【正文】 riot XI Channelcrossing aircraft of 1909 and also copied in the earliest examples of the Etrich Taube. In this arrangement the main landing gear39。s attachment point to the airframe this led to a plex geometry for setting up the angles for the retraction mechanism39。s centre of gravity due to the deviation), and usually require special pilot training. Sometimes a small tail wheel or skid is added to aircraft with tricycle undercarriage, in case of tail strikes during takeoff. The Concorde, for instance, had a retractable tail bumper wheel, as delta winged aircraft need a high angle when taking off. The Boeing 727 also had a retractable 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。taildragger gear.39。 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。關(guān)鍵詞：起落架，CATIA，結(jié)構(gòu)設(shè)計，數(shù)字樣機中國民航飛行學院航空工程學院畢業(yè)論文ABSTRACT The development history of the landing gear and all kinds of structure form and retraction system are summarized. And some accident cause by landing gear are listed. Then the basic knowledge of CATIA V5 as covered, from the application character