Trajectory Design and Control Strategies for GPS Skywriting

Aircraft trajectories are normally of interest to pilots and air traffic controllers, although the accessibility of flight path tracking websites has resulted in substantial public interest. Flight tracking websites are often used to track the progress of commercial flights by those waiting to pick up friends or family arriving on those aircraft, or by aviation enthusiast curious about the operations of rare or specialized aircraft. While these websites show the current location of enroute aircraft, they also show the entire trajectory, represented by a line or pattern over the ground. The permanence and public accessibility of flight tracks has led many pilots to fly trajectories that form words, symbols, phrases, or designs. These flights resemble classic skywriting flights in which a barnstorming airplane may use smoke to write a word or draw a shape by means of the flight path. GPS skywriting, in contrast to skywriting with smoke, allows pilots to fly large, complex paths that yield persistent designs that can be only be visualized using GPS flight path tracking software. This paper provides an overview of the process used by pilots to plan, design, and fly a trajectory intended for GPS skywriting. The challenge can be visualized as illustration with a pen traveling at 100+ MPH that cannot be lifted from the paper, stopped, or moved in any way that violates the limited flight performance of the aircraft. The constituent maneuvers in a GPS skywriting flight depend on choices made during planning along with environmental and aircraft constraints.