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NASA NTRSDate not supplied

Aeroelastic Trim Drag Optimization of Mach 0.8 TransonicTruss-Braced Wing Aircraft with Variable Camber ContinuousTrailing Edge Flap

This paper presents an aeroelastic trim drag optimization study of the Mach 0.8 Tran-sonic Truss-Braced Wing (TTBW) aircraft with the Variable Camber Continuous TrailingEdge Flap (VCCTEF). An aero-structural analysis solver VSPAERO with transonic small dis-turbance, integral boundary-layer, and wing-strut interference corrections coupled to modeshapes computed by NASTRAN using the Galerkin method is developed to provide a rapidaircraft aeroelastic performance evaluation. Aeroelastic trim drag optimization studies areconducted for a VCCTEF configuration with 6-spanwise sections. Three different flight condi-tions corresponding to Mach 0.8 are selected for the aeroelastic trim drag optimization at thedesign and off-design cruise lift coefficients. The preliminary optimization results show thatthe TTBW aircraft with the optimized VCCTEF deflection achieves a drag reduction of about 9.2 counts, 9.6 counts, and 12.3 counts corresponding to the lift coefficients 0.661, 0.695, and0.729, respectively. When accounting for the actuator weight penalty, the corresponding dragreductions are 1.77%, 1.82%, 2.41%. A high-fidelity CFD solver FUN3D is used to validatethe aeroelastic trim drag optimization.

Aeroelastic trim drag↗
NASA NTRSDate not supplied

Aeroelastic Simulation of Transonic Truss-Braced Wing Aircraft for Flight Dynamic Stability Analysis

This paper presents aeroelastic simulation of the Mach 0.8 Transonic Truss-Braced Wing (TTBW) aeroelastic model using CFD solver FUN3D for the flight dynamic and control stability analysis. A jig twist optimization is performed to obtain a flight optimized jig twist for the flexible Mach 0.8 TTBW model. The developed aeroelastic model steady-state stability derivatives with respect to the angle of attack, angle of sideslip, and airspeed are calculated with perturbations in the angle of attack, angle of sideslip, and Mach number, respectively. A series of unsteady simulations is conducted for the developed aeroelastic model in pitch oscillation at various reduced frequencies. The dynamic stability derivatives are estimated using a frequency domain estimation method. The control derivatives of the elevator, rudder, and ailerons of the developed aeroelastic model are estimated for control stability analysis.

TTBW↗
NASA NTRSDate not supplied

Effects of Aeroelasticity on Buffet Onset of Mach 0.8 Transonic Truss-Braced Wing

This paper presents a buffet simulation of the Mach 0.8 Transonic Truss-Braced Wing (TTBW) aeroelastic model using CFD solver FUN3D. A jig twist optimization is performed to obtain a flight optimized jig twist for the flexible Mach 0.8 TTBW model. A series of Delayed Detached Eddy Simulation (DDES) aeroelastic simulations has been conducted at Mach number 0.8 and altitude 40,000 ft using a structural damping of 2% to compare the pitch break prediction and the buffet behavior for the TTBW aeroelastic model. The unsteady pressure begins to grow at angle of attack of 4.0 ◦ , which might indicate the buffet onset, and rises one order of magnitude larger at angle of attack of 4.5 ◦ . In contrast, the buffet onset for the TTBW 1g model appears to be at the angle of attack of about 3.5 ◦ . The delay in the buffet onset of the aeroelastic model is due to the load relief from the aeroelastic effect.

TTBW↗
NASA NTRS1976

Aeroelasticity - Frontiers and beyond /von Karman Lecture/

The lecture aims at giving a broad survey of the current reaches of aeroelasticity with some narrower views for the specialist. After a short historical review of concepts for orientation, several topics are briefly presented. These touch on current flight vehicles having special points of aeroelastic interest; recent developments in the active control of aeroelastic response including control of flutter; remarks on the unsteady aerodynamics of arbitrary configurations; problems of the space shuttle related to aeroelasticity; and aeroelastic response in flight.

Garrick, I. E.↗
NASA NTRS1978

Application of the finite element method to rotary-wing aeroelasticity

Recent research in rotary-wing aeroelasticity has indicated that all fundamental problems in this area are inherently nonlinear. The non-linearities in this problem are due to the inclusion of finite slopes, due to moderate deflections, in the structural, inertia and aerodynamic operators associated with this aeroelastic problem. In this paper the equations of motion, which are both time and space dependent, for the aeroelastic problem are first formulated in P.D.E. form. Next the equations are linearized about a suitable equilibrium position. The spatial dependence in these equations is discretized using a local Galerkin method of weighted residuals resulting in a finite element formulation of the aeroelastic problem. As an illustration the method is applied to the coupled flap-lag problem of a helicopter rotor blade in hover. Comparison of the solutions with previously published solutions establishes the convergence properties of the method. It is concluded that this formulation is a practical tool for solving rotary-wing aeroelastic stability or response problems.

Friedmann, P.↗
NASA NTRS1980

An assessment of the future roles of the National Transonic Facility and the Langley Transonic Dynamics Tunnel in aeroelastic and unsteady aerodynamic testing

The characteristics and capabilities of the two tunnels, that relate to studies in the fields of aeroelasticity and unsteady aerodynamics are discussed. Scaling considerations for aeroelasticity and unsteady aerodynamics testing in the two facilities are reviewed, and some of the special features (or lack thereof) of the Langley Research Center Transonic Dynamics Tunnel (TDT) and the National Transonic Facility (NTF) that will weigh heavily in any decisions conducting a given study in the two tunnels are discussed. For illustrative purposes a fighter and a transport airplane are scaled for tests in the NTF and in the TDT, and the resulting model characteristics are compared. The NTF was designed specifically to meet the need for higher Reynolds number capability for flow simulation in aerodynamic performance testing of aircraft designs. However, the NTF can be a valuable tool for evaluating the severity of Reynolds number effects in the areas of dynamic aeroelasticity and unsteady aerodynamics. On the other hand, the TDT was constructed specifically for studies and tests in the field of aeroelasticity. Except for tests requiring the Reynolds number capability of NTF, the TDT will remain the primary facility for tests of dynamic aeroelasticity and unsteady aerodynamics.

Hanson, P. W.↗
NASA NTRS1981

Aeroelasticity matters - Some reflections on two decades of testing in the NASA Langley Transonic Dynamics Tunnel

In 1955, work was started on the conversion of a subsonic wind tunnel to a 16-foot transonic tunnel with Freon-12 or air as the test medium. The new facility, designated the Transonic Dynamics Tunnel (TDT), became fully operational in 1960. A description is presented of aeroelastic testing and research performed in the TDT since 1960. It is pointed out that wind-tunnel tests of aeroelastic models require specialized experimental techniques seldom found in other types of wind-tunnel studies. Attention is given to model mount systems, launch vehicle models, aircraft models, aircraft buffet, gust response, stability derivative measurements, and subcritical testing techniques. Aspects of vehicle development testing are considered along with aeroelastic 'fixes', aeroelastic 'surprises', approaches for controlling aeroelastic effects, and unsteady pressure measurements.

Reed, W. H., III↗
NASA NTRS1982

Simplified aeroelastic modeling of horizontal axis wind turbines

Certain aspects of the aeroelastic modeling and behavior of the horizontal axis wind turbine (HAWT) are examined. Two simple three degree of freedom models are described in this report, and tools are developed which allow other simple models to be derived. The first simple model developed is an equivalent hinge model to study the flap-lag-torsion aeroelastic stability of an isolated rotor blade. The model includes nonlinear effects, preconing, and noncoincident elastic axis, center of gravity, and aerodynamic center. A stability study is presented which examines the influence of key parameters on aeroelastic stability. Next, two general tools are developed to study the aeroelastic stability and response of a teetering rotor coupled to a flexible tower. The first of these tools is an aeroelastic model of a two-bladed rotor on a general flexible support. The second general tool is a harmonic balance solution method for the resulting second order system with periodic coefficients. The second simple model developed is a rotor-tower model which serves to demonstrate the general tools. This model includes nacelle yawing, nacelle pitching, and rotor teetering. Transient response time histories are calculated and compared to a similar model in the literature. Agreement between the two is very good, especially considering how few harmonics are used. Finally, a stability study is presented which examines the effects of support stiffness and damping, inflow angle, and preconing.

Wendell, J. H.↗
NASA NTRS1983

Formulation and solution of rotary-wing aeroelastic stability and response problems

The state of the art in the formulation and solution of rotary-wing aeroelastic stability and response problems is reviewed in detail. The approximations used in the structural, inertia and aerodynamic operators are discussed. The important role of geometric nonlinearities, due to moderate deflections, and aerodynamic stall in the aeroelastic stability and response problem are identified. It is also shown that geometric nonlinearities are of primary importance in aeroelastic stability calculations, and have a more limited, though important, role in response calculations. Next, formulation of coupled rotor/fuselage problems is described, for both air and ground resonance type problems. Both topics, the isolated blade problem and the coupled rotor/fuselage problem, are treated for both hover and forward flight. Solution of aeroelastic stability and response problems proceeds in two stages. First, the spatial dependence is eliminated by using Galerkin's method, or by using the finite element method. Next the nonlinear, or linear, ordinary differential equation with periodic coefficients have to be solved for stability or response. Efficient numerical methods for accomplishing these objectives are presented in a comprehensive manner. The paper contains a number of illustrative numerical results which are intended to clarify various aspects of the modeling process and serve as representative results for both aeroelastic stability and response calculations for a variety of blade and rotor configurations.

Friedmann, P. P.↗
NASA NTRS1983

Approach to establishing the effect of aeroelasticity on aerodynamic characteristics of the space shuttle orbiter

The static aeroelastic effects on the longitudinal stability and elevon/aileron effectiveness of the space transportation system (STS) Space Shuttle orbiter were estimated by a simplified approach called the elevon torsional stiffness (ETS) method. This method employs rigid model wind tunnel test results to predict aeroelastic effects. Lateral/directional stability and rudder effectiveness were based on results of a wind tunnel test in which a flexible tail model was used. Comparisons with selective flight data are made in this paper. Results of correlations with flight data (although limited at the present time) verify the predicted aeroelastic effects for the orbiter. The orbiter's structural characteristics are such that the effects of aeroelasticity, whether estimated using analytical techniques or simplified methods, do not appear to affect the vehicle performance to any great extent. The large amount of scatter in the flight-extracted data made verification of the aeroelastic corrections very difficult. Generally, the simplified elevon torsional stiffness method provided better correlation with flight test results than he analytical method and reduced the verification effort and cost.

Schlosser, D. C.↗
NASA NTRS1984

Application of transonic codes to aeroelastic modeling of airfoils including active controls

A study is performed using aeroelastic modeling to investigate the stability behavior of airfoils in small-disturbance transonic flow. Two conventional airfoils, NACA 64.A006 and NACA 64A010, and a supercritical airfoil, MBB A-3, are considered. Three sets of unsteady aerodynamic data are computed using three different transonic codes (LTRAN2-NLR, LTRAN2-HI, and USTS) for comparison purposes. Stability results obtained using a constant matrix, state-space, aeroelastic model are presented in a root-locus format. Use of the state-space model is demonstrated through application to flutter suppression using active controls. Aeroelastic effects due to simple, constant gain, partial feedback, control laws that utilize displacement, velocity, and acceleration sensing are studied using a variety of control gains. Calculations are also performed using linear subsonic aerodynamic theory to reveal the differences between including and not including transonic effects in the aeroelastic model. Aeroelastic stability behavior of these airfoils is physically interpreted and discussed in detail.

Batina, J. T.↗
NASA NTRS1985

Aeroelasticity at the NASA Langley Research Center Recent progress, new challenges

Recent progress in aeroelasticity, particularly at the NASA Langley Research Center is reviewed to look at the questions answered and questions raised, and to attempt to define appropriate research emphasis needed in the near future and beyond. The paper is focused primarily on the NASA Langley Research Center (LaRC) Program because Langley is the lead NASA center for aerospace structures research, and essentially is the only one working in depth in the area of aeroelasticity. Historical trends in aeroelasticity are reviewed broadly in terms of technology and staffing particularly at the LaRC. Then, selected studies of the Loads and Aeroelasticity Division at LaRC and others over the past three years are presented with attention paid to unresolved questions. Finally, based on the results of these studies and on perceptions of design trends and aircraft operational requirements, future research needs in aeroelasticity are discussed.

Hanson, P. W.↗
NASA NTRS1986

Transonic aeroelasticity of wings with tip stores

The presence of tip stores influences both aerodynamic and aeroelastic performances of wings. Such effects are more pronounced in the transonic regime. In this study, transonic aeroelasticity of wings with tip stores is studied for the first time by a theoretical method using the unsteady-small disturbance transonic aerodynamic equations coupled with modal structural equations of motion. The aerodynamic and structural equations of motion are simultaneously integrated by a time-accurate numerical scheme. To validate the tip store simulation, aeroelastic computations are made for a typical rectangular wing with a tip store and results are correlated with available wind tunnel data for the corresponding wing without a tip store at various flight conditions. Aeroelastic computations are also made for a typical fighter wing with a tip store. Present computations show that it is important to account for the aerodynamics of the tip store, particularly in the transonic regime where the tip store can make the wing aeroelastically unstable.

Guruswamy, G. P.↗
NASA NTRS1985

Structural and aeroelastic analysis of the SR-7L propfan

A structural and aeroelastic analysis of a large scale advanced turboprop rotor blade is presented. This 8-blade rotor is designed to operate at Mach 0.8 at an altitude of 35,000 ft. The blades are highly swept and twisted and of spar/shell construction. Due to the complexity of the blade geometry and its high performance, it is subjected to much higher loads and tends to be much less stable than conventional blades. Four specific analyses were conducted: (1) steady deflection; (2) natural frequencies and mode shapes; (3) steady stresses; and (4) aeroelastic stability. State-of-the-art methods were used to analyze the blades including a large deflection, finite element structural analysis, and an aeroelastic analysis including interblade aerodynamic coupling (cascade effects). The study found the blade to be structurally sound and aeroelastically stable. However, it clearly indicated that advanced turboprop blades are much less robust than conventional blades and must be analyzed and fabricated much more carefully in order to assure that they are structurally sound and aeroelastically stable.

Hirschbein, Murray↗
NASA NTRS1987

Recent trends in rotary-wing aeroelasticity

The purpose of this paper is to survey the principal developments which have occurred in the field of rotary-wing aeroelasticity during the past five-year period. This period has been one of considerable activity and approximately one hundred papers have been published on this topic. To facilitate this review the field has been divided into a number of areas in which concentrated research activity has taken place. The main areas in which recent research is reviewed are: (1) structural modeling; (2) aerodynamic modeling; (3) aeroelastic problem formulation using automated or computerized methods; (4) aeroelastic analyses in forward flight; (5) coupled rotor/fuselage analyses; (6) active controls and their application to aeroelastic response and stability; (7) application of structural optimization to vibration response; and (8) aeroelastic analysis and testing of special configurations. These areas are reviewed with different levels of detail and some useful observations regarding potentially rewarding areas of future research are made.

Friedmann, Peretz P.↗
NASA NTRS1986

Recent trends in rotary-wing aeroelasticity

The purpose of this paper is to survey the principal developments which have occurred in the field of rotary-wing aeroelasticity during the past five year period. This period has been one of considerable activity and approximately one hundred papers have been published on this topic. To facilitate this review the field has been divided into a number of areas in which concentrated research activity has taken place. The main areas in which recent research is reviewed are: (1) structural modeling; (2) aerodynamic modeling; (3) aeroelastic problem formulation using automated or computerized methods; (4) aeroelastic analyses in forward flight; (5) coupled rotor/fuselage analyses; (6) active controls and their application to aeroelastic response and stability; (7) application of structural optimization to vibration reduction; and (8) aeroelastic analysis and testing of special configurations. These areas are reviewed with different levels of detail and some useful observations regarding potentially rewarding areas of future research are made.

Friedmann, Peretz P.↗
NASA NTRS1990

Using transonic small disturbance theory for predicting the aeroelastic stability of a flexible wind-tunnel model

The CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) code, developed at the NASA - Langley Research Center, is applied to the Active Flexible Wing (AFW) wind tunnel model for prediction of the model's transonic aeroelastic behavior. Static aeroelastic solutions using CAP-TSD are computed. Dynamic (flutter) analyses are then performed as perturbations about the static aeroelastic deformations of the AFW. The accuracy of the static aeroelastic procedure is investigated by comparing analytical results to those from previous AFW wind tunnel experiments. Dynamic results are presented in the form of root loci at different Mach numbers for a heavy gas and air. The resultant flutter boundaries for both gases are also presented. The effects of viscous damping and angle-of-attack, on the flutter boundary in air, are presented as well.

Silva, Walter A.↗
NASA NTRS1990

Aeroelastic analysis of wings using the Euler equations with a deforming mesh

Modifications to the CFL3D three-dimensional unsteady Euler/Navier-Stokes code for the aeroelastic analysis of wings are described. The modifications involve including a deforming mesh capability which can move the mesh to continuously conform to the instantaneous shape of the aeroelastically deforming wing, and including the structural equations of motion for their simultaneous time-integration with the governing flow equations. Calculations were performed using the Euler equations to verify the modifications to the code and as a first-step toward aeroelastic analysis using the Navier-Stokes equations. Results are presented for the NACA 0012 airfoil and a 45 deg sweptback wing to demonstrate applications of CFL3D for generalized force computations and aeroelastic analysis. Comparisons are made with published Euler results for the NACA 0012 airfoil and with experimental flutter data for the 45 deg sweptback wing to assess the accuracy of the present capability. These comparisons show good agreement and, thus, the CFL3D code may be used with confidence for aeroelastic analysis of wings. The paper describes the modifications that were made to the code and presents results and comparisons which assess the capability.

Robinson, Brian A.↗