Theoretical Experimental and Studies on the Influence of the Mast Mounted Sight (MMS) on the Dynamic Behavior of the Focal Isolation System (FIS) of Helicopter

This paper presents a theoretical-cum-experimental study on the dynamic behavior of Focal Isolation System of helicopter equipped with Mast Mounted Sight. A new simplified model of FIS/MMS/Fuselage with 5-Degree of Freedom (DOF) is proposed, where elasticity of the rotor shaft and the support structure of MMS are taken into account. In order to validate this model and make further investigation on MMS, a dummy MMS and its support are fabricated. Frequency and transfer function experiments are carried out on Z-X helicopter. Good correlation between theoretical and experimental results is achieved. A 39% decrease in 1st longitudinal frequency is noticed for FIS when the mass of MMS is 80kg, which is only 12% of the mass to be isolated. The elasticity of rotor shaft has great influence (403%) on the isolation efficiency of fuselage for prototype.