Stick-to-Stress Dynamic Flight Simulation for Predicting Fatigue Life and Scheduling Inspections of Aircraft

ABSTRACT: Both commercial and military aircraft are being flown/utilized for extended operational time. The aircraft cumulative flight hours often times extends the original design limits. Each different aircraft manufacturer calculates aircraft fatigue and damage using different techniques. A more accurate prediction of remaining life and inspection interval for an individual aircraft is required, as these aging aircraft are kept in operational status. ZONA Technology, Inc. has been working closely with The Boeing Company to develop a software process to more accurately predict the maneuver loads on an aircraft. This program is called"Stick-to-Stress Dynamic Flight Simulation"(StS-DFS) that can generate structural component loads and stresses due to a pilot stick input command. In the Phase I effort, we will further enhance StS-DFS to adopt previously recorded flight data as input and account for the mass variations due to fuel burn and mission-dependent stores to reflect the impact due to variations in pilot, payloads and fuel burn on the loads of the aircraft. The F-15 Saudi aircraft, an on-going Boeing's project for verifying an new"fly-by-wire"capability, will be selected to validate the enhanced StS-DFS with the newly acquired flight test data from the F-15 Saudi flight test. BENEFIT: Recently, the Air Force Research Laboratory has produced a long-term vision, called the Airframe Digital Twin that calls for the development of a physics based process of determining initial or remaining aircraft structural life. The outcome of the proposed Phase I effort will be one of the crucial early steps towards the Airframe Digital Twin vision. Several U.S. military aircraft such as F-16, F-15, C-5 and A-10 and commercial aircraft are reaching or are already beyond their originally designed fatigue lives. To identify their residual fatigue life or extend their fatigue life by retrofit, accurate loads spectra to perform fatigue analysis or ground fatigue tests on these aircraft is required. Such an accurate loads spectra can be generated by StS-DFS using the recorded flight test data of individual fleet members of these aircraft as input to keep track of the individual fatigue life as proposed in the USAF Digital Twin vision with the concept of improved fatigue calculation. In Phase II, the ZONA/Boeing team will develop a process that can extract the stresses generated by StS-DFS around the identified fatigue critical regions in the structure and use these stresses as input to their respective structural component damage tolerance models; leading to an updated life prediction and inspection interval of an individual aircraft.