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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 NTRS2013

Investigation of Maximum Blade Loading Capability of Lift-Offset Rotors

Maximum blade loading capability of a coaxial, lift-offset rotor is investigated using a rotorcraft configuration designed in the context of short-haul, medium-size civil and military missions. The aircraft was sized for a 6600-lb payload and a range of 300 nm. The rotor planform and twist were optimized for hover and cruise performance. For the present rotor performance calculations, the collective pitch angle is progressively increased up to and through stall with the shaft angle set to zero. The effects of lift offset on rotor lift, power, controls, and blade airloads and structural loads are examined. The maximum lift capability of the coaxial rotor increases as lift offset increases and extends well beyond the McHugh lift boundary as the lift potential of the advancing blades are fully realized. A parametric study is conducted to examine the differences between the present coaxial rotor and the McHugh rotor in terms of maximum lift capabilities and to identify important design parameters that define the maximum lift capability of the rotor. The effects of lift offset on rotor blade airloads and structural loads are also investigated. Flap bending moment increases substantially as lift offset increases to carry the hub roll moment even at low collective values. The magnitude of flap bending moment is dictated by the lift-offset value (hub roll moment) but is less sensitive to collective and speed.

Yeo, Hyeonsoo↗
NASA NTRS2017

Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement

High-resolution simulations of rotor/vortex-wake interaction for a UH60-A rotor under BVI and dynamic stallconditions were carried out with the OVERFLOW Navier-Stokes code.a. The normal force and pitching moment variation with azimuth angle were in good overall agreementwith flight-test data, similar to other CFD results reported in the literature.b. The wake-grid resolution did not have a significant effect on the rotor-blade airloads. This surprisingresult indicates that a wake grid spacing of (Delta)S=10% ctip is sufficient for engineering airloads predictionfor hover and forward flight. This assumes high-resolution body grids, high-order spatial accuracy, anda hybrid RANS/DDES turbulence model.c. Three-dimensional dynamic stall was found to occur due the presence of blade-tip vortices passing overa rotor blade on the retreating side. This changed the local airfoil angle of attack, causing stall, unlikethe 2D perspective of pure pitch oscillation of the local airfoil section.

CFD Validation↗
NASA NTRSDate not supplied

TPSAS-NF1676L-14332-DND

Motivation and Methodology UH60A Airloads Flight Test CFD/CSD correlations results from - Recent code-to-code comparisons show remarkably similar results from CFD: OVERFLOW / FUN3D / HELIOS CFD: OVERFLOW / FUN3D / HELIOS - Much less difference between various computed results than between computed results and flight data UH60A Airloads Wing Tunnel Test CFD/CSD correlations - Simplified geometry (no Simplified geometry (no tail rotor/propulsion) tail rotor/propulsion) - Additional measurements provide new insights

Elizabeth M Lee-rausch↗
NASA NTRS1973

Analysis of helicopter maneuver-loads and rotor-loads flight test data

A study was conducted in which available airload and blade response data for the NH-3A and CH-53A rotors were analyzed in an attempt to provide greater insight into the sources of rotor vibratory loads in both level and maneuvering flight. Primary emphasis in the study was placed on examining and understanding causes of high-frequency rotor control loads. Secondary objectives were: (1) to examine the effect of number of rotor blades on hub vibratory shear forces and (2) to assess which of the many terms appearing in the hub vibratory shear force expression were of most significance.

Beno, E. A.↗
NASA NTRS1974

Comparison of three methods for calculation of helicopter rotor blade loading and stresses due to stall

A comparison is made of the results of three methods for calculating the effects of dynamic stall on the performance, airloads, and blade stresses of a helicopter rotor at high loading. The three dynamic-stall methods considered predict essentially the same performance and trim for the rotor. They give roughly the same mean bending moments, but the peak-to-peak torsion and bending moments differ by 25 to 40 percent, and there are differences in the details of the predicted blade motion and stresses. The latter are due to significant differences in the dynamic stall aerodynamic loads, particularly the aerodynamic pitch moment, predicted by the three methods.

Johnson, W.↗
NASA NTRS1975

The use of local basis functions in unsteady aerodynamics

This paper reports a successful demonstration of using local basis functions to solve Kussner's integral equation for unsteady airloads. Pressure basis functions are defined over relatively small subsets of the aerodynamic surface and are zero elsewhere. This formulation combines the accuracy and smoothness of distribution methods with the simplicity and versatility of panel methods. Application is made to subsonic compressible flow about oscillating planar surfaces with controls. Numerical results are presented. Convergence with respect to panel size, extensions to more general classes of solutions, and areas needing additional investigation are discussed.

Fromme, J.↗
NASA NTRS1975

Mated aerodynamic characteristics investigation for 0.04-scale model Boeing 747 CAM/external tank (model AX1284 E-5) combination in the University of Washington Aeronautical Laboratory F. K. Kirsten Wind Tunnel (CA11)

Experimental investigations of the aerodynamic characteristics of a 0.04-scale external tank (ET) force model in combination with a 0.04-scale Boeing 747 force model were conducted. Test purposes were: (1) to determine ET airloads for selected configurations and (2) to determine the effectiveness of ET position, incidence, and support structure and 747 vertical stabilizing surfaces on stability, control, and performance of 747/ET combinations. The 747 was tested alone to establish baseline data and to verify test results. Six-component aerodynamic force and moment data were recorded for the 747 CAM and ET combination. Six-component force and moment data were also recorded for the ET, which was mounted on an internal balance supported by the 747. Data were recorded for angles of attack from -4 deg to +24 deg in 2 deg increments and angles of sideslip of - deg to + or - 20 deg. Testing was conducted at Mach 0.15 with dynamic pressure deg at 36 psf and unit Reynolds number of 1.3 million per foot. Photographs of test configurations are shown.

Source record↗
NASA NTRS1975

Results of a Pressure Loads Investigation on a 0.030-scale Model (47-OTS) of the Integrated Space Shuttle Vehicle Configuration 5 in the NASA Ames Research Center 11 by 11 Foot Leg of the Unitary Plan Wind Tunnel (IA81A), Volume 1

Results of wind tunnel tests on a 0.030-scale model of the integrated space shuttle vehicle configuration 5 are presented. Testing was conducted in the NASA Ames Research Center 11 x 11 foot leg of the Unitary Plan Wind Tunnel to investigate pressure distributions for airloads analyses at Mach numbers from 0.9 through 1.4. Angles of attack and sideslip were varied from -6 to +6 degrees.

Chee, E.↗
NASA NTRS1977

Finite state modeling of aeroelastic systems

A general theory of finite state modeling of aerodynamic loads on thin airfoils and lifting surfaces performing completely arbitrary, small, time-dependent motions in an airstream is developed and presented. The nature of the behavior of the unsteady airloads in the frequency domain is explained, using as raw materials any of the unsteady linearized theories that have been mechanized for simple harmonic oscillations. Each desired aerodynamic transfer function is approximated by means of an appropriate Pade approximant, that is, a rational function of finite degree polynomials in the Laplace transform variable. The modeling technique is applied to several two dimensional and three dimensional airfoils. Circular, elliptic, rectangular and tapered planforms are considered as examples. Identical functions are also obtained for control surfaces for two and three dimensional airfoils.

Vepa, R.↗
NASA NTRS1977

Lateral equilibrium of asymmetrical swept wings - Aileron control vs geometric twist

A static aeroelastic phenomenon unique to an aircraft with asymmetrically swept wings is discussed. A simple formula is derived from the analysis of a highly idealized model. The validity of this formula is examined through the use of a more sophisticated numerical analysis. Among the results of this analysis are the following: aileron settings of a few degrees are sufficient to trim such aircraft in roll-for-g-flight; the use of built-in twist in the form of initial negative dihedral provides an efficient alternative to aileron trim; if the wing is elastically tailored in a proper fashion, it may be possible to design a wing whose elastic deformation under airloads provides a form of self-trim in roll at the cruise q of the aircraft.

Weisshaar, T. A.↗
NASA NTRS1977

Unsteady aerodynamic modeling for arbitrary motions

A study is presented on the unsteady aerodynamic loads due to arbitrary motions of a thin wing and their adaptation for the calculation of response and true stability of aeroelastic modes. In an Appendix, the use of Laplace transform techniques and the generalized Theodorsen function for two-dimensional incompressible flow is reviewed. New applications of the same approach are shown also to yield airloads valid for quite general small motions. Numerical results are given for the two-dimensional supersonic case. Previously proposed approximate methods, starting from simple harmonic unsteady theory, are evaluated by comparison with exact results obtained by the present approach. The Laplace inversion integral is employed to separate the loads into 'rational' and 'nonrational' parts, of which only the former are involved in aeroelastic stability of the wing. Among other suggestions for further work, it is explained how existing aerodynamic computer programs may be adapted in a fairly straightforward fashion to deal with arbitrary transients.

Edwards, J. W.↗
NASA NTRS1977

Unsteady aerodynamic modeling for arbitrary motions

Results indicating that unsteady aerodynamic loads derived under the assumption of simple harmonic motions executed by airfoil or wing can be extended to arbitrary motions are summarized. The generalized Theodorsen (1953) function referable to loads due to simple harmonic oscillations of a wing section in incompressible flow, the Laplace inversion integral for unsteady aerodynamic loads, calculations of root loci of aeroelastic loads, and analysis of generalized compressible transient airloads are discussed.

Edwards, J. W.↗
NASA NTRS1978

Prediction of unsteady separated flows on oscillating airfoils

Techniques for calculating high Reynolds number flow around an airfoil undergoing dynamic stall are reviewed. Emphasis is placed on predicting the values of lift, drag, and pitching moments. Methods discussed include: the discrete potential vortex method; thin boundary layer method; strong interaction between inviscid and viscous flows; and solutions to the Navier-Stokes equations. Empirical methods for estimating unsteady airloads on oscillating airfoils are also described. These methods correlate force and moment data from wind tunnel tests to indicate the effects of various parameters, such as airfoil shape, Mach number, amplitude and frequency of sinosoidal oscillations, mean angle, and type of motion.

Mccroskey, W. J.↗
NASA NTRS1978

Status and operational characteristics of the National Transonic Facility

The article discusses the development and capabilities of the National Transonic Facility which is planned for operation in 1981. The fan-drive, cryogenic-pressurized, closed-return facility will have operating parameters of: 0.1-1.2 Mach, 1-9 bars pressure, 78-340 K, 150 dB sound pressure, and plus or minus 0.001 rms turbulence intensity. These operating conditions have been selected on the basis of several current and future aircraft and space transportation systems. The facility will provide full-scale testing conditions for calculating subsonic drag, airloads, and stability and control information. Data for pre-test conditions, on-line information, and post-test analysis will be computer-processed.

Nicks, O. W.↗
NASA NTRS1979

Computation of aerodynamic interference effects on oscillating airfoils with controls in ventilated subsonic wind tunnels

Lift interference effects are discussed based on Bland's (1968) integral equation. A mathematical existence theory is utilized for which convergence of the numerical method has been proved for general (square-integrable) downwashes. Airloads are computed using orthogonal airfoil polynomial pairs in conjunction with a collocation method which is numerically equivalent to Galerkin's method and complex least squares. Convergence exhibits exponentially decreasing error with the number n of collocation points for smooth downwashes, whereas errors are proportional to 1/n for discontinuous downwashes. The latter can be reduced to 1/n to the m+1 power with mth-order Richardson extrapolation (by using m = 2, hundredfold error reductions were obtained with only a 13% increase of computer time). Numerical results are presented showing acoustic resonance, as well as the effect of Mach number, ventilation, height-to-chord ratio, and mode shape on wind-tunnel interference. Excellent agreement with experiment is obtained in steady flow, and good agreement is obtained for unsteady flow.

Fromme, J. A.↗
NASA NTRS1979

XV-15 Tilt Rotor Research Aircraft - Program report

This paper is a status report of the NASA/Army XV-15 Project. The basic tilt-rotor concept and the XV-15 Tilt-Rotor Research Aircraft are discussed and some results of full-scale wind-tunnel tests in the Ames 40- by 80-Foot Wind Tunnel are presented. Flight-test data are included to give preliminary performance, noise, and vibration data in hover and as far into transition flight as are available at the time of presentation. Information concerning vehicle aerodynamics and airloads obtained as a result of both wind-tunnel and flight tests are provided with some conclusions as to the ramifications of the data in terms of design criteria and configuration layout.

Magee, J. P.↗