Michele Frumusa, Vincenzo Vaccaro
DOI Number: N/A
Conference number: IFASD-2019-153
This paper describes activities carried out by Leonardo Aircraft Division (LAD), focused on the extension of control surfaces freeplay requirements for the M346 Aircraft. An engineering campaign was conducted, having the purpose of assessing the aeroelastic effects of backlash greater than the prescribed requirements, derived for MIL-A-8870. There were two main reasons for this choice. The first was the difficulty the actuator supplier had to provide spherical bearings respecting the current tolerance without incurring in production cost issues. On the other hand, backlash tests performed on in-service aircraft often failed thereby triggering expensive and time-consuming maintenance activity. Considering the complexity of the phenomenon, intrinsically nonlinear, this task was mainly based on a flight test campaign, preceded by analysis and two risk mitigation activities, meant to provide a preliminary insight on the expected outcome of the test, consisting in dedicated tests performed on the Iron Bird Test Rig and Resonance tests, conducted on the A/C with a simplified setup, to evaluate the effects of freeplay on modal frequencies and estimate the magnitude of nonlinear effects. Both these activities were focused on Horizontal Tail (allmovable) given the complexity of its kinematic layout with respect to aileron and rudder. The campaign was successfully concluded, demonstrating the possibility to extend backlash without occurrence of aeroelastic instabilities and Limit Cycle Oscillation (LCO) phenomenon.