The Prairie Bird was my first try at competing in the FAC Embryo Class. It is a very popular beginner Embryo with a long history.  A kit is available at https://www.wind-it-up.com/  A nice YouTube video of a successful flight has been posted by joshuawfinn entitled "Peck Prairie Bird, take 2"  June 2009.  A how to article may be found at http://www.theplanpage.com/things/pb/pb.htm  

My Prairie Bird has a demountable wing, and originally had a 6 inch Peck Plastic propeller, and an airframe weight of 18 grams  Wing Span is 16 inches and wing area is 48 sq. inches.  I used a rubber motor of 4 strands of 3/32 inch wide FAI Tan in 12 inch long loops, and got  flight times of 60 seconds by winding to 990 turns. With a 7 inch propeller, airframe weight goes up to 20,5 grams. Lengthening the rubber motor to 14 inches and winding to 945 turns, I got a 63 second flight.