engineered system of distribution and storage of energy would be much more efficient. Distribution of several smaller engines would also be superior.

To address the need for small engines that run on JP-8 fuel, ARL should review the recent successes at the Rochester Institute of Technology in the development of spark-ignited two-stroke heavy fuel engines.

Flapping Flight The experimental work being done on the flapping flight of nano-scale air vehicles is exceptional. However, the use of rotors and fans should also be investigated. Although some early research indicated that flapping flight may be more efficient than steady rotary motion at nano-scales, recent research does not support this idea. The power for steady motion of a rotor requires overcoming the induced drag and profile drag of the rotor. The power for flapping flight requires power for overcoming induced drag, profile drag, and the inertial power required to stop and reverse the flapping motion.

Flapping may not be the best use of the limited power available on nano-scale air vehicles. Comparing flapping to rotary wing flight might be an appropriate research task that probably should be done, but it might be easier to devote a similar effort to developing rotary winged nano-scale air vehicles. Current work on the quad fan and maple seed concepts may provide a starting point for rotary wing nano-scale air vehicles.

Another opportunity is the engineering of flapping systems; this involves not only their construction and testing, but also how to engineer these platforms. Because they are not fixed-wing aircraft, there is no coherent way to design these systems with respect to power, stability, and controls.

Palm-Sized Aerial and Ground Platforms The objective of this project is to provide the fundamental aeromechanics and ambulatory tools to enhance MAST objectives. The research involves very significant multi-university partnerships, with funding from multiple governmental agencies. Physics related to the vehicles are very different because of low Re and the dominance of the viscous effects. Traditional computational fluid dynamics codes do not have good predictive capabilities, and experimental results are not easy to replicate for the length scales under consideration. Flight vehicles are also highly susceptible to atmospheric disturbances and, therefore, call for new approaches to flight control. The approach consists of experimentation with concepts that loosely model winged flight in nature (e.g., small birds and insects). The focus is clearly on flapping-wing flight, although the lead investigator’s background in rotary wing flight has introduced innovative micro-air vehicles such as the quad rotor and the ducted fan rotor. The mass of the vehicles considered in the work ranges from 12 g to 100 g. A parallel effort to understand the mechanics of small ambulatory ground vehicles is less developed.

The work’s promise lies in developing a deep understanding of flapping-wing aerodynamics and a much better appreciation of the engineering scaling laws that apply in this environment. The progress in this regard can at best be characterized as limited. The computational fluid dynamics models have shown some promise in qualitatively characterizing the experimentally observed flow patterns for hovering flight. Simple flat plate models have been developed to study the highly coupled aero-structural behavior; a flapping-wing rig has also been built to do fundamental flow measurements to augment the simplistic computational models. Similarly, interaction of flows between two flapping wings has been visualized in the tunnel. If successful, there is considerable value in the work to push the envelope on developing micro-air vehicles. To date, however, the success has been limited, and such micro aerial platforms will develop largely through a build-and-test approach with limited understanding of the physics. The flight of the cyclocopter is an example of such an approach. The principal impediments to microscale ground vehicle ambulation are not well understood. The current approach emulates the mechanics of motion of small insects; designing mechanisms at this length scale may be the goal of this work. Design of both



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