Definition System and Criteria Related to the Static Stability of Airplanes. (Second Report). Static Pitch Stability.

This paper discusses the static stability of 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 of six static stability concepts was proposed. “Static flight speed stability” and “static angle of attack stability” were discussed in detail, and their stability criteria were obtained in terms of the aerodynamic characteristics of an airframe. In this second report, the definitions and the criteria on static pitch stability are discussed in detail, and besides “dδe⁄dΘ<0,” the derived form of definition “dδe⁄dU>0” is deduced from the fundamental definition “dM⁄dθ<0.” The general criterion is also obtained from the fundamental definition. This criterion gives “Cmα<0” as the aerodynamic requirement in a normal low subsonic flight region and in each condition in which the phenomena of “flight path divergence” and “tuck under” arise.