Experiences and research of Marloes van Son during the DordtYart Artist In Residence: April 1st - June 30th 2014, Dordrecht.
Due to the wing
tips being bent up in the downstroke the tip fortexes are
accelerated outwards. The resulting, seeming enlargement
of the wing span effects a decrease of the induced drag. http://ornithopter.de/english/gull.htm