Aircraft Landing Gear Layouts
Most aircraft today have three landing gear. Two main landing gear struts located near the middle of the aircraft usually support about 90% of the plane''s weight while a smaller no strut supports the rest. This layout is most often referred to as the "tricycle" landing gear arrangement. However, there are numerous other designs that have also been ud over the years, and each has its own advantages and disadvantages. Let''s take a clor look at the various undercarriage options available to engineers.
permittingTailwheel or Taildragger Gear
Though the tricycle arrangement may be most popular today, that was not always the ca. The tailwheel undercarriage dominated aircraft design for the first four decades of flight and is still widely ud on many small piston-engine planes. The taildragger arrangement consists of two main gear units located near the center of gravity (CG) that support the majority of the plane''s weight. A much smaller support is also located at the rear of the fulage 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 landing gear most attractive is its simplicity. The gear are usually relatively lightweight, and the two main gear can also be easily encad in streamlined fairings to produce low drag in flight. Another potential advantage results from the fact that the plane is already tilted to a lar
meet是什么意思>delicious是什么意思ge angle of attack 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 planes are generally easier for ground personnel to maneuver around in confined spaces like a hangar.让子弹飞 台词
However, the greatest liability of this landing gear layout is its handling characteristics. This design is inherently unstable becau the plane''s center of gravity is located behind the two main gear. 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 cau the aircraft to turn in an increasingly tighter "ground loop" that may eventually result in scraping a wingtip on the ground, collapsing the gear, 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 the handling problems by fitting a tailwheel 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 no that is tilted upward at a steep angle. It is also often difficult to load or unload heavy cargos becau of the steep slope of the cabin floor. Similarly, pilots and pasngers 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 planes have been known to have difficulty starting the engine becau it is uphill from the fuel supply.
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Good examples of taildragger aircraft include the Spitfire and DC-3 of World War II.
Tricycle or Nowheel Gear
quelNow the most popular landing gear arrangement, the tricycle undercarriage includes two main gear just aft of the center of gravity and a smaller auxiliary gear near the no. The main advantage of this layout is that it eliminates the ground loop problem of the taildragger. This arrangement is instea
d a stable design becau of the location of the main gear with respect to the center of gravity. As a result, a pilot has more latitude to land safely even when he is not aligned with the runway.
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Furthermore, the tricycle arrangement is generally less demanding on the pilot and is easier to taxi a
nd steer. The tricycle gear also offers much better visibility over the no as well as a level cabin floor to ea pasnger 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 nowheel makes it impossible for the plane to tip over on its no 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 nowheel strut. Whereas many taildraggers can afford to u non-retracting gear with minimal impact on performance, planes with nowheels almost always require retraction mechanisms to reduce drag. Some planes with tricycle gear also have difficulty rotating the no up during takeoff becau the main wheels are located so clo to the elevator, and there may be insufficient control effectiveness. Similarly, the cloness to the rudder reduces its effectiveness in counteracting crosswinds. Another critical factor when designing tricycle gear is to properly balance the load carried by the main gear versus the nowheel. Too little load on the main wheels reduces their braking effectiveness while too little on the nowheel reduces its steering effectiveness. Careful balancing of weight is also important to prevent the plane from tipping back on its tail while at rest on the ground.
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There are many examples of aircraft with tricycle landing gear, including the F-16 and Cessna 172.
Summary好翻译
Landing gear rves three primary purpos--to provide a support for the plane when at rest on the ground, to provide a stable chassis for taxiing or rolling during takeoff and landing, and to provide a shock absorbing system during landing. Regardless, all of the tasks are condary to the plane''s primary role as an efficient mode of travel through the air.
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To aircraft designers, landing gear are nothing more than a necessary evil since planes are designed primarily for their performance in flight rather than on the ground. There have even been attempts over the years to eliminate landing gear entirely. The most extreme ca was a study done by the Royal Navy to e if a jet plane could make a belly landing on the deck of an aircraft carrier coated with a rubberized surface. If successful, the method would eliminate the need for the very strong and heavy landing gear ud on carrier-bad aircraft. Unfortunately, the method proved impractical, but it shows the lengths some will go to while attempting to eliminate the need for landing gear!
We have en that landing gear come in many varieties and each option has its own advantages and disadvantages. Selecting the best arrangement for a given aircraft is a trade-off between the strengths and weakness as they apply to the environment the plane is designed for. As a result, designers try to lect the simplest, smallest, lightest, and least expensive solution possible to do the job while maintaining safety. That is why most planes only have three landing gear rather than four becau fewer gear weigh less, require less structure aboard the plane, take up less space when retracted, and generate less drag.
