The radar cross section (RCS) of a target describes its reflectivity towards the radar. It is a deterministic quantity - specific to the aspect angle of the target and the properties of the radar signal - and as such can be predicted with various methods when provided with an adequate physical model of the target. However, stochasticity is introduced when considering a target during flight and several factors increasing the uncertainty - typically about the location and orientation of the target in relation to the observing radar - have to be taken into account. It is possible to model these uncertainties when adequate information about physical properties of the target as well as about its flight path and motion mode is available. In this paper, we propose a method for incorporating such knowledge about the flight dynamics into the estimation of a momentary distribution for the RCS. We use a simulated trajectory to demonstrate the method and present comparisons to the Swerling I model.