Bird strike Analysis
Livia Xavier Fernandes
Professional Engineer | Aerostructures Specialist | Mechanical & Aeronautical Engineer at Bombardier | Stress Engineer
Engineer: Livia Xavier Fernandes
ABSTRACT
??????????????The nature of the damage in collisions of aircraft with birds is significant enough to create a high risk for a safe flight, and this differs according to the size of the aircraft and the way it is designed. Small aircraft, the propeller (such as helicopters) are more likely to experience the dangerous effects of a collision, causing defects such as structural damage, such as the penetration of the cockpit's windshield or other types of damage. Large aircraft with jet engines are more likely to experience the dangerous effects of impact with birds in their structure. Depending on the place where there is a collision, it can lead to some consequences, such as partial or complete loss of aircraft control and loss of function of a flight instrument. Furthermore, it generates some side effects on the aircraft, which can interfere with the static system and malfunction of reading instruments.
Keywords: Aircraft, Birds, Collision, Jet Engine, Static System and Reading Instruments.
1.????Introduction
One of the biggest enemies of aviation today is bird accidents in the vicinity of airports because airports are close to places where a high number of birds are circulating.
From this premise, it was found that the collision between birds and aircraft has become a problem that concerns both the Brazilian and the world population. The reason for so much attention is the risk posed to flight safety and the financial loss for airlines regarding aircraft rework and replacement.
According to data provided by the Center for Investigation and Prevention of Aeronautical Accidents, it was found that accidents occur more frequently during the take-off, climb, approach to the ground and landing phases. The explanation for this is that, in cities, birds fly at low altitudes to the ground.
When a structure is designed, a range of analyses is required, such as material behaviour analysis, fatigue, rupture, inertia, load path, among others. However, it is at the time of certification that more accurate results are obtained for the behaviour of the structure after impact. Because of this, at the beginning of the project, a well-prepared stress x impact angle curve, taking into account the critical impact conditions and the materials most used in the design of an aircraft, can improve the time, the cost, and the scope of the project.
2.????DEVELOPMENT
During development, the mesh modelling was first carried out for study in the FEMAP software, where it receives input data (material data, meshes, boundary conditions and initial dimensioning). Later, DYTRAN was used to verify the FEMAP model and process the analysis of the FEM (Finite Element Methods). With PATRAN, the results obtained by the solver were verified, and its consistency with the expectations established at the beginning of the process was evaluated. If met, a point on the objective curve is plotted. If not, the geometry is modified the analysis restarts when necessary. Figure 2.1 shows the Project Analytical Framework.
FIGURE 2.1 – Project Analytical Framework
2.1.?General considerations
To promote knowledge and reliability, texts, articles, books and content from websites were reviewed. The most pertinent ideas to this work were selected based on standards, calculations, theories and software. From this, some general initial conditions were defined:
· The analysis model is set to a time of 6e-3s.
· Model boundary conditions are fixed on 6 axes.
· The firing target is always at the same point, regardless of the angle of the structure.
1.1.1.???COLLISION
In practice, in a bird impact, taking into account that one of the bodies will be "still," we can have 3 cases:
Total collision: The bird is perpendicular to the plane's surface, and there is no energy lost to the environment, hitting its surface with its full charge of kinetic energy. An elastic collision will occur.
Partial collision: The bird loses X percentage of kinetic energy to the environment, is facing away from the plane, and then immediately crashes into the surface of the aircraft. An inelastic collision will occur.
Almost zero collision: The bird is parallel to the plane, and both collide in the same direction, but due to the difference in speed, the bird is considered kinetic energy and almost zero amount of movement, which causes a minimal collision, causing no damage to the plane's surface. An inelastic collision will occur.
1.1.2.???APPLICATION OF THE ALE THEORY - ALGORITIMO LAGRANGE-EULERIAN ARBITRATION
Contact surfaces allow Lagrange meshes to interact with each other, that is, with the structure. This interaction can include contact, friction sliding and friction separation. The contact was used to model the structures, where the material can fold back on itself. With this, the interaction between Euler and Lagrange meshes is achieved through coupling. This is based on the creation of coupling surfaces in Lagrange structures. The engagement surface, which must form a closed volume (Dummy property), calculates the forces resulting from the interaction and then applies the forces to the material within the Eulerian mesh and the material in the Lagrange structure.
1.1.3.???AIRCRAFT STRUCTURE
The complete structure of the analyzed region can be seen in Figure 2.2. The set of the structure of the plane in this analysis is composed of three structures, which are 4 (Stringers) at 900mm each, 4 (Frames) at 530mm each and 1 (Skin).
FIGURE 2.2 – AIRCRAFT STRUCTURE
1.1.4. MECHANICAL PROPERTIES
The mechanical property of the material considered in the finite element model is described in the following topics.
TABLE 2.1 - PROPERTIES OF THE MATERIAL USED - AL 6061-T6
Source: MMPDS 5- Metallic Materials Properties Development and Standardization, 2010.
1.1.5.???BIRD MODEL
The shape of the bird is chosen to represent an experimental bird model. It follows the certification standard required by the FAA - Federal Aviation Administration. Its characteristics are described in table 2.2 and in Figure 2.3, the representation of the bird.
TABLE 2.2 – BIRD PROPRITIES
Source: FAA 25.571 – Damage tolerance & Fatigue evaluation of structure, 2011.
FIGURE 2.3 – BIRD MODEL
1.1.6.???IMPACT MODEL
The way in which the structure was designed, varying the angle of impact in relation to the bird, follows the models below, according to Figures 2.4, 2.5, 2.6, 2.7, 2.8 and in Figures 2.9 and 2.10 their respective Euler meshes (Dummy).
FIGURE 2.4 - STRUCTURE AND BIRD FOR 90o DEGREES
FIGURE 2.5 - STRUCTURE AND BIRD FOR 75o DEGREES
FIGURE 2.6 - FRAME AND BIRD FOR 60o DEGREES
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FIGURE 2.8 - STRUCTURE AND BIRD FOR 45o DEGREES
FIGURE 2.9 - FRAME AND BIRD FOR 30o DEGREES
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FIGURE 2.10 - STRUCTURE EULER MESH (DUMMY)
FIGURE 2.11 –BIRD EULER MESH (DUMMY)
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3.????RESULTS
In the elaborated curve, thickness x impact angle is taking into account the thickness of the skin. However, due to the concepts, we know that in this case, every set of thicknesses influences the final result of an impact.
The analyzed angles were respectively 90o, 75o, 60o, 45o, 30o. Following this order, the Figures below represent the behaviour of the thicknesses according to the established degree of success. - the bird does not break the material.
In Figures 3.1, 3.2, 3.3, 3.4, 3.5, the analysis of each point of the curve can be seen individually, the objective curve of this work can be seen in Figure 3.6 and Figures 3.7, 3.8, 3.9, 3.10 and 3.11 can be seen the time x strain curves for each analysis.
FIGURE 3.1 - STRUCTURE BEHAVIOR FOR 90o DEGREES - 10mm
FIGURE 3.2 - STRUCTURE BEHAVIOR FOR 75o DEGREES - 10mm
FIGURE 3.3 - STRUCTURE BEHAVIOR FOR 60o DEGREES - 5mm
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FIGURE 3.4 - STRUCTURE BEHAVIOR FOR 45o DEGREES - 5mm
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FIGURE 3.5 - STRUCTURE BEHAVIOR FOR 30o DEGREES - 5mm
FIGURE 3.6 - THICKNESS X IMPACT ANGLE CURVE
FIGURE 3.7 - TIME X DEFORMATION - 90o DEGREES - 10mm
FIGURE 3.8 - TIME X DEFORMATION - 75o DEGREES - 10mm
FIGURE 3.9 - TIME X DEFORMATION - 60o DEGREES - 5mm
FIGURE 3.10 - TIME X DEFORMATION - 45o DEGREES - 5mm
FIGURE 3.11 - TIME X DEFORMATION - 30o DEGREES - 5mm
4.????CONCLUSION
Bearing in mind that strength can be the main requirement in certain structures, after the analysis, we can see that, under the conditions of a direct impact, that is, a total and partial collision (90o and 75o degrees respectively). The structure would break with 1mm, 2.5mm, 5mm, 7.5mm thick for the skin and would only withstand the impact for a dimension of 10mm.
When applying a partial impact of 60o, 45o 30o degrees, the skin would only withstand a minimum of 5mm. Any thickness below this would cause the material to rupture.
We can also verify that the efforts present in the frames also felt the same effect, in some parts breaking, that is, plastically deforming. From this, it would lead us to a broader range of analyses. In this situation, it is worth saying that it would be necessary to study a dimensioning of the hardware (Stringers, frames) favourable for such proposed conditions to obtain satisfactory results following the specifications described herein.
Therefore, if an aircraft were developed with the proposed characteristics, without a preconception impact angle X thickness curve, at the time of project certification, it would fail, which would generate a rework, from engineering conception to final manufacturing. We conclude the importance of a curve like the one presented here to modify the entire project in the initial conception phase, to optimize the time spent for the most realistic development possible.
4.????REFERENCES
AMERICAN SOCIETY FOR TESTING AND MATERIALS – ASTM. 8M-94b Standard Test Methods for Tension Testing of Materials [Metric], 1994.
FAA- FEDERAL AVIATION ADMINISTRATION. FAA 25.571 – Damage tolerance & Fatigue evaluation of structure. Seattle. Jan, 2011.
HALLIDAY, RESNICK R. e WALKER J. Fundamentals of Physics: Mechanical Vol. 1., 2009
MICHEL VAN TOOREN. American Institute Of Aeronautics And Astronautics (Org.). Multi-disciplinary Design of Aircraft Fuselage Structures. Delft University Of Technology. Netherlands, p. 1-13.
MMPDS-05 - Metallic Materials Properties Development and Standardization. Estados Unidos, Ed FAA – Federal Aviation Adminstration, 2010.
MSC/DYNA Theory's Manual, The MacNeal-Schwendler Corporation. Ed. 2013.
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Project Manager | Operations | Compliance
3 年Amazing article! Congrats Lívia ????????