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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Advanced Technology Blade testing on the XV-15 Tilt Rotor Research Aircraft

The XV-15 Tilt Rotor Research Aircraft has just completed the first series of flight tests with the Advanced Technology Blade (ATB) rotor system. The ATB are designed specifically for flight research and provide the ability to alter blade sweep and tip shape. A number of problems were encountered from first installation through envelope expansion to airplane mode flight that required innovative solutions to establish a suitable flight envelope. Prior to operation, the blade retention hardware had to be requalified to a higher rated centrifugal load, because the blade weight was higher than expected. Early flights in the helicopter mode revealed unacceptably high vibratory control system loads which required a temporary modification of the rotor controls to achieve higher speed flight and conversion to airplane mode. The airspeed in airplane mode was limited, however, because of large static control loads. Furthermore, analyses based on refined ATB blade mass and inertia properties indicated a previously unknown high-speed blade mode instability, also requiring airplane-mode maximum airspeed to be restricted. Most recently, a structural failure of an ATB cuff (root fairing) assembly retention structure required a redesign of the assembly. All problems have been addressed and satisfactory solutions have been found to allow continued productive flight research of the emerging tilt rotor concept.

Wellman, Brent↗
NASA NTRS1993

Accuracy of Tilt Rotor Hover Performance Predictions

The accuracy of various methods used to predict tilt rotor hover performance was established by comparing predictions with large-scale experimental data. A wide range of analytical approaches were examined. Blade lift was predicted with a lifting line analysis, two lifting surface analyses, and by a finite-difference solution of the full potential equation. Blade profile drag was predicted with two different types of airfoil tables and an integral boundary layer analysis. The inflow at the rotor was predicted using momentum theory, two types of prescribed wakes, and two free wake analyses. All of the analyses were accurate at moderate thrust coefficients. The accuracy of the analyses at high thrust coefficients was dependent upon their treatment of high sectional angles of attack on the inboard sections of the rotor blade. The analyses which allowed sectional lift coefficients on the inboard stations of the blade to exceed the maximum observed in two-dimensional wind tunnel tests provided better accuracy at high thrust coefficients than those which limited lift to the maximum two-dimensional value. These results provide tilt rotor aircraft designers guidance on which analytical approaches provide the best results, and the level of accuracy which can be expected from the best analyses.

Felker, Fort F.↗
NASA NTRS1944

Effect of Tilt of the Propeller Axis on the Longitudinal-stability Characteristics of Single-Engine Airplanes

Report presents the results of tests of a model of a single-engine airplane with two different tilts of the propeller axis. The results indicate that on a typical design a 5 degree downward tilt of the propeller axis will considerably reduce the destabilization effects of power. A comparison of the experimental results with those computed by use of existing theory is included. A comparison of the experimental results with those computed by use of existing theory is included. It is shown that the results can be predicted with an accuracy acceptable for preliminary design purposes, particularly at the higher powers where the effects are of significant magnitude.

Goett, Harry J↗
NASA NTRS1994

Piloted simulation study of two tilt-wing flap control concepts, phase 2

A two phase piloted simulation study has been conducted in the Ames Vertical Motion Simulator to investigate alternative wing and flap controls for tilt-wing aircraft. This report documents the flying qualities results and findings of the second phase of the piloted simulation study and describes the simulated tilt-wing aircraft, the flap control concepts, the experiment design and the evaluation tasks. The initial phase of the study compared the flying qualities of both a conventional programmed flap and an innovative geared flap. The second phase of the study introduced an alternate method of pilot control for the geared flap and further studied the flying qualities of the programmed flap and two geared flap configurations. In general, the pilot ratings showed little variation between the programmed flap and the geared flap control concepts. Some differences between the two control concepts were noticed and are discussed in this report. The geared flap configurations had very similar results. Although the geared flap concept has the potential to reduce or eliminate the pitch control power requirements from a tail rotor or a tail thruster at low speeds and in hover, the results did not show reduced tail thruster pitch control power usage with the geared flap configurations compared to the programmed flap configuration. The addition of pitch attitude stabilization in the second phase of simulation study greatly enhanced the aircraft flying qualities compared to the first phase.

Birckelbaw, Lourdes G.↗
NASA NTRS1994

Piloted simulation study of two tilt-wing control concepts

A two-phase piloted simulation study was conducted to investigate alternative wing and flap controls for tilt-wing aircraft. The initial phase of the study compared the flying qualities of both a conventional (programmed) flap and an innovative geared flap. The second phase of the study introduced an alternate method of pilot control for the geared flap and further studied the flying qualities of the programmed flap, and two geared flap configurations. In general, the pilot rating showed little variation between the programmed flap and the geared flap control concepts. Some differences between the two concepts were noticed and are discussed in this paper. The addition of pitch attitude stabilization in the second phase of the study greatly enhanced the aircraft flying qualities. This paper describes the simulated tilt-wing aircraft and the flap control concepts and presents the results of both phases of the simulation study.

Birckelbaw, Lourdes G.↗
NASA NTRS1994

Imaging the effect of dipole tilt on magetotail boundaries

Eight years of Interplanetary Monitoring Platform (IMP) 8, four years of International Sun Earth Explorer (ISEE) 2, and one year of IMP 7 magnetometer data have been combined to produce an 'image' of the average magnetic field for a YZ cross section (aberrated GSM) of the magnetotail at a downtail distance of 25 R(sub E). The shape of the neutral sheet and magnetopause boundaries can be observed directly from the images. A fitting function that qualitatively matches the observed boundary shape can then be chosen. This approach improves on previous fits to possible unsuitable functional forms specified independently of the data. In addition, as a refinement of previous studies, we have corrected for varying solar wind dynamic pressure and the effects of tail flaring. We find the magnetopause is displaced above the XY plane with increasing dipole tilt. The neutral sheet is found to curve slightly more than the model of Fairlfield (1980) during times of large dipole tilt and near the flanks appears to differ substantially from the neutral sheet shape given by the analytic model of Voigt (1984), the more recent neutral sheet model of Dandouras (1988) based on the Voigt model, and the semi-empirical model of Tsyganenko (1989).

Hammond, C. Max↗
NASA NTRS1994

Microvascular responses to body tilt in cutaneous maximus muscle of conscious rats

We investigated microvascular responses to head-up tilt (HUT) and head-down tilt (HDT) in striated muscle of conscious male rats. To observe the microcirculation in the cutaneous maximus muscle, a transparent polycarbonate chamber was implanted aseptically into a skin fold created between the shoulders. Rats were trained to sit quietly during HUT and HDT while positioned on a horizontal microscope that rotated in the sagittal plane. At 4-5 days after surgery, arteriole and venule diameters were recorded using videomicroscopy while the rat experienced 10 min each (in random order) of HUT or HDT at 20 deg or 40 deg separated by 2-h rest periods. HUT had no affect on microvessel diameter; 20 deg HDT had little affect. In response to 40 deg HDT, 'large' arterioles constricted by 18 +/- 2% and 'small' arterioles dilated by 21 +/- 3%; this difference suggested variation in mechanisms controlling arteriolar responses. Venules exhibited a larger fluctuation in diameter during 40 deg HDT compared with other body positions, suggesting that venomotor activity may be induced with sufficient fluid shift or change in central venous pressure. These observations illustrate a viable model for studying microvascular responses to gravitational stress in conscious rats.

Puri, Rohit K.↗
NASA NTRS1995

Tilting A Small Reflector For Vernier Pointing Of A Large Antenna

Simple vernier pointing technique devised to facilitate scanning beam pointing of large paraboloidal reflector so line of sight of antenna sweeps out narrow cone about fixed axis (conical scan, also known as "conscan" in art). Scan effected by one of relatively small beam-waveguide reflectors or mirrors that couple signals between antenna and distant transmitting and/or receiving electronic circuits. Easier to tilt small mirror than to tilt massive antenna structure.

Veruttipong, Watt↗
NASA NTRS1995

Variable-Tilt Helicopter Rotor Mast

Variable-tilt helicopter rotor mast proposed to improve helicopter performance and reduce vibration, especially at upper end of forward-speed range of helicopters. Achieved by use of universal coupling in main rotor mast or by tilting entire engine-and-transmission platform. Performance, energy efficiency, and safety enhanced.

Kelley, Henry L.↗
NASA NTRS1995

The tilts of corotating interaction regions at mid heliographic latitudes

Ulysses observations of corotating interaction regions (CIRs) at mid heliographic latitudes have shown that the flow downstream of the forward shock (or wave) on the leading edge of a CIR generally turns northward and westward, while the flow downstream of the reverse wave on the trailing edge generally turns southward and eastward. These systematic flow deflections are a natural consequence of large scale pressure gradients associated with the CIRs, and indicate that the forward waves tend to propagate toward and across the equator with increasing heliocentric distance, while the reverse waves tend to propagate toward the pole. Recent determinations of CIR shock normals using the Ulysses magnetic field data appear to confirm these plasma results (Burton, private communication). Numerical simulations indicate that these effects (which imply that CIRs are systematically tilted in the north-south direction at mid latitudes) are a natural consequence of the tilt of the solar magnetic dipole axis relative to the solar rotation axis. The present work utilizes a variety of techniques to analyze the flow deflections observed within CIRs from which we can infer the overall orientations of the CIRs and the speeds and directions of propagation of the waves. Where possible, the observations are quantitatively compared with the results of 3-dimensional MHD simulations.

Riley, Pete↗
NASA NTRS1995

Calf venous compliance measured with head-up tilt equals supine calf compliance

Elevated calf compliance may contribute to orthostatic intolerance following space flight and bed rest. Calf venous compliance is measured conventionally with venous occlusion plethysmography in supine subjects. With this well-established technique, subjects undergo inflation of a pressure cuff around the thigh just above the knee, which increases calf venous pressure. A plethysmograph simultaneously measures calf volume elevation. Compliance equals calf volume elevation per mm Hg thigh occlusion (calf venous) pressure in relaxed legs of the supine subjects. Compliance may also be measured during stepwise head-up tilt (HUT) as calf volume elevation per mm Hg gravitational venous pressure elevation produced by HUT. However, during HUT on a tilt table with a footplate, calf muscles activate to counteract gravity: this is an obvious and natural response to gravitational force. Such muscle activation conceivably could reduce calf compliance, yet relatively little calf muscle activation occurs during HUT and orthostasis (less than 10% of maximal voluntary levels; 4, 8, 10). Also, this activation produces minimal calf volume change (less than 0.3%; 3). Therefore, we hypothesized that calf compliance measured with HUT equals that measured with supine venous occlusion.

Watenpaugh, D. E.↗
NASA NTRS1961

Large-Scale Wind-Tunnel Tests of an Airplane Model with an Unswept, Tilt Wing of Aspect Ratio 5.5, and with Four Propellers and Blowing Flaps

Tests were made of a large-scale tilt-wing deflected-slipstream VTOL airplane with blowing-type BLC trailing-edge flaps. The model was tested with flap deflections of 0 deg. without BLC, 50 deg. with and without BLC, and 80 deg. with BLC for wing-tilt angles of 0, 30, and 50 deg. Included are results of tests of the model equipped with a leading-edge flap and the results of tests of the model in the presence of a ground plane.

Weiberg, James A.↗
NASA NTRS1960

Wind-Tunnel Investigation of a Small-Scale Model of an Aerial Vehicle Supported by Tilting Ducted Fans

A wind-tunnel investigation has been made to study the static longitudinal and lateral stability characteristics of a simplified aerial vehicle supported by ducted fans that tilt relative to the airframe. The ducts were in a triangular arrangement with one duct in front and two at the rear in order to minimize the influence of the downwash of the front duct on the rear ducts. The results of the investigation were compared with those of a similar investigation for a tandem two-duct arrangement in which the ducts were fixed (rather than tiltable) relative to the airframe, since the three-duct configuration had been devised in an attempt to avoid some of the deficiencies of the tandem fixed-duct configuration. The results of the investigation indicated that the tilting-duct arrangement had less noseup pitching moment for a given forward speed than the tandem fixed-duct arrangement. The model had less angle-of-attack instability than the tandem fixed-duct arrangement. The model was directionally unstable but had a positive dihedral effect throughout the test speed range.

Smith, Charles C., Jr.↗
NASA NTRS1959

Flight Investigation of the Stability and Control Characteristics of a 1/4-Scale Model of a Tilt-Wing Vertical-Take-Off-and-Landing Aircraft

An experimental investigation has been conducted to determine the dynamic stability and control characteristics of a tilt-wing vertical-take-off-and-landing aircraft with the use of a remotely controlled 1/4-scale free-flight model. The model had two propellers with hinged (flapping) blades mounted on the wing which could be tilted up to an incidence angle of nearly 90 deg for vertical take-off and landing. The investigation consisted of hovering flights in still air, vertical take-offs and landings, and slow constant-altitude transitions from hovering to forward flight. The stability and control characteristics of the model were generally satisfactory except for the following characteristics. In hovering flight, the model had an unstable pitching oscillation of relatively long period which the pilots were able to control without artificial stabilization but which could not be considered entirely satisfactory. At very low speeds and angles of wing incidence on the order of 70 deg, the model experienced large nose-up pitching moments which severely limited the allowable center-of-gravity range.

Tosti, Louis P.↗
NASA NTRS1959

Force-Test Investigation of the Stability and Control Characteristics of a 1/4-Scale Model of a Tilt-Wing Vertical-Take-Off-and-Landing Aircraft

A wind-tunnel investigation has been made to determine the aerodynamic characteristics of a 1/4-scale model of a tilt-wing vertical-take-off-and-landing aircraft. The model had two 3-blade single-rotation propellers with hinged (flapping) blades mounted on the wing, which could be tilted from an incidence of 4 deg for forward flight to 86 deg for hovering flight. The investigation included measurements of both the longitudinal and lateral stability and control characteristics in both the normal forward flight and the transition ranges. Tests in the forward-flight condition were made for several values of thrust coefficient, and tests in the transition condition were made at several values of wing incidence with the power varied to cover a range of flight conditions from forward-acceleration (or climb) conditions to deceleration (or descent) conditions The control effectiveness of the all-movable horizontal tail, the ailerons and the differential propeller pitch control was also determined. The data are presented without analysis.

Newsom, William A., Jr.↗
NASA NTRS1999

Tilt Modulation Distortions in Wave Topography Measured by a Scanning Radar Altimeter

Work continues on estimating tilt modulation distortions in the wave topography measured by a scanning radar altimeter. To quantify this effect, a two-dimensional simulation has been performed in the cross-track plane only which assumed that sinusoidal waves of constant wavelength propagate in the cross-track direction (and are infinitely long-crested in the along-track direction). The initial results reported earlier for a Gaussian surface scattering model indicated that when the highest reasonable value of mss is used in the simulation (the Plant limit of 0.08), the nadir values of the ratio of the apparent to actual wave height are the same as for the omnidirectional scattering case. But as the off-nadir angle increased, the apparent wave height increased and became larger than the actual wave height by about 10 degrees off-nadir. And the shorter the wavelength, the larger the apparent wave height increase. This represented a systematic over-estimate of the wave amplitude for waves propagating in the cross-track direction. For lower values of mss the situation worsened. The simulation has been improved by incorporating actual variations of backscattered power with incidence angle measured by the SRA instead of the Gaussian model. The resulting distortion was about half that originally reported. The 3-dimensional simulation to model waves propagating at various azimuthal angles relative to the cross-track plane is still in progress. The results of this model will be verified by comparing them with Scanning Radar Altimeter (SRA) data and optimum correction procedures will be developed. An assessment of the improved 2-dimensional model indicates that the distortion will generally be small in the data taken during the Southern Ocean Waves Experiment (SOWEX) presently be analyzed. But tilt modulation effects are of great concern for SRA data collected during the 1998 hurricane season since the minimum aircraft altitude was 1.5 km and it frequently flew higher. For a given wave length and steepness, the effect increases with increasing aircraft altitude, and is larger for waves propagating in the cross-track direction, which was generally the situation during the hurricane flights.

Walsh, Edward J.↗
NASA NTRS1994

Peripheral Microvascular Responses to Whole-Body Tilting, G(z) Centrifugation, and Lower Body Negative Pressure Stresses in Humans

The response of the cutaneous microcirculation to orthostatic stress varies along the length of the body due to the interaction of central controls with regional responses to local blood pressure. We hypothesize that artificial orthostatic stresses such as Gz centrifugation and LBNP differ from whole-body tilting in terms of the distribution of microvascular blood flow. Cutaneous microvascular flows were measured by laser Doppler flowmetry at the neck, thigh, and leg of 15 normal subjects. Volunteers underwent stepwise head-up tilt (HUT) and short- and long-arm centrifugation protocols from supine control (0 Gz) to 0.2, 0.4, 0.6, 0.8, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 Gz at the feet, for 30-s periods with 10-s transitions between levels. The same subjects underwent a corresponding supine LBNP protocol, up to 100 mmHg (in 20 mmHg increments) and back to zero pressure, which produced transmural pressure across blood vessels in the foot approximately equal to the HUT protocol. In general, application of all orthostatic stresses produced significant flow reductions in the lower body (p less than 0.05) and inconsistent changes in the neck. At low levels of each stress (0.4 Gz, 40 mmHg), LBNP generated the greatest relative reduction in flow in the lower body (-66.9+/-5.7%, thigh; -60.6 +/-5.7%, leg, mean +/- SE). HUT caused a less severe flow reduction than LBNP at the thigh and leg (-39.9 +/- 8.1% and -55.9+/-4.8%), while the effects induced by both forms of centrifugation were the least profound. Higher levels of each stress generally resulted in similar responses. These responses exhibit a consistent relationship to hypothesized changes in local microvascular transmural pressure, suggesting that myogenic and veno-arteriolar reflexes play a significant role in determining microvascular perfusion during orthostatic stress.

Breit, G. A.↗
NASA NTRS1998

Technology Investigations With the Tilt Rotor Aeroacoustic Model (TRAM)

This paper introduces the Tilt Rotor Aeroacoustic Model (TRAM) project. The TRAM project is a key infrastructure investment for NASA tiltrotor research. The TRAM project consists of the development and testing of two modular, hardware-compatible, test stands: an isolated rotor configuration and a fullspan model (dual rotors with a complete airframe representation). These two test stands are inclusively called the Tilt Rotor Aeroacoustic Model (TRAM). The baseline proprotors and airframe of the TRAM test stands are nominally 1/4-scale representative of the V-22 Osprey aircraft. The research objectives of the project, the TRAM hardware design features and capabilities, illustrative examples of the type and quality of data that can be acquired with the TRAM, and the current status of the overall project will be discussed in this paper.

Young, Larry A.↗