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A simple wing leading-edge modification has been developed that delays outer wing panel stall, thus maintaining roll damping to higher angles of attack and delaying the onset of autorotation. The stall angle of attack of the outer wing panel has been shown to be a function of the spanwise length of the leading-edge modification. The margin of spin resistance provided by the modification is being explored through flight tests. Preliminary results have been used to evaluate spin resistance in terms of the difference in angle of attack between outer wing panel stall and the maxiumum attainable angle of attack.

An investigation has been conducted in the Langley 30- by 60-Foot Wind Tunnel to evaluate the performance and stability and control characteristics of a full-scale general aviation airplane equipped with a natural-laminar-flow wing. The study focused on the effects of natural laminar flow and boundary layer transition, and on the effects of several wing leading-edge modifications designed to improve the stall resistance of the configuration. Force and moment data were measured over wide angle-of-attack and sideslip ranges and at Reynolds numbers from 1.4 × 106 to 2.1 × 106 based on the mean aerodynamic chord. Additional measurements were made using hot-film and sublimating-chemical techniques to determine the condition of the wing boundary layer, and wool tufts were used to study the wing stalling characteristics. The investigation showed that large regions of natural laminar flow existed on the wing which would significantly enhance the cruise performance of the configuration.

To meet the challenge of future deep space programs an accurate and efficient engineering code for analyzing the shielding requirements against high-energy galactic heavy radiations is needed. Such engineering design codes require establishing validation processes using laboratory ion beams and space flight measurements in realistic geometries. In consequence, a new version of the HZETRN code capable of simulating HZE ions with either laboratory or space boundary conditions is currently under development. The new code, GRNTRN, is based on a Green's function approach to the solution of Boltzmann's transport equation and like its predecessor is deterministic in nature. Code validation in the laboratory environment is addressed by showing that GRNTRN accurately predicts energy loss spectra as measured by solid-state detectors in ion beam experiments.

High-speed computational procedures for space radiation shielding have relied on asymptotic expansions in terms of the off-axis scatter and replacement of the general geometry problem by a collection of flat plates. This type of solution was derived for application to human rated systems in which the radius of the shielded volume is large compared to the off-axis diffusion limiting leakage at lateral boundaries. Over the decades these computational codes are relatively complete and lateral diffusion effects are now being added. The analysis for developing a practical full 3D space shielding code is presented.

The results of theory/experiment correlative studies at subsonic and supersonic Mach numbers are presented in this paper. These studies were conducted by using theoretical design tools consisting of the Method of Characteristics, newly-developed integral compressible boundary-layer methods for infinitely swept wings, namely, laminar boundary layer with suction, prediction of neutral instability and transition due to amplification of Tollmien-Schlichting (T.S.) waves and crossflow (C.F.), and a method for predicting separating turbulent boundary-layer characteristics. Results of correlations have indicated that the present integral boundary layer methods are quite successful in predicting transition phenomenon both at transonic and supersonic speeds.

Prior studies have been performed where basic fabric lay-ups of the current Shuttle spacesuit were tested for radiation shielding capabilities. It was found that the fabric portions of the suit give far less protection from radiation than previously estimated. This is due to the porosity and non-uniformity of the fabrics and LCVG components. These findings were incorporated into the spacesuit model developed at NASA Langley Research Center to estimate exposures for mission planning and evaluation of safety during radiation field disturbance. Overall material transmission properties were also less than optimal. In order to evaluate the radiation protection characteristics of some proposed new spacesuit materials, fifteen test target combinations of current baseline and new proposed spacesuit materials were exposed to a low-energy proton beam at Lawrence Berkeley National Laboratory. Each target combination contained all of the necessary spacesuit layers, i.e.

A model scaled test apparatus has been designed and assembled to simulate supersonic plume/aircraft structure Interaction for the cruise configuration. Preliminary results have been obtained to demonstrate the severity of the associated acoustic fatigue loads. Two rectangular supersonic nozzles with aspect ratios of 7 and 7.7 ware fabricated with internal convergent-divergent contours designed for Mach numbers of 1.35 and 2.00. A large flat plate was located beneath each nozzle at various nozzle height separations. The plate was instrumented to measure surface dynamic pressure and mean wall temperature. Phase averaged schliern measurements revealed the presence of high intensity acoustic emission from the supersonic plume above the plate and directed upstream. This radiation can be associated with the shock noise generation mechanism. Narrow band spectra of wall dynamic pressure show spectral peaks with amplitude levels as high as 1 PSI.

NASA and the FAA conducted two flight campaigns to quantify onboard weather radar measurements with in-situ measurements of high concentrations of ice crystals found in deep convective storms. The ultimate goal of this research was to improve the understanding of high ice water content (HIWC) and develop onboard weather radar processing techniques to detect regions of HIWC ahead of an aircraft to enable tactical avoidance of the potentially hazardous conditions. Both HIWC RADAR campaigns utilized the NASA DC-8 Airborne Science Laboratory equipped with a Honeywell RDR-4000 weather radar and in-situ microphysical instruments to characterize the ice crystal clouds. The purpose of this paper is to summarize how these campaigns were conducted and highlight key results. The first campaign was conducted in August 2015 with a base of operations in Ft. Lauderdale, Florida.

Recently, a new Green’s function code (GRNTRN) for simulation of HZE ion beams in the laboratory setting has been developed. Once fully developed and experimentally verified, GRNTRN will be a great asset in assessing radiation exposures in both the laboratory and space settings. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple elastic scattering, and nuclear reactive processes with use of Neumann-series expansions with non-perturbative corrections. The code contains energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and down shifts. Previous reports show that the new code accurately models the transport of ion beams through a single slab of material. Current research efforts are focused on enabling the code to handle multiple layers of material and the present paper reports on progress made towards that end.

This paper reviews the status of analytical and empirical propeller noise prediction methods with specific emphasis on those that are suitable for General Aviation propellers. Specifically, the paper reviews the capabilities and limitations of methods that are simple enough for ease of use by industry while providing sufficient accuracy to guide the development of new propeller designs or the modification of existing propeller driven airplanes to satisfy increased certification stringency or cabin comfort objectives.

With the resurgence of the General Aviation industry, the incentive to develop new airplanes for the low-end market has increased. Increased production of small airplanes provides the designers and manufacturers the opportunity to incorporate advanced technologies that are not readily retrofitable to existing designs. Spin resistance is one such technology whose development was concluded by NASA during the 1980’s when the production of small airplanes had slipped into near extinction. This paper reviews the development of spin resistance technology for small airplanes with emphasis on wing design. The definition of what constitutes spin resistance and the resulting amendment of the Federal Aviation Regulations Part 23 to enable certification of spin resistant airplanes are also covered.

An extensive general aviation stall/spin research program is underway at the NASA Langley Research Center. Flight tests have examined the effects of tail design, wing leading edge design, mass distribution, and minor airframe modifications on spin and recovery characteristics. Results and observations on test techniques are presented for the first airplane in the program. Configuration changes produced spins varying from easily recoverable slow, steep spins to unrecoverable, fast flat spins.

Meeting radiation protection requirements during EVA is predominantly an operational issue with some potential considerations for temporary shelter. The issue of spacesuit shielding is mainly guided by the potential of accidental exposure when operational and temporary shelter considerations fail to maintain exposures within operational limits. In this case, very high exposure levels are possible which could result in observable health effects and even be life threatening. Under these assumptions, potential spacesuit radiation exposures have been studied using known historical solar particle events to gain insight on the usefulness of modification of spacesuit design in which the control of skin exposure is a critical design issue and reduction of blood forming organ exposure is desirable.

The development of “next generation” human-rated space vehicles, surface habitats and rovers, and spacesuits will require the integration of low-cost, lightweight materials that also include excellent mechanical, structural, and thermal properties. In addition, it is highly desirable that these materials exhibit excellent space radiation exposure mitigation properties for protection of both the crew and onboard sensitive electronics systems. In this paper, we present trapped electron and proton space radiation exposure computational results for a variety of materials and shielding thicknesses for several earth orbit scenarios that include 1) low earth orbit (LEO), 2) medium earth orbit (MEO), and 3) geostationary orbit (GEO). We also present space radiation exposure (galactic cosmic radiation and solar particle event) results as a function of selected materials and thicknesses.

The development of a Green’s function approach to ion transport greatly facilitates the modeling of laboratory radiation environments and allows for the direct testing of transport approximations of material transmission properties. Using this approach radiation investigators at the NASA Langley Research Center have established that simple solutions can be found for HZE ions by ignoring nuclear energy downshifts and dispersion. Such solutions were found to be supported by experimental evidence with HZE ion beams when multiple scattering was added. Lacking from the prior solutions were range and energy straggling and energy downshift and dispersion associated with nuclear events. In a more recent publication it was shown how these effects can be incorporated into the multiple fragmentation perturbation series. Analytical approximations for the first two perturbation terms were presented and the third term was evaluated numerically.

One goal of space radiation research is to reduce the computational time and increase the accuracy of various radiation calculations to aid in their use in a collaborative engineering environment. For example, a fast turn around time is a feature needed for comparison of radiation shielding effects associated with various design configurations of the International Space Station. Research toward this effort has been conducted on various forms of the low energy neutron Boltzmann equation. Simplified models involving the straight ahead approximation, which have fast computational speeds, have been developed at NASA Langley Research Center during the late 1980's as part of a larger high energy ion transport code. Various modifications to improve the accuracy of these computer codes have been an ongoing project. The goal to increase the accuracy of low energy neutron transport without effecting the fast computational times has been a successful ongoing research effort.

An automatic trim system for reducing the control forces after an engine failure on a light twin has been investigated on the Langley General Aviation Simulator. The system schedules open-loop trim tab deflections as a function of differential propeller slipstream dynamic pressure and freestream dynamic pressure. The system is described and the airplane-system static and dynamic characteristics are documented. Three NASA research pilots evaluated the effectiveness of the system for takeoff and landing maneuvers. A variety of off-nominal system characteristics were studied. The system was judged to be generally beneficial, providing a 2 to 3 point improvement in pilot rating for the tasks used in the evaluations.

A detailed spacesuit computational model is being developed at the Langley Research Center for exposure evaluation studies. The details of the construction of the spacesuit are critical to an estimate of exposures and for assessing the health risk to the astronaut during extra-vehicular activity (EVA). Fine detail of the basic fabric structure, helmet, and backpack is required to assure a valid evaluation. The exposure fields within the Computerized Anatomical Male (CAM) and Female (CAF) are evaluated at 148 and 156 points, respectively, to determine the dose fluctuations within critical organs. Exposure evaluations for ambient environments will be given and potential implications for geomagnetic storm conditions discussed.

Most of the neutrons seen in the habitable environment of spacecraft in LEO are produced in local materials of the spacecraft structures by the impact of the LEO radiation environment. There are two components of the neutron spectra: one produced near the forward direction and a diffuse isotropic component. The forward component satisfies a Volterra equation and is solved by standard marching procedures. The diffuse component is generally of lower energy and nearly isotropically scattered as they diffuse through the spacecraft structures. Leakage at near boundaries marks the diffusion process and solutions are strongly dependent on forward and backward boundaries with minor contributions from lateral diffusion along spacecraft wall structures. The diffuse neutron equation is solved using multigroup methods with impressed forward and backward boundary conditions.

As shielding materials are developed for protection against the hazards of galactic cosmic rays, it is desirable to develop a protocol for rapid assessment of shielding properties. Solid state energy loss detectors are often used to estimate the charge and energy of particles in ion beam experiments. The direct measurement is energy deposited in the detector. As a means of separating the charge components in typical shield transmission studies with observation, a stack of many such detectors is used. With high-energy beams and thin targets, surviving primaries and fragments emerging from the target have nearly-equal velocities and deposited energy scales with the square of the charge, simplifying the data analysis. The development of a transport model for the shield and detector arrangement and evaluation of prediction of the energy loss spectrum for direct comparison with the experimentally derived data allows a rapid assessment of the shield transmission characteristics.