The Joined-Wing layout is often seen to provide a significant gain in design space and offer additional alternatives in propulsion, aeroelasticity, flight dynamics, aeroelasticity aerodynamics, and other areas. Real-time structural deformation measurement is crucial in structural health monitoring (SHM), methodology validation, safety evaluation, and structural control.
Fiber Optic Sensors (FOS) in Aviation Applications
Fiber optic sensors have emerged as the top option for structural health monitoring (SHM) in aviation applications due to their many benefits, including resistance to electromagnetic interference, multiplexing capabilities, compact size, and low weight. In addition, fiber optic sensing presents a very promising alternative to the current shape-sensing methods that rely on laser scanners, inclinometers, cameras, accelerometers, and electrical strain sensors by having the capacity to constantly and dynamically follow the form.
Fiber Bragg Gratings (FBG)
Fiber Bragg Gratings (FBG) are the most often used optical fiber sensors and have a broad range of applications among the numerous strain-sensing technologies in fiber optic sensing. FBG sensors provide significant benefits such as high reliability, excellent strain sensing accuracy, a cheap cost, a large sensing length, and more, despite the limitations in distributed sensing capacity. FBG sensors are still preferred in engineering applications over-dispersed sensing based on Rayleigh or Brillouin scattering.
Previous Studies on Joined-Wing Aircraft
The Joined-Wing aircraft have not been extensively studied in relation to the shape-sensing issue. The Joined-Wing aircraft often has the front wing and aft wing, as opposed to the single main wing in the standard layout, which makes the deformation more challenging. Additionally, defined boundary constraints were often taken into account in earlier investigations.
Nevertheless, throughout the flight, the aircraft may encounter various boundary conditions. It is difficult to change modal forms in response to boundary circumstances. Therefore, it makes sense to calculate structural displacement using a single computation's modal data.
How the Study was Conducted
This study expands the traditional modal technique to accommodate a range of boundary conditions by incorporating additional constraint equations. An FBG sensor is utilized to detect strain, and a FOSS, including both software and hardware, is created to be adaptable to the target Joined-Wing platform.
Joined-Wing Aircraft Construction
A joined-wing airplane with diamond-shaped wings was created. The plane had a fuselage length of around 25 meters and a span length of about 60 meters. The front, aft, and outboard wings make up the main wing. Two nacelles, linked to the aft wing, joined the front wing to the outboard wing. The aircraft's primary framework was constructed from composite materials.
Fiber Optic Sensing System
The wing spar strain data was gathered using the FOSS, which was also utilized to forecast the 3D deformation of the complete wing. The hardware and software systems were part of the FOSS's overall design.
The hardware system was split into two separate systems to gather and store sensor data from the left and right wings. Each system comprised a memory module, a GPS, an onboard computer, and an FBG interrogation module. The software system's purpose was to present the findings after transforming the preprocessed sensor data into structural deformation.
The new modal approach was tested on a cantilever beam supported in the middle. The beam's cross-section was rectangular, measuring 0.035 m in width and 0.0015 m in height, with elastic modulus and density of 210 GPa and 7750 kg/m3, respectively. The beam's tip delivered a focused force of 0.1 N with vertical components. In MSC NASTRAN, the beam was resolved using a discretization of 50 elements. The initial CAD model in MSC NASTRAN served as the foundation for the Finite Element (FE) model. Composite plate parts represented most of the structures, including the wing spars and skin.
Significant Findings of the Study
This study proposes a comprehensive framework for Fiber Optic Sensing-based structural displacement prediction of a Joined-Wing aircraft. The intended Joined-Wing aircraft was equipped with a FOSS that included hardware and software components. The ground test was used to confirm the system after that. It is typical in real applications to modify the traditional modal method to accommodate different boundary conditions. Numerical analyses on a cantilever beam model and the Joined-Wing aircraft were used to confirm the improved Strain-to-Displacement Transformation SDT method.
According to the numerical and experimental data, the suggested SDT method can correctly anticipate the aircraft's overall configuration or the deformations of a specific spot. The relative inaccuracy of the displacement at the support point in the ground test is 6.6%. Less than 7% of the total deformation is inaccurate globally, while the average inaccuracy is just 2.62%. As a result, it was established that the FOSS had a good degree of accuracy and the possibility for further flight testing.
Meng, T., Bi, Y., Xie, C., Chen, Z., & Yang, C. (2022) Application of Fiber Optic Sensing System for Predicting Structural Displacement of a Joined-Wing Aircraft. Aerospace, 9(11), 661. https://www.mdpi.com/2226-4310/9/11/661/htm