Advanced Materials Research Vols 476-478 (2012) pp 406-412 © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.476-478.406 Online: 2012-02-27 Analysis of the Dynamic and Static Load of Light Sport Aircraft Composites Landing Gear Pu-Woei Chen1,a, Shu-Han Chang2,b and Tsung-Hsign Yu1,c 1 Department of Aerospace Engineering, Tamkang University, No.151, Yingzhuan Rd., Tamsui Dist., New Taipei City 25137, Taiwan 2 General Education Center, Hsiuping University of Science and Technology, No.11 Gongye Rd, Dali Dist., Taichung City 41280,Taiwan a pchen@mail.tku.edu.tw, bshc@mail.hust.edu.tw, ceostre34@yahoo.com.tw Keywords: Light Sport Aircraft, Landing Gear, Composites, Finite Element Analysis Abstract. Composites have become extensively used in aircraft, including the latest Airbus A380 and Boeing 787 models. Due to their high specific strength ratio, the composites can help to reduce fuel consumption. For this reason, small business jets and light aircraft have begun to use composites in their fuselage designs. The main purpose of this study is to analyze the reaction of the composite landing gear of a light sport aircraft (LSA), under loading. Finite element analysis software was used to analyze and compare the static and dynamic loads on the LSA landing gear. Takeoff weight and sink speed, defined by FAR and ASTM, were used as parameters. This work investigated three different types of landing gear materials: aluminum alloy, glass fiber reinforced composite and carbon fiber reinforced composite. The maximum stress, maximum strain and displacement of landing gear of different shapes (leaf, column and tube shapes) was also measured. Of all the samples tested, tube-shaped glass fiber reinforced composite landing gear exhibited the lowest maximum stress under a static load; it also exhibited the smallest maximum strain and y-axis displacement. The results for dynamic load show taht column-shaped landing gear exhibits the smallest maxiumum stress. The results also show that landing gear made with glass fiber reinforced composite exhibits the lowest maximum strain under a dynamic load, while landing gear made with carbon fiber reinforced composite exhibits the largest displacement of the three materials. Introduction The Federal Aviation Administration (FAA) issued regulations for LSA in 2004. A total of 3,000 LSA had been certified by 2008 [1]. Another article [2] indicates that, in the past 6 years, 115 new types of LSA have been developed. Because of the unavoidable effects of the global financial crisis, the US LSA market experienced low growth rate of 36% in 2008, compared with its phenomenal 98% growth in 2007. However, when compared to the overall situation for general aviation, LSA still demonstrate a stable market demand [3]. The 2010 statistics [4], released by the General Aviation Manufacturers Association (GAMA), showed that by the end of 2009, there were a total of 6,547 LSA registered with the FAA in the USA. The LSA market is clearly likely to experience future development. Composites are already widely used in the primary structure of transport airplanes, such as the Boeing 787 (50 % of its structural components use composites) and Airbus A380 (25 % of its weight is accounted for by composites). Manufacturers have begun to use composites in general aviation aircraft. For example, 1,376 of the 2,675 reciprocating engine airplanes produced in 2007 were composite airplanes, 51.4 % of all production [5]. From the 1980s to the 1990s, many light airplane manufacturers started to introduce airplanes with composite components into the market: the Slovak Republic’s Aerospool s.r.o. obtained European ultra-light airplane certification for its two-seat WT9 Dynamic composites airplane in 2001, and the light airplane, FM250 Mystique, with an entire structure constructed of carbon fiber reinforced composite, was specially designed by Flying Machines s.r.o for the U.S. LSA market. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 141.117.125.76, Ryerson University Lib, Toronto-26/04/15,16:37:17) Advanced Materials Research Vols. 476-478 407 Despite their increased application, there are differences between the substance and characteristics of composites and traditional aluminum alloy in areas such as lighting strike resistance, environmental durability and even in terms of fatigue, impact and damage tolerance. While some civil aviation regulations and industry standards can be used as a reference, there is still a lack of accumulated long-term usage data. Neither is there an appropriate simulation platform that can be used to test design criteria. The main purpose of this research is to measure the differences between LSA landing gear made of composites and that made of traditional aluminum alloy, under both dynamic and static loads. This work also measures the differences between leaf (plate)-, column- and tube- shaped landing gears, under various types of loads. Literature Review Current studies of airplane structural improvement fall into two major categories: structural crashworthiness/impact resistance and lightweight structures using composites. In terms of impact resistance, studies have used struts or an energy absorbing floor or sub-floor material in the fuselage frame. In NASA’s 1999 drop tests for the Boeing 737, that plane’s drop speed was 30 ft/s and the test results were mainly used to compare and correct the computer simulations [6]. In 1999, the US National Aerospace Laboratory (NLR) [7] performed a crashworthiness test and a simulation for a theoretical commuter aircraft, similar to the ATR-42/72, with a composite fuselage material. The main objective was to establish a simulation platform for composite fuselage crashworthiness. In 2004, the NLR cooperated with SP Aerospace to convert the main landing gear torque link of the NH-90 helicopter and the main landing gear drag brace of the F-16 from aluminum alloy to composites, and performed the drop test. On September 6, 2007, Boeing announced that their latest commercial airplane, the 787, had completed fuselage drop tests. These tests were performed under the requirements set by the FAA to prove that the crashworthiness of the fuselage of the 787, which mainly uses carbon fiber reinforced composites, is comparable, in terms of impact resistance, to aircraft that use traditional aluminum alloy. The company also conducted 10-foot long fuselage drop tests for the Apache helicopter in August of the same year. Boeing claim that they have established a computer simulation platform for this test and no longer need to conduct drop tests or crash impact tests with actual airplane fuselages under development. Airbus also announced that their A380 airplane had passed landing gear drop tests [8]. This test placed an object of the same weight as the airplane on the landing gear, and dropped it at a speed of 12 ft/s, to test the structural integrity of the landing gear. However, those studies focused on the improvement of general aviation and large commercial airplanes and placed little emphasis on any applicability to light airplanes. In the literature that investigates the impact resistance of light aircraft, Chen et al. [9] used ANSYS and LS-DYNA to analyze the crashworthiness of aluminum alloy fuselages. A study by Li and Xu (2008) [10] examined the use of core pipe, a rod system, tubular structures and foam material to replace the floor structure of light aircraft. In studies related to light aircraft landing gear and composites, Goyal [11] replaced the landing gear of a light aircraft with a composite structure and used ANSYS for simulation. That study demonstrated that when using GFRP/EPOXY composite material landing gear and aluminum alloy landing gear under conditions of maximum load, the weight ratio of the composite material was lighter than that of the aluminum alloy. Bossak and Kaczkowski [12] used finite element analysis and the test results for the crashworthiness of a PZL I-23 composite material airplane to explore how the floor affected fuselage displacement and personnel survival rates, for different angles of impact. When large airplanes land, they rely on the sub-floor and landing gear as energy absorption structures. However, light aircraft have only the fuselage and the landing gear structures with which to withstand the impact of each landing. According to the special light-sport aircraft (S-LSA) statistics, certified by the FAA [13], the market share for light aircraft using composites is 53 %, while the share 408 New Materials and Processes for all metal planes is 47 %. The use of composites is already common in more than half of the light aircraft market and composites have apparently become standard materials for the light aircraft market. The structure of the landing gear of light aircraft is divided by shape into leaf-shaped and rounded cross-section (column-shaped and tube-shaped) landing gear. About 48 % of the light aircraft in the S-LSA market use leaf-shaped landing gear; the remaining 52% use rounded cross-section landing gear. Therefore, this conducted a load analysis of the different cross-sectional shaped landing gears. Experiments This study used a Zenith STOL CH 701 LSA as the sample for computational analysis. HyperMesh and LS-DYNA finite element analysis software were used to establish grids, to establish parameters and to analyze the results. The steps taken in this study were as follows: (1) Pro-E was used to establish a 3D model of CH 701 landing gear; (2) the wheels were then removed and the features of the holes, chamfers and filleted corners on the landing gear were ignored, to simplify the computational model; (3) ANSYS was used for the pre-processing, computation and post-processing of the static simulation analysis and (4) HyperMesh was used to pre-process the dynamic simulation, which included grid construction and the entry of the boundary conditions of the material parameters and drop speed. LS-DYNA was used for computation and post-processing. This work used 6061-T6 aluminum alloy, S-glass fiber reinforced composites and carbon fiber reinforced composites for the loading analysis of landing gear. The properties of the three materials are listed in Table 1. During testing, the landing gear was fixed to the fuselage junction and the load was exerted on both sides of the tail end of the landing gear. Two types of load parameters were used as the conditions for the static load simulation: the maximum takeoff weight of CH 701, 450 kg, and the maximum LSA weight of 600 kg, as regulated in FAR Part 1. Table 1. Material parameters for the aluminum alloy material and composites used in this study Material Specific Weight Elastic Modulus Shear Modulus Poisson’s ratio Aluminum Alloy 6061-T6 2.7 g/cm3 68.9 GPa 26 GPa 0.33 S-Glass Fiber Composite 2.48 g/cm3 86.9 GPa 35 GPa 0.22 Std CF Fabric Composite 1.6 g/cm3 70.0 GPa 5 GPa 0.1 The parameter for the dynamic load was set to only 450 kg. The dynamic simulation followed the guidelines of ASTM F2245-07 [14], which stipulate that the landing speed must not to exceed 1.3 Vso. Vso is the stalling speed with flaps deployed, when landing. Its value was obtained from the CH 701 flight manual [15]. The stalling speed with flaps deployed is 27 kts, so, according to the ASTM standards, the landing speed should not exceed 35.1 kts (18.05 m/s). In the ideal condition of a glide slope of 3° [14], the vertical downward speed is 1 m/s. Therefore, if the maximum permissible glide slope is 5°, the vertical downward speed is 1.57 m/s. The calculation parameters were set for these two different speeds. The dynamic simulation results were verified by the following requirements: (1) total energy (both dynamic and potential energy) should be conservative; (2) hourglass energy cannot exceed 5 % of internal energy and (3) sliding energy must be positive, when the landing gear impacts the solid plate. Advanced Materials Research Vols. 476-478 409 Results and Discussion Static load Figures 1 and 2 respectively show the meshed landing gear model and the simplified model of the CH 701 airplane landing gear. Figure 3 shows the stress distribution of the leaf-shaped 6061-T6 aluminim alloy landing gear, under a load of 450 kg. Its maximum stress point is located at the junction between the landing gear and the fusleage. Similar results were found for other materials and shapes under load. Fig. 1 Meshed landing gear model. Fig. 2 Simplified landing gear model Fig. 3 Distribution of stress for leaf-shaped 6061-T6 aluminum alloy landing gear, under a 450 kg load. Fig. 4 Trends of stress in landing gear of different shapes with different carbon fiber shear modulus, under a 450 kg load. Table 2 shows the results of stress, strain and y-axis displacement, for landing gear made of 6061-T6 aluminum alloy and fiber reinforced composites, under a 450 kg and 600 kg of static load. These results show that landing gear made with the above materials does not exceed the yielding or maximum stress and strain of the material, under different static loads. Under loads of 450 kg and 600 kg, the leaf-shaped landing gear made of carbon fiber reinforced composites exhibits the lowest maxiumum stress of the three types of material. However, the maximum stress of column- and tube-shaped landing gear made of carbon fiber reinforced composites, under loads of both 450 kg and 600 kg, is about 1.5 times that of both aluminum alloy material and glass fiber reinformced composites. For shapes other than the leaf shape, the strain and displacement produced by the carbon fiber reinforced composite landing gear is three to four times that of the other materials. A possible reason for this is that the shear modulus of the carbon fiber reinforced composites is only 5 GPa, which is much lower than the 26 GPa of the 6061-T6 aluminum alloy and the 35 GPa of the glass fiber reinforced composite. Therefore, an attempted was made to increase the shear modulus of the carbon fiber reinforced composite to measure its effect on maximum stress. Figure 4 shows the maximum stress corresponding to different shear moduli, in carbon fiber reinforced composite landing gear under a load of 450 kg. This figure shows that the maximum stress of the leaf-shaped landing gear does not change, for different shear moduli. However, the maximum stress in the column and 410 New Materials and Processes tube-shaped landing gear does clearly drop, as shear modulus increases. For example, when the shear modulus increases to 30 GPa, the maximum stress in the column and tube-shaped landing gear is 79 MPa and 66 MPa, which is a result similar to the maximum stress values of the other two materials. Table 2. Results of aluminum alloy and composite landing gear static load simulation Yield Stress Max. Tensile Strength Max. Strain Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Max. Displacement in the Y-Direction (mm) Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Max. Displacement in the Y-Direction (mm) Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Max. Displacement in the Y-Direction (mm) Aluminum Alloy 6061-T6 276 MPa 310 MPa S-Glass fiber Composite 0.004 0.05 Leaf 450 114.73 0.00221 22.834 600 152.973 0.002953 30.446 4,585 MPa 450 108.51 0.001523 18.155 600 144.681 0.002031 24.206 Std CF Fabric Composite 600 MPa 0.0085 450 100.508 0.001579 22.649 600 134.01 0.002106 30.199 450 126.168 0.004097 3.129 600 161.608 0.005726 4.424 450 102.644 0.003195 2.287 600 136.885 0.00426 3.049 Column 450 88.543 0.001709 1.07 600 102.529 0.001979 1.511 450 83.474 0.001175 0.863862 600 98.969 0.001393 1.22 Tube 450 66.809 0.00126 0.775091 600 89.078 0.00172 1.033 450 66.605 0.000636 0.625189 600 88.806 0.001248 0.833585 A comparison of the effect of different shapes shows that the maximum stress, strain and displacement produced in the tube-shaped landing gear under static stress are all clearly lower than those in the leaf-shaped and column-shaped landing gear, regardless of material. Of all the samples tested, the tube-shaped glass fiber reinforced composite material landing gear exhibited the lowest maximum stress and the lowest maximum strain and y-axis displacement. Dynamic Impact Load For the dynamic load simulation, the ASTM F2245-07 standards for light aircraft were mainly used, in which the landing speed must not exceed 35.1 knots (18.05 m/s). When converting to the CH 701 airplane with an optimal glide slope of 3° and a maximum permissible glide slope of 5°, the vertical downward speeds are 1.0 m/s and 1.57 m/s, respectively. These two drop speeds were used as dynamic simulation parameters. Figure 5 shows the changes over time in the internal and the hourglass energy for the column-shaped aluminum alloy landing gear, during drop test simulation. This figure shows that, in the collision process, the landing gear is compressed to its lowest point at t = 0.005 s and it rebounds Advanced Materials Research Vols. 476-478 411 at t = 0.008 s. After it rebounds, the internal energy remains constant and the hourglass energy is lower than 5 % of the internal energy. The temporal relationship for the sliding energy of the same landing gear in the impact process is shown in Fig. 6. The sliding energy remains positive, throughout the time period for the whole collision. Landing gear of different materials and different shapes also exhibit similar results. These two results confirm the correctness of the dynamic loading simulation platform established by this study. Fig. 5 Change in hourglass energy and internal energy for the column-shaped aluminum alloy landing gear . Fig. 6 Change in sliding energy for the column-shaped aluminum alloy landing gear. The results for a dynamic load with a landing speed of 1 m/s are shown in Table 3. The maximum stress in 6061-T6 aluminum alloy landing gear under 450 kg and 600 kg loads is slightly larger than its yielding stress, for leaf and tube-shaped landing gear; but not for the column shape. The maximum stress and strain in all composite landing gear does not exceed the maximum tensile strength. A comparison of the three different shapes of landing gear shows that the column-shaped landing gear sustains the lowest maximum stress. Under impact load, the column-shaped carbon fiber reinforced composites landing gear exhibits the lowest maximum stress. However, of the three materials, the landing gear made with glass fiber reinforced composite exhibits the lowest maximum strain under dynamic load; while that made of carbon fiber reinforced composite exhibits the highest strain. Similar results are achieved for a drop speed of 1.5 m/s. Table 3. Results of dynamic load simulation at 1 m/s landing speed for aluminum alloy and composite landing gear. Yield Stress Max. Tensile Strength Max. Strain Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Landing Gear Profile Load (kg) Max. Stress (MPa) Max. Strain Aluminum Alloy 6061-T6 276 MPa 310 MPa S-Glass fiber Composite Std CF Fabric Composite 4,585 MPa 600 MPa 0.004 0.05 Leaf 0.0085 450 278.862 0.0022 600 283.601 0.0023 450 260.611 0.0013 600 278.486 0.0016 450 278.703 0.0015 600 280.694 0.017 450 600 337.46 380.132 0.00163 0.00199 Column 450 600 277.126 298.956 0.0013 0.0014 Tube 450 600 298.659 332.53 0.0012 0.0014 450 287.434 0.0027 600 317.355 0.0031 450 212.206 0.0041 600 235.306 0.0047 450 267.237 0.0049 600 290.486 0.0054 412 New Materials and Processes Summary This study aimed to complete a static and dynamic load simulation for a LSA landing gear. Using light aircraft landing gear made of glass and carbon fiber reinforced composite instead of the traditional aluminum alloy material, reduces weight by 8 % and 41 %, respectively. Three different shapes of landing gear: leaf, column and tube shapes, were also compared. Under a 450 kg static load, the leaf-shaped carbon fiber reinforced composites exhibited the lowest maximum stress. The results for the aluminum alloy and glass fiber reinforced composites show that under static load, the tube-shaped landing gear is clearly superior to the other two shapes. The results of the dynamic load test show that landing gear of different materials and shapes have different characteristics. However, the maximum stress in the column-shaped landing gear is clearly lower than that in the other shapes. These results show that the column-shaped carbon fiber reinforced composite landing gear exhibits the lowest maximum stress. However, its maximum strain is 3.15 times that of the column-shaped aluminum alloy and glass fiber reinforced composite landing gear. References [1] James Stephenson and Deborah Stephenson, “Light Sport Aircraft Industry Takes Flight on ASTM International Standards”, ASTM Standardization News, November/December 2008. [2] Pierre A. Kandorfer, “Success Story: 115 New Light Sport Airplane Models on the Market”, June 4, 2011. [3] Dan Johnson, “Enroute to Sebring! Leaving 2008, Arriving 2009”, http://www.bydanjohnson.com, January 19, 2009. [4] General Aviation Statistical Databook & Industry Outlook, 2010, General Aviation Manufacturers Association. [5] Sara Black, “Flying High on Composite Wings”, Composites, Sept. 2008. [6] Joseph R. Chambers, “Concept to Reality: Contributions of the NASA Langley Research Center to U.S. Civil Aircraft of the 1990s”, NASA SP-2003-4529, NASA, October 17, 2003. [7] J.F.M. Wiggenraad, A.L.P.J. Michielsen, D. Santoro, F. Lepage, C. Kindervater, F. Beltran, “Development of a Crashworthy Composite Fuselage Structure for a Commuter Aircraft”, National Aerospace Laboratory, NLR-TP-99532, December 1999. [8] Tim Brown, “Crashworthiness of Aircraft for High Velocity Impact”, June 19~26, 2006. [9] Pu-Woei Chen, Shu-Han Chang, Yuyang Hsieh and Taising Sun, “Crashworthiness Simulation Analysis of Light Sport Aircraft Fuselage Structure”, Advanced Materials Research, pp. 48-53, vols. 199-200, 2011. [10] Wei Li, Huimin Xu, “Light Aircraft Airframe Modifications Based on Crashworthiness”, Journal of Nanjing University of Aeronautics and Astronautics, Vol. 40, No. 4, Aug. 2008. [11] Amit Goyal, “Light Aircraft Main Landing Gear Design and Development”, M. S. Ramaiah, School of Advanced Studies, INDIA, 2002. [12] M. Bossak, J. Kaczkowski, “Global/Local Analysis of Composite Light Aircraft Crash Landing”, Warsaw University of Technology, Poland, 2003. [13] Special Light-Sport Aircraft, http://www.sportpilot.org/learn/slsa/ [14] “Standard Specification for Design and Performance of a Light Sport Airplane”, ASTM F 2245-07, 2008. [15] Flight Manual, ZENAIR STOL CH 701, Czech Aircraft Works, edition 3, March 1999. New Materials and Processes 10.4028/www.scientific.net/AMR.476-478 Analysis of the Dynamic and Static Load of Light Sport Aircraft Composites Landing Gear 10.4028/www.scientific.net/AMR.476-478.406