Browse Topic: Springs
This work focuses on steps towards the ability to use tight coupling between computation fluid dynamics (CFD) and rotorcraft comprehensive analysis (CSD) to predict aeroelastic stability of a rotor. First, the Rotorcraft Comprehensive Analysis System (RCAS) analysis is used to carry out traditional linear stability analysis. Next, a method of using trim springs to artificially increase the stability of the wing so that a periodic solution during the RCAS trim procedure is presented. RCAS is then used to complete time-integrated transient analysis using a lifting-line aerodynamic model following a system perturbation through a vertical force located at the wing tip. CFD/CSD coupling is used for the first time to simulate a fully-elastic semi-span tiltrotor model. Loose coupling is used to achieve a trimmed solution for a sweep of airspeeds. Tight coupling is used to observe the transient behavior of the system following a perturbation. Low-speed results are promising and clearly demonstrate differences between the higher-fidelity method and comprehensive analysis indicating Helios is capturing previously missed aerodynamic effects. At higher speeds, the perturbation used here is found to be inadequate for activating the wing beam bending mode. Finally, the tight coupling procedure predicts an unstable rotor mode that is not predicted by comprehensive analysis. The primary objective of this work is to demonstrate new capabilities introduced to the CREATE-AV software Helios and RCAS which allow for a first fully-elastic semi-span simulation of a tiltrotor using high-fidelity analysis through both loose and tight coupling methodologies.
ABSTRACT Helicopter Sling Load (HSL) missions pose significant safety risks to the ground personnel involved with hooking up payloads to the helicopter. The goal of this project is to develop a materiel solution to increase the safety of an HSL hookup team by eliminating the personnel subjected to the hazards of the HSL mission. The research reviewed in this paper discusses two concepts that were evaluated for HSL auto hookup capabilities: a grapple hook design with three spring articulating arms and a system that used a cone on cone design. For this project, flight evaluations were conducted on prototypes of the two concepts with the following Army helicopters: LUH-72 Lakota, UH-60 Blackhawk, and CH-47 Chinook. There are two modes of HSL that were looked at for this project: single point sling load and dual point sling loads.
ABSTRACT It is a great challenge to perform an accurate and efficient fatigue life prediction of a bonded composite structure with the presence of geometry and material heterogeneity induced stress concentration. The present fatigue damage characterization of composite structures is still dominated by the use of a phenomenological stress-life (S-N) approach due to the availability of extensive S-N data and lower cost in generation of S-N data from fatigue tests at different applied stress ratios. Because of the inaccurate life prediction using the S-N approach for the structure with stress concentrators, a more rational fracture mechanics approach based on a Paris type crack growth law can be applied to compute the crack growth driving force provided that an initial flaw has to be introduced. In order to simulate both the crack initiation and propagation, a dual spring model is implemented at each nodal point where the static failure is simulated using springs of a cohesive type material model while fatigue crack propagation is calculated using springs of an elastic penalty stiffness coupled with a virtual crack closure technique (VCCT). In order to validate the dual spring model for the fatigue damage prediction, two types of Tee-joints are fabricated and tested by the National Institute for Aviation Research (NIAR) with and without a Teflon insertion. A calibration analysis is performed to determine the fatigue crack growth parameters using Tee-joints with a Teflon insert followed by the blind fatigue prediction of the specimens without a Teflon insert.
ABSTRACT The current method used for bonding liners onto dynamic components requires the use of spring-loaded clamps, vacuum bags, and ovens. This process works well for our smaller articles although has posed problems for our larger bonding requirements. The primary problem for our large bonded components is our ovens would take up to 3.5 hrs. to heat the thickest areas up to bonding temperature. For the adhesives that we use the recommended temperature ramp-up time is 20-60 minutes. In addition, the thinner areas reach temperature sooner and would exceed the recommended maximum curing time of 60 min. A minimum of 25 pounds per square inch (PSI) is required to achieve a sound bondline. The clamps used during cure cycles rely on springs to apply pressure to the liner being bonded. The pressure they exert is not exact, and tends to vary. A vacuum bag can only apply the pressure that is supplied by shop air, 14.7 psi. The solution to achieving uniform and accurate pressure during bonding operations is to have a flexible zoned system that can bring all the areas, thick and thin, to temperature simultaneously, apply even amounts of pressure to the liners, and record all zones of temperature and pressure during the bonding process. Through the entire process, the zones are monitored, recorded, and graphed. This system can be moved anywhere within the factory because the heating elements and the air bladders are incorporated into the fixture.
The following SAE Recommended Practice furnishes sample forms for helical compression, extension and torsion springs to provide a uniform method for specifying design information. It is not necessary to fill in all the data, but sufficient information must be supplied to fully describe the part and to satisfy the requirements of its application. For detailed information, see “Design and Application of Helical and Spiral Springs - SAE HS 795”, also “Helical Compression and Extension Spring Terminology - SAE J1121”. Both of these documents use SI (metric) Units in accordance with the provisions of SAE TSB 003, as does SAE J1122. Here, however, the U.S. Customary Units (in, lb, psi) have been added in parentheses after each SI Unit for the convenience of the user who must furnish specifications on a project where all requirements are listed in non-metric terms.
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