Tuft testing rear window of early model Beetle
 

I ran across this guys blog, complete with video of the test.

Wool Tuft test

http://www.gerrelt.nl/roofspoiler/wo...r_100kmh_2.jpg

I disagree with his analysis; it's totally bass-ackwards to want separation and a rolling vortice with spoiler at the top of the back glass and then think attached flow down the back glass is bad. :confused:

Despite Porsche's best efforts to mimic Jaray and Ledwinka's work, the Beetle is a lost cause in this department.