A quantitative method to analyze helicopter longitudinal-lateral coupling characteristics was put forward

including amplitude characteristics

time characteristics

and integration characteristics of couplings among state variables of a motional mode. Relative strengths of couplings could be reflected by amplitude characteristics. Time ratios of couplings with intensifying or diminishing effects could be described by time characteristics. And divergence or convergence rates of state variables caused by couplings could be represented by integration characteristics. With the typical longitudinal oscillatory mode of a hovering Puma helicopter as an example

the couplings characteristics among state variables of the mode were analyzed through comparison between longitudinal-lateral decoupled and coupled conditions. It showed that

because of longitudinal-lateral couplings

both lateral velocity and roll rate had effects on pitch rate

and their strength was almost three times the effect of longitudinal velocity on pitch rate

and the divergence rate of pitch rate was accelerated. Longitudinal-lateral couplings had a great effect on coupling characteristics of the mode

and the dynamic stability was influenced further.