Hover Performance Correlation for Full‐Scale and Model‐Scale Coaxial Rotors

Abstract

The hover performance data of full-scale and model-scale coaxial rotors have been compared with CAMRAD II predictions having a free vortex wake analysis. Performance correlations of a coaxial rotor were made with a variation of key parameters including the rotor spacing and height. To understand aerodynamic behavior of the U.S. Army Aeroflightdynamics Directorate (AFDD) coaxial rotor operating over a range of Reynolds numbers from 36,000 to 180,000, the Reynolds number scaling effect was explored using an airfoil design code, MSES. It was found that the coaxial rotor spacing effect on hover performance was minimal for the rotor spacing larger than 20% of the rotor diameter. The measured performance data showed that more thrust was lost from the lower rotor of a coaxial than the upper rotor due to a larger rotor-to-rotor wake interference effect, and the lower rotor kept only an 81% of the single rotor OGE (out-of-ground effect) thrust whereas the upper rotor maintained a 90%. The lower rotor IGE (in-ground effect) thrust increased quickly by 26% as the rotor approached to the ground from the position of an 80% of the rotor diameter to 10%, and the corresponding IGE power increased by 17%. These thrust and power characteristics were well predicted. Overall, the performance prediction for the coaxial rotor was satisfactory when compared with the measured data. Nomenclature C P rotor power coefficient C T rotor thrust coefficient c chord c d drag coefficient c l lift coefficient D rotor diameter G rotor height above the ground K D scaling factor for the drag K L scaling factor for the lift M Mach number Re Reynolds number r radial distance from the hub center r c vortex core radius r c0 initial vortex core radius S rotor spacing between two rotors t w wake age in time v kinematic viscosity α angle of attack δ vturbulence viscosity parameter

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

“…The simulations did not use any low Mach preconditioner, even though the tip Mach number is as low as 0.15. The performance results did not agree as well with the experiments as the results from CAMRAD II [57] did with the experimental data. The over-prediction in thrust was even more pronounced.…”

“…al [57] applied the comprehensive analysis code, CAMRAD II to the scaled coaxial rotor experimental setup of McAlister et al [52]. In this study, each rotor's wake were modeled separately using a vortex lattice method.…”

Flight Dynamics Investigation of Compound Helicopter Configurations

“…This partitioning of the rotor thrusts and the higher pitch of the lower rotor are both consistent with findings from other trimmed coaxial rotors in hover (Refs. 22,32,33). As the CCH model moves away from hover the thrust sharing ratio tends towards unity and θ diff tends towards zero as the aerodynamic interference between the rotors lessen as µ begins to dominate the coaxial inflow equations (1) and (2).…”

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

“…The coaxial rotor helicopter model was reconstructed by the integrative approach that has been validated by the experimental data. [26][27][28] As to teetering two-blade configuration for the upper and lower rotor whose blade are identical in NACA0012 blade sections, blade parameter radius, twisted rates, cut-out, and other body parameters are shown in Table 1. Then, the state and control matrices were computed by taking use of the small perturbation theory through the quasi-steady assumption as follows 29 …”