Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “path”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Spectral characteristics of earth-space paths at 2 and 30 FHz

Spectral characteristics of 2 and 30 GHz signals received from the Applications Technology Satellite-6 (ATS-6) are analyzed in detail at elevation angles ranging from 0 deg to 44 deg. The spectra of the received signals are characterized by slopes and break frequencies. Statistics of these parameters are presented as probability density functions. Dependence of the spectral characteristics on elevation angle is investigated. The 2 and 30 GHz spectral shapes are contrasted through the use of scatter diagrams. The results are compared with those predicted from turbulence theory. The average spectral slopes are in close agreement with theory, although the departure from the average value at any given elevation angle is quite large.

Baxter, R. A.↗
NASA NTRS1979

Thermal stress analysis of ceramic gas-path seal components for aircraft turbines

Stress and temperature distributions were evaluated numerically for a blade-tip seal system proposed for gas turbine applications. The seal consists of an abradable ceramic layer on metallic backing with intermediate layers between the ceramic layer and metal substrate. The most severe stresses in the seal, as far as failure is concerned, are tensile stresses at the top of the ceramic layer and shear and normal stresses at the layer interfaces. All these stresses reach their maximum values during the deceleration phase of a test engine cycle. A parametric study was carried out to evaluate the influence of various design parameters on these critical stress values. The influences of material properties and geometric parameters of the ceramic, intermediate, and backing layers were investigated. After the parametric study was completed, a seal system was designed which incorporated materials with beneficial elastic and thermal properties in each layer of the seal. An analysis of the proposed seal design shows an appreciable decrease in the magnitude of the maximum critical stresses over those obtained with earlier configurations.

Kennedy, F. E.↗
NASA NTRS1979

Development of a plasma sprayed ceramic gas path seal for high pressure turbine applications

Development of the plasma sprayed graded, layered ZrO2/CoCrAlY seal system for gas turbine engine blade tip seal application up to 1589 K (2400 F) surface temperature was continued. Methods of improvement of the cyclic thermal shock resistance of the sprayed zirconia seal system were investigated. The most promising method, reduction of the ceramic thickness and metallic substrate stiffness were selected based upon potential and feasibility. Specimens were fabricated and experimentally evaluated to: (1) substantiate the capacity of the geometry changes to reduce operating stresses in the sprayed structure; and (2) define the abradability, erosion, thermal shock and physical property characteristic for the sprayed ceramic seal system. Thermal stress analysis was performed and correlated with thermal shock test results.

Shiembob, L. T.↗
NASA NTRS1980

Large-volume multiple-path nuclear-pumped laser

Output of nuclear pumped laser is increased using mirrors, so multiple optical reflections enlarge lasing-mode volume. Design requires comparatively low thermal neutron flux, uses flux more efficiently. Flux for lasing approaches that available from steady-state reactor. Outputs over 100 watts have been reached.

Hohl, F.↗
NASA NTRS1979

A study of partial coherence for identifying interior noise sources and paths on general aviation aircraft

The partial coherence analysis method for noise source/path determination is summarized and the application to a two input, single output system with coherence between the inputs is illustrated. The augmentation of the calculations on a digital computer interfaced with a two channel, real time analyzer is also discussed. The results indicate possible sources of error in the computations and suggest procedures for avoiding these errors.

Howlett, J. T.↗
NASA NTRS1980

Some considerations of the performance of two honeycomb gas path seal material systems

A standard Hastelloy-X honeycomb material and a pack aluminide coated honeycomb material were evaluated as to their performance as labyrinth seal materials for aircraft gas turbine engines. Consideration from published literature was given to the fluid sealing characteristics of two honeycomb materials in labyrinth seal applications, and their rub characteristics, erosion resistance, and oxidation resistance were evaluated. The increased temperature potential of the coated honeycomb material compared to the uncoated standard could be achieved without compromising the honeycomb material's rub tolerance, although there was some penalty in terms of reduced erosion resistance.

Bill, R. C.↗
NASA NTRS1980

Development of improved high pressure turbine outer gas path seal components

A plasma sprayed graded layered ceramic/metallic (ZrO2/CoCrAlY) seal was evaluated for JT9D turbine application by rig and engine tests. Four cyclic thermal shock rig tests were conducted during the program. Three completed 1000 simulated engine thermal cycle tests and the fourth completed 500 cycles without severe cracking or spalling. Three ceramic seals were installed in a JT9D experimental engine to evaluate the effect of the engine thermal environment on the seals. All three seals completed the test successfully without severe cracking or spalling. The three seals did have slight laminar cracks at the 85/15-40/60 ZrO2/CoCrAlY interface. The second engine test evaluated the rub capabilities of the seal. Six ceramic seals were installed in the engine with fourteen abrasive tip blades. Three of the six seals rubbed to a depth of 24 mils. Eight of the fourteen abrasive tip blades showed evidence of wear. Three of the eight blades wore a maximum of five mils. Engine rub test results demonstrated the potential of reducing turbine clearances and thereby improving engine performance by use of sprayed ceramic seals.

Shiembob, L. T.↗
NASA NTRS1980

Study of rolling element dynamic interactions with separator and raceway paths. Roller skewing measurements in roller bearings

Measurements of roller skewing in a 118 mm bore roller bearing operating at shaft speeds to 12000 rpm are reported. High speed motion pictures of a modified roller were taken through a derotation prism to record skewing as the roller moved through loaded and unloaded regions of the bearing. Subsequent frame by frame measurement of the photographic film provided information on roller skewing. Radial and tangential skew amplitudes of .4 to .5 degrees were observed with .5 degree misalignment.

Nypan, L. J.↗
NASA NTRS1980

Evaluation of a computer-generated perspective tunnel display for flight path following

The display was evaluated by monitoring pilot performance in a fixed base simulator with the vehicle dynamics of a CH-47 tandem rotor helicopter. Superposition of the predicted future vehicle position on the tunnel image was also investigated to determine whether, and to what extent, it contributes to better system performance (the best predicted future vehicle position was sought). Three types of simulator experiments were conducted: following a desired trajectory in the presence of disturbances; entering the trajectory from a random position, outside the trajectory; detecting and correcting failures in automatic flight. The tunnel display with superimposed predictor/director symbols was shown to be a very successful combination, which outperformed the other two displays in all three experiments. A prediction time of 4 to 7 sec. was found to optimize trajectory tracking for the given vehicle dynamics and flight condition. Pilot acceptance of the tunnel plus predictor/director display was found to be favorable and the time the pilot needed for familiarization with the display was found to be relatively short.

Grunwald, A. J.↗
NASA NTRS1981

Propagation path length variations due to bending of optical fibers

The geometric effect and material stress effects are included. Calculations are shown that put an upper limit on the expected phase shift in single mode fibers. The fractional change in propagation constant is presented. Moding effects in multimode fibers cause extraneous phase shifts of unusually high magnitude. This does not occur in single mode fibers, rendering them very insensitive to bending with a theoretical limit given by the above relation.

Lau, K. Y.↗
NASA NTRS1981

Evaluation of Microwave Landing System (MLS) effect on the delivery performance of a fixed-path metering and spacing system

Metering and spacing (M & S) system's algorithms described assume an aircraft two dimensional are navigation capability. The three navigation systems compared were: very high frequency omnidirectional range/distance measuring equipment (VOR/DME) and ILS, VOR/DME and + or - 40 MLS, and VOR/DME and + or - 60 MLS. Other factors studied were M & S tentative schedule point location, route geometry effects, and approach gate location effects. Summarized results are: the MLS offers some improvement over VOR/DME and ILS if all approach routes contain computer assisted turns; pilot reaction to moving the gate closer to the runway threshold may adversely affect M & S performance; and coupling en route metering to terminal scheduling transfers most of the terminal holding to more full efficient, higher altitude en route delay.

Credeur, L.↗
NASA NTRS1981

A program-management plan with critical-path definition for Combustion Augmentation with Thermionic Energy Conversion (CATEC)

Thermionic energy conversion (TEC) is discussed. In recent TEC-topping analyses, overall plant efficiency (OPE) and cost of electricity (COE) improved slightly with current capabilities and substantially with fully matured technologies. Enhanced credibility derives from proven hot-corrosion protection for TEC by silicon-carbide clads in fossil fuel combustion products. Combustion augmentation with TEC (CATEC) affords minimal cost and plant perturbation, but with smaller OPE and COE improvements than more conventional topping applications. Risk minimization as well as comparative simplicity and convenience, favor CATEC for early market penetration. A program-management plan is proposed. Inputs, characteristics, outputs and capabilities are discussed.

Morris, J. F.↗
NASA NTRS1980

Multiyear slant-path rain fade statistics at 28.56 GHz for Wallops Island, Va.

The multiyear rain fade statistics collected in the Wallops Island, Va., area at 28.56 GHz during 1977 through 1979 showed that the overall fade distributions for the individual years showed small differences. Exceedance time variations were observed in the monthly and time of day fade data from year to year, but the second year fades relative to the first year had less than 20% rms deviation. These results are useful to designers of earth-satellite communications systems which require reliable fade statistics for establishing link-margin requirements. The Wallops Island fade distribution had an rms decibel deviation of less than 14% when compared with the International Radio Consultative Committee prediction model.

Goldhirsh, J.↗
NASA NTRS1981

Technology - The path to the next 50 years

The paper stresses the importance of committing time and resources to space technology based on the premise that an accurate appraisal of the impact of technology and other influences on the present state of aviation will facilitate the planning of space technology. The paper presents the technological advances in aviation since 1903 by dividing the era of aviation into four distinct segments and, by analogy, distinct phases are also seen in the evolution of space flight. One factor seen as limiting advances in space is cost. Processes in space must now be shown to be affordable; a demonstration of technological feasibility is no longer sufficient. For this reason, technology must focus on ensuring the affordability and utility of space processes. A commitment to making space affordable will yield the tools necessary to embark on future space ventures.

Williams, D. P.↗
NASA NTRS1981

Development of low modulus material for use in ceramic gas path seal applications

Three candidate materials were examined: Brunsbond (R) Pad; plasma sprayed porous NiCrAlY; and plasma sprayed low modulus microcracked zirconia. Evaluation consisted of mechanical, thermophysical, and oxidation resistance testing along with optical microscopy and a feasibility demonstration of attaching the material to a suitable substrate. The goals of the program were the following: feasibility of fastening or depositing the low modulus system onto a broad range of substrate alloys; feasibility of depositing or forming the low modulus system to a thickness of 0.19 cm to 0.38 cm; potential to attain a modulus of elasticity in the range of 3.4 to 6.9 GPa (0.5 to 1.0 MSI), and an ultimate strength of 17.2 MPa (2.5 ksi); suitable thermal conductivity; and static oxidation life of at least 1000 hours at 1311 K. The results of the program indicate that all three systems offer attractive properties as a strain isolator material.

Eaton, H. E.↗
NASA NTRS1982

Aerodynamic investigations to determine possible ice flight paths

After flights with the VFW 614 under severe icing conditions, damage to the engine was found. In wind tunnel tests a determination of the origin of this ice was made; it is supposed that the damage was caused by this ice. On the modified flight test model of the VFW 614 on a 1:15 scale, measurements were conducted in the VFW-Fokker wind tunnel with exposed particles which represented the free ice. The results of this testing are presented.

Burgsmueller, W.↗