Lift Coefficient and Drag Coefficient Characteristics of Autogiro Rotors of Coaxial Shafts - Two Rotors Contra-rotating Type and Single Shaft - Single Rotor Type

Abstract

This article reported the comparative experimental study of lift and drag coefficients of 2 typesautogiro rotors, i.e., the co-axial 2-rotors contra-rotating and the conventional single shaft rotor. Thecontra-rotating type consisted of 2 hubs, whereas the single shaft rotor engaged only 1 hub. Each hub of anyparticular rotor type was identical in size and attached with a similar size of 2 rotor blades. Each blade wasClark Y airfoil section, rectangular platforms, non-twist with a constant chord of 6 cm. and 37.5 cm. length.With the thickness-to chord ratio of 0.116. Test was conducted using an open type low speed wind tunnel.Three combinations of dependent parameters were emphasized, i.e., the effective setting pitch angle ofblade in the range of 0° to -15°, the tilt angle of rotor shaft setting in the range of 0° to 45° and variable offree air stream to the maximum of 9 m/s. The result showed that both rotor types did not rotate if setting atthe tilt angle of 0° and any blade pitch angle of 0° to -15°, as well as the particular tilt angle of 45° but withthe blade pitch angle of 0°. It was also being observed that the increasing magnitudes of air velocity,including the blade pitch angle, as well as the tilt angle caused the escalating of lift and drag coefficients forboth rotor types, however those action caused retreating of the tip speed ratio. For the contra-rotating rotor,the best lift and drag coefficients can be obtained under the following combination; that blade pitch angle of0° with tilt rotor shaft angles of 15° and 30°, and at the blade pitch angle of -2° with the tilt rotor shaft angleof 45°. For the contra-rotating rotor, maximum identical values of the lift and drag coefficients werereached at 4.130, at the particular tilt angle of 45° and with the blade pitch angle being set at -2°. Correspondingly,at the same tilt angle of 45° and the blade pitch angle of -2°, for the single shaft-single rotorcanbe accessible to the lift and drag coefficients at the vicinity of 2.471. In conclusion, contra-rotatingrotor when compare to a single rotor, offered higher values of both lift and drag coefficients at 54.21%,52.53% and 47.25% at the tilt of rotor shaft of 15°, 30° and 45° respectively.

Keywords : Autogiro Rotor / Coaxial Shafts - Two Rotors Contra-rotating / Single Shaft-SingleRotor / Lift Coefficient / Drag Coefficient