Design, Manufacture and Wind Tunnel Test of a Modular FishBAC Wing with Novel 3D Printed Skins

This paper introduces a new modular Fish Bone Active Camber morphing wing with novel 3D printed skin panels. These skin panels are printed using two different Thermoplastic Polyurethane (TPU) formulations: a soft, high strain formulation for the deformable membrane of the skin, reinforced with a stiffer formulation for the stringers and mounting tabs. Additionally, this is the first FishBAC device designed to be modular in its installation and actuation. Therefore, all components can be removed and replaced for maintenance purposes without having to remove or disassemble other parts. A 1m span, 0.27m chord morphing wing with a 25% chord FishBAC was built and tested mechanically and in a low-speed wind tunnel. Results show that the new design is capable of achieving the same large changes in airfoil lift coefficient (approximate ΔCL≈0.55) with a low drag penalty seen in previous FishBAC work, but with a much simpler, practical and modular design. Additionally, the device shows a change in the pitching moment coefficient of ΔCM≈0.1, which shows the potential that the FishBAC has as a control surface.

Analysis of the skin wrinkling in out-of-plane joints of CFRP hat-shaped structure

Out-of-plane joints, between hat (omega) stiffeners and skin panels are asymmetric parts of the composite structure. Studies show that physical-mechanical conditions in these joints significantly affect skin forming quality. In the present article, aimed to investigate the mechanism of the skin wrinkle in the joints of carbon fiber reinforced plastics (CFRP) hat-shaped structure, the pressure testing apparatus based on the Pascal principle is used to surveillance the resin pressure dynamically in out-of-plane joints. In this regard, several influencing factors such as first-order holding time, forming pressure and relative volume of unidirectional fillers are studied. Obtained results show that increasing the first stage holding time can prolong the viscous flow state of the resin, and time to achieve pressure equalization at each detection point, thereby improving the dispersion of the pressure and reducing the possibility of wrinkles. It is found that as the forming pressure increases, the degree of skin wrinkles in the out-of-plane joints ameliorates. Moreover, for fillers with a relative volume within the range of 0–50%, the pressure transfer effect and the skin flatness is relatively dissatisfactory. It is concluded that the filler with a relative volume of 80–120% improves the skin wrinkle in out-of-plane joints.

Modular Test Stand for Fatigue Testing of Aeronautical Structures – Verification of Assumptions

The Modular Test Stand was developed and manufactured to decrease the cost of fatigue testing and reduce the time of its completion as well as to enable testing specimens under more complex load conditions. The stand consists of three connected sections, similar to a wing box, all being loaded in the same way. Thanks to that, several specimens can be tested simultaneously. This configuration requires that stress and strain distribution should be reasonably uniform, as assumed in the design stage. The structure can be loaded with bending or torsion. A whole section, selected structural node or a specimen mounted in the structure as well as a repair or a sensor can be a test object. Two stands, one for bending and one for torsion were prepared. This paper presents the verification of the assumed strain and stress distributions on the skin panels. The measurements were performed with the use of Digital Image Correlation (DIC) as well as strain gauges. DIC measurements were performed on one skin panel of the central section. Five strain gauge rosettes were installed on both panels of the one section. In addition, one rosette was applied to one skin panel in each of two other sections. Measurements were performed on the stand for torsion as well as on the stand for bending. The results of DIC analysis and strain gauge measurement during torsion show uniform shearing strain distributions on the panels. During bending, on the tensioned side, the strains obtained indicate quite uniform strain distributions. On the compressed side, local buckling of the skin panels results in high strain gradients. Strain levels obtained with the use of a DIC analysis and strain gauge measurements were similar. Moreover, horizontal displacements of markers in the spar axis during bending was determined based on a series of photographic. The deflection line obtained in this way has a shape similar to arc, which is characteristic of the constant bending moment. The stand was tested with torsional and bending loads in order to verify the design assumptions. The results of strain distributions on the skin panels with the use of DIC and strain gauges as well as the deflection line of the spar axis indicate that the Modular Test Stand performs as assumed and can be used for tests.

Computational Modal Analysis of Half Scale Generic Business Jet Substructures

The primary objective of this work was to determine the modal parameters of two substructures of a half scale generic business jet model with pre-stressed skin panels. The effect that pre-stiffened skin panels has on the modal parameters of an aircraft fuselage subsection is not well documented in the literature. First, bending pre-stress on stiffened plates was empirically determined to increase stiffness without changing mode shapes. Second, preliminary finite element models of the substructures determined that the effect of skin pre-stress was significant in one of the two substructures. Finally, an updating technique to account for stiffening effects was proposed and validated to be effectively used in the substructure, improving computational results across all metrics. It is recommended that the model updating procedure developed in this work be used to model skin pre-stress for aircraft fuselage substructures. The improved accuracy of the updated computational model should be of significant interest to the aerospace industry. Future work can be performed to further develop the model updating technique introduced in this work to allow for widespread application.

Anisotropy Oriented Tolerance Analysis of Composite Assembly With T-Maps Method

Anisotropy is an outstanding characteristic of the composite parts, and should be considered during the course of the tolerance analysis. The paper presents a tolerance analysis method for composite elevator assembly using T-Maps method, mainly concerning the variations originated from the anisotropy of the composite materials. The composite elevator is composed of the forward spar, the skin panels, and the ribs. Variations of the composite forward spar and the composite panels in different directions are represented by the T-Maps. Mating clearances of the composite spar and the metallic joints are mapped to the hypothetical Euclidean space. Since the different axial deviations are represented in the same Euclidean point-space, anisotropy oriented tolerance analysis of the composite parts assembly could be conducted with more accurate results. This procedure is found to be effective for anisotropy oriented tolerance analysis. The assembly of the composite elevator is investigated intensively by the proposed method. The procedures outlined in the paper are quite general and can be used for tolerance analysis of any anisotropic parts assembly process.