【正文】 craft and negating some of the benefits of the reduced drag of the retracted gear. While retracting the gear could improve the performance of the plane, it might require a bigger engine and more fuel not to mention more money. In fact, it was this delicate tugofwar between the extra weight of the gear and the reduced drag that was most important for the overall acceptance of retractable landing gear. Drag increases with speed and therefore reducing drag bees more important as an aircraft39。 the aircraft then relies on titanium skids on the wingtips for landingFigure 26 Takeoff dollyFigure 27 Aircraft U2Some main gear struts on World War II aircraft, in order to allow a singleleg main gear to more efficiently store the wheel within either the wing or an engine nacelle, rotated the single gear strut through a 90176。s shock absorption was taken up by a vertically sliding bungee cordsprung upper member. The vertical post along which the upper member slid to take landing shocks also had its lower end as the rotation point for the forward end of the main wheel39。s nose in the down position for better ground handling, with a retracted position that placed the main wheels at some angle behind the main gear39。39。在本文的最后，總結(jié)各種不足和待改進(jìn)之處，并且對CATIA建模的優(yōu)缺點進(jìn)行總結(jié)及展望。分類號 V22 編 號 U D C 621TH12 密 級 公 開 中國民航飛行學(xué)院畢業(yè)設(shè)計（論文）題 目 基于CATIA的大型飛機(jī)起落架建模與分析 The mercial aircraft landing gear modeling and analysis based on CATIA 作者姓名 專業(yè)名稱 熱能與動力工程 指導(dǎo)教師姓名及職稱 提交日期 2012年 6月 12 日 答辯日期 2012年 6月13 日 答辯委員會主任 評 閱 人 2012年6月12日I中國民航飛行學(xué)院航空工程學(xué)院畢業(yè)論文基于CATIA的大型飛機(jī)起落架建模與分析學(xué)生： 指導(dǎo)教師：摘 要本文首先總結(jié)了飛機(jī)起落架的發(fā)展歷史、收放系統(tǒng)及各種結(jié)構(gòu)形式，簡單的列舉了一些由起落架故障引發(fā)的事故。下一步對組裝好的部件進(jìn)行接合，進(jìn)行數(shù)字樣機(jī)收放演示。s speed increases. As aircraft speeds continued to increase during the 1930s, particularly as aircraft began to reach speeds of 200 miles per hour, the increased weight of retractable gear became less important than reducing drag, and retractable landing gear became monplace to most aircraft. Today, many lowspeed private aircraft still have fixed landing gear because of cost and maintenance concerns. Some even have the streamlined pants coverings over their wheels. But virtually all larger and faster aircraft have pletely retractable landing gear. Designing such gear presents engineers with a number of problems, particularly how to mount them on the airplane without affecting other parts of the aircraft design. Large mercial airliners like the 747 and Airbus A340 have enough internal volume so that the landing gear can fit inside the fuselage diameter. But some smaller mercial aircraft have to promise. Their fuselages are so small that fitting the landing gear inside the primary fuselage would result in a large bump inside the cabin that passengers would have to walk over. So their landing gear are often fitted inside bulges that stick outside of the fuselage. This is also mon to large military transport aircraft like the C5 and C17(Figure 23), which use up every inch of interior space and need long flat floors inside so that tanks and other equipment can be rolled inside.[10]Figure 23 C17 transport aircraft Different types of gear Tricycle gearThis type of landing gear is the most mon type of landing gear. It often used on the mercial aircraft. We can see it’s structured like a tricycle(Figure 24), with one nose wheel in the front and two wheels located midway on the fuselage. The nose gear is steerable by using the rudder pedals easily than other types of landing gear. This type of landing gear is advantageous in many ways: it allows the pilot to apply the brakes more forcefully without making the plane nose over, offers better stability because the rear wheels are close to the center of gravity and permits better visibility for the pilot during takeoff, landing and taxiing. The majority of modern aircraft are fitted with tricycle landing gear. The following modeling of CATIA is this type of landing gear.Figure 24 Tricycle gear TaildraggerThis type of landing gear is often used on many small pistonengine planes(Figure 25). It consists of two main gear units located near the center of gravity and a tail unit located at the rear of the fuselage. Because the plane appears to drag its tail onto the runway upon landing, this type of landing gear is also known as 39。 angle during the rearwardsretraction sequence to allow the main wheel to rest flat above the lower end of the main gear strut, or flush within the wing, when fully retracted. Examples are the Curtiss P40, Vought F4U Corsair, Grumman F6F Hellcat, Messerschmitt Me 210 and Junkers Ju 88. The Aero Commander family of twinengined business aircraft also shares this feature on the main gears, which retract aft into the ends of the engine nacelles. The rearwardretracting nosewheel strut on the Heinkel He 219 and the forwardretracting nose gear strut on the later Cessna Skymaster similarly rotated 90 degrees as they retracted.On most World War II singleengined fighter aircraft (and even one German heavy bomber design) with sideways retracting main gear, the main gear that retracted into the wings was meant to be raked forward, towards the aircraft39。s suspension fork, allowing the main gear to pivot on moderate crosswind landings. Landing gear and accidentsMalfunctions or human errors related to retractable landing gear have been the cause of numerous accidents and incidents throughout aviation history. Distraction and preoccupation during the landing sequence played a prom