This work presents the development and estimation results of using information from Inertial Navigation System (INS) and two separate GPS antennas placed along the longitudinal axis of an Unmanned Aerial Vehicle (UAV) in order to extract attitude information. The equations for direct calculation of the pitch and yaw angles were derived and implemented, revealing their insufficiency in estimating these angles directly. Methods were compared that use various combinations of attitude information from three different sources: rate gyroscopes, gravity vector, and dual GPS position. Attitude estimation results were evaluated using UAV flight data including an accurate 'truth' measurement from a mechanical vertical gyroscope. The dual GPS position information was shown to be effective in regulating INS drift, but only provided marginal improvement when also fused with gravity vector information.