Abstract— Propellers are being used as propulsive devices since the early days of aviation. However, if they are not properly designed, they can have poor efficiency, especially at low Reynolds numbers environments such as the case of the high altitude airships envisioned in the MAAT project. Experimental data those operating conditions are crucial to effectively improve and validate new numerical design tools. This work presents the development of an experimental setup for low Reynolds propeller testing. The experimental data were successfully compared against reference data to validate the test rig. In addition, the performance data for commercially available propellers that were not characterized in the existing literature is also presented. Keywords— Airships, Low Reynolds Propellers, MAAT Project, Wind Tunnel Experiments. I. INTRODUCTION N the last years, high-altitude airships have been considered as a platform for different purposes [1]. Particularly, for application as telecommunication platforms, surveillance, monitoring and for transportation of people and goods [2-8]. In Europe, the Multibody Concept for Advanced Airship for Transport (MAAT [9]) airships are being developed as an alternative medium and long range transportation system. The project involves 12 different institutions and aims to develop a heavy lift cruiser–feeder airship system. Since the cruiser will operate at stratospheric altitudes, propellers are a valid option for propulsion [6,10-16]. Due to the high altitudes the MAAT airship propellers will operate in a Low Reynolds Number (LRN) flow environment. LRN effects can decrease the performance of propellers and the ability of the available numerical methods to predict that performance. To deal with this, JBLADE [17] software is being developed, as an open-source propeller design code, using a modified [18] Blade Element Momentum (BEM) M. A. R. Silvestre is with the Aerospace Sciences Department of University of Beira Interior, Edifício II das Engenharias, Calçada Fonte do Lameiro, n.º 1, 6201-001 Covilhã, Portugal (corresponding author, phone: +351 275 329 732 e-mail: mars@ubi.pt). J. Morgado is with the Aerospace Sciences Department of University of Beira Interior, Covilhã, Portugal. P. Alves is with the Aerospace Sciences Department of University of Beira Interior, Covilhã, Portugal. P. Santos is with the Aerospace Sciences Department of University of Beira Interior, Covilhã, Portugal. P. Gamboa is with the Aerospace Sciences Department of University of Beira Interior, Covilhã, Portugal. J. C. Páscoa is with Electromechanics Department of University of Beira Interior, Covilhã, Portugal. theory which accounts for three dimensional flow equilibrium. The software is coupled with XFOIL [19, 20]for its suitability in predicting LRN airfoil performance [21] JBLADE will be used to design different propellers as well as to estimate their off-design performance. To improve the prediction capability of JBLADE, accurate LRN propeller performance data is needed. Experimental work on propeller performance was abundant before WWII [22, 23] and a sound database of propeller performance characteristics got established. That was the golden age of propeller driven aircraft. After WWII, the widespread of jet propulsion [24] limited the use of propellers to light aircraft. However, in recent times, the small Unmanned Aerial Vehicles (UAV) advent has triggered the interest in the LRN wing and propeller aerodynamics. UIUC Applied Aerodynamics Group is a world leading institution, very active in the study of LRN aerofoils and propellers, with several publications describing experimental studies on propeller performance [25-28]. This paper describes the development of a test rig for measuring propeller performance and the experimental tests procedure simulating the LRN environment found at high altitudes. A number of wind tunnel tests performed on different small propellers is reported. In addition, the validation of the experiments is described in detail and performance data not found in the literature is presented for a couple of well-known commercial propellers. II. METHODOLOGY A. Experimental Setup The design chosen for the propeller thrust balance closely resembles the T-shaped pendulum concept implemented by UIUC [25]. A sketch of the design is shown in Fig. 1. An effort was made to reduce the complexity of the assembly inside the wind tunnel, in order to ensure minimal flow and measuring disturbances. The T-shaped pendulum is pivoted about two flexural pivots while being constrained by a load cell outside of the tunnel in an area above the test volume, where plenty of room is available. The flexural pivots are frictionless, stiction-free bearings with negligible hysteresis that are suited for applications with limited angular travel. The pivots are made with flat, crossed flat springs that support rotating sleeves. These flexural pivots were chosen over the standard bearings since they greatly reduce the adverse tendencies that bearings are prone to, when used in static applications, namely stiction and hysteresis. Propeller Performance Measurements at Low Reynolds Numbers Silvestre, M.A.R., Morgado, J., Alves, P., Santos, P., Gamboa, P., and Páscoa, J.C. I INTERNATIONAL JOURNAL OF MECHANICS Volume 9, 2015 ISSN: 1998-4448 154