Search Results

The rising cost of Military Aircraft Systems during a period of declining purchasing power has forced the military and industry to make trade-offs of system and component performance against cost, even during the advanced technology stages of development. An evaluation tool is needed for use by the conceptual designer/evaluator to characterize these trade-offs properly. A computerized Life Cycle Cost Model has been developed that uses parametric data to help the designer to determine these trade-offs/cost values during advanced technology engine development stages. This computerized model includes airframe and mission considerations.

A T-63 combustor rig has been used to study the sensitivity of combustor performance to the physical and chemical properties of fuels. The purpose was to determine the impact of broadening fuel specifications and using non-specification fuels in emergencies. The fuel properties of special concern were the composition, the distillation curve and viscosity. The first property is associated with the chemistry of carbon formation while the latter two are related to mixing as they affect the atomization and vaporization. Six fuels were blended from a JP-5 base fuel and used to determine the effects of aromatic content, types of aromatics, and end point. Three JP-5s derived from coal, shale oil, and tar sands, were used to see if they correlated the same as the petroleum-derived fuels despite their different chemistry. Seven more fuels that were blends of marine diesel, JP5, and gasoline were used to examine all aspects but with emphasis on viscosity and distillation curve.

The F/A-18 Program is among the first to apply the Naval Air Systems Command “New Look Acquisition Fundamentals” from contract award. The New Look establishes firm requirements and incentives for achieving reliability and maintainability. It imposes stringent disciplines on design, test, and manufacturing to assure compliance to those requirements. In the case of the radar (at least), the level of reliability and maintainability specified could not be achieved by these disciplines alone. A substantial simplification of system architecture and its hardware (over previous tactical radars) was also required. This paper describes how that simplification was achieved, while at the same time gaining substantially in multimission capability. It also summarizes the status of key elements of the New Look program at this early stage of the development program.

The Department of Defense consumes approximately 2.7 percent of the total U.S. demand for petroleum. The Air Froce usage accounts for 57 percent of the DOD consumption with approximately 82 percent being consumed as jet fuel. The cost of this fuel to the Air Force has increased greatly since the 1973 oil embargo. The bill in 1973 was slightly over one-half billion dollars for 112 million barrels of JP-4, whereas, it is now approximately 1.6 billion dollars or about 6 percent of the Air Force annual budget for only 80 million barrels. This paper discusses an Air Force program which will result in adequate fuel availability for the Air Force at an acceptable cost. Results of recent processing studies on alternative hydrocarbon sources from shale oil are presented, together with combustor studies directed to determining the effects of property variations on combustor performance, durability and level of harmful emissions.

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.

A description of the Lynx transmission is linked with the basic factors which determined its general form. This gear system is compared with other alternatives and an improved Lynx system is also shown which gives even higher load capacity. Some of the characteristics of the output stage Conformal gears are given, together with a description of a few of the development stages through which the gears have passed.

The successful procurement of hardware items with reliability R, maintainability M, and system safety SS requirements and R, M, and SS program requirements involves no particularly new or unusual techniques. It does require the consistent, disciplined use of several of the tools presently available, i.e., the item specification, a really comprehensive statement of work (SOW) and a data requirements list (CDRL). These all must be closely coordinated so that they “track together”. Clear distinctions between tasks to be accomplished, requirements for the design, and data items to be prepared are essential. Also, most system contractors need to better inform their potential suppliers.

V/STOL aircraft propulsion systems are required to provide vertical lift, horizontal thrust, attitude control, and distribution of power for engine-out cases with high efficiency, low weight, and high reliability. These V/STOL requirements have been converted into specific design objectives for mechanical drive components including the gears, bearings, clutches, and shafting that interconnect the engines, lift and propulsion fans, and rotors in various V/STOL aircraft defined in recent system studies.

Utility systems in regions where seismic activity occurs frequently (especially in California) face the added task of monitoring the motion of their facilities due to ground shaking. This paper discusses the seismic instrumentation system of one Southern California electric utility. The company's instrumentation falls into three categories: 1. Company initiated, supported and operated, 2. California State agency initiated, supported and operated, and 3. Federal agency initiated, company supported and operated.

This paper summarizes the results of a 3 year research program to advance the state-of-the-art in helicopter free-wheel units (overrunning clutches) by permitting operation at 20,000 rpm. By designing the free-wheel unit to operate at engine input speed instead of at the speed of the 2nd reduction where it is usually located, the torque, and hence size and weight of the unit, will be reduced. High-speed designs, test results, and application of the designs to the UH-60A BLACK HAWK are presented for spring, sprag, and ramp roller types of overrunning clutches.

Due to the critical nature of the application, diesel generator standby systems for nuclear power stations are required by law to be able to survive seismic disturbances and remain functional. Due to the large physical size and weight of this equipment, special considerations would have to be given, to arrive at a balance between reliability and cost. This paper describes the method used, the required engineering judgment and quality level of the results. Prior to the application of diesel generators as emergency standby power source for nuclear power plants, the effects of seismic disturbance were not seriously considered, although the diesel generators have proven over the years to be very reliable as well as durable in conventional applications.

The purpose of this paper is to show the importance of interactive connections between the engine and airframe sections of an aircraft life-cycle-cost model in performing trade-off studies. A model is defined that can accept engine descriptions at the part level, and aircraft mission descriptions for each segment. An important feature of the model is airframe and engine resizing as a result of changes in mission and engine design parameters. Three different trade-off studies are shown to illustrate the versatility of this type of model. The effects of not resizing the airplane and engine are also shown.

Essential facilities are those buildings whose functions are required for the welfare of the public after an earthquake. They include hospitals, communication centers, police and fire stations. A considerable amount of attention has been paid to these facilities to assure that they are structurally competent. Very little significance has been placed on the nonstructural equipment necessary for them to continue operation after an earthquake. This paper describes the operational system and seismic category approach that can be used by the design team to assess the relative worth with respect to overall facility operation of the nonstructural equipment. The various methods of seismic qualification such as shake table testing, complex analysis, simple analysis and engineering judgment are also discussed for nonstructural equipment.

This paper describes the occurance of and presents a solution to shaft failures caused by an unstable asynchronous critical speed, which occurred on a two-part high-speed shaft coupled to a gearbox. The two-part shaft exhibited a first bending synchronous critical speed just below or in the lower portion of the operating speed range of the gearbox. It also exhibited a re-exitation of the same critical speed at a frequency below the rotational speed in the upper portion of the operating speed range. This subsynchronous re-exitation was attributed to the friction generated at the pilot/spline interfaces between the gearbox input shaft and the shaft coupled to it. Because the gearbox operating speed is well defined and limited, the solution to the problem was to raise the first bending frequency beyond the operating range, by redesigning the shafts to increase stiffness, thus eliminating the critical frequency and its re-exitation as a problem.

A nonlinear computer program for Freight Car Response Analysis and Test Evaluation (FRATE) has been developed under the sponsorship of the Federal Railroad Administration. The computer program incorporates a model of a Trailer on Flat Car (TOFC) configuration. Validation of the FRATE/T0FC program is being accomplished through comparison of analysis results to the results of vibration tests performed on a TOFC configuration at the Rail Dynamics Laboratory in Pueblo, Colorado. Validation criteria include resonant frequency, deflection shape at resonance and amplification of input motions. This paper presents a brief review of the FRATE/TOFC computer program, a summary of TOFC vibration test results and comparisons of test and analysis results. Procedures followed to achieve acceptable agreement between test and analysis are reviewed.

For a number of years Grumman Aerospace Corporation has made use of radio controlled models on many of its development programs. Benefits of radio controlled model usage are found in technical areas where they are regarded as valid for certain tasks in the airplane design business as well as in economic areas due to the inexpensiveness of the variety of models which are considered herein relative to their performances.

Finite element models of large structural systems, such as the Space Shuttle or its major components, may contain thousands of finite elements with tens of thousands degrees of freedom. Dynamic analysis to predict structural frequencies and mode shapes is performed after transforming the mass and stiffness matrices, through a series of static reductions, to a reduced set of coordinates which still may include several hundred degrees of freedom. The objective of the present methodology is two-fold: (1) to process test data obtained from either modal survey tests, or slow sine-sweep tests, to extract a set of orthogonal modes best matching the test data while being commensurate with the dynamic model, and (2) to modify submatrices of the dynamic model mass and stiffness matrices to adjust the model to best fit the test data. The method has been implemented using a linear statistical sequential estimator for computation on a CDC computer.

Modal testing has become very popular today for dynamic structural definition and problem resolution of a multitude of dynamic problems. A criterion of purity is presented which is applicable to all modal data regardless of the method of excitation. The modal acceptability and purity ratio allows a one-number linear ratio that describes a percentage deviation from zero, where zero is defined as a pure, natural mode. This ratio was used on the Space Shuttle modal program to provide instant visibility of modal data quality as well as a real-time guide to potential problems associated with certain modes.

The single point excitation procedure employed to experimentally determine the natural modes of the Space Shuttle Main Propulsion Test Article (MPTA) installed in the static firing test stand at the National Space Technology Laboratory is described. Test techniques, equipment, and associated software are described and a comparison to math model results is included. Three single point hydraulic exciters were individually used to apply random excitation forces to the MPTA thrust structure supporting the main engines. Resulting accelerations and force signals were processed with mini-computer test equipment to determine resonant frequencies, mode shapes, and damping values below 50 Hz. Two configurations, one involving empty H2 and LOX tanks and the other involving 40% full LOX tank and feed lines, were tested. Results were obtained with minimum Main Propulsion Test schedule impact and at minimum cost.

A comparison of the performance of modern modal data analysis methods on test data from the Voyager Jupiter/Saturn payload is presented. Four different test/data-analysis combinations are compared--multiple-point sine excitation tests, single-point random-excitation tests using two different techniques of manipulating Fourier transform data, and a time-domain method for analyzing random data. Results indicate that all four methods can give comparable results. Of the four, the time-domain approach detects more modes in the test data and, at the same time, shows the greatest promise for reducing the time and cost of modal testing.