THE BUNGEE MODE IN TOWED SAILPLANE FLIGHT

Abstract

Simple mathematical modeling combined with ground test characterization of a tow rope predicts the existence of a low-frequency, lightly-damped oscillatory bungee mode during sailplane towing operations. Tow rope tension and sailplane longitudinal accelerometer measurements made in a towed flight test program confirm the existence of the bungee mode. Low damping of the bungee mode combined with in-flight disturbances cause virtually continuous excitation of the mode while on tow. Dynamic tow tension excursions are typically large; peak tension values greater than 300 lb during takeoff and oscillatory components in steady flight of 50 lb peak-to-peak are not uncommon. Continuous excitation of the bungee mode makes accurate measurement of the static component of tension difficult. In-flight measurements of the static component of tow tension are somewhat larger than the tension values predicted by simple performance-based calculations.