Evaluation of critical parameters in the design of a trainer aircraft landing gear

A Landing gear system supports aircrafts during the aircrafts on the ground and allow the taxiing, take-off and landing. Hence, it can be accepted that landing gears are one of the basic parts of aircrafts. Design of landing gear is related with different engineering disciplines such as structures, weights, economics and runway design. Besides, landing gears are complex structures which are intricate with aircraft structures, automation systems and aerodynamics. In this study, the ways of analysis to evaluate best-fit landing gears for an aircraft considered is explicitly conducted. The configurations created are tested in order to obtained optimum landing gears designed. The dynamic equations of the wheelbase and wheel track which described the aircraft can be laterally stabilized on the ground are given. The dimensioning of the shock absorbers which are the basic components of the landing gears and stroke, the dimensions and pressure of landing gear wheels are obtained. Firstly, main landing gear location must be determined in this chapter. In the wing type has been selected for storage bay but the exact position must be known. It can be said that the attachment point must be between main and rear spar, this attachment have to be attached to a strong element and there must be proper volume for retracted landing gear. Hence the main gear will be attached to behind of the trainer aircraft's spar. During selection of this attachment point similar aircrafts are considered and main wheel position must locate between 12° - 18° angles to the normal line of the aircraft's aft center of gravity. This point is also a proper location for take-off rotation ground clearance and ground clearance since it is the nearest point of the trainer aircraft to the ground. After, according to wheelbase calculations nose landing gear can be located easily. The landing gear preliminary design is generally carried-out by responding to requirements of maximum weight, overall dimensions and maximum attainable load factor. The oleo-pneumatic mechanism is conceived with the aim of maximizing the oleo-pneumatic efficiency, since it is critically depending on the maximum vertical load factor and on the strut length, whereas the structure is generally sized by combining the design vertical loads with the maximum expected horizontal loads. In this part, oleo sizing, ground stability, tire sizing, tire pressure, brakes, steering systems, locks, calculation of stroke had been determined detailed way. In the preliminary design, layout design of the nose landing gear and main landing gear determined by designer. In the detailed design phase, component loads are estimated and material selection are done. The horizontal drag component simulating the force required to accelerate the tires and wheels up to the landing speed (spin-up) and the forward acting horizontal load resulting from rapid reduction of the spin-up drag loads (spring-back) must be evaluated. Dynamic analysis and simulation is carried out to fine tune certain design parameters for energy absorption, shimmy suppression and retraction/extension. According to CS 23.473 ground load conditions, maximum take-off weight and design landing weight must be consider for various landing conditions. The selected landing velocity for trainer aeroplane between 13 to 16 fps since trainer aircrafts are exposed over loads during the balked landing. In the EASA Certification, landing gear must be designed for ten different landing scenarios namely; level landing condition, main landing contact, tail-down landing, inboard side loads, outbord side loads, braked roll condition, supplementary nose wheel aft, supplementary nose wheel forward, supplementary nose wheel side, supplementary nose wheel steering. As can be seen from the calculations; even though the maximum loads are acting on main landing gear for main landing contact and tail-down landing scenarios, the most critical case among these landing conditions for main landing gear is inboard side loads because of the superposing loads. Consequently, loads from different directions can occur combined stresses, thereby designers take into consideration this case for calculations and design. In addition, the nose landing gear is exposed maximum loads on a direction during the braked roll condition although the most critical condition is supplementary nose wheel aft scenario since superposing the loads which are acting from different two directions can cause combined stress. All lessons learned and best practices evolved over the years are utilized in the detail design to realize a reliable design. Landing gear components and links are exposed important loads during the touch-down. To model these critical loading cases, critical scenarios are taken from EASA CS-23 subpart C loads sections in order to optimize the design. These external and internal loads are applied the models. Under the effect of these loads the structural behavior of the landing gear components are analyzed. For the analysis the geometric model of the landing gear created by using The CATIA V5. Three-dimensional drawings of the landing gears are also created according to the calculation results. Altair Hyperworks Optistruct software FEA solver is used in order to anaylse the landing gear. The results of the analysis are evaluated and suitability of the design is stated. Furthermore, most critical case results are compared by using linear implicit solver. Altair Hyper-mesh program is successfully conducted for FEM modeling and Altair Hyperworks Optistruct Solver is used in order to analyse the landing gear design. Result of the analysis compared and evaluated for detailed design of the trainer aircraft landing gear. As stated in the section 7 factor of safety taken as 1.5 for analysis, the maximum vonMises stress on the fork of nose landing gear 159 MPa and also 139 MPa on the inner oleo strut. The steel namely AISI 4340 has yield stress value approximately 470 MPa consequently, according to vonMises stress theory nose landing gear is able to endure these loads. Furthermore, another theory is called maximum displacement theory must be consider thereby maximum displacement on the oleo strut exactly 5.88 mm at the end of the nose landing gear oleo strut. The results are conveint for both of the finite element anaylsis for nose landing gear design. Finally, the purpose of this project is the design of a fixed tricycle landing gear for a single-engine, tandem two-seat, all metal airplane adhering to the CS-23 Certification Specifications by which it is intended to be certified. Using the design process defined in the introduction, makes it possible to adequately structure the landing gear design into phases of design. The initial design phase defines the landing gear design requirements. Subsequently the preliminary design phase defines the initial landing gear layout, load conditions, and various other aspects of the landing gear design such as wheel and tire selection. The necessary load conditions are prescribed by the CS-23 Certification Specifications and calculated for the specific initial data defined in the design requirements. The detailed design phase consists of individual component sizing and stress analysis. The final results of this project are expressed in the form of technical documentation contained in section 7.