Advanced Rotorcraft Technology (United States)

An aeromechanical analysis of a scaled rotor with lift compounding is conducted to understand the impact of various wing configurations on performance and loads. An assessment of the half-retreating side wing and full-wing configurations is conducted for advance ratios up to 0.7, for two wing incidence angles (4° and 8°), and three rotor shaft angles (−4°, 0°, and 4°). Aircraft performance, blade pitch control angles, blade structural loads, hub vibratory loads, and aerodynamic interactions between the rotor and wing are evaluated using the University of Maryland Advanced Rotorcraft Code (UMARC). Additionally, UMARC coupled rotor-wing analysis is validated with the wind tunnel data of lift and thrust-compounded rotor configurations. The study shows that the half, asymmetric, wing configuration is beneficial for peak vehicle performance (lift-to-drag ratio) due to rotor lift offset, though the full-wing configuration minimizes blade structural loads. Maximizing wing lift sharing minimizes hub vibratory loads.

Inicialmente, demarca-se o processo vivenciado coletivamente pelos técnicos da diretoria para construção de um desenho institucional que contemplasse os objetivos da Diretoria de Estudos e Políticas Regionais, Urbanas e Ambientais (Dirur) e os seus próprios interesses de atuação profissional. O lançamento do Boletim Regional, Urbano e Ambiental, em 2008, representou o compromisso com uma produção continuada e relevante, o que este número especial comemorativo retrata por meio dos artigos ora publicados. Em seguida, discute-se a permanência das desigualdades regionais e a demora em cumprir, efetivamente, o art. 3. da Constituição Federal de 1988. O artigo reconhece que, nos últimos anos, o país instalou uma dinâmica econômica puxada pelo agronegócio, com implicações no padrão de divisão inter-regional do trabalho, alterando também sua posição na Divisão Internacional do Trabalho (DIT), ao retomar sua condição de produtor e exportador de produtos primários. Ademais, o país enfrenta a intensificação do processo de desindustrialização, na ausência de políticas industriais consistentes. Este contexto coloca dificuldades, restrições e desafios para a concepção e implementação de um programa de desenvolvimento de longo prazo para o país que priorize a redução das desigualdades regionais e atenda às exigências inadiáveis de preservação do meio ambiente e de enfrentamento ao aquecimento global já em curso.

Multirotor analytical dynamic inflow models in the literature, such as pressure potential superposition inflow model or velocity potential superposition inflow model (VPSIM), have been shown to capture the fundamental inflow interference effects between the rotors. Some of the differences in inflow predictions seen between these analytic models and high-fidelity wake models are attributed to missing real flow effects such as wake distortion, contraction, decay, swirl, etc. As such, correction terms are needed in the analytically derived multirotor finite-state inflow models, because of the potential flow and rigid wake assumptions they are based on, in order to capture some of the missing real flow effects in them. This paper develops a systematic methodology for arriving at the needed correction terms in the VPSIM through comparisons of its inflow predictions with those of a viscous vortex particle model (VVPM). Also, a procedure is developed to assess the relative importance of individual real flow effects and the associated corrections needed for improving the overall fidelity of the VPSIM. The developed methodology is applied to the Harrington coaxial rotor using its geometric and aerodynamic data from the literature. It is shown that the addition of swirl coupling correction terms to the VPSIM significantly improves its correlations with the VVPM. Further, it is shown that the required corrections are reasonably insensitive to thrust sharing ratio conditions between the rotors.

The air disturbance (or airwake) resulting from the interaction of ship motion and air flow, has a significant effect on shipboard rotorcraft operations. It is essential to develop capabilities to accurately model the rotor/ship aerodynamic interactions which can subsequently be used to implement an efficient and accurate virtual dynamic interface (VDI) simulation. The aerodynamic interaction of the rotorcraft and ship involves the mutual interference between the rotors, fuselage and ship structure. The ship airwake produces unsteady loads on the helicopter as a result of shear layers and turbulence. Therefore modeling rotor/ship aerodynamic interaction requires a high fidelity approach due to complex physical mechanisms that drive the flow phenomena. The interactions between rotor and ship have known to be highly non-linear, therefore the airwake due to an isolated ship has different flow characteristics compared to the ship airwake in presence of a rotorcraft. Moreover the coupled airwake has a feedback effect on the rotor wake geometry and vorticity strength which creates a two-way coupling scenario. In this study, a methodology was developed to couple a CFD ship airwake solver with a viscous Vortex Particle Method (VPM) for rotor wake solution to study rotor/ship aerodynamic interaction. The CFD and VPM solvers were used to compute the time accurate ship airwake and rotor wake, respectively, from first principles. This coupling methodology is demonstrated for a helicopter ground effect study. The coupling simulations were subsequently run for helicopter performing shipboard operations. The simulations showed the complex interactions of ship airwake with rotor wake including the ground effect that rotor experiences in the vicinity of the deck.

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

High-altitude, long-endurance (HALE) aircraft are highly flexible, requiring nonlinear aeroelastic analysis. NATASHA (Nonlinear Aeroelastic Trim and Stability of HALE Aircraft) is a computer program developed to analyze the aeroelastic behavior of HALE aircraft. The underlying formulation is based on the published geometrically exact, fully intrinsic beam equations. This paper presents a wide range of results from NATASHA, comparing them with well-known solutions of beam stability and vibration problems, experimental data, or results from well-established computer codes. Despite the simplicity of the underlying formulation, results obtained confirm the accuracy of the analysis and its suitability for conceptual and preliminary design of HALE aircraft.

This article describes the architecture, components, capabilities, and validation of the rst version of the Helios platform, targeted towards rotorcraft aerodynamics. Capabilities delivered in the rst version include fuselage aerodynamics with and without momentumdisk rotor models, and isolated rotor dynamics for ideal hover and forward ight coupled with aeroelasticity and trim. Helios is based on an overset framework that employs unstructured mixed-element meshes in the near-body domain combined with high-order Cartesian meshes in the o-body domain. In addition, the aerodynamics solution is coupled with structural dynamics and trim using a delta-coupling algorithm. The near-body CFD, obody CFD, CSD and trim modules are coupled using a Python infrastructure that controls the execution sequence of the solution procedure. Specic validation studies presented include the Slowed Rotor Compound fuselage, Georgia Tech rotor body, TRAM rotor in hover and UH-60A rotor in forward ight. In all cases, Helios predictions are compared with experimental data and other state-of-the-art codes to demonstrate the accuracy, eciency and scalability of the code.

The passive control of compressible dynamic stall has been experimentally demonstrated in a dynamically oscillating airfoil test at Reynolds numbers near two million and Mach numbers ranging from M = 0.3 to 0.4. A rotorcraft-type airfoil was retrofitted with a leading edge glove, and tested with and without integral molded vortex generators. Even at relatively low free-stream Mach numbers (M = 0.3 to 0.4), the dynamic stall process on the basic airfoil was initiated by a strong shock boundary layer interaction near the airfoil leading edge. When installed on the original airfoil, the vortex generators failed to control leading edge stall as the free-stream Mach number increased from M = 0.3 to 0.4 due to this locally supersonic leading edge flow at high lift. Although not successful in eliminating dynamic stall, the aerodynamic shape of the glove reduced the extent of a supersonic pocket near the leading edge and the subsequent shock strength; as a result, the airfoil retained trailing edge stall behavior during the dynamic stall event. Without the vortex generators, the glove switched the stall from leading edge to trailing edge, but did not alleviate the stall. The combined use of a transonic leading edge glove and vortex generators lead to the alleviation of dynamic stall pitching moments; the two concepts worked together to alleviate the severe pitching moments during stall, even though neither one was successful when used independently. In some light stall cases the adverse pitching moment associated with dynamic stall was completely eliminated up to M = 0.40. For deep stall cases, the adverse pitching moments were alleviated up to a Mach number of M = 0.375, however the method failed for deep stall at M = 0.40 for this configuration.