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Human occupant modeling and injury risk assessment have been identified as areas of research for improved prediction of rotorcraft crashworthiness within the NASA Aeronautics Subsonic Rotary Wing Program. As part of this effort, an experimental program was conducted to assess the impact performance of a skid gear for use on the WASP kit-built helic...
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... test article and two 95 percentile Aerospace ATDs were instrumented with a total of 26 accelerometers and 2 lumbar load cells. Test data were collected at 50,000 samples per second using a digital data acquisition system. The vertical drop test was performed by attaching lifting cables to the test article, raising the test article through its CG, and then releasing the test article to impact a smooth concrete surface. The test article was lifted to a height of 13 inches and released to impact a smooth concrete surface at 8.4-fps. Post-test measurements of permanent deformation show that the measured spread of the skid gear was 4.4 inches. No permanent deformation of either the Styrofoam stack or the polyisocyanurate foam blocks was visible post-test. Comparisons of the two Aerospace ATD occupants’ filtered vertical acceleration responses of the head, chest, and pelvis are shown in Figure 5. Data were post-processed using an SAEJ211 equivalent low-pass filter with a cut-off frequency of 33.5 Hz [9]. The peak magnitudes of the acceleration responses range from 6 to 9g. The acceleration responses of the head have the lowest magnitude (6g) and the pelvic acceleration responses have the highest magnitude (9g). Some minor differences are seen between the ATD-1 and ATD-2 acceleration responses for the head and chest; however, both curves have similar magnitudes. ATD-2 exhibits a higher peak acceleration of 9-g in the pelvis, than seen for ATD-1 ...
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Citations
... More focused activities have investigated the crashworthiness of single helicopter components or sections, such as in [17,[20][21][22]. Landing gears-mainly skid landing gears-also have been included in the crashworthiness research programs, aiming at providing and optimizing effective structures for safe landings [23][24][25][26][27]. ...
... The investigation is performed in various attitudes and soil conditions, and the sensitivity to soil friction factor is investigated. Another work concerning a skid landing gear was published in 2007 by the NASA, describing an experimental program to assess the impact performance of a skid gear for the use on the Wasp kit-built helicopter [23]. In recent years the application of automated robotic landing gears has seen the light. ...
Maximum loads acting on aircraft structures generally arise when the aircraft is undergoing some form of acceleration, such as during landing. Landing, especially when considering rotorcrafts, is thus crucial in determining the operational load spectrum, and accurate predictions on the actual health/load level of the rotorcraft structure cannot be achieved unless a database comprising the structural response in various landing conditions is available. An effective means to create a structural response database relies on the modeling and simulation of the items and phenomena of concern. The structural response to rotorcraft landing is an underrated topic in the open scientific literature, and tools for the landing event simulation are lacking. In the present work, a coupled sequential simulation strategy is proposed and experimentally verified. This approach divides the complex landing problem into two separate domains, namely a dynamic domain, which is ruled by a multibody model, and a structural domain, which relies on a finite element model (FEM). The dynamic analysis is performed first, calculating a set of intermediate parameters that are provided as input to the subsequent structural analysis. Two approaches are compared, using displacements and forces at specific airframe locations, respectively, as the link between the dynamic and structural domains.
... where g is the acceleration of gravity. The DRI is used to evaluate the potential for spinal injury during aircraft crashes [10] [11] [12] [13] and also in the operation of high speed marine craft [14]. In this model, the natural frequency ω = ck m ⁄ and the damping ratio ζ = c K2√kmO ⁄ are taken to be 52.9 rad/s and 0.224 respectively. ...
This paper studies the ability of the fuselage’s lower lobe to absorb the energy during a crash landing, where the introduction of the composite materials can improve the crash survivability thanks to the crushing capability of structural parts to limit the effects of deceleration on the occupants. Providing a protective shell around the occupants and minimizing the risks of injuries during and immediately after the crash in the post-crash regime is a safety requirement.
This study consists of: (1) numerical and experimental investigations on small components to verify design concepts using high performance composite materials; (2) analyses of full scale crashes of fuselage lower lobes.
This paper outlines an approach for demonstrating the crashworthiness characteristics of the airframe performing a drop test at low velocity impact to validate a numerical model obtained by assembling structural components and materials’ properties previously obtained by testing coupons and sub-elements.
... Better protection against injuries in the case of potentially survivable accidents has attracted increasing attention. Consequently, based on the crashworthy design principles [20,34], in order to improve occupant safety for the car and aircraft mishaps, special consideration is taken into account in the design of some critical structural components with lightweight energy absorber (EA), such as bumpers [22], aircraft frame [7], landing gear [3,10], energy absorbing seat [15,19] or subfloor [30], and so on. ...
With the limitation of available space inside the aircraft and automotive structure, it is difficult to effectively improve the performance of energy absorber. To overcome this drawback, a fan-shaped deployable energy absorber (FDEA) is developed in this paper and numerical simulation is carried out to study the crushing characteristics of FDEA under quasi-static loading condition. The calculated results show that the crush pattern of FDEA can be divided into three categories: progressive symmetrical collapse, global bending collapse and mixed modes, which have different contribution to the energy absorption. Systematic parametric studies are also implemented with consideration of deployment angle, hinge radius and wall thickness of middle cells. Results indicate that the energy absorption decreases as the deployment angle increases, but increases with hinge radius and wall thickness. In addition, in consideration of practical application, a finite element model of multi-block is built and compared with single-block model. The specific energy absorption of multi-block is calculated to be higher than that of single-block, though the energy absorption is slightly lower. The outcome of this study can provide a design reference for the use of FDEA as energy absorbers in applications.
... Given the high number of necessary simulations, the numerical model is analyzed by using an implicit integration scheme. Although this is not the confirmed methodology used by other authors ( [10,[26][27][28]36]), the results achieved are reasonably similar as is found comparing the current solution with the one reported in [37]. The spatial distribution of the elastic problem solution is not affected by this choice. ...
A landing that exceeds design conditions is usually referred to as a hard or harsh landing. This condition is delimited between the usual operational conditions and the crash event. Helicopter structural damage due to harsh landings is generally not as severe as during a crash, but it may lead to unscheduled maintenance events, involving costs and idle time. The aim of the current paper is to define a methodology, which estimates (by means of hybrid, multi-environment analyses) the damage state of a part of a helicopter fuselage after a harsh landing event. In particular, a mixed multibody finite element modeling strategy is used to achieve computationally efficient results, which are obtained for various landing conditions, in terms of drop heights and the helicopter attitude at landing. The obtained model may be useful both in a design scenario and in exploring structural health monitoring applications. With the latter in mind, output data were deeply investigated with a dedicated focus on the correlation between the damage position and landing conditions. Stringers in a particular zone of the fuselage were identified as the most affected zone (by localized plasticization) during harsh landings. This result provides a possible basis for using focused structural health monitoring strategies. With this in mind, a zone selection criterion, as a tradeoff between sensorization extension and performance, was proposed.
... However, as discussed further in this paper, care must be exercised in interpreting the force measurements vis-a-vis the placement of the force sensor relative to the body being impacted. In some applications, accelerometers have become a popular choice for instrumenting either the impactor, as is done in Pal and Ghosh (1993) and Lifshitz et al. (1995), or multiple locations on the impacting body as, for example, when experiments are conducted with large structures (Jackson and Fuchs, 2007). In the present investigation, the accelerometer is placed on the body to be impacted, which in our setup is free to move during the impact. ...
Contact and impact dynamics modeling of rigid bodies continues to be an intensive research area, as new applications of contact dynamics simulation develop in engineering practice. Yet, relatively few studies are dedicated to the experimental investigation of rigid-body impacts and associated issues. In this manuscript we report our findings for a sphere to flat impact experiments conducted for a range of low impact velocities, such as those that may be encountered in multibody systems. A unique feature of our investigation is that the impact forces between the impacting objects are reconstructed from force and acceleration measurements, the latter obtained from an accelerometer mounted on the impacted surface body. It is noted that when the impacted body is free to move during impact, it may experience high accelerations which must be taken into account. The reconstructed impact force responses are compared to those predicted with the dynamics model of the experimental scenario, which in turn is based on a nonlinear compliant model of the impact force. The experiments, in addition to generating novel impact measurements, provide a number of insights into both the study of impacts and the impact response.
... The three curves are nearly identical, each exhibiting three peaks ranging in magnitude from 4.7 to 7.7 g. The LS-DYNA finite element model of the skid gear test article is shown in Figure 5. Details of the model are described in the paper by Fuchs et al., (2008). A linear elasticplastic material model was defined for the aluminum representing the skid gear saddles and an elastic model was defined for the remainder of the skid gear and steel plate. ...
... The analytical results accurately predict the peak acceleration values, as well as the general acceleration trends. The findings from this research task provide confidence in the use of LS-DYNA occupant models (Fuchs et al., 2008). In the future, these models will be used in the development of a system-integrated simulation of a full-scale helicopter crash. ...
This paper provides an overview of rotorcraft crashworthiness research being conducted at NASA Langley Research Center under sponsorship of the Subsonic Rotary Wing (SRW) Aeronautics Program. The research is focused in two areas: development of an externally deployable energy attenuating concept and improved prediction of rotorcraft crashworthiness. The deployable energy absorber (DEA) is a composite honeycomb structure, with a unique flexible hinge design that allows the honeycomb to be packaged and remain flat until needed for deployment. The capabilities of the DEA have been demonstrated through component crush tests and vertical drop tests of a retrofitted fuselage section onto different surfaces or terrain. The research on improved prediction of rotorcraft crashworthiness is focused in several areas including simulating occupant responses and injury risk assessment, predicting multi-terrain impact, and utilizing probabilistic analysis methods. A final task is to perform a system-integrated simulation of a full-scale helicopter crash test onto a rigid surface. A brief description of each research task is provided along with a summary of recent accomplishments.
Nowadays the assessment of a harsh landing condition for helicopters is based on the pilot's judgment. This can lead to a misclassification of the landing condition, thus affecting the system safety or requiring unnecessary maintenance. The availability of a tool for the automatic assessment of the harshness of the landing condition will improve the efficiency of the current helicopter operations. This paper describes a preliminary step for the validation of a coupled multibody - finite element modelling environment, useful to estimate the most critical zones within the fuselage as well as the occurrence of plastic damage. Experimental harsh landing tests have been carried out on a retired Mil Mi-8 helicopter and 3D-scan measures of the helicopter geometry have been taken during helicopter tests. Repeated drops from increasing altitude have been performed, each time recording the 3D surface geometry at some critical locations, thus allowing the validation of the numerical model.
The crashworthiness of aviation is a significant aspect of airworthiness, because it helps a lot in keeping crew safety and reducing economic losses. For the purpose of improving the crashworthiness performance of a kind of general aviation-type helicopter, an innovative light-weight composite energy-absorbing component has been developed in this paper. This component consists of carbon fiber woven cylindrical thin-walled tube and external triggers. The triggers let the cylindrical thin-walled tube split and break along its longitudinal axis and the energy is absorbed at the same time. In order to verify the results, a serial of test components were made and several tests were carried on. Finally, a digital simulation was carried on, whose results correspond with those of the tests.
The objective of this work is to identify design parameters for a capacitive sensor designed to recognize and record helicopter harsh landing events. Harsh landing events are typically associated with landing speeds exceeding 2.5 m/s (1) and require mandatory structural inspection resulting in down-times that could last a week or longer. In cases where no visible damage occurs, harsh- landing events might be difficult to identify and record. This paper presents a finite element analysis of the acceleration profile at different locations of the skid of a Bell 206 L4 helicopter which is then used to design and test a low-cost capacitive sensor for monitoring harsh landing events. Time history and histograms of the acceleration signal during normal and harsh landings are presented. The capacitive accelerometer is designed to operate in the 10g to 360g range. The sensor is integrated directly on a wiring board and is readout by a micro-controller with a capacitive ASIC. Details of the sensor design, fabrication, and testing are presented. The presented material also provides hard-to-find design data on the structural accelerations which can occur during harsh landing. Keywords- drop test, harsh landing, hard landing, accelerometer, condition based maintenance
