7.0 CONCLUSION The Defense Advanced Research Projects Agency (DARPA) is working on the development of a new class of flight vehicles called micro air vehicles (MAVs). The high level of current interest in developing small flight vehicles is the result of the nearly simultaneous emergence of their technological feasibility and an array of compelling new military needs. MAVs are fully functional, militarily capable, six-degree-of-freedom aerial robots whose mobility can deploy a useful micro payload to a remote or otherwise hazardous location where it may perform any of a variety of missions. Initial development of the MAVs is being spurred by military interest, however, MAVs could ultimately also be adapted to many civilian applications.

The definition employed in DARPA’s program limits these aircraft to a size less than 15 centimeters (6 in.) in length, width, or height [1]. MAVs must have a weight of 50 grams or less and must be capable of staying aloft for 20 to 60 minutes for a distance of 10 kilometers. Interest groups from the military, universities, and private companies have proposed multiple designs of MAVs. There are several possibilities on which to model the new MAVs. Some possible modeling sources include insects, birds, and small aircraft.

Hummingbirds’ characteristics make them a perfect candidate for MAV modeling. In the Fall of 1997, Alex Meyer and Stephen Serniak, of IMB, became the first group to study the motion of hummingbirds’ wings in flight. Besides writing up their progress and results, Meyer and Serniak documented recommendations for future groups to follow. As such, Ultra Flite implemented the recommendations provided and continued the previous research for their own analysis.

After the midterm presentation and report, Ultra Flite restructured its previous four objectives for this semester. Due to time constraints and the degree of difficulty, Ultra Flite and their sponsors, Dr. Stearman and Tifenn Boisard, discontinued the aeroelastic analysis of the hummingbird. Also, more emphasis was placed on conducting and post-image processing of the CT-Scan. Also, since the aeroelastic analysis was postponed, these results cannot be related to MAV technology. Ultra Flite did, however, do extensive research on MAV applications.

In order to complete its first objective, Ultra Flite reviewed the previous semester’s video footage and found it to be inadequate. Therefore, a decision was made by Ultra Flite to refilm the hummingbird in hovering flight to attain a more precise record of its flight characteristics. Filming of the hummingbird began when the three departments involved in the research coordinated a meeting time. The Department of Mechanical Engineering provided use of their high-speed video camera. The hummingbird and test assembly are located in the Zoology Department, and the engineers are from the Aerospace Engineering Department.

As a recommendation from IMB, Ultra Flite built a mirror assembly that was properly aligned at a 45º angle with the horizontal. This allowed correct positioning and no movement during the testing process as in last semester’s project. The correct alignment of the mirror allowed for consistent results between filming sessions. Also, better lighting allowed for improved contrast between the bird and the background in the footage of the film. This provided a picture more suitable for the analysis of the hummingbird’s wing characteristics.

After filming, each segment of the footage was downloaded individually from the high-speed video camera onto the tape. Two segments of the side-view, one segment of the top-view, and one segment of the rear-view were downloaded onto the tape. Each segment of the video was approximately 4 minutes long with one frame per second which gave us multiple cycles of the wing motion.

In order to obtain a computerized movie, we used Apple Video software to capture each segment. Connections from the VCR to the computer allowed for information transfer. After creating each movie of the different views, individual pictures were obtained from each frame for analysis. In the picture, it shows the frame number, the number of frames per second during recording, and the number of frames per second during playback. With all this information, we were able to keep track of each image and its order in the wing motion cycle.

In Figure 5.7, the hummingbird is shown flying at a roll and yaw angle. The picture doesn’t depict a symmetrical hummingbird. This same problem was encountered last semester, and it was determined that the previous mirror assembly was the cause. After Ultra Flite built a new and more reliable mirror assembly, the same problem was encountered. Therefore, it was determined that the hummingbird flies at a roll and yaw angle.

Ultra Flite engineers believe that the hummingbird flies at a roll and yaw angle for various reasons. One theory is that the feeder has a large entrance which does not require the hummingbird to fly straight into the feeder. Knowing the feeder can be approached from any angle, the hummingbird does not have to fly directly perpendicular to feed. As a result, the hummingbird in the video is not positioned symmetrically. Another theory proposed by Dr. Chai is that the hummingbird is aware of our presence in the room. As the hummingbird feeds, her situational awareness keeps her from flying in a normal state.

Ultra Flite engineers examined the side-view multiple times. Each test came from different time cycles of the hummingbird during hovering flight. After reviewing the data from three trials of the side view, the same airfoil pattern appeared. There is no doubt our hummingbird wing-tip traced an airfoil shape pattern instead of the traditional figure-eight outline.

The second objective of Ultra Flite was to construct a space-frame model of the hummingbird. In creating a space-frame model of any object, one must have extensive knowledge of the internal structure of that specimen. In order to complete this task, a CT-Scan of the hummingbird will be used to present data on the physiology of the hummingbird, especially the much needed bone structure. A step towards this objective was accomplished by using a CT-Scanner from the Geology Department to three-dimensionally model a preserved hummingbird body. The CT-Scanner uses x-rays that slice the specimen for analysis at certain thicknesses while simultaneously rotating it to get a three-dimensional model.

The specifications of the CT-Scan included a slice thickness of 0.1 mm to be used on Dr. Rowe’s bird. Ultra Flite was informed the specimen, although not an adult, was considered almost fully grown. The first scan was initiated, and the density spectrum of the hummingbird was gathered. The image data was downloaded to the LRC after the CT-Scan Lab finished the processing. Ultra Flite then downloaded 577 images in the TIFF format. Since the images include everything from bone to muscle, it was necessary to separate the bones from the rest of the bird in order to create a 3-D model of the bone structure. An image processing program, Adobe Photoshop v 4.0, was used to accomplish this task.

A problem with the scan was discovered after the thresholding procedures had been completed. During the scan, a shift in the position of the hummingbird occurred several times. This meant the CT-Scan data was useless. This discovery was forwarded to the CT-Scan Laboratory which decided to redo the scan. Also, the size of the image confirmed that the hummingbird was a baby, rather than an adult. The problem with a baby besides the size difference, is that the bones are soft compared to an adult which causes difficulty in recognizing the bone from the tissue. Nonetheless, Ultra Flite decided to create a 3-D model of the hummingbird’s head and beak since no shifts had occurred in that range of images.

When the new CT scan is successful and the data collected is filtered, creation of the space-frame model of the hummingbird can be accomplished with the use of Structural Dynamics Research Corporation's (SDRC) I-DEAS software package. The advantage of using I-DEAS is that the information collected from the CT-Scan can be imported into I-DEAS. Also, it is much more practical to use I-DEAS to generate grid points of the space-frame model; therefore, it may be used to transfer the generated grid points to NASTRAN.

This model can then be used to complete the initial third objective which was to use NASTRAN to analyze the space-frame model. An aeroelastic analysis can be done to the three-dimensional hummingbird model in order to study the unsteady loading on the bird during hovering flight. Finally, results from the filming and the aeroelastic analysis of the model can be related to MAV technology. This will allow for the ultimate goal: constructing a robotic hummingbird.