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Jet engine components are considered that influence propulsion system integration on the airframe and related aircraft drag areas. Emphasis is placed on high Mach number inlet geometries, boattailed nozzle configurations, propulsive wing installation, wing surface blowing lift, fuselage mounted nacelles, and thrust reversal.
The National Aerospace Plane (NASP) program's preliminary analyses indicate that the ability to reach orbit is governed by average thrust/drag, average propulsion efficiency, and the ratio of takeoff fuel weight to total takeoff weight; examinations of each of the governing parameters have in turn pointed to the technology development efforts that must be undertaken for the realization of such a single-stage-to-orbit airbreathing vehicle. The key to the achievement of high thrust/drag, in particular, is the integration of engine intake compression and exhaust expansion functions with the airframe. The portion of the vehicle cross-sectional area thus employed in leading the airstream into the engine inlet should be as close to 100 percent as possible.
NASA's Quiet Aircraft Technology Project is developing physics-based understanding, models and concepts to discover and realize technology that will, when implemented, achieve the goals of a reduction of one-half in perceived community noise (relative to 1997) by 2007 and a further one-half in the far term. Noise sources generated by both the engine and the airframe are considered, and the effects of engine/airframe integration are accounted for through the propulsion airframe aeroacoustics element. Assessments of the contribution of individual source noise reductions to the reduction in community noise are developed to guide the work and the development of new tools for evaluation of unconventional aircraft is underway. Life in the real world is taken into account with the development of more accurate airport noise models and flight guidance methodology, and in addition, technology is being developed that will further reduce interior noise at current weight levels or enable the use of lighter-weight structures at current noise levels.
Presented is a computer-based tool that connects several disciplines that are needed in the complex and integrated design of high performance reusable single stage to orbit (SSTO) vehicles. Every system is linked to every other system, as is the case of SSTO vehicles with air breathing propulsion, which is currently being studied by NASA. The deficiencies in the scramjet powered concept led to a revival of interest in Rocket-Based Combined-Cycle (RBCC) propulsion systems. An RBCC propulsion system integrates airbreathing and rocket propulsion into a single engine assembly enclosed within a cowl or duct. A typical RBCC propulsion system operates as a ducted rocket up to approximately Mach 3. At this point the transitions to a ramjet mode for supersonic-to-hypersonic acceleration. Around Mach 8 the engine transitions to a scram4jet mode. During the ramjet and scramjet modes, the integral rockets operate as fuel injectors. Around Mach 10-12 (the actual value depends on vehicle and mission requirements), the inlet is physically closed and the engine transitions to an integral rocket mode for orbit insertion. A common feature of RBCC propelled vehicles is the high degree of integration between the propulsion system and airframe. At high speeds the vehicle forebody is fundamentally part of the engine inlet, providing a compression surface for air flowing into the engine. The compressed air is mixed with fuel and burned. The combusted mixture must be expanded to an area larger than the incoming stream to provide thrust. Since a conventional nozzle would be too large, the entire lower after body of the vehicle is used as an expansion surface. Because of the high external temperatures seen during atmospheric flight, the design of an airbreathing SSTO vehicle requires delicate tradeoffs between engine design, vehicle shape, and thermal protection system (TPS) sizing in order to produce an optimum system in terms of weight (and cost) and maximum performance.
The benefit of the boundary layer ingestion (BLI) is described in the perspective of the propulsion and engine development. A power saving map of the BLI engines is derived based on the correlation of the shape factor of the ingested boundary layer and the propulsive efficiency. The ratio of the mass flow rate between BLI and non-BLI propulsors is introduced to quantify the power saving of the BLI engine relative to a corresponding clean inlet flow engine that generates the same amount of net thrust. The wake recovery factor from the jet flow is applied to find the optimum sizing of the engine for the given design requirement. The effects of the fan pressure ratio of the propulsor toward the power saving are also investigated to seek out the feasible range of the BLI propulsor design. The derived correlation is validated with CFD analyses. Simulation models using variously sized engines relative to an influencing body are developed so that a numerical experiment is carried out with the various shape factors. The effect of the propulsion airframe integration toward the aerodynamic forces on the fuselage and nacelle is investigated via parametric study of the engine sizing and fan pressure ratio for the wake ingestion models. The propulsor efficiency is quantified toward the saving in the actual shaft power and correlated with the efficiency penalty of the BLI propulsor. The correlation is also validated via comparison of the turbo-machinery CFD results for BLI2DTF and conventional transonic fan stages.
An aircraft system noise assessment was conducted for a hybrid wing body freighter aircraft concept configured with three open rotor engines. The primary objective of the study was to determine the aircraft system level noise given the significant impact of installation effects including shielding the open rotor noise by the airframe. The aircraft was designed to carry a payload of 100,000 lbs on a 6,500 nautical mile mission. An experimental database was used to establish the propulsion airframe aeroacoustic installation effects including those from shielding by the airframe planform, interactions with the control surfaces, and additional noise reduction technologies. A second objective of the study applied the impacts of projected low noise airframe technology and a projection of advanced low noise rotors appropriate for the NASA N+2 2025 timeframe. With the projection of low noise rotors and installation effects, the aircraft system level was 26.0 EPNLdB below Stage 4 level with the engine installed at 1.0 rotor diameters upstream of the trailing edge. Moving the engine to 1.5 rotor diameters brought the system level noise to 30.8 EPNLdB below Stage 4. At these locations on the airframe, the integrated level of installation effects including shielding can be as much as 20 EPNLdB cumulative in addition to lower engine source noise from advanced low noise rotors. And finally, an additional set of technology effects were identified and the potential impact at the system level was estimated for noise only without assessing the impact on aircraft performance. If these additional effects were to be included it is estimated that the potential aircraft system noise could reach as low as 38.0 EPNLdB cumulative below Stage 4.
Supersonic aircraft are challenging to optimally design due to the widely varying constraints and flight conditions they experience. Additionally, a large number of disciplinary subsystems must be considered due to highly complex design requirements. One subsystem that has a major effect on overall performance is the engine. In this work, we construct a supersonic mixed-flow variable cycle engine and perform multipoint gradient-based optimization using this model. We see that the operational variables allow the optimizer to tailor performance at each individual flight condition, leading to better overall performance. To simulate airframe integration constraints, we run successive optimizations with increasingly restrictive inlet areas and see decreases in engine performance. This work is part of a larger effort to incorporate engine design into aero-thermal-mission optimization of a supersonic aircraft.
A historical view of multi-jet engine installations is given that emphasizes integration of the powerplant and the airframe in aircraft design for improved reduction in external nacelle drag and interference drag characteristics.
A comparison of the in-airframe performance and efficiency of the advanced engine concepts is presented. The results indicate that the proposed advanced engines can significantly improve the performance and economy of general aviation airplanes. The engine found to be most promising is the highly advanced version of a rotary combustion (Wankel) engine. The low weight and fuel consumption of this engine, as well as its small size, make it suited for aircraft use.
The Boeing 777 carries with it basic and applied research, technology, and aerodynamic knowledge honed at several NASA field centers. Several Langley Research Center innovations instrumental to the development of the aircraft include knowledge of how to reduce engine and other noise for passengers and terminal residents, increased use of lightweight aerospace composite structures for increased fuel efficiency and range, and wind tunnel tests confirming the structural integrity of 777 wing-airframe integration. Test results from Marshall Space Flight Center aimed at improving the performance of the Space Shuttle engines led to improvements in the airplane's new, more efficient jet engines. Finally, fostered by Ames Research Center, the Boeing 777 blankets that protect areas of the plane from high temperatures and fire have a lineage to Advanced Flexible Reusable Surface Insulation used on certain areas of the Space Shuttle. According to Boeing Company estimates, the 777 has captured three-quarters of new orders for airplanes in its class since the program was launched.
The performance of the N3-X, a 300 passenger hybrid wing body (HWB) aircraft with turboelectric distributed propulsion (TeDP), has been analyzed to see if it can meet the 70% fuel burn reduction goal of the NASA Subsonic Fixed Wing project for N+3 generation aircraft. The TeDP system utilizes superconducting electric generators, motors and transmission lines to allow the power producing and thrust producing portions of the system to be widely separated. It also allows a small number of large turboshaft engines to drive any number of propulsors. On the N3-X these new degrees of freedom were used to (1) place two large turboshaft engines driving generators in freestream conditions to maximize thermal efficiency and (2) to embed a broad continuous array of 15 motor driven propulsors on the upper surface of the aircraft near the trailing edge. That location maximizes the amount of the boundary layer ingested and thus maximizes propulsive efficiency. The Boeing B777-200LR flying 7500 nm (13890 km) with a cruise speed of Mach 0.84 and an 118100 lb payload was selected as the reference aircraft and mission for this study. In order to distinguish between improvements due to technology and aircraft configuration changes from those due to the propulsion configuration changes, an intermediate configuration was included in this study. In this configuration a pylon mounted, ultra high bypass (UHB) geared turbofan engine with identical propulsion technology was integrated into the same hybrid wing body airframe. That aircraft achieved a 52% reduction in mission fuel burn relative to the reference aircraft. The N3-X was able to achieve a reduction of 70% and 72% (depending on the cooling system) relative to the reference aircraft. The additional 18% - 20% reduction in the mission fuel burn can therefore be attributed to the additional degrees of freedom in the propulsion system configuration afforded by the TeDP system that eliminates nacelle and pylon drag, maximizes boundary layer ingestion (BLI) to reduce inlet drag on the propulsion system, and reduces the wake drag of the vehicle.
The major contribution of this research was the exposition of the fact that airframe and engine interactions could be present, and their effects could include loss of stability and performance of the control systems. Also, the significance of two directional, as opposed to one-directional, coupling was identified and explained. A multivariable stability and performance analysis methodology was developed, and applied to several candidate aircraft configurations. In these example evaluations, the significance of these interactions was underscored. Also exposed was the fact that with interactions present along with some integrated control approaches, the engine command/limiting logic (which represents an important nonlinear component of the engine control system) can impact closed-loop airframe/engine system stability. Finally, a brief investigation of control-law synthesis techniques appropriate for the class of systems was pursued, and it was determined that multivariable techniques, including model-following formulations of LQG and/or H infinity methods, showed promise. However, for practical reasons, decentralized control architectures are preferred, which is an architecture incompatible with these synthesis methods. The major contributions of the second phase of the grant was the development of conditions under which no decentralized controller could achieve closed loop system requirements on stability and/or performance. Sought were conditions that depended only on properties of the plant and the requirement, and independent of any particular control law or synthesis approach. Therefore, they could be applied a priori, before synthesis of a candidate control law. Under this grant, such conditions were found regarding stability, and encouraging initial results were obtained regarding performance.
The International Civil Aviation Organization (ICAO), the U.S. Environmental Protection Agency (EPA), local environmental groups, and the public have become increasingly concerned over damage to local air quality from aircraft emissions and the impact of producing greenhouse gases. The NASA Glenn Research Center has been working to develop revolutionary technologies to minimize environmentally harmful engine emissions, such as nitrogen oxides, carbon dioxide, aerosols, and particulates. The two objectives of UEET are (1) to develop technologies to reduce nitrogen oxide (NOx) emissions by 70 percent below 1996 ICAO regulations and (2) to decrease carbon dioxide emissions (CO2) by dramatically increasing performance and efficiency. High temperature engine materials, ultra-low-NOx combustor designs, efficient, highly loaded turbomachinery, and propulsion-airframe integration analysis are technologies being developed at Glenn to meet these goals. Technology developed in the previous Advanced Subsonic Technology Program is being put into commercial production for large and regional aircraft to reduce NOx emissions 50 percent below 1996 ICAO regulations for landing and takeoff cycles. UEET will take the technology to the next quantum leap-reducing emissions to 70 percent below the ICAO regulations level. In addition, NASA-developed research will significantly reduce carbon monoxide, unburned hydrocarbons, and corresponding cruise NOx levels for the next generation of aircraft engines. Glenn's UEET research will be useful across the whole range of flight: subsonic, supersonic, and hypersonic. It will improve the subsonic transportation that the public depends on, contribute to supersonic commercial aircraft, improve military aircraft, and contribute to the design of a future hypersonic vehicle. These technologies are contributing to a better quality of life on Earth.
In connection with a request for a report coming from a U.S. Senate committee, NASA formed a Small Transport Aircraft Technology (STAT) team in 1978. STAT was to obtain information concerning the technical improvements in commuter aircraft that would likely increase their public acceptance. Another area of study was related to questions regarding the help which could be provided by NASA's aeronautical research and development program to commuter aircraft manufacturers with respect to the solution of technical problems. Attention is given to commuter airline growth, current commuter/region aircraft and new aircraft in development, prospects for advanced technology commuter/regional transports, and potential benefits of advanced technology. A list is provided of a number of particular advances appropriate to small transport aircraft, taking into account small gas turbine engine component technology, propeller technology, three-dimensional wing-design technology, airframe aerodynamics/propulsion integration, and composite structure materials.
The latest version of the NASA Flying Controls Testbed (FLiC) integrates commercial-off-the-shelf components including airframe, autopilot, and a small turbine engine to provide a low cost experimental flight controls testbed capable of sustained speeds up to 200 mph. The series of flight tests leading up to the demonstrated performance of the vehicle in sustained, autopiloted 200 mph flight at NASA Wallops Flight Facility's UAV runway in August 2006 will be described. Earlier versions of the FLiC were based on a modified Army target drone, AN/FQM-117B, developed as part of a collaboration between the Aviation Applied Technology Directorate at Fort Eustis, Virginia and NASA Langley Research Center. The newer turbine powered platform (J-FLiC) builds on the successes using the relatively smaller, slower and less expensive unmanned aerial vehicle developed specifically to test highly experimental flight control approaches with the implementation of C-coded experimental controllers. Tracking video was taken during the test flights at Wallops and will be available for presentation at the conference. Analysis of flight data from both remotely piloted and autopiloted flights will be presented. Candidate experimental controllers for implementation will be discussed. It is anticipated that flight testing will resume in Spring 2007 and those results will be included, if possible.
The process of developing an empirical model for jet-surface interaction noise is described and the resulting model evaluated. Jet-surface interaction noise is generated when the high-speed engine exhaust from modern tightly integrated or conventional high-bypass ratio engine aircraft strikes or flows over the airframe surfaces. An empirical model based on an existing experimental database is developed for use in preliminary design system level studies where computation speed and range of configurations is valued over absolute accuracy to select the most promising (or eliminate the worst) possible designs. The model developed assumes that the jet-surface interaction noise spectra can be separated from the jet mixing noise and described as a parabolic function with three coefficients: peak amplitude, spectral width, and peak frequency. These coefficients are fit to functions of surface length and distance from the jet lipline to form a characteristic spectra which is then adjusted for changes in jet velocity and/or observer angle using scaling laws from published theoretical and experimental work. The resulting model is then evaluated for its ability to reproduce the characteristic spectra and then for reproducing spectra measured at other jet velocities and observer angles; successes and limitations are discussed considering the complexity of the jet-surface interaction noise versus the desire for a model that is simple to implement and quick to execute.
The process of developing an empirical model for jet-surface interaction noise is described and the resulting model evaluated. Jet-surface interaction noise is generated when the high-speed engine exhaust from modern tightly integrated or conventional high-bypass ratio engine aircraft strikes or flows over the airframe surfaces. An empirical model based on an existing experimental database is developed for use in preliminary design system level studies where computation speed and range of configurations is valued over absolute accuracy to select the most promising (or eliminate the worst) possible designs. The model developed assumes that the jet-surface interaction noise spectra can be separated from the jet mixing noise and described as a parabolic function with three coefficients: peak amplitude, spectral width, and peak frequency. These coefficients are t to functions of surface length and distance from the jet lipline to form a characteristic spectra which is then adjusted for changes in jet velocity and/or observer angle using scaling laws from published theoretical and experimental work. The resulting model is then evaluated for its ability to reproduce the characteristic spectra and then for reproducing spectra measured at other jet velocities and observer angles; successes and limitations are discussed considering the complexity of the jet-surface interaction noise versus the desire for a model that is simple to implement and quick to execute.
Hybrid- and all-electric aircraft concepts use electric motors for power rather than a conventional jet engine. Electric propulsors open the door to new ways to synergistically integrate the propulsion system with the airframe. For example, many small electric propulsors can be distributed along the wing to increase the effective bypass ratio for better overall efficiency. Furthermore, these propulsors can be attached to the wing surface for boundary layer ingestion(BLI) to further the efficiency gains. However, these novel methods of aeropropulsive integration also create challenges such as nonuniform inflow and complex nacelle geometries. Here we use gradient-based aerodynamic shape optimization to address the design challenges of the wing-mounted distributed electric propulsion system of the Subsonic Single Aft Engine (SUSAN)concept. In doing so, we aim to more accurately benchmark the flow power of SUSAN’s mail slot propulsors relative to a conventional propulsion system in both an isolated and BLI configuration. Our preliminary results found relative to an optimized podded propulsor the optimized mailslot and BLI mailslot design required 8% and 17% more flow power respectively.The methods and key design insights also apply to other aircraft concepts that utilize distributed electric propulsion and boundary layer ingestion.