Waiting for the snow to melt so I can take some field measurements of a building, so I cut up a business card and compared a Ducktail to an alternate location a bit higher.
Would be made of clear Polycarbonate or Acrylic.
Not sure yet what would happen with the flow/vortex and pressure level above the engine cooling inlet.
This is a side-by-side comparison, would not double Duck, although I guess one could.
As I understand it, the Ducktail, Teatray, and Whaletail all try to correct the approximately 30 degree roof angle to mimic an approximate 20 degree slope (
almost like a louver - steps).
Image of wind tunnel smoke in link below.
https://www.gettyimages.com/detail/news-photo/norbert-singer-measures-the-rear-wings-of-the-porsche-911-news-photo/653712864#norbert-singer-measures-the-rear-wings-of-the-porsche-911-rs-27-in-picture-id653712864