Airborne Acquisition of Blade Tip Displacements and Vortices on a Coaxial Ultralight Helicopter

Abstract

A series of comprehensive flight tests investigated the flight dynamics and explored the flight envelope of a newly developed ultralight, coaxial, counter-rotating helicopter from the company edm aerotec. The present paper focuses on optical measurement techniques that were applied to study the minimum blade tip clearance and convection of blade tip vortices around the dual-rotor system. A calibrated single-camera system was used to quantify the movement and distances of the blade tips at a critical rotor azimuth for multiple steady and unsteady flight maneuvers. The measurements allowed critical flight conditions to be identified and provided flight data for the validation of comprehensive rotor codes. In an additional flight test, an airborne background-oriented schlieren (BOS) system was operated aboard a second helicopter to visualize the blade tip vortices of the ultralight helicopter in forward flight. The BOS measurements resulted in the first visualization of blade-vortex and vortex-structure interaction effects on a full-scale coaxial helicopter. The application of optical measurement systems in the present flight tests gives valuable insight into the aerodynamics and blade dynamics of a free-flying counter-rotating helicopter and demonstrates how these methods can effectively support the development process of new rotorcraft.