Lateral stability of tailless aircraft

Abstract

Information was required on the probable effect on lateral behaviour of a change from conventional to tailless types. The essential features of a tailless design are represented by large reductions in the absolute values of the derivatives yv, nv, nr. As few tailless models have been studied, a numerical survey of stability boundaries has been made over a range of these parameters which probably covers the limits set by the all-wing design without end fins. Curves of constant period and constant damping have been drawn in a few cases and from these curves a numerical comparison of the stability characteristics of conventional and tailless aircraft has been made. For the larger values of n~ and y,, considered, oscillatory instability is more likely to occur at low speed than at high, and instability at high speed is unlikely. For the smaller values of n, and y~, oscillatory instability is more likely at high speed than at low speed, and stability at high speed can be attained only with a small value of -- l,. Spiral instability is probable at all speeds, but at high speed the rate of growth.of this motion will be small. The survey stresses the need for systematic measurements of y~, n,., n, (particularly the last) in the tailless range.