An Exploratory Investigation of the Effects of Large Variations in Rotor System Dynamics Design Parameters on Helicopter Handling Characteristics in Nap-of-the-Earth Flight

This paper presents some results of a coordinated analysis and ground simulator experiment designed to investigate the effects of large variations in several rotor-system design parameters on the handling characteristics of single-rotor helicopters without stability augmentation in nap-of-the-earth (NOE) flight. The rotor-system design parameters investigated were flapping hinge restraint, flapping hinge offset, blade Lock number, and pitch-flap coupling. Forty-four combinations of these four parameters, which cover teetering, articulated and hingeless families of rotor systems, were investigated using a common fuselage, tail rotor, and empennage in a simplified generic nine-degree-of-freedom single main-rotor helicopter math model. In the experimental task, three kinds of obstacle course designed to emphasize vertical maneuvers, lateral maneuvers, and a combination of the two, were negotiated. A fixed-base simulator was used with a visual scene generated from a 1:400 scale NOE terrain board. The results of the study are presented as pilot ratings, pilot commentary, and some objective performance measures. In particular, criteria for satisfactory vehicle damping and control sensitivity are reexamined with the additional factors of cross-coupling due to pitch and roll rates, longitudinal static stability, and pitch coupling with collective pitch.