Some notes on an approximate solution for the free oscillation characteristics of non-linear systems typified bc x + F (x, x) = 0.
Beecham, L. J.,author.
Great Britain.Ministry of Defence,issuing body.
Tichener, I. M.,author.
Great Britain.Her Majesty's Stationery Office.
Aeronautical Research Council (Great Britain)
August 1969.