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An Ameliorated Prediction of the Empennage In-Flight Gust Loads for a General Aviation Aircraft

Philippe Marchand, Embry-Riddle Aeronautical University - Daytona Beach


Airplanes often operate beyond their original design load profiles. Aviation opens so many new possibilities and wide variety of possible activities that it is hard for designers to foresee all loading spectra that the airplane structure will experience throughout its life. Nevertheless, the aircraft structures are required to be designed to failsafe or safe-life criteria to be certified by the FAA. AFS-120 provides a database of normal accelerations that can be used to derive airplane wing loads. ACE-100 describes an acceptable method for determining the fatigue life of an empennage based on the same normal acceleration data provided in AFS-120. However, this data have not been demonstrated to be applicable for empennage loads.

Earlier works have shown that maneuver induced-loads on the empennage can be predicted from motion parameters measured near the airplane center of gravity. Maneuver loads are pilot induced and do not account for weather related loads. During flight, the airplane is subjected to atmospheric turbulence and a method for determining empennage gust loads is desired. Embry-Riddle, with financial support from the FAA, has flight-tested a C-172P equipped with sensors to develop an ameliorated prediction of the empennage in-flight gust loads for a general aviation aircraft using Neural Networks. Both the power spectral density and the FAA 'two-second' methods have been applied to separate maneuvers and gusts. Findings were unexpected in that for this airplane, aircraft rotational motion appears to dampen empennage gust loads considerably and for the conditions tested, gust loads were not as significant as maneuver loads.