【正文】 rom one to four Unix operating systems, including IBM AIX, Silicon Graphics IRIX, Sun Microsystems SunOS, and HewlettPackard HPUX.In 1998, V5 was released, which was an entirely rewritten version of CATIA, with support for UNIX, Windows NT and Windows XP since 2001.In 2008, Dassault announced and released CATIA V6. While the server can run on Microsoft Windows, Linux or AIX, client support for any operating system other than Microsoft Windows is dropped.[5] In November 2010, Dassault launched Catia V6R2011x, the latest release of its platform while still continuing to support and improve its Catia V5 software. In June 2011, Dassault launched V6 R2012.Commonly referred to as a 3DProduct Lifecycle Management software suite, CATIA supports multiple stages of product development (CAx), from conceptualization, design (CAD), manufacturing (CAM), and engineering (CAE). CATIA facilitates collaborative engineering across disciplines, including surfacing amp。 shape design, mechanical engineering, equipment and systems engineering. CATIA provides a suite of surfacing, reverse engineering, and visualization solutions to create, modify, and validate plex innovative shapes. From subdivision, styling, and Class A surfaces to mechanical functional surfaces. CATIA enables the creation of 3D parts, from 3D sketches, sheet metal, posites, and molded, forged or tooling parts up to the definition of mechanical assemblies. It provides tools to plete product definition, including functional tolerances, as well as kinematics definition. CATIA facilitates the design of electronic, electrical as well as distributed systems such as fluid and HVAC systems, all the way to the production of documentation for manufacturing.CATIA can be applied to a wide variety of industries, from aerospace and defense, automotive, and industrial equipment, to high tech, shipbuilding, consumer goods, plant design, consumer packaged goods, life sciences, architecture and construction, process power and petroleum, and services. CATIA V4, CATIA V5, Pro/ENGINEER, NX (formerly Unigraphics), and SolidWorks are the dominant systems.Chapter2 Overview the landing gear Definition of landing gearThe undercarriage or landing gear in aviation is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land. Typically wheels are used, but skids, skis, floats or a bination of these and other elements can be deployed, depending on the surface.Aircraft designers of the 1920s knew that reducing drag on an airplane in flight was important to improving speed and fuel efficiency, as well as maneuverability and controllability. But they still had relatively little understanding of what actually caused drag on airplanes. Various structures obviously caused drag, but they had first to identify the most important sources before they could address them.In 1927, the National Advisory Committee for Aeronautics (NACA) opened its new Propeller Research Tunnel (PRT) at Langley Memorial Aeronautical Laboratory in Virginia. The PRT was a very large wind tunnel for the time, with a diameter of 20 feet ( meters). It was designed to allow the testing of an entire airplane fuselage with engine and propeller, as opposed to simply a part of an airplane or a scale model. NACA aeronautical engineers suspected that the aircraft landing gear contributed to much of the drag of an airplane, and the PRT was the first wind tunnel that would allow them to test this.Landing gear consists of the wheels that stick out below the fuselage so that an airplane can roll down the runway during landing and takeoff. In early aircraft, they were fixed in an open position so that they protruded at all times, even while the plane was flying and nowhere near the ground. Tests in the PRT immediately demonstrated that landing gear contributed up to 40 percent of fuselage drag, which shocked the researchers. They realized that reducing the drag produced by the landing gear would significantly improve the performance of the airplane in flight. There were several ways to reduce the drag of the landing gear. The two most obvious methods were to either retract the landing gear inside the aircraft or redesign a fixed landing gear so that it produced less drag while still protruding below an aircraft. Retracting landing gear were not a pletely new idea in the 1920s. . Wartin39。s Kitten, built in 1917, had retractable gear (but could not actually fly). The Dayton Wright RB1(Figure 21) of 1920 and the Verville Sperry R3 of 1922 also had retractable gear. But these aircraft were rarities and most airplanes had fixed landing gear at the end of metal struts because they were easy to design, strong, and relatively lightweight.Figure 21 Aircraft RB1When designing an aircraft, engineers have always had to address five conflicting requirements. These are: performance, weight, cost, reliability, and maintenance. The best solution to the performance requirement was to pull the landing gear pletely inside the fuselage and cover them over, presenting a smooth surface that produced no drag. But while ideal from a performance standpoint, this approach affected all of the other requirements at weighed more, cost more, was less reliable, and required more maintenance. The wind tunnel data from the PRT caused aircraft designers to look immediately for ways of developing landing gear that provided better performance and hopefully did not have too many other costs associated with them.The Boeing Monomail, which first appeared in 1930, and the Lockheed Orion are generally considered pioneers in the development of retractable landing gear, proving that it was practical. But airplane designer Jack Northrop, who was very interested in streamlining aircraft to improve performance, produced the Northrop Alpha, Beta, and Gamma with fixed landing gear during the 1930s. These aircraft had streamlined coverings tha