Researchers in aviation were inspired by the flight abilities of birds. Therefore many investigations regarding the bird’s flight have been performed. Even though the mechanisms of bird’s flight remain widely unknown. For an understanding of the flight, it is needed to know the shape and kinematic of the morphing wing during flight. Currently there are only low resolution informations available for flying birds.
Therefore the project “Analysis of the bird’s flight” was established within the priority program 1207 “Nature-inspired fluid mechanics” (funded by the German Research Foundation DFG). Goal of this project is to adapt advanced optical measurement methods and to perform high resolution wing shape measurements on bird wings during free flight. There are three partners within this project (RWTH Aachen, UniBW Munich, DLR Göttingen) which combine their expertise.
The aim of DLR is to adapt the surface measurement method PROPAC to determine the shape of bird wings during free flight in high resolution. Another target is that the disturbance of the bird during the measurements should be as less as possible.
For this purpose a frame was build with a minimum aperture from two times the wingspread of the bird under investigation (see fig. 1). Cameras are mounted on this frame in the way that they observe the bird during flight through. In addition there are projectors mounted on the frame which project a random dot pattern onto the bird wing. In fig. 2 a part of a measurement picture obtained during free flight is presented. The natural pattern of the wing together with the projected dot pattern can be identified. Based on these pictures gathered from multiple cameras a three-dimensional surface can be calculated by means of the PROPAC method (see fig. 3).
The performed free flight experiments took place in Aachen, where the birds are trained from the RWTH Aachen. Barn owls (Tyto alba) are chosen as test animals and trained to fly along a specific flight path.
For the gliding flight tests the camera frame was positioned in the flight path and the owl was observed while gliding through the frame. The frame was steady in these test campaigns.
For the flapping flight tests the frame was moved along the flight path by a dolly–rail system. By use of this movement system it was possible to move the cameras synchronized to the bird. Therefore it was possible to cover complete wing beat cycles.