A Snowplow Model of Hypersonic Unsteady Flows.
Application of simple Newtonian snowplow theory to the complex problem of unsteady forces on a slender, linearly accelerating airfoil or body of revolution traveling at hypersonic speed. The theory provides a quantitative estimate of the effect of acceleration; the significant parameter is a Froude number equal to body length times acceleration divided by speed squared. Only in extreme cases does acceleration or deceleration exert a significant effect on the aerodynamic forces. The theory is extended to unsteady forces acting on two-dimensional oscillating airfoils. A pressure formula valid for linear and nonlinear oscillations is obtained. Comparisons with results using the exact linearized gas dynamic theory indicate that Newtonian theory is qualitatively correct but not quantitatively accurate for the calculation of unsteady stability derivatives.