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Hi,here is an old advanced helicopter concept from 1970s,designed by Sikorsky company;http://www.dtic.mil/dtic/tr/fulltext/u2/729860.pdf
Hi,
here is an old advanced helicopter concept from 1970s,designed by Sikorsky company;
http://www.dtic.mil/dtic/tr/fulltext/u2/729860.pdf
