AIRCRAFT PROPELLER VIBRATION MEASUREMENT SYSTEM.

A slip ringless propeller-mounted data system was designed, fabricated and tested for the measurement of propeller blade strain during flight and ground operation of an instrumented aircraft. This data system is self-powered through the rotary motion of the test propeller, employs a 16 channel constant bandwidth Frequency Modulated FM Multiplex and signals are capacitively coupled from the propeller to the aircraft. The FM Multiplex consists of 17 channels of information including propeller rpm and 16 strain gage channels containing information from dc to 1 kHz. An environmentally protected strain gage installation was also a consideration of this program. The FM Multiplex is split into four groups of signals with a frequency translation process in order to conserve bandwidth andor recording time on an airborne tape recorder. Seven additional data channels are provided on board the aircraft for inclusion of parameters needed to define the aircraft operating conditions. The data system was demonstrated for a period of 50 hours on an engine test stand during which the demodulated signals were observed and additional data were obtained relative to the system stability. Author