Subsonic Cruise Research Articles

Aging characterization of advanced polymer systems

Aging of three advanced polymer systems used as adhesives in the aerospace industry is characterized by Fourier transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR-FTIR), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS).Since significant changes in mechanical properties were observed for AF191, FM®73, and FM®5 bonded joints, the purpose of this work was to identify whether there is any chemical and physical degradation for the adhesives used in these joints. Each of the adhesives has been evaluated after exposing to Hot/Wet and Hot/Dry environments for 5000 h. They were also thermally cycled in conditions that represent subsonic and supersonic cruise. Hot/wet exposures demonstrated a greater amount of possible degradation than hot/dry or thermally cycled exposures. The hot/wet aging condition resulted in more pronounced O-H, C-H, and N-H infrared absorptions, reduced glass transition temperature of adhesives, and reduced tensile and fracture properties of corresponding bonded systems. Overall, these adhesives were chemically very stable under the environments to which they were exposed, even though some of the joints showed reduced fracture toughness due to the exposure. Additional work is needed to understand the mechanism causing the change in joint properties when exposed to these environments.

Exploring the Feasibility of Pulsed Jet Separation Control for Aircraft Configurations

This paper describes experiments aimed at demonstrating the effectiveness of pulsed vortex generator jets (PVGJs) in controlling separation on aircraft wings. The demonstration is accomplished by applying the jets to two relevant cone gurations and evaluating their effectiveness in a wind tunnel. The jet design and placement for both experiments was based on parametric studies described in a previous paper. In the e rst application, pulsed jets prevented separation over the wings on a three-dimensional lambda-wing e ghter cone guration at low speeds and high angles of attack. This experiment shows that the e ow control method can enhance the lift, and hence the maneuverability, of advanced e ghters in post-stall e ight. The lambda-wing experiments also demonstrated that jets can be operated asymmetrically for lateral maneuvering control at high angles of attack. The second set of experimentstestedhigherspeed ranges, applying jets to an airfoilsection in an M =0.3‐0.5 e ow.Thiscone guration is relevant to subsonic cruise. The results show that PVGJs can increase lift and lift-to-drag ratios, but they were less effectiveat supercriticalspeedswhereseparation isinduced by hingelineshocks. In all cases, thejetsincreased lift over their effective range although their drag effect was small.

Theoretical analysis of environmental and energetic performance of very high temperature turbo-jet engines

Current progress in gas turbine performance is achieved mainly by increasing the turbine inlet temperature. State of-the-art military aircraft gas turbines operate with turbine inlet temperatures exceeding 2 000 K, and future development plans call for even higher temperature levels. At such high temperatures, the hot combustion gases can no longer be considered as chemically inert, and it becomes important to account for the chemically reactive nature of the expanding flow. In this paper, the authors present a one-dimensional model of the chemically reactive flow through the first turbine stage of an aircraft turbo-jet engine. The model is used to study the impact of chemical reactivity on pollutant emission characteristics and engines performance (i.e. overall efficiency and specific thrust). Three different casess are considered: sea-level static operation (take-off), commercial aircraft in subsonic cruising at 10 000 m altitude, and military aircraft in supersonic flight at 20 000 m altitude. The results of this study show, for instance, that the production of environmental pollutants in the turbine as a result of chemical reactivity is particularly significant for turbo-jets operating at subsonic cruise velocities. Moreover, in both flight conditions considered, the increase of operating temperature decreases the overall efficiency.

Technology Readiness and Development Risks of the New Supersonic Transport

Realistic specifications for the new supersonic transport call for a 2.2 Mach, 270 passenger, 5,500 NM range aircraft, requiring $15–20 billion for research and development. Nonlinear aerodynamic analysis methods promise an enhanced lift-to-drag ratio of about 45% in subsonic cruise and 25% in supersonic cruise. Adequate sonic-boom suppression does not appear feasible. The resized increment in weight reduction due to the elimination of the droop nose is estimated at 4,500 kg. Considerable progress has been made in meeting FAR-36/Stage-3 noise requirements through the use of a mixed-flow turbofan with ejector or a mid-tandem fan variable cycle engine. A 5–15% lower specific fuel consumption is projected, while the dominant combustion philosophies are the lean-premixed-prevaporized and the rich-burn/quick-quench/lean-burn processes. Research is aimed at a nitrogen oxide emission index of 5, resulting in less than 1% annual ozone depletion. The estimated market needs of about 550 units by 2020 justify a satisfactory return on investment (~12%) for only one manufacturer. A well-structured international consortium could reduce development risks, time, and expenditures through technology transfer and the sharing minimization of nonrecurring costs. The date of entry-into-service can be placed between 2010 and 2015.

A novel concept for the next generation civil supersonic transport propulsion system: the retractable fan

Suggests that the next civil supersonic passenger aircraft project will pose a number of challenges. The propulsion system for this aircraft will have to achieve economic operation for both supersonic and subsonic cruise modes. In addition, the current and intended noise and pollutant emissions legislation will have to be met. Suggests that, while there are a number of proposed engines for the next generation civil supersonic aircraft, they all exhibit difficulties in meeting the compromises inherent in the engine duty. Offers a novel solution based on a unique design. Discusses the underlying issues and presents the design based on retractable fans driven by a single stage double pass tip turbine.

95/00673 Keeping cool when the heat is on

This chapter discusses several air breathing jet engines in detail. The conditions under which the operational efficiencies of these jet-propelled engines are calculated are taken as optimum or ideal. Air is sucked in through the inlet lip, compressed and mixed with pressurized and heated fuel, and accelerated through a nozzle to produce thrust. Here, the principles of thermodynamics describe more fully how such engines perform. The chapter examines nine different situations and includes the following: the turbojet in take-off, high subsonic cruise, and afterburning supersonic cruise, the ramjet in high supersonic cruise, the turbofan engine in take-off, high subsonic cruise, and afterburning supersonic cruise. The thermodynamic cycle of the ideal jet engine is basically that of the Brayton cycle and involves isentropic compression, heat addition at constant pressure, and isentropic expansion. Fuel–air ratio for various compressor pressure ratios and turbine inlet stagnation temperatures at take-off, turbine exit stagnation temperatures (K) for various compressor pressure ratios and turbine inlet stagnation temperatures at take-off are two of many charts detailing various facets of calculations to give the reader a grasp of the preliminaries of jet engines.

Experimental study of the turbulent boundary layer on a transport wing in subsonic flow

The upper-surface boundary layer on a transport wing model was extensively surveyed with miniature yaw probes at a subsonic cruise condition. Significant variation in flow direction with distance from the surface was observed near the trailing edge, everywhere except at the wing root and tip. Values of streamwise displacement thickness, normalized by the local chord, were maximum at the highly loaded midsemispan stations. The data are intended to provide a test case for computational fluid dynamics code validation.

Acoustic interference of counter-rotation propellers

The noise fields from the rotors of counter-rotating propellers having the same number of blades and angular frequency tend to cancel or reinforce each other depending on the relative phase of the two fields at the point of observation. Because of this, the total noise field at the blade passage frequency or harmonics forms a characteristic standing wave pattern. A general investigation of this acoustic interference phenomenon is carried out. Unlike previous works, the present analysis allows the front and the rear rotor to have different blade geometry and loading. Further, the effect of forward flight is included. Numerical results indicate that at high subsonic cruise Mach number the acoustic interference pattern differs substantially from that at static condition.

Some Effects of Cruise Speed and Engine Matching on Supersonic Inlet Design

An analytical study was conducted to determine the impact of flight Mach number on inlet type selection for a supersonic cruise aircraft. External and mixed-compression axisymmetric and two-dimensional inlets were considered. The internal contraction of the mixed-compression inlets was limited to achieve self-starting. At Mach 2.0, the axisymmetric mixed-compression inlet provided the best aircraft range. At Mach 2.3, the two-dimensional mixed-compression inlet was the most attractive if enough variable geometry were incorporated to minimize spillage during subsonic cruise. Increases in takeoff-to-cruise air flow ratio gave lower aircraft range.

Domain of the convertible rotor

The convertible rotor (CR) is a means that provides lift in the hover mode and propulsion in the cruise mode of a VTOL aircraft. In the wide disk loading spectrum of this family of aircraft, ranging from 2-2000 psf, various aspects are examined, especially that of noise. The need for a balanced VTOL is demonstrated. Such various solutions are feasible depending on operational requirements, namely, the helicopter rotor (for low cruise speed and prolonged hover) and the fan lift engine (for supersonic cruise speed). The convertible rotor with a disk loading of approximately 25 psf is shown to be the best solution when economy at high subsonic cruise speed is required. This loading is also near the maximum that can be tolerated on account of noise, for operation in builtup areas. The aerodynamic mechanism of the convertible rotor is explained and reasons for its high efficiency given. Operating costs, together with journey times between city centers, of a typical convertible rotor VTOL aircraft are given in comparison with those of helicopters and fixed-wing transport aircraft. It is concluded that, subject to technical problems as yet unresolved, the convertible rotor can win an important domain in the field of air transportation.