Editing Flathead engine (section)

===Flathead aero-engines===
The simplicity, lightness, compactness and reliability might seem ideal for an [[aircraft engine|aero-engine]], but because of their low efficiency, early flathead engines were deemed unsuitable. Two notable exceptions were the American [[Aeronca E-107]] opposed twin [[aero engine]] of 1930 and the [[Continental A40]] flat four of 1931, which became one of the most popular light aircraft engines of the 1930s. Two modern flatheads are the Belgian [[D-Motor]] [[flat-four]]s and [[flat-six]]es.<ref>Although very small and compact, the D-Motor flat-six displaces nearly 4 litres.</ref> These are extremely [[oversquare]] and compact aero-engines with direct drive to a propeller.<ref>{{cite web |url=http://d-motor1.vpweb.be/Recent-information.html |title=Kapelstraat 198 8540 Deerlijk – Recent information |publisher=D-motor.eu |access-date=2011-12-06 |url-status=dead |archive-url=https://web.archive.org/web/20120328094443/http://d-motor1.vpweb.be/Recent-information.html |archive-date=March 28, 2012 |df=mdy-all }}</ref><ref name="WDLA15">Tacke, Willi; Marino Boric; et al: ''World Directory of Light Aviation 2015-16'', pages 256-257. Flying Pages Europe SARL, 2015. {{ISSN|1368-485X}}</ref>