Abstract In the present paper a theory for 2D slender bodies at high angle of attack in hypersonic flow has been developed to determine the aerodynamic derivatives in pitch for diferent Mach numbers. The present theory has been applied to a sharp thick wedge with attached shock case. Using the theory, a relation for a piston moving in a cylinder at any velocity and relations for stifness and damping derivatives are obtained for zero incidence of the wedge and it is found to be dependent on flight Mach number and wedge semi vertex angle. The present method includes the thin wedge case as well, which was covered by Lighthill piston theory, and applies only for small amplitude and low reduced frequency case. Efect of viscosity and secondary wave reflections have been neglected. The results are obtained for wedges of diferent semi vertex angles and Mach numbers. It is observed that the stifness and Damping derivatives increase with increase in the semi vertex angle and decrease with an increase in Mach number. At very high Mach number the Mach number independence principle holds good. Estimation of Aerodynamic Derivatives in Pitch of A Wedge in Hypersonic Flow S. Pavitra 1* , S. Lavanya 2 , S. A. Khan 3 , and Asha Crasta 4 1 Department of Mathematics, B. I. T, Mangalore - 574153, Karnataka, India; pavitrashanbag@gmail.com 2 Department of Mathematics, P.A.C.E, Mangalore - 574153, Karnataka, India 3 Department of Mechanical Engineering, Faculty of Engineering, IIUM, Gombak Campus, Kuala Lumpur, Malaysia 4 Department of Mathematics, MITE, Moodbidre - 574225, Karnataka, India Keywords: Aerodynamic Derivative, Hypersonic Flow, Mach Number, Semi Vertex Angle, Stability Derivative 1. Introduction Te idea of hypersonic similitude is due to in 1 , who investigated the two-dimensional and axi -symmetric irrotational equations of motion. Equivalence of a steady hypersonic fow on a slender body with an unsteady fow in one fewer space dimensions was pointed out by in 2 . Unsteady supersonic fow has been well studied by using the potential theory. Unsteady hypersonic fow has been studied by many researchers using unsteady analogues of either the shock expansion theory or the tangent wedge approximation 2,3 . For an oscillating wedge, more theoreti- cal studies have been made, such a theory of oscillating aero foils at high Mach number is developed in 4 . Here the pitching oscillation is taken into consideration. In results that to a good approximation, any plane slab of fuid, initially perpendicular to the undisturbed fow, remains so as it is swept downstream and moves in its own plane under the laws of one dimensional unsteady motion. A parameter is introduced, whose purpose will be to serve as a measure of the maximum inclination angle of Mach waves in the fow feld. Here it is assumed that 1 1 ≤ τ M and is of the order of maximum defection of a stream line. So in the fow past an aerofoil at high Mach number, the perturbations and gradients are much larger in the lateral direction than those in the axial direction. Sychev’s law of plane sections for 3-D slender bodies at high angles of attack in hypersonic fow 5 has been dis- cussed. Based on this a new piston analogy has been given for a 2-D slender body at high angle of attack in hyper- sonic fow. Te new piston analogy has been frst applied to get the stifness and damping coefcients of an oscillat- ing fat plate at high angle of incidence for which the bow shock is attached. Next assuming that two fat plates have formed a sharp wedge, closed form formulae for stifness and damping coefcients have been obtained for it. In have obtained hypersonic 6 and supersonic 7 similitude’s for planar wedges using Ghosh’s theory. In have obtained *Author for correspondence Indian Journal of Science and Technology, Vol 9(34), DOI: 10.17485/ijst/2016/v9i34/100958, September 2016 ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645