A systematic study of membrane wings for flapping flight has been undertaken to assess aerodynamic performance and propulsive efficiency. Many pairs of wings were constructed using nylon fabric or thin Mylar. The wings were placed on a custom built flapping mechanism on a three component sting balance in the wind tunnel. Tests were performed at flapping frequencies from 0 to 4 Hz, at wind speeds from 0 to 6 m/s, and at angles of attack from -5° to +10°. The balance allowed for measurement of lift, thrust/drag, and pitching moment.Aspect ratio and weight behind the spar were found to be important factors in a wing's performance. It was also found that a crank or rearward bend in the spar can improve performance in certain cases.