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NASA NTRS2015

Ultimately Reliable Pyrotechnic Systems

This paper presents the methods by which NASA has designed, built, tested, and certified pyrotechnic devices for high reliability operation in extreme environments and illustrates the potential applications in the oil and gas industry. NASA's extremely successful application of pyrotechnics is built upon documented procedures and test methods that have been maintained and developed since the Apollo Program. Standards are managed and rigorously enforced for performance margins, redundancy, lot sampling, and personnel safety. The pyrotechnics utilized in spacecraft include such devices as small initiators and detonators with the power of a shotgun shell, detonating cord systems for explosive energy transfer across many feet, precision linear shaped charges for breaking structural membranes, and booster charges to actuate valves and pistons. NASA's pyrotechnics program is one of the more successful in the history of Human Spaceflight. No pyrotechnic device developed in accordance with NASA's Human Spaceflight standards has ever failed in flight use. NASA's pyrotechnic initiators work reliably in temperatures as low as -420 F. Each of the 135 Space Shuttle flights fired 102 of these initiators, some setting off multiple pyrotechnic devices, with never a failure. The recent landing on Mars of the Opportunity rover fired 174 of NASA's pyrotechnic initiators to complete the famous '7 minutes of terror.' Even after traveling through extreme radiation and thermal environments on the way to Mars, every one of them worked. These initiators have fired on the surface of Titan. NASA's design controls, procedures, and processes produce the most reliable pyrotechnics in the world. Application of pyrotechnics designed and procured in this manner could enable the energy industry's emergency equipment, such as shutoff valves and deep-sea blowout preventers, to be left in place for years in extreme environments and still be relied upon to function when needed, thus greatly enhancing safety and operational availability.

Scott, John H.↗

NASA NTRS1993

X-ray based displacement and strain measurements for hostile environments

A completely new method of non-contacting, hostile environment displacement and strain measurement based on the focus and scanning of x-rays, has been developed and demonstrated. The new technique has the ability to overcome many of the limitations associated with available methods. The system is based on the focus and scanning of low energy, hard x-rays such as those emanating from table top copper or molybdenum sources. The x-rays are focused into a narrow and intense line image which can be swept onto targets that fluoresce secondary x-ray radiation. By monitoring the secondary radiation intensity and comparing it with the focused x-ray image's position as it is swept over the target edge, the position of the target edge relative to the focused image can be determined. The present system has a resolution of 0.5 micron, which has been shown to be limited by bearing backlash (or 'yaw' error) in the linear translation table. Its use has been demonstrated in the presence of an open flame with a resultant target temperature in excess of 2000 degrees Fahrenheit (1000 degrees Celsius). Strain measurements have been conducted in a laboratory environment at both room temperature and at a specimen temperature of 1300 degrees Fahrenheit, with an accuracy of within 20 microstrain (primarily a function of the 0.5 micron resolution limit). The main advantage of the technique lies in the penetrating, non-refractive nature of x-rays, which are virtually immune to the presence of refracting gas layers, smoke, flame or intense thermal radiation.

Canistraro, Howard A.↗

NASA NTRS2003

Foot-Ground Reaction Force During Resistance Exercise in Parabolic Flight

An interim Resistance Exercise Device (iRED) was designed to provide resistive exercise as a countermeasure to space flight-induced loss of muscle strength and endurance as well as decreased bone mineral density. The purpose of this project was to compare foot-ground reaction force during iRED exercise in normal gravity (l-g) versus micro gravity (O-g) achieved during parabolic flight. METHODS: Four subjects performed three exercises using the iRED (squat, heel raise, and deadlift) during I-g and O-g at a moderate intensity (60% of maximum strength during deadlift exercise). Foot-ground reaction force was measured in three axes (x,y,z) using a force plate, and the magnitude of the resultant force vector was calculated (r = ~X 2 + y2 + Z2 ). Range of motion (ROM) was measured using a linear encoder. Peak force (PkF) and total work (TW) were calculated using a customized computer program. Paired t-tests were used to test if significant differences (p.::::0.05) were observed between I-g and O-g exercise. RESULTS: PkF and TW measured in the resultant axis were significantly less in O-g for each of the exercises tested. During O-g, PkF was 42-46% and TW was 33- 37% of that measured during I-g. ROM and average time to complete each repetition were not different from I-g to O-g. CONCLUSIONS: When performing exercises in which body mass is a portion of the resistance during I-g, PkF and TW measured during resistive exercise were reduced approximately 60-70% during O-g. Thus, a resistive exercise device during O-g will be required to provided higher resistances to induce a similar training stimulus to that on Earth.

Lee, Stuart M. C.↗

NASA NTRS1993

The (FHCl)- molecular anion - Structural aspects, global surface, and vibrational eigenspectrum

State of the art ab initio electronic structure methods have been used to investigate the (FHCl)- molecular anion. It is proposed that the geometric structure and binding energies of the complex are r(e)(H-F) = 0.963 +/- 0.003 A, R(e)(H-Cl) = 1.925 +/- 0.015 A, and D0(HF + Cl(-)) = 21.8 +/- 0.4 kcal/mol. A Morokuma decomposition of the ion-molecular bonding give the following electrostatic, polarization, exchange repulsion, dispersion, and charge-transfer plus higher-order mixing components of the vibrationless complexation energy: -27.3, -5.2, +18.3, -4.5, and -5.0 kcal/mol, respectively. A couples cluster single and doubles global surface is constructed from 208 and 228 energy points for linear and bent configurations, respectively, these being fit to rms errors of only 3.9 and 9.3/cm, respectively, below 8000/cm. Converged J = 0 and J = 1 variational eigenstates of the (FHCl)- surface to near the HF + Cl(-) dissociation threshold are determined. The fundamental vibrational frequencies are found to be nu1 = 247/cm, nu2 = 876/cm, and nu3 = 2884/cm. The complete vibrational eigenspectrum is analyzed.

Klepeis, Neil E.↗

NASA NTRS2004

Foot-ground reaction force during resistive exercise in parabolic flight

INTRODUCTION: An interim resistance exercise device (iRED) was designed to provide resistive exercise as a countermeasure to spaceflight-induced loss of muscle strength and endurance as well as decreased bone mineral density. The purpose of this project was to compare foot-ground reaction force during iRED exercise in normal gravity (1 G) vs. microgravity (0 G) achieved during parabolic flight. METHODS: There were four subjects who performed three exercises (squat, heel raise, and deadlift) using the iRED during 1 G and 0 G at a moderate intensity (60% of maximum strength during deadlift exercise). Foot-ground reaction force was measured in the three orthogonal axes (x, y, z) using a force plate, and the magnitude of the resultant force vector was calculated (r = square root(x2 + y2 + z2)). Linear displacement (LD) was measured using a linear transducer. Peak force (Fpeak) and an index of total work (TWi) were calculated using a customized computer program. Paired t-tests were used to test if significant differences (p < or = 0.05) were observed between 1 G and 0 G exercise. RESULTS: Fpeak and TWi measured in the resultant axis were significantly less in 0 G for each of the exercises tested. During 0 G, Fpeak was 42-46% and TWi was 33-37% of that measured during 1 G. LD and average time to complete each repetition were not different from 1 G to 0 G. CONCLUSIONS: Crewmembers who perform resistive exercises during spaceflight that include the movement of a large portion of their body mass will require much greater external resistive force during 0 G than 1 G exercise to provide a sufficient stimulus to maintain muscle and bone mass.

Physical Education and Training↗

NASA NTRS2005

Designing Adaptive Low-Dissipative High Order Schemes for Long-Time Integrations

A general framework for the design of adaptive low-dissipative high order schemes is presented. It encompasses a rather complete treatment of the numerical approach based on four integrated design criteria: (1) For stability considerations, condition the governing equations before the application of the appropriate numerical scheme whenever it is possible. (2) For consistency, compatible schemes that possess stability properties, including physical and numerical boundary condition treatments, similar to those of the discrete analogue of the continuum are preferred. (3) For the minimization of numerical dissipation contamination, efficient and adaptive numerical dissipation control to further improve nonlinear stability and accuracy should be used. (4) For practical considerations, the numerical approach should be efficient and applicable to general geometries, and an efficient and reliable dynamic grid adaptation should be used if necessary. These design criteria are, in general, very useful to a wide spectrum of flow simulations. However, the demand on the overall numerical approach for non-linear stability and accuracy is much more stringent for long-time integration of complex multiscale viscous shock/shear/turbulence/acoustics interactions and numerical combustion. Robust classical numerical methods for less complex flow physics are not suitable or practical for such applications. The present approach is designed expressly to address such flow problems, especially unsteady flows.

Yee, H. C.↗

NASA NTRS1976

Stability and Relative Stability of Linear Systems with Many Constant Time Delays

A method of determining the stability of linear systems with many constant time delays is developed. This technique, an extension of the tau-decomposition method, is used to examine not only the stability but also the relative stability of retarded systems with many delays and a class of neutral equations with one delay. Analytical equations are derived for partitioning the delay space of a retarded system with two time delays. The stability of the system in each of the regions defined by the partitioning curves in the parameter plane is determined using the extended tau-decomposition method. In addition, relative stability boundaries are defined using the extended tau-decompositon method in association with parameter plane techniques. Several applications of the extended tau-decomposition method are presented and compared with stability results obtained from other analyses. In all cases the results obtained using the method outlined herein coincide with and extend those of previous investigations. The extended tau-decomposition method applied to systems with time delays requires less computational effort and yields more complete stability analyses than previous techniques.

Barker, Larry Keith↗

NASA NTRS1996

Conversion-Integration of MSFC Nonlinear Signal Diagnostic Analysis Algorithms for Realtime Execution of MSFC's MPP Prototype System

NASA's advanced propulsion system Small Scale Magnetic Disturbances/Advanced Technology Development (SSME/ATD) has been undergoing extensive flight certification and developmental testing, which involves large numbers of health monitoring measurements. To enhance engine safety and reliability, detailed analysis and evaluation of the measurement signals are mandatory to assess its dynamic characteristics and operational condition. Efficient and reliable signal detection techniques will reduce the risk of catastrophic system failures and expedite the evaluation of both flight and ground test data, and thereby reduce launch turn-around time. During the development of SSME, ASRI participated in the research and development of several advanced non- linear signal diagnostic methods for health monitoring and failure prediction in turbomachinery components. However, due to the intensive computational requirement associated with such advanced analysis tasks, current SSME dynamic data analysis and diagnostic evaluation is performed off-line following flight or ground test with a typical diagnostic turnaround time of one to two days. The objective of MSFC's MPP Prototype System is to eliminate such 'diagnostic lag time' by achieving signal processing and analysis in real-time. Such an on-line diagnostic system can provide sufficient lead time to initiate corrective action and also to enable efficient scheduling of inspection, maintenance and repair activities. The major objective of this project was to convert and implement a number of advanced nonlinear diagnostic DSP algorithms in a format consistent with that required for integration into the Vanderbilt Multigraph Architecture (MGA) Model Based Programming environment. This effort will allow the real-time execution of these algorithms using the MSFC MPP Prototype System. ASRI has completed the software conversion and integration of a sequence of nonlinear signal analysis techniques specified in the SOW for real-time execution on MSFC's MPP Prototype. This report documents and summarizes the results of the contract tasks; provides the complete computer source code; including all FORTRAN/C Utilities; and all other utilities/supporting software libraries that are required for operation.

Jong, Jen-Yi↗

NASA NTRS2012

CREME96 and Related Error Rate Prediction Methods

Predicting the rate of occurrence of single event effects (SEEs) in space requires knowledge of the radiation environment and the response of electronic devices to that environment. Several analytical models have been developed over the past 36 years to predict SEE rates. The first error rate calculations were performed by Binder, Smith and Holman. Bradford and Pickel and Blandford, in their CRIER (Cosmic-Ray-Induced-Error-Rate) analysis code introduced the basic Rectangular ParallelePiped (RPP) method for error rate calculations. For the radiation environment at the part, both made use of the Cosmic Ray LET (Linear Energy Transfer) spectra calculated by Heinrich for various absorber Depths. A more detailed model for the space radiation environment within spacecraft was developed by Adams and co-workers. This model, together with a reformulation of the RPP method published by Pickel and Blandford, was used to create the CR ME (Cosmic Ray Effects on Micro-Electronics) code. About the same time Shapiro wrote the CRUP (Cosmic Ray Upset Program) based on the RPP method published by Bradford. It was the first code to specifically take into account charge collection from outside the depletion region due to deformation of the electric field caused by the incident cosmic ray. Other early rate prediction methods and codes include the Single Event Figure of Merit, NOVICE, the Space Radiation code and the effective flux method of Binder which is the basis of the SEFA (Scott Effective Flux Approximation) model. By the early 1990s it was becoming clear that CREME and the other early models needed Revision. This revision, CREME96, was completed and released as a WWW-based tool, one of the first of its kind. The revisions in CREME96 included improved environmental models and improved models for calculating single event effects. The need for a revision of CREME also stimulated the development of the CHIME (CRRES/SPACERAD Heavy Ion Model of the Environment) and MACREE (Modeling and Analysis of Cosmic Ray Effects in Electronics). The Single Event Figure of Merit method was also revised to use the solar minimum galactic cosmic ray spectrum and extended to circular orbits down to 200 km at any inclination. More recently a series of commercial codes was developed by TRAD (Test & Radiations) which includes the OMERE code which calculates single event effects. There are other error rate prediction methods which use Monte Carlo techniques. In this chapter the analytic methods for estimating the environment within spacecraft will be discussed.

Adams, James H., Jr.↗

NASA NTRS2017

Improvement of Automated POST Case Success Rate Using Support Vector Machines

During early conceptual design of complex systems, concept down selection can have a large impact upon program life-cycle cost. Therefore, any concepts selected during early design will inherently commit program costs and affect the overall probability of program success. For this reason it is important to consider as large a design space as possible in order to better inform the down selection process. For conceptual design of launch vehicles, trajectory analysis and optimization often presents the largest obstacle to evaluating large trade spaces. This is due to the sensitivity of the trajectory discipline to changes in all other aspects of the vehicle design. Small deltas in the performance of other subsystems can result in relatively large fluctuations in the ascent trajectory because the solution space is non-linear and multi-modal [1]. In order to help capture large design spaces for new launch vehicles, the authors have performed previous work seeking to automate the execution of the industry standard tool, Program to Optimize Simulated Trajectories (POST). This work initially focused on implementation of analyst heuristics to enable closure of cases in an automated fashion, with the goal of applying the concepts of design of experiments (DOE) and surrogate modeling to enable near instantaneous throughput of vehicle cases [2]. Additional work was then completed to improve the DOE process by utilizing a graph theory based approach to connect similar design points [3]. The conclusion of the previous work illustrated the utility of the graph theory approach for completing a DOE through POST. However, this approach was still dependent upon the use of random repetitions to generate seed points for the graph. As noted in [3], only 8% of these random repetitions resulted in converged trajectories. This ultimately affects the ability of the random reps method to confidently approach the global optima for a given vehicle case in a reasonable amount of time. With only an 8% pass rate, tens or hundreds of thousands of reps may be needed to be confident that the best repetition is at least close to the global optima. However, typical design study time constraints require that fewer repetitions be attempted, sometimes resulting in seed points that have only a handful of successful completions. If a small number of successful repetitions are used to generate a seed point, the graph method may inherit some inaccuracies as it chains DOE cases from the non-global-optimal seed points. This creates inherent noise in the graph data, which can limit the accuracy of the resulting surrogate models. For this reason, the goal of this work is to improve the seed point generation method and ultimately the accuracy of the resulting POST surrogate model. The work focuses on increasing the case pass rate for seed point generation.

Zwack, Matthew R.↗

NASA NTRS2000

Comparison of On-Orbit Performance of Rate Sensing Gyroscopes

This work presents results from the study of a large volume of spacecraft flight data pertaining to gyroscope performance. We have examined long and short term trends of gyroscope biase of first, an exact solution for the time-dependence of the attitude part of the state error covariance, averaged over the three spacecraft axes, is given. This solution is more complete than the usual cubic polynomial for the variance in that it includes coupling among the three gyroscope axes and includes an important term arising from the initial correlations. Second, several continuous 24-hour spans of gyroscope data are examined to verify the short-term statistical model. This analysis demonstrates that in-flight data can be used to determine the strength of the white noise driving the random walk of the gyroscope bias. This may be useful for postlaunch improvement to the noise model and for diagnosing the health of the gyroscope. Third, the long-term trends in gyroscope biases show a nearly linear systematic variation over time scales of years. This has been found on three different missions. While the random walk model is adequate as a basis for onboard Kalman filters or for state estimation using relatively short time spans, these trends indicate that some applications could benefit by accounting for the secular changes in the biases. One example is a new gyroscope calibration method that is under development that allows for multi-epoch bias solutions.

Sedlak, Joseph↗

NASA NTRS2018

Trusted Communication: Utilizing Speech Communication to Enhance Human-Machine Teaming Success

An area of increasing interest for the next generation of aircraft is autonomy and the integration of increasingly autonomous systems into the national airspace. Such an integration requires humans to work closely with autonomous systems, forming teams. Our hypothesis is that a team composed of both humans and autonomous systems will operate better than either entity alone. We have existing procedures for certifying pilots to operate in the national airspace and are currently working on methods for validating the function of autonomous systems, however we have no method in place for assessing the interaction of these two disparate systems. Communication is one avenue. This paper will examine the use of language as a metric for ascertaining human-machine teaming effectiveness. A proof-of-concept of the application of two communication-based analysis techniques, Linguistic Inquiry and Word Count (LIWC) and Latent Semantic Analysis (LSA), for the prediction of success in human/chatbot teaming was conducted. By running these analyses over data from the 2014 and 2015 Loebner Prize competitions of human/chatbot teaming, numerical scores were obtained that can be associated with scores provided by human judges during the competition. Correlating their LIWC and LSA data with the scores provided by the judges, and using linear regression over this correlation, formulae were obtained that predict the score of human/chatbot interaction. These formulae were tested over the 2013 Loebner Prize transcripts, determining that, though there was strong correlation between predicted and actual scores, the predictive success of this method was not strong. However, with specialized topic spaces and lexica, as well as larger data sets, the predictive power of these metrics will improve. Given the importance of providing metrics for human-machine system team success and given the promise shown by the communication-basedLIWCand LSAmethods, continuing research in this area is necessary. After examining the potential for using communication and spoken language as a metric for the success of human/autonomous system teaming, this paper then examines aspects inherent to communication systems that may contribute to unreliability and reduced trust. Modern natural language processing tools rely on deep learning algorithms to create language rules that produce accurate results, but these rules are uninterpretable. The resulting blackbox system lacks transparency necessary for full validation and complete trust. Additionally, speech-based interfaces pose other difficulties to developing coordinated teamwork between humans and autonomous systems. Human communication is infrequently limited to speech only, instead usually relying on a combination of verbal, gestural, and general body language communication. Reducing an analysis of team effectiveness to a study of spoken language alone is problematic as it leaves these other equally important forms of communication out. This paper will examine these problems and the general deficiencies in speech-based metrics for human-machine teaming.

E L Meszaros↗

NASA NTRS1994

Echo mapping of active galactic nuclei broad-line regions: Fundamental algorithms

We formulate and test a series of algorithms for echo mapping the emission-line regions near active galactic nuclei from measurements of correlated variability in their line and continuum light curves. The linear regularization method (LRM) employs a direct inversion of evenly spaced light-curve data, with a regularization parameter that can be used to control the trade-off between noise and resolution. Matrix formulas express the formal solution as well as its variance and covariance in terms of uncertainties in the measurements. Unlike the maximum-entropy method (MEM), LRM applies to kernels with both positive and negative values, but the results are somewhat limited by ringing effects. A positivity constraint proves effective in controlling the ringing. MEM combines regularization and positivity in a natural way, but similar results are also found using positivity constraints with nonentropic regularization functions. Direct inversions of unevenly sampled light curves require interpolating the noisy data. In this case better results are found by solving for both the continuum light curve and kernel function in a simultaneous fit to the data. Our conclusion is that while echo mapping currently gives ambiguous results, the algorithms are not the limiting factor. Progress depends on efforts to increase the accuracy and completeness of sampling of the observed light curves.

Vio, Roberto↗

NASA NTRS2001

On the Definition of Surface Potentials for Finite-Difference Operators

For a class of linear constant-coefficient finite-difference operators of the second order, we introduce the concepts similar to those of conventional single- and double-layer potentials for differential operators. The discrete potentials are defined completely independently of any notion related to the approximation of the continuous potentials on the grid. We rather use all approach based on differentiating, and then inverting the differentiation of a function with surface discontinuity of a particular kind, which is the most general way of introducing surface potentials in the theory of distributions. The resulting finite-difference "surface" potentials appear to be solutions of the corresponding continuous potentials. Primarily, this pertains to the possibility of representing a given solution to the homogeneous equation on the domain as a variety of surface potentials, with the density defined on the domain's boundary. At the same time the discrete surface potentials can be interpreted as one specific realization of the generalized potentials of Calderon's type, and consequently, their approximation properties can be studied independently in the framework of the difference potentials method by Ryaben'kii. The motivation for introducing and analyzing the discrete surface potentials was provided by the problems of active shielding and control of sound, in which the aforementioned source terms that drive the potentials are interpreted as the acoustic control sources that cancel out the unwanted noise on a predetermined region of interest.

Tsynkov, S. V.↗

NASA NTRS1988

Linear response theory for annealing of radiation damage in semiconductor devices

A theoretical study of the radiation/annealing response of MOS ICs is described. Although many experiments have been performed in this field, no comprehensive theory dealing with radiation/annealing response has been proposed. Many attempts have been made to apply linear response theory, but no theoretical foundation has been presented. The linear response theory outlined here is capable of describing a broad area of radiation/annealing response phenomena in MOS ICs, in particular, both simultaneous irradiation and annealing, as well as short- and long-term annealing, including the case when annealing is nearing completion. For the first time, a simple procedure is devised to determine the response function from experimental radiation/annealing data. In addition, this procedure enables us to study the effect of variable temperature and dose rate, effects which are of interest in spaceflight. In the past, the shift in threshold potential due to radiation/annealing has usually been assumed to depend on one variable: the time lapse between an impulse dose and the time of observation. While such a suggestion of uniformity in time is certainly true for a broad range of radiation annealing phenomena, it may not hold for some ranges of the variables of interest (temperature, dose rate, etc.). A response function is projected which is dependent on two variables: the time of observation and the time of the impulse dose. This dependence on two variables allows us to extend the theory to the treatment of a variable dose rate. Finally, the linear theory is generalized to the case in which the response is nonlinear with impulse dose, but is proportional to some impulse function of dose. A method to determine both the impulse and response functions is presented.

Litovchenko, Vitaly↗

NASA NTRS1950

Transonic Stability and Control Investigation of a 1/80-Scale Model of the Consolidated Vultee Skate 9 Seaplane, TED No. NACA DE 345: Transonic-Bump Method

An investigation of the longitudinal stability and of the all-movable horizontal tail and aileron control of a 1/80-scale reflection-plane model of the Consolidated Vultee Skate 9 seaplane has been made through a Mach number range of 0.6 to 1.16 on the transonic bump of the Langley high-speed 7- by 10-foot tunnel. At moderate lift coefficients (0.4 to 0.8) and below a Mach number of 1.0 the model was statically unstable longitudinally. The static longitudinal stability of the model at low lift coefficients increased with Mach number corresponding to a shift in aerodynamic center from 37 percent mean aerodynamic chord at a Mach number of 0.60 to 64 percent at a Mach number of 1.10. Estimates indicate that the tail deflection angle required for steady flight and for accelerated maneuvers of the Skate 9 airplane would probably not vary greatly with Mach number at sea level, but for accelerated maneuvers at altitude the tail deflection angle would probably vary erratically with Mach number. The variation of rolling-moment coefficient with aileron deflection angle was approximately linear, agreed well with theory, and held for the range of aileron deflections tested (-17.1 deg to 16.6 deg). At low lift coefficients the drag rise occurred at Mach numbers of 0.95 and 0.90 for the wing alone and the complete model, respectively. The effects of the canopy on the model were small. For the ranges investigated, angle-of-attack and Mach number changes caused no large pressure drops in the jet-engine duct.

Riebe, John M.↗

NASA NTRS1961

Analysis of Effects of Interceptor Roll Performance and Maneuverability on Success of Collision-Course Attack

An attempt has been made to determine the importance of rolling performance and other factors in the design of an interceptor which uses collision-course tactics. A graphical method is presented for simple visualization of attack situations. By means of diagrams showing vectoring limits, that is, the ranges of interceptor position and heading from which attacks may be successfully completed, the relative importance of rolling performance and normal-acceleration capability in determining the success of attacks is illustrated. The results indicate that the reduction in success of attacks due to reduced rolling performance (within the limits generally acceptable from the pilots' standpoint) is very small, whereas the benefits due to substantially increasing the normal-acceleration capability are large. Additional brief analyses show that the optimum speed for initiating a head-on attack is often that corresponding to the upper left-hand corner of the V-g diagram. In these cases, increasing speed beyond this point for given values of normal acceleration and radar range rapidly decreases the width of the region from which successful attacks can be initiated. On the other hand, if the radar range is increased with a variation somewhere between the first and second power of the interceptor speed, the linear dimensions of the region from which successful attacks can be initiated vary as the square of the interceptor speed.

Phillips, William H.↗

NASA NTRS1962

Linearized Theory of Wind-tunnel Jet-boundary Corrections and Ground Effect for VTOL-STOL Aircraft

A linearized theory is developed to obtain interference factors for wind tunnels and ground effect. The calculated results, presented in tabular form in NASA Technical Notes D-933, D-934, D-935, and D-936, indicate that the degree to which the wake is deflected downward has a primary effect on the magnitude of the interference. When the wake is undeflected the corrections are essentially the same as those of classical theory. When the wake is deflected severely downward, the corrections are primarily determined by the floor of the wind tunnel. Under these conditions, the corrections are, in general, much larger than those given by previously available results. Because of deformations at the lower boundary of the jet, the corrections for an open wind tunnel are uncertain. Testing at low speeds and high lift coefficients in open wind tunnels, therefore, is not recommended. Although the theory is developed expressly for single-element, vanishingly small models, methods, with sample calculations, are given for extending the results to multielement and finite span models. The theory is at least partially verified by available test data; however, complete verification would require a substantially more detailed experimental study.

V/STOL aircraft↗