Empirical Wake Turbulence Model of Tiltrotor Aircraft

This paper describes the methods used to collect and reduce wake turbulence data behind two distinct types of tiltrotor aircraft using a Light Detection and Ranging (LIDAR) measurement system, which uses laser velocimetry to measure the velocity of dust particles in air that has been disturbed by the passage of an aircraft. The test aircraft flew at various combinations of weight, rotor speed, airspeed and configuration. The MIT LL LIDAR system measured the wake vortices with minimal pre-test preparation; we obtained a large quantity of high quality data in only a few days of testing. The data shows tiltrotor and fixed-wing wake characteristics are very similar. Data reduction methods used a classical horseshoe vortex system as a template, and employed a vortex that had a rotational core and an irrotational outer field. Intersecting polynomials that are linear in downstream distance and bi-linear in downstream distance and mast angle adequately modeled vortex strength. A bi-quadratic polynomial function of downstream distance and mast angle adequately modeled core size.