Maxwell Blair

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.

A JOINED-WING STRUCTURAL WEIGHT MODELING STUDY

An integrated design process for generating high fidelity analytical weight estimations of joined-wing concepts is described. Elements of configuration, structures, aerodynamics and aeroelastic analyses are incorporated. Drag and loads are modeled for sizing fuel and structures to meet range and loiter requirements. The joined-wing is a radical departure from the worlds inventory of vehicles. We are motivated because the joined-wing concept may offer weight savings where structural stiffness is a design constraint. Two crucial non-linear phonomena contribute to structural failure: large deformation aerodynamics and geometric non-linear structures. A correct model of the non-linear aeroelastic model offers the possibility of a successful design that leverages these non-linear effects to the benefit of joined-wing designs.

Structural Optimization of a Joined Wing Using Equivalent Static Loads

The joined wing is a new concept of the airplane wing. The forewing and the aft wing are joined together in a joined wing. The range and loiter are longer than those of a conventional wing. The joined wing can lead to increased aerodynamic performance and reduction of the structural weight. In this research, dynamic response optimization of a joined wing is carried out by using equivalent static loads. Equivalent static loads are made to generate the same displacement field as that from dynamic loads at each time step of dynamic analysis. The gust loads are considered as critical loading conditions and they dynamically act on the structure of the aircraft. It is difficult to identify the exact gust-load profile; therefore, the dynamic loads are assumed to be a one-cosine function. Static response optimization is performed for the two cases: one uses the same design variable definition as dynamic response optimization, and the other uses the thicknesses of all elements as design variables; the results are then compared.

Joined-wing sensor-craft configuration design

An optimized configuration design using both structural and aerodynamic analyses of a joined-wing configuration is presented here. The joined-wing aircraft concept fulfills a proposed long-endurance surveillance mission and incorporates a load-bearing antenna structure embedded in the wing skin. A range of joined-wing configurations were trimmed for critical flight conditions and then structurally optimized for trimmed flight and gust loads to achieve a minimum weight for each single configuration. A response surface statistical analysis was then applied to determine optimized joined-wing aircraft configurations. The optimal configurations were then reanalyzed and verified by examining nonlinear structural deflection characteristics and analyzing material and aerodynamic distributions.

Nonlinear Response Structural Optimization of a Joined Wing Using Equivalent Loads

The joined wing is a new concept of the airplane wing. The forewing and the aft wing are joined together in the joined wing. The joined wing can lead to increased aerodynamic performances and reduction of the structural weight. The structural behavior of the joined wing has a high geometric nonlinearity according to the external loads. Therefore, the nonlinear behavior should be considered in the optimization of the joined wing. It is well known that conventional nonlinear response optimization is extremely expensive; thus, the conventional method is almost impossible to use for large-scale structures such as the joined wing. In this research, geometric nonlinear response optimization of a joined wing is carried out by using equivalent loads. The used structure is a joined wing that is currently being developed in the U.S. Air Force Research Laboratory. Equivalent loads are the load sets that generate the same response field in linear analysis as that from nonlinear analysis. In the equivalent loads method, the external loads are transformed to the equivalent loads for linear static analysis, and linear response optimization is carried out based on the equivalent loads. The design is updated by the results of linear response optimization. Nonlinear analysis is carried out again and the process proceeds in a cyclic manner until the convergence criteria are satisfied. It was verified that the equivalent loads method is equivalent to a gradient-based method; therefore, the solution is the same as that of exact nonlinear response optimization. The fully stressed design method is also used for nonlinear response optimization of a joined wing. The results from the fully stressed design and the equivalent loads method are compared.

SENSOR-CRAFT STRUCTURAL OPTIMIZATION AND ANALYTICAL CERTIFICATION*

A structural and aerodynamic optimization of a composite joined-wing configuration is presented here. The configuration fulfills a proposed long-endurance surveillance mission and incorporates a load-bearing antenna structure embedded in the composite wing skin. An alternate composite model without embedded antenna structure is also analyzed. PanAir aerodynamic and MSC.NASTRAN structural analysis is managed through Adaptive Modeling Language (AML) software. A baseline configuration is trimmed for critical flight conditions and then structurally optimized for the trimmed flight loads. Non-linear analysis verifies the ability of the aft-wing to safely undergo large deformations.

Aeroelastic Scaling of a Joined Wing for Nonlinear Geometric Stiffness

This study demonstrates an aeroelastic scaling procedure that accounts for geometric nonlinearity by scaling the eigenvalue associated with the buckling load. The Goland wing model was used as a case study to demonstrate that both the natural frequencies andmode shapes must be matched to properly scale the aeroelastic response. A variant of the Goland wing joined with a strut was developed as the case study for scaling geometric nonlinearity. Scaling its first buckling eigenvalue together with the natural frequencies and mode shapes resulted in accurate aeroelastically scaled response in the initial nonlinear range. The fully nonlinear response of the scaledmodel decreased in accuracy as the critical load predicted by the buckling eigenanalysis was approached.

CREATE-AV DaVinci: Computationally-Based Engineering for Conceptual Design

Historically, decisions made during early phases of systems design and acquisition determine the majority of the life-cycle costs for those systems. Physics-based, high fidelity models that can support rapid analysis (minutes to hours) and rapid design (hours to days) would improve the quality of early acquisition decisions. The DaVinci software product is being developed in direct response to these needs. DaVinci is designed around a unified lifecycle engineering model encompassing multi-fidelity analysis for a wide range of applications. At its core, DaVinci provides next generation modeling capability for functional analysis, alternative design evaluation, trade-space exploration, and acquisition planning. The DaVinci infrastructure and architecture will enable a collaborative environment for all aspects of early acquisition processes and provide a much more effective mechanism for transferring detailed models and product descriptions between phases of acquisition throughout the life of the program. DaVinci will couple a rich graphical user interface with pre-engineered system components and large scale computing to allow systems engineers and acquisition stakeholders the use of computationally based engineering to enable rapid system engineering development iterations for requirements traceability, physics-based systems representations, and the creation of high-fidelity models suitable for early preliminary design.

NON-LINEAR AEROELASTIC SCALING OF A JOINED-WING CONCEPT

High-Altitude and Long-Endurance joined-wing concepts present unprecedented aeroelastic design challenges that will require special consideration in the development of flight testing procedures. Numerous aeroelastic phenomena dictate a large test matrix of flight conditions. Aeroelastic scaled model performance can streamline the flight test point matrix by providing confidence throughout the flight envelope. Risk factors that can be mitigated by this approach include instabilities due to geometric nonlinearies, not normally investigated in preliminary design This paper presents design plans for a low-cost aeroelastically scaled flight test concept that will significantly reduce developmental risk. Initial flight tests and plans for aeroelastic scaling on a half-span wind tunnel model and full-span remotely piloted model are discussed. One of these test vehicles will provide the opportunity to modify and calibrate existing aeroelastic test practices to account for non-linear structural responses. Nonlinear scalings procedures will focus on replicating deflections due to the worst case flight conditions in the envelope, the gust response. Linear scaling will be based on dynamic response at this condition to include investigation of flutter instabilities. Flutter clearance is considered critical in developing new aircraft configurations and typically involves the development and testing of dynamically and aeroelastically scaled wind tunnel models prior to full-scale prototype development. However, experimental aeroelasticity is expensive and typically involves flight testing of the full-scale aircraft. Modern aircraft may benefit from an increased emphasis on wind-tunnel testing of scaled models. This paper describes how the classical aeroelastic scaling laws are applied when developing scaled models. Scaling a model such that it is dynamically similar to an aircraft requires that its characteristics under steady loads match those of the aircraft. A model that is statically scaled to flight vehicle deflects to the same shape and with scaled magnitude under scaled static loads. Relevant assumptions, restrictions, limitations and implications of this methodology are also discussed. 2. SensorCraft Background AFRL maintains a number of airborne concepts that serve as integration concepts for any number of technologies. These airborne concepts provide a context for both the technology developer and the technology investor. These concepts address a variety of missions that include Long Range Strike, Space Access, Mobility and others. One such concept is the AFRL SensorCraft 1 . It is a conceptual flying antenna farm whose design intent is to replace several flight systems (currently in service) with a single integrated system. The technologies that come out of the AFRL SensorCraft program will benefit both new and existing systems.

Experimental Nonlinear Static Deflections of a Subscale Joined Wing

Vanessa L. Bond∗ Air Force Operational Test and Evaluation Center, Edwards Air Force Base, California 93523 Robert A. Canfield Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 Jonathan E. Cooper University of Liverpool, Liverpool, England L69 3GH, United Kingdom and Maxwell Blair United States Air Force Research Laboratory, Wright–Patterson Air Force Base, Ohio 45433