İki Kişilik Hafif Askeri Eğitim Uçaği Burun İniş Takimi

Abstract

Bu tez çalışması burun iniş takımı dizaynın sınıf I ve sınıf II metodlan ile dizaynlarını içerir. Sınıf I dizaynında sadece burun iniş takımı değil genel iniş takımlarının bir bütün olarak kabaca bir yerleştirimi yapılır. Bu yerleştirimlerde teker açıklığı, teker izi, ağırlık merkezine göre konumlarının belirlenmesi işlemler tanımlanır. Özellikle sınıf I dizaynda yer aralığı ve devrilme kriterlerinin karşılanması ile de iniş takımı dikmeleri boyunun kaba bir yaklaşımı elde edilir. Bununla beraber iniş takımının lastik boyutları ve teker açıklığı ile tekerlek izi elde edilir. Bunların elde edilmesi için bir önceki adım olarak Sınıf I ağırlık analizinin yapılması gerekir. Bu analizde kanat, gövde, kuyruk, motor ve bunun gibi uçak parçalarının ağırlık merkezlerinin tesbit edilmesiyle genel uçağın ağırlık merkezi tesbit edilir. Çeşitli durumlara görede uçağın en ön ve en arka ağırlık merkezleri tesbit edilir. Sınıf II dizaynında bu ilk yaklaşımlardan sonraki hassas incelemeler içerilir. Sırasıyla lastik seçimi, lastik aralık gerekleri, jant incelemen, iniş ve kalkış sırasında iniş takımlarına gelen yükler, bu yüklerin FAR şartlarına göre minimum ve maksimum halleri, bu şartlara göre iniştakımı dikmelerinin boyutlandırılması, burun iniş takımları hakkında genel dizayn mütalaaları incelenir. Lastik seçimi herbir lastiğe gelen yüklere göre yapılır. Lastik seçildikten sonra bu lastiğin birebir boyutları çizilir. Daha sonra lastiğin genel ömrü boyunca göstereceği ve santrifüj kuvvetlerine maruz kaldığı zaman göstereceği genleşmeler belirlenir ve çevresi ile mesafe düzenlemesi yapılır. FAR şartlarından iniş takımına gelecek maksimum ve minimum yükler belirlenir. Bunlara göre burun iniş takımının şok absorbe boyu ve çapı belirlenir. Yapılan bu inceleme ve hesaplamalar üzerine verilen dizayn kararlarına ait uygulamalar ise hem bölümlerin kendi içlerinden hemde tezin son bölümünde sunulacaktır. Bu çizimler IDEAS ve Autocad yazılımlarının desteği kullanılarak gerçekleştirilmiştir. Ayrıca IDEAS yazılımı mukavemet ve mekanizma tasarımındada kullanılmıştır. Bu çalışma. Zeki KESKİN'in oluşturduğu ana iniştakımı dizaynı, Selami KORKMAZ'ın oluşturduğu flap dizaynı ve Hüsamettin PAYAT'ın oluşturduğu gövde dizaynıyla bir bütünlük arzeder.

The Nose Landing Gear Design of Light Aircraft Nose gear design is a part of the landing gear design and this is a part of exact aircraft design. So, firstly we must have some aircraft design data for analyzing of landing gears. This items was performed in previous sections. And now we use them and get the nose landing gear characteristics. The choose of type of gear in most cases is arbitrary, often dictated by project engineer or the landing gear specialist. Each one generally has a good argument to justify his selection, such as; simplicity, weight savings, requirement for operating from rough fields, company previous experience or tradition. The basic components of a nose landing gear are generally similar to those of a main gear except that provisions must be made for a steering or castering mechanism. In most designs some form of damper device is also incorporated to suppress shimmy. In conventional tractor airplanes the nose gear is usually supported by the engine mount or from the firewall. In some designs the nose gear is supported and housed by a forward extension of the fuselage structure forming the lower half of the engine cowling.. In design we provide two methods; class I and class II. The purpose of class I method is to provide a rapid method to determine the following landing gear characteristics. These are; number, type, and size of tires, length and diameter of strut(s), preliminary disposition, retraction feasibility. The main wheels should be located aft of the most rearward C.G to insure that the aircraft will not tip on its tail under normal circumstances, but this point should not be too far aft; otherwise, the load on the nose wheel will be too high. In turn, the load on the nose wheel should be as far forward of the C.G. as possible and compatible with the structure or retraction requirements. The normal nose Wheel load is in the order of 10 to 20% of the aircraft weight. Too much nose wheel load may require high elevator down load to rotate the aircraft during takeoff. A too light nose wheel load will make steering inadequate. The best compromise is to have approximately 15% of the weight of the airplane on the nose Wheel at the static level attitude, and also to make sure that the tail will not tip down as explained before. Also it was found that when the nose wheel load is less than 10%, for example 8%, a slow oscillation in pitch, called "porpoising", may occur. This oscillation in pitch has not been encountered with more forward position of C.G. Xll In class I design steps, we firstly decide which landing gear system to use: retractable or non retractable. As a general rule, if the cruise speed of airplane is above 150 knots, a fixed gear imposes an unacceptably high drag penalty. So we choose the retractable gear. After that we decide which landing gear configuration will use on aircraft. From an ease of ground maneuvering viewpoint as well as a ground looping viewpoint the nose wheel configuration is to be preferred. One after step is decide how can we dispose the landing gears. In this stage, some of the criteria must be satisfy. For example; longitudinal tip-over criteria, lateral tip over criteria, longitudinal ground clearance criteria, lateral ground clearance criteria. After satisfying these criteria, the maximum static load per strut can be calculated. The continuous step is choose the number of wheels to be used. After that, Pn/W-ro and nsPm/WTo ratios and approximate tire size are selected from standard tire data tables. At this stage of the preliminary design process it is useful to verify the retraction capability with the help of a so-called 'stick diagram'. With the gear layout defined, we perform the weight and calculations and if necessary, iterate back to first step until the gear location satisfies all criteria. The class II method is provide methods and data to assist in preparing satisfactory landing gear design layouts. Firstly we define the function of the landing gear components. There are five reasons for incorporating landing gears in airplanes. These are; to absorb landing shocks and taxiing shocks, to provide ability for ground maneuvering, to provide for breaking capability, to allow for airplane towing, to protect the ground surface. Now we can select the landing gear type. Two major decisions which must be made before the landing gear layout process can be started are; decide on a fixed or a retractable gear and decide on use of a tricycle, bicycle, tail wheel or unconventional gear. The first decision is a trade off between gear induced aerodynamic drag, weight and complexity (or cost). Second decision depends strongly on the airplane mission. The tricycle gear configuration has become the most frequently used gear layout. Important reasons are: good visibility over the nose during ground operation, stability against ground loops, good steering characteristics, level floor while on the ground. The load on each landing gear strut as well as the load on each tire may not exceed values which: cause structural damage to the gear or to the airplane, cause tire damage, cause runway damage or excessive surface deformations. To allow for adequate nose wheel steering, a minimum normal force must act on the nose gear so that the approximate levels of friction forces needed for steering can be generated. The normal force on the nose gear should not be less than 0.08 Wto for adequate steering. For tree types runway, discussion is completed. These runways are; runways with unprepared or simply prepared surfaces, runways with flexible pavement, runways with rigid pavement (concrete). Xlll The Federal Aviation Agency controls civilian aircraft tire standards through technical standards order TSO-C62. The following general provisions shall apply: Landing gear tires shall be of a proper fit on the rim of the wheels, and their approved rating shall be such that it is not exceeded under the following conditions: 1. Airplane weight equal to the design takeoff weight. 2. Load on each main wheel tire equal to the corresponding static ground reaction at the critical center of gravity position. 3. Load on nose wheel tires (to be compared with the dynamic rating established for such tires) equal to the reaction obtained at the nose wheel, assuming the mass of the airplane concentrated at the most critical center of gravity and exerting a force of l.Og downward and 0.3 lg forward, the reactions being distributed to the nose and main wheels by the principles of statics with the drag reaction at the ground applied only at those wheels which have brakes. The maximum dynamic nose tire rating (load during main wheel braking) can be determined by multiplying the maximum tire rating by a factor of 1.45. the required ply rating and inflation pressure for a nose tire can be determined by rationing its load during maximum braking to the allowable tire dynamic rated load and pressure as long as the ply rating and inflation pressure does not become less than the pressure required using static load and pressure data. It is important that the selection of an nose wheel tire be reviewed form both a static load requirement and also a dynamic braked condition. Again the tire should meet the above load, speed requirements and care should be taken during initial selection of the tire to program in some allowance for loading growth to avoid possible retrofitting n the future. In the case of nose wheel tire, the load/speed requirements should be based upon the aircraft most forward center of gravity location and the most severe ground operational load/speed at maximum altitude, hot day operation. One after discussion about tire and wheels is completed. The following information is presented in this section: a discussion of tire types, tire construction, and tire descriptions, a discussion of tire performance, load deflection and shock absorption capability, a discussion of tire clearance requirements, a method for determining the correct tire size for airplane applications, tabulated data on tire geometry, tire load carrying capability and tire applications. Tire manufacturers rate tires in terms of play rating, maximum allowable static loading, recommended inflating pressure, maximum allowable runway speed. The ply rating or tires identifies the tire with its maximum recommended static load and corresponding inflation pressure XIV when used in a specific type of operation. The ply rating is an index of tire strength and does not indicate the actual number of fabric core plies. Tires participate significantly in the process of shock absorption following touchdown. How much the tires participate, depends on the design of the shock absorbers. In selecting airplane tires, it is usually a good idea to keep future airplane growth capabilities in mind. It is recommended to allow for 25 percent growth in tire load in selecting tires for a new airplane. The following tire clearance requirements must be observed; wheel well clearance (after retraction), tire-to-fork and/or tire to strut clearance. The physical reasons for these tire clearance requirements are; tires grow in size during their service life and tires grow in size under influence of centrifugal forces. This type of growth depends on the maximum tire operating speed on the ground. Wheels are manufactured of magnesium or aluminum alloy and are of the divided type. The two wheel sections are held together by bolts secured with self locking nuts. Each wheel has two tapered roller bearings which are seated in hardened steel bearing cups. When we select previous items we can compute the loads that act on the landing gears. The maximum vertical load factor encountered on landing depends upon the descent velocity, the shock absorption characteristics of landing gear, including the tire and the attitude of the airplane with respect to the ground, making it necessary to investigate various load conditions to make sure that the landing gear components are sufficiently strong. Wheels, tires and brakes with T.S.O (Technical Standard Order) do not have to be investigated by the aircraft designer, since their strength and shock absorption characteristics have been approved on the basis of the static load shown in the catalogs. The most severe ground loads affecting the landing gear usually occur at the moment of touchdown. Less critical loads generally occur during the landing run, due to application of brakes, an uneven runway or turning the aircraft. The main factors affecting the magnitude of the loads applied to the landing gear are; weight of airplane, landing speed, shock absorber travel, tire deflection, runway surface roughness, angle of approach, angle of drift and/or yaw. The federal aviation regulations, part 23 (far 23) for normal, utility and acrobatic airplanes with maximum gross weight of 12,500 lbs. Specify all the requirements that have to be met by USA manufacturers. These regulations also used by many other countries. In determining the ground loads on nose wheels and affected supporting structures, and assuming that the shock absorbers and tires are in their static positions, the following conditions must be meet: (a) For aft loads, the limit force components at the axle must be- (1) A vertical component of 2.25 times the static load on the wheel; and (2) A drag component of 0.8 times the vertical load XV (b) For forward loads, the limit force components at the axle must be- (1) A vertical component of 2.25 times the static load on the wheel; and (2) A forward component of 0.4 times the vertical load. (c) For side loads, the limit force components at ground contact must be- (1)A vertical component of 2.25 times the static load on the wheel; and (2) A side component of 0.7 times the vertical load. The third chapter presents some of drawings. These drawings include nose gear components, such as main cylinder, scissors, bearings, piston, tire, wheel and other parts. These drawings are based upon previous calculations.