Aerodynamic characteristics of rigid coaxial rotor by wind tunnel test and numerical calculation

This paper briefly reviews the history and development of compounds, tiltrotors and hingeless rotors. Largely through a quirk of history, the compound has been neglected for over three decades. The mission performance potential of the compound is re-examined based on basic aerodynamic principles and by surveying recent NASA and Army mission design studies. A rational case can be made that the compound is the preferred rotorcraft for intermediate-speed missions and that it can be a worthy complement to the helicopter and tiltrotor. Past US Army Aeroflightdynamics Directorate (AFDD) aeromechanics research in aeroelastic stability and prediction methodology is reviewed in support of advancing both conventional and compound rotorcraft. This paper describes ten research and development (R&D) initiatives to revitalise advanced rotorcraft research for both conventional and future compound rotorcraft.

/pdf/revitalising-advanced-rotorcraft-research-and-the-compound-3twy42u3wz.pdf

Revitalising advanced rotorcraft research – and the compound helicopter

A 1:17 scale model of a notional rotor hub of a large helicopter was tested in the Pennsylvania State University Applied Research Laboratory 12 in. test-section water tunnel. Objectives of the expe...

https://arc.aiaa.org/doi/pdf/10.2514/1.C034250

Scaling and configuration effects on helicopter rotor hub interactional aerodynamics

A study was done in the NASA 14- by 22-Foot Wind Tunnel at Langley Research Center on the parasite drag of different helicopter rotor hub fairings and pylons. Parametric studies of hub-fairing camber and diameter were conducted. The effect of hub fairing/pylon clearance on hub fairing/pylon mutual interference drag was examined in detail. Force and moment data are presented in tabular and graphical forms. The results indicate that hub fairings with a circular-arc upper surface and a flat lower surface yield maximum hub drag reduction; and clearance between the hub fairing and pylon induces high mutual-interference drag and diminishes the drag-reduction benefit obtained using a hub fairing with a flat lower surface. Test data show that symmetrical hub fairings with circular-arc surfaces generate 74 percent more interference drag than do cambered hub fairings with flat lower surfaces, at moderate negative angle of attack.

An Experimental Investigation of Helicopter Rotor Hub Fairing Drag Characteristics

A numerical investigation was carried out to predict the mutual interference between helicopter components.
The investigation was based on the solution of RANS equations in three dimensions using unstructured
grids. Results are presented for six different test cases under steady forward flight conditions at Mach
number equal to 0.204. These test cases refer to different combinations of reduced scale models of
helicopter fuselage, rotor hub and main rotor modelled by an actuator disc. Analysis of the results revealed
that while significant correlation between the hub and fuselage loads, and a non trivial influence of the
actuator disc on these loads could be observed, the drag breakdown of the hub was not effectively altered.

/pdf/numerical-analysis-of-hub-and-fuselage-interference-to-5ghn3v5zpe.pdf

Numerical Analysis of Hub and Fuselage Interference to Reduce Helicopter Drag

A wind-tunnel test was conducted to obtain data on several rotorcraft hub and shaft fairing drag reduction configurations. Aerodynamic loads and moments were acquired for each test configuration. Limited wake pressure measurements and flow visualization (tuft) photographs were obtained for some configurations. All hub and shaft fairing configurations were tested on a 1/5-scale XH-59A model fuselage. Both coaxial and single rotor configurations were tested. All rotor assemblies were modeled with nonrotating hardware. The drag reduction methods tested included cambered elliptical hub fairings, several different shaft fairings, and strakes. Test data show that significant drag reductions can be attained with certain fairing configurations. The lowest drag values for the single rotor configurations were obtained for a cambered elliptical hub fairing with a large thickness airfoil shaft fairing. The lowest coaxial configuration drag values were obtained with cambered elliptical hub fairings and a long chord intermediate shaft fairing.

D. R. Graham

Papers

Experimental investigation of rotorcraft hub and shaft fairing drag reduction