Stick-to-Stress Dynamic Flight Simulation for Virtual Flight Test

ABSTRACT: The overall technical objectives of the Phase II efforts are to develop, implement, and validate a computationally efficient and accurate buffet load predictive capability in ZONA's Stick-To-Stress Dynamic Flight Simulation (STS-DFS). This capability will allow a continuous simulation of the aircraft in STS-DFS for smoothly varying angle of attack and speed providing aircraft attitude, structural deformations and stresses, as well as accumulated fatigue damage due to buffet loads in additional to maneuver loads and in the entire range of Mach numbers. To achieve the Phase II technical objectives, CFD generated data will be combined with experimental data to build a compact buffet model that is valid for a wide range of angles of attack and speeds. This compact buffet model will be incorporated in STS-DFS to complement its current wide ranging capabilities to further include buffet loads to the aircraft. To address the fatigue life concerns due to buffet loads, a fatigue module will also be added in STS-DFS which builds upon its current stress predictive capabilities. The time histories of these stresses will be processed through a rainflow cycle counting which will provide increments in fatigue damage estimated using one of several accumulation rules broadly used. BENEFIT: The U.S. Air Force, Navy, and Army will benefit from the STS-DFS capabilities to simulate the key aeroelastic coupling mechanism between structural dynamics and nonlinear unsteady aerodynamics, the store ejection, maneuver, gust, and buffet loads, including the effects of uncertainty associated with aircraft-to-aircraft variability. The buffet loads predictive capability will be particularly useful to identify potential fatigue problems on U.S. advanced fighters such as the F-35 and F-22 because both have twin-vertical-tail designs. These twin vertical tails are immersed in the separated flow during high-angle-of-attack maneuvers and suffer from high buffet loads. Application of the STS-DFS to those fighters will permit the fatigue life estimation of their vertical tail structures. Several U.S. military aircraft such as the F-16, F-15, C-5 and A-10 are reaching or are already beyond their originally designed fatigue life. To identify their residual fatigue life or extent their fatigue life by retrofit, accurate loads spectra to perform ground fatigue test on those aircraft are required. To establish such loads spectra, engineers must perform simulations for various mission scenarios that the aircraft may experience during their life cycle. Such loads spectra can be generated by STS-DFS using its broad simulation capabilities for loads generation.