Wind Tunnel Test of the Modified Goldschmied Model with Propulsion and Empennage: Analysis of Test Results

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Wind Tunnel Test of the Modified Goldschmied Model with Propulsion and Empennage: Analysis of Test Results

F. R. Goldschmied

An extensive test program was carried out in DTNSRDC's 8x10 low-speed wind-tunnel for experimental verification of the integrated hull boundary-layer control/propulsion lighter-than-air design. The 1957 Goldschmied wind-tunnel model was overhauled with a new suction-slot inlet configuration, a suction/propulsion fan, a new aftbody and a tailboom/empennage assembly. The fan air power coefficient of the operational model with empennage ranged in steady flight from 0.0130 (free transition) to 0.0155 (transition tripped at 10% length) at the volume Reynolds number of two millions. Considerable excess thrust could be generated with an average incremental propulsive efficiency of 72%. As compared to wind-tunnel tests of conventional streamlined bodies with empennage at exactly the same volume Reynolds number, the integrated design offers 50% less equivalent drag for both free and tripped transitions. The empennage provided neutral static stability over the complete test range of 8 degrees; the ratio of total fin planform over volume equivalent was 0.404. It was found that efficient and stable BLC could be achieved only by the combination of Ringloeb cusp at the slot's leading-edge with suction flow and with the presence of the tailboom. The fan (or pump) design is an essential part of the system design: a procedure was developed for determining the optimum fan design parameters from the vehicle's wind-tunnel test data. As an example, a tested NACA axial rotor/stator stage could be employed with 93% adiabatic efficiency for the vehicle with empennage and tripped transition. Keywords: Airships; Aerodynamics; Hydrodynamics; Jet propulsion.