COMPARISON OF CLASSICAL SPEED-TO-FLY THEORY USING SECOND, THIRD, FOURTH, AND FIFTH DEGREE POLYNOMIAL SPEED POLARS

Abstract

With the introduction of natural laminar flow airfoils and more precise manufacfuring methods, the modern sailplane has developed into a sophisticated aircraft. The advances have also led to the creation of more complex speed polars. Typical speed to fly models employing second degree polynomials are imprecise and sacrifices must be made, tyiically at the high speed end of the polar. This paper will analyze and compare speed-to-fly models built upon second, third, fourth, and fifth degree polynomial polars. It will be shown that the lesser polynomial models are very inefficient, as much as under-estimating by 4 knots as the speed passes 100 knots, but are still good approximations, within 1 knot, in the lower speed end of the Polar.