Prof James Delaurier in Canada has done a lot of research about flapping wing flight and has written several good articles in the subject. He also has the craziest ongoing project that I have ever seen. A fullscale ornithopter!!
Have a look at his homepage at http://www.ornithopter.net

Several of Delauriers articles can be downloaded from his homepage. One article describes an aerodynamic model for computing lift and thrust of a flapping wing. If you are going to build an ornithopter I would recommend that article. I have used the model to create a small electric ornithopter with successful result. See the video I have attached below.

http://www.m.lintek.liu.se/usr/m98da...rd_of_prey.wmv

/David