Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Rear aero project

brucepick · 10-15-2011, 11:41 AM

V. 2 of the spoiler was the three stiffeners added.
V. 3 is with four aluminum bar stock stiffeners; two of those are upgrades of ones that were there in v. 2. The two new stiffeners are longitudinal, placed between the center panel's center stiffener and the outer edges (sorry, no photo handy). I can say that the stiffeners resulted in a pretty stable panel that vibrated only about 1/8" up/down at the trailing edge at highway speeds. Also there was tape joining the leading edge to the car's rear glass. Otherwise the configuration was the same as in v. 2.

Did some coastdown testing this morning. Unfortunately the results are not good. Apparently I still haven't improved on what the Honda engineers built into the 6th Gen. Civic Coupe. I tested between two consistent points on the interstate, not the same two points as on the first coastdown test. The "Northbound" runs had a decent tailwind of about 15 mph so the speed loss there was less than on the southbound runs, which had a headwind. Admittedly, this was only an A-B test and not A-B-A. And, there was only one southbound run of each type. However the results are pretty consistent between runs so I think it's reasonable to draw a conclusion from what I recorded.

Northbound test runs, with spoiler:
START - - - END - - DELTA (MPH)
64.9 - - - - 52.8 - - 12.1
64.0 - - - - 52.0 - - 12.0

Northbound test runs, without spoiler:
START - - - END - - DELTA (MPH)
66.7 - - - - 57.8 - - 08.9
64.3 - - - - 54.1 - - 10.2

Southbound test run, with spoiler:
START - - - END - - DELTA (MPH)
59.6 - - - - 41.0 - - 18.6

Southbound test run, without spoiler:
START - - - END - - DELTA (MPH)
61.5 - - - - 43.5 - - 18.0

So this project will have to go back to the drawing board. I've already mentioned some possible options.

1) taper the side panels inward towards the rear
2) eliminate the "fins"; the part of side panel that's above the center panel
3) take a completely different approach that would be closer to a Kamm back, with a panel starting above the rear glass and going down to a trailing edge similar to this version's trailing edge - but likely narrower at the rear than this one.

10-15-2011, 11:41 AM	#58 (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	v. 3 - Coastdown Tests V. 2 of the spoiler was the three stiffeners added. V. 3 is with four aluminum bar stock stiffeners; two of those are upgrades of ones that were there in v. 2. The two new stiffeners are longitudinal, placed between the center panel's center stiffener and the outer edges (sorry, no photo handy). I can say that the stiffeners resulted in a pretty stable panel that vibrated only about 1/8" up/down at the trailing edge at highway speeds. Also there was tape joining the leading edge to the car's rear glass. Otherwise the configuration was the same as in v. 2. Did some coastdown testing this morning. Unfortunately the results are not good. Apparently I still haven't improved on what the Honda engineers built into the 6th Gen. Civic Coupe. I tested between two consistent points on the interstate, not the same two points as on the first coastdown test. The "Northbound" runs had a decent tailwind of about 15 mph so the speed loss there was less than on the southbound runs, which had a headwind. Admittedly, this was only an A-B test and not A-B-A. And, there was only one southbound run of each type. However the results are pretty consistent between runs so I think it's reasonable to draw a conclusion from what I recorded. Northbound test runs, with spoiler: START - - - END - - DELTA (MPH) 64.9 - - - - 52.8 - - 12.1 64.0 - - - - 52.0 - - 12.0 Northbound test runs, without spoiler: START - - - END - - DELTA (MPH) 66.7 - - - - 57.8 - - 08.9 64.3 - - - - 54.1 - - 10.2 Southbound test run, with spoiler: START - - - END - - DELTA (MPH) 59.6 - - - - 41.0 - - 18.6 Southbound test run, without spoiler: START - - - END - - DELTA (MPH) 61.5 - - - - 43.5 - - 18.0 So this project will have to go back to the drawing board. I've already mentioned some possible options. 1) taper the side panels inward towards the rear 2) eliminate the "fins"; the part of side panel that's above the center panel 3) take a completely different approach that would be closer to a Kamm back, with a panel starting above the rear glass and going down to a trailing edge similar to this version's trailing edge - but likely narrower at the rear than this one. __________________ Coast long and prosper. Driving '00 Honda Insight, acquired Feb 2016. Last edited by brucepick; 10-15-2011 at 01:21 PM..