It seems that the author developed the underlying kinematics needed to implement an inertial measurement unit (src: http://en.wikipedia.org/wiki/Inertial_measur

It seems that the author developed the underlying kinematics needed to implement an inertial measurement unit (src: http://en.wikipedia.org/wiki/Inertial_measurement_unit http://en.wikipedia.org/wiki/Inertial_measurement_unit ), though with his introduction of GPS, he could probably convert it to an inertial navigation system (http://en.wikipedia.org/wiki/Inertial_navigation_system http://en.wikipedia.org/wiki/Inertial_navigation_system). I wonder if the author is aware of the Extended Kalman Filter (src: http://en.wikipedia.org/wiki/Extended_Kalman_filter http://en.wikipedia.org/wiki/Extended_Kalman_filter ) -- he could fuse the noisy sensor data with the aircraft's kinematic model to cancel out some of the error he was mentioning getting. The best resource I've found online about how to use Kalman filters and EKFs is course notes from a simultaneous localization and mapping workshop taught at Drexel University in 2006 (src: http://prism2.mem.drexel.edu/~billgreen/slam/slam.html http://prism2.mem.drexel.edu/~billgreen/slam/slam.html ).