High Speed Civil Transport Aircraft Research Articles

Forward Flight Effects on Fan Noise from Supersonic 2-D Inlets

THE success of high-speed civil transport aircraft depends on the minimization of its environmental impact. Foremost among these is the aircraft community noise due to takeoff and landing. In addition to jet noise, forward-propagated engine fan noise is a significant component of the overall noise. The noise radiation directivity pattern is influenced by the design of the inlet. This is especially13; true for supersonic inlets where features such as translating centerbody, support struts, and auxiliary doors are contributing factors.

Performance characterization of the dynamic programming obstacle detection algorithm

A computer vision-based system using images from an airborne aircraft can increase flight safety by aiding the pilot to detect obstacles in the flight path so as to avoid mid-air collisions. Such a system fits naturally with the development of an external vision system proposed by NASA for use in high-speed civil transport aircraft with limited cockpit visibility. The detection techniques should provide high detection probability for obstacles that can vary from subpixels to a few pixels in size, while maintaining a low false alarm probability in the presence of noise and severe background clutter. Furthermore, the detection algorithms must be able to report such obstacles in a timely fashion, imposing severe constraints on their execution time. For this purpose, we have implemented a number of algorithms to detect airborne obstacles using image sequences obtained from a camera mounted on an aircraft. This paper describes the methodology used for characterizing the performance of the dynamic programming obstacle detection algorithm and its special cases. The experimental results were obtained using several types of image sequences, with simulated and real backgrounds. The approximate performance of the algorithm is also theoretically derived using principles of statistical analysis in terms of the signal-to-noise ration (SNR) required for the probabilities of false alarms and misdetections to be lower than prespecified values. The theoretical and experimental performance are compared in terms of the required SNR.

Intake-engine matching for high-speed civil transport powerplant design and analysis

Abstract This paper addresses the necessity to incorporate an intake-engine matching procedure in any procedure to analyze the off-design performance of engines designed to power high-speed civil transport aircraft. Most methods known to the author that are useable in the conceptual design phase of the aircraft (a phase characterized by the fact that very few design variables are known) only analyze the performance of the engine, without taking into account the design and performance of the intake. It will be shown in this paper, that the intake and the design exhibit a strong mutual influence, that cannot be neglected. An alternative method of analysis is presented. Particular reference will be made to the phenomenon of excess air and the resulting spillage drag. It will be shown that spillage air can be quite large in case of an HSCT design, especially in case the engine is designed for a high cruise Mach number. Assuming the presence of a sophisticated intake system generating multiple shocks in order to optimize the intake efficiency at the cruise condition, excess air at lower Mach numbers can amount to more than 60%.

Pneumatic Lift and Control Surface Technology for High Speed Civil Transports

Experimental evaluations have been conducted of blown high-lift devices and control surfaces applied to improve the low-speed terminal-area performance of generic High Speed Civil Transport (HSCT) aircraft. Plain blown flaps and advanced pneumatic high-lift devices have been integrated into highly swept vortex-dominated wings. These produced large lift increases, as well as significant drag reductions greater than full jet thrust recovery. Because conventional horizontal tails were inadequate to trim these configurations, blown canards were employed. In addition to providing positive lift increments for pitch trim, the canards were found to favorably influence the higher angle-of-attack vortex-lift characteristics of the wings. The downwash from these canards resulted in a delay of wing vortex burst. Details of these investigations and test results that confirm the effectiveness of combined pneumatic high-lift devices and control surfaces on these HSCT aircraft configurations are presented

Statistical Approximations for Multidisciplinary Design Optimization: The Problem of Size

Despite the steady increase of computing power and speed, the complexity of many of today's engineering analysis codes seems to keep pace with computing advances. Furthermore, the design and development of complex systems typically requires the integration of multiple disciplines and the resolution of multiple conflicting objectives. A departure from the traditional parametric design analysis and singleobjective optimization approaches is necessary for the effective solution of multidisciplinary, multiobjective complex design problems that rely on computer analyses. Statistical design of experiments and response surface modeling have been used extensively to create inexpensive-to-run approximations of expensive-to-run computer analyses and combat the problem of size associated with large, multidisciplinary design problems. However, these statistical approaches also break down because of the curse of dimensionality, wherein the number of design variables becomes too large to build accurate response surfaces efficiently. Speculations have been offered in the literature regarding the manageable problem size when these approaches are employed. In this paper, the limitations of these approaches are investigated and demonstrated explicitly by pushing the limits in a large-scale design problem. The design of a high-speed civil transport aircraft wing is used to illustrate 1) the use of these statistical techniques to facilitate multidisciplinary design optimization and 2) the resulting curse of dimensionality associated with large variable design problems. Our current research efforts in system partitioning and hierarchical modeling, and kriging (an alternative statistical approximation technique) are discussed as remedies for the problem of size.

Neural Network and Regression Approximations in High-Speed Civil Aircraft Design Optimization

Nonlinear mathematical-programming-based design optimization can be an elegant method. However, the calculations required to generate the merit function, constraints, and their gradients, which are frequently required, can make the process computational intensive. The computational burden can be greatly reduced by using approximating analyzers derived from an original analyzer utilizing neural networks and linear regression methods. The experience gained from using both of these approximation methods in the design optimization of a high speed civil transport aircraft is the subject of this paper. The Langley Research Center's Flight Optimization System was selected for the aircraft analysis. This software was exercised to generate a set of training data with which a neural network and a regression method were trained, thereby producing the two approximating analyzers. The derived analyzers were coupled to the Lewis Research Center's CometBoards test bed to provide the optimization capability. With the combined software, both approximation methods were examined for use in aircraft design optimization, and both performed satisfactorily. The CPU time for solution of the problem, which had been measured in hours, was reduced to minutes with the neural network approximation and to seconds with the regression method. Instability encountered in the aircraft analysis software at certain design points was also eliminated. On the other hand, there were costs and difficulties associated with training the approximating analyzers. The CPU time required to generate the input-output pairs and to train the approximating analyzers was seven times that required for solution of the problem.

Transport between the tropical and midlatitude lower stratosphere: Implications for ozone response to high‐speed civil transport emissions

Several recent studies have quantified the air exchange rate between the tropics and midlatitudes in the lower stratosphere using airborne and satellite measurements of chemical species. It is found that the midlatitude air is mixed into the tropical lower stratosphere with a replacement timescale of 13.5 months (with 20% uncertainty) for the region from the tropopause to 21 km [Volk et al., 1996] and at least 18 months for the region of 20–28 km [Schoeberl et al., 1997]. These estimates are used to adjust the horizontal eddy diffusion coefficients, Kyy, in a two‐dimensional chemistry transport model. The value of Kyy previously used to simulate the subtropical barrier, 0.03 × 106 m2/s, generates an exchange time of about 4 years, and the model without subtropical barrier (Kyy = 0.3 × 106 m2/s) has an exchange time of 5 months. Adjusting the Kyy to 0.13 × 106 m2/s from the tropopause to 21 km and 0.07 × 106 m2/s above 21 km produces the exchange timescales which match the estimates deduced from the measurements. The subtropical barrier prevents the engine emissions of the high‐speed civil transport (HSCT) aircraft from being transported into the tropics and subsequently lifted into the upper atmosphere or mixed into the southern hemisphere. The model results show that the calculated ozone response to HSCT aircraft emissions using the Kyy adjusted to observed mixing rates is substantially smaller than that simulated without the subtropical barrier.

A knowledge-based system integrated with numerical analysis tools for aircraft life-cycle design

An integrated design and manufacturing approach allows economic decisions to be made that reflect an entire system design as a whole. To achieve this objective, we have developed and utilized integrated cost and engineering models within a focused design perspective. A framework for the integrated design of an aircraft system with a combined performance and economic perspective is described in this article. This framework is based on the concept of Design Justification using a Design-for-Economics approach. We have developed a knowledge-based system that can be used to evaluate aircraft structural concept material and process selections. The framework consists of the knowledge-based system, integrated with numerical analysis tools including an aircraft performance/sizing code and a life-cycle cost analysis code. Production cost estimates are applied for evaluation of process trades at the subcomponent level of design. Life-cycle cost estimates are used for evaluation of process trades at the system level. Results of a case study are presented for several advanced wing structural concepts for a future supersonic commercial transport aircraft. Cost versus performance studies indicate that a high-speed civil transport aircraft with a hybrid wing structural concept, though more expensive to manufacture than some homogeneous concepts, can have lower direct operating costs due to a lower take-off gross weight and less mission fuel required.

Effects of Micro- and Macroscale Turbulent Mixing on the Chemical Processes in Engine Exhaust Plumes

Abstract Turbulent mixing and chemical reactions in the near field of an engine exhaust jet plume have been investigated using a mixing model that explicitly incorporates both large- and small-scale turbulent mixing and the molecular diffusion effects. A reduced reaction mechanism that accurately reproduces results of a detailed mechanism for the lower stratosphere was used to simulate the exhaust plume dynamics of a typical high-speed civil transport aircraft. This study shows that, compared to predictions based on models that do not include small-scale mixing and/or molecular diffusion effects, 30% less O3 and 15% less NOx are depleted in the near field of the plume. This suggests that the lack of local mixing can have an inhibiting effect on ozone depletion in the near-field plume. Inclusion of heterogeneous kinetics involving the formation of nitric and sulfuric acid due to water condensation on soot particles showed that 15% of the available NOx is converted into its inactive form but has a negligibl...

The effects of sulfur emissions from HSCT aircraft: A 2‐D model intercomparison

Four independently formulated two‐dimensional chemical transport models with sulfate aerosol microphysics are used to evaluate the possible effects of sulfur emissions from high‐speed civil transport (HSCT) aircraft operating in the stratosphere in 2015. Emission scenarios studied are those from Baughcum and Henderson [1995], while assumptions regarding the form of emitted sulfur are similar to those of Weisenstein et al. [1996]. All models show much larger increases in aerosol surface area when aircraft sulfur is assumed to be emitted as particles of 10 nm radius rather than as gas phase SO2. If we assume an emission index (EI) for SO2 of 0.4 gm (kg fuel burned)−1 in 2015, maximum increases in stratospheric sulfate aerosol surface area range from 0.1 μm2 cm−3 to 0.5 μm2 cm−3 with sulfur emitted as SO2 gas and from 1.0 μm2 cm−3 to 2.5 μm2 cm−3 with sulfur emitted as particles. Model differences in calculated surface area are deemed to be due mainly to differences in model transport. Calculated annual average ozone perturbations due to aircraft emissions with EI(NOx) = 5, EI(H2O) = 1230, and EI(SO2) = 0.4 range from −0.1% to −0.6% at 45°N for sulfur emission as SO2 gas and from −0.4% to −1.5% with sulfur emission as 100% particles. The effect of zonal and temporal inhomogeneities in temperature on heterogeneous reactions rates is accounted for in the Atmospheric and Environmental Research model and the Université degli Studi L'Aquila model and significantly increases the calculated ozone depletion due to HSCT, particularly for the cases with concurrent increases in aerosol surface area. Sensitivities to polar stratospheric clouds, background chlorine amount, additional heterogeneous reactions, and background aerosol loading are also explored.

EFFECTS OF CHOKING ON THE AEROACOUSTICS OF AN AXISYMMETRIC SUPERSONIC INLET

An experimental study was conducted to determine the effect of choking on the aerodynamic and acoustic performance of a supersonic inlet. The investigated inlet was a prototype model of a mixed compression, axisymmetric supersonic inlet designed for the high speed civil transport aircraft. A 10·4 cm (4·1 in) turbofan engine simulator was used in conjunction with the inlet. The inlet was tested with the centerbody in the fully extended position at different fan speeds. Results show that “soft choking”, as characterized by a reduction in forward propagating fan noise, can occur when the Mach number at the inlet throat exceeds 0·5. In the forward sector (0°–60° from the inlet axis), the overall sound pressure level was reduced by about 7 dB as the fan speed increased from 50,000 to 70,000 rpm, due to the increase in the Mach number at the inlet throat. Additional comparison was made between the inlet configurations with the centerbody fully extended and fully retracted at a fan speed of 50,000 rpm. The results show that the higher Mach number at the inlet throat for the full retracted centerbody configuration was successful in reducing the overall sound pressure level by about 4 dB between 0° and 30° angular sector. While there is no measurable difference in the total pressure recovery for the two inlet configurations, there is, however, a significant increase in the circumferential flow distortion at the fan face for the higher throat Mach number test case.

Statistical Experimentation Methods for Achieving Affordable Concurrent Systems Design

We describe an affordable method for designing in the conceptual stage using relatively high-fidelity concurrent systems analysis. Our method is rooted in three domains, namely, the design of experiments, the response surface methodology, and the compromise decision support problem. A sequential experimentation strategy as well as the heuristic rules for creating high-order response surface models are introduced as a cost-effective approach to applying the statistical experimentation methods in design of complex systems. A high-speed civil transport aircraft design is used as an example to illustrate the potential of our approach.

What we do with Human Factors Data and Theory: A Flight Deck Design Philosophy for the High Speed Civil Transport Aircraft

This paper reports on the results and lessons learned from constructing a design philosophy for a new aircraft. The High Speed Civil Transport aircraft is the next-generation supersonic transport, planned for initial operating capability in 2005. Current objectives for the aircraft include cruise speeds of Mach 2.4, ability to take off and land in low visibility, and restricted forward vision. These objectives necessitate consideration of major changes in some of the functions currently allocated to the human flight crew. An explicit design philosophy was defined as the first step in ensuring that system development proceeded with clear emphasis on supporting the human operators in accomplishing the goals of transporting their passengers and cargo safely, comfortably, efficiently and on schedule. This paper discusses the development and details of the integrated flight deck design philosophy that will be used to guide the development of a High Speed Civil Transport flight deck. The paper describes • the goals, scope and benefits of the flight deck design philosophy; • the effect on the current system development process; • the method used to produce the design philosophy; • examples of the philosophy and guideline statements, with rationale; • and finally, suggestions for improving the transfer of basic and applied research into the system design process.

Possible effects of CO2 increase on the high‐speed civil transport impact on ozone

The role of heterogeneous chemistry on the potential impact on ozone of a commercial fleet of high speed civil transport aircraft (HSCT) has been recently studied with assessment models. Here an attempt is made to model the effects of the carbon dioxide increase which is predicted in the future atmosphere when HSCT should be operational. For this purpose we have first used a three‐dimensional model for the radiative and dynamical calculations and then a photochemical two‐dimensional model including an explicit gas‐particle interaction in the process of aerosol formation. The denoxification and denitrification associated with the formation of nitric acid trihydrate (NAT) aerosols is shown to significantly affect the partition of chemical families. The radiative perturbation introduced by the CO2 increase is shown to perturb the stratospheric dynamics in such a way that the lower stratospheric residual circulation is enhanced. This has the effect of reducing by about 15% the stratospheric residence time of odd nitrogen injected by the aircraft, so that the overall perturbation of stratospheric chemistry due to HSCT is mitigated with respect to the reference case in which CO2 is kept at the present level. Another effect is found to be produced by the stratospheric temperature cooling following the CO2 increase. Our model predicts a large enhancement of the surface area density of NAT aerosols in the arctic region, so that the additional denitrification produces a further decrease of the relative role of the NOx catalytic cycle for ozone destruction in the lower stratosphere. For this reason, the ClO and OH decreases associated with the HSCT‐induced NOx increase are found to be dominant in the ozone budget, thus producing a global ozone increase in the case of 500 ppmv CO2 (+0.27% for mach 2.4 and NOx emission index 15). The balance between the different tendencies of ClO, NOx, and OH cycles is found to be closer in the reference case of 335 ppmv CO2, where a small column ozone depletion by HSCT is predicted (−0.53% globally).

Modelling of ozone reduction by stratospheric aircraft

Using a two-dimensional model of the atmospheric circulation and composition, different scenarios of the effects of stratospheric aircraft on ozone layer destruction were calculated. It is shown that the ozone loss depends strongly on the altitude and composition of engine emissions from high-speed civil transport aircraft. The inclusion in the two-dimensional model of the effects of chemical eddies results in significantly reduced ozone losses in the high latitudes of the northern hemisphere during wintertime, when the dynamics of the stratosphere are strongly disturbed by planetary waves. This result can be connected with the increase of stratosphere/troposphere exchange.

Effects on stratospheric ozone from high‐speed civil transport: Sensitivity to stratospheric aerosol loading

The potential impact of high‐speed civil transport (HSCT) aircraft emissions on stratospheric ozone and the sensitivity of these results to changes in aerosol loading are examined with a two‐dimensional model. With aerosols fixed at background levels, calculated ozone changes due to HSCT aircraft emissions range from negligible up to 4–6% depletions in column ozone at northern high latitudes. The magnitude of the ozone change depends mainly on the NOx increase due to aircraft emissions, which depends on fleet size, cruise altitude, and engine design. The partitioning of the odd nitrogen species in the lower stratosphere among NO, NO2, N2O5, and HNO3 is strongly dependent on the concentration of sulfuric acid aerosol particles, and thus the sensitivity of O3 to NOx emissions changes when the stratospheric aerosol loading changes. Aerosol concentrations 4 times greater than background levels have not been unusual in the last 2 decades. Our model results show that a factor of 4 increase in aerosol loading would significantly reduce the calculated ozone depletion due to HSCT emissions. Because of the natural variability of stratospheric aerosols, the possible impact of HSCT emissions on ozone must be viewed as a range of possible results.

Plume and wake dynamics, mixing, and chemistry behind a high speed civil transport aircraft

The environmental perturbations caused by the exhaust of a high speed civil transport (HSCT) depend on the deposition altitude and the amount and composition of the emissions. The chemical evolution and the mixing and vortical motion of the exhaust need to be analyzed to track the exhaust and its speciation as the emissions are mixed to atmospheric scales. Elements of an analytic model of the wake dynamical processes are being developed to account for the roll-up of the trailing vorticity, its breakup due to the Crow instability, and the subsequent evolution and motion of the reconnected vorticity. The concentrated vorticity is observed to wrap up the buoyant exhaust and suppress its continued mixing and dilution. The chemical kinetics of the important pollutant species will be followed throughout the plume and wake. Initial plume mixing and chemistry are calculated using an existing plume model, standard plume flowfield (SPF), with additional H/C/O, OH/SO2, and NOj, chemistry and equilibrium H2O condensation included. The species tracked include those that could be heterogeneously reactive on the surfaces of the condensed solid water (ice) particles when condensation occurs, and those capable of reacting with exhaust soot particle surfaces to form active contrail and/or cloud condensation nuclei (ccn).

Two- and three-dimensional grid generation by an algebraic homotopy procedure

An algebraic method for generating two- and three-dimensional grid systems for aerospace vehicles is presented. The method is based on algebraic procedures derived from homotopic relations for blending between inner and outer boundaries of any given configuration. Stable properties of homotopic maps have been exploited to provide near-orthogonality and specified constant spacing at the inner boundary. The method has been successfully applied to analytically generated blended wing-body configurations as well as discretely defined geometries such as the High-Speed Civil Transport Aircraft. Grid examples representative of the capabilities of the method are presented.

Impact of heterogeneous chemistry on model‐calculated ozone change due to high speed civil transport aircraft

Heterogeneous chemistry could have a very significant effect on the predicted impact of engine exhaust from high speed civil transport (HSCT) aircraft on atmospheric ozone. Two‐dimensional models including only gas phase chemistry indicate that deposition of nitrogen oxides from aircraft exhaust in the lower stratosphere would significantly perturb the natural nitrogen budget, most likely resulting in ozone depletion. The model calculates that an injection of 1 megaton of NO2 per year at 17–20 km would decrease the column ozone by 3–6% at northern mid latitudes using gas phase chemistry only. Inclusion of the reaction acting on the global sulfate aerosol layer greatly decreases the sensitivity of ozone to injection of nitrogen oxides, with the calculated ozone column increasing by up to 0.4% for the same emission scenario. Additional simulations showed that this response is only slightly sensitivity to changes in chlorine content and aerosol loading.

Polyimide Matrix Composites: Candidates for High Speed Commercial Aircraft or not?

Several aerospace companies are actively pursuing the development of a 'high speed civil transport aircraft' (HSCT). Flight profiles and weight considerations dictate the use of high temperature advanced composites. This paper briefly examines two such contenders-PMR-15 and bismaleimides (BMIs). Materials are compared in the categories of thermo-oxidative stability, resistance to thermal cycling, damage tolerance, toxicity and ease of fabrication. At present, it would appear that neither PMR-15 nor BMIs, in general, are capable of meeting HSCT requirements. PMR-15 seems to be hampered by its susceptibility to microcracking, monomer toxicity and difficult fabrication. On the other hand, the use of BMIs seems to be hampered by their relatively poor thermo-oxidative stability. These views assume an aircraft with a maximum operating temperature of about 350°F. Should this requirement change, then the picture will change also and other materials could be considered.