{"id":13,"date":"2013-07-04T21:20:00","date_gmt":"2013-07-05T02:20:00","guid":{"rendered":"http:\/\/charles-oneill.com\/blog\/?p=13"},"modified":"2014-07-31T11:16:59","modified_gmt":"2014-07-31T16:16:59","slug":"divergent-trailing-edge","status":"publish","type":"post","link":"https:\/\/charles-oneill.com\/blog\/divergent-trailing-edge\/","title":{"rendered":"Divergent Trailing Edge"},"content":{"rendered":"<p>&#8220;Why does a divergent trailing edge airfoil work? Wouldn&#8217;t this <i>increase<\/i> drag?&#8221; A colleague recently asked this question. Good question!<\/p>\n<table align=\"center\" cellpadding=\"0\" cellspacing=\"0\" style=\"margin-left: auto; margin-right: auto; text-align: center;\">\n<tbody>\n<tr>\n<td style=\"text-align: center;\"><a href=\"http:\/\/charles-oneill.com\/blog\/wp-content\/uploads\/2013\/07\/Airfoil-DTE.jpg\" style=\"margin-left: auto; margin-right: auto;\"><img loading=\"lazy\" decoding=\"async\" border=\"0\" height=\"217\" src=\"http:\/\/charles-oneill.com\/blog\/wp-content\/uploads\/2013\/07\/Airfoil-DTE-300x163.jpg\" width=\"400\" \/><\/a><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\">Divergent Trailing Edge Airfoil (Image from Patent US4858852 Fig.2)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>First, we need understand the philosophy of use (application) for this type of airfoil: high subsonic and transonic aircraft designed for low drag about a specified lift coefficient: think long-range transport aircraft from the Boeing or Airbus families. Traditionally (since the 1960s), this application was served by <a href=\"https:\/\/en.wikipedia.org\/wiki\/Supercritical_airfoil\">supercritical airfoils<\/a> such as the NASA SC(2) family. <\/p>\n<p>Here&#8217;s a quick discussion of three major reasons the concept works.<\/p>\n<ul>\n<li>The divergent angles allows for an optimized lower-surface trailing-edge cusp to fill out the pressure profile without cusp separation bubbles. <i>Result: lower Cd<\/i><\/li>\n<li>&nbsp;The divergent trailing edge tends to decrease the blunt trailing edge pressure. This decrease tends to promote less upper-surface boundary layer separation. <i>Result: better Cdc, likely less AC shift<\/i><\/li>\n<li>The mid-chord (say 60% to 80% chord) tends to be significantly thicker. This allows for more flexibility in flap geometry. <i>Result: better low speed performance<\/i><\/li>\n<\/ul>\n<p>McDonnell Douglas Aircraft patented this in 1989: <a href=\"http:\/\/charles-oneill.com\/docs\/US4858852.pdf\">Patent US4858852<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>&#8220;Why does a divergent trailing edge airfoil work? Wouldn&#8217;t this increase drag?&#8221; A colleague recently asked this question. Good question! Divergent Trailing Edge Airfoil (Image from Patent US4858852 Fig.2) First, we need understand the philosophy of use (application) for this type of airfoil: high subsonic and transonic aircraft designed for low drag about a specified [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":53,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts\/13"}],"collection":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/comments?post=13"}],"version-history":[{"count":0,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/posts\/13\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/media\/53"}],"wp:attachment":[{"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/media?parent=13"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/categories?post=13"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/charles-oneill.com\/blog\/wp-json\/wp\/v2\/tags?post=13"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}