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Theoretical And Experimental Studies On Airloads Related To Hypersonic Aeroelastic Problems Of General Slender Pointed Configurations

Report Number: ASD TR 61-7
Author: Zartarian, Garabed
Author: Tan Hsu, Pao
Corporate Author: Massachusetts Institute of Technology
Laboratory: Flight Dynamics Laboratory
Date of Publication: 1961-04
Pages: 145
Contract: AF 33(616)-5651
Project: 1370
Task: 13478
AD Number: AD0267036

Two approximate techniques for estimating inviscid hypersonic airloads on pointed slender configurations, originally developed for airfoil and bodies of revolution and presented in Ref. (1), are extended to cover other cross-sectional shapes. The first, an unsteady shock-expansion method, is illustrated by application to two ogives with nearly-elliptic, similar cross sections. As a check, steady-flow pressure and total lateral force were measured on two such models, one with a straight and the other with a cambered body axis, in the range of the hypersonic parameter 1.1 ≤ K ≤ 1.75. Experimental pressures are substantially higher than the predicted ones, although the shapes of the circumferential distributions are in good agreement. At low incidences, incremental pressures due to angle of attack generally show good agreement on the windward side and only fair on the leeward side. The predicted slopes of the normal force coefficients are slightly higher and the centers of pressure slightly further aft than those revealed by experiment. The bulk of the discrepancy is attributed to boundary layer effects.

The second theoretical technique, a variational-Ritz procedure valid for lower values of the hypersonic parameter, is applied to a cone and an ogive, both with faired triangular cross sections, following a suitable transformation. At the present stage of its development, this method, although shown to be feasible and to correlate satisfactorily when tested against other theories, is quite cumbersome numerically. All efforts to alleviate the analytical difficulties and to systematize the computations have been unsuccessful this far.

Included in the final section is a preliminary investigation of the effects of aerodynamic nonlinearity, arising from large-amplitude oscillations, on the flutter characteristics of a typical wing section. A limited number of applications based on third-order piston theory indicate that the velocity boundary UF for flutter instability is slightly lower for large initial disturbances than the value predicted on the basis of infinitesimal oscillations.

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