Subsonic Aircraft Research Articles

Design and power calculation of HLFC suction system for a subsonic short-range aircraft

Hybrid laminar flow control (HLFC) can be a possible solution for future sustainable energy-efficient aviation. The current study proposes a MATLAB-based numerical tool for the design of the suction system for an airfoil optimized for a subsonic short-range HLFC application. Considerable energy losses may occur when the air passes through the perforated metallic outer surface and the inner structure of the suction system. A semi-empirical approach is used to design a layout that provides a target suction velocity based on measured pressure losses through porous medium and substructures. Flowbench measurements were performed on 3D-printed internal core test samples to quantify the pressure losses that can be used to create a lower pressure below the porous sheet matching the target suction velocity. The actual suction realized on the airfoil using this substructure concept has a discrete nature that increases with the distance between two adjacent walls. Finally, the suction system’s power requirement is calculated. The power requirement for distributed suction accounts for the pressure loss characteristics of the porous material, the internal core structure, and throttling holes. However, the study does not include the ducting losses from the substructure to the compressor. Approximately 80% of the total suction power is utilized to eject the sucked air back to the freestream conditions for a system with a compressor and propulsive system efficiency equal to one. The study analyses the performance of the designed internal core layout to different flight conditions and addresses the suction power requirement variation with lift coefficient and flight altitude.

Feasibility Study of Concave Wing Design for Subsonic Aircraft (NACA 2412)

In this current world of technology, airfoil has been produced for concave wing in many different shapes in terms of root size, tip, existence of winglet and different thickness.Concave wing isthe tendency of a wing to bend during flying at a certain height of deflection. Itincreased higher velocity of the aircraft,mainly due to the increase of lift force produced above the wing.However bySolidWorks,airfoil design for concave wing with NACA 2412 has been choosen.In this study, 0.2m deflection shows the highest lift coefficient andlift drag ratio compared to other height of deflection.The maximum value of CLobtained is 1.517, while for CL/CDis 37.708. This indicates that the airfoil can produce high lift even at low angle of attack, which is beneficial when aircraft wants to take-off, climbing and landing.

Modeling and Analysis of Meteorological Contour Matching with Remote Sensor Data for Navigation

This paper outlines the methods, results, and statistical analysis of a model we developed to demonstrate the feasibility of applying remote sensor meteorological data to navigation by using meteorological contour matching (METCOM). Terrain contour matching (TERCOM), a contemporary navigation system, possesses inherent performance flaws that may be resolved and improved by METCOM for subsonic and hypersonic missile or aircraft navigation. Remote sensor imagery data for this model was accessed from the Geostationary Operational Environmental Satellites-R Series operated by the National Oceanic and Atmospheric Administration by using Amazon Web Services through a script we developed in Python. Data processed for the model included imagery data and corresponding geospatial data from the legacy atmospheric profile products: legacy vertical temperature and legacy vertical moisture. Our analysis of the model included an error assessment to determine model accuracy, geostatistical analysis through semivariograms, meteorological signal of model data, and a combinatorial analysis to evaluate navigation performance. We conducted a model assessment which indicated an accuracy of 66.2% in the data used as a combined result of instrument error and interference of cloud formations. Results of the remaining analysis offered methods to evaluate METCOM performance and compare different meteorological data products. These results allowed us to statistically compare METCOM and TERCOM, yielding several indications of improved performance including an increase by a factor of at least 13.5 in data variability and contourability. The analysis we conducted served as a proof of concept to justify further research into the feasibility and application of METCOM.

On the Fundamental Possibility of a Supersonic Civil Aircraft to Comply with ICAO Noise Requirements Using Existing Technologies

Compliance with environmental protection regulations, in particular, community noise requirements, constitutes one of the major obstacles for designing future supersonic civil aircraft. Although there are several noise sources that contribute to the total noise level of supersonic aircraft, it is the turbulent jet that appears most problematic; jet noise is a dominant noise source for low-to moderate- bypass-ratio engines, and at present there are no effective methods of jet noise reduction other than decreasing jet speed by increasing bypass ratio, which, in turn, is constrained by aerodynamic requirements for supersonic flight. The present study considers a concept of supersonic civil aircraft under the assumption that its total noise is determined by turbulent jets; it is shown that compliance of the supersonic aircraft with the current regulations for subsonic aircraft noise (Chapter 14 Volume I Annex 16 ICAO) would require the decreased jet speed that corresponds to a prohibitively high bypass ratio of aircraft engines. To enable jet noise reduction without necessarily increasing bypass ratio, a novel configuration of supersonic aircraft is proposed that meets the requirements of Chapter 14, thereby demonstrating that the norms of Chapter 14 are achievable for future supersonic civil aircraft with the use of existing technologies.

Identifying the ozone-neutral aircraft cruise altitude

Depletion of stratospheric ozone, and the associated increase in population exposure to UV radiation, is an environmental consequence of high-altitude, supersonic aviation. Assessments of the impacts of emissions from subsonic aircraft – which fly at lower altitudes – have instead shown that they produce a net increase, rather than decrease, in global net ozone, suggesting the existence of an intermediate “column ozone neutral” cruise altitude. Knowing this altitude and its variation with factors such as latitude, season, and fuel composition could provide a pathway towards reducing the environmental impacts of aviation, but would require a prohibitive number of atmospheric simulations. We instead use the newly developed GEOS-Chem tropospheric-stratospheric adjoint to identify the location of the column ozone-neutral aircraft cruise altitude as a function of these factors. We show that, although the mean ozone neutral altitude is at 13.5 km globally, this varies from 14.6 km to 12.5 km between the equator and 60°N. This altitude varies by less than a kilometer between seasons, but the net depletion resulting from flying at greater altitudes varies by a factor of two. We also find that eliminating fuel sulfur would result in a neutral altitude 0.5–1.0 km greater than when conventional jet fuel is burned. Our results imply that a low Mach number supersonic aircraft burning low-sulfur fuel (e.g. biofuels) may be able to achieve net zero global ozone change. However, for a fleet to achieve ozone neutrality will require careful consideration of the non-linear variation in sensitivity with altitude and latitude.

Aerodynamic analysis of bionic winglet- slotted wings

The work concerned represents a winglet design inspired by birds with slotted wings. Slotted wings are known to exhibit optimum characteristics in terms of reducing the generation of vortices, enhancing roll stability, countering induced drag, and enhancing lift and stall characteristics. Light is shed on these parameters while designing the model. Key aerodynamic parameters are also highlighted. The model is further simulated to obtain the change in the characteristics of multiple aerodynamic parameters, concerned with wingtips and winglets. The main area of concern is the reduction in the values of drag, specifically the induced drag, as it is a major contributing factor in a subsonic aircraft’s overall drag generation. The work included in this paper is a study on an albatross wing to improve its maneuverability and its aerodynamic characteristics so that it can be used in a bionic UAV with better endurance and roll control. These slots can later be made to actuate at different angles. This study acts as a base for further research.

Drag Reduction Technology for Subsonic Aircraft

Drag Reduction Technology for Subsonic Aircraft

The jet fuels anti-wear properties indicator

There are three main fuel brands for jet engines of civil aviation used: domestic TS-1 and RT and foreign, produced in relatively small volumes in Russia, JET A-1 (JET A-1). Since the end of the 2000s, foreign manufacturers have made claims to the quality of the mass-used domestic fuel brand TS-1, and these claims have not been specified. However, the service life of a number of foreign engines operating on TS-1 fuel has been reduced by 50%. This circumstance can be caused by both subjective reasons – commercial and political interests of equipment manufacturers, and the objective ones. The main objective reason may be that recently several Russian plants producing TS-1 fuel have begun to produce composite propellant under the same name, where products of secondary oil refining processes are added to the straight-run fractions. These fuels meet the requirements of the standard (GOST 10227-86), which does not contain an indicator that characterizes the anti-wear properties of jet fuels. In the standard for JET A-1 fuel, anti-wear properties are normalized, and they are also normalized in the standard for domestic fuels for supersonic aviation. The article presents comparative tests of anti-wear properties of samples of jet fuels used in the civil aviation. The article substantiates the relevance of the anti-wear properties indicator in the standard for domestic brands of jet fuels for subsonic aircraft introduction, as well as the comparative analysis of the anti-wear properties of fuels produced by various Russian oil refineries. Indicators and methods for assessing the anti-wear properties of aviation fuels can be different. As such an indicator, it is proposed to use the anti-wear properties indicator calculated after testing fuel samples on a four-ball friction machine.

Numerical Study on the Effect of Natural Gas on Aircraft Turbofan Engine Propulsion

The world has been concerned and worried about the depletion of the liquid oil fuel, besides new environmental rules are to be followed to reduce pollution hazards and global warming. The utilization of natural gas (as a near term fuel) and hydrogen (as long-term fuel) are receiving great attention, because they have less pollution effects. Since the aviation has a great deal in environmental pollution effects due to the cruise flight in the upper troposphere (supersonic aircraft) or in the lower stratosphere (subsonic aircraft) where most of the ozone concentrate, which helps in protecting the earth form ultra violet radiation. Therefore, the use of alternate fuel has a great attention in aviation. In the present study, the thrust specific fuel consumption and specific thrust for the aircraft during aircraft flight profile are predicted, when using aviation fuel and natural gas. The P&W JT9D –7R-turbofan jet engine is taken as a base line engine propelling the Boeing 747-200 aircraft as a base line aircraft with four engine nacelles mounted on wings. The model engine fuel-air cycle representation is carried out for design point calculations based on sea level static conditions and variable specific heats along engine components. The predicted engine performance results compared very well with the reported values by the manufacture. Predictions carried out using aviation fuel and natural gas show an increase in the specific thrust by 3% and decrease in the thrust specific fuel consumption by 14% and fuel to air ratio by 11%, when using natural gas.

AN ALTERNATIVE APPROACH TO INDUCED DRAG REDUCTION

Induced drag constitutes approximately 40% of the total drag of subsonic civil transport aircraft at cruise conditions. Various types of winglets and several non-planar concepts, such as the C-wing, the joined wings, and the box plane, have been proposed for its reduction. Here, a new approach to induced drag reduction in the form of a combination of an elliptical and an astroid hypocycloid lift distribution is put forward. Lift is mainly generated from high circulation in the center part of the wing and fades away along the semi-span towards the wing tip. Using lifting line theory, the analysis shows that for fixed lift and wingspan the combined lift distribution results in an induced drag reduction of 50% with respect to the elliptical distribution. Due to its wing planform the combined lift distribution leads to a 51.5% higher aspect ratio. If structural constraints are placed, then the higher aspect ratio may affect wing weight. Although any substantial increase of wing weight is not envisaged, further study of the matter is required. Zero-lift drag and lift-dependent drag due to skin friction and viscosity-related pressure remain unaffected. The proposed lift distribution is particularly useful in a blended wing-body design.

A transonic, viscous nonlinear frequency domain Vortex Lattice Method for aeroelastic analyses

The Unsteady Vortex Lattice Method has interesting capabilities for nonlinear subsonic aeroelastic analyses. This paper aims to develop an aeroelastic framework based on the UVLM that is suitable for compressible, transonic and viscous unsteady flows. To achieve these modeling capabilities, the UVLM is first extended to the nonlinear frequency domain using the harmonic balance approach. Secondly, sectional corrections are applied from a steady 2D/2.5D database of aerodynamic forces computed with high-fidelity Euler/RANS flow solvers. The angle of attack coupling scheme on the lift force is complemented by a least-square procedure also coupling the pitching moment. Finally, an approximation of the retarded time is implemented in the influence kernel of the harmonic balance formulation of the UVLM to account for unsteady compressibility. The aerodynamic model is verified against time domain high-fidelity solutions with pitching airfoils in 2D and in 3D with a pitching constant chord NACA 0012 swept wing. Thereafter, the HB/LCO approach is applied with the frequency domain UVLM to 2D and 3D aeroelastic problems and compared against high-fidelity solutions. The proposed framework is capable of capturing strong nonlinear Limit Cycle Oscillation behaviors at high Mach numbers, as well as the flutter boundary for a wide range of Mach numbers while maintaining a low computational cost. As a result, the proposed framework could be of interest for preliminary design and Multi-Disciplinary Design (MDO) optimizations in the context of subsonic and transonic aircraft design.

Mathematical Modeling of Interferential Flow around the Finned Body in the Transport Compartment and When Exiting Thereof at Subsonic Aircraft Movement

Mathematical Modeling of Interferential Flow around the Finned Body in the Transport Compartment and When Exiting Thereof at Subsonic Aircraft Movement

Application of Noise Certification Regulations within Conceptual Aircraft Design

ICAO Annex 16 regulations are used to certify the acoustic performance of subsonic transport aircraft. Each aircraft is classified according to the measured EPNL levels at specific certification locations along the approach and departure. By simulating this certification process, it becomes possible to identify all relevant parameters and assess promising measures to reduce the noise certification levels in compliance with the underlying ICAO regulations, i.e., allowable operating conditions of the aircraft. Furthermore, simulation is the only way to enable an assessment of novel technology and non-existing vehicle concepts, which is the main motivation behind the presented research activities. Consequently, the ICAO Annex 16 regulations are integrated into an existing noise simulation framework at DLR, and the virtual noise certification of novel aircraft concepts is realized at the conceptual design phase. The predicted certification levels can be directly selected as design objectives in order to realize an advantageous ICAO noise category for a new aircraft design, i.e., simultaneously accounting for the design and the resulting flight performance. A detailed assessment and identification of operational limits and allowable flight procedures for each conceptual aircraft design under consideration is enabled. Sensitivity studies can be performed for the relevant input parameters that influence the predicted noise certification levels. Specific noise sources with a dominating impact on the certification noise levels can be identified, and promising additional low-noise measures can be applied within the conceptual design phase. The overall simulation process is applied to existing vehicles in order to assess the validity of the simulation resultsfcompared to published data. Thereafter, the process is applied to some DLR low-noise aircraft concepts to evaluate their noise certification levels. These results can then be compared to other standard noise metrics that are typically applied in order to describe aircraft noise, e.g., SEL isocontour areas. It can be demonstrated that certain technologies can significantly reduce the noise impact along most of an approach or departure flight track but have only a limited influence on the noise certification levels and vice versa. Finally, an outlook of the ongoing developments is provided, in order to apply the new simulation process to supersonic aircraft. Newly proposed regulations for such concepts are implemented into the process in order to evaluate these new regulations and enable direct comparison with existing regulations.

A history of jet noise research at the National Aeronautics and Space Administration.

This paper reviews jet noise research conducted at the National Aeronautics and Space Administration (NASA) from the early 1950s to the present day. Research conducted by NASA's predecessor, the National Advisory Committee for Aeronautics (NACA), and during the early years of NASA focused on turbojet noise, where a common approach for reducing jet noise was to limit the jet exit velocity to speeds that provided acceptable noise levels. Suppressors tested during this time resulted in thrust losses that were too severe to be implemented. With the introduction of turbofan engines in the 1960s, NASA shifted research to programs for both subsonic and supersonic aircraft applications with specific noise reduction goals. Subsonic research focused on increasing the bypass ratio of the engine to reduce the jet exit velocity of the core exhaust and adding mixers to the dual exhaust streams. Advances in computational methods improved aerodynamic designs and jet noise prediction tools. Supersonic applications proved to be more troublesome as programs aimed at large commercial transports required higher specific thrust engines. Changing the engine cycle to reduce jet noise was not compatible with mission range and speed requirements. Research for supersonic commercial aircraft remains an area of interest today at NASA.

Improving single flyover noise prediction for subsonic aircraft

Current ICAO Doc 9911 provides the algorithm to calculate aircraft noise levels for any kind of airport flight scenario. The essential difference exists between the measured and calculated sound levels, especially for single flight noise events. Doc 9911 recommends using this method for equivalent sound levels L and noise indices L first of all. A number of national noise regulations still require for single noise event assessment. An article analyzes a number of reasons to explain the inaccuracy of noise event calculations. For example, the differences between calculated balanced flight parameters (thrust and velocity first of all) and supervised in real flights may influence the accuracy first of all. Statistical data was gathered to make more general view on these differences and some proposal to use them in calculations has being proved. Also, the assumptions of the ICAO Doc 9911 method may contribute to the inaccuracy of calculations. Among them are the homogeneous atmosphere for sound propagation, generalized for overall fleet noise directivity pattern, etc. Ground effect model defines the values for aircraft absent in operation currently. The first assumption provides a conflict with flight path calculations for varied atmosphere parameters with height over the surface.

Performance Improvement of Subsonic aircraft wing by Dimple Effect

Improving lift and drag ratio is the most important parameter that helps to improving the aerodynamic efficiency of the wing Vortex generators are used to delay flow separators for higher angle of attacks. Simple on surface of body tend provide vortex to delay flow separators and make boundary layer attached with the surface. NACA 0018 symmetrical aerofoil is considered for analysis of dimple in various position on the wing like leading edge, middle of the wing and end of the wing to predict optimum position. In that dimple in middle of the wing shows good improvement in delaying the flow separation this improves the lift to drag ratio compared to other position of the wing.

Utilization of Low-Potential Energy Through to the Use in Aircraft Fuel System

The article discusses the possibility of improving the main characteristics (efficiency, specific thrust) of a gas turbine engine by using liquefied natural gas (LNG) as fuel. This possibility is considered on the example of using as fuel instead of aviation kerosene on PS-90A and NK-93 engines. The parameters of the engine were determined at various stages in the cruise flight mode when operating on kerosene and LNG. The parameters evaluating the fuel consumption of the engine are calculated and compared for both fuels. The performance characteristics for kerosene and LNG were evaluated in the system of the Tu-330 subsonic transport aircraft. Energy losses during storage of cryogenic fuel on board the aircraft are estimated.

A completely reusable aerospace system based on subsonic carrier with the return of the first stages to the starting point

The concept of aerospace system based on air launch from subsonic twin-fuselage aircraft and the rocket launch into orbit is investigated. The scheme of aerospace system trajectory providing a return to the starting point both of the carrier and the first rocket stage with liquid-fuel motors is proposed. It was shown that the use of subsonic carrier as a launching platform of the rocket system increases the payload mass by 1.2% of the rocket segment MTOW as compared to autonomous ground take-off. The comparative analysis of three versions of carrier aircraft and three fuel options at the first rocket stage was carried out. Analysis showed that compared to kerosene variant the hydrogen hypersonic booster makes it possible to significantly increase the payload mass while the launching costs stay the same.

Steady tangential control jet for improving the effectiveness of a rudder under one-engine inoperative condition

The aim of the research is to numerically investigate the use of a steady tangential control jet (CJ) at the hinge of the vertical stabilizer as an active flow control (AFC) technique to improve the effectiveness of a rudder on a subsonic aircraft during one-engine inoperative (OEI) condition by keeping the flow attached to the control surface. The goals are in two folds: firstly to investigate the effects of CJ parameters, specifically the jet-to-freestream velocity ratio (rV ) and the jet slot height ratio (rH ), on the vertical stabilizer performance, and secondly to find the optimum CJ condition that yields the improved and optimal performance. In this regard, the optimal condition of the CJ is prescribed as the condition that gives the maximum side force to drag ratio under the requirements that the required minimum trim side force can be achieved and there is an improvement in control surface margin for yawing motion. The investigation is carried out through computational fluid dynamics (CFD) using the Spalart-Allmaras turbulent model. Under the optimal CJ condition, its implementation can provide the required minimum rudder side force coefficient (Cy, trim ) of 1.19 at a rudder drag coefficient (Cd ) of 0.0013, a decrease in drag coefficient of 95% over the baseline case of plain flap without CJ. In addition, there is an improvement in rudder margin with the maximum side force coefficient increase by 42%, and the corresponding drag force coefficient decrease by 25% for the aircraft to yaw in a direction of the still-active engine.

Review of environmental noise policies and economics in 2014-2016

This review has highlighted the important developments relating to noise issues performed by international organizations and the activities in some developed and developing countries to improve environmental noise management.
 The World Health Organization is in the process of finalizing the WHO Environmental Noise Guidelines for the European Region as an update of the WHO Community Noise Guidelines of 1999/2000.
 The International Civil Aviation Organization, in Chapter 14, has lowered the current chapter 4 standards for subsonic jet aircraft and propeller driven aeroplanes.
 In 2014-2016 the European Parliament and the Council and the European Commission have achieved significant progress in amending laws and regulations and creating new legislation. Efforts referred to regulating the EU type-approval of all new buses and trucks with regard to their sound level and the introduction of noise-related operating restrictions at airports, in accordance with ICAO’s Balanced Approach. The EC amended the END and arranged for the evaluation of the END based on the criteria of relevance, coherence, effectiveness and impacts, efficiency, and EU added value. Two new regulations addressed the issues of technical specification for interoperability of high-speed trains related to sound emission levels and the implementation of provisions establishing noise-differentiated track access charges.
 The European Environment Agency published the ‘Noise in Europe’ report describing the impacts of noise exposure in terms of cases of premature death, hospital admissions, cases of hypertension and annoyance. In addition, the European Environment Agency developed a good practice guide on quiet areas, refined the methodology for a quietness suitability index, and published its report on “Quiet areas in Europe”.
 In the United Kingdom, the Civil Aviation Authority reported new and updated evidence on attitudes to aviation noise around airports in England, and the Airports commission published recommendations for development in the aviation sector around London. The Department of Transport formulated a draft Airports National Policy Statement on expansion options for South East England airports.
 Switzerland published its Environment Report 2015 and estimated the annual external costs of road traffic, railway and aircraft noise which are quite substantial.
 Developing countries become increasingly aware that noise levels have gone up abnormally high and can cause acute and chronic health impacts on the human population. In consequence, Costa Rica has lowered the permissible sound pressure levels, and India, Iraq and Mexico have set new daytime and night-time noise standards. Tanzania has approved permissible sound pressure limits, which were prepared by the National Environment Management Council almost a decade ago. The Egyptian Environmental Affairs Agency developed a national plan to combat noise, which is currently implemented on a collaborative effort of 11 ministries, a rare phenomenon in developing countries. Kenya is currently committed to develop a strategy for environmental noise management.