Browse Topic: Logistics
This specification establishes the requirements for brush plating of cadmium by electrodeposition.
The paper presents a general framework for building an aeromechanic model in FLIGHTLAB, suitable for high fidelity, pilot-in-the-loop simulator. The focus is on aerodynamic modeling of AW609 tiltrotor in Airplane Mode flight regime. The framework can be extended to helicopter and conversion modes with additional considerations for rotors-airframe aerodynamic interference. It can also be adapted to different tiltrotor geometries, with some adjustments depending on their peculiarities. The model uses Blade Element Theory loads evaluation of lifting surfaces, corrected with tabulated distributed loads to tune FLIGHTLAB predictions against high-fidelity aerodynamic references. Bluff bodies are modeled using force and moment tabulated data. Verification was conducted against reference data in wind tunnel mode and against flight data in trim analysis. The proposed method allowed to match lift distribution on slender bodies, as well as lift and drag integral loads, with aerodynamic references
Execution of a Modular Open Systems Approach (MOSA) on government procurement programs is enacted into United States law (Ref. 1-2) and, if implemented properly, can enable more efficient accomplishment of business and technical objectives for an organization (Ref. 3-8). Open Systems are well defined (Ref. 9) and mature. Successful implementations of open standards have governance and conformance processes associated with them (Ref. 10-12). By using open system standards for integration of complex cyber-physical systems, like Future Airborne Capability Environment (FACETM) (Ref. 13) and Open Mission System (OMS) (Ref. 14), it is a straightforward exercise to determine if open system requirements of a MOSA are adequately addressed. However, adherence to these standards alone is insufficient to fully realize MOSA’s benefits (Ref. 10). This paper focuses solely on how to develop enterprise modularity as one part contributing to a comprehensive enterprise MOSA strategy.
Traditional safe-life methodologies for rotorcraft structural components often result in overly conservative life estimates, increasing maintenance costs and reducing aircraft availability. This study explores the integration of digital twin concepts with probabilistic modeling and machine learning to enhance structural life assessment, demonstrated through a practical case involving the Royal Canadian Air Force CH-146 Griffon helicopter. A probabilistic fatigue model determines a fatigue life distribution by incorporating material variability and uncertain operational loads inferred directly from flight data. Unlike conventional approaches, this method dynamically estimates load spectra, including uncertainty instead of relying on conservative assumptions. Monte Carlo simulations are used to quantify structural risk and assess the impact of load and material uncertainties. Sensitivity analyses highlight these uncertainties’ contributions to failure probability. The proposed approach
A velocity potential-based finite state model (VPBFSM) has been developed to analyze an isolated rotor in ground effect. The model uses mass source distributions to represent the ground and enforces the non-penetration of flow boundary condition. In previous VPBFSM approaches to impose this boundary condition, the r = j terms were excluded to avoid singularities. This exclusion required adjustments to the source strengths and ground rotor size in order to impose the boundary condition properly, which reduced the model’s robustness. In the present study, the r = j terms are incorporated using a solution for the gradient of the velocity potential from the literature, which avoids singularities. This inclusion allows for effectively enforcing the boundary condition without requiring adjustments. The model is applied to an isolated rotor in full, inclined, and partial ground effect cases, including analysis of the R−50 rotor using geometric and aerodynamic data from the literature. Results
Whirl testing of a full-scale rotor with positive flap-bending/twist composite coupled blades was performed to evaluate the dynamic and performance effects of the coupling. A positive flap-bending/twist coupling, in which a flap up deformation induces a nose down elastic twist, was introduced in the blades through tailoring of the laminate layups; the magnitude of the coupling was maximized through an optimization of the layup, with the intent of maximizing the potential impact of the coupling for correlation purposes. An uncoupled version of the blade using the same geometry and materials was also fabricated to provide a baseline set of measurements for comparison, with the coupled blade optimized to also minimize changes in bending and axial stiffness properties in an effort to isolate the effect of coupling by itself. Rap testing was conducted to measure blade modal frequencies and shapes in a free-free environment. Whirl testing was performed for both the coupled and baseline
Acoustic flight testing of rotorcraft often involves generating noise source hemispheres to gain an understanding about the aircraft's acoustic emissions. However, aerodynamically complex Urban Air Mobility and Future Vertical Lift vehicles may not maintain a steady aerodynamic state during flight, making source hemispheres measured using traditional linear arrays unreliable or difficult to interpret. To address this challenge, all emission angles need to be measured simultaneously. This has lead to the concept of the two dimensional 'snapshot' array layout. A mathematically defined microphone distribution was utilized to achieve uniform coverage on the source hemisphere. Within the chosen distribution, two lower microphone count distributions are embedded, allowing for a comparison of the effects of number of microphones. The array was deployed as part of a joint Army/NASA acoustic research flight test in July of 2024. Data were collected using an MD530F helicopter as the test vehicle
This study investigates Reynolds number effects on rotor wake vortex development using a hyperbaric rotor facility capable of pressurizing air up to 100 bar. Background-oriented schlieren (BOS) and hot-wire anemometry (HWA) were applied to characterize vortex trajectories, core growth, and circumferential velocity distribution. BOS measurements revealed consistent blade-to-blade trajectory deviations and vortex pairing across all operating conditions, despite that the investigated three-bladed rotor was milled from a single piece of aluminum, ensuring precise manufacturing and a highly symmetric geometry. A statistical scheme was developed to analyze the radial structure of fluctuating tip vortices, which traverse the pointwise fiber-film sensor in a fixed position. With increasing vortex Reynolds number, the tip vortices are more compact with a reduction in core growth. The circulation in the vortices grows with the vortex radial coordinate, and converges at a radial position
Rotor performance in a Martian environment was analyzed with an objective of increasing thrust with minimal impact on efficiency. The Sample Recovery Helicopter (SRH) and Rotorcraft Optimization for the Advancement of Mars Exploration (ROAMX) rotors were studied by varying solidity, blade count, and chord distribution to determine which configuration delivered the most desirable performance. For all configurations, the ROAMX rotor displayed better performance than the SRH rotor. It was observed that increasing solidity reduced the blade loading required to achieve the peak figure of merit, and beyond a solidity ratio of 0.3 the figure of merit was negatively impacted. For both rotors a 6-bladed configuration with a solidity ratio of 0.3 delivered the optimal figure of merit.
Dynamic rollovers represent a major hazard for helicopters during near-ground operations, often resulting in significant aircraft damage and passenger injuries. To improve safety in operations, recent studies have focused on developing a Helicopter Flight Data Monitoring framework to provide data-driven insights on operational safety. This work contributes to that effort by proposing an approach to identify precursors to dynamic rollovers. According to NTSB reports, approximately 60% of such incidents occur during in-flight phases like hover, hover-taxi, or landing. To capture the complex non-linear dynamics of helicopters, physics-based simulations were conducted to estimate a first hitting time metric, defined as the time until blade-ground contact, across a wide range of initial conditions for an inflight initial state of the helicopter. Eight parameters were identified as driving the first hitting time, and a probabilistic model was created to predict the distribution of that
Structural testing of full-scale blade geometries with flap-bending/twist composite coupling was performed to evaluate the impact of coupling. Full-scale spar geometries were first fabricated with three different coupling distributions, including two with a uniform positive flap-bending/twist coupling, in which a flap up deformation induces a nose down elastic twist. The third spar geometry incorporated a mixed coupling, with a uniform positive coupling at the inboard end and a uniform negative coupling at the outboard end, where the negative flap-bending twist coupling produces a nose up elastic twist when experiencing flap up deformation. A full-scale blade was then fabricated with a positive flap-bending/twist coupling. Measurements of the structural twist distribution of the cured spars were taken to ensure the coupling did not result in any hygrothermal instabilities. Tip twist and strains were then measured under various combinations of flatwise bending and torsional bending
This paper demonstrates extraction of linear models from a state-space free wake model by applying analytical linearization, extending the research presented in (Ref. 1). Two distinct Linear Time Invariant (LTI) models are developed: the first is a high-order LTI model derived from the direct conversion of the analytical Linear Time Periodic (LTP) model, and the second is a reduced-order LTI model generated by first applying the Proper Orthogonal Decomposition (POD) model order reduction technique to the LTP model, followed by conversion. In both cases, the LTP-to-LTI conversion is achieved using harmonic decomposition. A substantial reduction in the number of wake states, from 15552 to 4050, is accomplished while maintaining a similar degree of accuracy. The time domain responses of step and doublet inputs for rotor collective and cyclic pitch are analyzed by comparing the GENHEL rotor model coupled with the LTI wake against the non-linear free wake model. Good agreement is observed
Stretch broken carbon fiber (SBCF) offers enhanced formability as compared to continuous carbon fiber (CCF). However, robust, quantitative evaluation of forming defects remains a challenge. This study introduces a unified formability index (UFI) that integrates multiple defect types, including texture anomalies, bridging, wrinkling, thickness variation, spring-back, and resin distribution variation (RDV), into a single weighted score. Each defect is ranked on a scale of 0-5 using normalized metrics with a tunable parameter, α, allowing users to balance defect magnitude and frequency as desired. The full scoring pipeline is demonstrated for texture defects using measured data, while normalized legacy scores from previous work are used for non-texture defects to enable complete formability index computation. Case studies on three laminates illustrate how variations in α affect both texture scoring and the overall formability index and demonstrate the geometry-agnostic nature of the
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