Ice accretion on stratospheric airships, which affects the net buoyancy and reduces the ascent speed, thereby leading to component failure and further necessitating flight termination, has received considerable attention. In this study, the formation of ice occurred when the airship hit supercooled water droplets during the non-forming ascending process. Theoretical descriptions of an ice accretion model, a thermal model, and a dynamic model for airships were established to estimate the flight performance with ice mass. Then, validation of the simulation and the cloud chamber test was carried out, which indicated that the temperature, liquid water content (LWC), and pressure considerably influenced the ice mass. A lower temperature had a positive effect on ice accretion. The mass of ice accretion increased with the increase in LWC. Ice did not form easily under low pressure due to evaporation and sublimation. Finally, the effects of the ambient LWC and initial helium mass were analyzed. It was shown that an LWC of 0.5 g/m³ resulted in severe degradation of the ascent performance. When the initial helium mass was not sufficient, the airship landed due to ice accumulation. However, redundant inflation increased the ice mass and lowered the cruising altitude.

Large unmanned cargo airships may support heavy-lift logistics in regions without runway infrastructure, but payload release produces a rapid buoyancy surplus and changes the vehicle mass properties. This study develops a simulation framework coupling six-degree-of-freedom variable-property flight dynamics, an active seawater ballast system, and constrained ballast-flow allocation. The dynamics are referenced to a fixed body origin and retain the spatial-mass-matrix derivative and declared exchange-momentum wrench. A one-dimensional Method-of-Characteristics (MOC) solution provides a numerical reference for the reduced line-inertance runtime model. Fitting yields $L_{\mathrm{eff}}=55.240$ m and a 15.3% closure-interval normalized root-mean-square error (NRMSE), providing cross-model verification rather than experimental validation. Under the nominal 1201 s mission, the variable-property-aware case satisfies the predeclared criteria with a final-altitude error of 2.985 m and a steady-climb pitch RMS error of ${0.165}^{\circ }$. A fair frozen-inertia ablation also passes and produces slightly lower nominal errors (2.806 m and ${0.157}^{\circ }$); hence, nominal superiority is not claimed. Across the five-point pitch-inertia sweep (0.70 to 1.30 times nominal), the variable-property-aware controller keeps the steady-climb pitch RMS error within ${0.137}^{\circ }$–${0.165}^{\circ }$, whereas the frozen-inertia proportional–integral–derivative (PID) controller spans ${0.153}^{\circ }$–${0.230}^{\circ }$; at 1.30 times nominal inertia, the variable-property-aware controller reduces pitch RMS error by 31.8% and settles 12.9 s earlier. All 21 independently rerun cases that jointly scale the nominal pump and valve time constants from 1.0 to 3.0 satisfy the declared criteria. In the $N=20$, $\pm 5\%$ local parameter-dispersion study, all plotted trajectories remain state-bounded, while the wide altitude spread precludes a uniform tracking or reliability claim. The evidence supports numerical feasibility within the explicitly tested nominal, inertia, and actuator-time-constant cases while requiring configuration-specific trim and controller rematching before extrapolation; it does not constitute a reliability probability or global stability proof.