Exploratory flight loads investigation of the p-2v aircraft in aerial firefighting operations

Abstract

An exploratory analysis has been performed on a small number of flights of the P-2V aircraft operating in the firefighting mode as opposed to the anti-submarine and search-and-rescue operations for which it was designed. The data consists of 38 flights from the 2005 and 2007 fire seasons, for the same aircraft, totaling approximately 35 flight hours. Each flight has been divided into two ground and five flight phases and analyzed separately, with emphasis on the loads and atmospheric turbulence experienced by the aircraft. Some aircraft usage data has also been extracted and shown. Aircraft usage information in terms of operating altitudes and airspeeds, as well as maximum loads and V-n diagrams, have been examined for each flight phase. Flight loads for each phase have been separated into gusts and maneuvers using the “Two-Second Rule” and have been normalized per 1000 hours and per nautical mile. Atmospheric gust velocities for each phase have also been extracted and presented in both forms. Finally, the resultant gust and maneuver flight loads have been compared with standard design gust loads and Mil-8866 maneuver loads. A number of general trends have been observed by comparing the phases before and after the release of retardant. It has been shown that the release of retardant weight would significantly decrease wing loading and thus both the cruise speed and response to atmospheric turbulence. This has been demonstrated as being caused by weight by showing the levels of atmospheric turbulence to be the same before and after the drop. The effect of the changing weight on loads has also been examined in detail. The decrease in the weight of the aircraft during the taxi after the drop has been shown to increase the frequency of all loads as well as their severity compared to taxi loads prior to the drop. A similar effect has been highlighted for the cruise phases before and after the drop. Maneuver loads while delivering the retardant have been shown to be the highest in both sets of data. However, a significant part of the increased vertical acceleration is believed to be due to the change of mass while releasing the retardant and not due to maneuvering of the aircraft as is commonly believed to be. The derived and continuous gust velocities are shown not to be remarkably different before and after the release of retardant. The results suggest that the atmospheric turbulence is largely the same before and after the drop with a trend of lower severity at higher altitudes. Comparisons of the results with the military standards for design gust and maneuver loads are provided and show that lower-magnitude accelerations can be as much as 10 times more frequent than design conditions predicted. This is not deemed to pose a threat to exceeding the limit load factor for the airframe, but it can lead to a lower than expected fatigue life for the aircraft. These results indicate that these aircraft are operated in environments different from those for which they were designed. Therefore, maintenance schedules developed for their naval missions may not be applicable for their operation as firefighters.