Capacitive transducer for condition based maintenance after harsh landing events

The objective of this work is to identify design parameters for a capacitive sensor designed to recognize and record helicopter harsh landing events. Harsh landing events are typically associated with landing speeds exceeding 2.5 m/s [1] and require mandatory structural inspection resulting in down-times that could last a week or longer. In cases where no visible damage occurs, harsh-landing events might be difficult to identify and record. This paper presents a finite element analysis of the acceleration profile at different locations of the skid of a Bell 206 L4 helicopter which is then used to design and test a low-cost capacitive sensor for monitoring harsh landing events. Time history and histograms of the acceleration signal during normal and harsh landings are presented. The capacitive accelerometer is designed to operate in the 10g to 360g range. The sensor is integrated directly on a wiring board and is readout by a micro-controller with a capacitive ASIC. Details of the sensor design, fabrication, and testing are presented. The presented material also provides hard-to-find design data on the structural accelerations which can occur during harsh landing.