Quote:
Originally Posted by freebeard
I agree they seem to be about lift and parachute deployment, but they also seem to be constrained in length.
If I can get 100% boat-tail in three feet, would the trailing vortexes feed into reattachment on top of the tail?
I'm starting to picture the vortexes, which I always associated with large spirals trailing along behind the car, being more about an inch-thick sheet of air that is tripping over the edge of the drip rail and creating a flattened oval spiral shape that eventually normalizes to counter-rotating circles far behind the car.
Doe the center-lines of the vortexes stay the width of the B-pillar apart, or are they pulled into the tapering wake? Maybe the outer limit of the vortex moves straight back, and the center moves down and in?
The current design would have a curved tube lower frame with coroplast/aluminum underbody, two curved laminated redwood panels that meet at 45°, and a black fabric tonneau cover that slips over the top of the engine lid and snaps to the redwood panels. This would weigh nothing, and serve as foundation for experiments with V-shaped Tropfenwagen backlights or vortex sucking air intakes.
I'll work on a picture.
EDIT: As promised. I took the liberty of pencilling in Coanda nozzles that would be fed by a plenum ducted from the engine cooling air.  |
According to Hucho,the vortices induce a downwash which helps maintain attached flow down the centerline over a long path.The vortices begin quite small and grow until they reach the road surface,trailing for hundreds of feet behind the car.The bummer is that you get a high vortex-induced drag which increases the overall drag.
If the tail is like Mair's,or like the 'Template',there won't be any vortices,only attached flow out to wherever you make the truncation.
The Beetle has a lot of body side camber,so your boat tail actually begins at the B-pillars.
*Mair's tail is 1.9X body 'width.'
*Rumpler's tail is 1.951X body width
*GM's EV1' tail is 2.13X body width
*Daihatsu's UFE-III tail is 2.98X body width
*U.C.Davis' SHAMU' tail is 1.103X body width
*If it were mine,I'd use the profile for the minimum drag section profile on the last page of the 'Template' thread.It's known to provide the lowest drag possible.
*Also,the rear fenders will have to integrated into the tail some how or their effect will adversely impact the tails performance.
*As far as the COANDA stuff,I'm no help to you.