Flying qualities design criteria applicable to supersonic cruise aircraft

A comprehensive set of flying qualities design criteria was prepared for use in the supersonic cruise research program. The framework for stating the design criteria is established and design criteria are included which address specific failures, approach to dangerous flight conditions, flight at high angle of attack, longitudinal and lateral directional stability and control, the primary flight control system, and secondary flight controls. Examples are given of lateral directional design criteria limiting lateral accelerations at the cockpit, time to roll through 30 deg of bank, and time delay in the pilot's command path. Flight test data from the Concorde certification program are used to substantiate a number of the proposed design criteria

Application of Calspan pitch rate control system to the Space Shuttle for approach and landing

A pitch rate control system designed for use in the shuttle during approach and landing was analyzed and compared with a revised control system developed by NASA and the existing OFT control system. The design concept control system uses filtered pitch rate feedback with proportional plus integral paths in the forward loop. Control system parameters were designed as a function of flight configuration. Analysis included time and frequency domain techniques. Results indicate that both the Calspan and NASA systems significantly improve the flying qualities of the shuttle over the OFT. Better attitude and flight path control and less time delay are the primary reasons. The Calspan system is preferred because of reduced time delay and simpler mechanization. Further testing of the improved flight control systems in an in-flight simulator is recommended

Mission-oriented requirements for updating MIL-H-8501: Calspan proposed structure and rationale

This report documents the effort by Arvin/Calspan Corporation to formulate a revision of MIL-H-8501A in terms of Mission-Oriented Flying Qualities Requirements for Military Rotorcraft. Emphasis is placed on development of a specification structure which will permit addressing Operational Missions and Flight Phases, Flight Regions, Classification of Required Operational Capability, Categorization of Flight Phases, and Levels of Flying Qualities. A number of definitions is established to permit addressing the rotorcraft state, flight envelopes, environments, and the conditions under which degraded flying qualities are permitted. Tentative requirements are drafted for Required Operational Capability Class 1. Also included is a Background Information and Users Guide for the draft specification structure proposed for the MIL-H-8501A revision. The report also contains a discussion of critical data gaps and attempts to prioritize these data gaps and to suggest experiments that should be performed to generate data needed to support formulation of quantitative design criteria for the additional Operational Capability Classes 2, 3, and 4

Flight Evaluation of an Aircraft with Side and Center Stick Controllers and Rate-Limited Ailerons

As part of an ongoing government and industry effort to study the flying qualities of aircraft with rate-limited control surface actuators, two studies were previously flown to examine an algorithm developed to reduce the tendency for pilot-induced oscillation when rate limiting occurs. This algorithm, when working properly, greatly improved the performance of the aircraft in the first study. In the second study, however, the algorithm did not initially offer as much improvement. The differences between the two studies caused concern. The study detailed in this paper was performed to determine whether the performance of the algorithm was affected by the characteristics of the cockpit controllers. Time delay and flight control system noise were also briefly evaluated. An in-flight simulator, the Calspan Learjet 25, was programmed with a low roll actuator rate limit, and the algorithm was programmed into the flight control system. Side- and center-stick controllers, force and position command signals, a rate-limited feel system, a low-frequency feel system, and a feel system damper were evaluated. The flight program consisted of four flights and 38 evaluations of test configurations. Performance of the algorithm was determined to be unaffected by using side- or center-stick controllers or force or position command signals. The rate-limited feel system performed as well as the rate-limiting algorithm but was disliked by the pilots. The low-frequency feel system and the feel system damper were ineffective. Time delay and noise were determined to degrade the performance of the algorithm

A study of pulsed thermography for life assessment of thin EB-PVD TBCs undergoing oxidation ageing

This paper presents an assessment of ageing for thin Thermal Barrier Coatings (TBC) using active thermography. As TBCs undergo ageing during their service life, sintering changes the porosity, elements migrate from the substrate, and micro-cracks build up in the structure of the material, exhibiting a change in thermal conductivity and diffusion properties. As the material ages and these properties change over time, it is possible to exploit trends in this change for characterisation of coating ageing, which would provide a diagnostics tool to estimate remaining useful life. In this study, through-depth diffusivity measurement has been applied to thin EB-PVD coatings which are artificially aged via oxidation furnace cycles. In order to address the difficulties of capturing a fast thermal event in a thin coating, a novel parametric study approach has been carried out to optimise data capture and analysis, maximising available frames for the model fitting step. Through-depth diffusivities have been measured during ageing for six samples, yielding a repeatable trend in thermal diffusivity measurements, with three features, which can be exploited for ageing characterisation of thin EB-PVD TBCs, and used as an alarm of imminent failure

Insensitivity of alkenone carbon isotopes to atmospheric CO₂ at low to moderate CO₂ levels

Atmospheric pCO2 is a critical component of the global carbon system and is considered to be the major control of Earth’s past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document pCO2 for the past 800 kyrs, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO2: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ11B) of foraminifer shells. Here we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B records, suggesting caution in the interpretation of alkenone-based records at low pCO2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO2

Nitrogen loss (NH3, N2O) patterns in bench-scale composting.

Nitrogen (N) losses during composting reduce the value of the end product as a fertilizer. Nitrogen is lost during composting mainly by ammonia (NH3) volatilization in the thermophilic phase. We used three bench-scale aerobic bioreactors with a controlled temperature difference (CDT) system as an experimental approach to investigate the pattern of N losses during composting. N2O peak emission occurred much earlier (7h) than NH3 volatilization (48-60h) during the thermophilic phase (~55°C) of bench-scale composting. The NH3 volatilization peak rate occurred following the greater biological activity (O2 consumed/CO2 evolved) at 40°C which could coincide with greater ammonification, but immobilization of NH4+/NH3 also occurs at this point affecting NH3 volatilization. Differences in temperature curves and accumulated NH3-N were related to the biological activity in each vessel. Therefore, O2 consumed/CO2 evolved measurements must be part of the evaluation of composting in further studies for comparisons of techniques to reduce NH3 volatilizatio

Stress-Particle Smoothed Particle Hydrodynamics: an application to the failure and post-failure behaviour of slopes

We present a new numerical approach in the framework of Smooth Particle Hydrodynamics (SPH) to solve the zero energy modes and tensile instabilities, without the need for the fine tuning of non-physical artificial parameters. The method uses a combination of stress-points and nodes and includes a new stress-point position updating scheme that also removes the need to implement artificial repulsive forces at the boundary. The model is validated for large deformation geomechanics problems, and is able to simulate strain localisation within soil samples and slopes. In particular, the new model produces stable and accurate results of the failure and post-failure of slopes, consisting of both cohesive and cohesionless materials, for the first time

Changing expectations about speed alters perceived motion direction

SummaryOur perceptions are fundamentally altered by our knowledge of the world. When cloud-gazing, for example, we tend spontaneously to recognize known objects in the random configurations of evaporated moisture. How our brains acquire such knowledge and how it impacts our perceptions is a matter of heated discussion. A topic of recent debate has concerned the hypothesis that our visual system ‘assumes’ that objects are static or move slowly [1] rather than more quickly [1–3]. This hypothesis, or ‘prior on slow speeds’, was postulated because it could elegantly explain a number of perceptual biases observed in situations of uncertainty [2]. Interestingly, those biases affect not only the perception of speed, but also the direction of motion. For example, the direction of a line whose endpoints are hidden (as in the ‘aperture problem’) or poorly visible (for example, at low contrast or for short presentations) is more often perceived as being perpendicular to the line than it really is — an illusion consistent with expecting that the line moves more slowly than it really does. How this ‘prior on slow speeds’ is shaped by experience and whether it remains malleable in adults is unclear. Here, we show that systematic exposure to high-speed stimuli can lead to a reversal of this direction illusion. This suggests that the shaping of the brain's prior expectations of even the most basic properties of the environment is a continuous process