Sikorsky Aircraft Corporation (United States)

Carbon fiber reinforced plastics (CFRPs) are widely used in industry due to their high strength-to-weight ratio, and interest exists in improving their mechanical and multifunctional properties. The aerospace industry, in particular, values prepreg CFRPs for their ease of use and superior performance, and carbon nanotubes (CNTs) have shown promise as a multifunctional reinforcement material for CFRPs due to their exceptional nano-scale properties. However, CNT morphology control is required because CNTs tend to agglomerate and that limits their effectiveness as an additive. In this study, we developed a novel approach that involves using a B-staged epoxy film with magnetically aligned CNTs as a method to introduce CNTs into prepreg CFRPs. A hot press and vacuum bag were used to consolidate and cure the laminates. A magnetic field of 180 G was applied at different stages of the laminate fabrication process to effectively align the CNTs while minimizing agglomeration while the polymer is flowing. Laminate properties were assessed through short beam shear (SBS) testing, and although interlaminar shear stress (ILSS) did not significantly improve or degrade, trends regarding magnetic field application in various parts of the process and the effect on ILSS were observed. This knowledge will be used in the future for deciding processing conditions that can maximize mechanical reinforcement with the final goal of attempting to integrate aligned CNTs to the entire prepreg laminate volume. Future work includes further adjustment of magnetic field application for improved CNT distribution, and multi-functional property characterization of CNT-integrated CFRPs.

View Video Presentation: https://doi.org/10.2514/6.2021-0031.vid Developmental flight testing on the United States Marine Corps (USMC) CH-53K King Stallion heavy lift program identified significant engine integration technical challenges including Exhaust Gas Reingestion (EGR), engine compartment cooling and engine exhaust impingement on the aircraft’s fuselage. These challenges limited the mission envelope and threatened to delay the CH-53K King Stallion heavy lift helicopter program. Immediate resolution of these issues was required for the USMC to proceed with the planned deployment of CH-53K. The CH-53K all digital design, advanced computer modeling techniques, rapid prototyping and flight test data reduction methodologies were brought together by the U. S. Navy and industry team to solve these problems and progress the program. This paper discusses the work conducted in parallel and immediately after the Computational Fluid Dynamics (CFD) modeling validation effort; CFD was deployed in a massive way in order to examine the air vehicle impacts of different EGR solution proposals at both critical EGR flight conditions as well as across the CH-53K flight envelope. CFD data extractions, focused on EGR attributes and engine integration risks, were then used in a multi-disciplinary systems engineering trade study that weighted pertinent air vehicle impacts, including, e. g. , aircraft performance, weight, engine life, cost of implantation and human factors. The system engineering score was used to downselect high confidence aircraft configurations for flight test assessment.

This work documents high-speed wind-tunnel experiments conducted on a pitching airfoil equipped with an array of combustion-powered actuators. The main objective of these experiments was to demonstrate the stall-suppression capability of combustion-powered actuators on a high-lift rotorcraft airfoil (the VR-12) at relevant Mach numbers. Through unsteady pressure measurements at the airfoil surface, it was shown that combustion-powered actuators could positively affect the stall behavior of the VR-12 at Mach numbers up to 0.4. Static airfoil results demonstrated 25 and 50% increases in poststall lift at Mach numbers of 0.4 and 0.3, respectively. Deep dynamic stall results showed cycle-averaged lift coefficient increases up to 11% at Mach 0.4. Furthermore, it was shown that these benefits could be achieved with relatively few pulses during the downstroke and with no need to preanticipate the stall event. The flow mechanisms responsible for stall suppression were investigated using particle image velocimetry. The flow structures found at these Mach numbers appeared to be very similar to the flow structures noted previously at very low Mach numbers.

An evaluation of the computational toolset HPCMP CREATE-AV Helios, a multidisciplinary set of tools developed by the DOD for rotorcraft analysis and design, was performed by application to the coaxial X2 TechnologyDemonstrator aircraft. The principle objective of the study was to perform this demonstration and evaluation by application to a full aircraft simulation that addresses an interesting engineering phenomenon: the effect of rotor wake impingement and propeller induction on horizontal empennage airloads for aircraft stability. Comparisons of unpowered and powered (rotor only and rotor/propeller) solutions in terms of integrated forces as well as flow field visualizations were performed to illustrate the impact of the rotor wake and propeller induction on the horizontal tail surfaces at high angle-of-attack. Unpowered Helios simulations were compared to similar solutions from a commercial solver (StarCCM+) and wind tunnel data to evaluate Helios’s ease of use, speed, and relative accuracy.

A hybrid Navier-Stokes/Free Wake methodology is applied to helicopter rotors in hover. Three tip planforms were analyzed: the S-76 rotor with a swept tip, a rectangular planform, and a swept tip with anhedral. The solidity of the three rotors was matched. A pitch sweep was conducted. Computed thrust, power, and figure of merit values have been compared with test data. Where available, comparisons with other calculations for these quantities and the near wake tip vortex trajectory have been done. The simulations are in reasonable agreement with published data for the thrust, power, and figure of merit. The simulations differ from full Navier-Stokes calculations in the predictions for tip vortex descent rate and contraction rate. The simulations correctly predicted the trends. The swept tapered anhedral tip had the highest figure of merit, followed by the swept tapered tip. The rectangular planform had the lowest figure of merit.

The AIAA Applied Aerodynamics Technical Committee’s Rotorcraft Simulation Working Group put together standardized evaluation of the S-76 planform in hover. The objective of this paper was to construct a hybrid analysis framework for the baseline S-76 planform and compute performance predictions for various collective settings and compare with experiments. The hybrid method consists of a near-body rotor-blade Navier-Stokes solver coupled with a farfield Lagrangian wake evolution model. Apart from thrust, torque coefficients and rotor figure of merit, the computed wake structure and surface pressure distributions are also obtained. The paper concludes with some observations on the suitability of hybrid methods for hover computation. Nomenclature μ advance ratio Cp power coefficient CT rotor thrust coefficient FM figure of merit αs shaft angle of attack σ solidity CnM 2 sectional normal loads CmM 2 sectional pitching moments

Most steel gears are carburized and quenched prior to service to obtain the desired specific strength (σ/ρ) and hardness requirements. Use of carburization and quenching of steel gears creates a compressive residual stress on the carburized surface, which is beneficial for improving both bending and contact fatigue performance. Also, higher carbon content in the carburized surface decreases the starting temperature for formation of the martensitic phase and delaying the martensitic transformation at the part surface during the quenching hardening process. During the martensite phase formation, the material volume expands. The delayed martensitic transformation, coupled with the associated delayed volume expansion, induces residual compressive stress on the surface of the quenched part. The carburized case depth and distribution of carbon affect both the magnitude and the depth of the resulting residual compressive stress. In this article, the effect of carbon distribution on the residual stress in a spur gear is presented and discussed using finite element modeling to understand the intrinsic material mechanics contributing to the presence of internal stress. Influence of the joint on thermal gradient and the influence of phase transformation on the development of internal stresses are discussed using results obtained from modeling. The residual stress arising due to heat treatment is imported into single-tooth bending and dynamic contact stress analysis models to investigate the intrinsic interplay among carbon case depth, residual stress, bending load, and torsional load on potential fatigue life. Three carburization processes, followed by oil quenching, are examined. A method for designing minimum case depth so as to achieve beneficial residual stresses in gears subjected to bending and contact stresses is suggested.

Multi-scale modeling of synthetic jet devices is em ployed to investigate the effect of active flow control (AFC) on fuselage drag reduction. The flow field in the vicinity of the synthetic jet devices was modeled using a Lattice Boltzmann equation (LBE) approach, while the external flow over the fuselage was modeled using a Reynolds-averaged Navier-Stokes (RANS) methodology. Computations with and without flow control also reported for flowfield around the isolated fuselage of ROBIN-mod7 model. The computed results, in the absence of flow control, have been compared with the measured data for ROBIN-mod7 model and show good agreement. Results from the CFD simulation with AFC using LB/NS coupled methodology indicate in an estimated 18% drag reduction.

<div class="section abstract"><div class="htmlview paragraph">Sikorsky Aircraft certificated the Model S-92A™ helicopter for flight in icing conditions in 2005. Since that time, the aircraft has flown in icing conditions throughout the world and the approval to launch a flight when icing conditions are forecast or reported has been valuable to operators. However, when the rotor ice protection system was inoperative due to a system failure, use of the aircraft on days of forecast icing was prohibited. Sikorsky Aircraft, therefore, elected to obtain certification of the S-92A helicopter to an EASA limited icing Special Condition so that UK and Norwegian operators in the North Sea sector could complete a mission when icing conditions were forecast, should the RIPS be inoperative on that day. A review of previously available icing data indicated that the S-92A helicopter could meet the requirements of the EASA Special Condition, but that additional flights were required to demonstrate full compliance. The S-92A demonstrated compliance with the Special Condition for ambient temperatures equal to or greater than -5°C, liquid water content equal to or below 0.5 g/m₃, and pressure altitudes equal to or below 8,000 feet. The S-92A helicopter is now allowed to operate with RIPS inoperative in known or forecast icing in the North Sea sector within these conditions.</div></div>