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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Aeroelastic stability characteristics of an oblique wing aircraft

Two different studies are presented involving a transport category aircraft with an oblique or asymmetrically swept wing. The first study concerns itself with the effect on flutter of changes in certain of the aircraft structural and inertial parameters. The second portion examines the subcritical damping characteristics of a flexible oblique wing aircraft. For this purpose, a recent version of the NASTRAN computer code is used. A comparison is made between the flutter speeds found using the traditional k analysis and the results found from computation of subcritical response using the p-k or 'British' flutter method.

Crittenden, J. B.↗
NASA NTRS1977

Effects of dynamic aeroelasticity on handling qualities and pilot rating

Pilot performance parameters, such as pilot ratings, tracking errors, and pilot comments were determined for a longitudinal pitch tracking task using a large, flexible bomber with parametric variations in the undamped natural frequencies of the two lowest frequency symmetric elastic modes. This pitch tracking task was programmed on a fixed base simulator with an electronic attitude-director display of pitch command, pitch angle, and pitch error. Low frequency structural flexibility significantly affects the handling qualities and pilot ratings in the task evaluated.

Yen, W. Y.↗
NASA NTRS1978

Geometry requirements for unsteady aerodynamics in aeroelastic analysis and design

Aircraft geometry requirements for unsteady aerodynamic computations are discussed and differences between requirements for steady and unsteady flow are emphasized within the framework of a general potential-flow aerodynamic formulation. Its implementation in a computer program called SOUSSA (Steady, Oscillatory, and Unsteady Subsonic and Supersonic Aerodynamic is detailed.

Yates, E. C., Jr.↗
NASA NTRS1978

Effects of dynamic aeroelasticity on handling qualities and pilot rating

Pilot performance parameters, such as pilot ratings, tracking errors, and pilot comments, were recorded and analyzed for a longitudinal pitch tracking task on a large, flexible aircraft. The tracking task was programmed on a fixed-base simulator with a CRT attitude director display of pitch angle command, pitch angle, and pitch angle error. Parametric variations in the undamped natural frequencies of the two lowest frequency symmetric elastic modes were made to induce varying degrees of rigid body and elastic mode interaction. The results indicate that such mode interaction can drastically affect the handling qualities and pilot ratings of the task.

Swaim, R. L.↗
NASA NTRS1979

Characteristics of aeroelastic instabilities in turbomachinery - NASA full scale engine test results

Several aeromechanical programs were conducted in the NASA/USAF Joint Engine System Research Programs. The scope of these programs, the instrumentation, data acquisition and reduction, and the test results are discussed. Data pertinent to four different instabilities were acquired; two types of stall flutter, choke flutter and a system mode instability. The data indicates that each instability has its own unique characteristics. These characteristics are described.

Lubomski, J. F.↗
NASA NTRS1979

Numerical computation of aeroelastically corrected transonic loads

A numerical scheme is presented for the computation of transonic aerodynamic loads on flexible wings. The method consists of iteratively applying the loads computed by a 3D transonic aerodynamics code to a structural model to obtain elastic twist, and then recomputing the loads. Because this iteration is performed concurrently with the iterations performed in computing the aerodynamics, flexible loads are obtained in roughly the same amount of computing time as required to obtain rigid loads. Applications of this method to a flexible supercritical transonic transport wing are presented and compared with model test data.

Chipman, R.↗
NASA NTRS1979

Characteristics of aeroelastic instabilities in turbomachinery - NASA full scale engine test results

Several aeromechanical programs have been conducted in the NASA/USAF Joint Engine System Research Programs. The scope of these programs, the instrumentation, data acquisition and reduction, and the test results are discussed. Data pertinent to four different instabilities were acquired; two types of stall flutter, choke flutter and a system mode instability. The data indicates that each instability has its own unique characteristics. These characteristics are described.

Lubomski, J. F.↗
NASA NTRS1979

Agard Two-Dimensional Aeroelastic Configurations

The development of reliable, efficient methods for the calculation of unsteady aerodynamic forces in the frequency-critical transonic speed regime can be enhanced by the availability of a limited number of test cases for the comparison of competing methods. Seven test cases are presented for airfoils with thickness from 6.0% to 16.5%: a biconvex parabolic arc airfoil, three conventional airfoils, and three cambered supercritical airfoils. The aerodynamic conditions such as Mach number, mean angle of attack, and oscillation amplitude and frequency are also given. Recommendations are made for uniformity in definition and reporting to enhance desired comparison for the aeroelastician.

S R Bland↗
NASA NTRS1980

Propeller dynamic and aeroelastic effects

Various aspects of propeller blade dynamics are considered including those factors which are exciting the blades and the dynamic response of the blades to the excitations. Methods for treating this dynamic system are described and problems are discussed which may arise with advanced turboprop designs employing thin, swept blades.

Mccormick, B. W.↗
NASA NTRS1980

An analytical study of effects on aeroelasticity on control effectiveness

Various uses of the Elastic Stability Derivative (ELASRAD) program are described. Topics include structural influence coefficient matrices of wings, arrow wing structural analysis, and graphic display of wing structures. The rigid and elastic stability derivatives were calculated for Transonic Aircraft Technology Project aircraft.

Mehrotra, S. C.↗
NASA NTRS1979

Aeroelastic stability and response of horizontal axis wind turbine blades

Coupled flap-lag-torsion equations of motion of an isolated horizontal axis wind turbine (HAWT) blade have been formulated. The analysis neglects blade-tower coupling. The final nonlinear equations have periodic coefficients. A new and convenient method of generating an appropriate time-dependent equilibrium position, required for the stability analysis, has been implemented and found to be computationally efficient. Steady-state response and stability boundaries for an existing (typical) HAWT blade are presented. Such stability boundaries have never been published in the literature. The results show that the isolated blade under study is basically stable. The tower shadow (wake) has a considerable effect on the out-of-plane response but leaves blade stability unchanged. Nonlinear terms can significantly affect linearized stability boundaries; however, they have a negligible effect on response, thus implying that a time-dependent equilibrium position (or steady-state response), based completely on the linear system, is appropriate for the type of HAWT blades under study.

Kottapalli, S. B. R.↗
NASA NTRS1979

Characterization of graphite/epoxy laminates for aeroelastic tailoring

A study of interaction between wing bending and twist by graphite/epoxy anisotropic laminates used in aircraft wing skins is presented. The laminates were used as covers for subscale box beams supported as a cantilever and tested in tip shear and tip torque, measuring beam response with a reflected light technique. The results indicated that the in-plane stiffness properties of anisotropic laminates can be predicted if the layer properties of the composite materials are known; thus, the coupled bending/twist response of wing type structures made from these laminates can be determined provided the limits of the laminate linear behavior are not significantly exceeded.

Shyprykevich, P.↗
NASA NTRS1981

Aerodynamics, aeroelasticity, and stability of hang gliders. Experimental results

One-fifth-scale models of three basic ultralight glider designs were constructed to simulate the elastic properties of full scale gliders and were tested at Reynolds numbers close to full scale values. Twenty-four minor modifications were made to the basic configurations in order to evaluate the effects of twist, reflex, dihedral, and various stability enhancement devices. Longitudinal and lateral data were obtained at several speeds through an angle of attack range of -30 deg to +45 deg with sideslip angles of up to 20 deg. The importance of vertical center of gravity displacement is discussed. Lateral data indicate that effective dihedral is lost at low angles of attack for nearly all of the configurations tested. Drag data suggest that lift-dependent viscous drag is a large part of the glider's total drag as is expected for thin, cambered sections at these relatively low Reynolds numbers.

Kroo, I. M.↗
NASA NTRS1981

Aeroelastic characteristics of a cascade of mistuned blades in subsonic and supersonic flows

The effects of mistuning on flutter and forced response of a cascade in subsonic in subsonic and supersonic flow were investigated. The aerodynamic and structural coupling between the bending and torsional motions and the aerodynamic coupling between the blades were studied. It is shown that frequency mistuning always has a beneficial effect on flutter. For the cascade considered, the potential for raising flutter speed is greater in subsonic than in supersonic flow. Preliminary results for structural damping mistuning show that there are no additional benefits over adding damping mistuning may have either a beneficial or an adverse effect on forced response, depending on the engine order of the excitation and Mach number.

Kielb, R. E.↗
NASA NTRS1981

Optimization of fiber reinforced structures to satisfy aeroelastic requirements

A numerical procedure was developed for minimizing the structural mass of an aircraft structure which must have a specified minimum flutter velocity or divergence velocity. During the optimization process the arrangement of the structural members remains fixed, while the stiffness parameters of the structure are varied.

Rudisill, C. S.↗
NASA NTRS1981

Proposed aeroelastic and flutter tests for the National Transonic Facility

Tests that can exploit the capability of the NTF and the transonic cryogenic tunnel, or lead to improvements that could enhance testing in the NTF are discussed. Shock induced oscillation, supersonic single degree control surface flutter, and transonic flutter speed as a function of the Reynolds number are considered. Honeycombs versus screens to smooth the tunnel flow and a rapid tunnel dynamic pressure reducer are recommended to improve tunnel performance.

Stevenson, J. R.↗