飛機起落架設(shè)計外文文獻翻譯、中英文翻譯,飛機,起落架,設(shè)計,外文,文獻,翻譯,中英文 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 nose 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 used over the years, and each has its own advantages and disadvantages. Let''s take a closer look at the various undercarriage options available to engineers. Tailwheel or Taildragger Gear Though the tricycle arrangement may be 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 (CG) that support the majority of the plane''s 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 landing 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 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. However, the greatest liability of this landing gear layout is its handling characteristics. This design is inherently unstable because 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 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, 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 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 nose that is tilted upward at a steep angle. 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 planes 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 Gear Now 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 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 of 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 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 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 the nose up during takeoff because the main wheels are located so close to the elevator, and there may be insufficient control effectiveness. Similarly, the closeness 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 nosewheel. Too little load on the main wheels reduces their braking effectiveness while too little on the nosewheel 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. There are many examples of aircraft with tricycle landing gear, including the F-16 and Cessna 172. Summary Landing gear serves three primary purposes--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 these tasks are secondary to the plane''s primary role as an efficient mode of travel through the air. 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 case was a study done by the Royal Navy to see 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 used on carrier-based 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 seen 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 these strengths and weaknesses as they apply to the environment the plane is designed for. As a result, designers try to select 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 because fewer gear weigh less, require less structure aboard the plane, take up less space when retracted, and generate less drag. 飛機起落架設(shè)計 許多現(xiàn)代飛機使用三點式起落架。重心附近的兩個大的主輪，承擔(dān)約 90% 的重量，小輪子承擔(dān)余下部分。目前的飛機以前三點起落架為主，讓我們來回顧一下后三點起落架及其優(yōu)缺點。(意譯) 后三點尾輪式與后三點尾橇式起落架 雖然前三點起落架比較普遍，但是在幾十年前的飛機，及當(dāng)今的許多小型飛機是使用后三點起落架的。后三點起落架，由兩個在重心靠前位置的主輪支持大部分的飛機重量。一個非常小的尾輪裝置在機身，看上去這個小輪子是被拖著走，所以，英文 Taildragger 也因此而得名。它即可以是一個小尾輪，也可以是一個尾橇。 后三點起落架 后三點起落架最吸引人的優(yōu)點就是“簡潔”。后三點起落架通常重量都比較輕。兩支主輪子可以配置整流置用來減小飛行中的阻力。另一個潛在的優(yōu)點，是飛機在跑道滑行時，機翼已經(jīng)有一個較大的迎角。合適的大迎角，有利于在較低的速度下產(chǎn)生足夠的升力，以便于減少起飛滑跑距離。對于牽引式螺旋槳飛機，機頭向上抬起，使螺旋槳不會接觸跑道。(意譯) 同時，后三點起落架的飛機，更便于地勤人員把飛機拖到停機棚等窄小的空間里。 另一方面，后三點起落架也有一個最大的缺陷——著陸時的操縱(handling characteristics). 造成此天生缺陷的原因，是因為兩只主輪在重心的前面。如果著陸時起落架只有一只主輪前觸地，這時，飛機有向此輪子一邊轉(zhuǎn)彎傾向。嚴重時，這種轉(zhuǎn)彎的傾向(ground loop)將可能使翼尖觸地、起落架受損、滑出跑道。這就要求在飛機著陸觸地前，需要使用方向舵修正自己的航線，使它能夠筆直的滑翔直到安全觸地。使用尾橇，能減輕這種現(xiàn)象。(意譯) 前三點起落架與后三點起落架的安定性對比 后三點起落架的另一個缺點，許多飛機在地面滑跑, 機頭向上翹起時，會影響飛行員的視線。(意譯)對于貨機，飛機的迎角不利于貨物的裝卸。此問題，對于乘客來說，也是一樣的道理。(意譯) 發(fā)動機抬起，有時也不利于供油，造成啟動困難。 道格拉斯DC-3的后三點起落架 后三點起落架的典型例子：噴火戰(zhàn)斗機、道格拉斯DC-3。 前三點起落架 前三點起落架，由兩支在重心后的主輪，與一個在機頭的輔助前輪組成。(意譯)前三點起落架最大的優(yōu)點是不會像后三點那樣，著陸時容易打轉(zhuǎn)。這得益于主輪子在重心后部的設(shè)計。這樣，就算著陸時飛機沒有對準跑道，飛行員還是有辦法修正方向的。 前三點起落架 前三點起落架更容易操縱。(意譯)水平的機身，使視界比較好，而且便于裝貨及乘客行走。機翼的小迎角，螺旋槳在水平方向產(chǎn)生的力，有助于飛機更快獲得速度。(意譯) 另外，由于前輪距重心較遠，就不會出現(xiàn)后三點起落架容易發(fā)生的“拿大頂”現(xiàn)象。(意譯) 前三點起落架最大的缺點是，較重的重量及較大的阻力。(意譯)另一方面，固定式后三點起落架耐沖擊性能較強。而前三點起落架，需要收放式以減小飛行時的阻力。前三點起落架影響舵效。(意譯) 前三點起落架對飛機重心的要求也比較高。 747 加油次序不當(dāng)，造成機尾觸地的危險。 F16 與 Cessna 172 都是前三點起落架的經(jīng)典案例。 總結(jié) 起落架的三個主要任務(wù)： 一、把飛機停放在地面。 二、起飛及著陸時提供穩(wěn)定的支持。 三、著陸時減震。 飛機的飛行性能還是很重要的。(意譯) 飛機的飛行性能比在地面的性能重要的多。(意譯) 有人嘗試過不使用起落架，直接用機腹在航母甲板上著陸。(意譯) 很不幸，這個試驗暫未完成成功。(意譯) 我們看到，有各種各樣的起落架，每一種都有它自己的優(yōu)缺點。實用中，需要根據(jù)飛機及外界環(huán)境，綜合優(yōu)缺點考慮來進行選擇。在保障安全的前提下，最簡單的、最小的、最輕的、最便宜的方案是比較好的選擇。分析現(xiàn)在的飛機，就是按照上面的說法設(shè)計起落架的。如：重量更輕、簡潔的結(jié)構(gòu)、更小的阻力、收放式。(意譯)