Aerodynamic Optimization of the Sizing and Blade Designs of Hovering Corotating Coaxial Rotors

Corotating coaxial rotors are seeing renewed interest in distributed electric propulsion systems and electric vertical take-off and landing (eVTOL) aircraft. The recent literature reports many interesting investigations, using prescribed rotor blades, into the flow phenomena as well as aerodynamic and aeroacoustic benefits of corotating rotors. However, the subject of the design of blade geometries, optimized to a design goal, for corotating rotors is currently lacking in the literature. This paper is written from such a design perspective, by extending a previous generalized approach to the aerodynamic optimization of counterrotating rotors to corotating rotors. The previous requirement for upper and lower counterrotating rotor torques to be equal can now be lifted in the case of corotating rotors, enabling improved versatility in the optimization of corotating blade designs. The optimization is demonstrated on an application example to address the conflicting conditions that index angles (high) for aeroacoustic benefits of reduced noise are at odds with those (low) for aerodynamic efficiency. The approach demonstrated in this paper is to set the index angle for reduced noise and then recover back the aerodynamic efficiency by using the newly developed aerodynamic optimization technique.

Determination of the aerodynamic characteristics of the tiltrotor with the wingtip-mounted coaxial rotors

The article describes the study of rotor-to-wing aerodynamic interaction for the wingtip-mounted coaxial rotors configuration of the tiltrotor aircraft. The influence of the rotor slipstreams on lift-to-drag ratio characteristic was determined. Obtained results were compared with similar characteristics of the equivalent in thrust conventional single rotor slipstreams impact. Using the computational aerodynamics methods (panel-vortex method) the flow around the tiltrotor model with the wingtip-mounted single and coaxial rotors has been simulated. A study of the basic model configuration with conventional single rotors, based on the technical characteristics of the AgustaWestland AW609 tiltrotor, was conducted. Further researches were conducted for a modified model where single rotors were replaced with equivalent in thrust coaxial rotors. The influence of the rotor slipstreams on the aerodynamic characteristics of the model for both directions of rotors rotation in coaxial combination is considered. Also, the dependence of the maximum lift-to-drag characteristic due to the coaxial rotor diameters change has been determined. The results show that the coaxial rotor slipstreams-to-wing aerodynamic interaction effect is the similar to the effect of conventional single rotor, but less intensive. Comparison of the results showed that a tiltrotor equipped with wingtip-mounted single rotors has approximately 20% greater maximum lift-to-drag characteristic than one equipped with coaxial rotors with the same thrust. However, the use of coaxial rotors allows getting higher maximum speed, when conventional single rotors lose the efficiency significantly. Therefore, it is advisable to conduct further research for the possibility of using coaxial rotors for tiltrotor aircrafts. The research results are presented in graphical form. The obtained data provides a basis for further studies of the described problem, and also will be useful for new tiltrotor design works.

Distance and Rotational Speed Analysis of Coaxial Rotors for UTHM C-Drone

The prototype of UTHM C-Drone use a coaxial hexacopter concept for its propulsion system. A coaxial rotor consists of two motor and two propellers mounted above each other and aligned in relation to their axis of rotation. The propellers are based on the T-Motor U15XXL KV29 model used in UTHM C-Drone. The distance between the two propellers is usually relative to the radius of the propeller or can be lesser. The objectives for this study are to investigate the effect of distance between upper and lower propeller in a coaxial rotors system and the effect of rotational speed. This study is important to ensure the C-Drone power efficient and capable to lift 180 kg payload. The CAD model of the propeller and coaxial rotors system were designed based on the specification from T-Motor company by Solidworks software and the flow simulations were conducted using Solidworks Flow Simulation module. The total of six CAD models; one for a single propeller and five for coaxial rotors with five difference of distance cases were constructed. For each model, the total thrust was tested from 50% throttle power up to the 90% throttle power. It was found that the coaxial rotors system can generate more thrust than a single propeller but less than double. It was also found that if the lower propeller rotates faster than the upper propeller, the increment of total thrust is very small. However, if the upper propeller rotates faster than the lower propeller, the total thrust increase significantly. For the case of faster upper propeller, as the higher the throttle applied, the thrust increment ratio will decrease, and the efficiency of the thrust produced will be affected. In addition, for same rotation speed, the thrust generated was lesser when both propellers rotate in a same direction compared to when each propeller rotates in the opposite directions of each other.

Impact-Resistant Flying Platform for Use in the Urban Construction Monitoring

A case study drone that constitutes a shock-resistant aerial vehicle is discussed in the chapter. The aerial motor platform is placed in gimbal joints of the exclusive framework (shell). The platform is a helicopter type aerial vehicle powered with two coaxial rotors of contra rotation. Mathematical model of the platform spatial dynamics bases Lagrange's equations to bring reliable solutions so that advanced model-based control law design techniques can be used. Though the case study implies utilizing an automatic flight mode of the aerial vehicle, it can be piloted remotely on radio. The on-board video cameras and other sensors are used to bring about both navigational duties and surveillance missions such as building constructions monitoring.

Dynamic Stall Modeling Using Viscous Vortex Particle Method for Coaxial Rotors

Dynamic stall is an important source of vibrations on a rotor at high advance ratios. The periodic flow separation and reattachment during dynamic stall generates large unsteady loads. In this study, the flow separation is modeled as the shedding of concentrated vorticity from the leading edge of the airfoil. The viscous vortex particle method is used to calculate the evolution of the rotor wake. Blade loads are calculated using a reduced order model obtained from computational fluid dynamics, and dynamic stall loads are calculated using the ONERA dynamic stall model. Results are presented for single main rotor and coaxial rotors at advance ratios of μ = 0.3–0.4. The separated wake modifies the angle of attack distribution on the rotor and hence impacts the hub loads. The results indicate that the separated wake modifies the vibratory hub loads by 5–10% for a single main rotor at μ = 0.3. The vibratory hub loads for the coaxial rotor are modified by 10–20% at μ = 0.4 with the inclusion of the separated wake. The upper and lower rotor tip path planes are tilted such that the blade and wake interaction is greater on the retreating side of the upper rotor and decreased on the advancing side.