The CH-47 Chinook cargo helicopter of US Boeing is very easy to identify. In other words, it looks quite strange. It is all because of its` tandem-rotor design which makes itself rather different from other helicopters. Development of the medium lift Boeing models 114 and 414, CH-47 Series Chinook began in 1956. Since then successive product improvements carried out, the main variations include CH-47A, CH-47B, CH-47C and CH-47D.
美国波音公司的CH-47“支努干”运输直升机是一种很好辨认的直升机，因为它的外观很奇特。尤其是它的纵列双旋翼，使得它显得与众不同。CH-47系列源自波音公司1956年开始发展的114和414型号。随后出现了多种改进型号，主要包括CH-47A，CH-47B，CH-47C和CH-47D。该机是美陆军装备中最为主要的重型运输直升机型号。最新的CH-47F于2006年完成组装，并开始逐步交付美军使用。空军世界 http://www.airforceworld.com
The tandem rotors are both high above the fuselage. And the two engines are externally outside the rearward of the fuselage, the rotor on the head is driven by the rotors with a transmission shaft on the top of the cabin. This design means that the aircraft had a 50 feet long cabin capable of carry up to 45 fully-equipped troops, or 10 tonnes of cargo, or 155mm howitzer, or small vehicles internally or externally on one of three mopunting points, without any structure limit. That`s why the tandem rotors is chosen. At the end of the cabin, the tail of CH-47, there is a rear loading ramp door, easily load or unload the cargo. The small vechiles can be driven out of the cabin by themselves through this door. Two big size side doors are on the aircraft, too. The large payload makes CH-47 an ideal battlefield support aircraft.
点击查看：CH-47详解剖视图
CH-47的两个纵列旋翼安置在机身上方，两台发动机则外置在机身后部，发动机通过一条安装在机身顶部的传动轴驱动前旋翼(下图)。这种设计意味着CH-47的的机舱和外挂点不受机体结构影响，机舱长而平直，三个外挂点也容易布置。其货舱能够装载45名全副武装的士兵，或10吨货物，或155毫米榴弹炮，或小型汽车。外挂点也有相应的承载能力。这种宽大方便的机舱、外挂点设计要归功于纵列双旋翼布局。在CH-47机尾处有一个可放倒的跳板式机舱门，装载货物非常简便。小型车辆可通过这扇门自由进出机舱。另外机上还有两个大尺寸的侧门。由于有较大的载重量，CH-47算得上是一种理想的战场供应直升机。空军世界 http://www.airforceworld.com
Another good point of the tandem rotors is that no tail rotor is needed to counter the torque so that the power efficiency is excellent. But this counter-rotation also causes a problem that the blades must be synchronized to avoid them touching another
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