NINE FOOT HOVER FACILITY



Laser sheet illuminates a thin slice across two successive turns of the tip vortex from a
single-bladed rotor in hover. The rotor tip path plane is to the right of the image. GTEAG, 1990.

This is a double-walled , double-celled rotor test chamber. A 15hp DC motor drives the shaft at speeds from 0 to 1500 rpm. Rotor diameters up to 5 feet have been tested. A honeycomb screen with a wake inductor minimizes recirculation unsteadiness, enabling us to obtain steady tip vortex core trajectories as far as 360 degrees after generation. In the 1970s, this facility saw extensive use in developing Prescribed Wake and Free Wake methods. A single-bladed rotor with a counterwight provided a basic test case for helicopter aerodynamics, with wake geometry, thrust, torque, blade surface pressure and wake velocities ( using a split-film thermal anemometer) measured in detail. Tip modification experiments were conducted, with various geometrical modifications tested. In the 1980s, laser Doppler velocimetry was used with a unique Remote Off-Axis Scatter System, to make detailed measurements of the tip vortex core. The core was also visualized and its trajectory quantified using a synchronized laser sheet. In the late 80s and early 90s, an Advanced Blade Tip geometry was studied using pulsed high-power laser sheets and LDV. This facility continues to be used for various diagnostic developments, and for measurements on automobile components as well as rotor aerodynamics.

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