Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - REAR SPOILERS: Length-'Angles'

brucepick · 06-19-2011, 04:24 PM

Aerohead -
All other things being equal - which they never are of course,
would a spoiler angled upward 30º generate more downforce than a level one ending at the same point? And would that downforce carry a drag penalty?

Measured angles:

I measured some of the angles on the '96-00 Civic coupe using a print of the drawing that's been posted in these threads, and an old fashioned protractor. Also used a somewhat sketchy straightedge to establish the base lines, so absolute precision is not guaranteed!

The rear glass angle is about 20-22º downward, vs. horizontal. So, its local angle vs. the immediate prior roof is going to be less than 22º because the roof has already begun to curve downward at that point. This may explain the pretty good attached flow that I believe 98CaliformiaCivic found on the rear glass and trunk lid.
- - - tuft video
- - - damp tufts still #1
- - - damp tufts still #2

I measured the angle from roof to trunk lid edge, based from a point on roof slightly rear of the small side window's forward edge line. This is not the roof peak but is (to my eye) where it departs visibly from the template curve. I got 14º.

I measured from top edge of rear glass to trunk lid edge. I found about 16º there.
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I've seen recommendations for rear down angles of 14º from roof edge to trunk rear edge, and aerohead's recent suggestion to keep local angles at less than 22º. Based on those, it looks like the Civic coupe's stock back end is already in pretty good shape. However the trunk edge isn't anywhere near the template line. A "false trunk lid" to meet the template curve would be some 7"-9" higher than the original trunk, even if the false trunk lid is extended back a few inches to be even with the rear bumper. If not extended rearward, the false lid would need to be higher if it is to meet the template.

Aerohead, what do you think? Would there be gain in a false trunk lid if its sides are formed by extending the C-pillars rearward on their own existing angle? Or have the designers already worked the angles to the point where they've minimized the wake cross section - and a raised lid would only increase that cross section?

06-19-2011, 04:24 PM	#9 (permalink)
brucepick OCD Master EcoModder Join Date: Dec 2007 Location: Eastern CT, USA Posts: 1,936 Outasight - '00 Honda Insight Team Honda Gen-1 Insights 90 day: 54.18 mpg (US) Thanks: 431 Thanked 396 Times in 264 Posts	Civic Gen 6 coupe - measured angles Aerohead - All other things being equal - which they never are of course, would a spoiler angled upward 30º generate more downforce than a level one ending at the same point? And would that downforce carry a drag penalty? Measured angles: I measured some of the angles on the '96-00 Civic coupe using a print of the drawing that's been posted in these threads, and an old fashioned protractor. Also used a somewhat sketchy straightedge to establish the base lines, so absolute precision is not guaranteed! The rear glass angle is about 20-22º downward, vs. horizontal. So, its local angle vs. the immediate prior roof is going to be less than 22º because the roof has already begun to curve downward at that point. This may explain the pretty good attached flow that I believe 98CaliformiaCivic found on the rear glass and trunk lid. - - - tuft video - - - damp tufts still #1 - - - damp tufts still #2 I measured the angle from roof to trunk lid edge, based from a point on roof slightly rear of the small side window's forward edge line. This is not the roof peak but is (to my eye) where it departs visibly from the template curve. I got 14º. I measured from top edge of rear glass to trunk lid edge. I found about 16º there. --------------------------------- I've seen recommendations for rear down angles of 14º from roof edge to trunk rear edge, and aerohead's recent suggestion to keep local angles at less than 22º. Based on those, it looks like the Civic coupe's stock back end is already in pretty good shape. However the trunk edge isn't anywhere near the template line. A "false trunk lid" to meet the template curve would be some 7"-9" higher than the original trunk, even if the false trunk lid is extended back a few inches to be even with the rear bumper. If not extended rearward, the false lid would need to be higher if it is to meet the template. Aerohead, what do you think? Would there be gain in a false trunk lid if its sides are formed by extending the C-pillars rearward on their own existing angle? Or have the designers already worked the angles to the point where they've minimized the wake cross section - and a raised lid would only increase that cross section? __________________ Coast long and prosper. Driving '00 Honda Insight, acquired Feb 2016. Last edited by brucepick; 06-19-2011 at 07:49 PM..