IS A 'SPEED RING' NECESSARY?

Abstract

This paper prpsents a variation of the problem of maximizing cross-country speed. The intent is to emphasize that the variometer reading alone is sufficient for accomplishing this objective. The maximizing problen is formulated in terms of a sailplane parameter called the 'p' parameter. The variation of this parameter is investigated for both ideal and hypothetical sailplanes. The data used for actual sailplanes is a portion of that which has been publishid by Bikle. Sink rates to be used during an inter thermal glide are computed for a range of soaring conditions. The sink rates then may be used to infer the applicability of the approximate rule "fly at a down indication equal to the achieved rate of climb in the last thermal". It is shown that this rule is reasonable for the sailplanes considered. Finally, certain properties of the 'p' paraneter are identified; in particular, a high speed limit is approached which suggests that a sailplane can achieve a cross-country speed of two-thirds of the air-speed if atmospheric sink and wind are negligible.  It will be shown that the rule 'fly at a down indication equal to the achieved rate of climb in the last thermal is indeed quite good and could be applied for nominal conditions of soaring where climbs of 200 to 700 feet per minute are achieved.