SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-258 (AirForce)
Title:  Energy Harvesting (EH) for Small Air Vehicles
Research & Technical Areas:  Air Platform, Ground/Sea Vehicles

  Objective:  Conduct trade studies on and develop and flight test a small air vehicle that utilizes energy harvesting (EH).
  Description:  There is growing military interest in the development of small air vehicles (3m span or less) to provide reconnaissance capability. These vehicles might serve security forces, special forces, and other small units in the field, or they might report directly back to a command center or communicate via a network of similar vehicles. A common them among these types of vehicles is a near-continuous presence on station. This requirement introduces a serious design problem for vehicles that use combustion-based propulsion. Small vehicles simply cannot carry enough fuel to meet long endurance requirements without refueling. That being said, electric-based propulsion is even worse. The energy density of batteries does not compare well with chemical fuels. However, recharging (refueling) an electric vehicle is at least possible, although admittedly challenging. The usual method employed today is solar cell based. However, there are alternatives to solar cells for recharging electric-powered vehicles. All of these techniques can be classified generically as EH. Typical EH technologies under consideration include solar cells, piezoelectric devices for extracting energy from mechanical vibration (perched on vibrating machinery), thermal devices for converting heat into power, power line induction, soaring (seeking out thermals and ridge lift) and dynamic soaring (extracting energy from turbulence or other velocity gradients such as near ridges and ground effect). One of the main difficulties of EH technologies is system integration followed closely by a lack of real understanding the place of each EH technology. Adding to this lack of understanding is the rapid advancement in EH technology, especially in solar cells where relatively low weight and high efficiency are no longer mutually exclusive. Batteries are also an interesting problem and are advancing rapidly. Lithium polymers have recently begun taking over segments of the radio-controlled market due to their high energy density. However, in some circumstances, a high power density is required. As just mentioned, the biggest challenge for EH and storage technologies is system integration. The weight and volume budget for small vehicles is especially tight, which forces designers to think hard about multifunctional structure and structurally integrated concepts in order to get all of the required devices onto the vehicle. But what is the right mix of technologies, and how are they all connected? For example, solar cell selection is a strong function of mission requirements, and the best topology of the power train is not well understood. For example, if excessive power is available, should that power be sent directly to the motor or to the battery? Although sending it to the battery would mean two losses (into the battery and then out), the excess power available may simply be mismatched (voltage, current, impedance,ect) to the needs of the motor. Finally, the state of the art and even into the near future of these technologies indicates that EH alone may not provide enough power for continuous flight. The vehicle must be able to sense an energy source (sunny location, thermals, power lines, vibrating equipment) and be able to land or attach (perch) at that location. Both sensing and perching are nontrivial problems.

  PHASE I: Conduct trade space exploration on and compare and contrast various EH technologies. Identify good power train topologies. Vehicle size is not to exceed 1 m in span or length, and exploratory flight times will range from 20 to 60 minutes.
  
  PHASE II: Bench test several concepts to verify Phase I analysis. Produce a flight experiment vehicle based on the results from Phase I and Phase II bench testing. Test this vehicle both in EH and non-EH modes to verify EH performance.

  DUAL USE COMMERCIALIZATION: Military application: Reconnaissance (urban and field) for special and security forces and other small units, remote monitoring, and search and rescue. Commercial application: Pipeline, forest, and border patrols, homeland security, search and rescue

  References:  1. M. Dornheim. “Perpetual Motion”. Aviation Week and Space Technology. June 27, 2005, pp.48-51. 2. T. Nam. “A Generalize Aircraft Sizing Method and Application to Electric Aircraft,”. 13th Annual ASDL (Georgia Tech) EAB Meeting, Atlanta, Georgia May 3-5, 2005. 3. J. Berton,and J. Freeh, T. Wickenheiser, “An Analytic Performance Assessment of a Fuel Cell-Powered, Small Electric Airplane” NASA/TM-2003-212393, June 2003. 4. J.P Thomas, M. A. Qidwai, P. Matic,and R. K. Everett, “Multifunctional Structure-Plus-Power Concepts,” AIAA-2002-1239.

Keywords:  energy harvesting, solar cell, piezoelectric, power line induction, thermal, motor, battery, flapping

Additional Information, Corrections, References, etc:
There is interest in small air vehicles under 1m wingspan (the smaller the better, think MAV size) to go out into the field and act as sensors over long periods of time. Our vision is that the vehicle flies around until its energy storage is depleted. Then it lands or perches and harvests energy to recharge. The vehicle may also sense while perching if sufficient energy is available. The vehicle then launches, senses, and perches again. Ad infinitum.

Both electric and liquid fuel based solutions are acceptable as long as they fit into this mission. However, electrical power is required to power sensors and data links over periods of time ranging from hours to days to weeks possibly.

The goal of Phase I is to design a powertrain (motor/engine, energy storage, energy harvesting components, etc.) subsystem for a vehicle with wing span 1m or less. It is more about the powertrain subsystem design & trades rather than the vehicle design. Is there a “best” circuit topology? What mix of components is correct? Is there a role for supercapacitors? We are not primarily concerned with the design of the vehicle. However, there may be important trades between the energy harvesting design and the vehicle design – weight, cost, and volume for example. There may be component integration challenges that may required a look at certain aspects of the vehicle design, though. There may be synergy to be had by also considering the zeroth order design of the vehicle (wing loading, aspect ratio, camber, etc.). As far as the trades are concerned, there is no correct answer since we are not relating the figures-of-merit to measures-of-effectiveness. You may pick an existing vehicle as far as tacking the effects at the vehicle level. But remember, the major focus is the powertrain subsystem design and trades for vehicles with 1m wingspan or less.
Reference “Power Line Urban Sentries (PLUS) Program, Phase I," AFRL-IF-WP-TR-2005-1532(AD number B307886) is not publicly available and under limited distribution. The basic technique described in the reference can be found by using search terms like "powerline inductance harvesting".
There is interest in small air vehicles under 1m wingspan (the smaller the better, think MAV size) to go out into the field and act as sensors over long periods of time. Our vision is that the vehicle flies around until its energy storage is depleted. Then it lands or perches and harvests energy to recharge. The vehicle may also sense while perching if sufficient energy is available. The vehicle then launches, senses, and perches again. Ad infinitum.

Both electric and liquid fuel based solutions are acceptable as long as they fit into this mission. However, electrical power is required to power sensors and data links over periods of time ranging from hours to days to weeks possibly.

The goal of Phase I is to design a powertrain (motor/engine, energy storage, energy harvesting components, etc.) subsystem for a vehicle with wing span 1m or less. It is more about the powertrain subsystem design & trades rather than the vehicle design. Is there a “best” circuit topology? What mix of components is correct? Is there a role for supercapacitors? We are not primarily concerned with the design of the vehicle. However, there may be important trades between the energy harvesting design and the vehicle design – weight, cost, and volume for example. There may be component integration challenges that may required a look at certain aspects of the vehicle design, though. There may be synergy to be had by also considering the zeroth order design of the vehicle (wing loading, aspect ratio, camber, etc.). As far as the trades are concerned, there is no correct answer since we are not relating the figures-of-merit to measures-of-effectiveness. You may pick an existing vehicle as far as tacking the effects at the vehicle level. But remember, the major focus is the powertrain subsystem design and trades for vehicles with 1m wingspan or less.
Reference “Power Line Urban Sentries (PLUS) Program, Phase I," AFRL-IF-WP-TR-2005-1532(AD number B307886) is not publicly available and under limited distribution. The basic technique described in the reference can be found by using search terms like "powerline inductance harvesting".

Questions and Answers:
Q: 1. The Phase I indicates that comparisons and contrasts of various EH tehcnologis are to be made. Is it necesssary and required in the Phase I that we compare and contrast various EH technologies?

2. It does say "Identify good power train topologies". We prefer to document the proposed power train system and not make the comparisions with others, but make a bench prototype "power train" during the Phase I. Is that acceptable?
A: The original topic was too broadly written. Hopefully the SITIS website provided the necessary clarification. We are primarily interested in the design and integration of an energy harvesting (EH) powertrain on an MAV size vehicle. We are allowing any EH technologies and up to 1m wing span to accommodate a wide range of technologies. However, the size proposed must pose a challenge for the design and integration of the EH powertrain. We are not concerned at this point with system level trades or the vehicle design such as suggested in the original topic language.
You may use an off-the-shelf vehicle to demonstrate the integration, but the integration must still remain a challenge.

Phase I is a theoretical development of the powertrain, identification of integration challenges (and some thought on how to solve them), and simulation and/or benchtop testing of the powertrain. Exit criteria / entry criteria for Phase II is that:

1) We have a working powertrain topology
2) It is "flight traceable" (fits into a vehicle weight/volume/power budget) or there are no long poles in the tent to make it so. Breadboards are OK as long as we can be convinced you can easily make a physical circuit that does fit into the weight/volume/power budget. The more realistic the better however.
3) We know where the challenges are for physical integration and testing on an actual flight vehicle (which defines Phase II) and have at least some idea of how to attack those challenges.

To answer your specific questions in light of the clarification,

1. It is not necessary to compare and contrast EH technologies, especially if you have a particular technology in mind. Put your focus on making that technology work. In any case, the focus has to quickly shift to development of the powertrain.

2. Bench prototype is acceptable and desirable. The bench prototype must be flight traceable as described above.
Q: 1. The Phase I indicates that comparisons and contrasts of various EH tehcnologis are to be made. Is it necesssary and required in the Phase I that we compare and contrast various EH technologies?

2. It does say "Identify good power train topologies". We prefer to document the proposed power train system and not make the comparisions with others, but make a bench prototype "power train" during the Phase I. Is that acceptable?
A: The original topic was too broadly written. Hopefully the SITIS website provided the necessary clarification. We are primarily interested in the design and integration of an energy harvesting (EH) powertrain on an MAV size vehicle. We are allowing any EH technologies and up to 1m wing span to accommodate a wide range of technologies. However, the size proposed must pose a challenge for the design and integration of the EH powertrain. We are not concerned at this point with system level trades or the vehicle design such as suggested in the original topic language.
You may use an off-the-shelf vehicle to demonstrate the integration, but the integration must still remain a challenge.

Phase I is a theoretical development of the powertrain, identification of integration challenges (and some thought on how to solve them), and simulation and/or benchtop testing of the powertrain. Exit criteria / entry criteria for Phase II is that:

1) We have a working powertrain topology
2) It is "flight traceable" (fits into a vehicle weight/volume/power budget) or there are no long poles in the tent to make it so. Breadboards are OK as long as we can be convinced you can easily make a physical circuit that does fit into the weight/volume/power budget. The more realistic the better however.
3) We know where the challenges are for physical integration and testing on an actual flight vehicle (which defines Phase II) and have at least some idea of how to attack those challenges.

To answer your specific questions in light of the clarification,

1. It is not necessary to compare and contrast EH technologies, especially if you have a particular technology in mind. Put your focus on making that technology work. In any case, the focus has to quickly shift to development of the powertrain.

2. Bench prototype is acceptable and desirable. The bench prototype must be flight traceable as described above.

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