Numerical Analysis of Floatplane Porpoising Instability in Calm Water During Takeoff

Abstract

In the operation of floatplanes, porpoising must be avoided, but it is a common occurrence during takeoff, as it induces longitudinal instability and compromises the safety and comfort of passengers. The mechanism of porpoising and the factors or variables that influence the occurrence of this phenomenon are explored in this study. Based on a review of the literature, the position of the longitudinal center of gravity (LCG) and the deadrise angle were found to be the two most significant variables affecting the porpoising phenomenon. The mechanism of porpoising was simulated using a numerical model based on computational fluid dynamics (CFD). The simulation findings were then compared to the results of a related model’s towing tank experiment. With five velocity differences, a validated computational model was used to analyze the impact of LCG ordinates and deadrise angles on the frequency of porpoising. Compared to the LCG 50% length overall (LOA) configuration, the floater with an LCG 53% LOA configuration caused a higher heave porpoising amplitude by 4% for the floater with a 10° deadrise angle and 1% for the floater with a 20° deadrise angle at all speed variations. However, the pitch porpoising amplitude produced by the floater with an LCG 53% LOA configuration was found to be 4% higher than the LCG 50% LOA configuration for the floater with a 10° deadrise angle and -1% higher than the LCG 50% LOA configuration for the floater with a 20° deadrise angle. The results showed that the higher heave and pitch porpoising amplitude was generated by a low deadrise angle and a shift in the floater’s center of gravity toward the bow.

Keywords

• cfd
• deadrise
• floatplane
• porpoising
• take-off