On Sunday, December 6, 2015 at 5:53:04 PM UTC, Jonathan St. Cloud wrote:
What are the draw backs of using the DG Mandel type air exit as this seems more viable than the ES style vent?

Is it worthwhile fitting a vent unless the particular vent design and location are proven to be effective for your glider type? There is a little article on the JS website about the design of their one.

http://www.jonkersailplanes.co.za/airextractor.htm