On Thursday, April 2, 2015 at 1:44:59 PM UTC-7, Dave Nadler wrote:
Yikes.
http://ad.easa.europa.eu/ad/2015-0052-E

Excellent paper on torsional vibration in aviation drive trains.
http://www.vibrationdata.com/tutoria..._vibration.pdf

Not always a simple as it appears at first.

Cheers,
Craig
7Q