Load Relief for Light and Small Sailplanes?

Abstract

This paper addresses the question if relief from load and speed requirements as given by OSTIVAS is possible.  The answer is important for designers of very light or small sailplanes and gliders, as a relief may allow a lighter structure.  The answer depends primarily on the weather conditions the aircraft is operated in and, even more, on the aerodynamic quality of the aircraft in question.  Actual OSTIVAS and JAR-22/CS-22 cover operation in rough air defined by 15 m/s gusts and smooth air defined by 7.5 m/s gusts.  Operation is not approved in lee-wave rotors, thunderclouds, visible whirlwinds and severe turbulence near mountain.  After another review of the background of OSTIVAS, the author concluded the turbulence of the air mass operated in dominates the load factor together with the aerodynamic quality of the sailplanes.  The manoeuvre loads and speeds are set so they remain below the gust loads.  Only sailplanes designed for aerobatic manoeuvres must withstand high load factors just below human tolerances.  The highest design speed depends on aircraft weight and minimum drag.  So, very light and relatively high drag sailplanes may be approved with relief from OSTIVAS load and speed requirements.  The OSTIV Sailplane Development Panel must decide whether an adequate amendment to OSTIVAS is feasible or specific Airworthiness Standards for very light and small sailplanes must be drafted.