Ground and Flight Vibration Environment at Fuselage Station 505 in the C-2A Airplane

The purpose of this test was to collect ground and flight vibration data at Fuselage Station (FS) 505 in the C-2A airplane. Collection of this data was necessary to determine operational and structural compatibility of certain navigation equipment with this vibratory environment. Vibration data were collected using triaxial accelerometers mounted to the FS 505 overhead equipment shelf and to an H-764 Embedded Global Positioning System/Inertial Navigation System (EGI) mounted on the shelf. A total of 0.8 hr of ground testing and 3.6 hr of flight testing was conducted at Naval Air Warfare Center Aircraft Division Patuxent River, Maryland. Testing included mission-representative ground and flight maneuvers under normal operating conditions. Power Spectral Density (PSD) plots constructed from ground and flight events were the primary means of quantifying the vibration data from 0 to 1,000 Hz. Generally, on both the equipment shelf and the EGI box, vibration levels were highest in the vertical axis. Neither dynamic pressure nor Mach number had a significant effect on vibration levels. Instead, engine power, as determined by power lever position for a given set of flight conditions, was the most influential factor. The largest PSD peak responses occurred at the 4P frequency (four times the rotational speed of the propeller), approximately 73 Hz. The largest peak, recorded during a maximum power ground turn, had a magnitude of 0.25 g²/Hz in the vertical axis, and corresponded to a G_rms value from 0 to 1,000 Hz of 1.42 g. This peak exceeded the published functional envelope to which the H-764 EGI had been qualified. Throughout the rest of the frequency spectrum for all ground and flight conditions tested, response peaks were within the existing H-764 functional envelope. From the data collected, functional and endurance profiles were constructed and forwarded to the EGI manufacturer, Honeywell, Inc. Honeywell conducted random vibration bench testing of the H-764 EGI, and subsequently determined it is operationally and structurally compatible with the vibratory environment at FS 505 in the C-2A airplane.