High aspect-ratio, long-endurance aircraft require different design modeling from those with traditional moderate aspect ratios. High aspect-ratio, long endurance aircraft are generally more flexible structures than the traditional wing; therefore, they require modeling methods capable of handling a flexible structure even at the preliminary design stage. This work describes a design optimization method for combining rigid and inflatable wing design. The design will take advantage of the benefits of inflatable wing configurations for minimizing weight, while saving on design pressure requirements and allowing portability by using a rigid section at the root in which the inflatable section can be stowed. The multidisciplinary design optimization will determine minimum structural weight based on stress, divergence, and lift-to-drag ratio constraints. Because the goal of this design is to create an inflatable wing extension that can be packed into the rigid section, packing constraints are also applied to the design. / Master of Science

Performance of inflatable wings was investigated through laboratory, wind tunnel and flight-testing. Three airfoils were investigated, an inflatable-rigidazable wing, an inflatable polyurethane wing and a fabric wing restraint with a polyurethane bladder. The inflatable wings developed and used within this research had a unique outer airfoil profile. The airfoil surface consisted of a series of chord-wise \bumps.andamp;quot; The effect of the bumps or \surface perturbationsandamp;quot; on the performance of the wings was of concern and was investigated through smoke-wire flow visualization. Aerodynamic measurements and predictions were made to determine the performance of the wings at varying chord based Reynolds Numbers and angles of attack. The inflatable baffes were found to introduce turbulence into the free-stream boundary layer, which delayed separation and improved performance. Another area of concern was aeroelasticity. The wings contain no solid structural members and thus rely exclusively on inflation pressure for stiffness. Inflation pressure was varied below the design pressure in order to examine the effect on wingtip twist and bending. This lead to investigations into wing deformation due to aerodynamic loading and an investigation of wing flutter. Photogrammetry and laser displacement sensors were used to determine the wing deflections. The inflatable wings exhibited wash-in deformation behavior. Alternately, as the wings do not contain structural members, the relationship between stiffness and inflation pressure was exploited to actively manipulate wing through wing warping. Several warping techniques were developed and employed within this re-search. The goal was to actively influence the shape of the inflatable wings to affect the flight dynamics of the vehicle employing them. Researchers have developed inflatable beam theory and models to analyze torsion and bending of inflatable beams and other inflatable structures. This research was used to model the inflatable wings to predict the performance of the inflatable wings during flight. Design elements of inflatable wings incorporated on the UAVs used within this research are also discussed. Finally, damage resistance of the inflatable wings is shown from results of flight tests.

With a look towards the future, which involves a push towards utilizing renewable energy sources and cementing energy independence for future generations, the design of more efficient aircraft and novel energy systems is of utmost importance. This dissertation looks at leveraging some of the benefits offered by inflatable wings for use in tethered kite-like systems towards the goal of designing a High Altitude Aerial Platform (HAAP). Uses of such a system include Airborne Wind Energy Systems (AWES), among others. The key bene- fit offered by such wings is their lightweight construction and durability, but challenges to aerodynamic performance arise out of their flexible nature and non-standard airfoil profile. Studying the aerodynamic behavior of such wings forms the critical focus of this research. This effort primarily encompasses an experimental investigation of two swept, tethered, inflatable wings conducted in the Virginia Tech Stability Wind Tunnel, and numerical CFD computations of these wings. The experiment was conducted in the modular wall configuration of the anechoic test section at speeds ranging from 15 − 32.5 m/s for three different tether attachment configurations and wings constructed out of two different fabric materials. Along with static aeroelastic deformation data using a 3D photogrammetry system, aerodynamic measurements were taken in the form of Pitot and static pressure measurements in the wake of the wing, force and moment measurements at the base of the mount, and tension measurements at the tether attachment locations. This provides a data set for validating static aeroelastic modeling approaches for such a system and highlights the dramatic effect of the variability in test configuration on the wing's aerodynamics. In addition to the wind tunnel tests, 3D steady RANS CFD computations of the rigid 3D scanned inflatable wing geometry were conducted in the wind tunnel environment for these configurations to validate the CFD modeling approach and highlight the level of detail necessary to accurately characterize the wing aerodynamic performance. Static aeroelastic deformation data from the 3D photogrammetry system, at a speed of 27.5 m/s, were also used to deform the 3D scanned inflatable wing geometry, and RANS CFD computations of this deformed inflatable wing were conducted at a wind tunnel speed of 27.5 m/s. Several turbulence models were investigated and comparisons were made with the wind tunnel test data. Good agreement was found with experimental data for the forces and moments and wake Pitot pressure coefficient contours. Comparisons were also made with the rigid wing CFD computations at the same tunnel speed of 27.5 m/s to illustrate the effect of static aeroelastic deformations on the aerodynamic performance, wake Pitot pressure coefficient contours and wing-tip vortex structures, of these flexible inflated wings. In effect, this research utilizes the synergy be- tween wind tunnel experiments and numerical CFD computations to study the flow behavior over inflatable wings and provide a comprehensive verification and validation approach for modeling such complex systems. / Doctor of Philosophy / With a look towards the future, which involves a push towards utilizing renewable energy sources and cementing energy independence for future generations, the design of more efficient aircraft and novel energy systems is of utmost importance. This dissertation looks at leveraging some of the benefits offered by inflatable wings for use in tethered kite-like systems towards the goal of designing a High Altitude Aerial Platform (HAAP). Uses of such a system include Airborne Wind Energy Systems (AWES), among others. The key benefit offered by such wings is their lightweight construction and durability, but challenges to aerodynamic performance arise out of their flexible nature and non-standard airfoil profile. Studying the aerodynamic behavior of such wings forms the critical focus of this research. This effort primarily encompasses an experimental investigation of two swept, tethered, inflatable wings conducted in the Virginia Tech Stability Wind Tunnel, and computer simulations of the aerodynamic flow over these wings. The experiment was conducted in the modular wall configuration of the anechoic test section at speeds ranging from 15 − 32.5 m/s for three different tether attachment configurations and wings constructed out of two different fabric materials. Along with measurements of the wing deformations using a 3D photogrammetry system, aerodynamic measurements were taken in the form of pressure measurements in the wake of the wing, force and moment measurements at the base of the mount, and tension measurements at the tether attachment locations. This provides a data set for validating static aeroelastic modeling approaches for such a system and highlights the dramatic effect of the variability in test configuration on the wing's aerodynamics. In addition to the wind tunnel tests, detailed computer simulations of the scanned inflatable wing geometry were conducted in the wind tunnel environment for these configurations to validate the computational modeling approach and highlight the level of detail necessary to accurately characterize the wing aerodynamic performance. The wing deformation data from the 3D photogrammetry system, at a speed of 27.5 m/s, were also used to deform the scanned inflatable wing geometry, and computer simulations of this deformed inflatable wing geometry were conducted at a wind tunnel speed of 27.5 m/s. Good agreement was found between the experimental and computational forces and moments and wake Pitot pressure coefficient contours. Comparisons were also made with the undeformed wing computations at the same tunnel speed of 27.5 m/s to illustrate the effect of wing flexibility on the aerodynamic performance. In effect, this research utilizes the synergy between wind tunnel experiments and numerical CFD computations to study the flow behavior over inflatable wings and provide a comprehensive verification and validation approach for modeling such complex systems.

UAVs are becoming an accepted tool for sensing. The benefits of deployable wings allow smaller transportation enclosures such as soldier back packs up to large rocket launched extraterrestrial UAVs. The packing of soft inflatable wings and Hybrid inflatable with rigid section wings is being studied at the University of Kentucky. Rigid wings are volume limited while inflatable wings are mass limited. The expected optimal wing design is a hybrid approach. Previous wing designs have been packed into different configurations in an attempt to determine the optimal stowed configurations. A comparison of rigid, hybrid, and inflatable wings will be presented. Also a method for simulating optimally packed wings with respect to geometric constraints will be presented. A code has been written to study soft wing packing and verified the soft wing packing results. This code can be used during initial wing design to help predict wing size and packing configurations. In this thesis, an over view of the packing configurations as well as packing observations will be covered such , packing inefficiencies, wing mounting limits, long term storage, and scaling of packing.

Inflatable wings provide an innovative solution to unmanned aerial vehicles requiring small packed volumes, such as those used for military reconnaissance or extra-planetary exploration. There is desire to implement warping actuation forces to change the shape of the wing during flight to allow for greater control of the aircraft. In order to quickly and effectively analyze the effects of wing warping strategies on an inflatable wing, a finite element model is desired. Development of a finite element model which includes woven fabric material properties, internal pressure loading, and external wing loading is presented. Testing was performed to determine material properties of the woven fabric, and to determine wing response to static loadings. The modeling process was validated through comparison of simplified inflatable cylinder models to experimental test data. Wing model response was compared to experimental response, and modeling changes including varying material property models and mesh density studies are presented, along with qualitative wing warping simulations. Finally, experimental and finite element modal analyses were conducted, and comparisons of natural frequencies and mode shapes are presented.

This study is focused on designing conformal antennas to be deployed with the inflatable wings for unmanned aerial vehicles (UAV). The main emphasis is on utilizing the structure of the wing to develop antennas for various frequency bands, while maintaining the wing’s aerodynamic performance. An antenna modeler and optimizer software called 4NEC2 and a program called WIRECODE were used to design and determine the characteristics of the antennas. The effect of flexibility of the inflatable wing on the antenna characteristics during flight is also evaluated.