The momentum conservation law is applied to analyse the dynamics of a pulsejet engine in vertical
motion in a uniform gravitational field in the absence of friction. The model predicts the existence
of a terminal speed given the frequency of the short pulses. The conditions where the engine does
not return to the starting position are identified. The number of short periodic pulses after which
the engine returns to the starting position is found to be independent of the exhaust velocity and
gravitational field intensity for a certain frequency of pulses. The pulsejet engine and turbojet
engine aircraft models of dynamics are compared. Also the octopus dynamics is modelled. The paper is
addressed to intermediate undergraduate students of classical mechanics and aerospace engineering.