................................................................................2 1.2 Regenerative Soaring.....................................................................................................................3 1.3 Electric Aircrafts............................................................................................................................4 1.4 Features, Equipment and Instruments of the Proposed UAV........................................................5 1.5 Functions of the Control System....................................................................................................6 2 Feasibility Analysis................................................................................................................................7 2.1 The Aircraft....................................................................................................................................7 2.2 Energy Balance...............................................................................................................................9 2.2.1 Self Launch and Climb to 300m...........................................................................................11 2.2.2 Cruise for 20 minutes in search for updrafts........................................................................11 2.2.3 Recharge batteries to full capacity .......................................................................................12 2.2.4 Cruise till 50% of the battery capacity remains....................................................................12 2.2.5 Recharge batteries to full capacity and land.........................................................................13 2.2.6 Conclusion, energy balance..................................................................................................14 2.3 AI and Control System.................................................................................................................15 3 Estimated Project Impact.....................................................................................................................16 optimizes flight trajectory with regard to the mission objectives and power management. These try to avoid weather in order to get maximum exposure to sun and to protect their fragile lightweight construction. solves critical situations and responds to human issued instructions. The instructions are expected to be defined as partial and general objectives instead of detailed commands. Batteries of the UAV are recharged by regenerative soaring and solar power.1 Introduction 1. The advantages of the UAV are the following: • quiet and clean • fossil fuel independent • very low operational cost • can potentially remain aloft indefinitely • "parked" in air when not in use • has interesting application potential • study for manned regenerative soaring aircraft The possible applications include: • Long time surveillance of road traffic. • Weather forecast and study Many of the ongoing projects of electric aircrafts are aimed on high altitude solar powered UAV's. The UAV proposed here should operate in low altitudes in visual contact with the surface of Earth and take advantage of the vertical atmospheric motions. traffic jams avoidance • Bird eye view during rescue operations or catastrophic events • Search for missing persons at sea (flock of UAV's to cover large areas) • Transponding radio signals in mountainous areas • Following migrant birds. marine mammals etc.1 Outline of the Idea We propose an electric unmanned aerial vehicle (UAV) capable to take-off and fly using electric motor and to land with fully charged batteries. . The UAV is expected to stay aloft for a long time (hours and possibly days). During the time aloft the UAV searches autonomously for updrafts. In the typical scenario the sailplane searches for an updraft after initial climb (tow. Traditional sailplanes utilize updrafts to stay aloft and travel. Minimum sink rate determines how fast will the sailplane gain altitude and the glide ratio (usually expressed as X :1. aircraft design (Credit [4]). Illustration 2: Soaring in thermals . Most of the updrafts used by sailplanes are either thermal columns or upwind slope lifts.2 Regenerative Soaring Illustration 1: Regenerative soaring. Two important parameters the sailplane's performance are minimum sink rate and glide ratio. self launch …). gains altitude by circling in an updraft and then glides in direction of the intended destination.1. meaning the sailplane will glide to the distance of X kilometers if starting 1km above ground) determines how good will the sailplane utilize the gained altitude. pinwheels. In 2009 it became the first solarpowered aircraft to cross the Alps. Antares 20E of Lange Aviation.g. springs or twisted rubber bands. Electric Aircraft Corporation [1] produces . for new start and climb or to power devices on board of the aircraft. powered by solar cells. Its solar array charges Li-Polymer battery powering a 6kW electro motor. Antares 20E is equipped with 42kW electric motor. Several self launching electric sailplanes are available on the market. 1. Sunseeker II takes advantage of thermals if possible. Solar and atmospheric energy can be used to increase the range and the time in air. batteries and Illustration 4: Helios prototype Illustration 5: Sunseeker II hydrogen-air fuel cell. Helios prototype was a UAV of NASA.Thermal columns (thermals) are basically bubbles of rising warm air which was warmed over sun irradiated surfaces. Upwind slope lift arises when air is forced to flow over an obstacle. It is also possible to apply dynamic soaring – technique used by many migrant birds and remote control pilots. high speed maneuvers close to the ground. Electric aircrafts slowly start to appear also as commercial products. Batteries or ultracapacitors provide low energy to weight ratio which means that electric airplanes have small range.3 Electric Aircrafts Electric motors are widely used in remote controlled (RC) airplanes and in several manned airplanes. In the optimal case the aircraft will fly entirely without fuel or recharging on the ground. Sunseeker II was as of Dec. Regenerative soaring feature is easily added to most of the Illustration 3: Upwind slope lift self launching sailplanes. Because of the increased drag during regen the aircraft can not climb as fast as a clean sailplane but the energy generated by the turbine can be stored for future use. This energy can be used for free or emergency cruising. The most common means to store the energy are batteries. 13 minutes when the batteries are depleted. In this case the propeller (or propellers) serves as a wind turbine while flying in the updraft. this technique requires to make sharp. This technique uses the change of wind speed in the wind profile close to surface to gain energy. It climbs to 3000 meters in app. Max speed on solar power is 64kph. Albatrosses travel almost effortlessly thousands of kilometers in any direction using dynamic soaring. e. 2008 the only manned solar powered airplane in flying condition. ultralightweight flying wing aircraft with a wingspan of 75.3m. However. The limiting factor in application of electric motors in aviation is the energy storage. 6kWh lasts for 1-1.4 Features. Further examples of electric aircrafts are described in Chapter 2 Feasibility Analysis. pitch.two types of electric aircrafts: rigid wing Electraflyer-C and Electraflyer trike (motor hang glider with Stratus wing [3]). Their lithium-polymer battery pack with capacity 5.. Li-Ion . yaw) secondary controls: elevator trim.5kW brushless motor with 90% efficiency.5 hours flying. The electric motor used is 13.. airbrakes etc. wing flaps. Illustration 6: Electraflyer trike. Electric Aircraft Corporation 1. Equipment and Instruments of the Proposed UAV Propulsion system components: • • • • • • • • • • • propeller – large (more efficient) with symmetrical blades cross section possibly mounted as a ducted fan brushless electric motor (dual role as turbine) battery pack – (Li-polymer. ) battery heating system – to ensure optimal performance of the batteries solar cell array motor-generator controller charger primary controls: 3 (roll. (optional) retractable landing gear (optional) rocket parachute – deployed in critical situations Flight controls (fly-by-wire): Other equipment: . vision and ground AI data) "Parking" in air – when not in use aircraft is commanded to stay within certain space and fly autonomously until new mission objective is uploaded. The ground based AI system would be vital for night operation when thermal updrafts and solar array do not provide energy and UAV depends mostly on upwind slopes lift.5 Functions of the Control System The proposed control system intends to use ground based and on-board AI.) Force feedback (aerodynamic load on the steering surfaces) Diagnostic system Radio receiver: for data and commands Cameras and optional sensing devices Video and data transmission system Control computer Special devices: 1. This system will provide hints to the UAV regarding areas with high likelihood to produce updrafts. The onboard AI will be responsible for the following: • • • • • Automated take-off and landing Reaction in critical situations: stall and spin recovery. landing aids etc. The ground based system will analyze available meteorological data and 3D model of the surface of Earth. parachute deployment etc. . fire. g-force.Avionics and Instruments (digital): • • • • • • • • • • • • • GPS altimeter airspeed indicator rate-of-climb indicator (variometer) attitude indicator (gyro horizon) turn coordinator indicators (battery. stall. Optimization of flight trajectory with respect to the mission objective and to the atmospheric conditions (power management) Localization and utilization of updrafts (variometer. yet maintains exceptional performance at high speeds. achieving a lift-to-drag ratio of about 25:1. The propulsion system of Electraflyer trike is sold also adapted for regenerative soaring [2]. it weighs only 48 kg and is easily transported on the top of a car. It is sold in many countries including Japan. It takes off and lands like a hang glider. The motor and the propeller will enable to climb at estimated rate of 1ms -1. Table 1 summarizes the specifications of the SWIFT with the proposed adaptations. The propulsion system is taken from Electraflyer trike [1] which weights 112kg empty and approximately 200kg with a pilot. brushless electric motor (13. solar array. designed to combine some of the convenience of hang gliders with the soaring performance of sailplanes. observing the behavior of the control system. disk brake. radio transmission system etc. wheeled tiplets for taxing).1 The Aircraft We have chosen SWIFT rigid wing hang glider produced by Belgium based firm Aériane as an candidate aircraft [2]. It was designed by Bright Star Gliders in collaboration with engineers at Stanford University The SWIFT is a high performance sailplane. In fact. Instead of human pilot the payload of the aircraft will consist of lithiumpolymer battery pack (5. Although it is a fully-cantilevered rigid wing with aerodynamic controls and flaps.5kW [1]). The optional equipment of SWIFT includes rocket parachute and car roof transportation container. It will be necessary to develop a new propeller optimized . servos. making measurements and ensuring safe operation. Aériane produces also engine Illustration 7: SWIFT rigid wing hang glider kit (with combustion engine) which is easy to adapt to a standard SWIFT frame (with steerable front wheel. electric equipment (control computer. This ensures that the UAV will be sufficiently powered. The estimated payload weights approximately as much as an average pilot. human pilot can be on board of the aircraft during initial Illustration 8: SWIFT with engine kit experiments.2 Feasibility Analysis 2.6kWh [1]).) and other equipment used for adaptation of the aircraft. power dial and switch. design. The propeller for our purpose should be optimized to work also as a turbine with high efficiency which among other requires symmetrical blades sections [4]. fuse.5kW [1]) solar array 1 electric equipment other 24:1 0.estimated 5 Development. voltmeter.95g/-3.6kwh [1] Electraflyer propulsion kit 3 [1] Solar array (10m2. and digital motor temperature display with probe 4 Development.98g 48kg 74kg 35kg 12kg 10kg 7kg 10kg Gross weight Estimated costs : SWIFT LIGHT with pod + closed fairing [2] Air brakes [2] Rocket parachute [2] lithium-polymer pack 5.65g tested +7.6kWh [1]) el. motor (13.5m2 +5.2Mil Yen (80 000USD) 21820EURO 2000EURO 1850EURO 8500USD 4200USD 8000USD 10000USD 5000USD 3550EURO 1 With installation aids and accessories 2 Does not include electric equipment developed during the project 3 Includes: motor. electronic controller. with installation costs) Carbon fiber propeller 4 Other (modifications of SWIFT) 5 Transportation container [2] Table 1: Proposed UAV specifications.3g/-2.for regenerative soaring. Optional features of the propeller include adjustable pitch and collapsibility. manufacture costs . design.65ms-1 120 km/h 1ms-1 12. 2 122kg 7.estimated . manufacture costs . The commercially available propellers are optimized to provide maximum trust. Glide ratio (best. connectors. custom machined propeller hub. at 75km/h) [2] Minimum sink rate (at 45km/h) [2] Never exceed speed (VNE) [2] Climb rate (estimated) Wing area [2] Maximum load [2] Weight empty [2] Payload total: battery pack (5. ammeter and shunt. 3. 20 minutes cruise in search for updrafts. We assume that increasing the sink rate by 0. It is ignored that the plane can use the potential energy gained by climbing in the updrafts during regeneration for travel by gliding. By takeoff the proposed UAV weights 78kg less than Electraflyer trike. Assuming the potential energy is converted into kinetic energy and then to electric energy with the overall efficiency corresponding to the efficiency of the propeller-turbine times the efficiency of the generator the increase of the sink rate of the aircraft can be calculated if the gross weight of the aircraft is known. We estimate that 80% of the wing area can be used to install solar cells. But please note that traditional sailplanes utilize only this form of energy to fly over large distances (Free out-and-return distance record: 2 247. Therefore we estimate to obtain 687W on the output of the generator during regenerative soaring. only the energy balance considering the electric energy is shown here. The proposed propeller works with 85% estimated efficiency ([4]. If we assume the sailplane to be in level flight in steady air it is loosing potential energy at certain rate corresponding to the sink rate at given speed. [6]) and to stay aloft for long periods (~15 hours).When the propeller works in a turbine mode it creates drag which leads to increased sink rate.6 km. During regeneration are the solar cells estimated to provide on average 40% of their maximum output (the UAV is moving in banked turns and the wing is only part of the time exposed to the sun).2. Let us assume installing solar cells with 15% efficiency providing maximum output 150W per m 2. The battery charger works with 80% estimated efficiency (charging efficiency of the batteries is 99.2 Energy Balance The purpose of this section is to show that it is possible to build an electric aircraft capable of self launch.9%).) is estimated to consume on average 150W. Cruise till 50% of the battery capacity remains. 2. The electric equipment of the UAV (controll computer. long daytime flight and landing with a full battery. The charger works only when the power balance is positive. . consulted (see Acknowledgments) and adjusted to slightly under or over estimate the actual values against the benefit of the UAV. Also. The estimated values were carefully calculated. 5. The proposed aircraft is described in the previous section. The brushless electro motor used in this example is 90% efficient as a generator [2]. The efficiency of solar cells suitable for airplanes varies between ~6% to ~20% [5]. efficiency of airborne turbine is defined differently than efficiency of a ground based turbine and Betz limit does not apply here). Self launch and climb to 300m. The solar cells are estimated to provide on average 70% of their maximum output during cruising (the UAV flies sometimes under the shadows of clouds and the wing is not always in the optimal position relative to the sun). radio transmission system etc.5 hours in the UAV.75ms-1 will not seriously impair the flight performance of the UAV. If additionally electric energy is to be generated the sailplane has to loose potential energy at higher rate. Table 2. servos. Therefore is is assumed that the battery pack will last for at least 1. The scenario investigated consists of 5 phases: 1. Recharge batteries to full capacity and land The following calculation requires to estimate certain values. summarizes the values and estimates used in this example.5 hours of Electraflyer trike's powered flight. Recharge batteries to full capacity 4. The proposed battery pack lasts for 1-1. 5.2MJ) 1.4ms-1 .Battery pack [1] Average powered flight time [1] Electric motor [1] Average energy consumption rate – motor Equipment input Propeller efficiency (turbine mode) Electric motor efficiency (generator mode) Charger efficiency Generator output in regen [4] Solar power per m2 max [5] Solar cells surface Solar array output .cruising Solar array output . 90% efficient 3.5kW.regen Sink rate total in regen [2] Table 2: Values and estimates used for calculation.max Solar array output .7kW 150W 85% 90% 80% 687W 150W 10m2 1500W 1050W 600W 1.6kWh (20.5 hour 13. The values are rounded. The values are rounded. The electro motor is running at full power during the start only [2]. Table 4 summarizes the energy balance for this phase. energy balance.2 Cruise for 20 minutes in search for updrafts It is likely that the aircraft will encounter updraft in 20 minutes after start. During climbing electric energy is used to sustain flight (compensate the drag) and also converted to potential energy of the aircraft The only source of energy now is the solar array .2. Altitude gained = 300m Balance: Solar array Turbine (Regen) Equipment Motor (sustain flight) Motor (to potential energy) Total Battery capacity spent: Battery capacity spent total: Table 3: Self launch and climb to 300m.1 Self Launch and Climb to 300m 300m is an altitude suitable for search for thermal updrafts [4]. Altitude gained = 0m Balance: Solar array Turbine (Regen) Equipment Motor (sustain flight) Motor (to potential energy) Total Battery capacity spent: Battery capacity spent total: Table 4: Cruise for 20 minutes in search for updrafts. The climb is done at reduced power (high discharge rate more rapidly depletes the battery capacity).2. Table 3 summarizes the energy balance for this phase. As it maintains the same altitude the motor spends energy only to sustain flight level flight.2. energy balance. Time spent = 5 minutes Power (Watt) 1050 0 -150 -3733 -1197 -4030 6% 6% Energy (Joule) 315000 0 -45000 -1120000 -359046 -1209046 2. Time spent = 20 minutes Power (Watt) 1050 0 -150 -3733 0 -2833 17% 23% Energy (Joule) 1260000 0 -180000 -4480000 0 -3400000 . Altitude gained = Ignored Balance: Solar array Turbine (Regen) Equipment Motor (sustain flight) Motor (to potential energy) Total Recharge (80% eff.4ms-1 is the minimum sink rate in this phase) the aircraft gains altitude. upwind slope lift) and it is regenerating. If the updraft is strong enough (1. energy balance.2.) Battery capacity spent: Battery capacity spent total: Table 5: Recharge batteries to full capacity.2. energy balance. Altitude gained = 0m Balance: Solar array Turbine (Regen) Equipment Motor (sustain flight) Motor (to potential energy) Total Battery capacity spent: Battery capacity spent total: Table 6: Cruise till 50% of the battery capacity remains. The aircraft will continue to recharge until the batteries are full. Time spent = 59 minutes Power (Watt) 1050 0 -150 -3733 0 -2833 50% 50% Energy (Joule) 3735529 0 -533647 -13281882 0 -10080000 . It can then glide in the direction of the mission objective and continue recharging. Time spent = 85 minutes Power (Watt) 600 687 -150 0 NA 1137 909 -23% 0% Energy (Joule) 3041135 3480455 -760283 0 NA 5761307 4609046 2. The propeller works as a turbine. The efficiency of the charger has to be taken into account in this phase.4 Cruise till 50% of the battery capacity remains The aircraft is cruising freely and accomplishing the mission objectives.2.3 Recharge batteries to full capacity The aircraft has found an updraft (thermal. The turbine generated power is higher during the final descent what can shorten the recharge time before landing but the turbine power is considered to be constant during the entire final phase of the investigated scenario for simplicity.2.5 Recharge batteries to full capacity and land The aircraft is recharging and continues to accomplish the mission objectives.) Battery capacity spent: Battery capacity spent total: Time spent = 185 minutes Power (Watt) 600 687 -150 0 NA 1137 909 -50% 100% Energy (Joule) 6650974 7611767 -1662744 0 NA 12600000 10080000 .2. Altitude gained = NA Balance: Solar array Turbine (Regen) Equipment Motor (sustain flight) Motor (to potential energy) Total Recharge (80% eff. UAV could still use upwind slopes and dynamic soaring.2. fly and land with full battery. Using upwind slopes for lift would require reliable ground analysis of atmospheric conditions (information on wind speed and direction used to model air motion in a 3D map of the operation area).1 minutes for every minute of powered cruising to have the batteries fully charged by landing. To maximize the efficiency of the UAV the following should be considered: • • • • • solar cells should cover maximum of the suitable surfaces and have the highest possible efficiency power input of the equipment should be minimized drag of the aircraft should be minimized large and slow (more efficient) propellers should be used (possibly installed as ducted fans) the control system should efficiently search for strong updrafts enabling higher recharge rates.1 which means that the aircraft would need to regenerate for 3. energy balance Following this analysis it has been shown that it is possible to build an unmanned aircraft powered with solar power and regenerative soaring from an existing aircraft so that it would be capable to self launch. A grand challenge for the aircraft would be to stay aloft during the nighttime when two important sources of energy vanish: sun and thermal updrafts.g. Dynamic soaring requires precise flight control in sharp low altitude maneuvers (20-150m over ground) and a reasonably small and sturdy aircraft (dynamic soaring is often used by RC pilots). .6 Conclusion. In this configuration the ratio between free cruising and regen is 1:3.2. The analysis shows that using regenerative soaring shortens the recharge time significantly during the day. Regenerative soaring is the only source of energy for the aircraft during the night. the UAV can perform surveillance and regen at the same time). It should be considered that the regeneration time may be used to accomplish mission objectives (e. The total flight time in the investigated scenario was 5 hours and 53 minutes. climbed maximum 844m in a single updraft and gained 172 meters in an updraft in average. We propose to improve the performance of the UAV by using a vision system for recognition of typical signs of updrafts (cumulus clouds) and ground wind and weather analysis for Illustration 10: CloudSwift.g. Updrafts were only detected after the UAV had physically encountered them. Illustration 9: SoLong UAV. Stall speed: 33kt. The trained artificial neural network can be used as a subsystem of the control system. Span: 4. AC Propulsion. The plane sports a wingspan of 4. [8.75 m and weighs 12.9]).26m. These results indicate that it is possible for an UAV to autonomously search and utilize updrafts. The core of the control system is proposed to be rule based. Updraft detection sensors were not used. This can be done either off-line using recorded flight data or on-line because the proposed aircraft enables presence of human pilot on board during experiments. Recursive learning was used to center updrafts and neural networks were used to identify updraft positions. Weight: 6. The experiments were first performed in simulation. We also propose application of artificial neural network learning to fly by observing actions of a human pilot.2.58kg. NASA Dryden identification of areas producing updrafts (upwind slopes and thermals). 2005 over 48 hr nonstop fueled only by solar energy. . Since then several other works were focused on soaring UAV's (e. Algorithms were too intensive for real-time use at that time. NASA Dryden Flight Research Center supported a project of an autonomous soaring UAV [8] (CloudSwift. Mission speed: 46kph). Archimedes spiral pattern was chosen for the UAV to fly while searching for updrafts. CloudSwift UAV was used for real world experiments. During 17 test flights CloudSwift found 23 updrafts.6 kg.3 AI and Control System Autonomous soaring for UAV's was first proposed in 1998 [7]. Simulation results showed that a small UAV can benefit significantly by exploiting updrafts and simulation study assumed that a small UAV could autonomously detect and center updrafts. The SoLong unmanned aerial vehicle from AC Propulsion flew on June 13. These results could be important for development of completely autonomous UAV's for extra-terrestrial research e. Regenerative soaring has not been practically tested on an aircraft yet.g. The measurements taken could be helpful for future applied research. for Mars exploration. Comparison of performance of manned and unmanned aircraft would be possible. The possibilities of this design are important because it enables straightforward step to manned flight without fuel.3 Estimated Project Impact Results of this project would contribute to several scientific fields: aeronautical engineering. In this setup artificial neural network can be used to learn how to fly from a human pilot. electric engineering. robotics and artificial intelligence. The proposed UAV is intended to fly with or without a human pilot. . Important are also the results obtained in the field of artificial intelligence and robotics. He has 25-years of experience in the performance analysis and computer modeling of aerospace vehicles and subsystems at Northrop Grumman. in what is the first commercial offering of an electric aircraft. and flight mechanics. He is aviation writer for several Finnish and foreign aviation magazines.Acknowledgments I would like to thank to the following people who contributed to the project proposal by providing advice and consultation: Phil Barnes is Principal Engineer at Northrop Grumman Corporation. Jukka Tervamaki graduated from the Helsinki University of Technology in 1963 specialized in Aeronautical Engineering. designing and building has been everyday work as well as a hobby for him for four decades. He has logged total 2200 flight hours of which 150 hours in autogyros. He has a Master’s Degree in Aerospace Engineering from Cal Poly Pomona and a Bachelor’s Degree in Mechanical Engineering from the University of Arizona. He has won numerous awards and accolades for his work on electric flight and already has built an electric-powered ultralight and a single-seat motorglider. In April 2007 the Electric Aircraft Corporation began offering complete electric ultralights and engine kits under the ElectraFlyer brand name. creating. . Experimenting. to convert existing ultralight aircraft to electric power.Regenerative Soaring Feasibility Study” [4] Randall Fishman is the president of Electric Aircraft Corporation. He designed and build several rotary wing aircrafts (autogyros). a motor glider and cooperated on development of a fixed wing tow plane. Phil Barnes is the author of the paper “Flight Without Fuel . gears. Phil has authored technical papers on aerodynamics. I. 1318 Sept. United States Patent 7431243 .northwing.dfrc.nasa.sae. email correspondence with Philip Barnes. Herszberg (1998). (2005) Autonomous Soaring for Improved Endurance of a Small Uninhabited Air Vehicle. AIAA Electronic Publication .com/ [4] Philip Barnes . [5] NASA Dryden Fact Sheet .electraflyer.org/.aeriane. 26 2009.. as of Oct. http://www. Melb. Proc.Pelican Aero Group. Wichita. Session: Propulsion Dynamics and Advanced Engine Concepts. (ICAS '98. Stratus. Flight Without Fuel . http://dtrs.com [3] Northwing. http://www. Meeting Presentation AIAA-2005-1025. president of Electric Aircraft Corporation [2] Aériane SWIFT rigid wing hang glider http://www. email correspondence with Randall Fishman. Research Engineering. Wharington.fai.org/technical/papers/2006-01-2422. '98 . USA. http://www.CD ROM. Michael J. [7] J. presented at General Aviation Technology Conference & Exhibition. August 2006. [6] The Worlds Air Sports Federation http://records. Scott.Sources: [1] Electric Aircraft Corporation. Rodney S. Vic. 'Control of High Endurance unmanned air vehicle'. Thomson & Murray L. ISBN:1-56347-287-2 98-1141. eds. KS.com/. NASA Dryden Flight Research Center.RMIT Fishermen's Bend.html.nasa.Pathfinder Solar-Powered Aircraft http://www.gov/centers/dryden/ news/FactSheets/FS-034-DFRC.) [8] Allen. 21st Congress of the International Council of the Aeronautical Sciences.Regenerative Soaring Feasibility Study.gov/archive/00001168/ [9] Guidance and control for an autonomous soaring UAV.