Abstract: The longitudinal stability of elastic vehicles is studied with the effect of aeroelasticity considered. The transfer functions of an elastic vehicle with the first, second and third elastic modes taken into account are derived from the equations of its longit.udinal disturbance motion. The formulas obtained can be easily used on computers and extended to cases with higher elastic modes.The effect of aeroelasticity on the longitudinal stability of a vehicle is investigated, and a method for choosing the proper position of the gyro is proposed. Finally, the aeroelastic effect on the values of aerodynamic derivatives is estimated.The conclusions drawn from the analysis are as follows:（1） The aeroelastic effect on the stability of a vehicle is mainly due to the effect of the first elastic mode, while the effects of higher ones are relatively of less importance.（2） From the viewpoint of securing stability, the gyro should be located behind the valley of the ith elastic mode if the generalized force Fiδ and control moment Mδ for unit control deflection possess the same sign, and ahead of the valley if Fiδ, and Mδ possess opposite signs. In the case of the investigated vehicle the gyro should be located behind the valley of the first elastic mode and ahead of the valley of the second one.（3） The elastic aerodynamic coefficients for the investigated vehicle have values about 10-20% different from those of the corresponding rigid, vehicle.