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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

On the question of adequate hingeless rotor modeling in flight dynamics.

The somewhat controversial question of which elastic blade modes are essential in the flight mechanics of hingeless rotorcraft is studied on the basis of quasi-steady linear aerodynamics including reversed flow effects and uniform inflow. The modes are for the rotating blade, and intermode aerodynamic coupling terms are retained. The criteria for judging elastic mode effects include 19 hub moment and force derivatives, rotor trim data, rotor stability charts for lagged hub moment feedback, step gust and random gust responses. Fixed hub and constant chord blades with widely differing elasticity and inertia and with moderate twist are assumed.

Hohenemser, K. H.↗
NASA NTRS1974

Design and testing of a tandem row pump inducer

The design and testing of a tandem row pump inducer having a supercavitating first stage with a 0.60 hub ratio is presented. The second stage tested was a helical impeller with a 0.70 hub ratio. A cubic arc transition was utilized to accomplish the hub change. The first stage had two blades and the free-vortex design approach was empirically modified based on previous experience. The recommended second stage design having four blades and using cambered blade section is presented but the model was not built or tested. The more simple helix was built instead to reduce cost. Data taken included head generation, cavitation observations and unsteady head fluctuations over the 0-100Hz range.

Etter, R. J.↗
NASA NTRS1973

Temperature compensated sleeve type mirror mount

The primary mirror of a large (26-inch diameter aperture) solar telescope was made of glass ceramic and designed with an integral hub on the back of the center of the mirror. This permits heat from the mirror to radiate off its back to a nearby cold plate. To permit mounting without high stresses, the hub was ground down to a smooth cylindrical surface 3.5 inch in diameter. The ground surface was then acid-etched to remove 0.007 inch (on the diameter) by immersion for five minutes in a mixture of four parts 92% sulfuric acid and three parts 50% hydrofluoric acid. The acid etching removes microcracks from the ground Cer-Vit surface. An Invar sleeve was fabricated to fit over the hub with about 0.010 inch radial (0.020 inch diametral) clearance.

Source record↗
NASA NTRS1974

An application of Floquet theory to prediction of mechanical instability

The problem of helicopter mechanical instability is considered for the case where one blade damper is inoperative. It is shown that, if the hub is considered to be nonisotropic, the equations of motion have periodic coefficients which cannot be eliminated. However, if the hub is isotropic, the equations can be transformed to a rotating frame of reference and the periodic coefficients eliminated. The Floquet transition matrix method is shown to be an effective way of dealing with the nonisotropic hub and nonisotropic rotor situation. Time history calculations are examined and shown to be inferior to the Floquet technique for determining system stability.

Hammond, C. E.↗
NASA NTRS1975

Time-dependent transonic flow solutions for axial turbomachinery

Three-dimensional unsteady transonic flow through an axial turbomachine stage is described in terms of a pair of two-dimensional formulations pertaining to orthogonal surfaces, namely, a blade-to-blade surface and a hub-to-casing surface. The resulting systems of nonlinear, inviscid, compressible equations of motion are solved by an explicit finite-difference technique. The blade-to-blade program includes the periodic interaction between rotor and stator blade rows. Treatment of the boundary conditions and of the blade slipstream motion by a characteristic type procedure is discussed in detail. Harmonic analysis of the acoustic far field produced by the blade row interaction, including an arbitrary initial transient, is outlined. Results from the blade-to-blade program are compared with experimental measurements of the rotating pressure field at the tip of a high-speed fan. The hub-to-casing program determines circumferentially averaged flow properties on a meridional plane. Blade row interactions are neglected in this formulation, but the force distributions over the entire blade surface for both the rotor and stator are obtained. Results from the hub-to-casing program are compared with a relaxation method solution for a subsonic rotor. Results are also presented for a quiet fan stage which includes transonic flow in both the rotor and stator and a normal shock in the stator.

Erdos, J.↗
NASA NTRS1978

Composite hub/metal blade compressor rotor

A low cost compressor rotor was designed and fabricated for a small jet engine. The rotor hub and blade keepers were compression molded with graphite epoxy. Each pair of metallic blades was held in the hub by a keeper. All keepers were locked in the hub with circumferential windings. Feasibility of fabrication was demonstrated in this program.

Yao, S.↗
NASA NTRS1981

Free-flying solar reflector spacecraft

Results of investigations of requirements and design concepts for large solar-reflecting spacecraft are given. The emphasis is on the one kilometer diameter self contained spacecraft that can be packaged and launched in the space shuttle. The configuration consists of a compression rim stabilized by stays coming from each end of the central compression hub. The stays are stowed on reels on the ends of the hub. The hub consists of two Astromasts which are deployed after launch. The reflector membrane is a two micron thick Kapton film with a vapor deposited aluminum coating.

Hedgepeth, J. M.↗
NASA NTRS1982

Analytical performance prediction for large antennas

The coupled free-free modes of the 55M LMSS antenna configuration are shown. They were determined using modal synthesis. Reflector modes clamped at the hub were calculated adopting the efficient cyclic symmetry technique. Similarly, clamped hub modes of the offset boom structure were calculated. The modes of the two substructures were then combined through the process of modal synthesis on the assumption that the interface at the hub structure is rigid thus satisfying statically determinate matching conditions. For attitude control purposes, only modes associated with symmetric components zero and one involve net motions of the center of gravity of the reflector. This condition restricts the set of admissible eigenfunctions for modal synthesis. Modes with symmetric components higher than one are excited only by forces acting on the ribs. These modes are totally uncoupled from the boom dynamics.

El-Raheb, M.↗
NASA NTRS1982

LV measurements with an advanced turboprop

Nonintrusive measurements of velocity about a spinner-propeller-nacelle configuration were made at a Mach number of 0.8. A laser velocimeter (LV) specifically developed for these measurements was used to determine the flow field of the advanced swept SR-3 propeller. The data will be used to study the flow and to verify computer prediction codes. The usefulness of the LV data in detecting flow anomalies and to substantiate the data quality was demonstrated. Some typical results are given. Mach number profiles at the entrance of the propeller are compared with theoretical predictions. The LV data is in excellent agreement with the axisymmetric, compressible, inviscid theory (without blades) ahead of the propeller except near the hub. The data indicate blade blockage near the spinner. Blade to blade variations in axial velocity for four radial positions at the propeller exist are also given. The large apparent wake near the hub is associated with the hub choking. The blade to blade variation of axial velocity ahead of a shock within the blade passage is given.

Neumann, H. E.↗
NASA NTRS1983

Axial compressor middle stage secondary flow study

This report describes an experimental investigation of the secondary flow within and aft of an axial compressor model with thick endwall boundary layers. The objective of the study was to obtain detailed aerodynamic and trace gas concentration traverse data aft of a well documented isolated rotor for the ultimate purpose of improving the design phases of compressor development based on an improved physical understanding of secondary flow. It was determined from the flow visualization, aerodynamic, and trace gas concentration results that the relative unloading of the midspan region of the airfoil inhibitied a fullspan separation at high loading preventing the massive radial displacement of the hub corner stall to the tip. Radial distribution of high and low total pressure fluid influenced the magnitude of the spanwise distribution of loss, such that, there was a general decreases in loss near the hub to the extent that for the least loaded case a negative loss (increase in total pressure) was observed. The ability to determine the spanwise distribution of blockage was demonstrated. Large blockage was present in the endwall regions due to the corner stall and tip leakage with little blockage in the core flow region. Hub blockage was found to increase rapidly with loading.

Wagner, J. H.↗
NASA NTRS1983

Clamp-mount device

A clamp-mount device is disclosed for mounting equipment to an associated I-beam and the like structural member of the type having oppositely extending flanges wherein the device comprises a base and a pair of oppositely facing clamping members carried diagonally on the base clamping flanges therebetween and having flange receiving openings facing one another. Lock means are carried diagonally by the base opposite the clamping members locking the flanges in the clamping members. A resilient hub is carried centrally of the base engaging and biasing a back side of the flanges maintaining tightly clamped and facilitating use on vertical as well as horizontal members. The base turns about the hub to receive the flanges within the clamping members. Equipment may be secured to the base by any suitable means such as bolts in openings. Slidable gate latches secure the hinged locks in an upright locking position. The resilient hub includes a recess opening formed in the base and a rubber-like pad carried in this opening being depressably and rotatably carried therein.

Clark, K. H.↗
NASA NTRS1983

Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) concept definition

A program was performed to identify and evaluate a variety of candidate rotor hub configurations for the ITR/FRR. Design criteria were established for the development of the hub concepts. Eight initial hub configurations were examined and two were selected for further refinement and evaluation. The selected concepts were bearingless designs with and without lead-lag dampers. The selected concepts were refined to the point that their physical properties relative to the Government's technical goals and manufacturing aspects could be assessed. In addition, variations that could be incorporated for the FRR were identified and compatibility for installation on the RSRA was addressed.

Harse, J. H.↗
NASA NTRS1983

Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) concept definition

A program was performed to identify and evaluate a variety of candidate rotor hub configurations for the ITR/FRR. Design criteria were established for the development of the hub concepts. Five initial hub configurations were examined and two were selected for further refinement and evaluation. The selected configurations were bearingless designs. The Classic Elastic Pitch Beam (CEPB) and the Plain Elastic Pitch Beam (PEPB), both exhibit superior qualities for the criteria in the final evalution. The CEPB is favored over the PEPB primarily because it offers better capability for built in damping for stability and is judged to have a lower risk in development.

Howes, H. E.↗
NASA NTRS1983

Integrated technology rotor/flight research rotor concept definition study

As part of the Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) Program a number of advanced rotor system designs were conceived and investigated. From these, several were chosen that best meet the started ITR goals with emphasis on stability, reduced weight and hub drag, simplicity, low head moment stiffness, and adequate strength and fatigue life. It was concluded that obtaining low hub moment stiffness was difficult when only the blade flexibility of bearingless rotor blades is considered, unacceptably low fatigue life being the primary problem. Achieving a moderate hub moment stiffness somewhat higher than state of the art articulated rotors in production today is possible within the fatigue life constraint. Alternatively, low stiffness is possible when additional rotor elements, besides the blades themselves, provide part of the rotor flexibility. Two primary designs evolved as best meeting the general ITR requirements that presently exist. An I shaped flexbeam with an external torque tube can satisfy the general goals but would have either higher stiffness or reduced fatigue life. The elastic gimbal rotor can achieve a better combination of low stiffness and high fatigue life but would be a somewhat heavier design and possibly exhibit a higher risk of aeromechanical instability.

Carlson, R. G.↗
NASA NTRS1985

A comparative study of tail rotor noise mechanisms

A study was made of helicopter tail rotor noise, particularly that due to interactions with the wakes of the main rotor, hub, and fuselage, and with the engine exhaust. Both harmonic and broadband noise were analyzed. The disturbed flow into the tail rotor was modeled using combinations of aerodynamic and acoustic flow codes along with some necessary estimates of turbulence properties. Representative calculations show that the main rotor wake is the strongest contributor to both harmonic and broadband tail rotor noise. The fuselage separation wake and the engine exhaust flow are also very important to both harmonic and broadband noise. The hub and hub-shaft wakes are important contributors to the broadband noise only. The tip vortices do not seem to be important to broadband noise, but their effects on harmonic noise were not modeled accurately enough to draw any conclusions from this study.

George, A. R.↗
NASA NTRS1988

A comparison of theory and experiment for coupled rotor body stability of a bearingless rotor model in hover and forward flight

Seven cases were selected for correlation from a 1/5.86 Froude-scale experiment that examined several rotor designs which were being considered for full-scale flight testing as part of the Bearingless Main Rotor (BMR) program. The model rotor hub used in these tests consisted of back-to-back C-beams as flexbeam elements with a torque tube for pitch control. The first four cases selected from the experiment were hover tests which examined the effects on rotor stability of variations in hub-to-flexbeam coning, hub-to-flexbeam pitch, flexbeam-to-blade coning, and flexbeam-to-blade pitch. The final three cases were selected from the forward flight tests of optimum rotor configuration as defined during the hover test. The selected cases examined the effects of variations in forward speed, rotor speed, and shaft angle. Analytical results from Bell Helicopter Textron, Boeing Vertol, Sikorsky Aircraft, and the U.S. Army Aeromechanics Laboratory were compared with the data and the correlations ranged from poor-to-fair to fair-to-good.

Mirick, Paul H.↗
NASA NTRS1988

A comparison of theory and flight test of the BO 105/BMR in hover and forward flight

Four cases were selected for comparison with theoretical predictions using stability data obtained during the flight test of the Bearingless Main Rotor (BMR) on a Messerschmidt-Boelkow-Blohm BO 105 helicopter. The four cases selected form the flight test included two ground resonance cases and two air resonance cases. The BMR used four modified BO 105 blades attached to a bearingless hub. The hub consisted of dual fiberglass C-channel beams attached to the hub center at 0.0238R and attached to the blade root at 0.25R with blade pitch control provided by a torque tube. Analyses from Bell Helicopter Textron, Boeing Vertol, and Sikorsky Aircraft were compared with the data and the correlation ranged from very poor-to-poor to poor-to-fair.

Mirick, Paul H.↗
NASA NTRS1988

Euler analysis of a swirl recovery vane design for use with an advanced single-rotation propfan

Recent work has demonstrated the propulsive efficiency improvement available from single- and counter-rotation propfans as compared with current technology high bypass ratio turbofans. The concept known as swirl recovery vanes (SRV) is examined through the use of a 3-D Euler code. At high speed cruise conditions, the SRV can improve the efficiency level of a single-rotation propfan, but a concern is to have adequate hub choke margin. The SRV was designed with 2-D methods and was predicted to have hub choking at Mach 0.8 cruise. The 3-D Euler analysis properly accounts for sweep effects and 3-D relief, and predicts that at cruise the SRV will recover roughly 5 percent of the 10 percent efficiency loss due to swirl and have a good hub choke margin.

Miller, Christopher J.↗