外文翻译-飞机起落架设计.doc

1、Aircraft Landing Gear LayoutsMost aircraft today have three landing gear. Two main landing gear struts located near the middle of the aircraft usually support about 90% of the planes weight while a smaller nose strut supports the rest. This layout is most often referred to as the tricycle landing ge

2、ar arrangement. However, there are numerous other designs that have also been used over the years, and each has its own advantages and disadvantages. Lets take a closer look at the various undercarriage options available to engineers.Tailwheel or Taildragger GearThough the tricycle arrangement may b

3、e most popular today, that was not always the case. The tailwheel undercarriage dominated aircraft design for the first four decades of flight and is still widely used on many small piston-engine planes. The taildragger arrangement consists of two main gear units located near the center of gravity (

4、CG) that support the majority of the planes weight. A much smaller support is also located at the rear of the fuselage such that the plane appears to drag its tail, hence the name. This tail unit is usually a very small wheel but could even be a skid on a very simple design.What makes this form of l

5、anding gear most attractive is its simplicity. The gear are usually relatively lightweight, and the two main gear can also be easily encased in streamlined fairings to produce low drag in flight. Another potential advantage results from the fact that the plane is already tilted to a large angle of a

6、ttack as it rolls down the runway. This attitude helps to generate greater lift and reduce the distance needed for takeoff or landing. This attitude is also an advantage on propeller-driven planes since it provides a large clearance between the propeller tips and the ground. Furthermore, taildragger

7、 planes are generally easier for ground personnel to maneuver around in confined spaces like a hangar.However, the greatest liability of this landing gear layout is its handling characteristics. This design is inherently unstable because the planes center of gravity is located behind the two main ge

8、ar. If the plane is landing and one wheel touches down first, the plane has a tendency to veer off in the direction of that wheel. This behavior can cause the aircraft to turn in an increasingly tighter ground loop that may eventually result in scraping a wingtip on the ground, collapsing the gear,

9、or veering off the runway. Landing a taildragger can be difficult since the pilot must line up his approach very carefully while making constant rudder adjustments to keep the plane on a straight path until it comes to a stop. Many taildragger designs alleviate these handling problems by fitting a t

10、ailwheel that can be locked instead of swiveling on a castor. Locking the tailwheel helps keep the plane rolling in a straight line during landing.Another disadvantage of the taildragger is poor pilot visibility during taxiing since he is forced to peer over a nose that is tilted upward at a steep a

11、ngle. It is also often difficult to load or unload heavy cargos because of the steep slope of the cabin floor. Similarly, pilots and passengers are forced to walk uphill during boarding and downhill after arrival. Many aircraft also rely on gravity to bring fuel from tanks to the engine, and some pl

12、anes have been known to have difficulty starting the engine because it is uphill from the fuel supply.Good examples of taildragger aircraft include the Spitfire and DC-3 of World War II.Tricycle or Nosewheel GearNow the most popular landing gear arrangement, the tricycle undercarriage includes two m

13、ain gear just aft of the center of gravity and a smaller auxiliary gear near the nose. The main advantage of this layout is that it eliminates the ground loop problem of the taildragger. This arrangement is instead a stable design because of the location of the main gear with respect to the center o

14、f gravity. As a result, a pilot has more latitude to land safely even when he is not aligned with the runway.Furthermore, the tricycle arrangement is generally less demanding on the pilot and is easier to taxi and steer. The tricycle gear also offers much better visibility over the nose as well as a

15、 level cabin floor to ease passenger traffic and cargo handling. A further plus is that the aircraft is at a small angle of attack so that the thrust of the engine is more parallel to the direction of travel, allowing faster acceleration during takeoff. In addition, the nosewheel makes it impossible

16、 for the plane to tip over on its nose during landing, as can sometimes happen on taildraggers. The greatest drawback to tricycle gear is the greater weight and drag incurred by adding the large nosewheel strut. Whereas many taildraggers can afford to use non-retracting gear with minimal impact on performance, planes with nosewheels almost always require retraction mechanisms to reduce drag. Some planes with tricycle gear also have difficulty rotating th