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.
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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
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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.
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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