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Over 30 years ago, A. H. Vincent of Westland Helicopters demonstrated that if a structure is excited harmonically, the response at another position (at a fixed frequency) will trace a circle in the complex plane as a result of a dynamic stiffness modification between two points. As either the real or imaginary part of an introduced dynamic stiffness is varied from minus infinity to plus infinity, the structural or acoustic response on any position will map a circle in the complex plane. This paper reviews the basis for this little known principle for vibro-acoustics problems and illustrates the viability for a cantilevered plate example. The applicability of the method is then considered for strictly acoustic systems like intake and exhaust systems. Specifically, it is shown that the response traces a circle in the complex plane if either the real or imaginary parts of the source or termination impedance are varied from minus to plus infinity.

Many motor vehicles (fire-fighting cars and trucks, helicopters, airplanes, etc.) are used for conflagration extinguishing purposes. It is clear that their engines aspirate air containing combustion inhibitors, which are used for flame suppression, but until now there is no available information about the influence of this fact on engine performance. This paper presents results of an experimental study on the influence of combustion inhibitors, such as Halon 1301 (CF₃Br) and CO₂, contained in the ambient air, on the performance of compression ignition (CI) and spark ignition (SI) engines. Substantial differences in the response of CI and SI engines to the inhibitor presence in the aspirated air are revealed. Starting from relatively small concentrations of CF₃Br, an increase of the CI engine speed and a simultaneous decrease of the brake specific fuel consumption are observed. The speed rise may attain up to 80% of its initial value.

Recent researches [1, 2, 3 and 4] showed that the vibration is one of the common occupational risks. The exposition rising to the human body vibration, in hard working that operate tractors, machines diggers and too much vehicles is incomplete, however there are evidences that the regular exhibition to the vibration, can contribute in the pains generation in the back in professional drivers such as, drivers by bus, by tractors and helicopters. According to Griffin [2], to the exhibition to the human body vibration are related to problems in the activity muscular/postural, circulatory system problems and the appearance of inter-muscular disturbances. This way, with the increasing use of off-road vehicles and of new kinds of seats, the acceleration levels investigation and necessary comfort is done, as well as, the dynamic characterization of the same.

Five design schemes of helicopter nacelle ventilation cooling system were proposed to provide efficiently cooling for the nacelle. In order to evaluate the cooling effect of these design schemes, the characteristic of airflow and heat transfer in the nacelle was numerically calculated by a general CFD software. Unstructured mesh and finite volume method (FVM) were applied for calculation regions and governing equations discreteness, and standard k - ε model was adopted to solve turbulent governing equation. For five schemes of nacelle cooling system, the influence of cooling air inlet size, position, mass flow rate and ambient temperature under hover condition on the flow and temperature field distributions was discussed. Also transient calculations were carried out when the engine was shut down. The results provided a theoretical basis for design and optimization of nacelle ventilation cooling system.

Vehicle cabin gear whine levels have long been known to contribute to driver annoyance and perceptions of poor quality in passenger cars and trucks, as well as contributing to operator fatigue in helicopters and heavy machinery. For material handling vehicles, radiated gear whine not only influences annoyance and fatigue of operators, but also creates unwanted noise in the operational environment such as warehouses and plants. Upfront management of gear whine levels using predictive software tools is therefore critical for satisfactory design of gearboxes used in such applications. One challenge, however, is selecting the proper boundary conditions for modeling a gearbox acting as a load-bearing structural member used in the material handling vehicles.

The need to reduce weight of large and heavy components used by the automotive and aerospace industries such as engine block, cylinder head cover and helicopter gearbox housing has led to the development of new Mg gravity casting alloys that provide adequate properties and cost effective solution. The new Mg gravity casting alloys are designed for high stressed components that operate at a temperature up to 300°C. These new alloys exhibit excellent mechanical properties and creep resistance in T-6 conditions. The present paper aims at introducing three new Mg gravity casting alloys designated MRI 201S, MRI 202S and MRI 203S, which were recently developed by the Magnesium Research Institute of DSM and VW. Apart from the excellent high temperature performance of these alloys, they provide adequate castability and dimension stability along with good weldability and corrosion resistance.

This paper proposes new methods to assess the validity of reliability prediction models through a Bayesian approach. The concept of Bayesian hypothesis testing is extended to system-level problems where full-scale testing is impossible. Component-level validation results are used to derive a system-level validation measure. This derivation depends on the knowledge of interrelationships between component modules. Bayes networks are used for the propagation of validation information from the component -level to system-level. Validation of reliability prediction model for a single degree of freedom oscillator under high-cycle fatigue and fatigue life prediction of a helicopter rotor hub is illustrated for this purpose.

In this paper results are presented from a study that investigates the use of centrifugally driven pendulum vibration absorbers for the attenuation of engine torsional vibrations. Such absorbers consist essentially of movable counterweights whose center of mass is restricted to move along a specified path relative to the rotational frame of reference. These devices are commonly used in light aircraft engines and helicopter rotors. The most common designs use a circular path for the absorber, tuned to a particular order of rotor disturbance, although more recent developments offer a wider variety of paths. Our goal here is to evaluate the system performance for a range of path types with different types of tuning. This analytical study is carried out for a simple mechanical model that includes a rotor and an absorber riding along a quite general path. Approximate solutions are obtained using a perturbation scheme and compared with detailed computational results.

The objective of this study was to use the driving-point impedance and transmissibility techniques to evaluate and compare the resonance behavior of two male humans, the Hybrid III aerospace manikin, and a rigid body mass using a rigid seat and a selected helicopter seat cushion. All occupants represented the 95th percentile or higher of the male population for weight. The results showed that the resonance frequencies associated with the peak impedance, chest, and head transmissibilities were significantly higher in the manikin regardless of the seating configuration or input acceleration level. While the magnitude of the peak impedance was higher in the manikin, differences in the chest and head transmissibilities depended on both the seating configuration and acceleration level. Neither the manikin nor the rigid body were effective in predicting the primary human resonance effects occurring in the sensitive region of 4 to 8 Hz.

Airport land planning commissions often are faced with determining how much area around an airport is affected by the sound exposure levels (SELs) associated with helicopter operations. This paper presents a study of the effects changing the size and composition of a microphone array has on the computed SEL contour (ground footprint) areas used by such commissions. Descent flight acoustic data measured by a fifteen microphone array were reprocessed for five different combinations of microphones within this array. This resulted in data for six different arrays for which SEL contours were computed. The fifteen microphone array was defined as the “baseline” array since it contained the greatest amount of data. The computations used a newly developed technique, the Acoustic Re-propagation Technique (ART), which uses parts of the NASA noise prediction program ROTONET. After the areas of the SEL contours were calculated the differences between the areas were determined.

The paper describes two studies. In the first study the most comfortable position of headgear centre-of-mass is determined for three masses. The positions are described in a head-fixed co-ordinate system based on skull geometry and eye position, considering that these are essential to all headgear, and anticipating the growing use of 3D scan data in headgear design. In the second study the results were applied to a helicopter pilot helmet to improve comfort when using night vision goggles.

By applying a P.T.F.E. bearing material to the sealing lip, the life and capabilities of a radial lip shaft seal can be significantly improved. Puddles of oil on driveways, helicopter pads, and shop floors are unattractive and bothersome to consumers, maintenance experts, and design engineers of virtually every mechanical device produced today. To the understanding observer, this can indicate that a seal’s useful life has expired, thus requiring machine shutdown and seal replacement. The scope of this article is limited to radial lip shaft seals. A discussion of the major reasons for seal failure due to excessive lip wear is followed by recommendations to aid the engineer in deciding when P.T.F.E.-lined seals can be beneficial.

A parameteric study was made of the variables associated with a rotary brush air cleaner for helicopter gas turbine engines. Tests were conducted at air volumes ranging 3000-8000 ft3/min and brush speeds of 1200-3000 rpm. While centrifugal effects were found to be an important cleaning mechanism, impaction effects significantly improved dust separation at brush speeds above 2400 rpm. On a constant impaction area basis, brushes with 1 mm diameter wires were more efficient than brushes with 2 mm wires. Wires added in the axial direction were more effective than wires added in a radial direction. Separation efficiency at 8000 ft3/min of dust laden air and brush speeds of 3000 rpm approached 100% for size classified test dusts in the 15-35 μm size range. The separation efficiency on a 2.7 μm mass mean diameter test dust was a respectable 66%. Only 7 hp was required to rotate the brush shaft at 3000 rpm; the pressure drop of 4 in of H2O was independent of brush speed.

Detroit Diesel Allison (formerly Allison) Division of General Motors has, since 1965, been developing and producing several models of its small model T63/250 gas turbine engine. This paper discusses the continuing engine program by identifying models and applications of both turboshaft helicopter engines and turboprop fixed wing aircraft powerplants. Progress in development of higher horsepower versions which improve the performance and utility of business aircraft is also discussed.

The 1500 SHP T700 Engine is being developed for the U.S. Army UTTAS and AAH Helicopters. Prototype engines have been running well since testing began early in 1973. Qualification is expected in early 1976. Engine history and current details, design features, program milestones and possible future developments are reviewed. The unique T700 design will achieve unusually high levels of reliability and maintainability.

The purpose of this paper is twofold: (1) to show that Naval aviation has continuing requirements for shaft-power turbine engines, and (2) to describe briefly some of the more important aspects of turboprop and turboshaft engines under development to fill these requirements. Brief coverage will be given to performance, variations in configuration, applications, and, lastly, developmental problems still requiring action by American industry and ingenuity. By way of definition, the term “turboprop” applies to a shaft-power turbine engine primarily for use in fixed-wing aircraft. This engine is currently being advertized under the more sophisticated name of “prop-jet.” The term “turboshaft” applies to a shaft-power turbine engine primarily for use in helicopters and other aircraft with vertical or short take-off capability.

The U.S. Army CH-47D helicopter modernization program incorporates improvements in all major subsystems. The drive train has been redesigned to incorporate evolutionary improvements which will increase reliability, survivability, and maintainability. This paper describes the background experience that led to the selection of VASCO X-2 high-hot-hardness gear steel; it also discusses design improvements in the integration of components, in lubrication and diagnostic systems, in overrunning clutches, and in noise reduction. New capabilities to predict and measure gear bending stresses and resonant frequencies have been developed and are described as part of a systems design approach.

This paper describes the development and content of the NASA-developed structural analysis computer program called NASTRAN. This program is in extensive use in the automotive industry as well as the aerospace and helicopter industries, and has become a standard of reference among finite element programs.

Payload and time-on-station performance of long endurance aircraft is shown for aircraft equipped with conventional and regenerative turboprop engines. Incorporation of laminar flow control on the airframe and addition of regeneration to helicopter engines is discussed; these two design considerations appreciably improve performance. Also, for helicopter missions in excess of approximately 2 hr duration, improvement in performance can be obtained by addition of regeneration process to the turboshaft engine cycle.

The joint philosophies of “safe life,” “fail-safe,” and “failure safety,” are considered in the design of new rotary wing aircraft with particular regard to airline type operation. The methods of developing these characteristic in the aircraft are discussed -- including state-of-the-art and advanced concepts. The subjects include structural considerations of rotors, power transmission, airframe and landing gear; stability and control considerations; instruments and avionics; controls; and electrical and hydraulic systems. Lockheed believes these characteristics can be designed into rotary wing aircraft and thus provide flight safety that exceeds the excellent records of such operators as Los Angeles Airways, New York Airways, and San Francisco and Oakland Helicopter airlines.