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.