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At least 145 records · Page 8

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NASA NTRS2019

Orion Capsule Parachute Assembly System (CPAS) Overload Testing Approach and Results

The qualification of the Orion Capsule Parachute Assembly System (CPAS) system includes exposure to loads and dynamic pressures above the required values as validation of the parachutes' structural integrity. As outlined in the certification plan, each of the four parachutes of the system are to be subjected to 110% of their respective maximum dynamic pressure requirements. The Main and Drogue parachutes have satisfied this overload condition in drop testing and due to cost and schedule constraints, the Forward Bay Cover Parachute (FBCP) and Pilot parachute were subjected to the overload condition in the ground testing described in this document. The test objectives and pass/fail criteria were established and require the parachutes to achieve and maintain a target riser load (associated with a minimum of 110% dynamic pressure overload) for a minimum of three seconds while sustaining no failures of any structural members (vent hoop, radials, suspension line) or any damage which propagates into catastrophic failure of the canopy. Considering the assumptions and limitations associated with the ground testing (primarily non-uniform flow field of the ground test system and variations in parachute manufacturing), a method of establishing the desired overload condition was determined by the technical community and covers the 2-sigma bounds of the drag area distribution derived from drop testing. On June 27, 2017 the testing was executed at the High Velocity Airflow System (HiVAS) facility located at the Weapon Survivability Laboratory (WSL) at the Naval Air Warfare Center, Weapons Division (NAWCWD) China Lake. Engineering Development Unit (EDU) parachutes were used as pathfinders to gain experience with achieving the test conditions. Additional runs were executed to measure the airflow at the same location as the canopy skirt, although this data is not required to satisfy the test objectives and parachute pass/fail criteria. The qualification parachutes were successfully exposed to the target conditions and sustained only minor damage.

Daum, Jared S.↗

NASA NTRS2001

The Analysis and Modeling of the Deployment of NASA's X-38 Parafoil

NASA is currently working on developing the X-38 Crew Return Vehicle for the Internati6nal Space Station (ISS). The aerodynamics of the X-38 and its enormous 7500 square ft parafoil are extremeJy complicated and must be understood and modeled accurately before the vehicle is actually used for human space flight. A large amount of analysis has been performed on the steady state regions of the flight profile when the parafoil is already open. However, the deployment region of the flight profile has not been analyzed in much depth and is a particularly complicated dynamic flight period. During deployment, the X-38 system has its parafoil open up to its full area in five stages over a period of 20-30 seconds. The vehicle transitions from angles of attack around 90 deg to 0 deg in about two seconds and is extremely dynamic. This paper will detail the analysis work done to generate accurate flight profile characteristics of the deployment from flight data from vehicle test drops. Additionally, a computer simulation tool for steady state flight was modified to analyze and model the parafoil deployment. Eventually, a computer model was produced that generated accurate representations of the parafoil deployment dynamics for the vehicle test drops to date.

Ranier, Chris↗

NASA NTRS1972

Wind-tunnel simulation of store jettison with the aid of magnetic artificial gravity

A method employed in the simulation of jettison of stores from aircraft involving small scale wind-tunnel drop tests from a model of the parent aircraft is described. Proper scaling of such experiments generally dictates that the gravitational acceleration should ideally be a test variable. A method of introducing a controllable artificial component of gravity by magnetic means has been proposed. The use of a magnetic artificial gravity facility based upon this idea, in conjunction with small scale wind-tunnel drop tests, would improve the accuracy of simulation. A review of the scaling laws as they apply to the design of such a facility is presented. The design constraints involved in the integration of such a facility with a wind tunnel are defined. A detailed performance analysis procedure applicable to such a facility is developed. A practical magnet configuration is defined which is capable of controlling the strength and orientation of the magnetic artificial gravity field in the vertical plane, thereby allowing simulation of store jettison from a diving or climbing aircraft. The factors involved in the choice between continuous or intermittent operation of the facility, and the use of normal or superconducting magnets, are defined.

Stephens, T.↗

NASA NTRS2010

Parachute Drag Model

DTV-SIM is a computer program that implements a mathematical model of the flight dynamics of a missile-shaped drop test vehicle (DTV) equipped with a multistage parachute system that includes two simultaneously deployed drogue parachutes and three main parachutes deployed subsequently and simultaneously by use of pilot parachutes. DTV-SIM was written to support air-drop tests of the DTV/parachute system, which serves a simplified prototype of a proposed crew capsule/parachute landing system.

Cuthbert, Peter↗

NASA NTRS2003

Comparisons of the Impact Responses of a 1/5-Scale Model and a Full-Scale Crashworthy Composite Fuselage Section

A 25-fps vertical drop test of a 1/5-scale model composite fuselage section was conducted to replicate a previous test of a full-scale fuselage section. The purpose of the test was to obtain experimental data characterizing the impact response of the 1/5-scale model fuselage section for comparison with the corresponding full-scale data. This comparison is performed to assess the scaling procedures and to determine if scaling effects are present. For the drop test, the 1/5-scale model fuselage section was configured in a similar manner as the full-scale section, with lead masses attached to the floor through simulated seat rails. Scaled acceleration and velocity responses are compared and a general assessment of structural damage is made. To further quantify the data correlation, comparisons of the average acceleration data are made as a function of floor location and longitudinal position. Also, the percentage differences in the velocity change (area under the acceleration curve) and the velocity change squared (proportional to kinetic energy) are compared as a function of floor location. Finally, correlation coefficients are calculated for corresponding 1/5- and full-scale data channels and these values are plotted versus floor location. From a scaling perspective, the differences between the 1/5- and full-scale tests are relatively small, indicating that appropriate scaling procedures were used in fabricating the test specimens and in conducting the experiments. The small differences in the scaled test data are attributed to minor scaling anomalies in mass, potential energy, and impact attitude.

Jackson, Karen E.↗

NASA NTRS1984

Transonic wind-tunnel investigation of the Galileo Probe parachute configuration

Wind-tunnel tests have been made of 1/4-scale and 1/2-scale models of the Galileo Probe conical ribbon-parachute at flight conditions. For the Galileo mission, the parachute is deployed behind a blunt shape at transonic speed. The investigation was initiated to verify the solutions to the delayed main-parachute opening with squidding that was observed in the 1982 Galileo Probe system balloon drop test. In addition to varying model scale, the forebody shape, angle of attack, dynamic pressure, Mach number, and canopy trailing distance behind the forebody were varied to determine their effect on parachute performance. Both steady-state and deployment tests were conducted. Parachute drag was measured and was seen to degrade severely at canopy trailing distances of 5.5 and 7 forebody diameters. Performance was shown to be good at the trailing distances of 9 and 11 diameters. A second balloon drop test demonstrated the desired parachute performance at the system level.

Corridan, R. E.↗

NASA NTRS1991

Development of graphite/copper composites utilizing engineered interfaces

In situ measurements of graphite/copper alloy contact angles were made using the sessile drop method. The interfacial energy values obtained from these measurements were then applied to a model for the fiber matrix interfacial debonding phenomenon found in graphite/copper composites. The formation obtained from the sessile drop tests led to the development of a copper alloy that suitably wets graphite. Characterization of graphite/copper alloy interfaces subjected to elevated temperatures was conducted using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Auger Electron Spectroscopy, and X Ray Diffraction analyses. These analyses indicated that during sessile drop tests conducted at 1130 C for 1 hour, copper alloys containing greater than 0.98 at pct chromium form continuous reaction layers of approx. 10 microns in thickness. The reaction layers are adherent to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 deg or less. X ray diffraction results indicate that the reaction layer is Cr3C2.

Devincent, Sandra M.↗

NASA NTRS1992

Reaction layer formation at the graphite/copper-chromium alloy interface

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, auger electron spectroscopy, and x ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Devincent, Sandra M.↗

NASA NTRS2011

Feasibility Study of an Airbag-Based Crew Impact Attenuation System for the Orion MPCV

Airbag-based methods for crew impact attenuation have been highlighted as a potential lightweight means of enabling safe land-landings for the Orion Multi-Purpose Crew Vehicle, and the next generation of ballistic shaped spacecraft. To investigate the performance feasibility of this concept during a nominal 7.62m/s Orion landing, a full-scale personal airbag system 24% lighter than the Orion baseline has been developed, and subjected to 38 drop tests on land. Through this effort, the system has demonstrated the ability to maintain the risk of injury to an occupant during a 7.85m/s, 0 deg. impact angle land-landing to within the NASA specified limit of 0.5%. In accomplishing this, the airbag-based crew impact attenuation concept has been proven to be feasible. Moreover, the obtained test results suggest that by implementing anti-bottoming airbags to prevent direct contact between the system and the landing surface, the system performance during landings with 0 deg impact angles can be further improved, by at least a factor of two. Additionally, a series of drop tests from the nominal Orion impact angle of 30 deg indicated that severe injury risk levels would be sustained beyond impact velocities of 5m/s. This is a result of the differential stroking of the airbags within the system causing a shearing effect between the occupant seat structure and the spacecraft floor, removing significant stroke from the airbags.

Do, Sydney↗

NASA NTRS1993

Reaction layer formation at the graphite/copper-chromium alloy interface

Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.

Devincent, Sandra M.↗

NASA NTRS1974

Investigation of new radar-data-reduction techniques used to determine drag characteristics of a free-flight vehicle

An investigation was conducted of new techniques used to determine the complete transonic drag characteristics of a series of free-flight drop-test models using principally radar tracking data. The full capabilities of the radar tracking and meteorological measurement systems were utilized. In addition, preflight trajectory design, exact kinematic equations, and visual-analytical filtering procedures were employed. The results of this study were compared with the results obtained from analysis of the onboard, accelerometer and pressure sensor data of the only drop-test model that was instrumented. The accelerometer-pressure drag curve was approximated by the radar-data drag curve. However, a small amplitude oscillation on the latter curve precluded a precise definition of its drag rise.

Woodbury, G. E.↗

NASA NTRS1996

Internally damped, self-arresting vertical drop-weight impact test apparatus

A vertical dropped-weight impact test machine has a dropped-weight barrel vertically supported on upper and lower support brackets. The dropped-weight barrel is chambered to receive a dropped-weight assembly having a latch pin at its upper end, a damping unit in the middle, and a tup at its lower end. The tup is adapted for gathering data during impact testing. The latch pin releasably engages a latch pin coupling assembly. The latch pin coupling assembly is attached to a winch via a halyard for raising and lowering the dropped-weight assembly. The lower end of the dropped-weight barrel is provided with a bounce-back arresting mechanism which is activated by the descending passage of the dropped-weight assembly. After striking the specimen, the dropped-weight assembly rebounds vertically and is caught by the bounce-back arresting mechanism. The damping unit of the dropped-weight assembly serves to dissipate energy from the rebounding dropped-weight assembly and prevents the dropped-weight assembly from rebounding from the self-arresting mechanism.

Ambur, Damodar R.↗

NASA NTRS1995

Internally damped, self-arresting vertical drop-weight impact test apparatus

Ambur, Damodar R.↗

NASA NTRS1996

Internally damped, self-arresting vertical drop-weight impact test apparatus

Ambur, Damodar R.↗

NASA NTRS1982

Unsteady aerodynamics and motions of the Pioneer Venus probes

Helicopter drop tests were made of models of the Pioneer Venus probe descent configurations to characterize their unsteady forces and angular dynamics in equilibrium descent. The axial and normal forces were found to be unsteady in magnitude by about 10 and 5% of the mean axial force, respectively. A cycle of the axial variation takes place in flight distances of from 15 to 40 diameters. The unsteadiness almost certainly is associated with the wake. Angular motions which do not converge to zero angle of attack even in very long duration descent are excited by the unsteady pitching moments. The nearly spherical large probe model was aerodynamically more unsteady than the round-nosed conical small probe model. Data returned from Venus by the Pioneer Venus probes show unsteady axial forces and angular motions similar to those seen in the drop tests.

Seiff, A.↗

NASA NTRS1981

Designing for aircraft structural crashworthiness

This report describes structural aviation crash dynamics research activities being conducted on general aviation aircraft and transport aircraft. The report includes experimental and analytical correlations of load-limiting subfloor and seat configurations tested dynamically in vertical drop tests and in a horizontal sled deceleration facility. Computer predictions using a finite-element nonlinear computer program, DYCAST, of the acceleration time-histories of these innovative seat and subfloor structures are presented. Proposed application of these computer techniques, and the nonlinear lumped mass computer program KRASH, to transport aircraft crash dynamics is discussed. A proposed FAA full-scale crash test of a fully instrumented radio controlled transport airplane is also described.

Thomson, R. G.↗

NASA NTRS1961

Incipient- and Developed-Spin and Recovery Characteristics of a Modern High-Speed Fighter Design with Low Aspect Ratio as Determined from Dynamic-Model Tests

Incipient- and developed-spin and recovery characteristics of a modern high-speed fighter design with low aspect ratio have been investigated by means of dynamic model tests. A 1/7-scale radio-controlled model was tested by means of drop tests from a helicopter. Several 1/25-scale models with various configuration changes were tested in the Langley 20-foot free-spinning tunnel. Model results indicated that generally it would be difficult to obtain a developed spin with a corresponding airplane and that either the airplane would recover of its own accord from any poststall motion or the poststall motion could be readily terminated by proper control technique. On occasion, however, the results indicated that if a post-stall motion were allowed to continue, a fully developed spin might be obtainable from which recovery could range from rapid to no recovery at all, even when optimum control technique was used. Satisfactory recoveries could be obtained with a proper-size tail parachute or strake, application of pitching-, rolling-, or yawing-moment rockets, or sufficient differential deflection of the horizontal tail.

Lee, Henry A.↗

NASA NTRS2004

Alternative Test Methods for Electronic Parts

It is common practice within NASA to test electronic parts at the manufacturing lot level to demonstrate, statistically, that parts from the lot tested will not fail in service using generic application conditions. The test methods and the generic application conditions used have been developed over the years through cooperation between NASA, DoD, and industry in order to establish a common set of standard practices. These common practices, found in MIL-STD-883, MIL-STD-750, military part specifications, EEE-INST-002, and other guidelines are preferred because they are considered to be effective and repeatable and their results are usually straightforward to interpret. These practices can sometimes be unavailable to some NASA projects due to special application conditions that must be addressed, such as schedule constraints, cost constraints, logistical constraints, or advances in the technology that make the historical standards an inappropriate choice for establishing part performance and reliability. Alternate methods have begun to emerge and to be used by NASA programs to test parts individually or as part of a system, especially when standard lot tests cannot be applied. Four alternate screening methods will be discussed in this paper: Highly accelerated life test (HALT), forward voltage drop tests for evaluating wire-bond integrity, burn-in options during or after highly accelerated stress test (HAST), and board-level qualification.

Plante, Jeannette↗