Thomas A. Zeiler

Aerothermoelastic analysis of a NASP demonstrator model

The proposed National AeroSpace Plane (NASP) is designed to travel at speeds up to Mach 25. Because aerodynamic heating during high-speed flight through the atmosphere could destiffen a structure, significant couplings between the elastic and rigid body modes could result in lower flutter speeds and more pronounced aeroelastic response characteristics. These speeds will also generate thermal loads on the structure. The purpose of this research is develop methodologies applicable to the NASP and to apply them to a representative model to determine its aerothermoelastic characteristics when subjected to these thermal loads. This paper describes an aerothermoelastic analysis of the generic hypersonic vehicle configuration. The steps involved in this analysis were: (1) generating vehicle surface temperatures at the appropriate flight conditions; (2) applying these temperatures to the vehicles structure to predict changes in the stiffness resulting from material property degradation; (3) predicting the vibration characteristics of the heated structure at the various temperature conditions; (4) performing aerodynamic analyses; and (5) conducting flutter analysis of the heated vehicle. Results of these analyses and conclusions representative of a NASP vehicle are provided in this paper.

Integrated aeroservoelastic tailoring of lifting surfaces

An approach to the integration of two design activities, structural design and active control design, for a highly idealized aeroservoelastic system is presented. The particular design goal for this study is the maximization of the stable airspeed envelope of an idealized model of an aeroservoelastic system through rational and systematic variation of structural and control design parameters. The steady-state linear quadratic regulator is used to model the control subsystem; the structural subsystem is assigned characteristic design parameters, such as shear center position. The application of the procedure described here produces optimally controlled structures with stability characteristics superior to those of open-loop and initial closed-loop designs.

A flutter investigation of all-moveable NASP-like wings at hypersonic speeds

Six alternative all-moving wing configurations applicable to the NASP hypersonic/transatmospheric vehicle have undergone aeroelasticity testing in NASA-Langleys Mach-20-capable Helium Tunnel that yielded data for such parametric variations as airfoil profile and wing planform, wing-pivot flexure stiffness, and mass imbalance. While all wings fluttered at dynamic pressures lower than predicted by second-order piston-theory aerodynamics, this was of limited amplitude, suggesting nonlinear external-flow behavior. Slab airfoils were more stable than diamond-shaped ones; blunt leading edges enhance stability relative to sharp ones, and stiffer pivolts extert a stabilizing influence.

Calculating time-correlated gust loads using matched filter and random process theories

This paper describes and illustrates two ways of performing time-correlated gust-load calculations. The first is based on matched filter theory, the second on random process theory. Both approaches yield theoretically identical results, represent novel applications of the theories, are computationally fast, and may be applied to other dynamic-response problems. A theoretical development and example calculations using both matched filter theory and random process theory approaches are presented.

Results of Theodorsen and Garrick Revisited

References 1Norton,W. J., “Limit Cycle Oscillation and Flight Flutter Testing,” Proceedings of the 21st Annual Symposium, Society of Flight Test Engineers, Lancaster, CA, 1990, pp. 3.4-1–3.4–12. 2Cunningham, A. M., Jr., “Practical Problems: Airplanes,” Unsteady Transonic Aerodynamics, AIAA, Washington, DC, 1989, Chap. 3, pp. 83, 84. 3Denegri, C. M., Jr., “Limit Cycle Oscillation Flight Test Results of a Fighter with External Stores,” Journal of Aircraft, Vol. 37, No. 5, 2000, pp. 761–769. 4Airplane Strength and Rigidity—Vibration, Flutter, and Divergence, MIL-SPEC MIL-A-8870B, 20 May 1987, p. 3. 5Dreyer, C. A., and Shoch, D. L., “F-16 Flutter Testing at EglinAir Force Base,” AIAA Paper 86-9819, April 1986.

Time-correlated gust loads using matched filter theory and random process theory - A new way of looking at things

This paper describes and illustrates two ways of performing time-correlated gust-load calculations. The first is based on Matched Filter Theory; the second on Random Process Theory. Both approaches yield theoretically identical results and represent novel applications of the theories, are computationally fast, and may be applied to other dynamic-response problems. A theoretical development and example calculations using both Matched Filter Theory and Random Process Theory approaches are presented.

Preliminary Results of BE-1900D Operational Flight Loads Data Evaluation

Thepreliminaryresultsofastatisticalanalysisofe ightloadsdatafromBE-1900Dtwin-engineturbopropaircraft in normal commuter transport operations arepresented. Some details of data-reduction procedures are discussed, and e ight loads data are presented in statistical formats and discussed. Although these data are preliminary, they suggest that loading spectra typically used in design are generally more severe than thosederived from the present data.An exception tothisgeneralresultisatthelowerlevelsofincrementalmaneuverload factor. Someresultsalso suggest that there are circumstances in which aircraft are being e own at speeds in excess of required limits. Some issues related to quality and completeness of recorded data are discussed. Recommendations for improvement of future data gathering activities are made.