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  • 1
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    The Integrated Technology and Flight Research Rotor Technology demonstrators for the 1985-1995 timeframe (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The purposes and progress in the Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) Project, a joint effort by the U.S. Army and NASA, are outlined. The project goal is to integrate the disciplines of rotor design, aerodynamics, structures, materials, dynamics, and acoustics, to remove the risks in applying the technology, and to develop an advanced flight research rotor which permits significant variation in the rotor properties. Composite rotors are believed to be capable of displaying infinite fatigue lifetimes with fail-safe characteristics, and bearingless hubs simplify hub designs. The programs will also consider the flight control, propulsion, and structures. Concept definition contracts are presently distributed among five companies, and preliminary designs will lead to model tests in 1984.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Vertiflite (ISSN 0042-4455); 29; Sept
    Format: text
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  • 2
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    Experimentally determined flutter from two- and three-bladed model bearingless rotors in hover (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A series of experiments was performed on a 1.8-m-diam model rotor in hover for the principal purpose of investigating the lead-lag stability of isolated bearingless rotors. Incidental to those tests, at least three types of pitch-flap flutter were encountered. Type 1 flutter occurred approximately at the second flap-mode frequency on both two-and three-bladed rotors for both small and large pitch angles and appeared to be a classic pitch-flap flutter. Type 2 flutter showed mostly torsional motion and was seen on both two- and three-bladed rotors. Type 3 flutter was a regressing flap flutter that occurred for only the three-bladed rotor configurations and appears to be a wake excited flutter. Although flutter occurred on a number of different configurations, no rotor parameters were identified that were clearly stabilizing or destabilizing.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 69-88
    Format: application/pdf
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  • 3
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    Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same flow conditions. Nusselt numbers can be correlated in a fashion similar to Chu and Jones.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA-CR-198459 , E-10136 , NAS 1.26:198459
    Format: application/pdf
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  • 4
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    Characterization of annular two-phase gas-liquid flows in microgravity (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Second Microgravity Fluid Physics Conference; p 227-232
    Format: application/pdf
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  • 5
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    A Theoretical and Experimental Investigation of Flap-Lag Stability of Hingeless Helicopter Rotor Blades (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability of hingeless rotor blade oscillations in hover is examined theoretically using a simplified centrally-hinged, spring-restrained, rigid blade to approximate the deflections of actual elastic blades. The aerodynamic and inertial coupling between the flap and lead-lag degrees of freedom is primarily responsible for instability, however elastic coupling and kinematic pitch-lag coupling both exert a powerful influence on hingeless rotor blade stability. Experimental results obtained from a two-bladed 1.81m diameter model rotor designed for minimum elastic coupling have confirmed the results of linear theory. For this model configuration rotor blade stall at high pitch angles was found to counteract the destabilizing flap-lag coupling and increase the damping of lead-lag oscillations. It was possible to account for this effect with the theory by using drag data for stalled airfoils.
    Keywords: AIRCRAFT
    Type: NASA-TM-X-62179
    Format: application/pdf
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  • 6
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    An analog technique for the measurement of damping from transient decay signals (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A tracking filter that includes an output that is logarithmically proportional to the amplitude of the filtered signal is used to measure the damping exponent of a transient decay. This method is analogous to the digital technique referred to as the moving-block or peak-plot method. The method is simple to use and quite accurate, avoids the numerical computations associated with similar digital techniques, but is constrained by the poor time-domain response characteristics of commercial tracking filters presently available.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-X-73121 , A-6535
    Format: application/pdf
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  • 7
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    Hingeless helicopter rotor with improved stability (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Improved stability was provided in a hingeless helicopter rotor by inclining the principal elastic flexural axes and coupling pitching of the rotor blade with the lead-lag bending of the blade. The primary elastic flex axes were inclined by constructing the blade of materials that display non-uniform stiffness, and the specification described various cross section distributions and the resulting inclined flex axes. Arrangements for varying the pitch of the rotor blade in a predetermined relationship with lead-lag bending of the blade, i.e., bending of the blade in a plane parallel to its plane of rotation were constructed.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
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  • 8
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    An experimental investigation of hingeless helicopter rotor-body stability in hover (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Model tests of a 1.62 m diameter rotor were performed to investigate the aeromechanical stability of coupled rotor-body systems in hover. Experimental measurements were made of modal frequencies and damping over a wide range of rotor speeds. Good data were obtained for the frequencies of the rotor lead-lag regressing mode. The quality of the damping measurements of the body modes was poor due to nonlinear damping in the gimbal ball bearings. Simulated vacuum testing was performed using substitute blades of tantalum that reduced the effective lock number to 0.2% of the model scale value while keeping the blade inertia constant. The experimental data were compared with theoretical predictions, and the correlation was in general very good.
    Keywords: AERONAUTICS (GENERAL)
    Type: NASA-TM-78489 , AVRADCOM-TR-78-17(AM) , A-7430
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  • 9
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    New design of hingeless helicopter rotor improves stability (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Cantilever blades are attached directly to rotor hub, thereby substantially reducing cost and complexity and increasing reliability of helicopter rotor. Combination of structural flap-lag coupling and pitch-lag coupling provides damping of 6 to 10%, depending on magnitude of coupling parameters.
    Keywords: MECHANICS
    Type: ARC-10807
    Format: application/pdf
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  • 10
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    Ground Based Studies of Gas-Liquid Flows in Microgravity Using Learjet Trajectories (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A 1.27 cm diameter two phase gas-liquid flow experiment has been developed with the NASA Lewis Research Center to study two-phase flows in microgravity. The experiment allows for the measurement of void fraction, pressure drop, film thickness and bubble and wave velocities as well as for high speed photography. Three liquids were used to study the effects of liquid viscosity and surface tension, and flow pattern maps are presented for each. The experimental results are used to develop mechanistically based models to predict void fraction, bubble velocity, pressure drop and flow pattern transitions in microgravity.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA-CR-202554 , E-9563 , NAS 1.26:202554 , AIAA Paper 94-0829 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
    Format: text
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