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NASA NTRS2013

A History of Rotorcraft Comprehensive Analyses

A history of the development of rotorcraft comprehensive analyses is presented. Comprehensive analyses are digital computer programs that calculate the aeromechanical behavior of the rotor and aircraft, bringing together the most advanced models of the geometry, structure, dynamics, and aerodynamics available in rotary wing technology. The development of the major codes of the last five decades from industry, government, and universities is described. A number of common themes observed in this history are discussed.

Johnson, Wayne↗

NASA NTRS1987

Application of a comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD) to the McDonnell Douglas AH-64A helicopter

CAMRAD results on main rotor blade natural frequency and structural loads predictions are compared to flight test data and predictions of the Dynamic Analysis Research Tool (DART) and the Rotor/Airframe Comprehensive Aeroelastic Program (RACAP). Consideration is also given to the effects of various analytical options available in CAMRAD including dynamic stall, wake modeling, and the number of bending and torsion degrees of freedom included in the structural analysis. It is concluded that, while several modeling limitations are identified in the CAMRAD structural analyses, the structural loads predictions are as accurate as analysis codes which provide more representative models of the complex geometries and structures of the AH-64A rotor system. However, it is noted that the CAMRAD analysis cannot be considered fully reliable for dynamic predictions for more advanced bearingless rotor designs being proposed for future AH-64 configurations.

Callahan, C.↗

NASA NTRS1999

Tiltrotor Aeroacoustic Code (TRAC) Prediction Assessment and Initial Comparisons with Tram Test Data

A prediction sensitivity assessment to inputs and blade modeling is presented for the TiltRotor Aeroacoustic Code (TRAC). For this study, the non-CFD prediction system option in TRAC is used. Here, the comprehensive rotorcraft code, CAMRAD.Mod1, coupled with the high-resolution sectional loads code HIRES, predicts unsteady blade loads to be used in the noise prediction code WOPWOP. The sensitivity of the predicted blade motions, blade airloads, wake geometry, and acoustics is examined with respect to rotor rpm, blade twist and chord, and to blade dynamic modeling. To accomplish this assessment, an interim input-deck for the TRAM test model and an input-deck for a reference test model are utilized in both rigid and elastic modes. Both of these test models are regarded as near scale models of the V-22 proprotor (tiltrotor). With basic TRAC sensitivities established, initial TRAC predictions are compared to results of an extensive test of an isolated model proprotor. The test was that of the TiltRotor Aeroacoustic Model (TRAM) conducted in the Duits-Nederlandse Windtunnel (DNW). Predictions are compared to measured noise for the proprotor operating over an extensive range of conditions. The variation of predictions demonstrates the great care that must be taken in defining the blade motion. However, even with this variability, the predictions using the different blade modeling successfully capture (bracket) the levels and trends of the noise for conditions ranging from descent to ascent.

Burley, Casey L.↗

NASA NTRS2019

UH-60A Airloads Flight Test Program: Data Counter 8534

During the period between July 1993 and February 1994 the data collection portion of the UH-60A Airloads Program was conducted. At the time, UH-60A Airloads Program was the most comprehensive and data rich rotorcraft flight test program that NASA and the Army had ever attempted. It was part of the Modern Technology Rotor Program, where several different rotors were to be tested in small and full-scale wind tunnels combined with flight testing. This would allow for comparison between the various tests and comprehensive analyses. Results were to be stored in a comprehensive, easily accessed, database know as Tilt Rotor Engineering Database System, TRENDS. With over 30 years of rotor testing experience, the goal of NASA and the Army was to collect a wide and extensive amount of data to improve the understanding of rotors and prediction codes.

Kufeld, Robert M.↗

NASA NTRS1999

Tiltrotor Aeroacoustic Code (TRAC) Prediction Assessment and Initial Comparisons With TRAM Test Data

A prediction sensitivity assessment to inputs and blade modeling is presented for the TiltRotor Aeroacoustic Code (TRAC). For this study, the non-CFD prediction system option in TRAC is used. Here, the comprehensive rotorcraft code, CAMRAD.Mod 1, coupled with the high-resolution sectional loads code HIRES, predicts unsteady blade loads to be used in the noise prediction code WOPWOP. The sensitivity of the predicted blade motions, blade airloads, wake geometry, and acoustics is examined with respect to rotor rpm, blade twist and chord, and to blade dynamic modeling. To accomplish this assessment. an interim input-deck for the TRAM test model and an input-deck for a reference test model are utilized in both rigid and elastic modes. Both of these test models are regarded as near scale models of the V-22 proprotor (tiltrotor). With basic TRAC sensitivities established, initial TRAC predictions are compared to results of an extensive test of an isolated model proprotor. The test was that of the TiltRotor Aeroacoustic Model (TRAM) conducted in the Duits-Nederlandse Windtunnel (DNW). Predictions are compared to measured noise for the proprotor operating over an extensive range of conditions. The variation of predictions demonstrates the great care that must be taken in defining the blade motion. However, even with this variability, the predictions using the different blade modeling successfully capture (bracket) the levels and trends of the noise for conditions ranging from descent to ascent.

Burley, Casey L.↗

NASA NTRS1988

Two-dimensional aerodynamic characteristics of the OLS/TAAT airfoil

Two flight tests have been conducted that obtained extension pressure data on a modified AH-1G rotor system. These two tests, the Operational Loads Survey (OLS) and the Tip Aerodynamics and Acoustics Test (TAAT) used the same rotor set. In the analysis of these data bases, accurate 2-D airfoil data is invaluable, for not only does it allow comparison studies between 2- and 3-D flow, but also provides accurate tables of the airfoil characteristics for use in comprehensive rotorcraft analysis codes. To provide this 2-D data base, a model of the OLS/TAAT airfoil was tested over a Reynolds number range from 3 x 10 to the 6th to 7 x 10 to the 7th and between Mach numbers of 0.34 to 0.88 in the NASA Langley Research Center's 6- by 28-Inch Transonic Tunnel. The 2-D airfoil data is presented as chordwise pressure coefficient plots, as well as lift, drag, and pitching moment coefficient plots and tables.

Watts, Michael E.↗

NASA NTRS1993

Rotor design optimization using a free wake analysis

The aim of this effort was to develop a comprehensive performance optimization capability for tiltrotor and helicopter blades. The analysis incorporates the validated EHPIC (Evaluation of Hover Performance using Influence Coefficients) model of helicopter rotor aerodynamics within a general linear/quadratic programming algorithm that allows optimization using a variety of objective functions involving the performance. The resulting computer code, EHPIC/HERO (HElicopter Rotor Optimization), improves upon several features of the previous EHPIC performance model and allows optimization utilizing a wide spectrum of design variables, including twist, chord, anhedral, and sweep. The new analysis supports optimization of a variety of objective functions, including weighted measures of rotor thrust, power, and propulsive efficiency. The fundamental strength of the approach is that an efficient search for improved versions of the baseline design can be carried out while retaining the demonstrated accuracy inherent in the EHPIC free wake/vortex lattice performance analysis. Sample problems are described that demonstrate the success of this approach for several representative rotor configurations in hover and axial flight. Features that were introduced to convert earlier demonstration versions of this analysis into a generally applicable tool for researchers and designers is also discussed.

Quackenbush, Todd R.↗

NASA NTRS1994

SCISEAL: A CFD code for analysis of fluid dynamic forces in seals

A viewgraph presentation is made of the objectives, capabilities, and test results of the computer code SCISEAL. Currently, the seal code has: a finite volume, pressure-based integration scheme; colocated variables with strong conservation approach; high-order spatial differencing, up to third-order; up to second-order temporal differencing; a comprehensive set of boundary conditions; a variety of turbulence models and surface roughness treatment; moving grid formulation for arbitrary rotor whirl; rotor dynamic coefficients calculated by the circular whirl and numerical shaker methods; and small perturbation capabilities to handle centered and eccentric seals.

Athavale, Mahesh↗

NASA NTRS2005

Acoustic Predictions of Manned and Unmanned Rotorcraft Using the Comprehensive Analytical Rotorcraft Model for Acoustics (CARMA) Code System

The Comprehensive Analytical Rotorcraft Model for Acoustics (CARMA) is being developed under the Quiet Aircraft Technology Project within the NASA Vehicle Systems Program. The purpose of CARMA is to provide analysis tools for the design and evaluation of efficient low-noise rotorcraft, as well as support the development of safe, low-noise flight operations. The baseline prediction system of CARMA is presented and current capabilities are illustrated for a model rotor in a wind tunnel, a rotorcraft in flight and for a notional coaxial rotor configuration; however, a complete validation of the CARMA system capabilities with respect to a variety of measured databases is beyond the scope of this work. For the model rotor illustration, predicted rotor airloads and acoustics for a BO-105 model rotor are compared to test data from HART-II. For the flight illustration, acoustic data from an MD-520N helicopter flight test, which was conducted at Eglin Air Force Base in September 2003, are compared with CARMA full vehicle flight predictions. Predicted acoustic metrics at three microphone locations are compared for limited level flight and descent conditions. Initial acoustic predictions using CARMA for a notional coaxial rotor system are made. The effect of increasing the vertical separation between the rotors on the predicted airloads and acoustic results are shown for both aerodynamically non-interacting and aerodynamically interacting rotors. The sensitivity of including the aerodynamic interaction effects of each rotor on the other, especially when the rotors are in close proximity to one another is initially examined. The predicted coaxial rotor noise is compared to that of a conventional single rotor system of equal thrust, where both are of reasonable size for an unmanned aerial vehicle (UAV).

Boyd, D. Douglas, Jr.↗

NASA NTRS2019

UH-60A Airloads Flight Test Program: Data Counter 8513

The data collection portion of the UH-60A Airloads Flight Test Program was conducted between July 1993 and February 1994. At the time, the UH-60A Airloads Program was the most comprehensive and data-rich rotorcraft flight test program that NASA and the U.S. Army had ever attempted. It was part of the Modern Technology Rotors Program, where several different rotors were tested in small- and full-scale wind tunnels combined with flight testing. The UH-60A portion of this program allowed for comparison between other tests performed and served as a scientific quality database for validating current and new computational and simulation models. The UH-60A flight test data was stored in a comprehensive, easily accessed database known as the Tilt Rotor Engineering Database System, or TRENDS. With over 30 years of rotor testing experience, NASA and the Army’s goal of the Airloads Flight Test Program was to collect data for a wide range of operating conditions and provide an extensive amount of data to improve the understanding of rotors and validate and improve prediction codes. This report presents the entire archived data set from Counter 8513 (Run 85, point 13) from the UH-60A Airloads Flight Test Program. There were 1,078 total data set counters acquired and archived during 57 accumulated flight hours and 31 research flights. Over 900 counters were research flight data acquisition data points. Counter 8513 is a low-speed, level-flight test condition.

Kufeld, Robert M.↗

NASA NTRS2022

Application of Rotor Disk Model in the Overflow CFD Code

To reduce the complexity and to reduce the cost of turnaround time of simulating unsteady flows of rotating blades with moving overset grids, amid-fidelity option is provided in the OVERFLOW computational fluid dynamics analysis to model rotors and propellers as infinitely thin disks. The effect of the flow through the disk is represented by the momentum source terms in the governing Navier-Stokes equations. The model is loosely coupled with the rotorcraft comprehensive analysis CAMRADII. A brief description of the coupling algorithm is provided. Simulations of a single rotor and multiple rotors are shown, including comparisons with measurements and with the full rotor where all blades are modeled, and unsteady simulation performed with moving grids for rotating geometry,

ARMD↗

NASA NTRS1993

Optimum Design of High-Speed Prop-Rotors

An integrated multidisciplinary optimization procedure is developed for application to rotary wing aircraft design. The necessary disciplines such as dynamics, aerodynamics, aeroelasticity, and structures are coupled within a closed-loop optimization process. The procedure developed is applied to address two different problems. The first problem considers the optimization of a helicopter rotor blade and the second problem addresses the optimum design of a high-speed tilting proprotor. In the helicopter blade problem, the objective is to reduce the critical vibratory shear forces and moments at the blade root, without degrading rotor aerodynamic performance and aeroelastic stability. In the case of the high-speed proprotor, the goal is to maximize the propulsive efficiency in high-speed cruise without deteriorating the aeroelastic stability in cruise and the aerodynamic performance in hover. The problems studied involve multiple design objectives; therefore, the optimization problems are formulated using multiobjective design procedures. A comprehensive helicopter analysis code is used for the rotary wing aerodynamic, dynamic and aeroelastic stability analyses and an algorithm developed specifically for these purposes is used for the structural analysis. A nonlinear programming technique coupled with an approximate analysis procedure is used to perform the optimization. The optimum blade designs obtained in each case are compared to corresponding reference designs.

Chattopadhyay, Aditi↗

NASA NTRS2019

UH-60A Airloads Flight Test Program: Data Counter 9505

The data collection portion of the UH-60A Airloads Flight Test Program (ref. 1) was conducted between July 1993 and February 1994. At the time, the UH-60A Airloads Program was the most comprehensive and data-rich rotorcraft flight test program that NASA and the U.S. Army had ever attempted. It was part of the Modern Technology Rotors Program (ref. 2), where several different rotors were tested in small- and full-scale wind tunnels combined with flight testing. The UH-60A portion of this program allowed for comparison between other tests performed and served as a scientific quality database for validating current and new computational and simulation models. The UH-60A flight test data was stored in a comprehensive, easily accessed database known as the Tilt Rotor Engineering Database System, or TRENDS (ref. 3). With over 30 years of rotor testing experience (ref. 4), NASA and the Army’s goal of the Airloads Flight Test Program was to collect data for a wide range of operating conditions, and to provide an extensive amount of data to improve the understanding of rotors and validate and improve prediction codes. This report presents the entire archived data set from Counter 9505 (Run 95, point 5) from the UH-60A Airloads Flight Test Program. There were 1,078 total data set counters acquired and archived during 57 accumulated flight hours and 31 research flights. Over 900 counters were research flight data acquisition data points. Counter 9505 is a low altitude, moderate airspeed, level-flight test condition. Ground acoustic microphone data was acquired for this counter but the acoustic data is not included in this report.

Kufeld, Robert M.↗

NASA NTRS1987

Correlation of SA349/2 helicopter flight-test data with a comprehensive rotorcraft model

A comprehensive rotorcraft analysis model was used to predict blade aerodynamic and structural loads for comparison with flight test data. The data were obtained from an SA349/2 helicopter with an advanced geometry rotor. Sensitivity of the correlation to wake geometry, blade dynamics, and blade aerodynamic effects was investigated. Blade chordwise pressure coefficients were predicted for the blade transonic regimes using the model coupled with two finite-difference codes.

Yamauchi, Gloria K.↗

NASA NTRS1986

Correlation of SA349/2 helicopter flight-test data with a comprehensive rotorcraft model

Yamauchi, Gloria K.↗

NASA NTRS1988

Correlation of SA349/2 Helicopter Flight Test Data with a Comprehensive Rotorcraft Model

A comprehensive rotorcraft analysis model, CAMRAD, was used to predict blade aerodynamic and structural loads and performance for comparison with flight test data. The data were obtained from an SA349/2 helicopter with an advanced geometry rotor. Sensitivity of the correlation to wake geometry, blade dynamics, and blade aerodynamic effects was investigated. Blade chordwise pressure coefficients were predicted for the transonic regimes near the blade tip using the model coupled with two finite-difference codes.

Yamauchi, Gloria K.↗

NASA NTRSDate not supplied

ELISA: A Tool for Optimization of Rotor Hover Performance at Low Reynolds Number in the Mars Atmosphere

The Evolutionary aLgorithm for Iterative Studies of Aeromechanics (ELISA) was developed in support of the Rotorcraft Optimization for the Advancement of Mars eXploration (ROAMX) project. ELISA was developed to enable aerodynamic rotor hover optimization for low Reynolds number flows in the Mars atmosphere. The first objective of the algorithm allows for unconventional airfoil parameterization and multi-objective airfoil geometry optimization using OVERFLOW. The Pareto-optimal airfoil sets are converted to a set of Pareto-optimal airfoil decks, providing the lowest drag air foil geometry for each angle of attack, removing the need to arbitrarily select the airfoils to be used in the rotor optimization. The second objective allows for rotor geometry optimization with simultaneous maximization of blade loading and minimization of rotor power using the comprehensive analysis CAMRADII. The result is a Pareto-optimal rotor set, providing the lowest power rotor for each attainable blade loading, and one of the first tools for hover-optimized rotors for high-subsonic low Reynolds number conditions. The airfoil thickness can be modified after the airfoil optimization is complete, allowing for a post-airfoil-optimization adjustment of blade thickness to facilitate conforming to external structural analyses requirements. The relevance of the code is demonstrated with case studies for the ROAMX rotor optimization for Ingenuity-sized single rotors in the Mars atmosphere, a performance study optimizing the chord and twist of Ingenuity’s coaxial rotor resulting in the Sample Recovery Helicopters candidate rotor, and high-subsonic low Reynolds number airfoil optimization providing novel insights for higher-efficiency low Reynolds number airfoil geometries and flow physics.

ELISA↗

NASA NTRS2007

Modeling Tool Advances Rotorcraft Design

Continuum Dynamics Inc. (CDI), founded in 1979, specializes in advanced engineering services, including fluid dynamic modeling and analysis for aeronautics research. The company has completed a number of SBIR research projects with NASA, including early rotorcraft work done through Langley Research Center, but more recently, out of Ames Research Center. NASA Small Business Innovation Research (SBIR) grants on helicopter wake modeling resulted in the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM), a tool for studying helicopter and tiltrotor unsteady free wake modeling, including distributed and integrated loads, and performance prediction. Application of the software code in a blade redesign program for Carson Helicopters, of Perkasie, Pennsylvania, increased the payload and cruise speeds of its S-61 helicopter. Follow-on development resulted in a $24 million revenue increase for Sikorsky Aircraft Corporation, of Stratford, Connecticut, as part of the company's rotor design efforts. Now under continuous development for more than 25 years, CHARM models the complete aerodynamics and dynamics of rotorcraft in general flight conditions. CHARM has been used to model a broad spectrum of rotorcraft attributes, including performance, blade loading, blade-vortex interaction noise, air flow fields, and hub loads. The highly accurate software is currently in use by all major rotorcraft manufacturers, NASA, the U.S. Army, and the U.S. Navy.

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