Andy Ko

Ducted Fan UAV Modeling and Simulation in Preliminary Design

With the emerging need for unmanned aerial vehicle with the capability to hover, the ducted-fan UAV design is becoming a more acceptable design option over the conventional rotorcraft design. The unique flight characteristics of such vehicles necessitate a design environment that is able to model and simulate the flight dynamics of ducted fan vehicles accurately. AVID OAV is a design and modeling software tool for ducted fan vehicles that is capable of modeling the performance and flight dynamics during the conceptual and preliminary phases of vehicle design. It incorporates a multidisciplinary methodology that encompasses the prediction of vehicle aerodynamics, fan and stator performance, mass properties calculation and control surface performance. Mission-based optimization and trade studies operating on the vehicle model can be used to explore the design space. The ability to model and simulate the flight characteristics early in the preliminary design phase provides the opportunity for the designer to make fundamental design decisions early on in the vehicle development program while reducing the potential of unexpected flight behavior later on.

Conceptual Design Studies of a Strut-Braced Wing Transonic Transport

Recent transonic airliner designs have generally converged upon a common cantilever low-wing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing (SBW), which uses a strut for wing-bending load alleviation, allowing increased aspect ratio and reduced wing thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting the wing to unsweep for increased areas of natural laminar flow and further structural weight savings. High aerodynamic efficiency translates into smaller, quieter, less expensive engines and less pollution. A multidisciplinary design optimization (MDO) approach is essential to realize the full potential of this synergistic configuration caused by the strong interdependence of structures, aerodynamics, and propulsion. NASA defined a need for a 325-passenger transport capable of flying 7500 n miles at Mach 0.85 for a 2010 service entry date

Multidisciplinary Design Optimization of a Transonic Commercial Transport with Strut-Braced Wing

The multidisciplinary design optimization of a strut-braced wing (SBW) aircraft and its benee ts relative to a conventional cantilever wing cone guration are presented. The multidisciplinary design team is divided into aerodynamics, structures, aeroelasticity, and the synthesis of the various disciplines. The aerodynamic analysis uses simple models for induced drag, wave drag, parasite drag, and interference drag. The interference drag model is based on detailed computational e uid dynamics analyses of various wing ‐strut intersections. The wing structural weight is calculated using a newly developed wing bending material weight routine that accounts for the special nature of SBWs. The other components of the aircraft weight are calculated using a combination of NASA’ s e ight optimization system and Lockheed Martin aeronautical systems formulas. The SBW and cantilever wing cone gurations are optimized using design optimization tools (DOT) software. Ofe ine NASTRAN aeroelastic analysis results indicate that the e utter speed is higher than the design requirement. The minimum take-off gross weight SBW aircraft showed a 9.3% advantage over the corresponding cantilever aircraft design. The minimum fuel weight SBW aircraft showed a 12.2% fuel weight advantage over a similar cantilever aircraft design.

Multidisciplinary design optimization of a strut-braced wing transonic transport

Recent transonic airliner designs have generally converged upon a common cantilever low-wing configuration. It is unlikely that further large strides in performance are possible without a significant departure from the present design paradigm. One such alternative configuration is the strut-braced wing, which uses a strut for wing bending load alleviation, allowing increased aspect ratio and reduced wing thickness to increase the lift to drag ratio. The thinner wing has less transonic wave drag, permitting the wing to unsweep for increased areas of natural laminar flow and further structural weight savings. High aerodynamic efficiency translates into smaller, quieter, less expensive engines with lower noise pollution. A Multidisciplinary Design Optimization (MDO) approach is essential to understand the full potential of this synergistic configuration due to the strong interdependency of structures, aerodynamics and propulsion. NASA defined a need for a 325-passenger transport capable of flying 7500 nautical miles at Mach 0.85 for a 2010 service entry date. Lockheed Martin Aeronautical Systems (LMAS), as Virginia Tech’s industry partner, placed great emphasis on realistic constraints, projected technology levels, manufacturing and certification issues. Numerous design challenges specific to the strut-braced wing became apparent through the interactions with LMAS. *Student Member AIAA 7 Research Associate

Transport Weight Reduction through MDO: The Strut-Braced Wing Transonic Transport

Fred D. Durham Chair, Fellow AIAA 5 Professor, Associate Fellow AIAA ¶ Professor and Dept. Head, Associate Fellow AIAA # Professor of Aerospace Engineering, Mechanics and Engineering Science, Fellow AIAA Copyright

The Role of Constraints in the MDO of a Cantilever and Strut-B raced Wing Transonic Commercial Transport Aircraft

Multidisciplinary Design Optimization (MDO) has been used to investigate the use of anew concept for a transonic transport, the strut-braced wing. The incorporation of a strutinto more traditional transonic transport concepts required the application of computationaldesign techniques that had been developed at Virginia Tech over the previous decade.Formalized MDO methods were required to reveal the benefits of the tightly coupledinteraction between the wing structural weight and the aerodynamic performance. Toperform this study, a suite of approximate analysis tools was assembled into a complete,conceptual-level MDO code. A typical mission of the Boeing 777-200IGW was chosen as thedesign mission profile. Several single-strut configurations were optimized for minimumtakeoff gross weight, with the best single-strut configuration showing a nearly20% reductionin takeoff gross weight, a 29% reduction in fuel weight, a 28% increase in the lift-to-dragratio, and a 41% increase in seat-miles per gallon relative to a comparable cantileverconfiguration. The use of aeroelastic tailoring in the design illustrated ways to obtain furtherbenefits. The paper synthesizes the results of the five-year effort, and concludes with adiscussion of the effects various constraints have on the design, and lessons learned oncomputational design during the project.

PASSIVE LOAD ALLEVIATION IN THE DESIGN OF A STRUT-BRACED WING TRANSONIC TRANSPORT AIRCRAFT

This study examines the role of different design constraints applied to the multidisciplinary design optimization of a strut-braced wing (SBW) transonic passenger aircraft. Four different configurations are examined: the reference cantilever wing aircraft, a fuselage mounted engine SBW, a wing mounted engine SBW, and a wingtip mounted engine SBW. The mission profile was for 325-passengers, Mach 0.85 and a 7500 nautical mile range with a 500 nautical mile reserve. The sensitivity of the designs with respect to the individual design constraints was calculated using Lagrange multipliers. A design space visualization technique was also used to gain insight into the role of the different constraints in determining the design configuration. This design visualization technique uses a classic ‘thumbprint’ plot to represent the design space. As expected, all the designs are very sensitive to the range constraint. The designs are also sensitive to the field performance constraints. The design visualization revealed that the second segment climb gradient constraint was a limiting factor in all the designs. It was also found that the wing mounted engines SBW and tip mounted engines SBW designs are more constrained than the cantilever wing optimum and fuselage mounted engines SBW designs. INTRODUCTION Transonic passenger transport aircraft designs over the past 50 years have utilized the same general configuration, the cantilever low wing concept. Keeping the general layout the same, advances in this concept have relied on advances in individual technologies, such as better engines, airfoil designs, high lift devices and control system alternatives. It is quite unlikely that major improvements in performance will occur if new design configurations are not considered in the transonic passenger transport aircraft industry. One such design configuration is the strut-braced wing design concept. Although this design configuration is common among small general aviation aircraft, it is rare in the large passenger transport arena. The idea of using a truss-braced wing configuration for a transonic transport originated with Werner Phenninger [1] at Northrop in the early 1950s. The strut-braced wing (SBW) concept can be considered a subset of the trussbraced wing configuration. Other SBW aircraft investigations followed Phenninger’s work, notably by Kulfan et al. [2] and Park [3] in 1978. Turriziani et al. [4] considered the advantages of the strut-braced wing concept on a subsonic business jet with an aspect ratio of 25. He found that the strut-braced wing concept achieved approximately 20% in fuel savings compared to a similar cantilevered subsonic business jet.

Transonic Aerodynamics of a Wing/Pylon/Strut Juncture

This paper describes the multidisciplinary design optimization (MDO) of a transonic strutbraced wing aircraft. The optimization considers aeroelastic deformations of the wing and passive load alleviation. The calculations reveal that the strut twist moment provides substantial load alleviation and significant reductions in structural wing weight. To benefit from the potential of appl ying passive load alleviation during preliminary aircraft design, a flexible wing sizing module has been linked to the MDO design tool to optimize the design of three different strut-braced wing aircraft configurations featuring fuselage mounted engines, underwing mounted engines, and wingtip mounted engines.

Multidisciplinary design optimization of blended-wing-body transport aircraft with distributed propulsion

The Multidisciplinary Analysis and Design (MAD) Center at Virginia Tech investigated the strut-braced wing (SBW) design concept for several years. Our studies found that SBW configurations had savings in takeoff gross weight of up to 19% and in fuel weight of up to 25% compared to a similarly designed cantilever wing transport aircraft. In our work we assumed that computational fluid dynamics (CFD) could be used to achieve target aerodynamic performance levels. However, no detailed CFD design was done. This paper uses CFD to study the transonic aerodynamics of the wing/pylon/strut juncture of an SBW configuration. This is the critical aspect of the aerodynamic design. The goal was the reduction or elimination of interference drag at this juncture. Inviscid CFD analysis has been used to investigate the flow characteristics at this juncture. Initial results showed the presence of strong shocks at the juncture. Our analysis showed that the strut/wing intersection was behaving like a twodimensional nozzle between the bottom of the wing and the top of the strut, choking the flow at the minimum area point and expanding the flow downstream resulting in a strong shock near the trailing edge of the strut. We also found that the pylon did not have a major influence on the flow characteristics at the wing/pylon/strut intersection. Geometry changes were made to reduce the shock strength at the wing/pylon/strut intersection, eliminating the nozzle effect. Results showed that this design effectively reduced the shock strength and in some cases eliminated it.