Abstract: Through splitting the model of airship′s ballonet in CATIA, the values of the volume under different height of the ballonet was obtained. The least square method was used to establish the cubic curve fitting formula of ballonet’s center height and volume, and the phase laser rangefinder was used to get the height of the ballonet, so the volume of ballonet was calculating in real time by this formula. Furthermore, the static heaviness of the airship was evaluated and the pressure height of the airship and the ability of taking off and landing were abstained. During a flight test，the values of the height of ballonet was used to calculate the airship′s static heaviness, these results agreed with the weighting data on ground every time before taking off. It validated the feasibility of evaluating the static heft online by laser rangefinder. During a flight test, this method was used to analyze the variation the static heaviness and the pressure height was validated.

Key words: Airship, Ballonet, Volume, Laser rangefinder, Static heft, Pressure height