【正文】 tail bumper. Some aircraft with retractable conventional landing gear have a fixed tailwheel, which generates minimal drag (since most of the airflow past the tailwheel has been blanketed by the fuselage) and even improves yaw stability in some cases. Unusual types of gearSome aircraft use wheels for takeoff and then jettison them soon afterwards for improved aerodynamic streamlining without the plexity, weight and space requirements of a retraction mechanism. In these cases, the wheels to be jettisoned are sometimes mounted onto axles that are part of a separate dolly(Figure 26) (for main wheels only) or trolley (for a three wheel set with a nosewheel) chassis. Landing is then acplished on skids or similar other simple devices. Historical examples include the dollyusing Messerschmitt Me 163 rocket fighter, the Messerschmitt Me 321 Gigant troop glider, and the first eight trolleyusing prototypes of the Arado Ar 234 jet reconnaissance bomber. The main disadvantage to using the takeoff dolly/trolley and landing skid(s) system on German World War II aircraft, was that aircraft would likely be scattered all over a military airfield after they had landed from a mission, and would be unable to taxi on their own to an appropriately hidden dispersal location, which could easily leave them vulnerable to being shot up by attacking Allied fighters. A related contemporary example are the wingtip support wheels (Pogos) on the Lockheed U2(Figure 27) reconnaissance aircraft, which fall away after takeoff and drop to earth。然后從草圖工作臺入手，對各個(gè)部分進(jìn)行零部件設(shè)計(jì)及建模，并且展示出建模步驟。s Mirage fighter jet, then was adopted in the aerospace, automotive, shipbuilding, and other industries.Initially named CATI (Conception Assist233。s axis of rotation, with some aircraft, like the P47(Figure 28) Thunderbolt, even mandating that the main gear struts lengthen as they were extended down from the wings to assure proper ground clearance for its large fourbladed propeller. One exception to the need for this plexity in many WW II fighter aircraft was Japan39。 or tricycle undercarriage where there are two main wheels (or wheel assemblies) under the wings and a third smaller wheel in the nose. The taildragger arrangement was mon during the early propeller era, as it allows more room for propeller clearance. Most modern aircraft have tricycle undercarriages. Taildraggers are considered harder to land and take off (because the arrangement is unstable, that is, a small deviation from straightline travel is naturally amplified by the greater drag of the mainwheel which has moved farther away from the plane39。確定每一部分的具體數(shù)據(jù)，連接形式，以及運(yùn)動方式。e Tridimensionnelle Interactive — French for Interactive Aided Threedimensional Design ) — it was renamed CATIA in 1981, when Dassault created a subsidiary to develop and sell the software, and signed a nonexclusive distribution agreement with IBM. In 1984, the Boeing Company chose CATIA V3 as its main 3D CAD tool, being its largest customer. In 1988, CATIA V3 was ported from mainframe puters to UNIX. In 1990, General Dynamics Electric Boat Corp chose CATIA as its main 3D CAD tool, to design the . Navy39。s famous Zero fighter, whose main gear stayed at a perpendicular angle to the centreline of the aircraft when extended, as seen from the side.Figure 28 A Royal Air Force P47A multiple tandem layout was used on some military jet aircraft during the 1950s, pioneered by the Martin XB51, and later used on such aircraft as the U2, Yakovlev Yak25, Yak28 and the B47 Stratojet because it allows room for a large internal bay between the main wheels. A variation of the multi tandem layout is also used on the B52 Stratofortress which has four main wheel bogies (two forward and two aft) underneath the fuselage and a small outrigger wheel supporting each wingtip. The B5239。s center of gravity is located behind the main gear, it may be more difficult to have directional control. For this reason, specific training is required for using aircraft equipped with tailwheel landing gear.Figure 25 “Taildragger” landing gearAnother conventional type named taildragger undercarriage, where there are two main wheels towards the front of the aircraft and a single, much smaller, wheel or skid at the rear。然后進(jìn)行簡化，省略掉液壓管、電線、以及剎車等部件，再將其分為外筒、活塞桿、主支柱、斜支柱、輪軸、扭力臂和機(jī)輪等部分。s Virginia class submarine. In 1992, CADAM was purchased from IBM and the next year CATIA CADAM V4 was published. In 1996, it was ported from 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。s landing gear is also unique in that all four pairs of main wheels can be steered. This allows the landing gear to line up with the runway and thus makes crosswind landings easier (using a technique called crab landing). The challenge of designing a tandemgear layout is that the aircraft has to sit (on the ground) at the optimum flight angle for landing when the plane is nearly in a stalled attitude just before touchdown, both fore and aft wheels must be ready to contact the runway. Otherwise there will be a vicious jolt as the higher wheel fal