Systematic Definition on Static Stability of Airplanes (The Second Report)—Static Pitch Stability—

Abstract

This paper discusses a static stability theory for airplanes. The conventional definitions of static stability are neither clear nor systematic. On the basis of these situations, in the first report of this paper, a system of definitions on 6 static stability concepts was proposed, and the static flight-velocity stability and the static angle of attack stability were discussed. In this second report, static pitch stability or longitudinal static stability of aircrafts is discussed. This paper proposes that “dM/dθ<0” should be used as the fundamental definition. A general criterion for static pitch stability is deduced from this definition. From this criterion, “C_ma<0” is obtained as the requirement in the case of normal low subsonic flight conditions. Furthermore, this criterion gives the conditions that “flight-path divergence” phenomenon in high angle of attack region and “tuck-under” phenomenon in transonic flight region occur.