Helical Flight Path Trajectories for Autopilot Evaluation
A helical flight path trajectory (helix) involves flying exact circles over the ground while climbing or descending at a given flight path angle and speed profile. The manoeuvre is challenging to fly in windy conditions, since the path reference is inertial whereas the aircraft naturally tends to move with the air mass. Tracking a helix introduces periodical lateral and longitudinal wind shears in turn. This makes the helix an excellent manoeuvre for testing autopilot control laws, allowing to evaluate co-ordination of longitudinal and lateral modes, tracking accuracy along a curved flight path, combined tracking of inertial (flight path) and air mass-based references (airspeed), and to evaluate the trade-off between behaviour in turbulence and wind shear. Since helical flight path trajectories are not a standard option in most autopilot / flight management systems, this chapter derives generally applicable reference variables and high-level control strategies for use with typical autopilot structures. This allows the reader to fly the helix manoeuvre using his or her own autopilot design. As an example, simulation and flight test results for an autopilot developed for DLR’s test aircraft ATTAS will be discussed.
KeywordsWind Shear Side Slip Angle Bank Angle Ground Speed Speed Tracking
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