Study to investigate design, fabrication and test of low cost concepts for large hybrid composite helicopter fuselage, phase 1

The development of a frame/stringer/skin fabrication technique for composite airframe construction was studied as a low cost approach to the manufacture of large helicopter airframe components. A center cabin aluminum airframe section of the Sikorsky CH-53D helicopter was selected for evaluation as a composite structure. The design, as developed, is composed of a woven KEVLAR-49/epoxy skin and graphite/epoxy frames and stringers. To support the selection of this specific design concept a materials study was conducted to develop and select a cure compatible graphite and KEVLAR-49/epoxy resin system, and a foam system capable of maintaining shape and integrity under the processing conditions established. The materials selected were, Narmco 5209/Thornel T-300 graphite, Narmco 5209/KEVLAR-49 woven fabric, and Stathane 8747 polyurethane foam. Eight specimens were fabricated, representative of the frame, stringer, and splice joint attachments. Evaluation of the results of analysis and test indicate that design predictions are good to excellent except for some conservatism of the complex frame splice

Study to investigate design, fabrication and test of low cost concepts for large hybrid composite helicopter fuselage, phase 2

The development of a frame/stringer/skin fabrication technique for composite airframe construction was studied as a low cost approach to the manufacturer of larger helicopter airframe components. A center cabin aluminum airframe section of the Sikorsky CH-53D, was selected for evaluation as a composite structure. The design, as developed, is composed of a woven KEVLAR R-49/epoxy skin and graphite/epoxy frames and stringers. The single cure concept is made possible by the utilization of pre-molded foam cores, over which the graphite/epoxy pre-impregnated frame and stringer reinforcements are positioned. Bolted composite channel sections were selected as the optimum joint construction. The applicability of the single cure concept to larger realistic curved airframe sections, and the durability of the composite structure in a realistic spectrum fatigue environment, was described

Evaluation of graphite composite materials for bearingless helicopter rotor application

Small scale combined load fatigue tests were conducted on twelve unidirectional graphite-glass scrim-epoxy composite specimens. The specimens were 1 in. (2.54 cm) wide by 0.1 in. (.25 cm) thick by 5 in. (12.70 cm) long. The fatigue data was developed for the preliminary design of the spar for a bearingless helicopter main rotor. Three loading conditions were tested. Combinations of steady axial, vibratory torsion, and vibratory bending stresses were chosen to simulate the calculated stresses which exist at the root and at the outboard end of the pitch change section of the spar. Calculated loads for 150 knots (77.1 m/sec) level flight were chosen as the baseline condition. Test stresses were varied up to 4.4 times the baseline stress levels. Damage resulted in reduced stiffness; however, in no case was complete fracture of the specimen experienced

Decoherent time-dependent transport beyond the Landauer-B\"uttiker formulation: a quantum-drift alternative to quantum jumps

We present a model for decoherence in time-dependent transport. It boils down into a form of wave function that undergoes a smooth stochastic drift of the phase in a local basis, the Quantum Drift (QD) model. This drift is nothing else but a local energy fluctuation. Unlike Quantum Jumps (QJ) models, no jumps are present in the density as the evolution is unitary. As a first application, we address the transport through a resonant state $\left\vert 0\right\rangle$ that undergoes decoherence. We show the equivalence with the decoherent steady state transport in presence of a B\"{u}ttiker's voltage probe. In order to test the dynamics, we consider two many-spin systems whith a local energy fluctuation. A two-spin system is reduced to a two level system (TLS) that oscillates among $\left\vert 0\right\rangle$ $\equiv$ $\left\vert \uparrow \downarrow \right\rangle$ and $\left\vert 1\right\rangle \equiv$ $\left\vert \downarrow \uparrow \right\rangle$. We show that QD model recovers not only the exponential damping of the oscillations in the low perturbation regime, but also the non-trivial bifurcation of the damping rates at a critical point, i.e. the quantum dynamical phase transition. We also address the spin-wave like dynamics of local polarization in a spin chain. The QD average solution has about half the dispersion respect to the mean dynamics than QJ. By evaluating the Loschmidt Echo (LE), we find that the pure states $\left\vert 0\right\rangle$ and $\left\vert 1\right \rangle$ are quite robust against the local decoherence. In contrast, the LE, and hence coherence, decays faster when the system is in a superposition state. Because its simple implementation, the method is well suited to assess decoherent transport problems as well as to include decoherence in both one-body and many-body dynamics.Comment: 10 pages, 5 figure

Injection locking of two frequency-doubled lasers with 3.2 GHz offset for driving Raman transitions with low photon scattering in 43^{43}Ca+^+

We describe the injection locking of two infrared (794 nm) laser diodes which are each part of a frequency-doubled laser system. An acousto-optic modulator (AOM) in the injection path gives an offset of 1.6 GHz between the lasers for driving Raman transitions between states in the hyperfine split (by 3.2 GHz) ground level of $^{43}$Ca$^+$. The offset can be disabled for use in $^{40}$Ca$^+$. We measure the relative linewidth of the frequency-doubled beams to be 42 mHz in an optical heterodyne measurement. The use of both injection locking and frequency doubling combines spectral purity with high optical power. Our scheme is applicable for providing Raman beams across other ion species and neutral atoms where coherent optical manipulation is required.Comment: 3 pages, 3 figure

HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and "spiral-arm'' clouds

%methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to construct absorption spectra toward bright extra-galactic background sources at 195 kHz spectral resolution ($\approx$ 0.6 \kms). We used the IRAM Plateau de Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was observed in absorption from ``spiral-arm'' clouds in the galactic plane occulting W49. The complement of detectable molecular species in the 85 - 110 GHz absorption spectrum of diffuse/translucent gas is now fully determined at rms noise level $\delta_\tau \approx 0.002$ at \EBV\ = 0.32 mag (\AV\ = 1 mag) and $\delta_\tau$/\EBV\ $\approx\ 0.003$ mag$^{-1}$ overall.} %conclusions {As with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2) $\approx$ 0.1. We find N(CF\p)/N(H$^{13}$CO\p) $\approx 5$, N(CF\p)/N(\cch) $\approx$ 0.005-0.01 and because N(CF\p) increases with \EBV\ and with the column densities of other molecules we infer that fluorine remains in the gas phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(H$^{13}$CO\p) = 16 toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO) $\approx 10^{-9}$, about 10 times higher than in dark clouds. The behaviour of HCO is consistent with previous suggestions that it forms from C\p\ and \HH, even when \AV\ is well above 1 mag. The survey can be used to place useful upper limits on some species, for instance N(\hhco)/N(\HH CS) $>$ 32 toward 3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase formation route to \hhco.}Comment: A\%A in pres