Wind Tunnel Studies on a Micro Air Vehicle–Scale Cycloidal Rotor

Abstract

Systematic wind tunnel measurements were conducted on a small-scale cycloidal rotor (cyclorotor) with a span and diameter of approximately 15 cm. The three parameters varied in the studies were the blade pitch amplitude, phasing of blade pitch with respect to the freestream direction, and advance ratio. The measured quantities included the rotor lift, propulsive force, and power. At low advance ratios, both pitch amplitude and phase angle were effective in varying the rotor lift and propulsive force. At high advance ratios, the propulsive force was a stronger function of pitch amplitude than phase angle. At all advance ratios tested, power was a stronger function of pitch amplitude than phase angle. The parametric study results were interpolated to determine the power consumption, lift-to-drag ratio, and control input requirements of the cyclorotor in straight and level flight conditions. In the interpolation process, the blade pitch amplitude and pitch phase angle were assumed as the two primary control variables (rotational speed was held constant) and a 500-g twin-cyclorotor MAV was used as a reference for the baseline lift values. The effects of varying lift, propulsive force, and rotational speed on rotor power and control input requirements were examined at various forward speeds. The maximum forward speed tested for the cyclorotor in straight and level flight was 13 m/s (advance ratio = 0.94); at this speed, the power was 36% lower than in hover and the rotor operated at 1740 rpm with a lift of 2.82 N.

Force and flowfield measurements to understand unsteady aerodynamics of cycloidal rotors in hover at ultra-low Reynolds numbers

“…Systematic forward flight studies were also conducted in the wind tunnel, which showed the potential for a cyclorotor to perform efficient high-speed forward flight even beyond an advance ratio of 1.0 by a simple phasing of the cyclic blade-pitch schedule. 6,14 As shown in Figure 3(b), the power required decreased by almost 40% from hover to an advance ratio close to unity, which is phenomenal for an MAV-scale rotor. A twin-cyclocopter ( Figure 1) has five control degrees of freedom (three RPMs and two thrust directions).…”

“…Pioneering research on the cyclorotor concept for MAV applications has been conducted over the last 10 years. [4][5][6][7][8][9][10][11][12][13][14][15][16] This body of work represents one of the most comprehensive evaluations ever conducted on cyclorotors at MAV scales and involved systematic performance measurements in both hover 4,[8][9][10][11] and in a wind tunnel, [12][13][14] flowfield studies using particle image velocimetry (PIV), 4,8,9 computational fluid dynamic analysis, 12,13 and aeroelastic modeling. 15 These studies established a fundamental understanding of the cyclorotor performance and helped in formulating a set of design principles for an efficient cyclorotor operating at MAV-scale Reynolds numbers (Re < 40,000).…”

“…It is important to note that the key focus of the previous cyclorotor research was to understand the time-averaged rotor performance (lift, thrust, and power) in both hover and forward flight at Re $ 40,000, 4,[8][9][10][11][12][13][14] which is right at the median of the estimated operating Reynolds numbers for MAVs, which is Re $10,000-100,000. 1,[17][18][19] As it stands, there is a significant dearth in the understanding of the unsteady blade aerodynamics, which is even more important at the very low MAV Reynolds numbers at which the next generation of pocket-sized flying vehicles for reconnaissance and surveillance will operate.…”

Plasma Actuators for Cycloidal Rotor Thrust Vectoring Enhancement in Airships

“…In addition, by changing the pitching angle of the blades and controlling the rotational speed, the propulsive jet can be instantaneously controlled in terms of magnitude and direction, providing higher maneuverability and controllability to the aircraft [14]. Moreover, since cycloidal rotors operate at much lower rotational speeds than conventional propellers do, they produce considerably lower levels of noise [12,15].…”

Aerodynamic models for cycloidal rotor analysis

“…Cycloidal rotors have been studied for their application in vertical-axis wind and water turbines (Hwang et al , 2009; Maître et al , 2013; El-Samanoudy et al , 2010; Islam et al , 2008). Recent studies also investigated their application in unmanned micro aerial vehicles (Jarugumilli et al , 2014; Benedict et al , 2014, 2013, 2011; Benedict, 2010; Yun et al , 2007; Iosilevskii and Levy, 2006; Shrestha et al , 2014). Nowadays, their commercial use is limited to wind turbines and marine propellers.…”