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This paper elaborates on current testing techniques used to determine an aircraft's attenuation characteristics in the presence of High Intensity Radiated Fields (HIRF). This is not a theoretical discussion for the Electromagnetic expert, but rather a practitioner's overview for the avionics/electrical engineer who must oversee HIRF testing. Three testing techniques used to determine the attenuation of an aircraft will be discussed: (1) the Low Level Direct Drive (LLDD) test used for the 10 kHz to the first aircraft resonance frequency; (2) the Low Level Swept Current (LLSC) test used for the 1 to 400 MHz frequency band; and (3) the Low Level Swept Fields (LLSF) test used for the 100 MHz to 18 GHz frequency band.

Technological advances provide the means to implement designs to give the pilots improved and safer control of an aircraft throughout the whole flight regime from gate to gate. These advances also give the passengers access to everything they need to have a flying office and for en route entertainment all at feasible costs. These same advances in technology present many complex design, certification and operational issues that must be addressed to effectively use the information that is available for aircraft systems, flight crew and passenger use. This paper describes some of the issues involved and some of the avionics advances that can be expected.

An analytical/computational method of computing radiated noise from ducted rotor due to inflow distortion and turbulence is presented. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical productions are in reasonable agreement with experimental measurements.

Control of structure borne noise transmission into an aircraft cabin generated from component excitation, such as rotor/engine vibration imbalance or firing excitations or from auxiliary equipment induced vibrations, can be studied empirically via impedance characterization of the system components and application of appropriate component coupling procedures. The present study was aimed at demonstrating the usefulness of such impedance modeling techniques as applied to a Bell 206B rotorcraft and a Cessna TR182 general aviation aircraft. Simulated rotor/engine excitations were applied to the assembled aircraft systems to provide baseline structure borne noise transmission data. Thereafter, impedance tests of the system components were carried out to provide a data base from which system component coupling studies were carried out.

The Federal Aviation Administration (FAA)'s analysis of commuter aircraft accidents and ongoing research has indicated that the crashworthiness capabilities of smaller aircraft may be questionable. The small size of these aircraft results in a stiff structure and consequently higher impact loads experienced by the occupants. In 1993, the FAA issued a Notice of Proposed Rule Making (NPRM) 93-71 to increase the deceleration pulse amplitude of the sled tests under the Test-1 conditions (60-degree test) to 32G for the commuter type aircraft. To meet this condition, the seat design must exploit the energy absorption potential for its structural components. Energy absorbing components may include the seat legs, seat pan, and seat cushion. The intent is to design the seat so that it strikes well beyond the elastic limit to absorb the energy of the impact. To date, no seat has yet been able to pass the proposed criteria with an acceptable limit on the lumbar load (1500 pounds).

The aircraft seats facing bulkheads, interior walls, class dividers, lavatory, front seat back or instrument panels of aircraft have presented problems demonstrating the compliance with the Head Injury Criteria (HIC) requirement. Full scale sled tests provide means of assessing the response of the occupants and the potential head injuries in an aircraft crash which is extremely costly, time-consuming, and provide too much scatter on the HIC. These factors have motivated the Federal Aviation Administration, seat and airframe manufacturers as well as research providers such as the National Institute for Aviation Research (NIAR) to pursue alternative testing procedures to replace the full-scale sled tests. This paper presents the results of a series of baseline sled tests of the system seat/ATD/restraint/bulkhead conducted at the NIAR horizontal sled which will be used to validate component test devices.

This paper describes an IC engine fuel-system conversion to dual-fuel capability, on a carbureted Cessna 150. This conversion differs from others by adding a fuel injector in parallel to the existing carburetor. The fuel injector pump is activated when switching to ethanol. The advantage is conventional take-off and landing on either fuel with mixture full rich. Altitude leaning remains conventional. This is the first conversion to provide smooth in-flight fuel type change-over at cruise power, if the prescribed procedure is followed. This conversion method is applicable to all carbureted or fuel injected aircraft and automotive engines.

A flow modeling method has been developed to analyze the flow in the annular base (rear-facing surface) of a circular engine nacelle flying at subsonic speed but with a supersonic exhaust jet. Real values of exhaust gas properties and temperature are included. Potential flows of the air and gas streams are computed for the flow past a separated wake. Then a viscous jet mixing is superimposed on this inviscid solution. Conservation of mass, momentum and energy is achieved by mutiple iterations. Despite the iterations, the wake flow field is computed with modest computer requirements.

This paper has presented a technique for the determination of an optimal configuration of fuselage mounted piezoelectric actuators for active structural acoustic control of interior noise in aircraft. The technique has demonstrated much potential in preliminary experiments where actuators were configured to couple into the first principal component of the acoustically coupled fuselage vibration. In this test, average reductions of 6 dB at the error microphones and 4 dB at five auxiliary microphones were observed for a pure tone disturbance at the left forward engine pylon of a business jet. This disturbance was used to simulate an oscillating force due to engine unbalance.

Comparative studies between competing engineering techniques are complex, since the comparison depends upon the application. This paper focuses upon periodic vibration and noise in regional turboprops and in fuselage-mounted twin-jets. The vibrations under discussion are propeller harmonics of the turboprop and unbalance tones of the turbojet. Broadband noise (wind noise and combustion noise) is not discussed since no mature active technology is applicable to this type of noise. A large body of both active and adaptive/passive technology is applicable to periodic noise. Much of this technology is proprietary and unavailable to the public. Competing approaches are not openly compared; rather each technology is selectively promoted by its marketing team. This paper attempts a comparison. The authors of this paper are members of an engineering team that has recently finished the development of some adaptive/passive technologies.

This paper describes a series of ongoing experiments to capture the details of perpendicular vortex-airfoil interaction. Three test cases explored are: 1) a 21% thick symmetric airfoil at 1.1° angle of attack, 2)a thin flat plate of 2.5% thickness with rounded leading edge, sharp trailing edge and zero angle of attack and 3) A 12% thick symmetric airfoil at zero angle of attack. The tip vortex was generated by a NACA0016 wing at 5° AOA. The strength of the vortex was computed from the velocity profile measured upstream for the first two cases. Pressure measurements on the 21% airfoil were used to quantify the effect of the vortex as a function of its stand-off distance from the airfoil. Vortex trajectories over the airfoils were obtained from laser sheet videography. The vortex motion conforms to potential flow expectations except in regions of pressure gradient and during head-on interaction.

In support of a Dornier 328 aircraft completion with a corporate shuttle interior, a test program to show compliance with the occupant injury criteria was undertaken. Three seating configurations were developed utilizing two occupant protection technologies. Component-level testing was successfully used to predict the performance of one occupant protection system. Dynamic testing for injury purposes also indicated beneficial improvements to the seating system, including a change of the restraint system to a more reliable design. “Lessons learned” from the dynamic testing experience are also reviewed. A novel method of using simple equipment to develop head trajectory information from filmed data was devised, and is explained.

An experimental study of the effect of primary nozzle geometry on the performance characteristics of a rectangular subsonic ejector was conducted. Four primary nozzle configurations having rectangular and notched-rectangular exit geometries each with and without boundary layer swirl vanes were studied in these experiments. The ejector and all primary nozzles had equal aspect ratios (defined as the ratio of the large to small dimensions) of 2.8. The primary jet Mach number and Reynolds number were kept constant at M=0.06 and for all cases. After installation of each nozzle in the ejector throat, the mean and fluctuating velocity field at the ejector exit plane and three other downstream stations were mapped using a single hot wire probe. Mass flow ratio, spreading rate, and ejector pumping were calculated from the above measurements.

An experimental investigation on the effects of Gurney flaps on a reflection plane model was conducted. Two sizes of Gurney flaps were tested on a series of configurations which included a tapered wing (with a NLF-0215 airfoil section), a fuselage, a nacelle, and their permutations. The tests were conducted at a Reynolds number of 1.0 million based on mean chord. Results indicated that lift and drag were increased upon using the Gurney flaps; lift to drag and lift squared to drag ratios were also increased. In particular, the lift to drag ratio for the complete “airplane” was almost the same with or without a small Gurney flap. Pitching moment became more negative (nose-down) with the Gurney flap, and positive (nose-up) with the addition of the fuselage.

Traditionally, transonic wing design focuses on tailoring of pressure distributions, with little attention paid to spanwise lift distribution. While off-design considerations may constrain the span loading, it is useful nonetheless to know the optimal span loading. Further, induced drag minimization is useful for integration of other components with the wing, such as winglets and engine nacelles. An optimization scheme has been developed allowing Trefftz-plane drag minimization on complete aircraft configurations using high-order panel methods and full-potential CFD codes. Two applications of Trefftz-plane drag minimization for component integration are demonstrated.

The nonlinear development of stationary crossflow vortices over a 45° swept NLF(2)-0415 airfoil is studied. Previous investigations indicate that the linear stability theories are unable to accurately describe the transitional flow over crossflow-dominated configurations. In recent years the development of nonlinear parabolized stability equations (NPSE) has opened new pathways toward understanding transitional boundary-layer flows. This is because the elegant inclusion of nonlinear and nonparallel effects in the NPSE allows accurate stability analyses to be performed without the difficulties and overhead associated with direct numerical simulations (DNS). Numerical (NPSE) results are presented here and compared with experimental results obtained at the Arizona State University Unsteady Wind Tunnel (ASUUWT) for the same configurations.

DARcorporation is developing an interactive, user-friendly computer program to perform preliminary design and analysis functions for fixed wing general aviation airplanes. The system allows design engineers to rapidly evolve an aircraft configuration from weight sizing through detailed performance calculations, while working within regulatory constraints. This paper shows the main features of the newly developed user interface for general aviation airplane design in a windows based environment. The ease of use will bring computer aided design methods to people previously not exposed to these methods because of the high amount of difficult computer knowledge needed.

Since the birth of the computer age, the drive to bring products to market faster, better and cheaper has been a shared, unparalleled competitive pressure across every engineering design project, regardless of its size or purpose. While the rapid advances in computer power and technology over the past decade have ushered in such powerful technology drivers as CAD (Computer-Aided Design) and CAE (Computer-Aided Engineering), the greatest engineering design productivity bottleneck for most design projects still remains at the human level.

A reason of the lack of agreement between measured pollutants concentration in the air of urban areas and vehicle pollutant emissions evaluated by available emission models is the fact that catalyst performance variability is not considered. In this paper, an experimental study on the effect of performance variability of catalyst on emissions is presented. Average emissions have been measured using driving cycles representative of different levels of urban traffic, determined by statistical methods on the basis of data detected on-road by an instrumented car. For each driving cycle, representative of a certain traffic level, different thermal starting conditions of catalyst have been tested. These conditions have been determined by the characterization of catalyst performance at steady state and are representative of real catalyst conditions experienced on the road.

A method of predicting HC, CO and NOx emissions and fuel-used over drive cycles has been developed. This has been applied to FTP-75 and ECE+EUDC drive cycles amended to include cold-start and warm-up. The method requires only fully-warm steady state indicated performance data to be available for the engine. This is used in conjunction with a model of engine thermal behaviour and friction characteristics, and vehicle/drive cycle specifications enabling engine brake load/speed variations to be defined. A time marching prediction of engine-out emissions and fuel consumption is carried out taking into account factors which include high engine friction and poor mixture preparation after cold-start. Comparisons with experimental data indicate that fuel consumption and emissions can be predicted to quantitative accuracy. The method has been applied to compare and contrast the importance of various operating regimes during the two cycles.