AUTOMATIC ADJUSTMENT OF THE MACCREADY RING

Garry Speight

Abstract


To maximise the speed in a cross-country soaring flight using thermals, one must follow three rules: (i) Adopt a critical rate of climb, CC, (ii) Circle if, and only if, the rate of climb exceeds the critical rate of climb (Edwards Threshold theorem), (iii) Cruise at speeds Vc, such that Vg=(CC+Vs/(dVs/dVc) where Vs is the glider sink rate (MacCready Theorem). A MacCready Ring gives continuous advice for rule (iii) and indicates decision points for rule (ii). Speed directors do the same more effectively, but some of them neglect rule (ii). There is no instrument for advising on rule (i), although the selection of a critical rate of climb is complex. It is a function of thermal strength, thermal spacing, wind speed, wing loading, and altitude. This paper describes an instrument that computes critical rate of climb.

Keywords


Design, Training, Coaching

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