Thesis Joint development for a morphing wing skin

Thesis Joint development for a morphing wing skin

van Eemeren, Adri (TU Delft Aerospace Engineering; Fokker Aerostructures)

Sinke, J. (mentor)
van Goozen, Hans (graduation committee)

Delft University of Technology

Aerospace Engineering

Morphing Winglet Tab

2021-08-24

Both GKN Aerospace Fokker Aerostructures B.V. (Fokker) and Delft University of Technology (DUT) are partaking in a Clean Sky 2 program called MANTA. MANTA stands for: MovAbles in the Next generaTion Aircraft, and is a program created by the European Union in order to meet the ’ACARE Flightpath 2050 objectives’ by achieving cleaner air travel. The MANTA program aims to reduce the fuel consumption by 3% to 5% using the knock on effects of smart usage of movables.   The contribution of Fokker in the MANTA program is the Morphing Tab concept. This is a newly introduced tab which will be located in the wingtip and must allow load alleviation during manoeuvres. By deflecting the tab in a smart manner, it will be able to generate an internal moment in the wing structure opposite to the internal moment generated by the lift. These internal moments counteract one another, reducing the peak stresses which can result in a lighter wing structure. This will have multiple aerodynamic beneficial knock on effects such as the potential for a more slender wing.  The solution of Fokker. to keep the drag introduced by the tab to a minimum, is to use a morphing tab rather than a conventional tab. The morphing tab has a continuous inboard skin surface which morphs in the section between the Rigid winglet structure and the rigid tab. The continuous skin will add to the aerodynamic efficiency as airflow along the surface stays attached further along the wing chord and airflow leakage is largely avoided.  The morphing part of the winglet exists of multiple components. the component studied in this thesis is the flexible skin. More precisely, it is the attachment of the morphing skin to the non-morphing parts of the concept, the winglet and the tab. As the morphing skin is very thin, and the condition of use is an out-of-plain movement, a complex and rarely studied combination is formed. This has led to the following research question: What is the best method to connect a thin flexible skin element undergoing a peel-like motion to a rigid structure without disturbing the aerodynamic surface at the outside of the skin? Answering this question must lead to a solution for this specific situation as well as contribute to the body of knowledge to fill the current literature gap. Based on the findings of the literature study, the analysis started with selecting a joining method. This process was performed by a trade-off in which six groups of joining methods (Integral Structure, Bonding, Welding, Mechanical Fastening, a Piano Hinge and a Flexible Hinge Element) have been compared. This resulted in the selection of Mechanical Fastening as the best joining method. Within this category, Rivets have been selected as the best suited solution for the Morphing Tab Connection. Along with design guidelines, a comparison between the failure limits of the rivets and the loading conditions of the tab, led to the design of the riveted connection. A test had to be created in order to investigate whether the design is able to meet the requirements of the joint under the relevant loading conditions. No standardised test could be used as they did not create representative loading conditions. During the test, the stress and strain of the skin at the connection are measured via the machine output, Digital Image Correlation software and strain gauges. Additionally, video recordings are made of the test from the side in order to validate results. Three main test conclusions can be made: • The Aerodynamic Profile does not experience a significant effect of the Riveted connection. The required rotation angle and accuracy are achieved and the contour deformation is within the tolerance. • The Static Failure is caused by skin bending without interference of the fasteners. The Static Failure Level is higher than the required minimum stress. Therefore, the Static Load Requirements are met. • The rivets do not interfere on the skin behaviour during fatigue tests. The stiffness reduction due to the fatigue tests shows similar results with and without fasteners. Overall this means that the Riveted connection meets all Aerodynamic and Structural Requirements. Besides this, no indication was apparent during the tests that another joining method would lead to better performance. Also, the riveted connection outperformed the other joining methods in the other Trade-off categories. The combination of these two facts warrant the overall conclusion of this thesis: A riveted connection is the best method to connect a thin flexible skin element undergoing a peel-like motion to a rigid structure without disturbing the aerodynamic surface at the outside of the skin. The connection design created during in this thesis can be applied in further investigations in the Morphing Tab Concept.

Joint
Rivet
Morphing
Winglet
Mechanical fastener
Load Alleviation

http://resolver.tudelft.nl/uuid:fc7fb32f-d95c-4de3-8860-ecb0238d3c7b

2023-09-01

Student theses

master thesis

© 2021 Adri van Eemeren