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  • 1
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    A Comparison of Interactional Aerodynamics Methods for a Helicopter in Low Speed Flight (1997)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Recent advances in computing subsonic flow have been applied to helicopter configurations with various degrees of success. This paper is a comparison of two specific methods applied to a particularly challenging regime of helicopter flight, very low speeds, where the interaction of the rotor wake and the fuselage are most significant. Comparisons are made between different methods of predicting the interactional aerodynamics associated with a simple generic helicopter configuration. These comparisons are made using fuselage pressure data from a Mach-scaled powered model helicopter with a rotor diameter of approximately 3 meters. The data shown are for an advance ratio of 0.05 with a thrust coefficient of 0.0066. The results of this comparison show that in this type of complex flow both analytical techniques have regions where they are more accurate in matching the experimental data.
    Keywords: Aircraft Design, Testing and Performance
    Format: text
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  • 2
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    Wake Geometry Measurements and Analytical Calculations on a Small-Scale Rotor Model (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An experimental investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to quantify the rotor wake behind a scale model helicopter rotor in forward level flight at one thrust level. The rotor system in this test consisted of a four-bladed fully articulated hub with blades of rectangular planform and an NACA 0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the vortex geometry in the flow in planes parallel and perpendicular to the free-stream flow. Quantitative measurements of wake geometric proper- ties, such as vortex location, vertical skew angle, and vortex particle void radius, were obtained as well as convective velocities for blade tip vortices. Comparisons were made between experimental data and four computational method predictions of experimental tip vortex locations, vortex vertical skew angles, and wake geometries. The results of these comparisons highlight difficulties of accurate wake geometry predictions.
    Keywords: Aircraft Design, Testing and Performance
    Type: NASA-TP-3584 , L-17449 , NAS 1.60:3584 , ATCOM-TR-96-A-007
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic performance of the aircraft. To determine the effect of separated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operating at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and downstream directions. Measurements were taken at 13 stations downstream from the rotor hub. At each station, measurements were taken in both a horizontal and vertical row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolution. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Average turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum average value of turbulence was located near the rear-facing region of the fuselage.
    Keywords: Aircraft Design, Testing and Performance
    Type: NASA-TM-4738 , NAS 1.15:4738 , L-17524 , ATCOM-TR-97-A-001
    Format: application/pdf
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  • 4
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    Helicopter blade dynamic loads measured during performance testing of two scaled rotors (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A test to determine the performance differences between the 27-percent-scale models of two rotors for the U.S. Army AH-64 helicopter was conducted in the Langley 14- by 22-Foot Subsonic Tunnel. One rotor, referred to as the baseline rotor, simulated the geometry and dynamic characteristics of the production baseline rotor, and the other rotor, referred to as the advanced rotor, was designed to have improved hover performance. During the performance test, the dynamic pitch-link forces and blade bending and torsion moments were also measured. Dynamic data from the forward flight investigation are reduced and presented. The advanced blade set was designed to have dynamic characteristics similar to those of the baseline rotor so that test conditions would not be limited by potential rotor instability and blade resonances, and so that the measured performance increments could be considered to be due purely to aerodynamic causes. Data show consistent trends with advance ratio for both blade sets with generally higher oscillatory loads occurring for the advanced blade set when compared with the baseline blade set.
    Keywords: AERODYNAMICS
    Type: NASA-TM-89053 , L-16245 , NAS 1.15:89053 , AVSCOM-TM-87-B-7 , AD-A182870
    Format: application/pdf
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  • 5
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    Description of the US Army small-scale 2-meter rotor test system (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A small-scale powered rotor model was designed for use as a research tool in the exploratory testing of rotors and helicopter models. The model, which consists of a 29 hp rotor drive system, a four-blade fully articulated rotor, and a fuselage, was designed to be simple to operate and maintain in wind tunnels of moderate size and complexity. Two six-component strain-gauge balances are used to provide independent measurement of the rotor and fuselage aerodynamic loads. Commercially available standardized hardware and equipment were used to the maximum extent possible, and specialized parts were designed so that they could be fabricated by normal methods without using highly specialized tooling. The model was used in a hover test of three rotors having different planforms and in a forward flight investigation of a 21-percent-scale model of a U.S. Army scout helicopter equipped with a mast-mounted sight.
    Keywords: AERODYNAMICS
    Type: NASA-TM-87762 , L-16165 , NAS 1.15:87762 , AVSCOM-TM-86-B-4 , AD-A178047
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  • 6
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    Computational rotorcraft flowfield research at the U.S. Army AeroStructures Directorate (1990)
    In:  Other Sources
    Details
    Publication Date: 2018-12-01
    Description: Rotorcraft aerodynamic interaction investigations conducted experimentally and computationally by the U.S. Army at the NASA Langley subsonic tunnel are described. Consideration is given to fuselage velocity computation, an interactional aerodynamics method, a rotor/wake/fuselage method, predicted wake geometry, views of tip vortex trajectory, and an inflow velocity study. Calculations were found to predict the periodic geometry of a rotor wake. Details of its interactions with the fuselage surface are not well modeled with inviscid panel methods. For the cases investigated in the present study, the overall effects of the fuselage are relatively small. However, increasing the size of the fuselage or decreasing the fuselage-rotor space will amplify these effects.
    Keywords: AERODYNAMICS
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  • 7
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    Rotor design for maneuver performance (1986)
    In:  Other Sources
    Details
    Publication Date: 2018-12-01
    Description: A method of determining the sensitivity of helicopter maneuver performance to changes in basic rotor design parameters is developed. Maneuver performance is measured by the time required, based on a simplified rotor/helicopter performance model, to perform a series of specified maneuvers. This method identifies parameter values which result in minimum time quickly because of the inherent simplicity of the rotor performance model used. For the specific case studied, this method predicts that the minimum time required is obtained with a low disk loading and a relatively high rotor solidity. The method was developed as part of the winning design effort for the American Helicopter Society student design competition for 1984/1985.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
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  • 8
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    Navier-Stokes and potential theory solutions for ahelicopter fuselage and comparison with experiment (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A thin-layer Navier-Stokes code and a panel method code are used to predict the flow over a generic helicopter fuselage. The computational results are compared with pressure data at four experimental conditions. Both methods produce results that agree with the experimental pressure data. However, separation patterns and other viscous flow features from the Navier-Stokes code solution are shown that cannot be easily modeled with the panel method.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4566 , L-17325 , NAS 1.15:4566 , ATCOM-TR-94-A-013
    Format: application/pdf
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  • 9
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    Flapping inertia for selected rotor blades (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Aerodynamics of helicopter rotor systems cannot be investigated without consideration for the dynamics of the rotor. One of the principal properties of the rotor which affects the rotor dynamics is the inertia of the rotor blade about its root attachment. Previous aerodynamic investigation have been performed on rotor blades with a variety of planforms to determine the performance differences due to blade planform. The blades tested for this investigation have been tested on the U.S. Army 2 meter rotor test system (2MRTS) in the NASA Langley 14 by 22 foot subsonic tunnel for hover performance. This investigation was intended to provide fundamental information on the flapping inertia of five rotor blades with differing planforms. The inertia of the bare cuff and the cuff with a blade extension were also measured for comparison with the inertia of the blades. Inertia was determined using a swing testing technique, using the period of oscillation to determine the effective flapping inertia. The effect of damping in the swing test was measured and described. A comparison of the flapping inertials for rectangular and tapered planform blades of approximately the same mass showed the tapered blades to have a lower inertia, as expected.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-104125 , NAS 1.15:104125 , AVSCOM-TR-91-B-019 , AD-A243812
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  • 10
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    A multi-element vortex lattice method for calculating the geometry and effects of a helicopter rotor wake in forward flight (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-0664
    Format: text
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