Search Results

Aircraft manufacturers spend millions of dollars reworking blown fastener holes, especially in portable tool drilling situations. Oval, tapered, rifled, and oversize holes are costly rework issues currently commonplace in the industry. The most common causes of imperfectly drilled holes include spindle runout, insufficient clamp and feed force, out-of-balance drill feed forces, spindle windup, and lack of adequate feed control. This paper will focus on a next-generation drilling machine that utilizes a unique combination of hydraulics and pneumatics to solve the problems associated with legacy drilling units. Several design elements will be examined, such as the use of an on-board, 1000 PSI hydraulic pump, controlling both drill feed and clamp force. This greatly reduces the size and weight of the clamp and feed cylinders compared to legacy air systems, while increasing their force and rigidity.

This paper describes the typical development process for avionics hardware and how this relates to the systems and software processes. The decline in availability of military components and the consequential impact on equipment design, manufacturing and support is discussed. Some solutions to the problems arising are proposed.

The 757 and 767 airplanes provide maximum commonality in equipment, flight deck configuration and handling characteristics. Pilots with three-crew ratings will be qualified to fly either airplane with a three-crew requirement, and those with two-crew ratings will have the same flexibility. In addition to crew qualification, over 80% of the LRUs in the Flight Management System are interchangeable between similar crew configurations of the 757 and 767, i.e., they have the identical part number. Seventy-five percent of the LRUs are common to both the two-and three-crew configurations. Components that have engine-related software (the Thrust Management and Flight Management Computers) will be interchangeable between 757 and 767 aircraft powered by engines from the same manufacturer.

Commercial airlines use a variety of hydraulic fluid mixtures, some of which had been reported to cause increased valve erosion. An extensive test program was conducted to determine why certain mixtures of aircraft phosphate ester hydraulic fluids cause erosiveness in valves while others have negligible effect. Use of nonerosive mixtures is important to the aircraft industry to reduce the high cost of maintenance caused by erosion. Accelerated tests were conducted to identify erosive and nonerosive mixtures of presently available fluids. Chemical tests were conducted with a matrix of test fluids to establish methods that will predict the effects measured in erosion tests. Erosiveness of fluid mixtures can now be predicted by means of two laboratory measured electrochemical properties; wall current and threshold corrosion current density.

A review is given of air cargo economics over the past 15 years. Changing fleet mix, cargo handling techniques, and fuel cost are identified as significant determinats of economic patterns. In a forecast of the next 10 years, the impact of wide-bodied freighters is assessed, particularly with respect to their use in intermodal, air/highway movement of large, prepacked shipments. Estimates of different aircraft/load modes are given; container design, aircraft configuration, and loading equipment are crucial elements in cost projections.

Recent developments in sonic inlet technology are presented with particular emphasis on STOL propulsion systems. Inlet noise reduction requirements are discussed for an augmentor wing and an upper surface blowing type of propulsion system. The current state of the art is discussed with respect to performance and noise potential of different sonic inlet concepts. Acoustic and aerodynamic performance comparison is presented for several inlet configurations based on experimental results.

The sleeve cold-working process for fastener holes is a process that uses a tapered mandrel in conjunction with a disposable, prelubricated split sleeve to compressively prestress a significant zone around a fastener hole. This compressive prestressing offsets the stress concentration of the hole itself to produce substantial improvements in structural fatigue performance of fastened joints. The sleeve method allows higher degrees of prestressing than are possible with other methods and does not require precision controls and skills germane to other fatigue-rated hole preparation/fastener systems.