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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Folding tilt rotor demonstrator feasibility study

This study considers the modification of existing aircraft to the folding tilt rotor (FTR) design configuration, and then addresses the vehicle design requirements necessary to demonstrate the FTR concept throughout the hover/transition high-speed envelope. Three potential candidates are considered: (1) the Bell/Boeing V-22 Osprey combined with either the existing TF-34 convertible engine or a conceptual convertible engine utilizing the torque-converter-coupled fan configuration; (2) a combination of the same powerplants with a modified Lockheed S-3A Viking; and (3) the NASA/Army/BELL XV-15 airframe mated with a conceptual generic turbofan engine with a fixed-pitch fan coupled to the engine by means of a torque converter. Required aircraft modifications are identified and recommended R&D efforts for engine/rotor/airframe integration are presented.

Eisenberg, J. D.↗
NASA NTRS1986

The development of advanced technology blades for tilt-rotor aircraft

The paper discusses the development and ground testing of blades for the XV-15 tilt-rotor demonstrator aircraft. This work was performed under contract NAS2-11250 with NASA Ames Research Center. These blades, known as the Advanced Technology Blades (ATB), replace the rectangular, steel blades which were part of the XV-15 original design. The materials used in the primary structure of the ATB are fiberglass and high strain graphite epoxy laminates. This facilitates the use of 43 deg of nonlinear twist, a nonuniform tapered planform and thin airfoils required for aerodynamic efficiency. Instrumentation life is extended by encapsulating gages and wiring in the composite structure. Tip shells and cuff fairings are removable to provide access to tip weights and retention hardware; they are also replaceable with alternate research configurations. Extensive laboratory testing has validated predicted strength characteristics. Hover testing has demonstrated performance significantly superior to that predicted by contemporary methodology. Key elements of the test rig used for rotor performance measurement were developed as an ancillary part of the present program. The performance testing included measurement of near- and far-field noise. Induced inflow velocity distributions were also determined and photographs of tip vortex condensation trails were taken. These are providing guidance for modifications to hover peformance codes.

Alexander, Harold 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 NTRS1987

Modeling XV-15 tilt-rotor aircraft dynamics by frequency and time-domain identification techniques

Models of the open-loop hover dynamics of the XV-15 Tilt-Rotor Aircraft are extracted from flight data using two approaches: frequency domain and time-domain identification. Both approaches are reviewed and the identification results are presented and compared in detail. The extracted models are compared favorably, with the differences associated mostly with the inherent weighing of each technique. Step responses are used to show that the predictive capability of the models from both techniques is excellent. Based on the results of this study, the relative strengths and weaknesses of the frequency and time-domain techniques are summarized and a proposal for a coordinated parameter identification approach is presented.

Tischler, Mark B.↗
NASA NTRS1987

Reduction of tilt rotor download using circulation control

The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent.

Felker, Fort F.↗
NASA NTRS1986

Hover performance tests of baseline metal and Advanced Technology Blade (ATB) rotor systems for the XV-15 tilt rotor aircraft

Rotor hover performance data were obtained for two full-scale rotor systems designed for the XV-15 Tilt Rotor Research Aircraft. One rotor employed the rectangular planform metal blades (rotor solidity = 0.089) which were used on the initial flight configuration of the XV-15. The second rotor configuration examined the nonlinear taper, composite-construction, Advanced Technology Blade (ATB), (rotor solidity = 0.10) designed to replace the metal blades on the XV-15. Variations of the baseline ATB tip and cuff shapes were also tested. A new six-component rotor force and moment balance designed to obtain highly accurate data over a broad range of thrust and torque conditions is described. The test data are presented in nondimensional coefficient form for the performance results, and in dimensional form for the steady and alternating loads. Some wake and acoustic data are also shown.

Bartie, K.↗
NASA NTRS1988

Optical system design alternatives for the Moderate-Resolution Imaging Spectrometer-Tilt (MODIS-T) for the Earth Observing System (EOS)

The MODIS consists of two synergistic sensors with a total of 104 spectral bands in the 0.4-14.2-micron range. MODIS-T (Tilt) is one of these sensors. It is a 64-channel imaging spectrometer with a required 10 nm spectral resolution (FWHM) in the 400 to 1040 nm spectral range. The system will have a 1 km IFOV, a wide scan for global coverage in three days, and be capable of being pointed fore and aft of nadir by + or - 50 degrees.

Maymon, Peter W.↗
NASA NTRS1989

Extension-torsion coupling behavior of advanced composite tilt-rotor blades

An analytic model was developed to study the extension-bend-twist coupling behavior of an advanced composite helicopter or tilt-rotor blade. The outer surface of the blade is defined by rotating an arbitrary cross section about an initial twist axis. The cross section can be nonhomogeneous and composed of generally anisotropic materials. The model is developed based upon a three dimensional elasticity approach that is recast as a coupled two-dimensional boundary value problem defined in a curvilinear coordinate system. Displacement solutions are written in terms of known functions that represent extension, bending, and twisting and unknown functions for local cross section deformations. The unknown local deformation functions are determined by applying the principle of minimum potential energy to the discretized two-dimensional cross section. This is an application of the Ritz method, where the trial function family is the displacement field associated with a finite element (8-node isoparametric quadrilaterals) representation of the section. A computer program was written where the cross section is discretized into 8-node quadrilateral subregions. Initially the program was verified using previously published results (both three-dimensional elasticity and technical beam theory) for pretwisted isotropic bars with an elliptical cross section. In addition, solid and thin-wall multi-cell NACA-0012 airfoil sections were analyzed to illustrate the pronounced effects that pretwist, initial twist axis location, and spar location has on coupled behavior. Currently, a series of advanced composite airfoils are being modeled in order to assess how the use of laminated composite materials interacts with pretwist to alter the coupling behavior of the blade. These studies will investigate the use of different ply angle orientations and the use of symmetric versus unsymmetric laminates.

Kosmatka, J. B.↗
NASA NTRS1990

DSS 15, 45, and 65 34-meter high efficiency antenna radio frequency performance enhancement by tilt added to the subreflector during elevation angle changes

The focusing adjustments of the subreflectors of an az-el Cassegrainian antenna that uses only linear motions have always ended in lateral offsets of the phase centers at the subreflector's focus points at focused positions, which have resulted in small gain losses. How lateral offsets at the two focus points were eliminated by tilting the subreflector, resulting in higher radio frequency (RF) efficiencies at all elevation angles rotated from the rigging angles are described.

Katow, M. S.↗
NASA NTRS1990

The Bode integrals and wave front tilt control

This paper reviews four of Bode's (1940) integrals and what those integrals tell about feedback design in the frequency domain. The resulting design paradigm is known as the Bode ideal cutoff. The Bode ideal cutoff design can be done with pencil and paper and without requiring that the compensator be of a certain fixed order or even a rational function of frequency. The Bode ideal cutoff is applied to the preliminary feedback design of wave front tilt control by two mirrors on a space based interferometer. The design example illustrates how the Bode ideal cutoff takes into account bandwidth, sensor noise constraints, and uncertainties via stability margins, and then maximizes the feedback (loop gain or disturbance rejection) over a prescribed frequency band.

Kissel, Glen J.↗
NASA NTRS1990

Effects of acute hypoxia on cardiopulmonary responses to head-down tilt

Six male subjects were exposed on two separate occasions to simulated microgravity with 28 deg head-down tilt (HD) for 1 h with baseline followed by recovery at + 17 deg head-up. Pulmonary ventilation, gas exchange, spirometry, and central and cerebral blood flow characteristics were compared while breathing ambient air and reduced F(I)O2 equivalent to 14,828 ft. With hypoxia (HY), the increased tidal volume served to attenuate the drop in arterial saturation by reducing deadspace ventilation. Arterial and mixed venous PO2, values, estimated from peripheral venous samples and cardiac output (CO), were both maintained during HD in HY. Mixed venous PO2 was elevated by an increase in CO associated with a reduction in systemic resistance. Changes in spirometric indices during HD were not accentuated by HY, making the presence of interstitial edema unlikely. Cerebral flow and resistance showed minor reductions with HD. Tissue oxygenation and cardiopulmonary function were not notably effected by HD during HY, but a combination of these two stressors may predispose subjects to subsequent orthostatic intolerance during initial recovery.

Loeppky, J. A.↗
NASA NTRS1990

Offset, tilted dipole models of Uranian smooth high-frequency radio emission

The smooth high-frequency (SHF) component of the radio emission detected during the Voyager 2 encounter with Uranus (January 1986) is studied. An offset tilted dipole (OTD) investigation of the SHF emission at L shells is carried out within the range of the bursty source locations. A viable high L shell model is presented. It is suggested that Miranda, which reaches a minimum L shell at L = 5, may be related to the timing of several types of radio emissions.

Schweitzer, Andrea E.↗
NASA NTRS1990

Prediction of XV-15 tilt rotor discrete frequency aeroacoustic noise with WOPWOP

The results, methodology, and conclusions of noise prediction calculations carried out to study several possible discrete frequency harmonic noise mechanisms of the XV-15 Tilt Rotor Aircraft in hover and helicopter mode forward flight are presented. The mechanisms studied were thickness and loading noise. In particular, the loading noise caused by flow separation and the fountain/ground plane effect were predicted with calculations made using WOPWOP, a noise prediction program developed by NASA Langley. The methodology was to model the geometry and aerodynamics of the XV-15 rotor blades in hover and steady level flight and then create corresponding FORTRAN subroutines which were used an input for WOPWOP. The models are described and the simplifying assumptions made in creating them are evaluated, and the results of the computations are presented. The computations lead to the following conclusions: The fountain/ground plane effect is an important source of aerodynamic noise for the XV-15 in hover. Unsteady flow separation from the airfoil passing through the fountain at high angles of attack significantly affects the predicted sound spectra and may be an important noise mechanism for the XV-15 in hover mode. The various models developed did not predict the sound spectra in helicopter forward flight. The experimental spectra indicate the presence of blade vortex interactions which were not modeled in these calculations. A need for further study and development of more accurate aerodynamic models, including unsteady stall in hover and blade vortex interactions in forward flight.

Coffen, Charles D.↗
NASA NTRS1990

Model tilt-rotor hover performance and surface pressure measurement

A test of a small scale 3-bladed model rotor, with geometry typical of that used on tilt rotor aircraft, was conducted in the Army Aeroflightdynamics Directorate's anechoic hover chamber. The purpose was to determine the hover performance of the rotor and investigate the pressure distributions on a blade at various collective pitch angles and tip speeds. The measured pressures indicate that the rotor did not stall for high collective pitch angles up to theta sub c = 25 deg. This is clearly a 3-D effect since 2-D theory predicts flow separation at these high angles. The flow near the trailing edge separated above theta sub c = 25 deg which caused a sharp increase in power.

Tung, Chee↗
NASA NTRS1991

Navier-Stokes computation of wing/rotor interaction for a tilt rotor in hover

A method has been developed to analyze the wing/rotor interaction of tilt rotor aircraft in hover. The unsteady, thin-layer compressible Navier-Stokes equations are solved using an implicit, finite difference scheme that employs LU-ADI factorization. The rotor is modeled as an actuator disk which imparts a radial and azimuthal distribution of pressure rise and swirl to the flowfield. The 'chimera' approach of grid point blanking is used to update the rotor boundary conditions. Results are presented for both a rotor alone and for wing/rotor interaction where the thrust coefficient is 0.0164 and wing flap deflection is 67 degrees. Many of the complex flow features are captured including the fountain effect, leading and trailing edge separation, and the unsteady wake beneath the wing. Wing surface pressures compare fairly well with experimental data although the time-averaged download is about twenty percent higher than the measured value. This discrepancy is due to a combination of factors that are discussed.

Fejtek, Ian↗
NASA NTRS1990

The Moderate Resolution Imaging Spectrometer-tilt (MODIS-T)

There will be several state-of-the-art spectrometers in operation on the NASA Polar Oribting Platform (NPOP-1) as part of the Earth Observing System. The Moderate Resolution Imaging Spectrometer (MODIS) will consist of two imaging spectroradiometric instruments, one nadir-viewing (MODIS-N) and the other tiltable (MODIS-T) for ocean observation and land bidirectional reflectance studies. The MODIS-T instrument is required to cover the wavelength range of 400 to 880 nm in approximately 15 steps, have less than 2.3 percent instrument-induced polarization, be calibrated to an absolute radiometric accuracy of at least 5 percent over the full dynamic range of the instrument, have a 1.1 kilometer square instantaneous field of view at nadir, and be capable of + or - 50-deg along-track tilt.

Magner, Thomas J.↗
NASA NTRS1990

Fluid/electrolyte balance and cardiovascular responses - Head-down tilted rats

Results are presented on cardiovascular and fluid/electrolyte balance responses of rats to a 7-day-long whole-body suspension (WBS) with about 20-deg head-down tilt (HDT), followed by 7 days of recovery. Compared with horizontally positioned (N-HDT) rats serving as controls, the Na intake of HDT rats was significantly reduced during the first 3 days of HDT, and urinary and fecal Na loss exceeded the Na intake during days 5 and 6. Changes during the days of recovery showed adjustments and reestablishment of Na balance. Urinary K losses increased progressively during the 7 days of HDT, but, with the exception of days 1-3 of HDT, when the K intake was significantly reduced, the K balance was retained. Changes in cardiac responses (including elevations in mean, diastolic, and systolic arterial pressures) paralleled changes in fluid and electrolyte balance during the HDT period.

Musacchia, X. J.↗
NASA NTRS1991

Cardiopulmonary responses to acute hypoxia, head-down tilt and fluid loading in anesthetized dogs

Cardiopulmonary responses to acute hypoxia (HY), fluid loading by saline infusion (FL), and head-down tilt (HD) of mechanically ventilated anesthetized dogs were investigated by measuring thermodynamics and pulmonary gas exchange. It was found that HD decreased the total respiratory compliance both during HY and normoxia (NO) and that the reduction in compliance by FL was twice as large as by HD. Superimposing HD on HY doubled the increase in vascular resistance due to HY alone. In the systemic circulation, HD lowered the resistance to below NO levels. There was a significant positive correlation between the changes in blood volume and in pulmonary artery pressure for experimental transitions, suggesting that a shift in blood volume from systemic to pulmonary circulations and changes in the total blood volume may contribute substantially to these apparent changes in resistance.

Loeppky, J. A.↗