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Basic Information:

Title: Energy Harvesting (EH) for Small Air Vehicles
Program: SBIR
Technology Area: Air Platform, Ground/Sea Vehicles
Open Date: 12/6/2006
Close Date: 1/10/2007

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.

Conduct trade studies on and develop and flight test a small air vehicle that utilizes energy harvesting (EH).
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.
Commercialization Potential:

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

1. M. Dornheim. Perpetual Motion. Aviation Week and Space Technology. June 27, 2005, pp.48-51.

2. P. Marshall, and D. Abner. Power Line Urban Sentries (PLUS) Program, Phase I," AFRL-IF-WP-TR-2005-1532(AD number B307886).

3. 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.

4. 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.

5. J.P Thomas, M. A. Qidwai, P. Matic,and R. K. Everett, Multifunctional Structure-Plus-Power Concepts, AIAA-2002-1239.

SBIR Keywords

energy harvesting, solar cell, piezoelectric, power line induction, thermal, motor, battery, flapping
TechMatch Keyword(s):

Autonomous Systems
Aviation Technology
Energy Technologies
Energy Storage
Fuel Cells

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