Hummingbird aerodynamics

Todays lab meeting was fully devoted to hummingbird aerodynamics. Firstly, Marta Wolf, who has just returned from a 2-year postdoc in the flight lab at Berkeley University presented her fascinating results from studies of Anna's hummingbird. We learned a lot about how it is to work with hummingbirds, which seems to be easy on one hand but also difficult as birds mass is only about 4.5 g (like a rather lean goldcrest) and they can rapidly loose weight and may have to be released. Marta showed PIV data on the hovering wake, as well as nice illustrations about hummingbird hovering in a box.
Second on todays agenda was the paper from the Altshuler lab about the hovering wake in hummingbirds, which was published i Experiments in Fluids during the last week. The authors claim their data show that the wake consists of bilateral vortex loops, one shed from each wing. In this sense the hummingbird wake show similarities to the typical wake of bats. However, we had some difficulties on seeing what the authors could see in their smoke visualization movies, while we will have reason to return to these data.

Cleaning up and some nostalgia

An old TV monitor is removed

Organization is restored

The old optic rail

Laser optics from MG

Space under test section where the PIV
laser used to live

Yesterday, Friday,  all Lundian members of the lab spent most of the day cleaning and tidying up in the wind tunnel. The reason is that we will soon get new PIV equipment and we need to free space around the test section in order to accommodate the new laser and camera set-ups. We also took the opportunity to clean out and organize the "control room" (the wind tunnel lab office), where lots of computers and monitors have accumulated over the years, which are not used anymore. The biggest operation was the removal of our first PIV laser, a 10 Hz rep rate pulsed laser from Spectra Physics. This laser has served us well and was instrumental to our first custom-built PIV system  that resulted in the first DPIV study of a live animal in free flight (Spedding, Rosén and Hedenström 2003, J Exp Biol). The same laser stayed with us when we replaced the two-camera system with one camera, which we used for our first PIV study of bat flight (Science 2007). After that we have used a stereo-PIV system and Litron laser of 200 Hz. Now it is time to get the 3rd PIV laser to the Lund wind tunnel, and we are grateful to the old equipment that has worked so well over the years. Especially the Spectra Physics laser has been very reliable, but at 10 Hz it is time for retirement. We also removed the rail of mirrors and light sheet optics from Melles Griot, which has been replaced by modern optic arms attached directly to the laser.

Flight Lab 2013 initial efforts

The transition into 2013 has involved a well deserved holiday for members of the Animal Flight Lab, and we have now gathered  gain to resume activities. The Tuesday lab meetings are now populated by two more people than has been the rule the last year. Marta Wolf has returned back from her postdoc at Berkeley, California, and will now join us again, initially on her repatriation funds. Anders attended the annual meeting of the KTH Linnaeus FLOW centre, where he gave a talk about the research we have carried out over the last decade or so. After the meeting he visited the low turbulence windtunnel at the Department of Mechanics (see picture), where research on flow transition is a current point in focus.

Today the entire group made a joint effort to move the boxes containing the laser for our new PIV system. As last time we encountered some problems in getting the large and heavy wooden boxes into the wind tunnel building, but we completed with success. The image shows when we rejected the first method of getting the power supply in through the side door, an attempt that was abandoned in favour of the more direct route through the basement floor after having unpacked the box.

Kinematics and wing shape in flying bats: new paper from the lab

In a new study, originating from Rhea von Busse's PhD thesis, the kinematics and wing shape changes are analyzed in great detail in flying bats, Leptonycteris yerbabuenae. The movements of a great number of morphological landmarks on the wings were analyzed and interpreted with respect to aerodynamic output by the wings. For example, the wing area, angle of attack and camber of the wing all decrease as flight speed increases. This is reflecting the declining demands on the wings as force generating devices. It appears that kinematics change in ways to preserve a favorable flow regime around the wings. However, it remains to investigate how the bats gauge the flow above the wings and use that information to control the motor output, something that we hope to address in future experiments. The paper is published in the open access journal Biology Open.

Animal Flight Lab meets Prof. Marianna Braza

The lab was visited by Prof. Marianna Braza from the Institut de Mécanique des Fluides de Toulouse, France, who presented her research on smart wings and turbulence of airplane landing gears. Marianna has become interested in biomimetics, i.e. obtaining design solutions from nature, with special emphasis on bird wings and ailerons. We presented out work on animal flight and dissuasions were initiated about possible future projects involving bird-inspired aerodynamic solutions, hopefully some that can become useful for future airplane designs.

Autumn lab meetings have started

The members of the Animal Flight Lab at Lund are gathering for the autumn term, which is filled with activities. Our Tuesday morning meetings have resumed and on the last occasion a new paper from the Brown bat flight group was discussed. This paper, by Iriarte-Diaz et al, published in PLoS One, was about "Kinematics plasticity during flight in fruit bats: Individual variability in response to loading", showed that individual bats of the same species has different ways of modulating wing shape and kinematics to achieve increased lift as a response to loaded flight. There are many ways how to achieve increased lift coefficient, such as changing flap frequency, amplitude, wing area and camber, to mention a few. The Brown paper showed that three bats used different combinations of lift enhancing modulation. The group found this paper very interesting!

We will continue to publish updates about lab activities at this site, so stay tuned and you will receive interesting news coming soon, such as reports from field work that starts next week.

Birds Best Bats In Flying Game

The scientific news site LiveScience wrote a cool piece on one of our recent publications (Comparing Aerodynamic Efficiency in Birds and Bats Suggests Better Flight Performance in Birds, PLoS ONE). The title of the piece is 'Birds Best Bats In Flying Game', and particularly their summary is entertaining: 'The bats may be trading some of their flying efficiency to carry extra echolocation equipment aboard'.

You can find the article here.