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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Vortex Wake Geometry of a Model Tilt Rotor in Forward Flight

A full-span 0.25-scale V-22 tiltrotor was tested in the NASA Ames 40-by 80-Foot Wind Tunnel in November 2000. The main objective of the test was to acquire a comprehensive database to validate tiltrotor analyses. Figure 1 shows the model installed in the Ames 40- by 80-Foot Wind Tunnel. Rotor and vehicle performance measurements were taken in addition to wing pressures, acoustics, and flow visualization. A dual acoustic traverse system was installed to measure blade-vortex interaction (BVI) noise levels and directivity. Test conditions included hover and forward flight in helicopter mode. Angle-of-attack and thrust sweeps for three tunnel speeds were acquired before model problems caused the premature conclusion of the test. The test will resume in the Ames 80- by 120-Foot Wind Tunnel in late 2001. This paper will focus on the wake geometry measurements that were acquired during the test. The wake geometry measurements were a small subset of a larger matrix of planned measurements designed to study the development and structure of the dual vortex system generated during BVI conditions. The present paper will provide wake geometry data for four test conditions. In addition, the data will be compared with previously acquired wake measurements from an isolated tiltrotor

Wadcock, Alan J.↗
NASA NTRS1997

Simulation of Rotary-Wing Near-Wake Vortex Structures Using Navier-Stokes CFD Methods

This paper will use high-resolution Navier-Stokes computational fluid dynamics (CFD) simulations to model the near-wake vortex roll-up behind rotor blades. The locations and strengths of the trailing vortices will be determined from newly-developed visualization and analysis software tools applied to the CFD solutions. Computational results for rotor nearwake vortices will be used to study the near-wake vortex roll up for highly-twisted tiltrotor blades. These rotor blades typically have combinations of positive and negative spanwise loading and complex vortex wake interactions. Results of the computational studies will be compared to vortex-lattice wake models that are frequently used in rotorcraft comprehensive codes. Information from these comparisons will be used to improve the rotor wake models in the Tilt-Rotor Acoustic Code (TRAC) portion of NASA's Short Haul Civil Transport program (SHCT). Accurate modeling of the rotor wake is an important part of this program and crucial to the successful design of future civil tiltrotor aircraft. The rotor wake system plays an important role in blade-vortex interaction noise, a major problem for all rotorcraft including tiltrotors.

Kenwright, David↗
NASA NTRS2008

WRATS Integrated Data Acquisition System

The Wing and Rotor Aeroelastic Test System (WRATS) data acquisition system (DAS) is a 64-channel data acquisition display and analysis system specifically designed for use with the WRATS 1/5-scale V-22 tiltrotor model of the Bell Osprey. It is the primary data acquisition system for experimental aeroelastic testing of the WRATS model for the purpose of characterizing the aeromechanical and aeroelastic stability of prototype tiltrotor configurations. The WRATS DAS was also used during aeroelastic testing of Bell Helicopter Textron s Quad-Tiltrotor (QTR) design concept, a test which received international attention. The LabVIEW-based design is portable and capable of powering and conditioning over 64 channels of dynamic data at sampling rates up to 1,000 Hz. The system includes a 60-second circular data archive, an integrated model swashplate excitation system, a moving block damping application for calculation of whirl flutter mode subcritical damping, a loads and safety monitor, a pilot-control console display, data analysis capabilities, and instrumentation calibration functions. Three networked computers running custom-designed LabVIEW software acquire data through National Instruments data acquisition hardware. The aeroelastic model (see figure) was tested with the DAS at two facilities at NASA Langley, the Transonic Dynamics Tunnel (TDT) and the Rotorcraft Hover Test Facility (RHTF). Because of the need for seamless transition between testing at these facilities, DAS is portable. The software is capable of harmonic analysis of periodic time history data, Fast Fourier Transform calculations, power spectral density calculations, and on-line calibration of test instrumentation. DAS has a circular buffer archive to ensure critical data is not lost in event of model failure/incident, as well as a sample-and-hold capability for phase-correct time history data.

Piatak, David J.↗
NASA NTRS2012

Conceptual Design and Performance Analysis for a Large Civil Compound Helicopter

A conceptual design study of a large civil compound helicopter is presented. The objective is to determine how a compound helicopter performs when compared to both a conventional helicopter and a tiltrotor using a design mission that is shorter than optimal for a tiltrotor and longer than optimal for a helicopter. The designs are generated and analyzed using conceptual design software and are further evaluated with a comprehensive rotorcraft analysis code. Multiple metrics are used to determine the suitability of each design for the given mission. Plots of various trade studies and parameter sweeps as well as comprehensive analysis results are presented. The results suggest that the compound helicopter examined for this study would not be competitive with a tiltrotor or conventional helicopter, but multiple possibilities are identified for improving the performance of the compound helicopter in future research.

Russell, Carl↗
NASA NTRS2012

One Engine Inoperative (OEI) and Autorotation For Heavy Lift Rotorcraft Systems

Federal Aviation Administration will certainly require the Heavy Lift Rotorcraft to be operated under Category A performance and operations requirements. Because of the weight, no operation will be allowed except Category A according to FAA Part 29.1(c). This means that any where along the flight path, the aircraft must be able to land safely following an engine failure or continue flight. A repeatable flight profile must be developed and executed to ensure that the aircraft can be safely landed or flown away depending on its location on the flight profile. This means that there will be no Height-Velocity testing required as is currently required for Part 29 Category B. Since all the configurations shown to date are different than existing rotorcraft, each type would have to develop their individual requirements under existing special conditions FAA Part 21.17(b). This means the FAA will take the opportunity to negotiate additional requirements or change requirements to ensure safety. For example, since the tiltrotor did not fit normal rotorcraft category, new rules were negotiated between the applicant and the FAA. As a result of this negotiation, performance requirements for Category A were increased. The rules were written in terms of guaranteed performance instead of Category A requirements. Detailed discussion will follow later. The proposed tiltrotor would likely follow along with the current tiltrotor rules with the possibility of increase Category A performance requirements. Compounding with addition of wing and auxiliary thrust to both the tandem and coaxial rotor would result in new special condition aircraft. To my knowledge, no compound tandem or compound coaxial rotor has ever been certified by FAA.

Wood, Tom↗
NASA NTRS2017

Design and Control of an Experimental Tilt-Wing Aircraft

In this project, work has been done in the field of conceptual design of experimental tiltrotors. The main tools that have been used are NDARC (NASA Design and Analysis of Rotorcraft) and SIMPLI-FLYD. NDARC is a conceptual design tool for rotorcraft, and it is used to find trim points under various flight conditions. SIMPLI-FLYD is an integrated collection of software tools that enables a flight dynamics and control assessment of the rotorcraft vehicle design generated from NDARC. Two different tiltrotors have been investigated. Initially, work was done with the Bell XV- 15 tiltrotor. NDARCs ability to correctly model the tiltwing transition between airplane mode and hover mode was looked into. In addition, data from old flight tests were compared to the NDARC output, to see how accurately performance could be predicted. After the XV-15 analysis, an NDRARC model of a novel tiltwing concept from Elytron Aircraft was written and analyzed together with SIMPLI-FLYD. Elytron 2S is an experimental tiltwing aircraft, consisting of a joined-wing design with a small central wing for the proprotor. An alternative approach to hover control is used, where the typical rotor hub and swash plate are substituted for linear actuators controlling pitch, yaw and roll. The objective with the analysis of Elytron is to obtain a more complete understanding of the maneuverability and possible performance of this alternative aircraft configuration.

Conceptual Design↗
NASA NTRS1981

Greenlandair VTOL transportation study

An operational and economic analysis was conducted on Greenlandair, a large helicopter commuter operation. Results indicate that the airline could realize a significant increase in available seat miles with a decrease in total cost by replacing the fleet of helicopters and fixed-wing aircraft with Tiltrotors. The Tiltrotor can fly 2.5 times faster than the helicopters, and 25% faster than the presently used turboprop aicraft. Fuel consumption could be reduced by one half, and with additional savings on maintenance, crew costs, and ground support costs, plus expanded flight schedules, the airline could achieve a net yearly savings of over 2 million dollars.

Reber, R. R.↗
NASA NTRS1987

Calculated performance, stability, and maneuverability of high speed tilting proprotor aircraft

The feasibility of operating tilting proprotor aircraft at high speeds is examined by calculating the performance, stability, and maneuverability of representative configurations. The rotor performance is examined in high speed cruise and in hover. The whirl flutter stability of the coupled wing and rotor motion is calculated in cruise. Maneuverability is examined in terms of the rotor thrust limit during turns in helicopter configuration. Rotor airfoils, rotor hub configuration, wing airfoil, and airframe structural weights representative of demonstrated advanced technology are considered. Key rotor and airframe parameters are optimized for high speed performance and stability. The basic aircraft design parameters are optimized for minimum gross weight. To provide a focus for the calculations, two high speed tiltrotor aircraft are considered: a 46-passenger civil transport and an air-combat/escort fighter, both with design speeds of about 400 knots. It is concluded that such high speed tiltrotor aircraft are quite practical.

Johnson, Wayne↗
NASA NTRS1988

The role of aviation technology in the Caribbean Basin

Aviation technology can play a significant role in the development of the countries of the Caribbean Basin. A variety of applications of rotorcraft in the region, the benefits, both economic and political which can result from utilization of rotorcraft in both a public service and commercial role are presented. A computer simulation of rotorcraft used as emergency medical vehicles is applied to compare and evaluate the advantages of using rotorcraft technology such as civil derivatives of the new tiltrotor. It is concluded that by using a civil derivative of the tiltrotor, significant improvements can be obtained in the level of health service in the region. The potential for cargo and passenger transport applications are currently being investigated and a second computer simulation is being developed to be used to evaluate the potential benefits to be derived from such applications.

Smith, Robert W.↗
NASA NTRS1992

Open airscrew VTOL concepts

The following concepts, based on using open airscrew(s) for VTOL maneuvers, are re-examined in light of current technology: (1) tip-driven helicopters, (2) compound helicopters; and (3) high-speed VTOL aircraft, represented by tiltrotors, tiltwings, retractoplanes and stoppable rotors. Criteria, permitting one to compare performance of aircraft using diverse lifting and propelling methods are established. Determination of currently possible performance, indication of near-future potentials, and comparison of those items with the baseline levels (as represented by contemporary shaft-driven helicopters, first generation tiltrotors, and commercial turboprop fixed-wind aircraft) constitutes bulk of this report.

Stepniewski, W. Z.↗
NASA NTRS1996

In-Flight Rotorcraft Acoustics Program

A key part of NASA's aeronautics research is reducing noise to make helicopters and tiltrotors more acceptable to the public. The objective of the In-Flight Rotorcraft Acoustics Program (IRAP) is to acquire rotorcraft. noise data in flight for comparison to wind tunnel data. The type of noise of concern is "blade-vortex-interaction," or BVI, noise. Microphones on the wing tips and tail fin of the quiet NASA YO-3A Acoustics Research Aircraft measure BVI noise while the YO-3A descends in close formation with the helicopter or tiltrotor emitting the noise.The data acquired through IRAP is needed to validate wind-tunnel test results, or, where the results cannot be validated, to provide researchers with clues as to how to improve testing methods.

Peterson, Randall L.↗
NASA NTRS2002

Rotor/Wing Interactions in Hover

Hover predictions of tiltrotor aircraft are hampered by the lack of accurate and computationally efficient models for rotor/wing interactional aerodynamics. This paper summarizes the development of an approximate, potential flow solution for the rotor-on-rotor and wing-on-rotor interactions. This analysis is based on actuator disk and vortex theory and the method of images. The analysis is applicable for out-of-ground-effect predictions. The analysis is particularly suited for aircraft preliminary design studies. Flow field predictions from this simple analytical model are validated against experimental data from previous studies. The paper concludes with an analytical assessment of the influence of rotor-on-rotor and wing-on-rotor interactions. This assessment examines the effect of rotor-to-wing offset distance, wing sweep, wing span, and flaperon incidence angle on tiltrotor inflow and performance.

Young, Larry A.↗
NASA NTRS2002

A Tool for Low Noise Procedures Design and Community Noise Impact Assessment: The Rotorcraft Noise Model (RNM)

To improve aircraft noise impact modeling capabilities and to provide a tool to aid in the development of low noise terminal area operations for rotorcraft and tiltrotors, the Rotorcraft Noise Model (RNM) was developed by the NASA Langley Research Center and Wyle Laboratories. RNM is a simulation program that predicts how sound will propagate through the atmosphere and accumulate at receiver locations located on flat ground or varying terrain, for single and multiple vehicle flight operations. At the core of RNM are the vehicle noise sources, input as sound hemispheres. As the vehicle "flies" along its prescribed flight trajectory, the source sound propagation is simulated and accumulated at the receiver locations (single points of interest or multiple grid points) in a systematic time-based manner. These sound signals at the receiver locations may then be analyzed to obtain single event footprints, integrated noise contours, time histories, or numerous other features. RNM may also be used to generate spectral time history data over a ground mesh for the creation of single event sound animation videos. Acoustic properties of the noise source(s) are defined in terms of sound hemispheres that may be obtained from theoretical predictions, wind tunnel experimental results, flight test measurements, or a combination of the three. The sound hemispheres may contain broadband data (source levels as a function of one-third octave band) and pure-tone data (in the form of specific frequency sound pressure levels and phase). A PC executable version of RNM is publicly available and has been adopted by a number of organizations for Environmental Impact Assessment studies of rotorcraft noise. This paper provides a review of the required input data, the theoretical framework of RNM's propagation model and the output results. Code validation results are provided from a NATO helicopter noise flight test as well as a tiltrotor flight test program that used the RNM as a tool to aid in the development of low noise approach profiles.

Conner, David A.↗
NASA NTRS2004

Rotor Design Options for Improving XV-15 Whirl-Flutter Stability Margins

Rotor design changes intended to improve tiltrotor whirl-flutter stability margins were analyzed. A baseline analytical model of the XV-15 was established, and then a thinner, composite wing was designed to be representative of a high-speed tiltrotor. The rotor blade design was modified to increase the stability speed margin for the thin-wing design. Small rearward offsets of the aerodynamic-center locus with respect to the blade elastic axis created large increases in the stability boundary. The effect was strongest for offsets at the outboard part of the blade, where an offset of the aerodynamic center by 10% of tip chord improved the stability margin by over 100 knots. Forward offsets of the blade center of gravity had similar but less pronounced effects. Equivalent results were seen for swept-tip blades. Appropriate combinations of sweep and pitch stiffness completely eliminated whirl flutter within the speed range examined; alternatively, they allowed large increases in pitch-flap coupling (delta-three) for a given stability margin. A limited investigation of the rotor loads in helicopter and airplane configuration showed only minor increases in loads.

Acree, C. W., Jr.↗
NASA NTRS2003

Response of Damaged and Undamaged Tailored Extension-Shear-Coupled Composite Panels

The results of an analytical and experimental investigation of the response of composite I-stiffener panels with extension-shear coupling are presented. This tailored concept, when used in the panel cover skins of a tiltrotor aircraft wing has the potential for increasing the aeroelastic stability margins and improving the aircraft productivity. The extension-shear coupling is achieved by using unbalanced +/- 45 deg. plies in the skin. Experimental and STAGS analysis results are compared for eight I-stiffener panel specimens. The results indicate that the tailored concept would be feasible to use in the wing skin of a tiltrotor aircraft. Evaluation of specimens impacted at energy level of 500 in.-lbs indicate a minimal loss in stiffness and less than 30 percent loss in strength. Evaluation of specimens with severed center stiffener and adjacent skin indicated a strength loss in excess of percent.

Baker, Donald J.↗
NASA NTRS1997

A Study of the Effects of Blade Shape on Rotor Noise

A new rotor noise prediction system called the Tiltrotor Aeroacoustic Code (TRAC) has been developed under the Short Haul (Civil Tiltrotor) program between NASA, the Army, and the U.S. helicopter industry. This system couples the comprehensive rotorcraft code CAMRAD.Mod1 with either the high resolution sectional loads code HIRES or the full potential CFD code FPRBVI to predict unsteady blade loads, which are then input to the noise prediction program WOPWOP. In this paper, HIRES will be used to predict the blade-vortex interaction (BVI) noise trends associated with blade shape. The baseline shape selected was a 17% scale model of a contemporary design 4 bladed rotor. Measurements for this rotor were acquired in the Duits-Nederslandse Windtunnel (DNW). The code is used to predict noise for the base configuration and the results are compared to the measured data. This provides a firm foundation for investigating the BVI noise trends associated with blade shape. The shapes selected for study are based on variation of sweep and taper which reflect plausible "passive" design concepts. Comparisons of power required, integrated noise, and aerodynamics are made and important trends are noted.

Jones, Henry E.↗
NASA NTRS2004

Whirl Flutter Studies for a SSTOL Transport Demonstrator

A proposed new class of aircraft - the Advanced Theater Transport (ATT) will combine strategic range and high payload with 'Super-STOL' (short take-off and landing) capability. It is also proposed to modify a YC-15 into a technology demonstrator with a 20-deg tilt wing; four, eight-bladed propellers; cross-shafted gearboxes and V-22 engines. These constitute a unique combination of design features that potentially affect performance, loads and whirl-mode stability (whirl flutter). NASA Ames Research Center is working with Boeing and Hamilton Sundstrand on technology challenges presented by the concept; the purpose of NASA involvement is to establish requirements for the demonstrator and for early design guidance, with emphasis on whirl flutter. CAMRAD II is being used to study the effects of various design features on whirl flutter, with special attention to areas where such features differ from existing aircraft, notably tiltrotors. Although the stability margins appear to be more than adequate, the concept requires significantly different analytical methods, principally including far more blade modes, than typically used for tiltrotors.

Acree, C. W., Jr.↗
NASA NTRS2005

Failure Analysis of Discrete Damaged Tailored Extension-Shear-Coupled Stiffened Composite Panels

The results of an analytical and experimental investigation of the failure of composite is tiffener panels with extension-shear coupling are presented. This tailored concept, when used in the cover skins of a tiltrotor aircraft wing has the potential for increasing the aeroelastic stability margins and improving the aircraft productivity. The extension-shear coupling is achieved by using unbalanced 45 plies in the skin. The failure analysis of two tailored panel configurations that have the center stringer and adjacent skin severed is presented. Finite element analysis of the damaged panels was conducted using STAGS (STructural Analysis of General Shells) general purpose finite element program that includes a progressive failure capability for laminated composite structures that is based on point-stress analysis, traditional failure criteria, and ply discounting for material degradation. The progressive failure predicted the path of the failure and maximum load capability. There is less than 12 percent difference between the predicted failure load and experimental failure load. There is a good match of the panel stiffness and strength between the progressive failure analysis and the experimental results. The results indicate that the tailored concept would be feasible to use in the wing skin of a tiltrotor aircraft.

Baker, Donald J.↗