Experimental study of counter-rotating propellers for high-altitude airships

The experimental results on the thrust, power, and efficiency of a set of counter-rotating propellers (CRPs) at different low Reynolds numbers and various small advance ratios relevant for application for high-altitude airships was reported. The experiment data of the front and rear propellers have also been compared with an independent single-rotating propeller (SRP) at the same rotating rpm. The measurements reveal trends of reduction of thrust and propulsion efficiency of the front propeller, but increase of thrust and efficiency of the rear propeller, compared with the SRP, and an overall increase of thrust and efficiency. The front and rear components of the CRP model is exactly the same except for their opposite rotational directions. Each component is equipped with two straight blades with fixed pitch angle. The differences between front or rear propeller and SRP prove the existence of interference between front and rear propellers. Compared with two-blade SRPs, the thrust coefficient of the front propeller is slightly reduced because of the interference by the rear propeller. Meanwhile, the power coefficient of the front propeller has no obvious variation. This results in the slight decrease in efficiency of the front propeller.