The aerodynamic resistance of tethered balloons

Abstract

 Values of the co-efficient of aerodynamic resistance of tethered balloons almost spherical in shape, exposed to the natural wind, are presented. These are compared with the results of experiments on spheres conducted in the laboratory wind channel and in the open air and also with the results of experiments with pilot balloons rising freely in the open or still air. The resistance co-efficient of tethered balloons is found to decrease sharply with increasing Reynolds number to a value of about 0.24 at Reynolds number 0.8 x 10⁵, then slowly to about 0.075 at Raynolds number 4.0 x 10⁵, finally leveling out to a more or less constant value of 0.065 at Reynolds number 5.0 x 10⁵ and beyond. The nature of the curve is studied in some detail and possible inaccuracies from excessive air turbulence, lack of sphericity and neglect of effect due to the weight and aerodynamic resistance of the thread are discussed.