Elevator Tab Model and Aerodynamic Hinge Moment Variation Effect on Flutter Analysis of a Small Commuter Aircraft

Abstract

Investigation of flutter instability analysis is an important process during design phase and certification of an aircraft. Without proper analysis, the effect of modification at later stage of design process could come at high cost and risk. The present work examines detailed elevator tab model which could result in a more critical tab flutter speed. The present investigation of aerodynamic hinge moment variation effect on flutter analysis also shows a significant decrease in the flutter speeds.  Three configurations involving elevator trim tab and balance tab fixed/free mechanism are investigated.  Investigation of flutter sensitivity to tab rotational frequency and tab bending/torsion frequency was performed to determine the minimum tab rotational frequency requirement, so that it can be used as reference in design process.  Variation of Mach number (for Configuration 1) and elevator aerodynamic hinge moment (all configurations) are performed.  It is found that the aerodynamic variation takes effect when the mode involves both trim and balance tabs and tab elastic modes (e.g., tab torsion).  It is found also that the most critical flutter case is for Configuration 3 where the trim and balance tabs are not fixed (independent).  The result suggests that control surface tabs need to be modelled from the early design process, so that if any critical flutter appears and needs to be responded by a change in design, it can be implemented earlier and therefore avoid any costly risk.