Aerodynamic Optimization Study of a Coaxial Rotor in Hovering Flight

Abstract

A primary design goal with a coaxial rotor is to minimize the combined sources of losses on the upper and lower rotors that have their source in aerodynamic interference. To this end, parametric studies were conducted using a free-vortex wake method to study the aerodynamic interference effects of changing interrotor spacing, blade twist rates, and blade planform on the interdependent loads produced on the upper and lower rotors, respectively. A formal, multistep optimization process was then conducted by coupling the aerodynamic method to an optimization approach based on the method of feasible directions, the goal being to expeditiously find the individual blade geometries that would give the highest levels of efficiency from the coaxial as a system. Because of the inherent aerodynamic differences between the upper and lower rotors of a coaxial, it is shown that the best performing coaxial rotors may require the use of different blade shapes on each rotor, but substantially different blade designs may also achieve similar values of aerodynamic efficiency. It is also shown that the nonconvexity of the design problem for a coaxial rotor may limit the usefulness of formal optimization methods, and extensive parametric studies may still be required in the process of design.

RETRACTED: Flexible performance design for the H∞ loop-shaping control based on the linear matrix inequality approach: Application to the coaxial rotor helicopter

“…2,3,25 There were a few researches about modeling and control design of a coaxial rotor helicopter. Thus, modeling and robust control for a coaxial rotor helicopter need to be further promoted.…”

A Trimming Methodology for a New Coaxial Rotor Configuration of Robotic Helicopter Based on Rotor's Thrust Ratio

“…Therefore, the integration method was advocated to construct mathematical model of the robotic newconfiguration-coaxial-rotor helicopter.. In predicting thrust and power coefficient of coaxial rotor, it has been validated that blade element momentum theory was almost consistent with free-vortex method prediction [1], which given a better approximation to experimental data using full-scale and model scale coaxial rotors at its operating state and load sharing [12]. Then, BEMT was adopted to generate coaxial rotor's force and moment [13].…”

“…The forces and moments of the two rotors are calculated dependently with accounting for the interference effects by linear superposition which the upper rotor's slipstream wake interferes the inflow of lower, but the lower rotor doesn't affect the upper rotor's inflow [1]. Thus, blade element theory with the assumptions of two-dimensional and steady airfoils was applied to model the coaxial rotor.…”

“…Many researches have made significant progress on performance analysis, optimum coaxial rotor design and prototype demonstrator [1][2][3]. Comparing the single rotor helicopter, a coaxial rotor helicopter contains two nearly identical counter-rotating rotors and the tail rotor is eliminated.…”

Multiobjective Performance Optimization of a Coaxial Compound Rotorcraft Configuration

“…Blade aerodynamics are quasi steady, with lookup tables for lift, drag, and pitching moment coefficients as a function of Mach number and incidence angle, as well as radial flow drag corrections [19]. Rotor inflow is computed using a free vortex wake methodology [20][21][22][23][24]. The rotor flowfield is modeled using a rigid triangular sheet trailing from each blade that rolls up into a single tip vortex: the strength of which is computed from the peak of the bound circulation distribution along the blade.…”