Aircraft designed for naval aircraft carriers experience great airframe stress during landing due to the high vertical velocities that they must maintain as a consequence of the extremely short runway and shallow landing angle of attack. This creates a need for structural rigidity to counteract the forces that land-based aircraft never experience. This is not ideal if it otherwise limits the performance and flying capabilities of the aircraft that are otherwise necessary for the environments they might find themselves in. As such, a new approach to protecting the aircraft from the immense loads they experience during landing could be to add flexibility to the airframe and landing gear, promoting deflection instead of failure. This thesis aims to investigate this idea, starting with an elementary set of tests, looking into material flexibility, and then moving on to adding this concept to progressively more advanced structural systems. Using balls of varying material, preliminary drop tests indicated that material flexibility could assist the dissipation of landing energies, showing that the coefficient of restitution increases with the stiffness. Drop tests involving mass-spring-damper systems as well as cantilever plates and transverse beams also indicated that the strain energy a body can absorb from a set load case can be increased if its flexibility also grows. This finding led to the important conclusion and finding that a flexible body can transfer and store at least 10 times its initial contribution of energy to a system in the form of strain energy. Through these tests, it was shown that flexible structures can be a beneficial design feature in combatting and dissipating vertical landing energies. / Master of Science / Historically, airplanes landing on naval aircraft carriers are subject to high impact loads when they land because the plane is traveling at a high velocity downward and has a short runway to stop on. This impact on the runway is so severe that it requires the structure of the airplane to be reinforced, which in turn makes the plane heavier and less capable in flight. This reinforcement also implies that the plane is quite stiff in all of its components. One solution to this issue is to reverse the design logic historically taken, and impose flexible structures into the main body of the plane, which can bend and absorb some of the vertical energy that the plane possesses. This theory was investigated using a series of drop tests, starting with ball drop tests of varying materials. These tests showed that the material of a ball can affect the energy that it absorbs and how much is kept by the ball after it collides with the ground. Next, more complex structures were tested, using shock absorbers, metal plates, and metal beams. These components were combined to form drop systems, which were dropped to measure the bending in the plates and beams, as well as the shock absorbers. The conclusion made from these tests is that a more flexible structure can absorb a higher percentage of energy compared to its initial contribution, than its stiffer and heavier counterpart. This important conclusion shows that the application of flexible structures could be a vital step in improving the design of airplane wing and body structures to promote the longevity of the structure of the aircraft.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115060 |
| Date | 15 May 2023 |
| Creators | Schickling, Robert Scott |
| Contributors | Aerospace and Ocean Engineering, Kapania, Rakesh K., Seidel, Gary D., Philen, Michael Keith |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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