Flight environment of the propellers on commuter aircraft

Abstract

Data obtained from digital flight data recorders installed on a fleet of 27 Beech 1900Ds are used to assess the actual operational environment of propellers on commuter aircraft. The data consists of 910 complete flights and 589 flight hours. Aircraft operations have been separated into three ground operations categories and five flight phases. Parameters that pertain to the propellers are emphasized. Overall aircraft and subsystem usage is also considered to establish the commuter airline flight profile. Overall aircraft usage includes information on flight durations and time within each flight phase, time at various airspeeds and engine torque levels, and flap operations. Flights of commuter aircraft are shown to be of short duration, with the cruise phase accounting for the majority of airborne time. Ground phases highlight the operation of the propellers within prohibited shaft speed ranges. A noticeable length of time is shown to have been spent within these restricted ranges. The usage of reverse thrust during landing rollouts and ground operations is also considered. Reversals upon landing accounted for less than half of the total number of reverse cycles. The short duration takeoff rotation is shown to impose the most severe operating conditions on the propellers. Aerodynamic parameters indicate large inflow angles into the propeller disk, resulting in the most severe vibratory loads. Engine torque, propeller shaft speed, and airspeed are all considered as contributing factors to the large vibratory loads the propellers experience at takeoff rotation. Information pertaining to the in flight engine and propeller usage is also given, and shows no abnormal usage of these components. Cumulative frequency of occurrence of angle of attack for each of the five flight phases has been normalized per 1000 hours and per nautical mile. Each flight phase is shown to produce a unique pattern of frequency of occurrence of the angle of attack, driven by the associated airspeeds. Another aerodynamic parameter considered while in flight is the upwash angle. Upwash angle has been derived for a variety of aircraft weights and airspeeds. This parameter is shown to have a significant influence on the propeller inflow angle, especially at high aircraft weight and low airspeed conditions. The change in inflow angle due to gusts has also been extracted and normalized per 1000 hours and per nautical mile. This data is given in the form of plots of cumulative frequency of occurrence for each flight phase and altitude. Increasing altitude shows a significant reduction in the frequency and magnitude of variations in angle of attack caused by gusts. The information is presented in statistical formats that could enable the FAA, the propeller manufacturer, and the airline to better understand and control those factors that influence the structural integrity of these components.