Joined-wing Concept Research Articles

Static and dynamic characterization of a flexible scaledjoined-wing flight test demonstrator

High Altitude and Long Endurance (HALE) aircraft are capable of providing intelligence, surveillance and reconnaissance (ISR) capabilities over vast geographic areas when equipped with advanced sensor packages. As their use becomes more widespread, the demand for additional range, endurance and payload capability will increase and designers are exploring non-conventional configurations to meet the increasing demands. One such configuration is the joined-wing concept. A joined-wing aircraft is one that typically connects a front and aft wings in a diamond shaped planform. One such example is the Boeing SensorCraft configuration. While the joined-wing configuration offers potential benefits regarding aerodynamic efficiency, structural weight, and sensing capabilities, structural design requires careful consideration of elastic buckling resulting from the aft wing supporting, in compression, part of the forward wing structural loading. It has been shown already that this is a nonlinear phenomenon, involving geometric nonlinearities and follower forces that tend to flatten the entire configuration, leading to structural overload due to the loss of the aft wing\'s ability to support the forward wing load. Severe gusts are likely to be the critical design condition, with flight control system interaction in the form of Gust Load Alleviation (GLA) playing a key role in minimizing the structural loads. The University of Victoria Center for Aerospace Research (UVic-CfAR) has built a 3-meter span scaled and flexible wing UAV based on the Boeing SensorCraft design. The goal is to validate the nonlinear structural behavior in flight. The main objective of this research work is to perform Ground Vibration Tests (GVT) to characterize the dynamic properties of the scaled flight vehicle. Results from the experimental tests are used to characterize the modal dynamics of the aircraft, and to validate the numerical models. The GVT results are an important step towards a safe flight test program.

Performance Comparison of the Optimized Inverted Joined Wing Airplane Concept and Classical Configuration Airplanes

Abstract The joined wing concept is an unconventional airplane configuration, known since the mid-twenties of the last century. It has several possible advantages, like reduction of the induced drag and weight due to the closed wing concept. The inverted joined wing variant is its rarely considered version, with the front wing being situated above the aft wing. The following paper presents a performance prediction of the recently optimized configuration of this airplane. Flight characteristics obtained numerically were compared with the performance of two classical configuration airplanes of similar category. Their computational fluid dynamics (CFD) models were created basing on available documentation, photographs and some inverse engineering methods. The analysis included simulations performed for a scale of 3-meter wingspan inverted joined wing demonstrator and also for real-scale manned airplanes. Therefore, the results of CFD calculations allowed us to assess the competitiveness of the presented concept, as compared to the most technologically advanced airplanes designed and manufactured to date. At the end of the paper, the areas where the inverted joined wing is better than conventional airplane were predicted and new research possibilities were described.

Joined-wing test bed UAV

The future green aircraft will be required to meet demanding constraints, including weight reduction, high energy and aerodynamic efficiencies and high performance, to be compliant with pollutant emissions and noise generation regulations. The joined-wing concept is considered a trade-off variant for a green aircraft design with a lower cruise drag and lower structural weight. In addition, the requirements for low pollution and noise could be met using an all-electric aircraft. Hence, the aim of the present study is to design and produce a joined-wing unmanned aircraft test bed or flight laboratory. The basic design incorporates tip-joined front and rear wings with wing-tip vertical joints. The airframe is mainly composed of carbon and glass fibre composite materials. The power plant consists of an electric ducted fan, speed controller and Li-Po batteries. The aircraft integrates the Piccolo II Flight Management System, which offers a state-of-the-art navigation and flight data acquisition. Prior to production and flight testing of the prototype, aircraft aerodynamics and flight dynamics were analysed. Potential models with wind tunnel tests have been used to determine aircraft aerodynamics. One of the major problems found during simulation and flight experiments is the Dutch roll effect. This is thoroughly discussed in the paper. Some problems that concern autopilot tuning are also described.

Nonlinear Aeroelastic-Scaled-Model Optimization Using Equivalent Static Loads

A new methodology for designing nonlinear aeroelastically scaled models is developed that uses direct matching of linear and nonlinear static responses, while simultaneously satisfying modal-frequency constraints. To demonstrate this technique, a one-ninth scaled vehicle is designed to match the nonlinear aeroelastic response of a full-scale joined-wing concept. This is the first demonstration of an optimization that simultaneously considers equivalent static loads for nonlinear statics and modal-frequency constraints. This is also the first scaling demonstration to include nonlinear aeroelastic verification. The results show marked improvement over the results from a scaled vehicle designed using a traditional method intended for linear applications.

Joined-Wing Aeroelastic Design with Geometric Nonlinearity

An integrated process is presented that advances the design of an aeroelastic joined-wing concept by incorporating physics-based results at the system level. For instance, this process replaces empirical mass estimation with high-fidelity analytical mass estimations. Elements of nonlinear structures, aerodynamics, and aeroelastic analyses were incorporated with vehicle configuration design. This process represents a significantly complex application of aeroelastic structural optimization. Specific fuel consumption for a fixed lift-to-drag ratio was considered in the process for estimating fuel to size the structure to meet range and loiter requirements. This design process was implemented on a single configuration for which two crucial nonlinear phenomena contribute to structural failure: large deformation aerodynamics and geometrically nonlinear structures. A correct model of the nonlinear aeroelastic physics offers the possibility of a successful design. Unconventional features of a joined-wing concept are presented with the aid of this unique design model. Hopefully, insight derived from the nonlinear aeroelastic design might be leveraged to the benefit of future joined-wing designs.