Development and flight evaluation of an augmented stability active controls concept: Executive summary

A pitch active control system (PACS) was developed and flight tested on a wide body jet transport (L-1011) with a flying horizontal stabilizer. Two dual channel digital computers and the associated software provide command signals to a dual channel series servo which controls the stabilizer power actuators. Input sensor signals to the computer are pitch rate, column trim position, and dynamic pressure. Control laws are given for the PACS and the system architecture is defined. Discussions are given regarding piloted flight simulation and vehicle system simulation and vehicle system simulation tests that are performed to verify control laws and system operation prior to installation on the aircraft. Modifications to the basic aircraft included installation of the PACS, addition of a c.g. management system to provide a c.g. range from 25 to 39% mac, and downrigging of the geared elevator to provide the required nose down control authority for aft c.g. flight test conditions. Three pilots used the Cooper-Harper Rating Scale to judge flying qualities of the aircraft with PACS on and off. The handling qualities with the c.g. at 39% mac (41% stability margin) and PACS operating were judged to be as good as the handling qualities with the c.g. at 25% mac (+15% stability margin) and PACS off

Disparities in Weather Education Across Professional Flight Baccalaureate Degree Programs

The required meteorology coursework for 22 accredited professional flight baccalaureate degree programs was examined and compared. Significant differences were noted in both the number of required meteorology courses as well as the number of required meteorology credit hours. While all programs required at least one three-credit meteorology course, not all programs required an aviation-specific meteorology course. In addition to the required number of meteorology courses and credit hours, topics within the aviation-specific meteorology courses were also examined. The study showed the topics of “flight hazards” and “aviation weather reports and charts” were identified most frequently in course descriptions, followed third by “weather applications to flight.” However, based on the course descriptions alone, it was unclear if the meteorological theory of flight hazards was addressed in the courses or if the courses only addressed the interpretation of weather hazards charts. To improve and standardize aviation-meteorology education in professional flight-degree programs, a recommendation was made to either provide aviation-meteorology curriculum guidelines through the University Aviation Association (UAA) Curriculum Committee or to form a separate UAA Aviation-Meteorology Education Committee

Efficacy of the Localized Aviation MOS Program in Ceiling Flight Category Forecasts

(1) Background: Flying in instrument meteorological conditions (IMC) carries an elevated risk of fatal outcome for general aviation (GA) pilots. For the typical GA flight, aerodrome-specific forecasts (Terminal Aerodrome Forecast (TAF), Localized Aviation Model Output Statistics Program (LAMP)) assist the airman in pre-determining whether a flight can be safely undertaken. While LAMP forecasts are more prevalent at GA-frequented aerodromes, the Federal Aviation Administration (FAA) recommends that this tool be used as supplementary to the TAF only. Herein, the predictive accuracy of LAMP for ceiling flight categories of visual flight rules (VFR) and instrument flight rules (IFR) was determined. (2) Methods: LAMP accuracy was evaluated for the period of July–December 2018 using aviation-specific probability of detection (PODA), false alarm ratio (FARA) and critical success scores (CSSA). Statistical differences were determined using Chi-Square tests. (3) Results: LAMP forecasts (n = 823) across 39 states were accrued. LAMP PODA for VFR (0.67) and IFR (0.78) exceeded (p \u3c 0.031) the corresponding TAF scores (0.57 and 0.56). For VFR, the LAMP showed a non-significant (p = 0.243) higher FARA (0.25) than the TAF (0.19). For IFR forecasts, the LAMP FARA was lower (p \u3c 0.001) (0.48 and 0.81, respectively). LAMP CSSA scores exceeded the TAF for VFR (p = 0.012) and IFR forecasts (p \u3c 0.001). (4) Conclusion: These findings support the greater integration of LAMP into pre-flight weather briefings

Quantitative Examination and Comparison of Altimetry Rules-of-Thumb for General Aviation

General aviation rules of thumb (ROTs) for density altitude and true altitude are examined and developed. Both ROTs originate from the same basic principle of hydrostatic balance, but differ significantly in the assumptions made regarding the atmospheric temperature profile. While the ROT for DA assumes a standard atmospheric vertical temperature lapse rate, the ROT for true altitude requires information regarding the observed layer-mean temperature of the atmosphere. Since the layer-mean temperature between the aircraft and the surface is typically unknown, it must be inferred from the temperature at a single level by again assuming a linear lapse rate. This method is shown to perform poorly in cases of strong lower-tropospheric temperature inversions. Direct comparisons of the two ROTs are made to highlight the gross errors that can occur if the two are misused for one another

Sonic environment of aircraft structure immersed in a supersonic jet flow stream

Test methods for determining the sonic environment of aircraft structure that is immersed in the flow stream of a high velocity jet or that is subjected to the noise field surrounding the jet, were investigated. Sonic environment test data measured on a SCAT 15-F model in the flow field of Mach 1.5 and 2.5 jets were processed. Narrow band, lateral cross correlation and noise contour plots are presented. Data acquisition and reduction methods are depicted. A computer program for scaling the model data is given that accounts for model size, jet velocity, transducer size, and jet density. Comparisons of scaled model data and full size aircraft data are made for the L-1011, S-3A, and a V/STOL lower surface blowing concept. Sonic environment predictions are made for an engine-over-the-wing SST configuration

Development of an advanced pitch active control system and a reduced area horizontal tail for a wide-body jet aircraft

The development of an advanced pitch active control system (PACS) and a reduced area horizontal tail for a wide-body jet transport (L-1011) with a flying horizontal stabilizer is discussed. The advanced PACS control law design objectives were to provide satisfactory handling qualities for aft c.g. flight conditions to negative static stability margins of 10 percent and to provide good maneuver control column force gradients for nonlinear stability flight conditions. Validity of the control laws were demonstrated by piloted flight simulation tests on the NASA Langley Visual Motion Simulator. Satisfactory handling qualities were actually demonstrated to a negative 20 percent static stability margin. The PACS control laws were mechanized to provide the system architecture that would be suitable for an L-1011 flight test program to a negative stability margin of 3 percent which represents the aft c.g. limits of the aircraft. Reduced area horizontal tail designs of 30 and 38 percent with respect to the L-1011 standard tail were designed, fabricated and wind tunnel tested. Drag reductions and weight savings of the 30 percent smaller tail would provide an L/D benefit of about 2% and the 38% small tail L/D benefit would be about 3 percent. However, forward c.g. limitations would have to be imposed on the aircraft because the maximum horizontal tail lift goal was not achieved and sufficient aircraft nose-up control authority was not available. This limitation would not be required for a properly designed new aircraft

Development of an advanced pitch active control system for a wide body jet aircraft

An advanced PACS control law was developed for a commercial wide-body transport (Lockheed L-1011) by using modern control theory. Validity of the control law was demonstrated by piloted flight simulation tests on the NASA Langley visual motion simulator. The PACS design objective was to develop a PACS that would provide good flying qualities to negative 10 percent static stability margins that were equivalent to those of the baseline aircraft at a 15 percent static stability margin which is normal for the L-1011. Also, the PACS was to compensate for high-Mach/high-g instabilities that degrade flying qualities during upset recoveries and maneuvers. The piloted flight simulation tests showed that the PACS met the design objectives. The simulation demonstrated good flying qualities to negative 20 percent static stability margins for hold, cruise and high-speed flight conditions. Analysis and wind tunnel tests performed on other Lockheed programs indicate that the PACS could be used on an advanced transport configuration to provide a 4 percent fuel savings which results from reduced trim drag by flying at negative static stability margins

Extended flight evaluation of a near-term pitch active control system

Fuel savings can be achieved by moving the center of gravity of an aircraft aft which reduces the static stability margin and consequently the trim drag. However, flying qualities of an aircraft with relaxed static stability can be significantly degraded. The flying qualities can be restored by using a pitch active control system (PACS). This report documents the work accomplished during a follow-on program (see NASA CR-165951 for initial program report) to perform extended flight tests of a near-term PACS. The program included flying qualities analyses, piloted flight simulation tests, aircraft preparation and flight tests to demonstrate that the near-term PACS provided good flying qualities within the linear static stability envelope to a negative 3% static stability margin

Breakdown of ITCZ-like PV Patterns

The Inter-Tropical Convergence Zone (ITCZ) is a zonal belt of intense convection, responsible for the genesis of over 80% of all tropical cyclones. This region of intense diabatic heating and shear results in a maximum of Ertel\u27s potential vorticity (PV) meeting Rayleigh\u27s necessary condition for barotropic instability. A fundamental issue is understanding the necessary precursor events leading to the breakdown of the ITCZ and subsequent formation of tropical cyclones. Our research examines the non-linear PV dynamics of the breakdown of both finite-length and infinite-length vorticity strips of varying widths and shapes, simulating the ITCZ found near the tropical eastern Pacific region. We have also introduced regularly and irregularly-spaced mass sinks embedded in the strips to simulate pockets of enhanced diabatic heating. To study the evolution, we have developed a shallow-water, normal-mode spectral model in Cartesian coordinates on the f-plane. Since the absolute vorticity divided by the fluid depth is materially conserved in the shallow water framework, we can draw an analogy to the evolution of Ertel\u27s PV in a stratified fluid. While the analogy is not exact, it does offer insight into to the fundamental dynamics of PV rearrangement. Comparisons with linear stability theory and observed cases are made to determine the extent to which linear theory captures the non-linear dynamics

The Effects of Display Type, Weather Type, and Pilot Experience on Pilot Interpretation of Weather Products

The majority of general aviation (GA) accidents involving adverse weather result in fatalities. Considering the high weather-related fatality rate among GA flight operations, it is imperative to ensure that GA pilots of all experience levels can incorporate available weather information into their flight planning. In the past decade, weather product development has incorporated increasing levels of automation, which has led to the generation of high-resolution, model-based aviation displays such as graphical turbulence guidance and current icing potential, which rival the resolution of radar and satellite imagery. This is in stark contrast to the traditional polygonal-based displays of aviation weather hazards (G-AIRMETs and SIGMETs). It is important to investigate the effects of these changes on the end user. Therefore, the purpose of this study was to compare the interpretability of weather products for two areas of interest: display type (traditional polygons vs. model-based imagery) and type of weather phenomena (ceiling/visibility, turbulence, and icing), across a range of pilot experience levels. Two hundred and four participants completed a series of weather product interpretation questions. The results indicated significant effects of product display type, as well as significant effects of weather phenomena and pilot experience on product interpretation. Further investigation is needed to assess possible extraneous variables